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Influence of predation risk and food supply on nocturnal fish foraging distributions along a mangrove-seagrass ecotone
Abstract
Diverse taxa from many systems must make tradeoffs between food and safety. However, few studies have examined the response of multiple fish species to food and predation risk at night across their foraging landscape. In Biscayne Bay, Florida (USA), we investigated the influences of food and predation risk on nocturnal habitat use of gray snapper, bluestriped grunt and seabream along a distance gradient spanning from the mangrove-seagrass ecotone to 120 m offshore. Seine and submerged vegetation sampling were used to determine the distribution of fishes and their food resources. Tethering experiments were used to explore gradients in predator encounter rates. We used these data to test the following a priori predictions of fish distributions relative to food and risk as generated from foraging theory: (1) fishes will be distributed in proportion to their food supply (i.e. ideal free distribution, IFD); or (2) fishes will avoid high-risk areas such that their abundances will be lower than predicted by food resources in high-risk habitats (i.e. food-risk tradeoff). Results indicated that none of the fishes were distributed according to IFD. Seabream and gray snapper avoided foraging close to shore, where their food was abundant, but risk was highest. Bluestriped grunt responses to spatial variation in food supply and risk were less clear; they appeared to forage randomly across the distance gradient. Our results suggest that fish generally avoid the risky mangrove-seagrass ecotone, but responses to variation in food and risk are species-specific and may be dependent on specific anti-predator tactics or influenced by factors we did not measure.
... Habitat connectivity between man groves and adjacent habitats is less emphatic where small tidal amplitudes do not force animals into surrounding habitats at low tide, where beneficial habitats are un available nearby or where the cost to benefit ratio of the journey is unfavourable (Lugendo et al. 2006, Dorenbosch et al. 2007, Hammerschlag et al. 2010, Igulu et al. 2014). The effect is that home ranges of fishes in microtidal systems could be an order of magnitude smaller than those of conspecifics from macrotidal systems, and are rarely > 2 km (Krumme 2009). ...
... The effect is that home ranges of fishes in microtidal systems could be an order of magnitude smaller than those of conspecifics from macrotidal systems, and are rarely > 2 km (Krumme 2009). As mangrove creeks in the Caroni Swamp remain flooded at low tide, and weak tides do not expedite fish movement, the incentive to migrate to feed in adjacent habitats may fail to offset the energetic cost and risk of predation (Nøttestad et al. 1999, Hammerschlag et al. 2010. We collected mangrove fish specimens at 2−5 km from the Gulf of Paria, and even further from the mudflat. ...
... Fish size is also an important determinant of migratory behaviour (Nøttestad et al. 1999, Hammerschlag et al. 2010. Juveniles, including Lutjanus griseus and Anchovia clupeoides that were reported in the present study, do make regular feeding migrations in micro-and meso-tidal systems (Starck & Davis 1966, Giarrizzo 2007, Verweij & Nagelkerken 2007. ...
Seascape connectivity is crucial for healthy, resilient ecosystems and fisheries. Yet, our understanding of connectivity in turbid mangrove-lined estuaries - some of the world’s most productive ecosystems - is limited to macrotidal systems, and rarely incorporates highly mobile top predators. We analysed δ13C and δ15N isotope values of seven primary producers, 24 invertebrate taxa, 13 fishes, four birds and one reptile to reveal trophic interactions within and between a mangrove and adjacent mudflat in a microtidal system of the Gulf of Paria, Orinoco River estuary. Primary producers, invertebrates and fishes collected within the mangrove were significantly depleted in 13C and 15N compared to those collected on the mudflat. Stable isotope mixing models showed that mangrove-derived carbon was predominantly assimilated by invertebrates (78±5%) and fishes (88±11%) sampled in the mangrove. In contrast, invertebrates and fishes sampled in the mudflat derived less than 21% of their carbon from mangrove sources. Instead, microphytobenthos and phytoplankton underpinned the mudflat food web. Scarlet ibis (Eudocimus ruber) and night heron (Nyctanassa violacea) were also highly associated with mangrove carbon sources. However, osprey (Pandion haliaetus), snowy egret (Egretta thula), and caiman (Caiman crocodilus) obtained carbon from both mangrove and mudflat sources, effectively integrating the food webs. The present study demonstrates simultaneous aspects of food web segregation and connectivity, as well as the importance of surveying the entire food web across a range of tidal systems when investigating seascape connectivity.
... Laegdsgaard & Johnson (2001) suggested that one of the most important aspects of submerged mangrove habitats is structural complexity, which both maximizes prey resource availability and minimizes predation risks. Individuals of many marine species seek refuge below the waterline in the mangroves as a habitat-specific escape tactic when a predation threat is perceived (Cocheret de la Moriniere et al. 2004), though this habitat can actually be riskier at night (Hammerschlag et al. 2010). ...
... It has been hypothesized that use of mangrovefringed lagoons and creeks as nursery areas for juvenile lemon sharks in Bimini, The Bahamas (25°45' N, 79°15' W), is linked to both resource availability and predator avoidance (Morrissey & Gruber 1993a,b, Franks 2007, Hammerschlag et al. 2010, Newman et al. 2010), but the relative importance of each of these characteristics in driving movements within the nursery has rarely been investigated. Juveniles exhibit site fidelity to mangrove-fringed natal nurseries for several years before they are large enough to expand their home ranges into the wider lagoon (Morrissey & Gruber 1993a, Franks 2007, Chapman et al. 2009, Guttridge et al. 2012. ...
... Mangrove prop roots are known to be important for predator avoidance in juvenile teleost fishes (Cocheret de la Moriniere et al. 2004, Verweij et al. 2006, Nagelkerken & Faunce 2008, though they may actually be riskier at night (Hammerschlag et al. 2010). The present study is the first to use artificial mangrove structures to examine predator−prey interactions in a shark species. ...
Predation effects can occur either through consumption or as risk effects, which can include alterations in prey behavior to decrease encounters, detection and/or capture by predators. Perceived predation threats lead to behavioral responses which may manifest as changes in habitat use by the prey, and these effects can be significant and even greater in population-level consequences and across multiple trophic levels than consumptive effects. In Bimini, Bahamas, juvenile lemon sharks (Negaprion brevirostris, Poey 1868) use mangrove-fringed shorelines as nursery areas in part due to protection afforded from predators, namely large conspecifics. We investigated small-scale use (on the order of meters) of artificial mangrove structure by juvenile N. brevirostris as an antipredatory response to perceived predation risk. Controlled experimental trials were conducted on semi-captive individuals to compare the degree to which sharks used artificial subtidal refugia when solitary, with a size-matched conspecific and with a potential predator (large conspecific). Test shark size and predator presence were significant drivers of artificial mangrove use. There was a negative relationship between body size and refuge use in the presence of a predator, indicating size is an important factor influencing antipredatory behavior. Test sharks exhibited a high degree of social swimming behaviors with size-matched conspecifics, but the presence of a large conspecific predator elicited fright responses. This study provides the first experimental evidence of the influence of intraspecific predator-prey interactions on juvenile shark habitat use and demonstrates use of subtidal structure as a habitat-specific escape tactic.
... Intra-and interspecific variation in peak activity can consequently be related to predation risk, resource availability, environmental conditions, ontogenetic differences, evolutionary history, and human influences among others (Bennie et al., 2014;Flecker, 1992;Gaynor et al., 2018;Hammerschlag et al., 2010;Nichols & Alexander, 2018;Prugh & Golden, 2014;Tagg et al., 2018). ...
... Predation risk specifically has been shown to influence diel activity in many fish species, including minnows, guppies, carp, bluestripe grunt, gray snapper, and sea breams among others (Fraser et al., 2004;Hammerschlag et al., 2010;Metcalfe & Steele, 2001;Pettersson et al., 2001;Reebs, 2002). However, temperature variation, ontogeny, prey availability, nutritional status, lunar phase, and reproductive status have also been shown to be critical to the level of nocturnal activity in fish (Clark et al., 2009;Fraser et al., 1993;Gries et al., 1997;Metcalfe & Steele, 2001;Nagelkerken et al., 2000;Reebs, 2002;Reebs et al., 1984). ...
Although the nighttime ecology of organisms remains understudied, nocturnal surveys play an integral part in assessing fish assemblages and the selective forces shaping them. Eleuthera (Bahamas) contains an unusual population of lined seahorses (Hippocampus erectus) in an anchialine lake, possessing morphological characteristics distinct from those found in the ocean. Population surveys for seahorses and their potential predators were conducted at midnight and midday during wet and dry seasons, with belt transects perpendicular to the shoreline that increased in depth away from shore. Nocturnal surveys uncovered seahorse densities 259% higher than daytime transects on average. Sex ratios were consistently male-biased, and the frequency of animals from different reproductive categories varied significantly by time of day, with gravid males observed around the clock but females and nongravid males observed more often at night. Spatial and seasonal recruitment was detected for the first time in this species, with an increase in juveniles detected in the shallow ends of transects during dry season surveys. Juvenile recruitment is poorly understood across syngnathid fishes, so the detection of early recruits at night has broad implications for this fish family. Seahorses from all reproductive categories were perched significantly higher in the water column during the night regardless of their depth or season. Predator densities followed a similar pattern with higher densities observed at night, indicating that elevated nocturnal perch height may be a response to predator presence. However, the selective agents driving these nocturnal behaviors have yet to be identified. Considering H. erectus is listed on the IUCN Red List as "Vulnerable," the increase in nocturnal population size and the detection of juveniles has crucial implications for understanding their ecology, recruitment, and conservation.
... Coastal fish species utilize mangrove ecosystems for feeding grounds, shelter, and refuge from predators. Resident fish may forage in mangrove systems, while other fish utilize mangroves for shelter and refuge during the day and forage elsewhere at night (Rooker and Dennis, 1991;Nagelkerken et al., 2000;Hammerschlag et al., 2010;Vaslet et al., 2012). Fish also use mangrove wetlands as nursery habitat which supports populations of adult fish in many other coastal habitats, including coral reefs (Nagelkerken, 2009;Jones et al., 2010). ...
... Small and juvenile fish found in mangroves serve as food for larger fish, transporting carbon, nutrients, and energy up the food web. Fish move between adjacent habitats on a daily basis as they move with the tides, seek shelter, avoid predation, and forage for food (Rooker and Dennis, 1991;Nagelkerken et al., 2000;Krumme, 2009;Hammerschlag et al., 2010;Baker et al., 2013). Mangrove-associated fish frequently exhibit seasonal and ontogenetic migrations, as well (Rooker and Dennis, 1991;Jones et al., 2010). ...
Biscayne Bay is an urban bay in Southeast Florida, but the southern region of the Bay is dominated by mangroves. Mangrove wetlands provide important habitat for fish, but some regions are altered by drainage canals in southern Biscayne Bay. This study utilized a large public dataset to determine if fish formed distinct species assemblages throughout Biscayne Bay by examining fish surveyed at 12 different sites over 5 years. Six sites were in front of intact mangrove shorelines, while the other six sites were adjacent to mangrove sites altered by drainage canals or residential marinas. Cluster analyses revealed that fish did form distinct species assemblage clusters which were correlated with salinity and depth. Mangrove shoreline type (intact vs. canal-altered) and geographic location did not appear to affect species composition or diversity in fish assemblages across Southern Biscayne Bay.
... Marine fishes commonly reside in complex seascapes, and their population dynamics are inherently linked to connectivity via movements at the habitat-, ecosystem-, and/or ocean-basin scale (Mumby and Hastings 2008, Rooker and Secor 2005, Rooker et al. 2008, Nagelkerken et al. 2015. Foraging success and survival of marine fishes are affected by their differential use of habitats (Clark et al. 2009, Hammerschlag et al. 2010, and spatiotemporal shifts are often assumed to be behavioral adjustments that optimize foraging success and minimize predation risk (Werner et al. 1983, Lima andDill 1990). Given that many marine fishes require or utilize multiple habitats or ecosystems during ontogeny, the decline or loss of any component of a seascape can profoundly impact year-class strength (Dahlgren and Eggleston 2000). ...
... Several studies have observed shifts in habitat use (i.e., connectivity) within MSP ecosystems for grunts and snappers (Dorenbosch et al. 2007, Hitt et al. 2011a, Nagelkerken et al. 2015, and salient changes in habitat use by these taxa are presumably linked to predation risk (Hammerschlag et al. 2010). Direct or indirect behavioral adjustments due to predation risk are known to strongly influence the distribution and abundance of both aquatic (Hixon and Carr 1997, Almany and Webster 2006, Stier et al. 2014) and terrestrial (DeCesare et al. 2014, Chudzi nska et al. 2015 fauna. ...
The mangrove–seagrass–patch reef (MSP) ecosystem serves as the principal back‐reef nursery for many reef fishes in the Caribbean, but the functional roles of habitats that form this seascape remain unclear. We assessed ecosystem and trophic connectivity of two common reef fishes (schoolmaster, Lutjanus apodus; white grunt, Haemulon plumierii) and one predator (great barracuda, Sphyraena barracuda) in a Caribbean MSP ecosystem using acoustic telemetry and natural dietary tracers. Triangulated positions from an acoustic positioning system indicated that L. apodus and H. plumierii relied on multiple habitats within this MSP ecosystem, occupying areas with more cover (lower risk) during the day and areas with less cover (higher risk) at night. During the day, both species exhibited limited movement away from structured habitats (e.g., mangroves, patch reef) and avoided the primary activity space of S. barracuda in the central channel over sand bottom or seagrass. At night, L. apodus moved into the channel and adjacent seagrass beds on the margin of this high‐risk area when S. barracuda occurrence was reduced, suggesting that this species adjusts its foraging activities to minimize encounter rates with predators. Haemulon plumierii also displayed distinct day–night shifts with directed movements at twilight across higher risk habitat to nighttime locations in seagrass. Conspicuous changes in the rate of movement were also detected at different times of the day, and observed mismatches between movement rates of S. barracuda and our two potential prey species appeared to be a behavioral response to reduce their vulnerability. Dietary tracer analysis supported the premise that observed shifts to nocturnal habitats were associated with foraging, with significant contributions of organic matter derived from nighttime locations. Findings from this study clearly demonstrate that the configuration of habitats and spatiotemporal variability in predation risk are key determinants of movement and foraging activities for these species, indicating that an improved understanding of seascape connectivity is critical to the management of reef‐dependent species.
... This trade-off suggests that the availability of energetic resources will also influence foraging and antipredator behaviour, with individuals more likely to avoid risk when food is abundant. Conversely, if food is in limited supply, individuals will likely spend more time foraging or engaging in riskier behaviour to secure enough food (Uiblein et al. 1996, Hammerschlag et al. 2010. Climate change has the potential to alter both the food resources available to individuals and the energy required to sustain essential activities, including the energetic cost of basic cellular maintenance (Pörtner et al. 2004, Melzner et al. 2009. ...
... Juveniles exhibited a different behavioural response to predator cue depending on food ration, with fish reared on the low food ration exhibiting a proportional change in feeding strikes 1 to 7% less than their high food counterparts. This difference in behavioural response between the food rations is likely due to lower energetic reserves in fish on the low ration diet, which in turn can cause them to become bolder in the presence of a predator to secure more food (Uiblein et al. 1996, Hammerschlag et al. 2010. While there was an overall effect of food ration on feeding rate in the presence of predator cue, this change was minor compared with the overwhelming effect of elevated CO 2 , where there was a 67 to 75% difference in feeding rate between ambient and elevated CO 2 treatments. ...
The appropriate behavioural response to predation risk is critical to survival; however, behavioural responses can be subjected to trade-offs. For example, individuals may engage in riskier foraging behaviour to secure sufficient energy if resources are limited. Additionally, elevated CO2 can influence foraging and antipredator behaviour of marine organisms. Yet, how the availability of energetic resources may influence antipredator behaviour in an elevated CO2 environment is unknown. We tested the effects of food ration (low and high: 4 and 8% of body weight per day, respectively) on antipredator behaviour at ambient (489 µatm) and elevated (1022 µatm) CO2 in juvenile Amphiprion percula at 50 d post-hatching. Juveniles were from parents held at either ambient or elevated CO2, as parental exposure can influence phenotypic response in offspring. Antipredator behaviour was severely impaired by elevated CO2, with juveniles reared at elevated CO2 exhibiting no change in feeding rate in the presence of the predator cue compared with a >67% reduction in feeding rate in ambient CO2 fish. By contrast, food ration had a minor effect on the change in feeding rate in response to the predator cue, with only a 2.3% difference between high and low food ration fish. The effect of elevated CO2 on antipredator behaviour of juveniles was not influenced by food ration. Parental exposure to elevated CO2 influenced the baseline feeding rate and exhibited a small carry-over effect in elevated CO2 juveniles. These results suggest that reef fish could exhibit riskier behaviour at elevated CO2 levels, regardless of the energetic resources available.
... For example, snappers and grunts will leave the safety of coral reef refuges at night to feed in shallow seagrass beds on the invertebrates that emerge there at night (Goebel et al. this issue a,b). While such seagrass habitats have typically been considered nursery areas for juvenile fish, characterized by high food availability and low predation risk, recent research suggests that predation risk to juvenile fish from larger fish at night may be significant and thus juvenile fish experience food-risk trade-offs by foraging within these habitat at night (Hammerschlag et al. 2010a ,b). However, the occurrence of fish predators in these seagrass habitats can vary by species, life-stage and even distance from shore (Goebel et al. this issue a,b). ...
... Nocturnal teleosts and elasmobranchs represent approximately one third of the fish within any ecosystem (Helfman 1978Helfman , 1986), but in some habitats, such as tropical mangroves, they can represent over half (57%) of the species present and approximately 75% of the fish abundance (Ley and Halliday 2007). However, the majority of studies on the distribution, abundance, and habitat use of fish are based on diurnal sampling (but see Rooker et al. 1997, Annese and Kingsford 2005, Azzurro et al. 2007, Holzman et al. 2007Hammerschlag et al. 2010a,b). The use of passive and active acoustics (Meyer this issue) has greatly increased our understanding of fine scale fish movements. ...
In aquatic environments, what one observes during the day can differ substantially by night. The species composition and associated ecological processes that occur during the day are often different than night. In polar seas and at great depths, " night " can span, months, years, and beyond. Teleosts and elasmobranchs have evolved unique sensory and behavioral modalities for living in darkness. As a consequence, fishers have adopted unique strategies for exploiting fish at night or in dark systems. We propose that neglecting the night has led to an incomplete understanding of aquatic organismal ecology, population/community dynamics, and ecosystem function with consequences for fisheries conservation management. To address this knowledge gap and stimulate the exchange of new data and ideas on behaviors, patterns, and processes relating to fish and fisheries in darkness, Fish at Night: an International Symposium was held in Miami, Florida (USA), from 18 to 20 November, 2015. Here, we synthesize the findings from the symposium, providing an overview on the state-of-knowledge of fish studies in the dark, identifying critical information gaps, and charting a course for future research. We focus our commentary and synthesis on six areas: (1) nocturnal fish behavior and ecology; (2) fishing, fisheries, and enforcement; (3) deep and polar seas; (4) diel fish distribution and abundance comparisons; (5) methods for studying fish in darkness; (6) human threats to fish at night; and (7) larval fish at night. Taken together, we attempt to " shine a light " on fish at night, generating a greater interest and understanding of fishes and fisheries during darkness.
... Migrations occur in all postsettlement sizes, from newly settled (approximately 100-150 mm) to adult (>1500 mm) ). Two hypotheses have been proposed to explain the benefits of nocturnal migration in this and related species , Hammerschlag et al. 2010. First, nocturnal migration could increase foraging efficiency because of greater prey availability and/or decreased competition (e.g., Burke 1995). ...
... While some tethering studies have suggested that predation from piscivores is greater on reef than seagrass habitat (Danilowicz and Sale 1999), and greater in mangrove-seagrass interface than more distant seagrass habitat (Hammerschlag et al. 2010), differences found in such studies could be due at least in part to parasitic/micropredatory isopods. For example, heavy gnathiid loads produce visible "wounds" and wounded fish are susceptible to attacks by other, larger, microcarnivorous isopods (Stepien and Brusca 1985). ...
Tropical Atlantic reef fishes in the family Haemulidae (grunts) remain quiescent on reefs during the day and migrate to seagrass beds or sand flats at night. Hypothesized advantages of such nocturnal migrations are increased food availability and/or decreased predation risk. Here, we tested predictions of an alternative hypothesis that nocturnal migrations of French grunt, Haemulon flavolineatum (Desmarest, 1823), reduce exposure to blood-feeding gnathiid isopods. The departure of grunts from the reef coincides with increasing gnathiid activity. In field experiments, subadult fish placed in cages and deployed on the reef at night harbored significantly more gnathiids than those placed in the seagrass habitat. However, this was not the case during the day when gnathiid activity in all habitats is low. In another experiment, the timing of return to the reef was determined to coincide with the postdawn decrease in gnathiid activity. Estimates of cumulative gnathiid exposure at two sites revealed that grunts remaining in reef habitat at night would experience an average of 3 and 44 times more gnathiids than if they spent the night in the seagrass bed, and could reach more than 300 gnathiids on a single fish. In a final field experiment, even recently-settled (<2 cm) juvenile grunts were infested by gnathiids, supporting previous laboratory experiments showing that a single third-stage gnathiid will infest and kill grunts of this size. Combined, these findings suggest that nocturnal feeding migrations of French grunts and ecologically similar fishes result in reduced exposure to blood-feeding gnathiid isopods. Many animals undergo daily or seasonal migrations between habitats (Rubenstein and Hobson 2004, Møller and Szép 2011, Poulin et al. 2012). Given the costs of travel, evolutionary ecologists seek to understand the net benefits of migration, while community and population ecologists are interested in the ecological consequences of
... An other meta-analysis comparison between seagrass and salt marsh similarly found that seagrass habitats supported higher juvenile densities (Minello et al. 2003). Seagrass is also thought to provide a better food source than mangroves; behavioural observations in the tropics have shown that some fishes move between seagrass and mangroves for food and refuge, respectively (Verweij et al. 2006a, Hammerschlag et al. 2010). Growth is a more direct measure of food provision, whereas the relative similarity in densities between seagrass and mangroves, coral reefs, and rock/rubble/shell could also be an indication of refuge provided by these other habitats (Verweij et al. 2006a, Hammerschlag et al. 2010, Igulu et al. 2014). ...
... Seagrass is also thought to provide a better food source than mangroves; behavioural observations in the tropics have shown that some fishes move between seagrass and mangroves for food and refuge, respectively (Verweij et al. 2006a, Hammerschlag et al. 2010). Growth is a more direct measure of food provision, whereas the relative similarity in densities between seagrass and mangroves, coral reefs, and rock/rubble/shell could also be an indication of refuge provided by these other habitats (Verweij et al. 2006a, Hammerschlag et al. 2010, Igulu et al. 2014). Both Heck et al. (2003) and our meta-analysis show that survival is higher in non-vegetated structure habitats (i.e. ...
Identifying and protecting coastal nursery habitats is imperative as human impacts to these areas accelerate. Nursery habitats support higher juvenile (1) density, (2) growth, or (3) survival (hereafter nursery role metrics) than other habitats, resulting in a greater contribution to adult populations. Seagrass habitat is commonly referred to as a nursery, but its contribution to each nursery role metric across geographic regions and in comparison to other nursery habitats (e.g. mangroves, coral reefs, salt marshes) remains unclear. We conducted a global meta-analysis of juvenile fish and macro-invertebrate performance in seagrass relative to other habitats to assess the nursery role metric, geographic region, and taxonomic group for which seagrass is most beneficial. We compiled data from 51 papers, spanning temperate, subtropical, and tropical regions and including unstructured and structured comparative habitats. We found that, overall, seagrass provided better nursery habitat than other habitats, particularly for supporting high juvenile density and growth. Seagrass habitat was generally more beneficial in temperate and subtropical regions than in the tropics, and more important for juvenile invertebrates than for fishes. Seagrass appears to be highly valuable for provision of food, but supplies equivalent or less adequate refuge than other nursery habitats. Management efforts may benefit from prioritizing conservation of seagrass habitats as food sources for juveniles in combination with other structured habitats for refuge in temperate regions; in tropical regions, seagrass may be a less important nursery habitat to target for conservation, though the value of nursery habitats may shift with ongoing climate change.
... Larger sub-adults (> 170 mm, TL) fed primarily on fishes and larger crustaceans (Starck and Schroeder, 1970). Fish between 10 and 25 cm TL from Biscayne Bay, Florida fed primarily on Hardhead Silversides, Rainwater Killifish, pink shrimp, and caridean shrimp (Hammerschlag et al. 2010a). In a related study in the same area, Hammerschlag et al. (2010b) examined seasonal diet and feeding habit variation in juveniles in consecutive wet and dry seasons and found significantly lower feeding intensity during the dry season, perhaps the result of lower water temperatures. ...
... Predation: Gray Snapper larvae are pelagic and must disperse into the nearshore environment to settle onto benthic seagrass meadows and mangrove habitats (Starck and Schroeder 1970;Rutherford et al. 1989). Hammerschlag et al. (2010a) studied the relative influence of food and predation risk on the nocturnal habitat use by Gray Snapper along a distance gradient from the mangrove-seagrass ecotone to 120 m offshore. They determined the distribution of fishes and their food resources, then used tethering experiments to examine gradients in predator encounter rates. ...
To supplement information needed to support Essential Fish Habitat (EFH) and the Fisheries Ecosystem Plan (FEP), the SAFMC contracted the Florida Fish and Wildlife Research Institute (FWC-FWRI) in 2012 to create a database called Ecospecies (http://saecospecies.azurewebsites.net/). Major components of the Gray Snapper (Lutjanus griseus) species life history (SLH) include the following: Taxonomy, Geographic Range, Benthic Habitat, Water Column Habitat, Artificial Reefs, Shrimp Trawl Bycatch, Food Habits, Reproduction, Growth, Value and Status, Stock Enhancement, Population, Management Regulations, Ecological Interactions, and Human Impacts. Citations and references are available for each entry in the Ecospecies database. Almost everything published concerning this species is reviewed in the present SLH profile.
... The diel cycle is considered one of the key drivers of variation within marine ecosystems (Naylor 2005;Pulcini et al. 2008;Azzurro et al. 2012), although there remains a paucity of studies on the cause and associated ecological implications of diel activity patterns in fish (Reebs 2002; but see Birt et al. 2012 andHarvey et al. 2012a). While research has reported diel changes in fish behaviour using a variety of methods and outcomes (Howard 1989;Santos et al. 2002;Travers & Potter 2002;Hammerschlag et al. 2010;Al os et al. 2012;Harvey et al. 2012a), information on fine-scale temporal variation in the species composition of fish assemblages in temperate marine systems remains scarce. Studies that limit sampling to diurnal hours potentially underestimate the true diversity and complexity of the composition of fish assemblages (Carpentieri et al. 2005;Baumgartner et al. 2008;Harvey et al. 2012a). ...
... Studies that have used extractive fishing methods to sample diel variations in fish assemblages have found fish to be distributed in proportion to their available food supply and relative to changing risks of predation (Carpentieri et al. 2005;Ley & Halliday 2007;Hagan & Able 2008;Hammerschlag et al. 2010). Extractive or destructive techniques are affected by the differences in the catchability of different species (Nash et al. 1994). ...
The distribution, abundance and composition of marine fish assemblages are influenced by changes in behaviour and movement associated with the diel cycle. The majority of studies exploring day–night differences have demonstrated that there is a greater abundance and diversity of fishes during diurnal compared with nocturnal hours, and that fish assemblage composition varies with time of day or night. We investigated fine-scale (hourly) diel cycles in the composition and relative abundance of temperate reef fishes using unbaited remote underwater video systems. We observed short crepuscular changeover periods with the hours around dawn and dusk sharing many species, some of which are nocturnal and others diurnal. Diurnal surveys recorded a greater number of individuals (16,990) and species (70) than nocturnal surveys (1053 individuals and 19 species). There was a clear difference between the diurnal assemblage, which was characterized by benthic invertivores, and the nocturnal assemblage composition, which contained zooplanktivores and generalist feeders. Within the diurnal period the hourly temporal variation was relatively homogenous, indicating that standardization of diurnal sampling to a particular time of day may not be necessary.
... The costs and benefits of the occupation of vegetated wetlands and adjacent subtidal habitats are unlikely to be a simple linear function of time (i.e. flooding duration), since foraging in tidal systems is often focused during particular parts of the tidal cycle (Gibson, 2003) or at transition zones between different habitats (Hammerschlag et al., 2010). For example, small fish that find refuge in the complex habitat of mangrove roots may be particularly vulnerable to predation as they are forced from the mangroves by ebbing tides (Sheaves, 2005;Hammerschlag et al., 2010). ...
... flooding duration), since foraging in tidal systems is often focused during particular parts of the tidal cycle (Gibson, 2003) or at transition zones between different habitats (Hammerschlag et al., 2010). For example, small fish that find refuge in the complex habitat of mangrove roots may be particularly vulnerable to predation as they are forced from the mangroves by ebbing tides (Sheaves, 2005;Hammerschlag et al., 2010). So while our simple metrics of mangrove flooding duration, frequency, and depth serve to highlight the substantial geographic variation in accessibility of mangroves, these factors may interact in complex ways to regulate the functional values of tidal wetlands for aquatic fauna. ...
Intertidal habitats are only available to most nekton when inundated by tides. We assessed the variability of access to mangrove habitats for aquatic organisms over 3500 km of Australia’s east coast. After determining the elevation of the lower mangrove edge across 19 locations, we used 6 years of historic hourly tide gauge readings to estimate wetland edge flooding frequency, duration, and depth at each location. Although mangrove edges broadly tracked mean sea level along the east coast, deviations in edge elevation corresponded to substantial geographic variation in flooding dynamics. Mangrove edges were flooded from as little as 20% of the time in central Queensland sites, to as much as 90% of the time during some seasons in northern New South Wales. Flooding frequency and depth were also highly variable, with some mangrove edges flooding and draining almost twice as frequently as others. Flooding depth profiles revealed dynamic patterns of flooding of mangrove habitat. The variability in flooding dynamics demonstrates that the availability of mangrove habitat to aquatic organisms varies significantly among locations. This variability in flooding patterns suggests the nature of mangrove use and the functional value of these habitats for fishes and nektonic crustaceans may differ substantially among regions.
... The question is, why is it that fish emerge at night and venture into unprotected areas? I suggest that fish use the open habitats to forage, interact, and carry out ASR at night at a lower risk of predation (e.g., Hammerschlag et al., 2010 ;Hobson, 1973 ;Nagelkerken et al., 2000 ;Saint-Paul and Soares, 1987 ;Sikkel et al., 2017). Although the low DO in the swamp protects fish from large predators, such as the Nile perch (Chapman and Chapman, 1998 ;Chapman et al., 2002), there is some risk of predation during the daytime due to the presence of visuallyoriented piscivorous birds, such as the hamerkop (Scopus umbretta) and the pied kingfisher (Ceryle rudis). ...
In dieser Arbeit wurden die Morpho-Physiologie und das Verhalten zweier Arten Afrikanischer schwach elektrischer Fische, Marcusenius victoriae und Petrocephalus degeni, im Labor und in einem ihrer natürlichen Habitate im Lwamunda Sumpf in Uganda untersucht. Die zwei Hauptziele dieser Arbeit waren (i) tageszeitabhängige Verhaltensrhythmen (Aktivität, Habitatnutzung) im Labor und im Freiland zu untersuchen und (ii) die Ausprägung und Plastizität der morpho-physiologischen Merkmale von P. degeni zu untersuchen, die ihnen erlauben bei natürlich vorkommender, geringer Sauerstoffverfügbarkeit (Hypoxie) zu überleben. Tageszeitabhängige Verhaltensrhythmen beider Arten wurden im Labor über 42 Stunden und im natürlichen Habitat dieser Fische für sechs Tage erfasst. In den Laborversuchen verbrachten beide Arten tagsüber annähernd 100% der Zeit in einem bereitgestellten Versteck und schwammen nachts heraus um aktiv ihre Umwelt zu erkunden. Im Habitat wurden die meisten Fische in strukturell komplexen Habitaten unter schwimmenden Pflanzen detektiert. Nachts schwammen die Fische aktiv in die offenen und ungeschützten Bereiche der Lagune, vermutlich um nach Futter zu suchen und zu interagieren. Die Begleitende in-situ Messung der Sauerstoffverfügbarkeit zeigte, dass beide Arten präsent und vermutlich sogar am aktivsten waren während Phasen extremer nächtlicher Hypoxie. Zur Untersuchung der respiratorischen Merkmale von P. degeni wurden Respirometrieversuche mit hypoxie-akklimatisierten Tieren durchgeführt, Hämoglobin- und Laktatkonzentration im Blut gemessen, und morphologische Parameter an den ersten beiden Kiemenbögen erfasst. Die Fische zeigten niedrige Sauerstoffverbrauchsraten, welche sie bis zu einem sehr niedrigem äußeren Sauerstoffpartialdruck aufrechterhielten. Zusätzlich zeigten sie hohe Hämoglobin- und Laktatkonzentrationen im Blut. Bis zu 75 Tage Normoxie-Akklimatisierung führte zu reduzierter Hämoglobinkonzentration und kürzeren Kiemenfilamenten.
... We also found that moon phase affected ray movements, with higher presences during the new moon compared to the full moon. Selection of high tides at night and the new moon phase suggests more successful foraging at night on intertidal flats only accessible during high tides, and that moon phases with lower illumination mean that rays can forage more easily (Hammerschlag et al. 2010(Hammerschlag et al. , 2017 by taking advantage of the darkness to increase foraging efficiency and reduce predation risk. The South Australian Marine Park Network and sanctuary zones were established in 2014 to protect and conserve biological diversity and habitats (Marine Parks Act 2007, Version: 19.3.2021. ...
The environmental conditions determining the distribution of the southern eagle ray Myliobatis tenuicaudatus are mostly unknown. We tracked 40 southern eagle rays using a network of 28 acoustic receivers deployed in Coffin Bay and a second array of 6 receivers deployed along the Fleurieu Peninsula, both in South Australia, to investigate the spatiotemporal changes in space use and residency and the influence of biotic (disc width, sex) and abiotic (water temperature, salinity, tides, moon illumination, time of day) factors. We also assessed the efficacy of a small sanctuary zone to reduce anthropogenic pressures. Tagged southern eagle rays in Coffin Bay were semi-permanent residents (residency index ~ 0.35), with a seasonal exodus from late autumn to spring, high residency from mid-spring to mid-autumn, and selection of Kellidie Bay (located within Coffin Bay). Most (67%) rays were detected in the Kellidie Bay Sanctuary Zone, but spent <15% of their time in Coffin Bay within the sanctuary. Individual variation in the amount of time spent in the Kellidie Bay Sanctuary Zone was high, ranging 0-42%. In contrast, tagged southern eagle rays along the Fleurieu Peninsula had high site fidelity throughout the year (residency index ~ 85%). Our study provides new information on space use and movement patterns of southern eagle rays, highlighting that intraspecific variation should be accounted for in future management considerations.
... The question is, for what purpose do fish emerge at night and venture into unprotected areas? We suggest that fish use the open habitats to forage, interact, and carry out ASR at night at a lower risk of predation (e.g., Hobson, 1973;Nagelkerken et al., 2000;Hammerschlag et al., 2010;Sikkel et al., 2017). Although the low DO in the swamp protects fish from large predators, such as the Nile perch (Lates niloticus, Chapman and Chapman, 1998;Chapman et al., 2002), there is some risk of predation during the daytime due to the presence of visually oriented piscivorous birds, such as the hamerkop (Scopus umbretta) and the pied kingfisher (Ceryle rudis, Figure 8). ...
To understand animal ecology, observation of wildlife in the natural habitat is essential, but particularly challenging in the underwater realm. Weakly electric fishes provide an excellent opportunity to overcome some of these challenges because they generate electric organ discharges (EODs) to sense their environment and to communicate, which can be detected non-invasively. We tracked the EOD and swimming activity of two species of mormyrid weakly electric fishes (Marcusenius victoriae and Petrocephalus degeni) over diel cycles in the laboratory, and we recorded EODs and environmental dissolved oxygen (DO) concentration and temperature over several months in a naturally hypoxic habitat in Uganda. Under laboratory conditions, both species showed increases of activity and exploration behavior that were closely synchronized to the onset of the dark phase. In the wild, fish preferred structurally complex habitats during the day, but dispersed toward open areas at night, presumably to forage and interact. Nocturnal increase of movement range coincided with diel declines in DO concentration to extremely low levels. The fact that fish showed pronounced nocturnal activity patterns in the laboratory and in the open areas of their habitat, but not under floating vegetation, indicates that light intensity exerts a direct effect on their activity. We hypothesize that being dark-active and tolerant to hypoxia increases the resistance of these fish against predators. This study establishes a new technology to record EODs in the field and provides a window into the largely unknown behavior of mormyrids in their natural habitat.
... It is critical to understand the causes of commercially exploited fish population distribution [1,2], which could change due to density-independent and density-dependent processes [3,4]. Density-dependent changes are related to changes in predation intensity [5,6], food availability [7,8], or variation in habitat temperature [9,10]. There is also a consensus that density dependence is a feature of population dynamics for most species [11,12]. ...
The abundance of juvenile fish changes due to endogenous processes, and determining the functional relationships among conspecifics is essential for fisheries’ management. The hake (Merluccius gayi) is an overexploited demersal fish widely distributed in Chile, from 23°39′ S to 47°00′ S in shallow and deep water over the continental shelf and shelf break. We studied the spatiotemporal distribution of hake juveniles (from ages 0 and 1), emphasizing endogenous relationships among juveniles and adults. The abundance per age data were obtained from bottom trawl cruises carried out in the austral winter between 1997 and 2018. Generalized additive models showed a similar spatiotemporal pattern for ages between 0 and 1, and negative effects of adult hake aged seven and older on the abundance of the young generation. Regarding the changes in juvenile abundance, the residual deviance of selected models explained 75.9% (for the age 0) and 95.3% (for the age 1) of the null deviance, revealing a significant increase in juvenile abundance from 2002 to 2007 and subsequent abundance stability at higher levels. Furthermore, the expansion in the abundance of juveniles after 2002 was favored by the low abundance of older adult hake, most which are able to cannibalize young hake. Our results highlight the importance of endogenous factors in the spatial distribution of Chilean hake juveniles to identify nurseries or juvenile areas free of potential cannibal adults.
... Here, we define nursery species as those that spend their early life stages in seagrass meadows and shift to adult habitats when they outgrow the benefits to fitness and survival provided by their nursery habitat (Parrish, 1989;Dahlgren and Eggleston, 2000;Kimirei et al., 2013;Huijbers et al., 2015). In contrast, resident species spend all life stages in seagrass habitats, while transient species perform shorter temporal tidal or nocturnal migrations between habitat types, e.g. to forage in seagrass meadows during high tide or at night (Meyer and Schultz, 1985;Gullström et al., 2002;Hammerschlag et al., 2010). Many nursery and transient species are coral reef-associated and form an important ecological link between seagrass and reef ecosystems, via ontogenetic and feeding migrations (Meyer and Schultz, 1985;Nagelkerken et al., 2000;Pittman and McAlpine, 2003;Dorenbosch et al., 2005a;Harborne et al., 2016). ...
Tropical seagrass meadows are critical habitats for many fish species, yet few studies have investigated the influence of multiple scale-dependent factors and marine protected areas on seagrass fish species of differing life histories. We assessed the influence of fine-scale seagrass meadow characteristics and seascape-scale variables on the abundance of fish in a seagrass-dominated seascape in the Bazaruto Archipelago, Mozambique, particularly examining patterns of nursery-vs. resident species as well as mobile-vs. sedentary species. We found that fish distribution patterns in this seagrass-dominated seascape were dependent on species’ life history characteristics; nursery taxa showed lower abundance in seagrass meadows further from adult reef habitats, while resident species within seagrass meadows occurred in higher abundances far from reefs. For taxa utilizing both mangroves and seagrass meadows as nursery habitat, proximity to mangroves was an important factor. Fish abundances were generally influenced by variables at the seascape scale (km), while sedentary species were predominantly influenced by area variables, and smaller seascapes (<500 m in radius) better explained distribution patterns. The influence of protected areas was taxon-specific, with the strongest effects of protection on resident species. Our results indicate that protection efforts in seagrass-dominated seascapes can have varying impacts on fish distribution, depending on the life history of the species present, and the geographical placement of the reserve within the seascape. Further, we suggest that simple species attributes can be utilised to describe generalized abundance patterns of fish in seagrass seascapes.
... The majority of studies focus on diurnal surveying, particularly those utilizing BRUV survey methods (Barker et al. 2018, Harvey et al., 2012b which are constrained by low light conditions. Restricting surveys to diurnal periods may limit our understanding of ecosystem functioning; for example, differences in diel fish assemblages have been attributed to changes in the abundance of prey (Carpentieri et al., 2005) or predators (Hammerschlag et al., 2010) and habitat/shelter availability (Harvey et al., 2012a), all of which are ambiguous in the absence of nocturnal sampling. This is especially critical in enclosed ecosystems that are considered vulnerable to extrinsic pressures and where trophic interactions remain poorly understood. ...
Understanding the composition and structure of marine animal assemblages across space and time is essential in the establishment of effective management frameworks, particularly for holistic approaches to ecosystem conservation. Baited remote underwater video (BRUV) surveys are a well-established tool used in assessing relative abundances of marine fauna but are not commonly used in enclosed environments such as lakes. Sweetings Pond is an anchialine lake situated on the island of Eleuthera in The Bahamas that remains relatively undocumented, with only a single census available from 1983, yet has experienced an increase in stress from anthropogenic activity. Here, we investigated differences in community composition between sites and attempted to identify the species/benthic components driving changes using baited video surveys, before exploring differences in community structure between day-night periods. Nine species were identified over the 3780 min of BRUV footage analyzed, which was comparable to 1983 estimates. No difference in animal assemblages was seen between sites and no correlation with benthic composition was present. However, nocturnal replicates displayed higher median animal abundance and species richness than diurnal replicates, potentially resulting from a sequential food web aggregation around the light source. A number of unique, opportunistic feeding behaviors were also observed which opens avenues for future study. Overall, this study presents BRUVS as a viable and streamlined tool for managers of enclosed aquatic ecosystems to rapidly assess the system's macrofauna across day-night periods, supporting the requirements of an ecosystem-based management approach.
... What and where fish graze can be influenced by predation risk since animals must balance the need for food with the need for safety (Hammerschlag et al., 2010). One of the ways in which predators modify prey behavior is by creating a "landscape of fear" that impacts foraging activities (Laundre et al., 2010;Catano et al., 2016). ...
Invasive species are one of many anthropogenic challenges to maintaining a healthy marine ecosystem. Two rabbitfish species (Siganus rivulatus and Siganus luridus) are among the more successful migrants from the Red Sea to the Mediterranean, where their intense foraging has caused damage to the algae community, thus reducing primary production and habitat complexity, and impacting nurseries for early life stages. Anecdotal evidence suggests that the impact of rabbitfish on algae is lower in Marine Protected Areas (MPAs) although rabbitfish densities are similar in protected and fished areas. One explanation could be that fear of predators, more often present inside MPAs and an important component of a healthy marine ecosystem, reduces the ecological impacts of rabbitfish. This research aimed to test if such fear effects do occur in rabbitfish. Using controlled mesocosm experiments, we tested S. rivulatus reactions to two chemical predation cues: chemical alarm cues released from a recently killed conspecific fish, and water-borne cues from a tank with a live grouper predator, Epinephelus marginatus. We found that rabbitfish significantly reduce their overall food consumption as well as their bites per minute when exposed to the alarm cue, but not when exposed to the grouper water cue. These results support the idea that MPAs, which effectively increase the density of large piscivores and hence predation, can mitigate the impact of invasive herbivorous species. If the mesocosm results can scale up to natural systems, predation cues may be artificially introduced to other target areas in order to reduce rabbitfish grazing outside reserves. Thus, this study provides information that can be used to manage the ecological impacts caused by invasive rabbitfish, both inside and outside of marine reserves.
... Adult prey species migrate into mangroves during periods of tidal inundation, when the higher levels of turbidity found in mangroves obscure prey, and mangrove roots and pneumatophores provide structural protection (Abrahams and Kattenfeld, 1997;Huxham et al., 2004). On the other hand, fish such as seabream and gray snapper avoid the "risky" mangrove-seagrass zone to avoid predators, although the highest food abundance is within this zone (Hammerschlag et al., 2010). Thus, the foraging behavior of prey fish is species specific, and likely depends on factors such as predator avoidance, structural complexity, and shade (Cocheret de la Morinière et al., 2003). ...
Mangroves, seagrasses, and coral reefs interact in tropical regions throughout the world. These ecosystems exhibit strong synergies, as the health of each ecosystem supports the functioning of adjacent habitats. We present a global spatial analysis of mangrove, seagrass, and reef communities, identifying regions where these habitats co-occur. While only an estimated 18% of interaction zones are covered by protected areas, boundaries between mangroves, seagrasses, and reefs represent areas of high conservation efficiency, where benefits of conservation amplify synergistically as land-sea ecosystems are jointly managed. We discuss four types of conservation efficiencies in these coastal ecosystems: 1) increased resistance to disturbance through inter-ecosystem feedbacks, 2) high biodiversity within small geographic areas, 3) habitat portfolio effects giving rise to climate refugia, and 4) synergistic ecosystem services, where building one ecosystem service inherently increases others. Given these synergistic benefits, global campaigns to expand marine and terrestrial protection should focus on the tightly connective interface between mangroves, seagrasses, and reefs, in order to more efficiently build resilience within and between these habitats.
... Circadian rhythms influence fish movements among habitats, as well as their diel feeding and reproductive behavior (Nagelkerken et al., 2000). These rhythms can be modulated by internal mechanisms but also by external factors such as predation and other trophic interactions (Hammerschlag et al., 2010). Most tropical and temperate reef fish are diurnal (Helfman, 1986;Hobson, 1965), whereas only about 30% exhibit primarily nocturnal activity (Helfman, 1978). ...
Most methods for assessing reef fish assemblages at night require artificial light, but the use of different colors of light may influence the results. We used data from 135 underwater visual censuses (UVCs) performed with different colors of light (red, blue and white) to evaluate the structure of fish assemblages on subtropical rocky reefs along three depth intervals. We did not detect any effect of the color of light on total density or fish species richness per transect, nor on the structure of the entire assemblage. However, the density of some of the most abundant species varied according to the color used. Red light showed the highest values of frequency of occurrence for most species, while the white light resulted in decreased abundance of some fish species. Our results emphasize the importance of choosing the color of light depending on the type of studies to be conducted. This will depend on the objectives of the research (e.g. inventory, behavior or community dynamics) and the target fish fauna (e.g. mobile or sedentary).
... Organisms prefer to spend time in areas rich in resources and low in predation risk [19,23,32,33]. For example, Swainson's Warblers (Limnothlypis swainsonii) space use corresponded to the patchy spatial distributions of certain plants and habitat types [3]. ...
Background:
The drivers of space use patterns of multi-species groups have been poorly studied, although mixed-species avian flocks are common throughout the world. In a mixed-species flock, multiple species move together and maintain proximity. The different species may or may not have conflicting preferences of space use. We hypothesized that the space use patterns of the flock are driven by a single species.
Methods:
We investigated the behavioral drivers of space use patterns of mixed-species flocks in Amazonian Peru by mapping 95% fixed-kernel home ranges of three flocks, which then we divided into high-use (inner 55% kernel utilization distribution) and low-use areas (lying outside the high-use area). We quantified the foraging and anti-predator behavior of individual birds in the flocks. We tested whether foraging and anti-predator behavior of different species were different in high use and low use areas of the flock.
Results:
We collected 455 spatial points and 329 foraging and anti-predator behavior observations on three flocks. The single best model for explaining the space use patterns of the flocks contained only vegetation density that surrounded Dusky-throated Antshrikes.
Conclusion:
The results are consistent with the hypothesis that a single species in mixed-species flocks has a disproportionately large influence on space use patterns. The surrounding vegetation density of the Dusky-throated Antshrike was the only driver of space use patterns of flocks supported by our data. The results may apply to flocks pantropically, many of which are led by species that behave similarly to the Dusky-throated Antshrike, e.g. Asian flocks led by drongos (Dicrurus spp.).
... While fishers did not show spatial avoidance of bobcats, bobcats were positively associated with snowshoe hares, meaning that sites with the most abundant food could also be the riskiest for fishers. Food-safety tradeoffs are common in ecology (Hammerschlag et al. 2010, Emerson and Brown 2015, Pomeroy and Lindström 2018, and this potential tradeoff highlights the challenges faced by mesopredators who compete for food with potential predators (Bischof et al. 2014). By selecting sites with moderate levels of prey availability, fishers may be responding to the risk of both competition and predation from bobcats. ...
One of the most common reasons for failure of wildlife reintroductions is releasing animals into low quality habitat that does not meet resource needs. Food availability and the presence of potential predators or competitors in the reintroduction area are integral aspects of habitat quality that are rarely assessed prior to reintroductions. The fisher (Pekania pennanti) is a commonly reintroduced species that requires complex forest structure for reproduction, relies on a variety of prey, and interacts with a number of other carnivore species. In this thesis, I assessed prey availability for a reintroduced population of fishers and modeled their habitat selection based on forest structure, prey, and predators to better understand what factors could influence reintroduction success of fishers. In the first chapter, I evaluated the relationship between forest management and prey availability for fishers. I conducted habitat surveys, live trapping, and sign surveys for mammalian prey in forests that differed in management history. I then assessed how
forest management and habitat influenced prey diversity and community structure. I found equally diverse but distinct prey communities in forests with different management histories. The prey community in old stands consisted of abundant small rodent species, while younger stands had higher abundance of snowshoe hares (Lepus americanus) and mountain beavers (Aplodontia rufa). I identified a potential disconnect between preferred habitats of fishers and two common prey species, mountain beavers and snowshoe hares. In the second chapter, I examined the relative importance of landscape features and species interactions in determining habitat selection of fishers. I used species detections at 134 remote cameras stations, remotely sensed forest structure data, and telemetry locations of fishers to construct a resource selection function assessing the relative importance of prey, predators, and forest structure in habitat selection by fishers. I found that the probability of fisher use increased in older forests, in close proximity to recently disturbed stands, and in areas with moderate snowshoe hare abundance. Additionally, I documented a potential food-safety tradeoff for fishers between bobcats (Lynx rufus) and snowshoe hares, which fishers may mediate through temporal avoidance of bobcats. Selection for old forests close to recently disturbed stands and the preference of important prey for young stands suggests that habitat mosaics of these forests are valuable for fishers in the Pacific Northwest. Managers should seek to create heterogeneous forest habitats where young stands are intermixed in a matrix of old forest to provide for all habitat needs of recovering fishers. I documented complex relationships between forest structure, prey, predators, and fisher habitat selection, highlighting the importance of addressing species interactions prior to reintroductions.
... Differences in behavior between blue crabs and pinfish can alter their susceptibility to predators in edge habitats [26••]. Furthermore, all fauna are a potential prey resource at some point in their life history, and their ability to respond to edge resources may be affected by the relative risk they experience in those areas [41,55,56]. Observing edge effects becomes more difficult at the community level. ...
Purpose of Review
After several decades of research on edge effects in marine habitats, we still have little understanding of how organisms respond to marine ecotones, and methodological gaps appear to be limiting our progress. Using recent literature (2010–2018), we synthesized responses and processes of organisms across several marine habitats. Specifically, we examined the uniformity of studies across biogenic habitats, the scales selected for exploring edge effects, the experimental approaches used, and the confounding influences that muddle our interpretation of results.
Recent Findings
The majority of edge effect studies are still conducted in seagrass systems and focused on response patterns. We found that the majority of studies were equally likely to report an increase, decrease, neutral, or equivocal effect depending on the context of the organism or habitat. Additionally, only a single measure, or a few related responses, is assessed and causal mechanisms are rarely tested. We note that most studies quantitatively defined an edge habitat as a linear distance from a habitat boundary (e.g., < 1 m, < 5 m), but the distances were not usually scaled to the size, trophic level, or mobility of focal organisms.
Summary
We provide a conceptual diagram as a roadmap for researchers for navigating the myriad influences that affect floral and faunal responses to marine habitat edges. Future efforts should seek to move beyond mensurative searches, explicitly incorporate potentially confounding variables, and more consistently test putative causal factors when known or hypothesized. Additionally, we advise expanding research on habitat types other than seagrasses (e.g., mangroves, shellfish, corals) and adjusting observational scales to more appropriately match mechanisms. Ultimately, we should move beyond pattern description, repeated in a limited subset of nearshore habitats, and toward a quantitative understanding of the processes acting in these unique and potentially impactful marine ecotones.
... For example, how behaviors during dark periods may differ according to individual life-stage or energetic condition, and behaviors in perpetually dark habitats. It is possible that juvenile elasmobranchs may reduce nocturnal activities to lower predation risk from larger conspecifics that actively forage during dark periods (Hammerschlag et al. 2010). Individuals may also base their foraging decisions on body condition and health, as individuals in poor energetic condition may opt to assume increased predation risk in exchange for access to food resources and increases in probability of hunting success under low light conditions (Brown and Kotler 2004). ...
... Modeled yellow perch evolved preference for limiting predation risk, which is a common behavior to program into movement rules ( Srinivasan et al., 2010;Wood and Ackland, 2007 ). Predation avoidance corroborates results from field studies where predation risk structures prey distributions ( Hammerschlag et al., 2010;Swain et al., 2015 ). Predator avoidance continued to evolve when predation pressure was removed, although not to as high of a degree in full simulations. ...
Agent-based, spatially-explicit models that incorporate movement rules are used across ecological disciplines for a variety of applications. However, appropriate movement rules may be difficult to implement due to the complexity of an individual's response to both proximate and ultimate cues, as well as the difficulty in directly assessing how organisms choose to move across their environment. Environmental cues may be complex and dynamic, and therefore, movement responses may require tradeoffs between preferred levels of different environmental variables (e.g, temperature, light level, and prey availability). Here, we present an approach to determine appropriate movement rules by setting them as heritable traits in an eco-genetic modeling framework and allowing movement rules to evolve during the model rather than setting them a priori. We modeled yellow perch, Perca flavescens, movement in a simulated environment and allowed perch to move in response to high-resolution vertical gradients in temperature, dissolved oxygen, light, predators, and prey. Evolving movement rules ultimately increased fish growth and survival over generations in our model, indicating that evolving movement rules led to improved individual performance. We found that emergent movement rules were consistent across trials, with evolved movement rules incorporating different weights of these environmental factors and the most rapid selection on temperature preference. This case study presents a flexible method using eco-genetic modeling to determine appropriate movement rules that can be applied to diverse scenarios in spatially-explicit ecological modeling.
... Although fishers did not show spatial avoidance of bobcats, bobcats were positively associated with hares, meaning that sites where hares were most prevalent could also be the riskiest for fishers. Foodsafety tradeoffs are not uncommon (Pomeroy and Lindström 2006, Hammerschlag et al. 2010, Emerson and Brown 2015, and highlight the challenges faced by mesopredators seeking prey (Bischof et al. 2014) and the challenges for reintroducing species in areas with numerous sympatric carnivores. By selecting sites with intermediate levels of prey activity, fishers may be responding to the risk of competition and predation Table 4. Model rankings of the 5 single-variable resource selection function (RSF) models to select the top forest structure covariate to include in our final RSF model for fishers in the southern Cascade Mountains, Washington, USA. ...
Habitat quality and quantity are key factors in evaluating the potential for success of a wildlife translocation. However, because of the difficulty or cost of evaluating these factors, habitat assessments may not include valuable information on important habitat attributes including the abundance and distribution of prey, predators, and competitors. Fishers (Pekania pennanti) are one of the most commonly reintroduced carnivores in North America, and they are a species of conservation concern in their western range. We examined the relative importance of landscape features and species interactions in determining habitat use of a reintroduced population of fishers in the southern Cascade Mountains, Washington, USA. We used detections of prey and predators at 134 remote camera stations, remotely sensed forest structure data, and telemetry locations of fishers in a resource selection function to assess the relative importance of prey, predators, and forest structure in fisher habitat selection. Fishers selected habitats based on forest conditions and activity levels of snowshoe hares (Lepus americanus), whereas bobcat (Lynx rufus) and coyote (Canis latrans) activity levels did not directly affect habitat selection. The probability of fisher use increased in older stands, close to recently disturbed stands, and in areas with intermediate levels of hare activity. Bobcat and hare activity levels were positively correlated, and fishers avoided areas with the greatest hare activity, suggesting that fishers may experience a food‐safety tradeoff in the study area. Temporal activity patterns in photo detections indicate that fishers may mediate this danger by avoiding bobcats temporally. Our findings suggest that fishers in Washington prefer habitat mosaics of old and recently disturbed stands where they have greater access to resting structures and hares. Management that maintains mosaics of young and old forest across large landscapes is likely to support fisher recovery. Future reintroduction efforts would benefit from an assessment of prey and predator abundance in proposed reintroduction areas before project initiation.
... This finding suggests that individuals are likely to use multiple habitat types within a seascape. Indeed, most nursery species use multiple habitat types (Nagelkerken et al. 2000a;Nagelkerken 2007) to optimise foraging and refuge throughout diel and tidal cycles (Dorenbosch et al. 2004;Hammerschlag et al. 2010). Furthermore, we found evidence that supported the presence of habitat shifts for some species between different juvenile stages (in the species where we could confidently identify different juvenile stages). ...
Context
Habitat characteristics are often equated with habitat function for animals. However, in heterogeneous landscapes, similar habitat types occur in different environmental contexts. In the marine realm, landscape studies have been confined to particular environments, rather than encompassing entire seascapes, due to incompatible sampling methods required in different situations.
Objectives
We examined the interactive structuring effects of local habitat characteristics and environmental context on assemblage composition.
Methods
We used a single technique—remote underwater video census—to explore the importance of habitat type (biotic structural components, substrate, and depth) and environmental context (marine vs estuarine) in structuring juvenile fish assemblages throughout an entire coastal region. In this model system, a range of structural habitat types were present in both estuarine and marine contexts.
Results
The 1315 video surveys collected show a clear hierarchy in the organisation of juvenile fish communities, with assemblages first distinguished by environmental context, then by habitat type. Marine and estuarine mangroves contained entirely different assemblages, and likewise for rocky reefs and submerged aquatic vegetation. Our results suggest that two functionally different ‘seascape nursery’ types exist at local scales within a single region, defined by their context.
Conclusions
The context of a location can be of greater significance in determining potential habitat function than what habitat-forming biota and substrates are present, and apparently similar habitat types in different contexts may be functionally distinct. These findings have important implications for local-scale management and conservation of juvenile fish habitats, particularly in regard to offsetting and restoration.
... Most recent studies on behavior of predators have been focused on the functional details of predator-prey interactions (e.g., [23,24]) but the dynamics of predation activity vary throughout diel periods [25,26]. Generally, the diel pattern of fish behavior is divided in two phases, one that is focused on food seeking and a resting phase where individuals avoid predators. ...
The dynamics of fish communities at tropical and subtropical rocky reefs are influenced in many cases by predation activity and predator-prey interactions. These processes usually follow specific diel patterns in reef areas with higher rates of these interactions occurring during the crepuscular periods. However, other factors such as habitat complexity and species specific behavior may alter these patterns, increasing variability in species interactions. A better understanding of the dynamics of these patterns and processes would allow us to manage and monitor fish communities in these productive and vulnerable areas more efficiently. We investigated behavioral changes of predators and prey fish in subtropical "live-bottom" (sandstone) reefs at Gray's Reef National Marine Sanctuary (GRNMS), located 20 nautical miles off the coast of Georgia, USA, using fisheries acoustic methods in association with visual census and direct observation using SCUBA. Changes in co-location and habitat preferences of predators and prey over time throughout the diel cycle were investigated using species distribution models (MAXENT) based on habitat predictors and by means of spatial statistics. The results indicate that predator and prey distribution patterns changed considerably throughout the day. Prey and predator species exhibited complex spatial dynamics and behavior over diel periods, with prey modifying patterns of habitat use and spatial distribution, likely as a response of their interactions with predators. Crepuscular periods were confirmed to be the most active phases in terms of predator-prey interactions and consequently the most variable. The combination of tools and approaches used in this study provided valuable sources of information that support the inferences of predation risk-driven habitat selection of prey in this subtropical reef system.
... Dusky-throated Antshrikes approached Longwinged Antwren playback sometimes but not always (68% of trials), which suggests that context may influence heterospecific attraction for Duskythroated Antshrikes. The Dusky-throated Antshrikes may gain foraging and antipredatory benefits from flocking, and therefore temporarily low food resources and high predation risk could increase following of heterospecifics (Pomara et al. 2003, Dupuch et al. 2009, Hammerschlag et al. 2010, Darrah and Smith 2013. If food resources or predation risk are important drivers of heterospecific attraction for antshrikes, future studies should record foraging and vigilance behavior before and after playback trials to investigate the contexts in which the Dusky-throated Antshrikes respond to the Longwinged Antwren playback. ...
In resident Amazonian mixed-species flocks, the pattern of attraction of transient species to nuclear Dusky-throated Antshrikes (Thamnomanes ardesiacus) and Long-winged Antwrens (Myrmotherula longipennis) and the pattern of heterospecific attraction between the nuclear species are undocumented. Patterns of attraction can help elucidate the nature of interspecific relationships (i.e., whether they are mutualistic, commensal, or parasitic). We played Dusky-throated Antshrike and Long-winged Antwren vocalizations to flocks and recorded how many transient species approached the playbacks, whether the antshrikes and antwrens were attracted to each other's playbacks, and how strongly they responded to the playbacks. More transient species were attracted to the antshrike vocalizations than antwren vocalizations, and more transient species were attracted to antwren than control vocalizations. Dusky-throated Antshrikes and Long-winged Antwrens approached each other's playback significantly more often than they approached control playbacks; the antwrens responded significantly more strongly to antshrike vocalizations than the antshrikes did to antwren vocalizations. Species may be more attracted to Dusky-throated Antshrikes because of their reliable alarm calling, whereas species may be attracted to antwrens because they serve as a flock indicator. Finally, Dusky-throated Antshrikes and Long-winged Antwrens likely confer benefits to each other, but those benefits may not be symmetrical.
... The fish and crustacean sampling was conducted in 2012 during the wet season (July−October). To maximize the probability of capture, the sampling was performed at night when many faunal species were actively foraging over seagrasses (Luo et al. 2009, Hammerschlag et al. 2010. In summary, the survey design included: 2 seascape types (FS and CS), 2 salinity zones (1 and 2), 3 replicates of each seascape type per salinity zone, 5 distance-to-shore strata within each plot, and 3 randomly located seine locations within each distance-to-shore stratum, for a total number of 180 seine locations. ...
Anthropogenic disturbances in coastal and marine environments have resulted in the transformation of vegetated benthic habitat spatial patterns, which is thought to influence the distribution, community composition, and behavior of marine fauna. In Biscayne Bay, Florida, USA, freshwater discharges into nearshore areas have resulted in the fragmentation of the spatial patterning of submerged aquatic vegetation (SAV). To understand the ecological consequences of the freshwater-induced SAV seascape fragmentation, fish and crustaceans were sampled using seine nets across seascapes with continuous and highly fragmented SAV spatial configurations and across salinity regimes. Fragmented SAV seascapes supported significantly higher species diversity of fish and crustaceans, especially in areas influenced by freshwater discharges. Also, fragmented seascapes supported a higher abundance of the pink shrimp Farfantepenaeus duorarum and the goby Gobiosoma robustum, and higher biomass of generalist predatory fishes than seascapes with continuous SAV. In contrast, pinfish Lagodon rhomboides was more abundant in seascapes with continuous SAV. Faunal assemblage composition differed between zones of contrasting salinity regimes, and the contribution of species occurrence and abundance to the differentiation of assemblage composition between seascape types was associated with the salinity regimes of the seascapes. Thus, water salinity and spatial properties of SAV seascapes are factors that interact to influence faunal community structure in Biscayne Bay. These findings highlight the importance of understanding how environmental context (e.g. salinity regimes) can modulate the influence of benthic spatial patterning on the abundance and biodiversity of nekton communities.
... The studies of food and feeding habits of fishes have a significant advantage in fishery biology. However, such studies can describe the ecological interactions and community structure of the fishes [1,2]. The dietary niche breadth of a fish population increase as preferred food resources become scarce [3,4]. ...
The food and feeding of four species of the young)0-group) fishes in Shatt al-Basrah were studied from February 2011 to April 2012. Twelve food groups were recorded during this study. Crustaceans (copepods, amphipods, shrimps and crabs) were the most important prey for tilapia (Tilapia zilli) and mosquitofish (Gumbosia affinis) (Relative Importance indices (% RII) = 82.7 and 40.2 respectively). Plant was the most important food for mullet (Liza subviridis) (86.8%). Plant and fishes were considered most important food for whitehead's thryssa (Thryssa white headi) (32.3% and 32.7% of the total RII respectively). Tilapia (T. zilli) clearly shows only significant overlap with (G. affinis) (Cλ= 0.76). The overall degree of dietary overlap among all the species was 41.7%. This information is when the complex association between fishes and identifying groups of species using similar resources.
... Fish behavior can be highly variable, with a number of factors affecting a fish's decision to move. For example, movement and habitat choice can vary with individual preference and habitat complexity (Popple and Hunte 2005), different degrees of predation pressure (Martin et al. 2010), resource availability (Hammerschlag et al. 2010), seasonally (Barbour et al. 2014;Ketchum et al. 2014), and between contingents of fish (Afonso et al. 2009). Here, we explore the movement behaviors of a relatively large mobile predator among different marsh complexes within a temperate estuary and the potential implications of this behavior on seascape-level connectivity of marsh complexes. ...
Large predatory fishes, capable of traveling great distances, can facilitate energy flow linkages among spatially separated habitat patches via extended foraging behaviors over expansive areas. Here, we tested this concept by tracking the movement of a large mobile estuarine fish, red drum (Sciaenops ocellatus). Specifically, we addressed the following two questions: (i) What are the spatial and temporal patterns of red drum movement (rates of dispersal) and activity space? (ii) Does red drum movement facilitate linkages among estuarine marsh complexes? Dispersal from the release location was greatest during the first 2 weeks at liberty before declining to less than 0.5 km·week–1 for the remainder of the study. Activity space initially increased rapidly before reaching an asymptote at 2.5 km² 2 weeks postrelease. Connectivity indices calculated among marsh complexes corroborated these observations, suggesting high residency and limited seascape-scale linkages via red drum movement behaviors. These data highlight potential within-estuary spatial structure for mobile fishes and could inform subsequent efforts to track energy flows in coastal food webs, predict the footprint of local habitat restoration benefits, and enhance the design of survey regimes to quantify overall population demography.
... On the other hand, shallower inshore areas with fewer predators pose a greater risk of stranding during ebbing tides (Krumme et al. 2004). Predation risk is not, however, the only factor shaping tidal connectivity, with fish movements also occurring in response to species environmental tolerances (e.g., salinity, turbidity, oxygen content, water temperature; Blaber 2000) and food availability (Hammerschlag et al. 2010). Clearly, there are areas within seascapes that are favourable in terms of the combined effects of optimal environmental factors, food supply, shelter availability and predator abundance (Fodrie et al. 2009;Yeager et al. 2012;Kimirei et al. 2015) and such areas may form hotspots of productivity and diversity . ...
The movement of animals and matter across landscapes structures populations and ecosystems on land and in the sea. This connectivity is fundamental for the persistence of all organisms and is central to the recovery of ecosystems from disturbance. This chapter provides a synthesis of published work on connectivity in coastal seascapes and outlines how new tools and techniques for quantifying connectivity will shape future research in this field. To illustrate diversity in the ecological effects of connectivity we summarise the state of knowledge for two model systems: (1) fish migration in tropical seascapes; and (2) carbon transfer the land-sea interface. Connectivity is a key concept in marine spatial planning, but it is often poorly integrated into conservation, restoration and fisheries management. We outline a stepped approach to better link connectivity with conservation, and identify eight priorities to help shape future research on connectivity in coastal seascapes.
... The functioning of tropical coastal ecosystems is contingent on processes that occur across multiple habitats (Sheaves 2009). Mobile nekton, especially fish, transfer energy among inshore habitats such as coral reefs and mangroves (Pittman & Olds 2014, Green et al. 2015) via short-term feeding and spawning migrations (Verweij et al. 2006, Hammerschlag et al. 2010) as well as longer-term ontogenetic move-ments (Jones et al. 2010). The relationship between connectivity and ecological processes has made identifying the pathways that mobile fauna take to move between habitats a primary focus for the conservation of ecosystem function in coastal areas (Nagelkerken et al. 2015). ...
Identifying pathways that animals use to move among ecosystems has become a focus for improving conservation planning. The function of habitat corridors in facilitating animal movement among terrestrial ecosystems is well established. By contrast, the role of habitat corridors for the movement of marine animals is poorly understood. We used underwater video cameras to evaluate the effects of seagrass corridors and water depth on fish abundance, and the arrival of prey and predatory species on intertidal coral reef flats in eastern Australia. Cameras were placed in intertidal seagrass and unvegetated habitats during incoming tides and recorded fish that moved across these habitats. We found some evidence that fish were more abundant over intertidal seagrass, particularly garfish Hyporhamphus regularis ardelio, striped barracuda Sphyraena obtusata and striped grunter Pelates sexlineatus, but most species did not appear to use the intertidal seagrass as a corridor. Prey fish were generally more abundant at shallower water depths, whereas predators were more common in deeper water, but many species were present over intertidal flats throughout the incoming tide. Our findings show that the movement of fishes across intertidal flats is dynamic, and depends on the species of interest, the composition of intertidal seascapes and tidal condition. Understanding how biotic and abiotic factors interact to influence fish movement and shape patterns in habitat use is a critical challenge for conservation planning in shallow coral reef seascapes.
... Although comparison of growth rate between different habitats was precluded in this study, the presence of a greater number of juveniles than adults of Africanaspis, conforms to this definition. Studies on extant show that few species are limited to a single nursery habitat, the majority utilizing a mosaic of connected habitats due to tidal conditions, feeding, protection and cover seeking behaviours [55][56][57][58]. The difficulty in incorporating dynamic processes such as ontogenetic niche shift and habitat connectivity within the definition of a nursery site is recognized, with most approaches criticized for being static [54]. ...
Here we present a new species of placoderm fish, Africanaspis edmountaini sp. nov., and redescribe Africanaspis doryssa on the basis of new material collected from the type locality of Africanaspis. The new material includes the first head shields of Africanaspis doryssa in addition to soft anatomy for both taxa. Hitherto Africanaspis was entirely described from trunk armour and no record of body and fin outlines had been recorded. In addition the first record of embryonic and juvenile specimens of Africanaspis doryssa is presented and provides a growth series from presumed hatchlings to presumed adults. The presence of a greater number of juveniles compared to adults indicates that the Waterloo Farm fossil site in South Africa represents the first nursery site of arthrodire placoderms known from a cold water environment. The preservation of an ontogenetic series demonstrates that variation within the earlier known sample, initially considered to have resulted from ontogenetic change, instead indicates the presence of a second, less common species Africanaspis edmountaini sp. nov. There is some faunal overlap between the Waterloo Farm fossil site and faunas described from Strud in Belgium and Red Hill, Pennsylvania, in north America, supporting the concept of a more cosmopolitan vertebrate fauna in the Famennian than earlier in the Devonian.
... Previous investigations have reported the habit of the lemon shark to herd schools of fi sh against the shoreline (Wetherbee, 1990;Morrissey, 1990;Reyer et al., 2008), and to patrol shorelines at low light levels in order to intercept fi shes moving between shallow waters and adjacent areas (Hammerschlag et al., 2010). However, photographic records and detailed descriptions as presented here are not available in the literature. ...
The hunting tactics of lemon sharks, Negaprion brevirostris, are described from underwater and cliff-top observations in the Fernando de Noronha Archipelago, western equatorial Atlantic, Brazil. Two main tactics were observed in the shallow waters of sandy beaches and reefs environments: (i) " substrate inspection " of crevices and holes over rocky and reef bottoms, and (ii) " sardine blitz " , which refer to striking schools of fishes (mainly sardines) in the surf zone. The first tactic was restricted to juveniles up to 2 m of total length, whereas subadult and adult sharks with total length larger than 2 m displayed the second. As lemon sharks use waters less than 5 m depth to hunt, perform social behaviours and predator avoidance, results highlight the importance of properly managing these habitats for their conservation, especially in areas where tourism has increased substantially.
... In the wild, animals time their activities to coincide with what for them is the most advantageous phase of the solar day, a concept widely known as biological rhythm (Reebs 2002). Differences in the diel distribution of fi sh assemblages have been related to several driving forces: feeding (Polunin and Klumpp 1989, Piet and Guruge 1997, Carpentieri et al. 2005, predator avoidance (Nagelkerken et al. 2000, Hammerschlag et al. 2010, shelter seeking (Hobson 1972), social interactions (Fréon et al. 1996, Bégout Anras et al. 1997, and reproductive behaviours (Samoilys 1997). Although the diel rhythms of some fi sh species are well known under controlled laboratory conditions, studies under natural conditions remain scarce (Willis et al. 2006, Azzurro et al. 2013, Myers et al. 2016, partly due to observational challenges in the marine environment. ...
Background. There is need for more information on behavioural rhythms of fishes in relation to their habitat use in few or not previously monitored areas, such as coralligenous habitats. Some studies have compiled inventories of observable fish species in this habitat, but no studies have been performed on the temporal patterning of fish behaviour, especially at the scale of the day. The presently reported study aims at providing knowledge on finescale fluctuations of abundances and behaviour of two fish species in coralligenous habitats throughout the diurnal period. Materials and methods. Fish fauna was filmed hourly, for several days, from dusk to dawn, with autonomous, programmable, and rotating video systems. Diurnal variations in abundances per count, considering size classes and behaviour, were studied for two diurnal fish species— the Mediterranean rainbow wrasse, Coris julis (Linnaeus, 1758) (Labridae), and the common two-banded seabream, Diplodus vulgaris (Geoffroy Saint-Hilaire, 1817) (Sparidae) in two study areas of coralligenous habitats on the French Riviera. Results. Significant temporal variability at the scale of the hour was revealed for abundances of C. julis in one of the two study areas, with few individuals in crepuscular periods and highest abundances in the morning and in the afternoon. These differences were mainly due to significant diurnal variations in abundances of small and medium C. julis, which were low in crepuscular periods, whereas large-sized individuals were equally abundant during the day. On the other hand, no discernible diurnal rhythmicity of mean abundances of D. vulgaris was observed, regardless of the study area. Crepuscular periods were associated with sudden changes of abundances and behaviour for both species, with a greater percentage of mobile and solitary individuals, and few feeding individuals compared to the rest of the day. Feeding occurred mainly in the morning for C. julis. In contrast, no dial-time preference for feeding was revealed for D. vulgaris. Conclusions. The study provided preliminary insights into fine-scale diurnal variations of abundances of different life stages and of fish behaviour. Variability in abundances of life stages and of fish behaviours at different times of day should be taken into account for population assessments and spatial comparisons. Moreover, our study confirmed the use of video-imaging as an efficient non-destructive tool for the study of fish fauna in structurally complex, highly valuable habitats.
... For example, how behaviors during dark periods may differ according to individual life-stage or energetic condition, and behaviors in perpetually dark habitats. It is possible that juvenile elasmobranchs may reduce nocturnal activities to lower predation risk from larger conspecifics that actively forage during dark periods (Hammerschlag et al. 2010). Individuals may also base their foraging decisions on body condition and health, as individuals in poor energetic condition may opt to assume increased predation risk in exchange for access to food resources and increases in probability of hunting success under low light conditions (Brown and Kotler 2004). ...
It is commonly assumed that elasmobranchs (sharks, skates, and rays) are most active during dark periods (dawn, dusk, night). However, this assertion has not been critically evaluated. It is also unclear whether dark periods are primarily utilized for the performance of important life-history events, such as mating. If this were the case, low-light periods would be of significance to elasmobranch conservation as some anthropogenic activities (night fishing, lighting) could disproportionately impact fitness of species that are more active in the dark. Here, we review and summarize previous studies on elasmobranch behavior during nocturnal and crepuscular periods focusing on patterns of movement, habitat use, foraging, and reproduction. A review of 166 studies provided mixed results for widely-assumed increased elasmobranch activity when dark. Frequency of foraging and horizontal movement (distance travelled, activity space) were reported as greater only during crepuscular periods in the majority (>50%) of reviewed studies (28 of 43 and 78 of 125 studies, respectively), a pattern not evident during night. No pervasive patterns emerged for increased habitat use or reproductive behaviors during dark. We did not find any particular habitat type consistently supporting increased activity during dark, nor did we find evidence that higher trophic level elasmobranchs were more active when dark. Thus, generalizations about increased elasmobranch activity during dark periods are currently not supported. While research on the behavior of elasmobranchs during dark periods has been increasing, many knowledge gaps remain and we present a set of research priorities to assist in the development of future investigations.
... The studies of food and feeding habits of fishes have a significant advantage in fishery biology. However, such studies can describe the ecological interactions and community structure of the fishes [1,2]. The dietary niche breadth of a fish population increase as preferred food resources become scarce [3,4]. ...
The food and feeding of four species of the young)0-group) fishes in Shatt al-Basrah were studied from February 2011 to April 2012. Twelve food groups were recorded during this study. Crustaceans (copepods, amphipods, shrimps and crabs) were the most important prey for tilapia (Tilapia zilli) and mosquitofish (Gumbosia affinis) (Relative Importance indices (% RII) = 82.7 and 40.2 respectively). Plant was the most important food for mullet (Liza subviridis) (86.8%). Plant and fishes were considered most important food for whitehead's thryssa (Thryssa white headi) (32.3% and 32.7% of the total RII respectively). Tilapia (T. zilli) clearly shows only significant overlap with (G. affinis) (Cλ= 0.76). The overall degree of dietary overlap among all the species was 41.7%. This information is when the complex association between fishes and identifying groups of species using similar resources.
... A habitat preference index (PI) was determined by dividing the proportion of browsed patches in a habitat with the proportion of the habitat available (Krueger, 1972;Uresk, 1984;Kauhala & Auttila, 2009). PI <1 was regarded as habitat avoidance and PI > 1 as habitat preference (Hammerschlag, Heithaus & Serafy, 2010). We investigated whether tree density, tree species diversity and tree height per patch for all patches (used and available) differed among habitat types. ...
Understanding foraging decisions made by wildlife at different spatio-temporal scales is important for wildlife management and conservation. We tested whether foraging decisions by Masai giraffe (Giraffa camelopardalis tippelskirchi Matschie) differed with scales; habitat, patch and tree in a heterogeneous savannah. We collected data from Arusha National Park, Tanzania, in March-May and August-October 2013. Visual observations were used to collect data on foraging behaviour. Measurements of tree height and stem height and scoring of accumulated browsing were made in 133 patches around trees where the giraffes had been seen browsing, and in a corresponding number of available patches. Giraffes selected Acacia shrub and Dodonea shrub habitats but not for water availability or predator avoidance. For patch use, giraffe selected high quantity of Acacia xanthophloea and Dodonea viscosa. Between plant species, A. xanthophloea was the most preferred and within plant species, tree quality was enhanced by tree height and high score of accumulated browsing. Generally, giraffes selected for A. xanthophloea at all scales.
... Few nocturnal studies of fish distributions have been conducted, so it is premature to generalize this result, and the mechanisms generating these patterns are not well understood. Predation rates on experimentally tethered pinfish prey were twice as high at night, compared to daytime, so avoidance of predation does not explain the nocturnal foraging behavior of these species (Hammerschlag et al., 2010a(Hammerschlag et al., , 2010b. However, rates of preda tion were highest near the mangrove edge and may explain why nocturnal foragers avoid that ecotone. ...
Mangrove habitats are among the most productive ecosystems on the Earth. Their low vegetational diversity belies a remarkable richness of associated species and trophic interactions. This contribution summarizes what is known about these interactions. Information on interaction strengths, top-down versus bottom-up control, and the consequences of species interactions for community structure is only available for a few systems. At a more fundamental level, our understanding of the relative contributions of different sources of primary productivity and the patterns and mechanisms of their exploitation by herbivores, detritivores, and deposit feeders remains quite limited. Even less is known about the movement of carbon, nitrogen, and other elements through mangrove food webs to higher trophic levels. Long-standing paradigms asserting minimal consumption of living plant tissues by herbivores and the paramount role of mangrove detritus as fuel for secondary production of crustaceans and fish are being challenged by data gathered with newer methodologies, most notably, stable isotope analysis. Much remains to be learned about the role of mangroves as nurseries for juvenile life history stages and the trophic links between mangroves and neighboring ecosystems. Ongoing and future investigations of these processes that employ a balanced mix of quantitative observation and field experiments promise to generate exciting new insights about mangrove community and ecosystem processes, and at the same time inform general food-web theory.
The food and feeding adaptations of 0-group fishes in the water of Shatt Al-Arab River were studied during the period between March 2011 to December 2012. A total of 1851 fish samples of were collected. The stomach fullness and contents were observed and analyzed using frequency of occurrence, numerical and point methods. The non-empty stomach recorded during the study could be attributed to food abundance and good feeding habits. Four major food groups Bacillariophyta, Chlorophyta, Cyanophyte, Copepods, Amphipods and Shrimp) were recorded. The result showed that Liza subviridis is herbivores and the remaining of the fish are omnivores feeders. The degree dietary overlap among the species investigated was in the region of 51.1% . Diet Similarity Index between each pair species was also calculated .The results indicate that these fish might be in direct competition for food.
Marine mammals in subtropical coastal habitats are sentinels of the health of the ecosystem and offer important ecosystem services. They rely on prey that pursues feeding opportunities, while both avoid unfavorable conditions. In many cases, these predator-prey dynamics fluctuate seasonally and are regulated by lunar, tidal, and/or diel cycles (hour). However, these rhythmical patterns may vary under different seasonal conditions. Bottlenose dolphins (Tursiops truncatus) in the Ensenada de La Paz in Baja California Sur, Mexico, were detected acoustically over the course of an annual cycle on 21 separate occasions, covering 640 h from June 2017 to May 2019. The presence of bottlenose dolphins was examined using Generalized
Additive Models (GAM) including variables that are related directly to their habitat (direct variables: hour, distance, depth) and to their prey (indirect variables: SST, moon
phase and tides). Seasonal differences in the presence of bottlenose dolphins were influenced more by indirect variables (explained deviance: 34.8% vs. 37.7%). Hourly acoustic detections occurred less frequently when SST exceeded 27.4 �C (Aug–End of
Nov.) and more frequently at moderate temperatures (22.7 �C to 26.3 �C) in May through July. Moreover, bottlenose dolphins were detected more frequently during waning and new moon phases, at the onset of flood and ebb tides, and during day (04:00 to 20:00). The seasonal differences in acoustic detections rates were highlighted
by the global GAM and hierarchical clustering. The strong seasonal pattern indicated possible interactions with rhythmic pattern of bottlenose dolphins. Four candidate variables (SST, moon, tide, and hour) were tested for plausible interaction terms
additional to their individual consideration, out of which only hour changed significantly between seasons. The patterns of presence likely increase feeding opportunities or may favor other behaviors such as socializing, resting, or nursing. These might prove responsible for the distinct occurrence and hourly patterns of bottlenose dolphins.
Coral reef ecosystems are under increasing anthropogenic pressures making it ever more important to monitor changes in fish communities to implement appropriate management. In contrast to long-term spatial and temporal variation which has been extensively documented, little work has been carried out to identify variability in fish assemblages on short time scales, with few studies testing patterns of fish assemblages between and within days. Here we investigated the diurnal changes in species richness, relative abundance and assemblage composition in a shallow coral reef fish community in Egypt. To do so, a section of coral reef was filmed during the morning (0600 h), midday (1000 and 1400 h) and afternoon (1800 h) over eleven days. Dusk (0600 h) and dawn samples (1800 h) showed higher species richness compared to late morning (1000 h) and mid-day samples (1400 h) and borderline significantly higher numbers of total individuals, likely associated with feeding activity and predator avoidance. Assemblage composition varied across days and time-of-day, showing greater variability during dusk and dawn associated with a transition between day-time and night-time assemblages. Our results have implications for designing coral reef fish surveys, emphasising that short-term changes in fish communities should be considered when designing experiments to monitor fish assemblages over time. Where possible, we suggest increasing replication within sites and time scales or randomising data within a specific time window at all sites, looking to exclude dusk and dawn.
Despite providing many important Ecosystem Services, mangroves are one of the most globally threatened forest types with loss rates at approximately 1% y-1, Ecuador has lost approximately one quarter of its mangroves; this loss has been predominately driven by aquaculture. Numerous studies have established the strong association between juvenile fish species (many of economic importance) and mangrove habitat. Although the Galapagos are more famed for their finches, tortoises, sea lions and iguanas, mangrove ecosystems are present across many of the islands and host much of the Archipelago’s biodiversity and are relatively underrepresented in its scientific literature.
The objectives were to document the fish assemblages and to evaluate mangroves as a nursery habitat for Lutjanidae and Haemulidae in different locations around Puerto Villamil, Isabela.
In this study, transect surveys were conducted from May to July 2013 by snorkelling to compare four different habitat types: Mangrove edge, Lower mangrove creek, Upper mangrove creek and Rocky sites. For each transect, environmental variables, the species’ abundance, and the sizes of the Lutjanidae and Haemulidae were recorded at approximately weekly intervals. Mangrove prop root densities were measured in quadrats at five metre intervals. In addition, an intensive tidal focus study was conducted over five days in the four different habitat types around the port.
Three species of Lutjanidae and three of Haemulidae were recorded in total. Haemulidae were found very infrequently and usually at the Rocky sites. Although the Mangrove edge and Rocky sites had the highest species richness and number of individual fish 10m-1, the Upper mangrove creek – which had the greatest mangrove habitat structure – had the highest numbers and proportional representation of Lutjanidae 10m-1, followed by the Lower mangrove creek. There was no evidence that smaller class sizes of Lutjanidae were found more frequently in the Mangrove sites, despite what might have been expected from the literature on the importance of mangroves as nurseries. Lutjanidae numbers and mangrove prop root density were significantly correlated; the root density explained 8% of the variation in Lutjanidae numbers, and 17% for L. argentiventris. Species richness did not significantly alter with different tidal states, and there was limited evidence that the number of individuals 10m-1 decreased at low tides in the Upper mangrove creek.
The mangrove creeks have been shown to be important habitats for large numbers of Lutjanidae, though this study has been unable to establish if they are used as a nursery. Further studies in deeper waters and the open ocean and additional tagging studies are recommended to create a more detailed understanding of the life cycles and ontogenetic movements of Lutjanidae and Haemulidae in the Galápagos.
Quantifying the spatial and temporal aspects of fish residency is needed to understand energy transfer, habitat function, contaminant exposure, and effective design of MPAs in estuarine systems. The spatial and temporal movements of 19 sea bream (Archosargus rhomboidalis), an ecologically important species in mangrove estuaries of the western Atlantic, were investigated in multiple bays on a Caribbean Island over two years using surgically implanted acoustic transmitters. Fish were almost continuously monitored (residency index 96–100%) by an array of hydrophones during the 11–13 month battery-life of their transmitters. Individual fish utilized small core areas (mean = 9.8 ha during daytime and 11.0 ha at night), displayed daily site fidelity (mean = 57% overlap in day night core area), showed no evidence of an ontogenetic increase in core habitat size, and many exhibited a change in the bays utilized during winter months which is coincident with suspected spawning. Fish captured from the same bay generally occupied the same spaces within the study area, and in similar proportions, compared to fish captured in adjacent bays. Fish from different bays did not mix and wander throughout the ecosystem even though it is all suitable habitat and is used by different groups of localized individuals. This similarity of occupancy patterns is limited to the spatial scale of bays and temporal scales of weeks or months. When considered at the resolution of individual receivers and hourly time steps, most fish are not in close proximity to one another for the vast majority of the time. Although some pairs of fish had as many as 84% of their hourly detections on the same receivers in the month after tagging, they gradually spent less time near each other, even though their overall pattern of movements was consistent at the scale of whole bays. This highlights the importance of examining movements of fish on multiple spatial scales and time-intervals to understand their interactions.
Bottlenose dolphins (Tursiops truncatus) are ecosystem sentinels. In the Gulf of California, Mexico, they are found in areas that overlap with human activities, as in the case of the Ensenada de La Paz lagoon. A custom-made recorder -moored at medium depth (2.0 m) in the entrance to the lagoon- recorded acoustic data from June to November 2017 (8 deployments; 293 h). Whistles -an indicative of bottlenose dolphin presences- were pooled over time to acquire acoustic encounters, which were analysed to infer continuity of animal presence and test for statistically significant differences between deployments, day and night, and hours. Whistles were recorded during all deployments and evidenced night-time presence of bottlenose dolphins in the lagoon. Significant differences of acoustic encounters were observed between ‘Jun-Jul’ and ‘Sep-Nov’. Acoustic encounters were higher at night but were not different at an hourly level. Acoustical data proved the continuous presence of bottlenose dolphins, highlighting the importance of the Ensenada de La Paz for their population. This initial study highlights the usefulness of long-term passive acoustic monitoring to inform stake holders involved in management and conservation plans.
Mangroves are critical fish and invertebrate habitats, however, identifying to what degree species are affiliated to mangrove systems remains challenging. Here we outline and apply two quantitative and one qualitative method for assessing the degree of mangrove affiliation globally at a species level, based on habitat-specific fish and invertebrate species densities extracted from an exhaustive search of the literature, for mangroves and their associated coastal habitats. We assessed all 121 species for which we had ≥7 mangrove records and where data allowed, quantified the percentage contribution of mangroves to the summed species density across all habitats. We set the threshold for identifying a species as "highly mangrove-affiliated" as ≥70% relative density, and examined its validity by subjecting a subset of species either side of the threshold to a thorough review of evidence for mangrove affiliation in the peer reviewed literature. We found that 53 were highly mangrove-affiliated, including 24 fish and three invertebrate species from the Atlantic East Pacific, and nine fish and 15 invertebrate species from the Indo West Pacific ( n = 2 had global distributions). 36 of the 53 species are of value to artisanal, subsistence or commercial fisheries; 21 in the Atlantic East Pacific, and 13 in the Indo West Pacific. While this list of highly mangrove-affiliated species is far from complete due to data limitations, it represents the first attempt to undertake a global overview of highly mangrove-affiliated species, and a proof of concept for a quantitative and objective method of assessment.
Diverse habitats composing coastal seascapes occur in close proximity, connected by the flux of materials and fauna across habitat boundaries. Understanding how seascape connectivity alters important ecosystem functions for fish, however, is not well established. For a seagrass‐dominant seascape, we predicted that configuration and composition of adjacent habitats would alter habitat access for fauna and trophic subsidies, enhancing nursery function for juvenile fish. In an extensive Zostera marina seagrass meadow, we established sites adjacent to (1) highly complex and productive kelp forests (Nereocystis luetkeana), (2) unvegetated sand habitats, and (3) in the seagrass meadow interior. Using SCUBA, we conducted underwater observations of young‐of the‐year (YOY) rockfish (Sebastes spp.) recruitment across sites. Using generalized linear mixed effects models, we assessed the role of seascape adjacency relative to seagrass provisions (habitat complexity and prey) on YOY recruitment. YOY rockfish collections were used to trace sources of allochthonous vs. autochthonous primary production in the seagrass food web, via a δ13C and δ15N isotopic mixing model, and prey consumption using stomach contents. Overall, seagrass nursery function was strongly influenced by adjacent habitats and associated subsidies. Allochthonous N. luetkeana was the greatest source of energy assimilated by YOY rockfish within seagrass sites. In seagrass sites adjacent to N. luetkeana kelp forests, YOYs consumed higher quality prey, which corresponded with better body condition relative to sites adjacent to sand. Moreover, kelp forest adjacency enhanced YOY rockfish recruitment within the seagrass meadow, suggesting that habitat complexity is a key seascape feature influencing the nursery function of nearshore habitats. In general, to promote seascape connectivity, the conservation and restoration of nursery habitats should prioritize the inclusion of habitat mosaics of high structural complexity and productivity. We illustrate and emphasize the importance of using a seascape‐level approach that considers linkages among habitats for the management of important nearshore ecosystem functions.
We consider a simple model in which an animal can control both its probability of starvation and its probability of predation. Probability of starvation is decreased by increasing the mean amount of food obtained in the day, but this increases the probability of predation. The optimal mean gain minimizes that total mortality. It is shown that as the amount of food that is required per day increases, the probability of starvation does not necessarily increase, and may actually decrease. This result arises because as the food requirement increases, the animal increases its predation risk in order to avoid starvation. The results suggest that it is inappropriate to argue that food alone or predation alone limits the size of a population when there is a strong interaction between them. Furthermore, the number of animals that die from starvation may not provide a reliable indication of the importance of food.
The influence of predation risk on patch choice was measured by examining the spatial distribution of 10 guppies (Poecilia reticulata) between two feeders, at one of which there was a risk of predation. The distribution was assumed to be ideal free. Nine unique situations were examined using all possible combinations of three risk levels and three diet levels, for each sex of guppy separately. Both sex and diet level influenced the effect of predation risk on patch choice. For the females the effect of risk was highest at the intermediate diet level. However, the males exhibited the opposite response: the effect of risk of predation was lowest at the intermediate diet level. A simple equation was then used to predict how much extra food (representing the energetic equivalent of risk) must be added to the risky patch for the guppies to become indifferent to the risk differences between the two types of patches. This manipulation caused a similar number of guppies to use both the risky and safe feeders, reducing or offsetting the influence of risk of predation. However, the male guppies were less influenced by this manipulation than were the females. The different results for the two sexes are consistent with known differences in their life histories, indicating that a knowledge of an animal's life history will often be necessary to understand how it makes trade-offs when choosing were to forage.
Manual acoustic telemetry techniques were used to study spatial and temporal patterns of movement of juvenile lemon sharks. Ultrasonic transmitters were implanted into the coelom of 38 sharks, yielding trackings totaling 2281 telemetry fixes. Activity space varied from 0.23 km2 to 1.26 km2 and was positively correlated with shark size. Three indices of site attachment demonstrated that juvenile lemon sharks establish a home range. An index of site defense and field observations indicated that no territoriality was observed against conspecifics.
Animals commonly choose among habitats that differ both in foraging return and mortality hazard. However, no experimental study has attempted to predict the level of increase in resources, or the decrease in mortality hazard, which will induce a forager to shift from a safer to a more hazardous (but richer) foraging area. Here we present and test a model that specifies the choice of foraging areas ("habitats") that would minimize total mortality risk while allowing collection of some arbitrary net energy gain. We tested the model with juvenile creek chubs (Semotilus atromaculatus) in an experimental field stream in which the foragers could utilize a foodless refuge and choose between two foraging areas that differed in experimentally manipulated resource densities (Tubifex spp. worms in sediments) and mortality hazard (adult creek chubs). For the case tested, the model specified a simple rule: "use the refuge plus the site with the lowest ratio of mortality rate (μ) to gross foraging rat (f)," i.e., "minimize μ./f." Independent prior measurements of mortality hazard (as a function of predator density) and gross foraging rate (as a function of resource density) allowed us to predict the resource level in the more hazardous foraging site that should induce a shift from the safer to the more hazardous site. The chubs' preferences in subsequent choice experiments agreed well with the theoretical predictions. The "minimize μ/f" rule (deaths per unit energy), perhaps in modified form, provides a simple alternative to the "maximize f" (energy per unit time) criterion that applies to long-term rate maximization when predation hazard does not differ among choices.
Problem: Infer relative danger from spatially segregated predators in large-scale marine systems, using individual differences in prey foraging behaviour. Mathematical models: Optimization of trade-offs between predation risk and energy gain. Key assumption: Foraging individuals choosing to incur higher risk of predation should experience higher energetic gain than individuals choosing safer foraging options. Organisms: Alaskan harbour seals foraging under predation risk from killer whales and Pacific sleeper sharks in shallow and deep strata, respectively. Sleeper sharks are elusive predators and their interactions with prey are difficult to measure directly. Method: Our method infers the relative danger from different predator types that is theoretically most plausible according to intermediate consumer behaviour. We predicted net energy gain and predation risk per foraging dive, parameterizing an analytical model with data on seal behaviour and the spatial distributions of predators and resources. We used assumptions about relative danger from different predator types as treatments in a computer experiment. We sought the treatment combination best supporting the assumption that individuals that risk more should gain more by plotting the individual seals' predicted cumulative energy gain against cumulative predation risk. Improved statistical fit for a positive and monotonic relationship implied greater support. Conclusions: Our key assumption was best supported when assuming that relative danger from sleeper sharks is much greater than that from killer whales, suggesting that sub-lethal effects of sharks on Alaskan harbour seals might be much stronger than previously thought.
Many fishes are thought to make diel, seasonal and/or ontogenetic migrations among seagrass, mangrove, and coral reef habitats. However, most evidence of such movement has been inferred from density and size structure differences among these habitats in tropical waters. The aim of the present study was to directly evaluate multiple habitat use by an ecologically and economically important reef fish, the gray snapper Lutjanus griseus, in subtropical waters. An integrated set of activities was conducted, including tagging and tracking of individuals and underwater video photography to examine the spatial and temporal dynamics of movements among neighboring mangrove, seagrass, and coral reef habitats in the northern Florida Keys, USA. Results of ultrasonic acoustic and mini-archival tagging indicated that L. griseus exhibits: (1) a distinct diel migration pattern, whereby shallow seagrass beds are frequented nocturnally and mangroves and other habitats with complex structure are occupied diurnally, and (2) bay-to-ocean movement, occurring during the known spawning season of L. griseus in this region. Video photography confirmed diel movement among seagrass and mangrove habitats. Results of this subtropical study corroborate direct and indirect evidence obtained in tropical waters of multiple inshore habitat use by L. griseus, as well as its seasonal movement into or towards offshore reefs. For resource managers charged with designing and implementing management plans for subtropical coastal habitats and fisheries, our findings provide direct support for the strategy of conserving both inshore seagrass and mangrove habitats as well as offshore coral reefs. tagging, Underwater video
The shallow-water refuge paradigm has been globally applied to help explain the high abundances of juvenile fishes that utilise shallow-water estuarine nursery habitats. Despite the wide application and acceptance of the paradigm, there is little direct evidence to indicate that small juvenile fishes benefit from reduced predation pressure in shallow water habitats relative to adjacent deeper waters. The present study employed chronographic tethering experiments to examine patterns in predation potential across a depth gradient (0.2 to 3 m) in the lower reaches of a tropical estuary in northeastern Queensland, Australia. Over 6 mo, 17 replicate experimental trials were conducted, deploying a total of 183 tethered fish prey. Despite the clear and consistent patterns found in the few previous studies elsewhere in the world, there was no significant effect of depth on predation pressure, and thus no evidence of lower predation pressure in the shallow relative to the adjacent deeper estuarine waters examined in the present study. The findings suggest that the shallow-water refuge paradigm may be too simplistic for diverse and complex tropical estuarine nursery grounds.
Similar to nearshore systems in temperate latitudes, the nursery paradigm for tropical back-reef systems is that they provide a habitat for juveniles of species that subsequently make ontogenetic shifts to adult populations on coral reefs (we refer to this as the nursery function of back-reef systems). Nevertheless, we lack a full understanding of the importance of the nursery function of back-reef systems to the maintenance of coral reef fishes and invertebrate populations; the few studies that have examined the nursery function of multiple habitats indicate that the relationship between juvenile production in back-reef habitats and their subsequent contribution to adult populations on reefs remain poorly understood. In this synopsis we (1) synthesize current knowledge of life history, ecological and habitat influences on juvenile distribution patterns and nursery function within back-reef systems; (2) outline a research strategy for assessing the nursery function of various habitat types in back-reef systems; and (3) discuss management recommendations, particularly in regard to how improved knowledge of the nursery function of back-reef systems can be used in fisheries and ecosystem management, including habitat conservation and restoration decisions. The research strategy builds on research recommendations for assessing the nursery function of temperate habitats and includes 4 levels of research: (1) building conceptual models to guide research and management; (2) identifying juvenile habitat use patterns; (3) measuring connectivity of juvenile and adult populations between habitats; and (4) examining ecological processes that may influence patterns assessed in Level 2 and Level 3 research. Research and modeling output from Levels 1 to 4 will provide an improved ecological understanding of the degree and importance of interconnections between coral reef and adjacent back-reef systems, and will provide information to managers that will facilitate wise decisions pertaining to habitat conservation, habitat restoration, and ecosystem-based management, and the maintenance of sustainable fisheries.
Little evidence is available on how juvenile fishes utilise seagrass beds and adjacent mangroves as feeding habitats. In this study we tested the degree to which Caribbean mangroves are utilised as feeding grounds by the fish community from adjacent seagrass beds. Stable carbon and nitrogen isotope analyses were performed on several potential food items from seagrass beds and adjacent mangroves, on muscle tissue of 23 fish species from seagrass beds on a Caribbean island (Curacao, Netherlands Antilles), and on juveniles of 2 common reef fish species, Haemulon flavolineatum and Ocyurus chrysurus, from seagrass beds in 7 bays on 5 Caribbean islands. Only the herbivore Acanthurus chirurgus and the carnivore Haemulon chrysargyreum appeared to feed predominantly in the mangrove habitat, whereas the carnivores Mulloidichthys martinicus and O. chrysurus (only on 2 islands) showed a stable carbon signature suggestive of food intake from the mangrove as well as the seagrass habitat. The piscivore Sphyraena barracuda foraged on fish schooling at the mangrove/seagrass interface. For the other 18 seagrass fish species, which contributed 86 % of the total seagrass fish density, the contribution of food sources from the mangroves was minor to negligible. The same was true for H, flavolineatum and 0, chrysurus on most of the other Caribbean islands. The results contrast with the situation in the Indo-Pacific, where intertidal mangroves serve as important feeding habitats for fishes from adjacent systems during high tide. This difference is most probably explained by both the absence of large tidal differences on Caribbean islands and the greater food abundance in seagrass beds than in mangroves.
Day-night changes in fish communities were quantified in 6 associated shallow-water biotopes within a single bay: mangroves, seagrass beds, algal beds, channel, fossil reef boulders, and notches in fossil reef rock. All biotopes, except the algal beds, showed a strong reduction in fish density and species richness at night, caused by absence of diurnally active fishes and migrations of Haemulidae and Lutjanidae to the seagrass beds. The fish fauna of the different biotopes showed a relatively high dissimilarity between day and night. This dissimilarity is largely caused by absence of Acanthuridae, Chaetodontidae, Labridae, Pomacentridae, Scaridae and Sparidae at night. These fishes seek shelter at night in, amongst others, the channel, notches and boulders. The balloonfish Diodon holocanthus utilised almost all biotopes as shelter as well as feeding sites. The wide distribution of its preferred food (molluscs) probably explains its distribution in most biotopes at night. The nocturnally active Haemulidae and Lutjanidae, on the other hand, migrated from their daytime shelter sites to the seagrass beds at night to feed. Some of these fishes also migrated to the algal beds to feed. The preference of Haemulidae and Lutjanidae for the seagrass bed as a feeding biotope, instead of other bay biotopes, appears to be related to the relatively high availability of their preferred food (Tanaidacea and Decapoda) as determined by digestive tract analysis. Other bay biotopes showed much lower densities of such food items compared to the seagrass beds.
Predation has long been implicated as a major selective force in the evolution of several morphological and behavioral characteristics of animals. The importance of predation during evolutionary time is clear, but growing evidence suggests that animals also have the ability to assess and behaviorally influence their risk of being preyed upon in ecological time (i.e., during their lifetime). We develop an abstraction of the predation process in which several components of predation risk are identified. A review of the literature indicates that an animal's ability to assess and behaviorally control one or more of these components strongly influences decision making in feeding animals, as well as in animals deciding when and how to escape predators, when and how to be social, or even, for fishes, when and how to breathe air. This review also reveals that such decision making reflects apparent trade-offs between the risk of predation and the benefits to be gained from engaging in a given activity. Despite this body of evidence, several areas in the study of animal behavior have received little or no attention from a predation perspective. We identify several such areas, the most important of which is that dealing with animal reproduction. Much work also remains regarding the precise nature of the risk of predation and how it is actually perceived by animals, and the extent to which they can behaviorally control their risk of predation. Mathematical models will likely play a major role in future work, and we suggest that modelers strive to consider the potential complexity in behavioral responses to predation risk. Overall, since virtually every animal is potential prey for others, research that seriously considers the influence of predation risk will provide significant insight into the nature of animal behavior.
Identical populations of 3 size-classes of bluegill sunfish Lepomis macrochirus were stocked on both sides of a divided pond (29m in diameter), and 8 piscivorous largemouth bass Micropterus salmoides were introduced to one side. Only the small size-class suffered significant mortality from the bass (each bass consumed on average about one small bluegill every 3.8 d); the 2 larger size-classes exhibited similar mortality rates on both sides of the pond. In the absence of the bass, habitat use of all size-classes was similar and the pattern of habitat use maximized foraging return rates. In the presence of the bass the 2 larger size-classes chose habitats to maximize return rates, but the small size-class obtained a greater fraction of its diet from the vegetation habitat, where foraging return rates were only 1/3 of those in the more open habitats. The small size-class further exhibited a significant depression in individual growth in the presence of the bass; the growth increment during the experiment was 27% less than that for small bluegills in the absence of the bass. -from Authors
The elk or wapiti (Cervus elaphus) and bison (Bison bison) of Yellowstone National Park have lived in an environment free of wolves (Canis lupus) for the last 50 years. In the winter of 1994-1995, wolves were reintroduced into parts of Yellowstone National Park. Foraging theory predicts that elk and bison would respond to this threat by in - creasing their vigilance levels. We tested this prediction by comparing vigilance levels of elk and bison in areas with wolves with those of elk still in "wolf-free" zones of the Park. Male elk and bison showed no response to the reintro- duction of wolves, maintaining the lowest levels of vigilance throughout the study (≈12 and 7% of the time was spent vigilant, respectively). Female elk and bison showed significantly higher vigilance levels in areas with wolves than in areas without wolves. The highest vigilance level (47.5 ± 4.1%; mean ± SE) was seen by the second year for female elk with calves in the areas with wolves and was maintained during the subsequent 3 years of the study. As wolves ex- panded into non-wolf areas, female elk with and without calves in these areas gradually increased their vigilance levels from initially 20.1 ± 3.5 and 11.5 ± 0.9% to 43.0 ± 5.9 and 30.5 ± 2.8% by the fifth year of the study, respectively. We discuss the possible reasons for the differences seen among the social groups. We suggest that these behavioural re- sponses to the presence of wolves may have more far-reaching consequences for elk and bison ecology than the actual killing of individuals by wolves. 1409
A total of 53 species of juvenile fish were caught over a 2 yr study period in 2 mangrove lined estuaries in Moreton Bay, eastern subtropical Australia. Comparing juvenile fish communities among mangrove forests, seagrass beds and mudflats identified significant differences in species richness and abundances of juveniles. Seagrass communities comprised distinct species of resident and nonresident fish species of little economic importance. Mangrove forests and mudflats had many shared species (but mangrove forests were dominated by smaller or younger juveniles in greater abundances; Laegdsgaard unpubl. data). Mudflat habitats appear to be transition zones between juvenile and adult habitats. Only 4 species were exclusive to seagrass whereas 27 species were exclusive to the mangrove/mudflat habitat. Juveniles of 7 of the 10 commercially harvested fish species in Moreton Bay were found in greatest numbers in mangrove forests. Salinity, temperature and turbidity were similar in all habitats so could not account for differences in habitat choice of juvenile fish. Most juvenile fish in mangroves during summer were nonresidents and species richness and abundance were highest in summer and lowest in winter. There were significant differences among sites and years in the numbers of species and individuals; however, the trends were similar and demonstrated clearly that mangrove sites within Moreton Bay play a more important role and have greater potential as nursery habitats than do adjacent habitats. Preferential selection of mangrove habitats by juvenile fish, particularly commercial species, indicates a need for conservation.
Mangroves and seagrass beds are important daytime shelter habitats for juvenile Caribbean reef fish species, but little is known about their relative importance as feeding grounds. In the present study, we tested the degree to which these 2 habitats are used as a feeding ground for 4 nocturnally active fish species on Curacao, Netherlands Antilles. Stable isotope analysis was used as a technique to distinguish between feeding in mangroves and seagrass beds. Individuals of the 4 species which were sheltering during the daytime in permanently inundated fringing mangroves subject to low tidal exchange showed a stable carbon isotope signature indicative of a mixed diet composed of crustaceans from mangroves as well as seagrass beds, with the contribution from mangrove food items lying between 57 and 92%. However, individuals of the same species sheltering on adjacent (
To balance conXicting demands for food and safety from predation, feeding animals have two useful tools. First, they can vary the amount of time they devote to harvesting patches that vary in predation risk and feeding rates. Second, they can use vigilance to trade-oV food and safety while feeding from a food patch. I present a model for predicting how an optimal forager should jointly use these two tools. Factors inXuencing the use of these tools include encounter rate with predators, predator lethality in the absence of vigilance, eVectiveness of vigilance in reducing predator lethality, the marginal value of energy to the forager and the forager's survivor's Wtness. Patch-use behaviours inXuenced by these factors include vigilance level, quitting harvest rate and giving-up density (GUD). All three of these patch-use behaviours should increase in response to an increase in encounter rate with predators, predator lethality and the forager's survivor's Wtness, and decrease with an increase in the marginal value of energy. In response to increasing the eVectiveness of vigilance, vigilance should increase and the GUD and quitting harvest rate should decline. The amount of food left by a forager in a depletable food patch, the GUD, provides an empirical link for testing the model's predictions. Giving-up densities should increase with increasing predation risk, and GUDs should increase with declining food-density- speciWc harvest rates. DiVerences in GUDs among food patches attributable to diVerences in quitting harvest rates measure the contribution of time allocation to managing diVerences in predation risk. DiVerences in GUDs attributable to diVerences in food-density-speciWc harvest rates measure the contribution of vigilance to managing predation risk.
Cover U often thought to be an important habitat characteristic for juvenile stream salmonids. In addition to providing protec- tion from predators, cover may be associated with reduced food availability. Thus, an individual's use of cover is likely to reflect a trade-off between the conflicting demands of growth and survival. We measured die influence of cover on foraging-site selection in groups of eight juvenile coho salmon (Oncorhynchus kisutch) by examining their distribution across two stream channel patches, one providing access to cover but little food (die "poor" patch), die other providing more food but no cover (die "good" patch). Because fish distributions in the absence of cover conformed to an ideal free distribution (IFD) for unequal competitors (Le., die distribution of competitive abilities matched die distribution of food), we used IFD dieory to quantify die energetic equivalence of cover to die fish. In die presence of cover and a model avian predator, use of die poor patch increased relative to die predictions of die IFD model. Using tiiis observed deviation from an IFD, we calculated how much extra food must be added to die good patch to return die distribution of fish to die previously observed IFD of unequal competitors. As predicted, adding this amount of food caused die fish to return to dieir previous distribution, demonstrating that IFD dieory can be used to relate energy intake and risk of predation in a common currency. Key words: coho salmon, foraging, habitat selection, ideal free distribution dieory, Oncorhynchus kisutch, predation risk, trade-offs, unequal competitors. (Behav Ecol 8: 437-447 (1997))
Fringing mangrove forests and seagrass beds harbor high densities of juvenile snappers and grunts compared to bare substrates, but their occupancy of these habitats is not homogeneous at ecologically meaningful scales, thus limiting our ability to compare habitat value. Here, density and size information were used to determine how gray snapper, Lutjanus griseus (Linnaeus, 1758) and bluestriped grunt, Haemulon sciurus (Shaw, 1803), use vegetated habitats during their ontogeny, and how their use of mangrove forests varied with season across broad spatial scales and physicochemical conditions. Both species exhibited a three-stage ontogenetic strategy: (1) settlement and grow-out (8-10 mo) within seagrass beds, (2) expansion to mangrove habitats at 10-12 cm total length, and (3) increasing utilization of inland mangroves during the dry season and with increasing body size. For fishes inhabiting mangroves, multivariate tests revealed that the factors distance from oceanic inlet and water depth were stronger predictors of reef fish utilization than the factors latitude, temperature, or habitat width. These findings highlight that the nursery function of mangrove shorelines is likely limited to the area of immediately accessible habitat, and that more expansive forests may contain a substantial number of larger adult individuals.
From 1998 to 2005, 537 visual fish surveys were conducted along a 50-km stretch of mangrove-lined shoreline in the vicinity of Biscayne Bay (southeastern Florida, USA). The shoreline lies directly downstream of a major wetlands restoration project that aims to return more natural salinity regimes to the western margin of the region's coastal bays. As part of a "baseline" ecological assessment, we applied the delta approach to examine spatial and temporal patterns of mangrove habitat use by three fishes: Lutjanus griseus (Linnaeus, 1758), Sphyraena barracuda (Walbaum, 1792), and Floridichthys carpio (gunther, 1866). Along a north-south gradient, seasonal variation in their size-composition and three abundance metrics (occurrence, concentration, and density) was quantified and overall correlations with water salinity, depth, and temperature were evaluated using multiple regression. Results indicated that the shoreline is used by subadult and adult L. griseus and by mostly juvenile S. barracuda; for both species, highest abundance metric values occurred during the wet season, generally increasing southwards. In contrast, F. carpio were almost exclusively of adult (mature) sizes, with greatest values during the dry season at the shoreline's northern extent. For all species, water depth and/or temperature had a significant effect on abundance metrics. positive correlations were found for L. griseus and S. barracuda abundance metrics, whereas the reverse was true for F. carpio. To date, most mangrove-fish studies have evaluated a single measure of fish abundance, usually density. We suggest consideration of occurrence and concentration, in addition to density, has value in an assessment and monitoring context as well as for gaining insight into how a given fish species disperses and clusters within habitats and across gradients.
Fringe mangroves associated with islands of the subtropical Atlantic/Caribbean region create extensive subtidal mangrove epibiont communities. While increasingly recognized as an important habitat, few studies have focused on the trophic structure of communities associated with mangrove prop-roots. We examined trophic linkages among primary producers (mangroves, seagrass, and algae) and consumers using stable carbon and nitrogen isotopes in fringe mangroves of the Bahamas and Biscayne Bay, Florida. The average 13C value of primary consumers (16.4) was similar to macroalgae (16.7) and seagrass epiphytes (14.6) and highly distinguishable from mangroves (27.4). Higher secondary consumers had enriched 13C values (10.1) relative to primary consumers, and were similar to average seagrass 13C values (10.5). The ranges of 15 N signatures of vertebrate (6.312) and invertebrate (0.410.7) consumers indicated a multi-trophic structure. Based on mixing equations, the majority of primary consumers diet was algal based, while secondary consumers depended on both algal and seagrass carbon. Mangroves do not appear to be the major source of carbon to consumers in fringe mangroves of subtropical lagoons. Rather, fringe island-associated mangroves constitute refugia for invertebrates and young reef fishes, and create substrate for a diversity of primary producers and consumers, thereby playing an important indirect role to the food web of these systems.
Biscayne Bay is a shallow subtropical lagoon on Florida's southeastern coast that is bordered to the west by the mainland and to the east by barrier islands and keys. Fish assemblages inhabiting two types of mangrove-lined shoreline that encompass the Bay were examined using a visual 'belt-transect' census method over four consecutive seasons. Several significant differences were evident between shoreline habitats in terms of fish species composition, taxonomic richness and taxon-specific densities; seasonal changes and fish size-structure differences were few. The mangrove shorelines along the mainland (ML) consistently harbored less fish taxa than those on the leeward side of the islands and keys (LK), but harbored higher densities of several euryhaline forms (i.e., killifishes and livebearers). Densities of fishes that are typically associated with coral reef habitats (i.e., snappers and grunts) tended to be higher within LK vs ML mangrove shorelines, but there were exceptions (e.g., great barracuda, Sphyraena barracuda). For five fish species, length-frequency distributions were compared between the Bay's mangrove shorelines and nearby coral reef habitats. These data comparisons lent partial support to an ontogenetic 'mangrove-to-reef' migration model for only two of the five species examined. Results suggest that these shoreline habitats play varying ontogenetic and trophic roles, depending on location, season and fish species. Biscayne Bay's mangrove shoreline fish assemblages appear to reflect: (1) proximity of the mangroves that they occupy to offshore reef habitats; (2) salinity regime along the shoreline; and (3) water depths within the mangrove forest interior. The fish assemblage information collected here may serve as a 'baseline' in future assessments of fishing impacts or the effects of other anthropogenic changes to Biscayne Bay and its watershed.
Predators may influence their prey populations not only through direct lethal effects, but also through indirect behavioral changes. Here, we combined spatiotemporal fine-scale data from GPS radio collars on lions with habitat use information on 11 African herbivores in Hwange National Park (Zimbabwe) to test whether the risk of predation by lions influenced the distribution of herbivores in the landscape. Effects of long-term risk of predation (likelihood of lion presence calculated over four months) and short-term risk of predation (actual presence of lions in the vicinity in the preceding 24 hours) were contrasted. The long-term risk of predation by lions appeared to influence the distributions of all browsers across the landscape, but not of grazers. This result strongly suggests that browsers and grazers, which face different ecological constraints, are influenced at different spatial and temporal scales in the variation of the risk of predation by lions. The results also show that all herbivores tend to use more open habitats preferentially when lions are in their vicinity, probably an effective anti-predator behavior against such an ambush predator. Behaviorally induced effects of lions may therefore contribute significantly to structuring African herbivore communities, and hence possibly their effects on savanna ecosystems.
Although both food availability and predation risk have been hypothesized to affect dolphin habitat use and group size, no study has measured both factors concurrently to determine their relative influences. From 1997 to 1999, we investigated the effect of food availability and tiger shark (Galeocerdo cuvier) predation risk on bottlenose dolphin (Tursiops aduncus) habitat use and group size in Shark Bay, Western Australia. Food availability was measured by fish trapping, while predation risk was assessed by shark catch rates, acoustic tracks, and Crittercam deployments. Dolphin habitat use was deter-mined using belt transects. The biomass of dolphin prey did not vary seasonally and was significantly greater in shallow habitats than in deeper ones. Tiger sharks were virtually absent during cold months of 1997 and 1998, abundant in warm months of all years, and found at an intermediate density during cold months of 1999. When present, shark density was highest in shallow habitats. Decreased echolocation efficiency in very shallow water and poor visual detection of tiger sharks (camouflaged over seagrass) probably further enhance the riskiness of such habitats, and the relative riskiness of shallow habitats is supported by the observation that dolphins select deep waters in which to rest. The observed dolphin group sizes were consistent with a food–safety trade-off. Groups were larger in more dangerous shallow habitats and larger during resting than during foraging. Foraging dolphins matched the distribution of their food when sharks were absent. However, during warm months, the distribution of foraging dolphins significantly deviated from that of their food, with fewer dolphins foraging in the productive (but dangerous) shallow habitats than expected on the basis of food alone. When shark density was intermediate, habitat use by foraging dolphins was more similar to the high-shark-density seasons than periods of low shark density. These results suggest that foraging dolphin distributions reflect a trade-off between predation risk and food availability. Because the distribution and abundance of tiger sharks are influenced by species other than dolphins, the distribution of the tiger sharks' primary prey may indirectly influence dolphin habitat use, suggesting that it is important to consider the community context in studies of habitat use. Key words: alternative prey; behavior; bottlenose dolphin (Tursiops aduncus); group size; habitat use; indirect effects; predation risk; predator–prey interactions; prey availability; seagrass ecosystems; tiger shark (Galeocerdo cuvier).
AbSTRACT In light of ongoing changes to marine ecosystems, there is a need for behav-ioral indicators that can identify critical habitats and assess anthropogenic im-pacts. Although the application of behavior to conservation has yielded mixed results, habitat selection behavior has promise as such an indicator. Terrestrial studies and a decade of work in Shark bay's pristine seagrass ecosystem show that habitat selection theory based on the ideal free distribution can be used to assess critical habitats based on food and safety and signal impacts of anthropogenic disturbance. One lesson from our studies of dugongs (Dugong dugon) and other species at risk from tiger sharks (Galeocerdo cuvier) is that physical attributes of habitats may influence the effects of predators, and, by extension, human disturbance. These species generally prefer seagrass bank edges, which facilitate escape from sharks, even though shark density is lower over interior portions of the banks. Thus, habitat selection indicates that a bank's quality is determined largely by its proportion of edge microhabitat rather than its size, and that the presence of predators in neighboring habitats can influence prey space-use decisions where predators are scarce or absent. by extension, efforts to curb the effects of human disturbance, which can mimic those of predation risk, may be unsuccessful if protected areas border those subject to continued disturbance. Future marine studies should assess habitat selection in more disturbed habitats and across a range of physical settings to better elucidate the conservation benefits of using habitat selection as a behavioral indicator.