Article

Relative predation risk for fishes along a subtropical mangrove–seagrass ecotone

Authors:
  • Shark Research Foundation
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Many fishes shelter in mangrove habitats by day and forage mostly in seagrass beds by night. This pattern of diel habitat use has been attributed to a predator avoidance strategy, whereby predation risk is reduced by alternating between the cover afforded by prop-roots during the day and darkness at night. We employed a series of diel tethering experiments in Biscayne Bay (Florida, USA) to empirically examine whether relative predation pressure on fishes is lower at night than during the day and to compare relative predation pressure on fishes at different distances from the mangrove- seagrass ecotone. Pinfish Lagodon rhomboides ranging from 10 to 17 cm in total length were tethered during day and night at 10, 50, and 110 m from the mangrove-seagrass ecotone. Pinfish removal rates at night were twice as high as during the day, which contradicts the idea that darkness provides 'cover' during nocturnal foraging in seagrass. Predation losses were highest nearest the mangrove edge and decreased with increasing distance from shore. Our results agree with those of other tethering studies that marine ecotones, or transition zones between refuges and feeding sites, can be areas of high predation pressure for fishes.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Generally, higher rates of predation and a greater abundance of predatory fish are found in habitat patches that are near other habitat types (e.g. seagrass patches located in close proximity to mangrove patches) (Hammerschlag et al. 2010;Skilleter et al. 2017;Jones et al. 2020). This occurs because well-connected habitats often support an elevated abundance and biomass of food items, and predatory fish can migrate between these distinct habitat types during different tidal cycles (Hyndes et al. 2014;Whitfield 2017). ...
... However, these patterns are not always consistent as greater rates of predation can also be recorded in habitats that are isolated from other habitat types (see Duncan et al. 2019). Predation is often greatest along the edges of mangrove and seagrass patches compared to habitat interiors (Bologna and Heck Jr 1999;Nanjo et al. 2011;Smith et al. 2011) and nearby unvegetated sediment (Peterson et al. 2001;Gorman et al. 2009;Hammerschlag et al. 2010). This occurs as many predators forage along the edges of seagrass and mangrove patches and consume prey items (e.g. ...
... Models assessing seascape context and condition factors that influenced predator species richness in seagrass and unvegetated sediment contained no factors in best-fit models Distance to mangroves (x 2 = 9.0, p = 0.002) + urban area (x 2 = 6.0, p = 0.01) 0.14 1 are required to further quantify levels of redundancy and complementarity that are present in each habitat for predation within estuaries. Greater rates of predation and a higher abundance and diversity of predatory fish are often recorded in larger habitats that are located near other habitat types (Sheaves 2009;Hammerschlag et al. 2010;Sridharan and Namboothri 2015;Skilleter et al. 2017;Jones et al. 2020). We found similar effects in this study, as greater predation probability was found in seagrass meadows that were more extensive and located closer to the estuary mouth, and within unvegetated sediments that had a greater extent of salt marsh nearby. ...
Article
Full-text available
Predation is important in maintaining the community structure, functioning and ecological resilience of estuarine seascapes. Understanding how predator community structure, seascape context and habitat condition combine to influence predation is vital in managing estuarine ecosystems. We measured relationships between predator species richness, predator abundance and individual species abundances as well as seascape context and habitat condition, on relative predation probability in mangrove forests, seagrass meadows and unvegetated sediment across 11 estuaries in Queensland, Australia. Predation was quantified using videoed assays of tethered invertebrates (i.e. ghost nippers, Trypaea australiensis) and fish assemblages were surveyed using remote underwater video systems. Yellowfin bream (Acanthopagrus australis) dominated predation in all three habitats; however, predation was not correlated with yellowfin bream abundance. Instead, predation increased fourfold in mangroves and threefold in unvegetated sediment when predatory species richness was highest (> 3 species), and increased threefold in seagrass when predator abundance was highest (> 10 individuals). Predation in mangroves increased fourfold in forests with a lower pneumatophore density (< 50/m2). In seagrass, predation increased threefold at sites that had a greater extent (> 2000 m2) of seagrass, with longer shoot lengths (> 30 cm) and at sites that were closer to (< 2000 m) the estuary mouth. Predation on unvegetated sediment increased threefold when more extensive salt marshes (> 15000 m2) were nearby. These findings demonstrate the importance of predator richness and abundance in supplementing predation in estuaries, despite the dominance of a single species, and highlight how seascape context and habitat condition can have strong effects on predation in estuaries.
... Spatial linkages among habitat patches of the same type (i.e., habitat proximity), and between different habitats (i.e., seascape proximity), structure the abundance, diversity and composition of fish assemblages in seagrass meadows, mangrove forests, and on coral reefs (reviewed by Bostrom et al. 2011;Berkstrom et al. 2012;Igulu et al. 2014;Nagelkerken et al. 2015). Proximity can also modify the distribution of key ecological functions performed by fishes, with higher rates of both herbivory and predation often reported from seagrass, mangroves and reefs that are closer together (i.e., within 1 km of each other) (Valentine et al. 2008;Hammerschlag et al. 2010;Olds et al. 2012c;Downie et al. 2013;Peterson et al. 2013). It is not clear, however, whether the effects of proximity on herbivory and predation occur over different scales, or how they are affected by the type of spatial linkage. ...
... Experiments that tether live prey are commonly used to measure relative predation rates in aquatic ecosystems (e.g., Baker and Sheaves 2007;Dorenbosch et al. 2009;Hammerschlag et al. 2010;Bosiger and McCormick 2014;Dupuch et al. 2014;Pelicice et al. 2015). We conducted tethering experiments using common hardyheads (Atherinomorus vaigiensis; Atherinidae) as prey species. ...
... Both rabbitfishes and snappers form large schools that migrate among reefs, and between reefs and other habitats, to feed, with changes in tidal state and diel period (Grober-Dunsmore et al. 2007;Igulu et al. 2014;Olds et al. 2016). For example, black rabbitfish migrate from coral reefs with the rising tide to feed in adjacent mangrove forests (Olds et al. 2012a;Davis et al. 2014), whilst snappers often feed during crepuscular periods or at particular stages of the tide (Krumme 2009;Sheaves 2009;Hammerschlag et al. 2010). Our fish surveys might not, therefore, have always recorded fish abundance at times when functionally important species were feeding. ...
Article
Full-text available
Context Connectivity is an important property of landscapes that shapes populations and ecosystem functioning. We do not know, however, whether and how different types of spatial linkages combine to influence ecological functions, and this hampers their integration into conservation planning. Objectives We used coral reef seascapes in eastern Australia as a model system to test whether the proximity of other reefs (habitat proximity) or the proximity of other habitats (seascape proximity) exert stronger effects on two key ecological functions (herbivory and piscivory). Methods We measured rates of herbivory (on fleshy macroalgae) and piscivory (on prey fish) on reefs that differed in their proximity to both other reefs and nearby mangroves and seagrass. Results The extent of habitat proximity between reefs significantly influenced both ecological functions, but in different ways: isolated reefs supported high herbivory but low piscivory, whilst, conversely, reefs that were closer to other reefs supported high piscivory but low herbivory. This was not caused by herbivores avoiding their predators, as the dominant piscivores (small predatory snappers) were too small to consume the dominant herbivores (large rabbitfishes). Seascape proximity (e.g., distance to mangroves or seagrass) was less important in shaping ecological functions on reefs in this system. Conclusions We suggest that the effects of seascape configuration on ecological functions depends on the type of spatial linkage, and the ecological functions in question. To better integrate connectivity into conservation, we must develop a deeper understanding of how different spatial linkages combine to shape ecosystem functioning across landscapes.
... connectivity and area of nearby habitats) can have strong effects on ecological functioning (i.e. predation, herbivory, and carrion consumption) in coastal ecosystems (Hammerschlag et al., 2010 ;Downie et al., 2013 ;Goodridge Gaines et al., 2020 ). Generally, larger habitat patches (e.g. ...
... mangroves and seagrass) support an elevated abundance and biomass of food items and coastal fish can regularly migrate between these distinct habitats at different tidal or diurnal cycles (Sheaves, 2009 ;Olds et al., 2018b ). Consequently, well-connected habitats offer an increased number of niches for coastal fish and lead to an increase in the rates of ecological functions, such as higher rates of predation and carrion consumption (Hammerschlag et al., 2010 ;Goodridge Gaines et al., 2020 ;Henderson et al., 2022 ;Mosman et al., 2023 ). However, human disturbances (e.g. ...
Article
Full-text available
Ecological functions are linked to the condition and stability of coastal ecosystems. Quantifying how human disturbance and seascape context influence biodiversity and how different forms of diversity (i.e. species richness and functional diversity) influence ecological functioning is important in managing coastal ecosystems. We measured if the rates of carrion consumption by fish and crustaceans were influenced by scavenger richness and functional diversity or the abundance of key scavenger species, and which environmental factors shaped carrion consumption in surf zones at 20 beaches in eastern Queensland, Australia. Carrion consumption was positively correlated with scavenger richness, functional diversity, and the abundance of two species: weeping toadfish (Torquigener pleurogramma) and ornate wobbegong (Orectolobus ornatus). Carrion consumption was highest at sites that were near rocky headlands (<1 km) and shark control programme equipment (<1 km) and was also characterized by functional complementarity as weeping toadfish consumed more carrion at sites with a smaller area of reef nearby (<0.1 km2), whilst ornate wobbegong consumed more carrion at sites with a larger area of reef nearby (>0.3 km2). We highlight the importance of scavenger richness and functional diversity in shaping carrion consumption in surf zones, particularly when the species performing the function do this in spatially distinct areas.
... Such small-scale barriers can have large-scale implications for the ecological dynamics of an environment, and have even been demonstrated to influence the spatial distributions of both predators and prey (e.g. Hammerschlag et al. 2010; Guttridge et al. 2012). In Bimini, Bahamas, variations in environmental conditions, such as tides, were demonstrated to elicit changes in the presence of sub-adult lemon sharks (Negaprion brevirostris), thereby influencing the utilization of shallow-water mangrovefringed inlets by neonate and juvenile N. brevirostris as an anti-predation mechanism (Guttridge et al. 2012). ...
... Previous research suggests that habitat transition zones can be beneficial predatory habitats that serve as hunting corridors (e.g. Hammerschlag et al., 2010). Prey species are subjected to peak predation risks when crossing through transition zones, as these zones are often correlated with predictable prey movement patterns and thus a greater probability of predation success (Martin et al., 2005). ...
Article
Large-scale and small-scale natural barriers have the ability to mediate the ecological dynamics within a region. In some instances, these barriers greatly influence the presence of predators and prey on spatio-temporal scales. For this study, we aimed to assess how varying densities of sea bamboo (Ecklonia maxima), a kelp species found within South African waters, could influence the presence of C. carcharias. Using baited remote underwater video systems (BRUVS), thirty-one different C. carcharias were identified and a total of 135 h of video were collected in high, moderate, and low kelp densities to create an organismal sighting index. Generalized linear models illustrated that the best fit model included the main effect of kelp density, with a clear inverse relationship between kelp density and C. carcharias sightings. However, although zero sharks were sighted within the high kelp density regions, ten different C. carcharias were sighted within the moderate kelp density regions, illustrating that the broad notion that C. carcharias do not navigate through kelp ecosystems is false and requires more specificity (e.g. high density kelp areas may result in decrease C. carcharias presence). In contrast, kelp density had no significant influence on the presence of five other elasmobranch species detected by the BRUVS. This study demonstrated that highly dense kelp forests (i.e. ≥1 stalk of kelp per 1 m 2) serve as a local natural barrier for large C. carcharias; however, the need for a more inclusive analysis (e.g. routine inclusion of current speed and multi-location assessment) is warranted.
... Mangroves provide nursery habitat and refuge for many species, including economically and ecologically important fish (Alongi, 2002;Barimo and Serafy, 2003;Faunce and Serafy, 2006;Nagelkerken et al., 2008). The structural complexity of prop roots and tidal variations are believed to provide shelter for small adult and juvenile fish while restricting access for large, predatory fish (Nagelkerken et al., 2000;Hammerschlag et al., 2010). The combination of high productivity and low predation allows juvenile fish to grow and mature with relatively little predation risk (Nagelkerken et al., 2000). ...
... Gray snapper exhibit diel migrations between mangrove and seagrass beds in Biscayne Bay. At night, individuals leave the safety of the mangrove prop roots to forage on invertebrates in adjacent seagrass beds (Luo et al., 2009;Hammerschlag et al., 2010). This movement pattern may be most easily facilitated in pool one due to its close proximity to the main channel leading to Biscayne Bay seagrass beds. ...
Article
Mangroves provide essential habitat for juvenile fish species. Restoration and monitoring are important conservation tools to ensure the recovery and maintenance of coastal mangrove habitats impacted by humans. In this study, Baited Remote Underwater Video Stations (BRVUS) were used to non-invasively examine the relative abundance and richness of fishes within restored mangrove pools in Biscayne Bay, Florida, 15 years after replanting. The potential influence of several environmental factors on fish abundance and richness within the restored mangrove pools was also evaluated. Limited seine sampling was also conducted to provide a comparison of the current fish assemblage with that of two prior surveys using seine nets. Twenty fish taxa were observed in the current study, consisting of five families, two genera, and thirteen species. Several environmental factors emerged as significant influences on the presence and abundance of different fish taxa, especially individual pools. A comparison of CPUE between current and prior seine studies found an increase in forage fish taxa and a shift from taxa that prefer a range of habitats to mangrove specific taxa, indicating an increased ecological function of these mangroves as fish habitat.
... Spartina). We do not yet know how mangroves are influencing wetland species but hypothesize that mangroves alter food webs through changes in the outcomes of predatory interactions (Hammerschlag et al., 2010) and/or by affecting abiotic conditions and resource availability to make habitats less suitable for some species (Alongi et al., 2004;Castañeda-Moya et al., 2013;Comeaux et al., 2012). Black mangrove edge habitats are used by predators as hunting corridors (Hammerschlag et al., 2010), and mangrove encroachment into Spartina marshes may alter food webs by changing the foraging environment for predators and prey. ...
... We do not yet know how mangroves are influencing wetland species but hypothesize that mangroves alter food webs through changes in the outcomes of predatory interactions (Hammerschlag et al., 2010) and/or by affecting abiotic conditions and resource availability to make habitats less suitable for some species (Alongi et al., 2004;Castañeda-Moya et al., 2013;Comeaux et al., 2012). Black mangrove edge habitats are used by predators as hunting corridors (Hammerschlag et al., 2010), and mangrove encroachment into Spartina marshes may alter food webs by changing the foraging environment for predators and prey. In sites with mangroves, fish and crabs were more abundant while infaunal organisms and grass shrimp, common prey items for fish and crabs, (Kneib and Wagner, 1994), were less abundant. ...
Article
Climate change is altering the distribution of foundation species, with potential effects on organisms that inhabit these environments and changes to valuable ecosystem functions. In the Gulf of Mexico, black mangroves (Avicennia germinans) are expanding northward into salt marshes dominated by Spartina alterniflora (hereafter Spartina). Salt marshes are essential habitats for many organisms, including ecologically and economically important species such as blue crabs (Callinectes sapidus) and Penaeid shrimp (e.g., Penaeus aztecus), which may be affected by vegetation changes. Black mangroves occupied higher tidal elevations than Spartina, and Spartina was present only at its lowest tidal elevations in sites when mangroves were established. We compared nekton and infaunal communities within monoculture stands of Spartina that were bordered by mangroves to nearby areas where mangroves had not yet become established. Nekton and infaunal communities were significantly different in Spartina stands bordered by mangroves, even though salinity and temperature were not different. Overall abundance and biomass of nekton and infauna was significantly higher in marshes without mangroves, although crabs and fish were more abundant in mangrove areas. Black mangrove expansion as well as other ongoing vegetation shifts will continue in a warming climate. Understanding how these changes affect associated species is necessary for management, mitigation, and conservation.
... Thus the risk of predation may be greatest close to the creeks leading to smaller fish being more abundant further away from creeks. Similar results were reported by Hammerschlag et al. (2010) in a seagrass-mangrove eco-tone in Biscayne Bay, Florida. The authors found using tethering trials that proportion of predation was highest closest to the mangrove-seagrass eco-tone, the transition zone from mangroves to seagrass meadows (Hammerschlag et al. 2010). ...
... Similar results were reported by Hammerschlag et al. (2010) in a seagrass-mangrove eco-tone in Biscayne Bay, Florida. The authors found using tethering trials that proportion of predation was highest closest to the mangrove-seagrass eco-tone, the transition zone from mangroves to seagrass meadows (Hammerschlag et al. 2010). Creeks within our study site, which showed the greatest proportion of predation, may be considered similar transition zones between mangrove forests and other habitats such as coral reefs. ...
Article
Full-text available
Mangrove forests in meso-tidal areas are completely drained during low tides, forming only temporary habitats for fish. We hypothesised that in such temporary habitats, where stranding risks are high, distance from tidal creeks that provided access to inundated areas during receding tides would be the primary determinant of fish distribution. Factors such as depth, root density and shade were hypothesised to have secondary effects. We tested these hypotheses in a tidally drained mangrove patch in the Andaman Islands, India. Using stake nets, we measured fish abundance and species richness relative to distance from creeks, root density/m2, shade, water depth and size (total length) of fish. We also predicted that larger fish (including potential predators) would be closer to creeks, as they faced a greater chance of mortality if stranded. Thus we conducted tethering trials to examine if predation would be greater close to the creeks. Generalised linear mixed effects models showed that fish abundance was negatively influenced by increasing creek distance interacting with fish size and positively influenced by depth. Quantile regression analysis showed that species richness was limited by increasing creek distance. Proportion of predation was greatest close to the creeks (0–25 m) and declined with increasing distance. Abundance was also low very close to the creeks, suggesting that close to the creeks predation pressure may be an important determinant of fish abundance. The overall pattern however indicates that access to permanently inundated areas, may be an important determinant of fish distribution in tidally drained mangrove forests.
... Yet despite their common benthivorous foraging mode and mutual reliance on invertebrate prey (Layman and Silliman 2002), mojarras and bonefish feeding together in the wild display little outward evidence of competitive interactions or behaviors that might signal scrounging or the exploitation of flushed prey (Haak et al. 2020). Meanwhile, juveniles of the two taxa share a common suite of predators in lemon sharks (Negaprion brevirostris), barracudas (Sphyraenidae) and snappers (Lutjanidae) that can impose high levels of mortality in the fringing mangrove habitats where mojarras and bonefish reside (Rypel et al. 2007;Hammerschlag et al. 2010), making risk-related cues reciprocally relevant. Moreover, basic similarities in the fishes' outward appearances, with both being characterized by reflective camouflage and similar patterns of dorsolateral pigmentation (Online Resource 1: Fig. ESM1), suggest that mojarras may be particularly well suited for conveying a variety of antipredator benefits to juvenile bonefish (Haak et al. 2020;Szekeres et al. 2020). ...
Article
Full-text available
Research from terrestrial communities shows that diminished predation risk is a principal driver of heterospecific grouping behavior, with foraging ecology predicting the roles that species play in groups, as more vulnerable foragers preferentially join more vigilant ones from whom they can benefit. Meanwhile, field studies examining the adaptive significance of heterospecific shoaling among marine fish have focused disproportionately on feeding advantages such as scrounging or prey-flushing. Juvenile bonefish (Albula vulpes) occur almost exclusively among mojarras (Eucinostomus spp.) and even elect to join them over conspecifics, suggesting they benefit from doing so. We evaluated the roles of risk-related and food-related factors in motivating this pattern of affiliation, estimating: (1) the relative levels of risk associated with each species’ search and prey capture activities, via behavioral vulnerability traits discerned from in situ video of heterospecific shoals, and (2) resource use redundancy, using stable isotopes (δ¹³C, δ¹⁵N, and δ³⁴S) to quantify niche overlap. Across four distinct metrics, bonefish behaviors implied a markedly greater level of risk than those of mojarras, typified by higher activity levels and a reduced capacity for overt vigilance; consistent with expectations if their association conformed to patterns of joining observed in terrestrial habitats. Resource use overlap inferred from stable isotopes was low, indicating that the two species partitioned resources and making it unlikely that bonefish derived substantive food-related benefits. Collectively, these findings suggest that the attraction of juvenile bonefish to mojarras is motivated primarily by antipredator advantages, which may include the exploitation of risk-related social cues.
... Wang et al. [31] recorded high dominance of gastropods in saltmarsh along the Yangtze Estuary and British coastal saltmarsh, but less abundant gastropods were recorded in the present study. It is hypothesized that the variation of predatory interactions in saltmarsh can change food webs [42] and/or affect physio-chemical factors and sediment composition to make habitats less suitable for some species [43][44][45], which might be the cause of availability or unavailability of some species. ...
Article
Full-text available
Saltmarsh is one of the most productive coastal habitats in the marine environment, and the macroinvertebrate community is crucial to its ecology and productivity. These productive ecosystems are currently under threat due to climate change and anthropogenic activities. However, macroinvertebrate communities and their functionality in saltmarsh from subtropical coastal areas have previously been largely ignored. In this study, we aimed to elucidate (i) the diversity and community assemblages, (ii) trophic structure, and (iii) changes of macroinvertebrate diversity under different seasons and climatic variables from a subtropical saltmarsh habitat. A total of 29 taxa in the eight (8) major groups were recorded in both seasons, with polychaetes being dominant (64%) in monsoon and crustaceans (50%) in post-monsoon. Among the trophic groups identified, surface deposit feeders and omnivores were dominant, accounting for 78.52% of the total groups. The highest value of diversity index (2.04) was observed at station S3 in monsoon and the lowest (1.408) at station S2 in post-monsoon. Strong seasonal variability was confirmed by two-way ANOVA and PERMANOVA, and SIMPER analysis identified that shrimp larvae (Macrobrachium sp.) were the taxa that contributed the most to grouping patterns between areas and seasons. In addition, non-metric multidimensional scaling (nMDS) revealed a great dissimilarity of macrobenthic faunal assemblages among the study stations and seasons. Spearman’s rank correlation analysis and canonical correspondence analysis (CCA) results revealed that the climatic factors water temperature, salinity, and alkalinity variation influenced the benthic community diversity.
... Seagrasses have also long been the focus of comparative experiments to understand how predation-generally in the form of tethered prey-varies across space and through time (Heck and Wilson, 1987). Nevertheless, fewer studies explore how consumption changes across multiple habitats within the same coastal seascape, and those that do have revealed inconsistent patterns in terms of the degree of consumption observed in different habitats (Chittaro et al., 2005;Hammerschlag et al., 2010). Indeed, a recent meta-analysis on nursery function uncovered only a dozen or so studies comparing among multiple habitats (coral reefs, mangroves, and/or seagrasses), and these failed to reveal any general patterns in terms of juvenile survival/predation risk associated with each (Lefcheck et al., 2019a). ...
Article
Full-text available
Herbivores, omnivores, and predators transfer energy and structure the communities of many coastal marine ecosystems, and the intensity with which they consume prey and contribute to ecosystem functioning varies substantially among habitats over short time periods. Whether generalities across habitats might emerge for longer time series and using standard methods remains largely untested. Here, we deployed standardized assays of consumption using dried squid (“squidpops”) and five common macrophytes (“weedpops”) to quantify consumption across coral fore reef and patch reefs, mangroves, seagrass meadows, and bare sand from 2015 to 2019 around Carrie Bow Cay, Belize. We also used video in 2017 to identify the species responsible for consumption. We found that both squid- and weedpop consumption were consistently highest on patch and fore reef habitats, moderate in mangroves, and lowest in seagrass and sand across all years of the survey. Videos showed that the majority of consumption on the reefs in 2017 could be attributed to < 5 fish species, and the identity of the dominant consumers differed among habitats. This study validates a key but implicit assumption in marine ecology that relative patterns in consumption across habitats are consistent through space and time in tropical nearshore environments, and reveals that high consumption rates may be the consequence of one or few species in each location.
... The distributions of migratory species are temporally dynamic, driven by complex dispersal behaviours that reflect variations in the environment (Faillettaz et al., 2019), prey availability (Tiews, 1978), predation risk (Hammerschlag et al., 2010), anthropogenic pressure (Nowacek et al., 2015), and ontogenetic development (De Grissac et al., 2016;Votier et al., 2017). During the current period of rapid global change (Poloczanska et al., 2013), these complex dispersal patterns, if not properly understood, can complicate regional conservation or management efforts (Studds et al., 2017). ...
Article
Full-text available
Atlantic bluefin tuna (ABT, Thunnus thynnus; Linneaus, 1758) is an ecologically important apex-predator with high commercial value. They were once common off the coast of the United Kingdom (UK), before disappearing in the 1960s. In regions lacking commercial fisheries for ABT, such as the UK and Ireland, spatial data can be scarce. In these cases, sightings and bycatch databases can offset information shortfalls. Here, we document the reappearance of ABT into territorial waters of the UK from 2014 onwards, and increased occurrence off Ireland. We analyse a novel, multi-source dataset comprising occurrence data (2008–2019; 989 sightings and 114 tonnes of bycatch) compiled from a range of sources (scientific surveys, ecotours and fisheries). We show an increasing trend in effort-corrected ABT occurrence in (i) the pelagic ecosystem survey in the western English Channel and Celtic Sea (PELTIC), (ii) an ecotour operator, and (iii) the Irish albacore fishery in on-shelf and off-shelf waters. Sightings of ABT by the PELTIC correlated with modelled abundance estimates of ABT and the Atlantic multidecadal oscillation. These data demonstrate that sightings of ABT have increased off the UK and Ireland since 2014, following the same increasing trend (2010 onwards) as the eastern ABT population.
... creek edges, as they have been doing within the GTM estuary (Williams et al. 2014), they can negatively impact nekton species by acting as a physical barrier to entry onto the marsh surface or even functioning as hotspots for predation on small fish (Hammerschlag et al. 2010;Smee et al. 2017). ...
Article
Full-text available
The marsh-mangrove ecotone along the southeastern US Atlantic coast occurs in northeast Florida within the Guana-Tolomato-Matanzas (GTM) estuary, where emergent vegetation transitions from marsh-dominated in the north to mangrove-dominated in the south. Dominant vegetation type has been shown to influence creek bank slope, nekton access to refuge, predation risk, and access to food. The northward distribution of mangroves in the estuarine mosaic is in flux in northeast Florida, and the effect on subtidal nekton, including commercially important species, is not known. To determine if estuarine nekton assemblages differ along the marsh-mangrove ecotone, a 60-km transition zone within GTM estuary was divided into 20 sub-zones where nearshore subtidal nekton communities were sampled monthly with trawls for 1 year. A total of 15,750 individuals consisting of 100 species were collected during the study period; 13 species made up 90% of the total catch. Subtidal nekton assemblages in marsh sites were dominated by typical salt marsh species (i.e., Leiostomus xanthurus, Anchoa spp., Bairdiella chrysoura) and had little overlap with assemblages in mixed and mangrove sites, which were dominated by structure-oriented species (i.e., Lagodon rhomboides and Eucinostomus spp.). Despite similar environmental conditions among the zones, there were clear differences in the subtidal nekton community along the marsh-mangrove ecotone, largely driven by fish species. This change in nekton community along the ecotone suggests that ecological processes such as food availability or predator/prey dynamics affected by changes in marsh surface habitats may result in differences in nekton species distribution and abundance across interconnected habitats such as in subtidal nekton that we observed in the GTM estuary.
... In case defects are suggested to be not negligible, it may be better to establish predator-free control quadrats in the study area and check mortality rate of the tethered fish and tether-come-off rate in the quadrats in a trial. In previous studies, tethers were attached to various positions including nostril, jaw, operculum, or caudal peduncle [see, for example, Hammerschlag et al. (2010), Horinouchi et al. (2013), Nanjo et al. (2014). See also Fig. 23.1b]. ...
... In addition to a more concentrated weekday and weekend boat traffic (Rider 2020), the City of Miami hosts a variety of boating shows and fishing events throughout the year. Nevertheless, the ecological shoreline of the Biscayne Bay HFA provides valuable hunting and foraging grounds for marine predators (Hammerschlag et al. 2010), and recent research has documented the use of this area by several shark species despite high levels of boat activity and vessel noise (Rider 2020). The considerable number of smalltooth sawfish detections recorded at receiver stations in urban areas is intriguing and leads to future questions about urbanization effects on habitat use by this species. ...
Article
Full-text available
As coastal urbanization increases globally, the subsequent effects on marine animals, especially endangered species, inhabiting nearshore waters have become a research priority. The smalltooth sawfish Pristis pectinata , once abundant in US waters, now only persists in a few parts of its former range, including South Florida. Many areas utilized by smalltooth sawfish are estuarine systems or other shallow coastal habitats, making this species particularly vulnerable to threats associated with coastal development. To date, P. pectinata has been understudied in the waters in and around Biscayne Bay, Florida, a coastal waterway subjected to the urbanization of adjacent Miami-Dade County. Here, we summarize data from reported smalltooth sawfish encounters dating as far back as 1895 (N = 90) and detail opportune recordings (incidental catches, acoustic detections, and baited remote underwater videos) of sub-adults and adults (N = 14 individuals) in Biscayne Bay and the adjacent reef tract. These data demonstrate historical and increased contemporary use of the study area by this imperiled species, suggesting potential local and regional recovery. Most documented sawfish occurrences were near the urban center, indicating a need to understand the effects of coastal urbanization on sawfish and on the species' recovery potential. We suggest priorities for future research on P. pectinata in the study area that will assist in addressing regional management goals and contribute to understanding the ecology of smalltooth sawfish under environmental change.
... Seagrass habitats most often reduce predation pressure on a wide array of invertebrates, but consumptive pressure on small prey may otherwise be higher in vegetated meadows if they attract and protect their predators (e.g. Stoner et al., 1998;Hammerschlag et al., 2010). Because seagrass meadows were overall sparse, leaving enough space for open species interactions, trophic dynamics may explain the lower abundance of sipunculids within Halophila decipiens patches. ...
Article
Seagrasses may enhance the abundance and diversity of benthic invertebrates through trophic facilitation. We investigated this potential ecological function for two seagrasses in SE Brazil: Halodule emarginata, a native species, and Halophila decipiens, a tropical seagrass recently established in the region. At Halophila sites, the organic matter (or carbon) in sediments decreased steadily from seagrass patches to isolated bare grounds, indicating surplus primary production. This was not observed at Halodule sites. At one of the two Halophila sites, localized trophic enrichment was also consistently linked to increased invertebrate abundance within patches, chiefly through increased carrying capacity of small mesoherbivores. Rather than spillover, edge effects were observed at bordering bare habitats, where polychaete predators were abundant. The transition from seagrass edges to isolated bare habitats was marked by an increase of the density of sipunculid worms. The current spread of Halophila may thus change the spatial distribution of benthic ecological functions.
... In case defects are suggested to be not negligible, it may be better to establish predator-free control quadrats in the study area and check mortality rate of the tethered fish and tether-come-off rate in the quadrats in a trial. In previous studies, tethers were attached to various positions including nostril, jaw, operculum, or caudal peduncle [see, for example, Hammerschlag et al. (2010), Horinouchi et al. (2013), Nanjo et al. (2014). See also Fig. 23.1b]. ...
Book
This book gives an overview of the diverse marine fauna and flora of Japan and includes practical guides for investigating the biology and ecology of marine organisms. Introducing marine training courses offered at a range of Japanese universities, this is the first English textbook intended for marine biology instructors and students in Japan. It provides essential information on experimental procedures for the major areas of marine biology, including cell and developmental biology, physiology, ecology and environmental sciences, and as such is a valuable resource for those in Asian countries that share a similar flora and fauna. It also appeals to visitors interested in attending Japanese marine courses from countries around the world.
... In case defects are suggested to be not negligible, it may be better to establish predator-free control quadrats in the study area and check mortality rate of the tethered fish and tether-come-off rate in the quadrats in a trial. In previous studies, tethers were attached to various positions including nostril, jaw, operculum, or caudal peduncle [see, for example, Hammerschlag et al. (2010), Horinouchi et al. (2013), Nanjo et al. (2014). See also Fig. 23.1b]. ...
Chapter
Ecologists study the interactions between organisms and their physicochemical and biotic environment. This spans biochemical, cellular and individual organism processes, as well as biological community and ecosystem levels of organization. Rocky shores have long been a testing ground for ecological theory as they are easily accessible and have strong gradients in abiotic and biotic conditions. A major branch of this field is the population ecology of commercially important species. Marine ecologists also study how species interact within seascapes and how energy and matter flow through ecosystems. This introduction explains the terms used to describe the zonation of marine life and provides an overview of the approaches available to investigate the ecology of Japanese waters where there are wide seasonal changes in temperature and an exceptionally high diversity of algae, plants, and animals.
... In case defects are suggested to be not negligible, it may be better to establish predator-free control quadrats in the study area and check mortality rate of the tethered fish and tether-come-off rate in the quadrats in a trial. In previous studies, tethers were attached to various positions including nostril, jaw, operculum, or caudal peduncle [see, for example, Hammerschlag et al. (2010), Horinouchi et al. (2013), Nanjo et al. (2014). See also Fig. 23.1b]. ...
Chapter
Full-text available
In the seventeenth century, Hugo Grotius developed the doctrine of the ‘freedom of the seas’, arguing that the ocean bounty was vast enough to share without ownership. However, the human population has trebled since 1950 with much of the recent growth located in coastal regions where we are witnessing a profound transformation of our relationship with the natural world. Over that time fertilizer consumption has increased from 40 to 280 million tonnes a year, quadrupling inputs of nitrogen to the coastal zone. Motor vehicle use is up from 30 million in the 1950s to 750 million vehicles on the road, and international tourism has risen from <1 million international arrivals of people per year to 600 million today. Our use of natural resources is accelerating and this, coupled with poor management, means the planet has entered a phase of mass extinction with widespread biodiversity loss. Within a generation, fishing using fossil fuels has removed large fish from ecosystems and homogenized continental shelf habitats, with extensive damage even on remote seamounts. This chapter sets out the scale of some of the challenges we face in managing the ways in which humans impact the oceans.
... In case defects are suggested to be not negligible, it may be better to establish predator-free control quadrats in the study area and check mortality rate of the tethered fish and tether-come-off rate in the quadrats in a trial. In previous studies, tethers were attached to various positions including nostril, jaw, operculum, or caudal peduncle [see, for example, Hammerschlag et al. (2010), Horinouchi et al. (2013), Nanjo et al. (2014). See also Fig. 23.1b]. ...
Chapter
Life on Earth began in the sea which covers 71% of our planet’s surface and its algae have produced half of the atmospheric oxygen that we breathe. Under the influence of worldwide water currents, marine organisms are distributed as neuston, plankton, nekton, or benthos. This chapter summarizes the major horizontal and vertical gradients in chemical and physical conditions that determine ocean productivity of the sea which is driven by sunlight and algae. Seawater is a dense, viscous medium and so marine life has an array of adaptations to take advantage of this environment. We introduce the different marine phyla present, which have a far greater biodiversity than terrestrial fauna. This introduction explains the highly interdisciplinary nature of marine biology and demonstrates that pioneering research in the life sciences continues to use marine organisms, including evolutionary biology, molecular biology, developmental biology and physiology. The islands of Japan have attracted marine scientists worldwide due to an exceptional variety of conditions (from tropical corals to high latitude kelp forests, abyssal deep sea to shallow lagoons). This gives the region an unusually rich flora and fauna coupled by highly productive fisheries. This overview sets the scene for our book on Japanese marine life.
... In case defects are suggested to be not negligible, it may be better to establish predator-free control quadrats in the study area and check mortality rate of the tethered fish and tether-come-off rate in the quadrats in a trial. In previous studies, tethers were attached to various positions including nostril, jaw, operculum, or caudal peduncle [see, for example, Hammerschlag et al. (2010), Horinouchi et al. (2013), Nanjo et al. (2014). See also Fig. 23.1b]. ...
Chapter
The marine environmental sciences lay at the interface between physics, chemistry and biology. Training in environmental science techniques provides skills that are highly transferable to the workplace and beyond. This subject typically involves collecting environmental data, collating it and then creating graphs and text to explain the key results. Employers within and outside the marine sciences actively seek people with these skills. Environmental scientists build an ability to conduct risk assessments, prepare reagents, calibrate instruments and design sampling protocols. You learn to plan and assess how to most effectively use your own time and to work in teams to decide upon what to measure to meet a particular set of objectives. By evaluating an environmental problem and honing a set of observations you will use the time-management and communication skills that are required for advising on policy or having input to evidence-based decision-making be it in environmental assessments or in running large organizations.
... Moving animals are conspicuous and vulnerable to predators (Furey, Armstrong, Beauchamp, & Hinch, 2018;Hammerschlag, Morgan, & Serafy, 2010). Prey movement can attract the attention of predators, requires energy that reduces the prey's ability to evade an attack, and may occur in unfamiliar space where the location of shelter is unknown (Banks, Norrdahl, & Korpimaki, 2000;Clarke et al., 1993). ...
Article
Full-text available
Prey evaluate risk and make decisions based on the balance between the costs of predation and those of engaging in antipredator behaviour. Economic escape theory has been valuable in understanding the responses of stationary prey under predation risk; however, current models are not applicable for directionally moving prey. Here we present an extension of existing escape theory that predicts how much predation risk is perceived by directionally moving prey. Perceived risk is measured by the extent antipredator behaviour causes a change in travel speed (the distance to a destination divided by the total time to reach that destination). Cryptic or cautious antipredator behaviour slows travel speed, while prey may also speed up to reduce predator–prey overlap. Next, we applied the sensitization hypothesis to our model, which predicts that prey with more predator experience should engage in more antipredator behaviour, which leads to a larger change in travel speed under predation risk. We then compared the qualitative predictions of our model to the results of a behavioural assay with juvenile Chinook salmon Oncorhynchus tshawytscha that varied in their past predator experience. We timed salmon swimming downstream through a mesh enclosure in the river with and without predator cues present to measure their reaction to a predator. Hatchery salmon had the least predator experience, followed by wild salmon captured upstream (wild‐upstream) and wild‐salmon captured downstream (wild‐downstream). Both wild salmon groups slowed down in response to predator cues, whereas hatchery salmon did not change travel speed. The magnitude of reaction to predator cues by salmon group followed the gradient of previous predator experience, supporting the sensitization hypothesis. Moving animals are conspicuous and vulnerable to predators. Here we provide a novel conceptual framework for understanding how directionally moving prey perceive risk and make antipredator decisions. Our study extends the scope of economic escape theory and improves general understanding of non‐lethal effects of predators on moving prey.
... It is also possible that these open and homogenous habitats provide increased escape routes to prey if needed, thus making them worth the "risk." Additionally, since predators are often transient in these habitats (Hammerschlag, Morgan, & Serafy, 2010), attacks may be less predictable. Therefore, our observed patterns for behavioral effects in these habitats may stem from a combination of resource provisioning and unpredictability of predation risk. ...
Article
Full-text available
The indirect effect of predators on prey behavior, recruitment, and spatial relationships continues to attract considerable attention. However, top predators like sharks or large, mobile teleosts, which can have substantial top–down effects in ecosystems, are often difficult to study due to their large size and mobility. This has created a knowledge gap in understanding how they affect their prey through nonconsumptive effects. Here, we investigated how different functional groups of predators affected potential prey fish populations across various habitats within Biscayne Bay, FL. Using baited remote underwater videos (BRUVs), we quantified predator abundance and activity as a rough proxy for predation risk and analyzed key prey behaviors across coral reef, sea fan, seagrass, and sandy habitats. Both predator abundance and prey arrival times to the bait were strongly influenced by habitat type, with open homogenous habitats receiving faster arrival times by prey. Other prey behaviors, such as residency and risk‐associated behaviors, were potentially driven by predator interaction. Our data suggest that small predators across functional groups do not have large controlling effects on prey behavior or stress responses over short temporal scales; however, habitats where predators are more unpredictable in their occurrence (i.e., open areas) may trigger risk‐associated behaviors such as avoidance and vigilance. Our data shed new light on the importance of habitat and context for understanding how marine predators may influence prey behaviors in marine ecosystems. Assessing behavioral risk effects of marine predators on mobile prey species across varying habitats in Biscayne Bay, FL. Providing new insights into the role marine predators play in influencing prey behavior in a variety of contexts.
... Second, numerous patch-level attributes may affect our ability to detect edge effects, such as patch size, shape, and within-patch variations in habitat complexity. For example, a number of studies scale the edge-core distances with patch size [18••, 20, 32•, 42, 43], or otherwise sample at a number of distances from the edge which inevitably increases with patch size [44][45][46][47]. High variability in distance between edge and core habitats can affect response detection. ...
Article
Full-text available
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.
... While we attribute much of the changes observed to the establishment of the MPA within DB, there could be other factors that could affect herbivory. We selected the same study location and the same depth as the 2007 experiment (Peterson et al. 2012) to eliminate the variability that might occur at a slightly different location within the seagrass meadow (Hammerschlag et al. 2010) or a different depth (Steele et al. 2014). Although we did not standardize leaf ranks (i.e., youngest to oldest leaves) between experiments when reassembling tethered shoots, we kept the method of selecting the youngest, inner leaves the same across experiments. ...
... Although tethering experiments have been noted as including potential artifacts, such as tether interference in prey behaviour and escape responses, thereby causing increased vulnerability to predators (Peterson and Black 1994), tethering has been widely recognized as effective for the direct examination in the field of relative predation risks among different habitats or microhabitats (e.g. Mclvor and Odum 1988;Ruiz et al. 1993;Aronson and Heck 1995;Halpin 2000;Linehan et al. 2001;Nakamura and Sano 2004;Horinouchi 2007;Rypel et al. 2007;Nakane et al. 2009;Hammerschlag et al. 2010;Nanjo et al. 2011;Banikas and Thompson 2012). ...
Article
To clarify the role of salt marsh creeks as fish refuges, predation risks for two small species (the nektonic Oryzias latipes and benthic Acanthogobius lactipes) were compared among three microhabitats (upper and lower areas of a creek, and marsh edge separate from the creek) in a salt marsh in Lake Hinuma, eastern Japan, in July 2016, using daytime tethering experiments. The survival rate of O. latipes was highest in the upper creek (96%) and lowest at the marsh edge (62%), whereas no significant differences were found among the microhabitats for A. lactipes, with high survival rates (> 90%) in all microhabitats. Individual numbers of larger piscivorous fishes, determined by fyke net sampling, were greatest at the marsh edge, whereas no individuals were recorded in the upper creek, which was characterized by shallower depths and lower dissolved oxygen levels. The results suggested that the upper creek provides potential refugia for O. latipes, which occupied the upper and middle layers of the water column and exhibited hypoxia tolerance. The higher survival rate of benthic A. lactipes at the marsh edge may be due to their cryptic coloration in relation to bottom sediments, which helps them to avoid predation.
... Such spatially-abrupt transition points between distinct ecological communities are evident in numerous terrestrial and aquatic ecosystems, such as tropical rainforests, lakes, and estuaries (Attrill and Rundle 2002). Often the transition in question is between vastly different systems, for example the progression of lower montane rainforest to tropical rainforest along an altitudinal gradient in temperature and moisture (Whittaker 1970), or a shift from subtropical mangrove to a seagrass habitat (Hammerschlag et al. 2010). We observed a similar spatial scaling around a tropical island but evidenced by more subtle transitions in functional group dominance. ...
Article
Full-text available
Understanding and predicting patterns of spatial organization across ecological communities is central to the field of landscape ecology, and a similar line of inquiry has begun to evolve sub‐tidally among seascape ecologists. Much of our current understanding of the processes driving marine community patterns, particularly in the tropics, has come from small‐scale, spatially‐discrete data that are often not representative of the broader seascape. Here we expand the spatial extent of seascape ecology studies and combine spatially‐expansive in situ digital imagery, oceanographic measurements, spatial statistics, and predictive modeling to test whether predictable patterns emerge between coral reef benthic competitors across scales in response to intra‐island gradients in physical drivers. We do this around the entire circumference of a remote, uninhabited island in the central Pacific (Jarvis Island) that lacks the confounding effects of direct human impacts. We show, for the first time, that competing benthic groups demonstrate predictable scaling patterns of organization, with positive autocorrelation in the cover of each group at scales < ~1 km. Moreover, we show how gradients in subsurface temperature and surface wave power drive spatially‐abrupt transition points in group dominance, explaining 48 – 84% of the overall variation in benthic cover around the island. Along the western coast, we documented ten times more sub‐surface cooling‐hours than any other part of the coastline, with events typically resulting in a drop of 1 – 4°C over a period of < 5 hr. These high frequency temperature fluctuations are indicative of upwelling induced by internal waves and here result in localized nitrogen enrichment (NO2 + NO3) that promotes hard coral dominance around 44% of the island's perimeter. Our findings show that, in the absence of confounding direct human impacts, the spatial organization of coral reef benthic competitors are predictable and somewhat bounded across the seascape by concurrent gradients in physical drivers. This article is protected by copyright. All rights reserved.
... The greater reduction in the larger size classes in comparison with the smaller ones may be explained by the differential response of larger fish to exploitation, related to ecological factors, such as their trophic guilds. In this context, piscivorous fishes are Subsistence fishing's impact on mangrove fish communities important consumers of fish biomass, and predation is an important source of mortality in fish communities, which is thought to be a fundamental structuring force in mangrove habitats (Hammerschlag et al., 2010). A size-spectrum approach, combined with an analysis of other factors (e.g. ...
Article
Full-text available
The data requirements and resources needed to develop effective indicators of fishing impacts on target stocks may often be great, especially for mangrove fisheries where, for example, tidal cycles sequentially flood and drain the habitat as a result of natural processes. Here, we used underwater video systems to evaluate the impact of small-scale fisheries on mangrove fish assemblages at four levels of fishing pressure (low, medium, high, and no pressure). The lowest values of species richness and abundance were recorded in the areas fished most intensively. Conversely, the highest species richness and the occurrence of larger-bodied fish were recorded in areas of reduced fishing activity, which was surprisingly similar to the "no fishing" areas. The slopes of the community size spectra steepened in response to exploitation, while the relative abundance of medium-sized fish (16-25 cm) declined. Fishing for local or regional markets, rather than subsistence, also led to a decrease in the abundance of larger fish (>41 cm). The marked response of population parameters to fishing pressure reflected the impact of unregu-lated small-scale fisheries on areas of mangroves. Fishery management practices that ignore contemporary changes in these environments are likely to overestimate long-term yields, leading to overfishing. Thus, size-based approaches to evaluating fishing pressure were suitable for detecting negative responses from the mangrove fish assemblages. A next step will be to integrate size-and species-based ecological approaches that provide mechanisms to address pronounced decreases in specific species as a more profitable indicator of fishing impacts on mangrove fish assemblages. This approach will allow the development of effective conservation and management strategies.
... We must move beyond valuation based simply on export of individuals (or their biomass) towards identification of the underlying connectivities, processes, and conditions that must be conserved to maintain nursery value functions . While seascape structure is important (Hammerschlag et al. 2010), additional factors need to be addressed including ecological interactions, environmental suitability, and resource dynamics (Dorenbosch et al. 2004;Weinstein 2003, 2004;Sheaves 2012;Weinstein et al. 2014;Litvin et al. 2014;Potter et al. 2015;Sheaves et al. 2017;Taylor et al. 2017). ...
Article
Estuaries and other coastal habitats are considered essential for the survival of early life stages of commercial, recreational, and other ecologically important species. While early designations simply referred to habitats with higher densities of juveniles as nurseries, the definition was improved by arguing that contribution per unit area to the production of individuals that recruit to adult populations is greater, on average, in nursery habitats. However, this and related approaches typically consider critical habitats as individual, homogeneous entities that are static in nature and do not specifically incorporate important dynamics that determine nursery function. The latter include environmental variability, estuarine hydrodynamics, trophic coupling, ontogenetic habitat shifts, and spatially explicit usage of habitat patches and corridors within larger seascapes. Subsequent studies have identified important factors that regulate nursery value, and researchers working independently across the globe have not only supported the advances made in defining the processes underlying nursery function but, as set forth in this narrative, have advanced it while suggesting that much work still needs to be done to improve our understanding of the links between juvenile nekton survival and the estuarine-coastal seascape. We discuss the current nursery role hypothesis and the data supporting (or refuting) it along with the implications for management of estuarine habitats for the conservation or restoration of nursery function.
... Despite this paucity of information, it is widely acknowledged that many organisms are nocturnally active, exhibit vastly different behavior, and display altered patterns of community structure (Eggleston et al. 1998. Organisms in ecosystems ranging from coral reefs to polar regions and the open ocean are known to have evolved important adaptations to take advantage of the lack of visual cues to both avoid predators and more effectively forage (Helfman 1986, Hammerschlag et al. 2010, Goebel et al. 2017. As such, disregarding potentially important diel patterns in habitat use patterns when conducting impact assessments of invasive species can overlook important negative effects. ...
Article
Full-text available
Gulf of Mexico estuaries contain an abundance of habitat-forming submerged vegetation that provide various ecosystem services. However, these estuaries now harbor numerous invasive macrophytes, such as Eurasian milfoil Myriophyllum spicatum. Previously, we showed that milfoil gained a foothold in the Mobile-Tensaw Delta, Alabama, USA, in protected waters north of a manmade causeway that significantly reduces wave action. Here, we collected associated organisms using a suction sampler and compared the composition and abundances of fauna residing in M. spicatum and wild celery Vallisneria americana, the most abundant native macrophyte, during day and night. North of the causeway, where water flow is limited, a 5-fold reduction in the abundance of organisms was documented in M. spicatum at night, while abundance in V. americana varied little. We found that this nocturnal decrease was accompanied by changes in community structure in M. spicatum north of the causeway, driven by reductions in invertebrates such as Gammarus amphipods, Neritina snails, and Callinectes sapidus crustaceans. In contrast, communities in V. americana, although distinct from M. spicatum, exhibited little spatial or temporal difference. Subsequent analyses indicated that reduced dissolved oxygen in M. spicatum north of the causeway at night drives assemblage patterns. These results suggest that hydrological alterations exacerbate M. spicatum's negative effects through the creation of hypoxic zones and that daily migrations into these habitats may be necessary for organisms to garner the benefits of this vegetation. Finally, this work highlights that our understanding of the concomitant impacts of altered hydrology and invasive macrophytes is incomplete without considering diel variability.
... One potential explanation may be related to organismal body size, as previous studies demonstrate that neonate and juvenile teleost and elasmobranch species can utilize and manoeuvre through complex benthic habitats (e.g. mangrove roots), whereas larger predators are excluded (Guttridge et al., 2012;Hammerschlag, Morgan & Serafy, 2010). Therefore, it is possible that body size, more specifically, body width, may be a key contributor to overall barrier exclusion efficacy as narrow marine organisms can simply manoeuvre through the barrier elements. ...
Article
Following a shark attack, local governments often rapidly respond by implementing indiscriminate shark culls. These culls have been demonstrated to have substantial localized and adverse effects on a variety of marine organisms, and therefore there is an increasing need for an eco‐friendly alternative that maximizes both beachgoer and marine organismal safety. In response to such culls, the novel magnetic barrier technology, the Sharksafe Barrier was developed and rigorously tested on a variety of sharks implicated in shark attacks (e.g. bull sharks – Carcharhinus leucas and white sharks – Carcharodon carcharias ). Although these studies exhibited promise in shark swim pattern manipulation and C. leucas exclusion, research was lacking in assessing if the technology could serve as an alternative to shark nets, or more specifically, if it could exclude motivated C. carcharias from bait. Using a 13 m × 13 m square exclusion zone, this study aimed to test the C. carcharias exclusion capabilities of the Sharksafe Barrier while additionally assessing the long‐term structural integrity of the system. After 34 trials and approximately 255 hours of total video collected over two years, data illustrate that all interacting C. carcharias were successfully excluded from the baited Sharksafe Barrier region, whereas teleosts and other small elasmobranch species were not. In addition, the long‐term deployment potential of this barrier system held promise owing to its ability to withstand harsh environmental conditions. Therefore, with the successful exclusion of a second large shark species, C. carcharias , from a baited region, continued long‐term research and implementation of this system at other locations should be considered to assess its viability and overall success as a bather and shark protection system.
... The entire process was fairly rapid (~10-15 s) and the tethered pinfish was quickly returned to the water without the need for recovery from anesthesia, which could have artificially inflated mortality. This same approach was previously used to tether pinfish in Biscayne Bay, Florida, USA (Hammerschlag et al., 2010) and is advantageous over more invasive methods (e.g., running tether through soma) as it minimizes tissue damage and the release of body fluids, which could increase detection by predators. Last, the tether was secured to the centerline using a loose loop, allowing pinfish to move in a vertical cylinder with a radius of 0.25 m ( Fig. 2) but preventing it from accessing adjacent habitats. ...
Article
Predator–prey interactions can be influenced by habitat at different spatial scales. In seagrass systems, blade density can provide refugia for prey at fine scales, which are further embedded within broad-scale features such as variation in biotic (e.g., predator assemblages) and abiotic attributes (e.g., turbidity, salinity). Fine-scale effects of seagrass habitats on predator–prey interactions involving invertebrates have been well studied while less is known about their effects on fish as prey. A field experiment was conducted in Tampa Bay, Florida, USA to examine and separate the effects of habitat across fine and broad scales on the relative predation rates of tethered pinfish (Lagodon rhomboides). Artificial seagrass units (ASUs) were used at three levels of blade density and deployed in different locations within the seascape. Predation rates on pinfish decreased with increasing seagrass blade density. The effects of blade density were consistent across locations, but overall mortality was higher in the lower Bay, where the water was less turbid, higher in salinity, and characterized by a different suite of predators compared to the mid Bay. Using controlled-laboratory experiments, it was found that pinfish reduced their activity levels in more turbid water as well as in response to the presence of a common predator in both clear and more turbid waters. Thus, predation rates were influenced by the combined effects of refugia (fine scale), variation in prey behavior (broad scale), and detection by predators (both scales). This study demonstrates the strong influence habitat can have at different spatial scales in mediating predator–prey interactions of mobile species in estuarine environments.
... They have consequently been considered to be successful nursery grounds (Reise 2012). These ecological features can make inshore habitats valuable hunting and foraging grounds for large predatory fishes such as sharks (Hammerschlag et al. 2010). Entrance into these habitats may, however, incur several costs to predators due to tidal fluctuations that can result in temporary periodicity of low dissolved oxygen levels (Sakamaki et al. 2006) and other water-quality stressors within inshore tropical shallow waters (e.g. ...
Article
Full-text available
Evidence suggests the great hammerhead shark, Sphyrna mokarran, is vulnerable to a variety of anthropogenic stressors, and is an understudied species of shark due to its cryptic nature and wideranging movements. While recognized as both a pelagic-coastal and a highly mobile predator, minimal anecdotal evidence exist describing shallow water habitat use by this species. This report describes six cases in which a great hammerhead shark utilizes an inshore shallow water flats environment (<1.5 m in depth), five of which involve prey capture. These observations permitted identification of two novel behaviors that may allow great hammerheads to inhabit these shallow habitats: a (1) prey-capture technique termed ‘grasp-turning’ that involves burst swimming at tight turning angles while grasping prey and (2) a post-predation recovery period whereby the shark maintains head-first orientation into the current that may facilitate respiration and prey consumption. These behavioral observations provide insights into the natural history of this species.
... 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. ...
Article
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.
... Indeed, aquatic macrophytes have been described as providing a refuge from predators for juvenile estuarine and coastal fishes (Adams et al. 2004;Sheppard et al. 2011;Andrades et al. 2014). One of the main challenges of fishes during the early stages of their lives is predation avoidance, which entails seeking refuge in a variety of habitats, including shallow estuarine waters (Hammerschlag et al. 2010). The first concise record of extension of R. bahiensis into Espírito Santo waters will allow inclusion of the species in future management and conservation plans under the environmental laws of Espírito Santo state, mainly in relation to the Environmental Protected Area of Conceição da Barra (APA de Conceição da Barra), which includes the São Mateus River estuary. ...
Article
Full-text available
This study provides the concise first record and range extension of Rhinosardinia bahiensis (Steindachner, 1879) in the Espírito Santo waters. The recruitment of R. bahiensis in the São Mateus river estuary probably occurs in the upper areas covered by dense macrophyte vegetation during the winter months.
... These amphipod species are recognized to inhabit macrophytes in Brazilian and Australian coastal waters (Robertson and Lucas, 1983;Guiss, 1991, 1992), which supports the idea that allochthonous drift algae may provide an additional feeding opportunity to fish. On the other hand, predation is considered to be one of the most important causes of mortality in juvenile fish in coastal ecosystems (Hammerschlag et al., 2010). According to Walters and Juanes (1993), YOY fish remain sheltered most of the day, leaving their refuges only during short periods to feed. ...
... MacDonald et al. (2009) showed that in the Caribbean, time spent by juvenile Lutjanus apodus and Sphoeroides testudineus in mangrove prop root habitats was related to size e smaller individuals spend more time in the prop root areas. Working with tethered Lagodon rhomboides in Florida, Hammerschlag et al. (2010) showed that predation losses were highest near the edge of the mangroves. Also using tethering experiments in southern Japan, Nanjo et al. (2011) demonstrated that although the density of piscivores may be higher in mangrove root areas, prey mortality varies according to the anti-predator strategies adopted by different species, e.g. ...
Article
Since 2002 there has been an increase in knowledge of many aspects of the biology and ecology of tropical estuarine fishes, as well as significant changes to many estuarine fisheries. Analyses of literature databases (2002–2012) show that: of the c. 600 relevant papers, 52% are primarily related to ecology, 11% to conservation, 11% to anthropogenic and pollution effects on fishes, 9% to fisheries, 7% to aquaculture, 4% to study techniques, and 1% each to fish larvae, effects of fishing, taxonomy, climate change, evolution and genetics. In terms of geographic spread 17% are from North America, 15% from south Asia, 14% from the Caribbean, 13% from Australasia, 12% from Africa and 9% each from South America and SE Asia. Research papers came from 50 countries of which the dominant were USA (15%), India (12%), Australia (11%) and Brazil (7%). Increasing numbers of studies in West Africa, SE and South Asia and South America have increased basic knowledge of the ecology of estuarine fish faunas. Increases in understanding relate to: roles of salinity, turbidity and habitat diversity; connectivity between habitats; water flow; ecological drivers of spatial variability; scale dependent variation; thermal tolerances; movement patterns; food webs; larval adaptations; and the viability of areas heavily impacted by human activities. New reviews both challenge and support different aspects of the estuarine dependence paradigm – still perhaps one of the main research issues – and the protective function of estuaries and mangroves for juvenile fishes has received attention in relation to e.g. predation risks and fisheries. There have also been significant advances in the use of guilds and biodiversity models. Fishing pressures have continued unabated in most tropical estuaries and are summarised and management issues discussed. Understanding of the relationships between fisheries production and mangroves has advanced and significant differences have emerged between Indo-West Pacific and Atlantic systems. The effects of fishing itself have also received attention and research is often related to conservation studies. The effects of anthropogenic activities are reviewed and important advances in mitigation are discussed. Restoration of estuarine habitats, such as mangroves, previously taking place mainly in countries such as Australia and USA, is now occurring in more countries. The design of reserves and the use of protected areas as management tools are gaining credence. Finally, the evidence for actual and potential effects of climate change is discussed.
... However, Baker and Sheaves (2006) demonstrated that some shallow coastal refuge sites may also be sites of high piscivorous predation and predator density, and questioned the paradigm that these areas actually reduce the risk of predation for small teleosts (Baker and Sheaves 2007). Recent testing of the shallow-water refuge hypothesis has not unequivocally demonstrated that it holds true (Hammerschlag et al. 2010; Ryer et al. 2010), with descriptions of piscivorous fishes (Able et al. 2009; Becker et al. 2011) and elasmobranchs (Ackerman et al. 2000; White and Potter 2004 ) also occurring in these habitats. Indeed , the processes driving the use of shallow intertidal habitats by fish assemblages are likely to be more complex than previously thought (Becker et al. 2011). ...
Article
Full-text available
Shallow intertidal habitats are recognised as critical for larval and juvenile fish, and are often assumed to function as refuge areas where predation risk is reduced. Yet there is growing evidence that suggest these areas may also be regularly inhabited by large bodied fish and be the site of high levels of juvenile fish predation. In the present study we examined the use of an intermittently available surf zone habitat in tropical northern Australia by a diverse community of large-bodied teleosts (mean total length 444 mm), sharks (mean total stretched length 658 mm) and rays (mean total stretched length 1,108 mm). Drawing on the methods and ecological knowledge of a local commercial fishery, gillnets were used to capture fish as they entered the surf zone on the flooding tide. Monthly surveys over a one-year period revealed a dynamic assemblage consisting of 30 species of teleosts (mostly caught as adults) and 14 species of sharks and rays (mostly caught as juveniles or young of the year). Although it is unclear why these fish use this habitat, we conclude that it may support a broad range of biological benefits including spawning for teleosts, parturition for elasmobranchs, as well as foraging and refuge. The unique findings of this study highlight existing knowledge gaps and the need to better understand what fish use the intertidal zone and why. This should be a high priority given the increasing anthropogenic pressures on coastal margins.
... Nevertheless, the present results and subsequent conclusions should be reasonable, reflecting predation rate patterns among the fishes examined and between the two microhabitats, because of the experimental manipulation and efforts made to overcome potential artifacts. In addition, the mangrove-root structured area harbored significantly greater numbers of resident piscivorous fishes, suggesting that in such a microhabitat, the potential predation risk is not necessarily low, as generally believed, but in fact rather high, as recently indicated by Hammerschlag et al. (2010a). ...
Article
Full-text available
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.
Article
Full-text available
The mechanisms that govern fauna-habitat associations across multiple spatial scales remain largely undefined. Can environmental factors structure fauna-habitat associations over both local and global spatial scales, alongside biogeographical processes and patterns? We compare the extent to which the use of mangroves by fishes is consistent within and between biogeographic locations, and whether any similarities and differences can be attributed to the environmental context of those forests, such as the physical environment, seascape composition and constraints on access by fishes. We focus on three important proxies of these structuring forces for fish—salinity, distance to reefs and tidal amplitude. Using directly comparable remote underwater visual census from a range of diverse environmental contexts in the Central and Eastern Indo-Pacific, we examine similarity in the family-level taxonomic composition of fish assemblages in mangrove forests. Local environmental context appears to explain similarities and differences in mangrove association by fishes at both regional and local scales across the Indo-Pacific. There were strong consistencies in taxonomic composition in similar environmental contexts despite geographic separation. Tidal amplitude was a powerful explanatory factor that interacted with both distance to reef and salinity in partitioning variation in fish assemblage structure. Substantial differences in the use of mangroves between regions appear to be independent of historical biogeography, relating instead to local context. Our findings suggest that the effects of local context on habitat suitability can play out over biogeographical scales, and global similarities in fauna-habitat associations may be partially explained by comparable environmental contexts, with important management implications.
Chapter
Ecological phenomena are usually complex because of natural variability in space and time, which in turn often makes the interpretation of results from field surveys difficult. To compensate for survey weakness, field/laboratory experiments are often applied to marine ecological studies. Well-designed experiments can discern between each ecological process, and consequently help to understand ecological mechanisms. This section describes practical examples of field/laboratory experimental methods, including those studying predation impacts, consumption rates, behavioral tactics, and symbiotic interactions.
Article
Full-text available
Habitat loss is accelerating a global extinction crisis. Conservation requires understanding links between species and habitats. Emerging research is revealing important associations between vegetated coastal wetlands and marine megafauna, such as cetaceans, sea turtles, and sharks. But these links have not been reviewed and the importance of these globally declining habitats is undervalued. Here, we identify associations for 102 marine megafauna species that utilize these habitats, increasing the number of species with associations based on current International Union for the Conservation of Nature (IUCN) species assessments by 59% to 174, accounting for over 13% of all marine megafauna. We conclude that coastal wetlands require greater protection to support marine megafauna, and present a simple, effective framework to improve the inclusion of habitat associations within species assessments.
Article
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.
Chapter
Small estuaries and non-estuarine habitats harboring mangroves are very important ecosystems which provide important ecosystem goods and services; such as provision of ecological niches for juvenile fishes and invertebrates, enhances fisheries, and in biodiversity conservation. Similar to large estuaries, they are highly perturbed which threatens their existence. This chapter uses beach seine, underwater visual census, and stable isotope data to discuss the importance of and threats to small estuaries and non-estuarine mangroves found in Dar es Salaam, Bagamoyo and Zanzibar, Tanzania. For example, mangroves of Kunduchi (Dar es Salaam) and Mbegani (Bagamoyo) which harbour predominantly higher densities of juveniles (≤10 cm) of two economically important species—Lutjanus fulviflamma and Lethrinus harak—than adjacent coral reefs. Evidence suggests further that the Kunduchi mangroves replenish fish populations on adjacent coral reefs; where over 90% and 29% of adult L. fulviflamma and L. harak individuals, respectively, have been identified to have lived in the mangroves as juveniles. In terms of habitat utilization by different size classes of fish, five of the 13 species (Lethrinus lentjan, L. variegatus, Pelates quadrilineatus, Siganus sutor and Sphyraena barracuda) found in Chwaka Bay (Zanzibar) were found as small-sized individuals in shallow and turbid mangrove areas with large juveniles and sub-adults in adjacent seagrass beds. The non-estuarine mangroves of Kunduchi and those of Mtoni estuary (Dar es Salaam) are subjected to pollution from urban activities. For example, stable isotope data of fishes indicate elevated levels of nitrogen in these mangroves with highest levels (δ15N = 15.2 ± 0.2) recorded in Mtoni estuary. In view of their importance and threats they face, these ecosystems require attention similar to large estuaries. If the current degradation rate of these ‘overlooked’ but equally important ecosystems continues, they may be declared ‘functionally disappeared’ in a few decades.
Article
Full-text available
Aim Connectivity structures populations, communities and ecosystems in the sea. The extent of connectivity is, therefore, predicted to also influence the outcomes of conservation initiatives, such as marine reserves. Here we review the published evidence about how important seascape connectivity (i.e. landscape connectivity in the sea) is for marine conservation outcomes. Location Global. Methods We analysed the global literature on the effects of seascape connectivity on reserve performance. Results In the majority of cases, greater seascape connectivity inside reserves translates into better conservation outcomes (i.e. enhanced productivity and diversity). Research on reserve performance is, however, most often conducted separately from research on connectivity, resulting in few studies (< 5% of all studies of seascape connectivity) that have quantified how connectivity modifies reserve effects on populations, assemblages or ecosystem functioning in seascapes. Nevertheless, evidence for positive effects of connectivity on reserve performance is geographically widespread, encompassing studies in the Caribbean Sea, Florida Keys and western Pacific Ocean. Main conclusions Given that research rarely connects the effects of connectivity and reserves, our thesis is that stronger linkages between landscape ecology and marine spatial planning are likely to improve conservation outcomes in the sea. The key science challenge is to identify the full range of ecological functions that are modulated by connectivity and the spatial scale over which these functions enhance conservation outcomes.
Book
Full-text available
In the tropical and sub-tropical regions of Asia, mangrove and seagrass habitats provide habitat for a wide range of species and plants, for some or all of their lifecycle. Many of these species are exploited for food and are the target of both artisanal and commercial fisheries. Mangroves provide a wide range of ecosystem services which are incidental to fisheries production, but important to coastal environments and the livelihoods of coastal populations. Mangroves provide a diverse range of fishery products, seed stock for some forms of aquaculture, forest products, timber and wildlife. The non-fishery ecosystem services of mangroves can include erosion control, mitigation of pollution and protection from storm or tsunami events. There is a widely held perception that mangrove and seagrass habitats underpin fish and shrimp fishery production by acting as a nursery habitat for commercially important fisheries species. However, the decline or degradation of these habitats and their apparent role in the lifecycle of fish and invertebrates gives rise to the question as to why large cumulative losses of these habitats have not been matched by commensurate declines in fishery production of these commercial species. This review brings together the findings in the scientific literature on the extent of mangrove and seagrass habitat and any relationships they may have to fisheries production. In doing so, it reveals that some popular perceptions regarding the role of mangroves and seagrass in fisheries production may be overstated or incorrectly interpreted. The review also finds that the linkages between fisheries and mangrove or seagrass vary both according to species and life stage and needs to be evaluated on a case by case basis. This does not diminish the value of mangrove and seagrass habitats and emphasizes the need for a more holistic approach to the management of coastal environments and the fisheries within them. This approach must adequately take into account the complexity and interactions between adjoining habitats, and the overarching need to manage fishing activity, especially fishing effort. This review provides an excellent overview of our state of knowledge of how mangrove and seagrass habitats interact with fisheries and concludes with recommendations on where our knowledge must be strengthened. In particular, the review concludes that studies on species specific life histories, and on the ecological connectivity between adjacent biotopes, are needed to clarify more explicitly the nature of any relationship between mangrove and seagrass habitats and fish or shrimp populations. It is expected that further studies using more sophisticated methods and statistical techniques will clarify more explicitly the nature of any relationship between mangrove and seagrass habitats and fish populations.
Article
Distribution and survival of fish are influenced by benthic habitat and complexity. While many studies have investigated the effects of algal cover on fishes in reef habitats, comparatively less is known regarding this relationship in mangrove habitats. Possible links between substrate macro-algal cover and fish distribution were studied in a Caribbean mangrove lagoon via visual surveys and algal removal experiments. In addition, the effects of algae on relative predation were tested by calculating survival of tethered brachyuran prey, whose predators are known to include larger lutjanid (snapper) juveniles. Comparisons of algae and fish distributions show that percent cover of algae and juvenile lutjanid, Lutjanus griseus (gray snapper) abundances were significantly negatively correlated. Results from the algae removal experiment showed that algae had a negative effect on abundance of carnivorous fishes in two (out of three) locations in the lagoon. In addition, tethered prey had significantly higher proportional survival in plots with algae-present relative to plots with algae-absent. We present here experimental evidence that increased algal growth in mangroves may reduce predator encounter rates by prey. These observations are important, as the presence of carnivorous fishes is a key factor for the maintenance of high diversity in mangrove and on neighboring coral reefs. Furthermore, findings from this study imply that algal cover must be considered when protecting mangrove habitat.
Article
Full-text available
The spatially explicit diel movement patterns of fish using coral reef ecosystems are not well understood, despite the widespread recognition that many common species undergo distinct migrations to utilize different resources during night and day. We used manual acoustic telemetry coupled with global positioning technology to track the detailed spatially explicit daily movements (24 h) of multiple individuals of two common Caribbean fish species, Haemulon sciurus (bluestriped grunt) and Lutjanus apodus (schoolmaster snapper). Movement pathways and day and night activity spaces were mapped and quantified in a Geographic Information System (GIS). Directional sun-synchronous migrations occurred close to astronomical sunset and sunrise. Site fidelity within day and night activity spaces was high. Nine of twelve individuals exhibited overlap of day and night activity spaces and three fish (L. apodus) exhibited complete spatial segregation. Night activity spaces (H. sciurus: 11,309 ± 3,548 m2; L. apodus: 9,950 ± 3,120 m2) were significantly larger than day activity spaces (H. sciurus: 2,778 ± 1,979 m2; L. apodus: 1,291 ± 636 m2). The distance between sequential position fixes (step lengths) was significantly greater at night than day, indicative of nocturnal foraging and day resting behavior. Integrating acoustic telemetry, GIS techniques and spatial statistics to study fish movement behavior revealed both individual variability and some broader generality in movement paths and activity spaces suggestive of complex underlying behavioral mechanisms influencing diel movements.
Article
Full-text available
Fishes moving onto the surface of a tidal freshwater marsh from an adjacent stream were sampled with flume nets in spring through autumn for 2 yr. Significantly higher numbers were found at sites adjacent to shallow-sloped depositional banks than at sites adjacent to deeper, steeper sloped erosional banks of the stream. Marsh surface features appeared similar, so explanations for this apparent habitat selection were sought in the subtidal portion of the stream. To determine whether the relative abundance of benthic invertebrate prey differed in the two environments, litter bags were placed in the subtidal for 4 wk. Despite higher numbers of invertebrates in erosional zones, both the wet biomass per sample and the mean wet biomass per organism were significantly greater in depositional sites. To test the hypothesis that invertebrate food is more available to fishes in the depositional subtidal, banded killifish (Fundulus diaphanus) were placed in feeding enclosures in both depositional and erosional subtidal habitats in two streams. These fish obtained significantly more food in the shallow depositional subtidal. To test the hypothesis that predation pressure differs with subtidal geomorphology, mummichogs (Fundulus heteroclitus) were tethered on the first half of the rising tide in both depositional and erosional environments in three creeks. Significantly more mummichogs disappeared from tethers and were presumed taken on erosional banks. We conclude that two mechanisms operate in the stream subtidal to give rise to the greater fish abundance at marsh surface sites adjacent to depositional areas. At low tide, when small fishes are confined to creek channels, they select shallow depositional habitats where (1) the availability of benthic invertebrate prey is greatest and (2) predator pressure is less. As the tide rises and inundates the marsh surface, these small fishes seek shelter on the marsh surface adjacent to their preferred low-tide refuge.
Article
Full-text available
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.
Article
Full-text available
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
Article
Full-text available
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.
Article
Full-text available
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.
Article
Full-text available
Eelgrass Zostera marina provides refuge to numerous fish species but is vulnerable to fragmentation through natural and anthropogenic disturbance. In Bonavista Bay, Newfoundland, eelgrass patch size was altered to measure changes in predation risk in Age-0 juvenile cod, Gadus morhua. Artificial eelgrass mats of 5 sizes (0.32, 1.1, 5.5, 11 and 22 m2) were deployed in duplicate at each of 2 sites in Newman Sound in Terra Nova National Park during summer/autumn in 1999 and 2000. Predator distribution was determined using a combination of weekly underwater transect surveys and biweekly seining. Relative predation rates were measured by tethering Age-0 cod at the center of each patch and recording the incidence of predation (n = 1116 tether sets). Predation rates were negatively correlated with patch size during both years, suggesting that larger patches reduce predator foraging ability. However, high predator densities in the largest eelgrass patch resulted in higher than expected rates of predation. Therefore, habitat dimension affected predation risk in juvenile cod via 2 opposing mechanisms. Our results stress the importance of considering both habitat areal extent and predator distribution when estimating the effects of habitat fragmentation on predation rates.
Article
Full-text available
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.
Article
Full-text available
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.
Article
Full-text available
Mangrove and nearshore seagrass macrofaunal communities were concurrently sampled in two areas of contrasting primary productivity (North Sound: low; South Bimini: high) off Bimini, Bahamas. Over 200,000 individuals, comprising 175 species, were identified from catches of block nets, seines, and trawls between March 2000 and March 2003. The Index of Relative Importance (IRI), which is typically used for dietary analysis and combines percentage weight, abundance and occurrence, was applied to catch data to enable easy spatial and temporal variations in community composition. Cluster-analysis revealed distinct mangrove and seagrass communities, with Morisita's index indicating a greater degree of spatial and temporal homogeneity in the North Sound. Catch diversity and biomass were significantly greater in the mangroves than over seagrass in both locations, and highest off South Bimini. Low productivity, faunal diversity, and abundance in the North Sound were probably due to extreme abiotic variables. Juveniles of most species were present in mangroves and seagrass beds around Bimini, and therefore the protection of mangroves in the Bahamas should be an issue of immediate concern.
Article
Full-text available
The elasmobranch fauna of Everglades National Park was studied using longline, gillnet, and rod and reel surveys. Thirteen species of elasmobranchs were identified including three species not previously reported in the park. Species richness was highest in the areas with the greatest influence of marine waters from the Gulf of Mexico and lower in estuarine areas and those subject to periods of hypersalinity. Most elasmobranch species were recorded as juveniles, with at least three species occurring as neonates, and there were few adults of any species. Electivity indices for salinity, temperature, and depth were calculated for Carcharhinus leucas (Valenciennes, 1841), Carcharhinus limbatus (Valenciennes, 1841), Ginglymostoma cirratum (Bonnaterre, 1788), and Negaprion brevirostris (Poey, 1868), and indicated possible habitat partitioning based on these environmental characteristics. Tag-recapture data suggested that N. brevirostris may have a high level of residency and probably remains inside the park for long periods, while all other species showed movements into and out of the park on a regular basis. Results demonstrate the utility of the park for the conservation and management of elasmobranch species and the need to consider how future changes to the environment will affect this important group of predators.
Article
Full-text available
Marine ecosystems throughout the Indo-Pacific region are highly threatened by anthropogenic stressors, yet the faunal interaction between different component habitats remains poorly understood. This information is vital as stress on one inter-connected habitat may have cascade effects on other habitats. The present study focused on the impact of inter-habitat connectivity on seagrass fish assemblages, specifically between seagrass, mangrove and reef habitats. Fish were sampled using a seine net within 3 seagrass habitats (seagrass near to reef, seagrass near to reef and mangrove, and seagrass near to mangrove) within eastern Indonesia. Visual surveys were also conducted within mangrove habitats. Fish abundance and species richness in seagrass beds in close proximity to mangroves was at least twice that found in seagrass beds that were distant from mangrove habitat. The trophic structures of seagrass fish assemblages change from being dominated by predators and omnivores close to the reef, to assemblages high in planktivores and herbivores close to mangroves. We found that mangroves enhance the fish assemblages of nearby seagrass beds probably by increasing the availability of shelter and food provision. This study indicates that Indo-Pacific seagrass beds play an important fish nursery role, which is influenced by the availability of nearby reef and mangrove habitats. Our research supports the need for ecosystem-level management of shallow water tropical habitats, but also suggests that successful management requires local-level knowledge of habitat interactions to successfully enhance or conserve fish assemblages
Article
Full-text available
Mangrove forests and seagrass beds frequently occur as adjacent habitats in the temperate waters of southeastern Australia. At low tide when fish cannot occupy mangroves they might utilise adjacent habitats, including seagrass. We first sampled small fish from seagrass beds close to and far from mangroves in the Pittwater estuary, NSW, Australia. Seagrass beds close to mangroves had a greater density of fish species than beds far from mangroves (close: mean 16.0speciesnet−1, SE 1.0; far: 13.2, 1.3; P<0.05). In particular, juvenile fish were in greater densities near to than far from mangroves (close: 5.3, 0.4; far: 3.1, 0.4; P<0.05). We then sampled the mangrove forests during the high tide and seagrass beds during the low tide, in beds along a continuum of distances from mangroves. Multivariate analysis showed that fish assemblages differed with distance from mangroves, and the differences were attributed to the composition of the fish assemblage (i.e. presence/absence of fish species), not the abundances of individual species. In particular, fish that utilise mangrove forests at high tide were found in greater species densities and species richness in seagrass nearer to mangroves. A negative relationship was found between the density of mangrove-utilising fish species and the distance of the bed from mangroves (R 2=0.37, P<0.05). This confirms the important connectivity between mangroves and seagrass for fish in temperate Australian waters.
Article
Full-text available
We tested the hypothesis for several Caribbean reef fish species that there is no difference in nursery function among mangrove, seagrass and shallow reef habitat as measured by: (a) patterns of juvenile and adult density, (b) assemblage composition, and (c) relative predation rates. Results indicated that although some mangrove and seagrass sites showed characteristics of nursery habitats, this pattern was weak. While almost half of our mangrove and seagrass sites appeared to hold higher proportions of juvenile fish (all species pooled) than did reef sites, this pattern was significant in only two cases. In addition, only four of the six most abundant and commercially important species (Haemulon flavolineatum, Haemulon sciurus, Lutjanus apodus, Lutjanus mahogoni, Scarus iserti, and Sparisoma aurofrenatum) showed patterns of higher proportions of juvenile fish in mangrove and/or seagrass habitat(s) relative to coral reefs, and were limited to four of nine sites. Faunal similarity between reef and either mangrove or seagrass habitats was low, suggesting little, if any exchange between them. Finally, although relative risk of predation was lower in mangrove/seagrass than in reef habitats, variance in rates was substantial suggesting that not all mangrove/seagrass habitats function equivalently. Specifically, relative risk varied between morning and afternoon, and between sites of similar habitat, yet varied little, in some cases, between habitats (mangrove/seagrass vs. coral reefs). Consequently, our results caution against generalizations that all mangrove and seagrass habitats have nursery function.
Article
Full-text available
The nurse shark is an extremely abundant shallow water species in Florida and the Caribbean, yet its biology is poorly known. Moreover, there is a great deal of misinformation about it in the literature. The maximum size and weight attained by the nurse shark have often been exaggerated. None of the specimens measured in this study exceeded 265cm TL and 114.5kg, and none of the specimens actually measured by other researchers exceeded 280cm. Females reach maturity at a length of 223–231cm, or at 86% of their maximum size. Males reach maturity between 214 and 214.6cm in length or at about 83% of their maximum size. Mating primarily occurs from mid-June to early July. The embryos are enclosed in sturdy egg capsules for the first 12–14 weeks of gestation. In a gravid female, the embryos are at different stages of development during the first four months of gestation. Embryos are lecithotrophic and there is no evidence of any supplemental mode of embryonic nourishment. Embryos measure 28–30.5cm at birth. The gestation period is estimated at about five to six months. Brood sizes are large, ranging from 21 to 50 young, with a median of 34 young. The reproductive cycle of the nurse shark consists of a five to six-month gestation period and a two-year ovarian cycle. Thus, the reproductive cycle is biennial and a female produces a brood every two years. The nurse shark is an opportunistic predator that consumes a wide range of small fishes, primarily grunts (Haemulidae).
Article
Full-text available
To examine variation in diet and daily ration of the bonnethead shark, Sphyrna tiburo (Linnaeus 1758), animals were collected from three areas in the eastern Gulf of Mexico: northwest Florida (∼29°40′N, 85°13′W), Tampa Bay near Anclote Key (∼28°10′N, 82°42.5′W), and Florida Bay (∼24°50′N, 80°48′W) from March through September, 1998–2000. In each area, diet was assessed by life stage (young-of-the year, juveniles, and adults) and quantified using five indices: percent by number (%N), percent by weight (%W), frequency of occurrence (%O), index of relative importance expressed on a percent basis (%IRI), and %IRI based on diet category (%IRIDC). Diet could not be assessed for young-of-the-year in Tampa Bay or Florida Bay owing to low sample size. Diet analysis showed an ontogenetic shift in northwest Florida. Young-of-the-year stomachs from northwest Florida (n=68, 1 empty) contained a mix of seagrass and crustaceans while juvenile stomachs (n=82, 0 empty) contained a mix of crabs and seagrass and adult stomachs (n=39, 1 empty) contained almost exclusively crabs. Crabs made up the majority of both juvenile and adult diet in Tampa Bay (n=79, 2 empty, and n=88, 1 empty, respectively). Juvenile stomachs from Florida Bay (n=72, 0 empty) contained seagrass and a mix of crustaceans while adult stomachs contained more shrimp and cephalopods (n=82, 3 empty). Diets in northwest Florida and Tampa Bay were similar. The diet in Florida Bay was different from those in the other two areas, consisting of fewer crabs and more cephalopods and lobsters. Plant material was found in large quantities in all stomachs examined from all locations (>15 %IRIDC in 6 of the 7 life stage-area combinations, >30 %IRIDC in 4 of the 7 combinations, and 62 %IRIDC in young-of-the-year diet in northwest Florida). Using species- and area-specific inputs, a bioenergetic model was constructed to estimate daily ration. Models were constructed under two scenarios: assuming plant material was and was not part of the diet. Overall, daily ration was significantly different by sex, life stage, and region. The bioenergetic model predicted increasing daily ration with decreasing latitude and decreasing daily ration with ontogeny regardless of the inclusion or exclusion of plant material. These results provide evidence that bonnetheads continuously exposed to warmer temperatures have elevated metabolism and require additional energy consumption to maintain growth and reproduction.
Article
Full-text available
The use of a coastal estuary by bonnethead sharks, Sphyrna tiburo, was examined by acoustic monitoring, gillnet sampling and tag- recapture studies. Acoustic monitoring data were used to define the residency and movement patterns of sharks within Pine Island Sound, Charlotte Harbor, Florida. Sharks were monitored for periods of 1–173days with individuals regularly moving in and out of the detection range of the acoustic system. Patterns of movement could not be correlated with tidal level or time of day. Home range sizes within the Pine Island Sound population were typically small with individuals using core areas on a daily basis. However, core areas shifted within the study site over time resulting in eventual usage of most of the available habitat. Gillnet sampling revealed that S. tiburo were abundant in shallow water near seagrass beds, but that presence of individuals at specific sites was variable. Tag-recapture data showed that most individuals remained within the Pine Island Sound region over time and did not appear to undergo long coastal migrations. The movement and residence patterns of S. tiburo suggest that individuals are resident within the estuary, but do not show site fidelity to specific areas within the estuary.
Article
Full-text available
We evaluated the influence of water depth on relative predation risk for mojarra (Eucinostomus spp.) in six tidal creeks on Andros Island, Bahamas. Relative predation risk was determined using a tethering protocol combined with underwater visual census. In one experiment, we found that relative predation risk increased predictably with water depth (r2 = 0.83), and survival of tethered mojarra decreased with water depth (r2 = 0.71). We identified three depth zones containing differing levels of predation threat: refugia (0–19 cm), transition (20–69 cm), and predation (> 70 cm). Predation on mojarra rarely occurred within the refugia zone (2% eaten) and always in the predation zone (100% eaten). Additional factors not examined in this study (e.g., mangrove complexity, predator density) likely drive variability of relative predation risk within the transition zone. In a second experiment, we directly examined influence of water depth on relative predation risk at fixed locations from high tide to low tide in a single creek. Mean relative predation risk was significantly higher during higher tides at deeper water depths. Results provide experimental evidence that exploitation of shallow water refugia by motile prey can significantly reduce predation risk. We expect the distribution of motile fishes is at least partially influenced by spatially-dynamic shallow water refugia.
Article
Full-text available
Distribution of mobile animals may reflect decisions on how to balance conflicting demands associated with foraging and avoiding predators. A simple optimality model predicts that mobile animals should respond to changes in mortality risk (mu) and growth rate (g) by shifting habitats in a way that maximizes net benefits. In this study, field caging and tethering experiments quantified habitat-specific growth rates and mortality risk, respectively, for three different sizes of a coral reef fish, Nassau grouper (Epinephelus striatus), during its juvenile tenure in off-reef nursery habitats. These sizes bracketed the size at which this species undergoes an ontogenetic habitat shift from the interstices of macroalgal clumps ("algal habitat") to areas outside, or adjacent to, macroalgae and other physically complex microhabitats ("postalgal habitats"). Experimental results were used in a cost-benefit analysis to test the following alternative (but not mutually exclusive) a hypotheses: (1) juvenile grouper shift habitats in a way that maximizes growth rates (g); (2) juveniles shift habitats in a way that minimizes mortality (predation) risk (mu); and (3) if trade-offs exist between maximizing growth rate and minimizing mortality risk, juveniles shift habitats in a way that minimizes the ratio of mortality risk to growth rate (mu/g). Results suggested that small fish face a trade-off between living in the relatively safe algal habitat and achieving high growth rates in postalgal habitats. The value of mu/g was significantly lower in the algal than postalgal habitats for small fish, which typically reside in the algal habitat, and significantly lower in postalgal habitats for medium and large fish, which typically reside in postalgal habitats. Thus, habitat use by juvenile Nassau grouper was consistent with the "minimize mu/g hypothesis." These results highlight how behavioral responses to ecological processes, such as changing predation risk with body size, determine distribution patterns of mobile animals.
Article
Full-text available
Between 1997 and 2003, there were 2088 natural predations by white sharks (Carcharodon carcharias) on Cape fur seals (Arctocephalus pusillus pusillus) and 121 strikes on towed seal-shaped decoys were documented from observation vessels at Seal Island, South Africa. White sharks at Seal Island appear to selectively target lone, incoming young of the year Cape fur seals at or near the surface. Most attacks lasted < 1 min and consisted of a single breach, with predatory success rate decreasing rapidly with increasing duration and number of subsequent breaches. A white shark predatory ethogram,composed of four phases and 20 behavioural units, is presented, including four varieties of initial strike and 11 subsequent behaviour units not previously defined in the literature. Behaviour units scored from 210 predatory attacks revealed that, for both successful and unsuccessful attacks, Polaris Breach was the most commonly employed initial strike, while Surface Lunge was the most frequent second event, closely followed by Lateral Snap. Examination of video footage, still images, and tooth impressions in decoys indicated that white sharks at Seal Island bite prey obliquely using their anterolateral teeth via a sudden lateral snap of the jaws and not perpendicularly with their anterior teeth, as previously supposed. Analysis of white shark upper tooth morphology and spacing suggest the reversed intermediate teeth of white sharks occur at the strongest part of the jaw and produce the largest wound. White sharks predatory success at Seal Island is greatest (55%) within one hour of sunrise and decrease rapidly with increasing ambient light; the sharks cease active predation on seals of sunrise and decreases rapidly with increasing ambient light; the sharks cease active predation on seals when success rate drops to +/- 40%; this is the first evidence of cessation of foraging at unproductive times by any predatory fish. At Seal Island, white shark predatory success is significantly lower at locations where frequency of predation is highest, suggesting that white sharks may launch suboptimal strikes in areas of greatest intraspecific competition; this is the first evidence of social influence on predation in any elasmobranch. Idiosyncratic predatory behaviours and elevated success rates of known individual white sharks at Seal Island suggest some degree of trial-and-error learning. A hypothetical decision tree is proposed that models predatory behaviour of white sharks attacking Capr fur seals at the surface.
Article
Full-text available
An important process thought to drive habitat selection during (post-)settlement of coral reef fish is predation. It is assumed that in back-reef habitats such as seagrass beds and mangroves predation is lower than on coral reefs. However, recent studies have suggested that significant piscivore assemblages are present in back-reef habitats. The assumption of reduced predation pressure in back-reef habitats can therefore be debated. We compared piscivore assemblages along the coast of a Caribbean island using underwater visual census surveys in a spatial gradient of coral reefs, seagrass beds and mangroves. We also performed predation experiments in combination with video observations in these habitats using tethered recently settled Haemulon flavolineatum. High piscivore densities and reduced survival showed the presence of significant piscivore assemblages in both reef and back-reef habitats. Both reef-associated piscivores and piscivores that use back-reef habitats as a juvenile habitat contributed to the piscivore assemblage in the investigated gradient. Habitat type had a significant effect on the composition of the piscivore assemblage, density, and prey survival. Piscivore density was highest on the reef, mangroves and notches, all of which are habitats with a high structural complexity. On the contrary, seagrass beds showed lowest piscivore density. Tethering experiments showed lowest survival on the reef but also reduced survival on backreef habitats located close to the coral reef. Seagrass beds and mangroves located farther away from the reef into the bay showed highest survival. The present study shows that the concept of reduced predation in back-reef habitats used by juvenile fish does not apply to all habitats, since these habitats can harbour significant piscivore assemblages. However, depending on the spatial setting in the seascape (distance to the reef and presence of other habitat types), some Caribbean seagrass beds show low densities of piscivores and increased survival when compared to other habitats.
Article
Factors affecting recruitment and early survivorship of juvenile coral reef fishes were studied on St Croix, US Virgin Islands. The faunal assemblage studied included diurnally active fishes found in the rubble/sand habitat. The most abundant members were: beaugregory Stegastes leucostictus, foureye butterflyfish Chaetodon capistratus, mahogany snapper Lutjanus mahogoni, surgeonfishes Acanthurus bahianus and A. chirurgus, and French grunt Haemulon flavolineatum. Recruitment of juveniles of almost all species in the rubble/sand fish assemblage occurred more heavily on reefs that were built 20-40 m away from the main reef (into the lagoon) than on those built at the edge of the backreef, probably due to differences in available shelter and differences in encounter rates with predators. Seagrass and algae, which provide shelter to very small juvenile fishes, are absent in a 'halo' zone close to the reef due to the feeding activities of reef-associated grazers (fishes and urchins). Part of the explanation for the observed spatial pattern of fish recruitment is the spatial pattern of the shelter provided by seagrass and algae. Risk of predation for small juvenile fishes was considerably higher close to the reef than it was 20 m away. -from Author
Article
Given a choice between habitats differing only in food availability, prey are known to select the habitat providing the highest energetic return. They do so in a frequency-dependent manner, accounting for the reduction in food availability caused by the presence of other individuals; this results in the well-known 'Ideal Free Distribution', an equilibrium solution to a spatial game. When habitats also differ in predation risk due, for example, to different predator densities, prey also appear able to take this into account. However, in most theory (and most experiments) the predation risk levels in the available habitats are assumed to be fixed. Here we ask what will happen if predators are able to adjust their distribution in response to the habitat choice decisions of their prey, i.e. we model a generalized habitat selection game between predators and prey. We first develop a basic model which captures the essence of the problem, and then expand it to include risk dilution and interference among predators. The model produces several new insights, notably that, in the absence of interference effects, the density of prey in a habitat is determined solely by the inherent 'riskiness' of that habitat (a habitat measure independent of predator density, which might reflect cover or light levels, for example) and is unaffected by habitat productivity (a measure of the food resource available to the prey). When interference exists between predators, prey density is also determined by habitat productivity but to a lesser extent than by riskiness. Consequently, prey may not respond significantly to changes in relative food resource availability among habitats if their predators are also free to choose the habitat which maximizes their expected fitness. We consider briefly the potential applications of game theory to diel vertical migration and other fish predator-prey scenarios.
Article
Abundances and size-frequency distributions of common epibenthic fish and crustaceans were compared among 3 depth zones (1-35, 35-70, 71-95 cm) of the Rhode River, a subestuary of Chesapeake Bay, USA. In the absence of submerged aquatic vegetation (SAV), inter- and intraspecific size segregation occurred by depth from May to October, 1989-1992. Small species (Palaemonetes pugio, Crangon septemspinosa, Fundulus heteroclitus, F. majalis, Rhithropanopeus harrisii, Apeltes quadracus, Gobiosoma bosci) were most abundant at water depths < 70 cm. Furthermore, the proportion of small individuals decreased significantly with depth for 7 of 8 species, with C. septemspinosa being the exception, exhibiting no size change with increasing depth. These distributional patterns were related to depth-dependent predation risk. Large species (Callinectes sapidus, Leiostomus xanthurus, and Micropogonias undulatus), known predators of some of the small species, were often most abundant in deep water (> 70 cm). In field experiments, mortality of tethered P. pugio (30 to 35 mm), small F. heteroclitus (40 to 50 mm), and small C. sapidus (30 to 70 mm) increased significantly with depth. We hypothesize that predation risk was size-dependent, creating the observed intra- and interspecific size differences among depth zones. For C. septemspinosa, burial may modify this size-dependency and create the unusual absence of intraspecific size increase with depth. Historically, P. pugio and Fundulus spp, (and other small species) were not restricted to shallow (< 70 cm) waters and were abundant in deeper SAV beds, which provided a structural refuge from predators. Since the recent demise of SAV in Chesapeake Bay, our results indicate many small species have shifted their distributions and now utilize primarily shallow water as an alternate refuge habitat.
Article
The significance of a sheltering effect of seagrass against predators influencing the distribution patterns of benthic juveniles of the streaked goby Acentrogobius sp. was investigated by field experimentation in and around seagrass habitats at Moroiso and Aburatsubo Bays, Miura Peninsula, Japan. In the former bay, juveniles were always restricted to the seagrass bed, whereas at the latter, they also occurred over the surrounding bare sand substrate. Juveniles never occurred inside predator-exclusion cages over unvegetated sand in Moroiso Bay. Additionally, a tethering experiment resulted in similarly small numbers of juveniles being preyed upon in both the seagrass bed and over bare sand, suggesting that the predation risk for juveniles may not differ between the habitat types and was thus not responsible for their distribution patterns. The availability of symbiotic shrimp burrows, which were scarce in bare sand in Moroiso Bay but abundant in a similar area in Aburatsubo Bay, was also hypothesized as a determinant of distribution pattern. In a manipulative experiment at Aburatsubo Bay, however, juveniles showed no response to alterations in the availability of symbiotic shrimp burrows, indicating that neither the sheltering effect of seagrass against predators nor the availability of symbiotic shrimp burrows was a significant factor in streaked goby juvenile distribution. Food availability may be a determinant, because food abundance patterns were concordant with the juvenile distribution pattern.
Article
Postsettled age 0 Atlantic cod (Gadus morhua) seek refuge from predation in eelgrass (Zostera marina) habitat within shallow, coastal nurseries. Laboratory and field experiments have demonstrated that predation risk on small fish is reduced in habitats of greater structure compared to less complex or barren environs. To determine if predation risk is linked to the areal extent of eelgrass coverage, we tested the hypothesis that predation risk of age 0 cod decreases with increasing eelgrass patch size. Predation on tethered age 0 cod (G. morhua and G. ogac) was quantified in eelgrass patches (1–80 m2) at three sites in northeastern Newfoundland, Canada, during September and October 1999 and 2000. Based on evidence of edge effects in terrestrial landscapes, we also tested the hypothesis that predation is elevated at ecotones separating eelgrass from adjacent barren mud substrate. We examined predation at the edge (i.e., 0 m) and both 5 and 10 m from this edge into and away from eelgrass cover along an 18 m long barren mud-gravel and eelgrass boundary, at two sites. Logistic regression analysis showed that the risk of predation, as measured by the odds ratio, increased with area over a small range of patch sizes (1–35 m2 in 1999). When the study was extended to a wider range of patch sizes (1–80 m2) in 2000, a parabolic relationship emerged, with patches on the order of 25 m2 providing the least safety and the largest patches (80 m2) providing the most safety. Predation on tethered cod was highest at the edge of eelgrass patches, compared with barren and eelgrass locations; predation generally decreased with distance from the eelgrass boundary. Our results are consistent with the hypothesis that predators are drawn to large patches of eelgrass because of increased prey numbers, that predators increase their success by searching edges, and that this results in greatest predation risk to prey in isolated patches of intermediate size.