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Ecosystem Function and Services of Aquatic Predators in the Anthropocene
Abstract
Arguments for the need to conserve aquatic predator (AP) populations often focus on the ecological and socioeconomic roles they play. Here, we summarize the diverse ecosystem functions and services connected to APs, including regulating food webs, cycling nutrients, engineering habitats, transmitting diseases/parasites, mediating ecological invasions, affecting climate, supporting fisheries, generating tourism, and providing bioinspiration. In some cases, human-driven declines and increases in AP populations have altered these ecosystem functions and services. We present a social ecological framework for supporting adaptive management decisions involving APs in response to social and environmental change. We also identify outstanding questions to guide future research on the ecological functions and ecosystem services of APs in a changing world.
... Marine ecosystems provide a multitude of goods and services for humans, including food, climate control, and cultural services such as tourism and recreation (Millennium Ecosystem Assessment, 2005;Hammerschlag et al., 2019;Tavares et al., 2019;Villéger et al., 2017). Among these cultural services, aesthetic values are instrumental, as they contribute to inspiration, cultural identity, spiritual connection, and opportunities for tourism and recreation. ...
... Aesthetic value plays a crucial role in shaping public perception and appreciation of natural environments, ultimately influencing conservation efforts. In marine ecosystems, these aesthetical aspects benefit human health and well-being by providing opportunities for outdoor activities and the enjoyment of unique scenic beauties (Hammerschlag et al., 2019;Spalding et al., 2017). Activities associated with reef ecosystems, for example, contribute significantly to economies, generating over US$144 million per year in high-income countries (Brander and Beukering, 2013). ...
... This is the case of the Blacktip Shark (Carcharhinus limbatus), a threatened predator that has a key role in prey control and nutrient transport (Heithaus et al., 2008), and of Greenback Parrotfish (Scarus trispinosus), an endemic Brazilian reef fish (Bonaldo, 2014;Francini-Filho and Moura, 2008). The loss of these species might not only harm reef functioning from altering nutrient transport and food web control (Heithaus et al., 2008;Tavares et al., 2019;Waechter et al., 2022), but also compromise the aesthetic value of reefs, a cultural ecosystem service that is essential to human well-being (Elliff and Kikuchi, 2017;Hammerschlag et al., 2019;Tavares et al., 2019). ...
The marine wildlife and seascape components of reef environments are part of peoples' senses and perceptions of nature and and ecosystem services. While people worldwide perceive and value reef components differently, such aesthetics evaluations often overlook marginal reefs, limiting our comprehensive understanding of their cultural significance. We interviewed 320 different users (e.g., recreational divers, researchers, recreational and commercial fishers, and beach tourists) using an online questionnaire with embedded pictures of 82 fish species and 65 seascapes. To assess people's perception about reefs, we related the aesthetic value (i.e., the preference rate) of each picture to body size, body shape and colour for bony and cartilaginous fish, and to the presence of predators, fish schools, benthic organisms, reef patches and area for the underwater and out-of-the-water seascape. We then created an index composed by site-level species aesthetic values, species relative abundances, under and out-of-water aesthetics and measuredthe overall aesthetic value of nine reef sites along the Brazilian province. The different users attributed similar aesthetic values to fish species, under and out-of-the-water components, yet preferences differed among them. Divers preferred large parrotfishes, while tourists preferred coloured fish. The most valued fish traits were the body shape of manta rays and colorful bony species. Out-of-the-water seascapes with emerging reef patches had the highest aesthetic values. When combining the different aesthetic value components in the index, we found that marginal biogenic reefs in Northeastern Brazil had the highest aesthetic value among the evaluated sites. These reefs hold immense value for national tourism, significantly contributing to the revenue of these states. Also, they harbour threatened species, which possess both high aesthetic value and great ecological importance. Therefore, incorporating aesthetic value in conservation initiatives has the potential to improve our ability to maintain and develop cultural reef services.
... Fish are an integral part of marine ecosystems, essential for the carbon functions of pelagic and blue carbon ecosystems, for the health of coastal ecosystems, and for ocean productivity, which in turn sustains fisheries [8][9][10][11][12][13]. Below we outline the key roles of fish for carbon storage, sequestration, and ocean productivity, including fertilization, habitat regulation, and climate change adaptation. ...
... Fish transform habitats as they move through and between them, influencing plant and animal life. In the open ocean, they provide structuring biomass and define habitats [10], while population control of grazers and digging animals by predatory fish enables biodiverse vegetated habitats, and the animals that live within them, to persist and thrive [11]. As such, removal of predatory fish can degrade vegetated coastal habitats and, in extreme cases, turn them into barren seascapes [12]. ...
... Likewise, fish targeted as a commodity have been excluded from the new UN instrument for the conservation and sustainable use of marine biodiversity in areas beyond national jurisdiction recently agreed and awaiting ratification [32]. At best, such policies may fail to reach their full potential, including achieving co-benefits and synergies that management of fish could achieve across such policies; at worst, neglecting the links between fish and ecosystem services may damage the ability of fish and their habitats to deliver essential functions [11,26,33] (Fig. 1). ...
Fish are essential components of the ocean carbon sink. Therefore, the carbon functions of fish should be incorporated into marine policies and management of carbon stocks in coastal and marine ecosystems, as well as sustainable fisheries. However, while there are ecosystem-based approaches to fisheries management that consider the impacts of fisheries on fish populations, habitats and environmental functioning, the focus remains on achieving maximum sustainable yield from the fish resource. Similarly, current approaches to blue carbon management focus on the conservation and restoration of coastal wetlands for the carbon they contain, mostly ignoring fish. We challenge these prevailing views and strategies and outline the different roles of fish in marine ecosystems and the risks posed by current approaches to blue carbon management and fisheries. We aim to contribute to a change in perspective and strengthen new approaches to ocean-climate regulation. To do so, we draw on the latest literature to show how fish are critical for carbon storage, sequestration (i.e., stored for 100 years or more), nutrient transfer, habitats and ecosystem function - all factors that are crucial for ocean productivity and ultimately sustain fisheries. On this basis, we argue that fish populations need to be considered as more than just a commodity to avoid carbon mismanagement, habitat loss, ecosystem collapse and food insecurity. We conclude by identifying ways in which science and policy can better integrate fish carbon functions into blue carbon management and fisheries management.
... A range of theoretical, observational, and experimental approaches have highlighted the importance of predator-prey interactions to ecosystem functioning [7]. Predators drive ecosystem processes by directly killing their prey, as reduced prey densities reshape trophic interactions, nutrient cycling, ecosystem engineering, and disease transmission, for example [8,9]. Predators also influence ecosystems nonlethally through the predation risk they pose [8]. ...
... Trends in Ecology & Evolution, Month 2023, Vol. xx, No. xx9 . ...
Predator-prey ecology and the study of animal cognition and culture have emerged as independent disciplines. Research combining these disciplines suggests that both animal cognition and culture can shape the outcomes of predator-prey interactions and their influence on ecosystems. We review the growing body of work that weaves animal cognition or culture into predator-prey ecology, and argue that both cognition and culture are significant but poorly understood mechanisms mediating how predators structure ecosystems. We present a framework exploring how previous experiences with the predation process creates feedback loops that alter the predation sequence. Cognitive and cultural predator-prey ecology offers ecologists new lenses through which to understand species interactions, their ecological consequences, and novel methods to conserve wildlife in a changing world.
... Freshwater megafauna species (i.e., animals that can reach a body mass ≥ 30 kg) include, for example, river dolphins, hippos, crocodilians, large turtles, sturgeons, and giant salamanders. They often have important ecological roles as ecosystem engineers or keystone species (Hammerschlag et al., 2019;Moore, 2006). For example, the hippopotamus (Hippopotamus amphibius) alters floodplain habitats and river morphology, and transfers large amounts of nutrients from grasslands to freshwater ecosystems, influencing the diversity of invertebrate and fish species in the ecosystems it occupies (Stears et al., 2018;Subalusky et al., 2015). ...
... For example, the hippopotamus (Hippopotamus amphibius) alters floodplain habitats and river morphology, and transfers large amounts of nutrients from grasslands to freshwater ecosystems, influencing the diversity of invertebrate and fish species in the ecosystems it occupies (Stears et al., 2018;Subalusky et al., 2015). Freshwater megafauna including river dolphins and piscivore megafish are top predators and have a profound influence on local trophic dynamics (Hammerschlag et al., 2019), while megafish species are often highly mobile and facilitate dispersal of smaller species (Correa et al., 2015;Lopes-Lima et al., 2017). Furthermore, many freshwater megafauna species are considered to be charismatic, and as such may play important roles in future conservation initiatives (e.g., as flagship umbrella species; He, Jähnig, et al., 2021a;Kalinkat et al., 2017). ...
1. Freshwater megafauna species (i.e., animals that can reach a body mass ≥30 kg, including fish, reptiles, mammals, and amphibians) play important roles in freshwater systems (e.g., by influencing habitat structure, trophic dynamics, or the dispersal of smaller species). As they tend to be large and charismatic, they may also function as flagship umbrella species in future freshwater conservation initiatives. Despite this, as a group they are highly threatened, and our knowledge of the nature of these threats is limited. In this study, we aim to improve our understanding of the impacts of alien species on native freshwater megafauna.
2. We undertook the first global assessment of the impacts of alien species on native freshwater megafauna using the Environmental Impact Classification for Alien Taxa (EICAT) framework. We conducted a literature review to identify published and grey literature on impacts, which we quantified and categorised by their severity and type, following the EICAT guidelines.
3. Negative impacts on native freshwater megafauna were caused by 61 alien species from a diverse range of taxonomic groups, including both freshwater and terrestrial alien species, and both vertebrates and invertebrates. They adversely affected 44 of 216 native freshwater megafauna species, including amphibians, fish, mammals, and reptiles. The Great Lakes Basin had the highest number of affected megafauna species (six of the 14 freshwater megafauna species it supports, mainly fish). Impacts occurred through a broad range of mechanisms (10 of the 12 identified mechanisms under EICAT); predation and competition were the most frequently reported mechanisms. Some impacts were relatively minor, adversely affecting the performance of individuals of native freshwater megafauna species. However, some reported impacts did cause declining populations of native freshwater megafauna species, and one impact contributed to the local extinction of the ship sturgeon ( Acipenser nudiventris ) in the Aral Sea. The vulnerability of native freshwater megafauna species to different types of impact varies during different life‐cycle stages (egg, juvenile, and adult).
4. Our understanding of impacts posed by alien species on native freshwater megafauna is limited because data are unavailable for many regions, particularly the Global South, including hotspots for freshwater megafauna diversity such as the Amazon, Congo, Mekong, and Ganges‐Brahmaputra basins. Freshwater megafauna species are often subject to multiple threats, which makes it difficult to determine the significance of alien species impacts relative to other threats such as habitat degradation and overexploitation. In addition, short‐term studies are likely to be masking the severity of the impacts identified. We call for more long‐term studies that attempt to identify population‐level impacts, and for studies that identify impacts in data‐deficient regions.
5. The EICAT assessments undertaken for this study will be reviewed by the EICAT Authority and subsequently incorporated into the IUCN EICAT database. They may be used to guide future research and conservation actions.
... some whale and sea turtle species, [12,13]), many sharks continue to experience high levels of overexploitation resulting in population declines [14]. Given that sharks display a variety of functional roles, including top-down control of food webs and connecting trophic levels through their foraging behaviour [15], their ongoing removal is likely to have long-term effects on the structure and function of marine ecosystems [16]. This therefore remains a critical area of research. ...
... C 3 versus C 4 photosynthetic versus chemoautotrophic production). Nitrogen isotopes complement carbon isotopes because of predictable, stepwise 15 N fractionation between predator and prey that reflects a consumer's trophic position within food webs [17]. When combined with isotopic end members (prey species that represent a single energetic resource channel, [18]), an animal's or population's reliance on multiple energetic pathways can be discerned, provided they are isotopically distinct [17,19]. ...
Understanding the factors shaping patterns of ecological resilience is critical for mitigating the loss of global biodiversity. Throughout aquatic environments, highly mobile predators are thought to serve as important vectors of energy between ecosystems thereby promoting stability and resilience. However, the role these predators play in connecting food webs and promoting energy flow remains poorly understood in most contexts. Using carbon and nitrogen isotopes, we quantified the use of several prey resource pools (small oceanic forage, large oceanic prey, coral reef, and seagrass) by 17 species of elasmobranch fishes (n = 351 individuals) in The Bahamas to determine their functional diversity and roles as ecosystem links. We observed remarkable functional diversity across species and identified four major groups responsible for connecting discrete regions of the seascape. Elasmobranchs were responsible for promoting energetic connectivity between neritic, oceanic, and deep-sea ecosystems. Our findings illustrate how mobile predators promote ecosystem connectivity, underscoring their functional significance and role in supporting ecological resilience. More broadly, strong predator conservation efforts in developing island nations, such as The Bahamas, are likely to yield ecological benefits that enhance the resilience of marine ecosystems to combat imminent threats such as habitat degradation and climate change.
... Both top-predatory sharks and meso-predatory rays have been identified as having keystone roles on coral reef and intertidal habitats, respectively Power et al., 1996;Ruiz & Wolff, 2011). According to recent estimates, 31% of all shark species and 36% of all ray species are currently threatened with extinction (Dulvy et al., 2021), jeopardizing their key-role in the functioning of marine ecosystems (Atwood et al., 2015;Ferretti et al., 2010;Hammerschlag et al., 2019). ...
... Galeocerdo cuvier, Carcharhinidae) and bull shark (Carcharhinus leucas, Carcharhinidae), occupy top-predatory niches and can control the abundance of lower trophic species(Atwood et al., 2015;Hammerschlag et al., 2019;Heithaus, 2001;Navia et al., 2016). In coastal areas, large sharks are often defined as generalist predators (e.g.Hussey et al., 2015;Nowicki et al., 2019), with a diet consisting of large teleost fishes, rays, smaller shark species and sea turtles (Figure 3b). ...
Intertidal habitats (i.e. marine habitats that are (partially) exposed during low tide) have traditionally been studied from a shorebird‐centred perspective. We show that these habitats are accessible and important to marine predators such as elasmobranchs (i.e. sharks and rays). Our synthesis shows that at least 43 shark and 45 ray species, of which 54.5% are currently threatened, use intertidal habitats. Elasmobranchs use intertidal habitats mostly for feeding and as refugia, but also for parturition and thermoregulation. However, the motivation of intertidal habitat use remains unclear due to limitations to observe elasmobranch behaviour in these dynamic habitats. We argue that elasmobranch predators can play an important role in intertidal food webs by feeding on shared resources during high tide (i.e. ‘high‐tide predators’), which are accessible and also consumed by terrestrial or avian predators during low tide (i.e. ‘low‐tide predators’). In addition, elasmobranchs are able to change the bio‐geomorphology of intertidal habitats by increasing habitat heterogeneity due to feeding activities and may also alter resource availability for other consumers. We discuss how the ecological role of elasmobranchs in intertidal habitats is being affected by the continued overexploitation of these species, and conversely, how the global loss of intertidal areas poses an additional threat to an already vulnerable taxonomic group. We conclude that studies on intertidal ecology should include both low‐tide (e.g. shorebirds) and high‐tide (e.g. elasmobranchs) predatory guilds and their ecological interactions. The global loss of elasmobranch predatory species and intertidal habitat provides additional compelling arguments for the conservation of these areas.
... Marine megafauna are an important component of marine ecosystems providing a range of cultural, regulating and provisioning ecosystem services to humans (Dunn et al., 2019;Hammerschlag et al., 2019). They transport energy, nutrients, and other materials vertically and horizontally through the oceans (Roman et al., 2014;Kiszka et al., 2015;Estes et al., 2016;Hammerschlag et al., 2019), and through their large size and often high mobility, influence other species through consumption and risk avoidance behaviour. ...
... Marine megafauna are an important component of marine ecosystems providing a range of cultural, regulating and provisioning ecosystem services to humans (Dunn et al., 2019;Hammerschlag et al., 2019). They transport energy, nutrients, and other materials vertically and horizontally through the oceans (Roman et al., 2014;Kiszka et al., 2015;Estes et al., 2016;Hammerschlag et al., 2019), and through their large size and often high mobility, influence other species through consumption and risk avoidance behaviour. Marine megafauna also include important focal species (Zacharias and Roff, 2001) in marine conservation and management, given their role as sentinel species or ecological indicators (Hazen et al., 2019). ...
This Research Topic covers a broad taxonomic representation, spanning seabirds, cetaceans, sea turtles, pinnipeds, elasmobranchs, teleosts, a sirenian, the polar bear, and a large crustacean, the red king crab (Paralithodes camtschaticus). Articles submitted address how biologging is being used to understand the movement behaviour and distribution of marine megafauna, and how this information can play a key role to prioritise conservation goals. The resulting 34 articles illustrate how biologging is informing conservation of marine megafauna, and in light of these studies, we discuss challenges, methodological implications and future directions for biologging in conservation.
... Fishing has had a profound effect on the biomass of carnivores in most marine ecosystems worldwide (McCauley et al., 2015). As a result, the functional role of carnivores in present-day fishery-driven ecosystems has been largely suppressed (Estes et al., 2011;Roff et al., 2016;Hammerschlag et al., 2019). Remaining predatory interactions are greatly reduced compared to those occurring prior to industrial fishing (Cheng et al., 2019;Eger and Baum, 2020), and the structure of marine food webs has been profoundly altered (Frank et al., 2005;Myers et al., 2007;Heithaus et al., 2012), a change that often started well before the monitoring of fishing impact (Saporiti et al., 2014;Bas et al., 2019;Ólafsdóttir et al., 2021). ...
... The restoration of the size structure of fish populations is one of the expected benefits of MPAs (Baskett and Barnett, 2015), because fish live longer, grow larger, and attain higher densities and biomass within well-managed MPAs (Halpern, 2003;Hilborn et al., 2004;Baskett and Barnett, 2015). This can in turn result in increased mortality rates for prey, compared to areas open to fishing (Cheng et al., 2019;Eger and Baum, 2020), and may elicit risk avoidance responses, thus modifying the habitat use patterns of herbivores and mesopredators (Bond et al., 2019;Hammerschlag et al., 2019). Those changes may trigger trophic cascades, and assessing their strength has been the focus of most of the previous research on the so-called "reserve effect" (Sala et al., 2012;Cheng et al., 2019;Eger and Baum, 2020). ...
Here, we assess whether fishery exploitation affects the trophic structure of carnivorous fish. We censused fish and analysed the stable isotope ratios of C and N of species targeted by fishermen in areas open to fishing and marine protected areas (MPAs) in the Mediterranean Sea and the north-eastern Atlantic Ocean. Results demonstrated a major impact of fishing on the biomass and size structure of nektobenthic carnivorous fish. However, those changes did not modify the diversity of the trophic resources used by the assemblage, the pattern of resource partitioning between species, or the degree of trophic redundancy. These results add to recent evidence suggesting that MPAs implemented in fished seascapes may fail to restore the original structure of the food webs that once existed in pre-fished ecosystems because regional decimation and extinction of highly mobile predators prevent recovering the original diversity of predators at local scales, even in no-take areas. If so, more strict local fishing regulations are unlikely to restore the original diversity of high trophic level carnivores and restoration goals should be reframed in terms of an objective that is less unrealistic than restoring the pre-fished condition while still recovering aspects of the historical trophic structure.
... Marine fisheries reduce the resilience of marine ecosystems through greenhouse gas emissions, lost gear and marine litter, and changes in food web structure that disrupt marine ecosystems. For instance, overfishing of cod in the 1990s caused changes in marine ecosystems that weakened the biological pump in the North Atlantic (Hammerschlag et al., 2019), further reducing ocean carbon sink functions; fishing activities on Caribbean reefs have led to a reduction in fish-mediated trophic capacity, further leading to a reduction in primary productivity (Allgeier et al., 2016); and overfishing herbivorous fish in Jamaica combined with climate change has led to a shift from highly productive coral-dominated habitats to lower productive algae-dominated habitats in some areas (Levin and Möllmann, 2015). ...
... However, as fishing activities and phytoplankton growth meet a certain threshold, complex trophic cascade effects, as well as eutrophication and competition interactions come into play (Van Denderen et al., 2018). Weakening of the biological pump through fishing (Hammerschlag et al., 2019) can reduce growth rates and even show a decreasing trend in marine NPP. A study in the Bohai Sea of China noted that the trophic cascade effect caused by fishing led to a shift in the Bohai Sea ecosystem, with the loss of large fish causing an increase in fish and jellyfish. ...
Human activities and climate change have profound effects on marine ecosystems, leading to changes in ecosystem functionality and even reduced resilience. Hence, a systematic assessment of the marine ecosystem resilience and the drivers of resilience is needed. This study provides an approach to help measure the resilience of reduction marine ecosystems by calculating early warning signs of marine net primary productivity, while introducing fishing activities and environmental data in the study area to evaluate the factors affecting marine ecosystem resilience. The results showed that in 36.29% of the Chinese exclusive economic zone, resilience was likely to be significantly decreased. There was a non-linear relationship between fishing activities and indicators of resilience reduction, with pixels with high-intensity fishing activities being more susceptible to resilience reduction. Fishing regulations are urgently needed in areas where marine ecosystem resilience may be reducing. Effective management and protection of marine ecosystems require assessment of the spatial overlap between marine ecosystems states and human activities. This study provides a scientific basis for sustainable management of social-ecological systems by comparing high-precision fishing data to marine environmental data, thereby analysing marine ecosystem resilience through the use of early warning indicators.
... The relatively low variance was predicted in the more coastal parts of the study area within each season, while higher uncertainty was instead revealed in the southernmost offshore area. This study highlighted the persistent presence of the common bottlenose dolphin in the investigated area both winter and summer, with a coherent distribution Introduction Multiple roles are recognized for apex predators in the marine environment, fulfilling key ecological, economic, and cultural functions (Hammerschlag et al., 2019). Apex predators are indeed affected by bottom−up processes and can influence food webs via consumptive effects on prey (top−down effects) (Heithaus et al., 2008;Steneck, 2012;Kiszka et al., 2022). ...
... Apex predators are indeed affected by bottom−up processes and can influence food webs via consumptive effects on prey (top−down effects) (Heithaus et al., 2008;Steneck, 2012;Kiszka et al., 2022). Hence, assessing their distribution is pivotal to understanding community interactions and defining management goals to be implemented (Hammerschlag et al., 2019). However, several challenges arise in both distribution estimates and predictions (Pace et al., 2019;Martino et al., 2021), generated by high movement ability and large home-ranges covered by these species, spatio-temporal knowledge gaps and the increasing use of different data sources to model their distribution (Watson et al., 2019). ...
Assessing the distribution of marine apex-predators is pivotal to understanding community interactions and defining management goals. However, several challenges arise in both estimates and predictions considering the distinctive and mutable biological/ecological requirements of these species and the influence of human activities. Thus, efforts to study apex-predators' spatial distribution patterns must deal with inherent uncertainty. Relying on different data sources (research programs and social media reports), physiographic and environmental covariates (depth, slope, surface temperature and chlorophyll-a), and specific source-related detection functions, this study selected a Spatial Log-Gaussian Cox Process to model the distribution patterns of an opportunistic apex-predator, the common bottlenose dolphin (Tursiops truncatus), over 14 years (2008−2021) in the Mediterranean Sea (Italy) using a total of 955 encounters. Both depth and slope showed a significant (95% significance) reduction effect in the encounters when deeper and steeper, respectively. Temperature (parabolic) shows a positive effect (90% significance), while chlorophyll-a values did not seem to have a significant effect on encounter intensities within each season. The estimated posterior mean and the coefficient of variation surfaces for the intensity by season showed higher intensity in summer near the Tiber River estuary than other regions. Almost homogeneous predictions were observed in winter, with marginal greater intensities where lower temperatures and higher chlorophyll-a concentration were observed. The relatively low variance was predicted in the more coastal parts of the study area within each season, while higher uncertainty was instead revealed in the southernmost offshore area. This study highlighted the persistent presence of the common bottlenose dolphin in the investigated area both winter and summer, with a coherent distribution Frontiers in Marine Science within each season, and rare transient occurrences in deeper waters (where uncertainty increases). Thanks to its versatile characteristics, the species seems to well adapt to different seasonal conditions and maintain its distributional range.
... The acquisition of these information is even more urgent for those species whose ecological role is not locally assessed, such as the case of the monk seal. This measure would enable the implementation of efficient conservation measures, deepening the local food web dynamics, and supporting the processes needed to preserve ecosystem services [54]. ...
The Mediterranean population of Mediterranean monk seal (Monachus monachus) is reported as "Critically endangered" by IUCN Red List and its spatial distribution seems to be fragmented in colonies, mainly found around the Ionian and Aegean islands. Monk seals are proved to be highly affected by human pressure such as boat traffic and fishery. Previous studies highlighted the occurrence of net depredation and interactions with artisanal small-scale fisheries. Accordingly, a source of concern is the little quantitative information on various aspects of the Greek small-scale fisheries. Thus, the landings composition of the Marathokampos Bay’s fleet between 2009 and 2011 has been analysed. Then, a dietary overlap index and multivariate analysis were used to analyse the overlap between resources exploited by fisheries and those consumed by monk seals.Results show that for a total of 565 days at sea, 57 % of those fishing days were performed with Trammel nets, 11.3 % with 8-9 mm Gillnets, 18.4 % with Longline, 12.6 % with Boat seine, 0.5 % with Kalami and 0.2 % for the Purse seine. The total landing biomass of 14.3 tons was composed of 68 species. Monk seal’s diets considered in the analysis showed the highest resource overlap with the Boat seines and the lowest with the Purse seines. Results of the cluster analysis showed that the similarity at 0.2 similarity level revealed a big group composed only by fishing métiers (Longline, Trammel net, Purse seine and total fleet). This study suggests that filling this gap of knowledge could support the implementation of conservation actions. Furthermore, some preliminary results regarding the characteristic of the Marathokampos Bay’s fishing fleet are provided, and the need to gather further data able to better quantify the impacts of both monk seals and fishery on the resources is underlined.
... The structure and regulation of such communities is partially driven by some key organisms such as high-rank predators, which trigger direct and indirect top-down effects on organisms of lower trophic rank (Hammerschlag et al., 2019;Thorp, 1986). However, freshwater predators exhibit various foraging characteristics (Cooper et al., 1985), which may influence the way they shape aquatic communities (Wellborn et al., 1996). ...
Freshwater vertebrate predators can exert trophic control over aquatic and littoral communities. Among these predators, post‐metamorphic anurans exhibit a biphasic trophic spectrum by foraging in both terrestrial and aquatic habitats. Many studies have described their diet through the classical taxonomic classification of prey. However, these singular diet habits imply a complex, time‐dependent, realised trophic niche in which predation pressure occurs over many consumers that fill diverse functional roles throughout the aquatic and terrestrial interface of ponds. Among anurans, marsh frogs ( Pelophylax ridibundus ) have been introduced outside their range in many countries and are now invading nationwide areas, particularly in western Europe. Focusing on their foraging specificities will therefore further the understanding of the trophic role of these alien taxa in pond environments that are highly colonised.
We collected stomach contents from 761 marsh frogs from introduced populations in 19 ponds in southern France once a month over 4 months of their active period in the spring. The populations of marsh frogs were studied in a geographic area that was devoid of native water frogs and their origin tracks back as far as south‐eastern Europe (i.e., more than 1,000 km from the studied sites, as evidenced previously by genetic analyses).
Marsh frogs exhibited generalist and opportunistic feeding strategies. The trophic niche was strongly asymmetrical and broader in the terrestrial environment than in the aquatic environment. However, predation occurred in communities of large freshwater macroinvertebrates and amphibians. Whereas the composition of the terrestrial diet exhibited strong seasonal variations, predation pressure was continuously exerted on the same aquatic organisms over time. Primary consumers and consumers at higher trophic levels frequenting aquatic benthic, vegetated, pelagic, and surface microhabitats were preyed upon, underlying the multidimensional extent of the predation spectrum.
The diversified feeding strategies of alien marsh frogs highlight the extent of potential ecological control by predation on pond communities. Because of their wide trophic niche, they exert predation pressure on most pond organisms, triggering possible top‐down control of the overall aquatic communities.
Our results show that the integration of the functional traits and microhabitats of consumed prey may aid in a better understanding of how predation by anurans may target specific components of pond communities. More particularly, this study raises concerns about the predatory role of introduced anurans in the context of biological invasions.
... Para cada una de las visitas realizadas por isla, se estimó la riqueza específica, la abundancia de individuos y la diversidad alfa mediante los índices de Shannon (basado en la equidad), de Margalef (basado en la riqueza específica) y de Simpson (basado en la dominancia;Moreno, 2001), utilizando el programa Past (Versión 3.16;Hammer et al., 2001).Estas islas sirven de zonas de alimentación, anidación, reposo y refugio de diversas especies de aves(Vilca-Taco et al., 2021) que cumplen a su vez, un rol importante en el ciclo de nutrientes y el control de plagas a través de las cascadas tróficas, dispersan semillas y contribuyen al valor científico y económico(Tàbara, 2006;Latta, 2012;Hammerschlag et al., 2019). Además, involuntariamente en sus patas o plumas transportan algas, crustáceos, huevos y estructuras reproductivas de diferentes organismos(Martínez, 1993).Para conocer la composición de las comunidades de aves presentes, se recorrieron a pie las seis islas del PNSAV, sumando seis desembarques en cada isla, de abril de 2021 a abril de 2022. ...
Antecedentes. Estudios previos en el Parque Nacional Sistema Arrecifal Veracruzano (PNSAV) han reportado que 48 % de las aves son migratorias de invierno y 52 % son residentes. Sin embargo, no se ha analizado previamente la estructura de las comunidades de aves de sus islas. Objetivos. Analizar la estructura de las comunidades de aves de las islas Sacrificios, Verde, Salmedina, Polo, de Enmedio y Santiaguillo. Métodos. Se realizaron seis censos de aves en cada isla de abril de 2021 a abril de 2022. Con los datos obtenidos se determinó la riqueza específica, la abundancia y la diversidad alfa mediante los índices de Shannon, Mar-galef y Simpson. Adicionalmente, luego de clasificar a las aves en marinas, acuáticas o costeras, rapaces y terrestres, se calculó el número de especies y la suma de máximos de estos grupos para cada isla. Con toda la información se analizó la conformación de las comunidades de aves para cada isla y sus variaciones en cuanto a la diversidad a lo largo del año de estudio. Resultados. La isla de Enmedio presentó los mayores valores de diversidad (abril y octubre 2021). Octubre 2021 fue el mes de mayor diversidad para Sacrificios, Verde y Santiaguillo. Salmedina y Polo presentaron mayor diversidad en julio 2021 y en enero 2022, en estas dos islas solo se observaron aves marinas y costeras, en las demás islas predominaron especies terrestres. En Polo, las aves marinas presentaron una elevada abundancia a pesar del reducido tamaño de la isla. Conclusiones. Parece existir una gran presión antrópica sobre los hábitats de reposo y reproducción de las aves marinas. Existe poca información de las islas, generarla es relevante para un manejo integral del PNSAV.
... Sharks play a key ecological role within and between marine ecosystems; yet, they are under increasing pressure from anthropogenic impacts, particularly fishing (Hammerschlag et al. 2019, Dulvy et al. 2021, Pacoureau et al. 2021). In addition, many shark species are especially vulnerable to population declines due to their conservative life history characteristics, complicating efforts to improve conservation outcomes for these species (Frisk et al. 2005, Pardo et al. 2016, Pacoureau et al. 2021. ...
Migratory sharks play a key ecological role through movements within and among marine ecosystems, yet many populations are declining. Addressing the decline is especially challenging for wide-ranging species, as they may undertake movements between countries with disparate conservation priorities. To investigate the transboundary migrations of threatened sharks between neighbouring South Africa and Mozambique, we tracked 4 commonly occurring carcharhinid species (bull, blacktip, tiger and grey reef sharks). A total of 102 individuals were fitted with long-life acoustic transmitters and monitored for 4 yr (2018-2022) on an acoustic receiver network of 350 receivers. During this period, 63% of tagged bull sharks (n = 19), 87% of blacktips (n = 13), 94% of tiger (n = 16) and 25% of grey reef sharks (n = 3) undertook transboundary movements. The frequency of mean transboundary movements per year ranged between 1.3 ± 1.5 (SD) for grey reef sharks and 81 ± 35.6 for tiger sharks. Blacktip, bull and tiger sharks all undertook long-distance transboundary migrations ranging from 980 to 2256 km. These data confirm high connectivity between neighbouring countries by threatened sharks undertaking persistent transboundary movements. This study emphasizes the need for collaborative transboundary cooperation between the 2 countries and the alignment of regional management plans and interventions to address declining shark populations in this region of the Western Indian Ocean.
... Globally, coastal ecosystems are threatened by anthropogenic stressors, such as pollution, coastal development and overexploitation, causing a collapse in richness and diversity of associated species (Worm et al., 2006, Cardinale et al., 2012, He and Silliman, 2019. The loss of species may hamper the functioning and health of ecosystems, and can lead to a loss of ecosystem services (Worm et al., 2006, Palumbi et al., 2009, Hammerschlag et al., 2019. Therefore, monitoring the status of biodiversity and individual species within ecosystems is essential to ensure future ecosystem health and the preservation of ecosystem services (Cardinale et al., 2012, Cooley et al., 2022. ...
Marine biodiversity loss is accelerating, leading to the elevated extinction risks of many species, including sharks and rays. To mitigate these losses, information on their distribution and community composition is needed. Monitoring these (often) mobile species is challenging, especially in remote, highly dynamic and turbid coastal areas. Here, we use an environmental DNA (eDNA) approach to: (1) establish the presence and distribution of elasmobranch species, (2) compare this to a conventional fisheries-dependent approach, and (3) determine the influence of season, area-based protection and habitat on elasmobranch community composition in the highly dynamic Bijagós Archipelago in Guinea-Bissau (West Africa). We collected 127 seawater samples and detected elasmobranch DNA in 58 (45.7%) of these samples, confirming the presence of 13 different elasmobranch species (2 sharks, 11 rays), including seven threatened species. Eight of the species detected by the eDNA-approach were also recorded in a fisheries observer program, which recorded another eight species not detected by the eDNA approach. The most commonly occurring species, based on the number of eDNA sampling locations were the pearl whipray (Fontitrygon margaritella), smalltooth stingray (Hypanus rudis), scalloped hammerhead shark (Sphyrna lewini), and the blackchin guitarfish (Glaucostegus cemiculus). Species composition and richness differed significantly before (January-March) and after the rainy season (November-December). Furthermore, we showed that community composition and species richness did not differ between protected (MPA) and non-protected areas of the archipelago. Thus, we confirm that eDNA approaches are a valuable and non-invasive tool to study threatened shark and ray species in data-deficient and dynamic coastal areas, especially when combined with conventional monitoring methods such as fisheries-dependent information.
... Vegetated coastal wetlands, in particular, provide intermittent but important foraging and/or breeding habitats for at least 174 species of megafauna globally, accounting for over 13% of all extant marine megafauna (12). Megafauna, in turn, play important and unique roles in shaping coastal ecosystems and providing valuable ecosystem services where they reach naturally occurring densities (13)(14)(15). For example, high abundance of large predatory sharks and tunas can act as a stabilizing force in coastal fish communities through topdown control (16), and whale watching is estimated to generate more than $2.5 billion in yearly tourism revenue worldwide (17), providing substantial economic benefits to coastal communities. ...
To fulfill sustainable development goals, many countries are expanding efforts to conserve ecologically and societally critical coastal ecosystems. Although megafauna profoundly affect the functioning of ecosystems, they are neglected as a key component in the conservation scheme for coastal ecosystems in many geographic contexts. We reveal a rich diversity of extant megafauna associated with all major types of coastal ecosystems in China, including 218 species of mammals, birds, reptiles, cephalopods, and fish across terrestrial and marine environments. However, 44% of these species are globally threatened, and 78% have not yet been assessed in China for extinction risk. More worrisome, 73% of these megafauna have not been designated as nationally protected species, and <10% of their most important habitats are protected. Filling this wide "megafauna gap" in China and globally would be a leading step as humanity strives to thrive with coastal ecosystems.
... Our study reveals that the species facing the greatest risk of extinction are frequently functionally distinct species (D10 species), often contributing to unique niches and functions in the ecosystem (Hammerschlag et al., 2019). We showed that 38% of the species threatened with extinction according to the IUCN Red . ...
Aim
The criteria used to define the International Union for Conservation of Nature (IUCN) Red List categories are essentially based on demographic parameters at the species level, but they do not integrate species' traits or their roles in ecosystems. Consequently, current IUCN‐based protection measures may not be sufficient to conserve ecosystem functioning and services. Some species may have a singular combination of traits associated with unique functions. Such functionally distinct species are increasingly recognized as a key facet of biodiversity since they are, by definition, functionally irreplaceable. The aim of this study is to investigate whether threatened species are also functionally rare and to identify which traits determine extinction risk.
Location
European continental shelf seas.
Time period
1984–2020.
Major taxa studied
Marine fish.
Methods
Using newly compiled trait information of 425 marine fish species in European waters, and more than 30 years of scientific bottom trawl surveys, we estimated the functional distinctiveness, restrictedness and scarcity of each species and cross‐referenced it with their IUCN conservation status.
Results
In European continental shelf seas, 38% of the species threatened with extinction (9 out of 24 species) were identified as the most functionally distinct. By mapping extinction risk in the multidimensional species trait space, we showed that species with the greatest risk of extinction are long‐lived and of high trophic level. We also identified that the most functionally distinct species are sparsely distributed (4% of the total area on average) and have scarce abundances (<1% of the relative mean abundance of common species).
Main Conclusions
Because a substantial proportion of threatened species are functionally distinct and thus may play unique roles in ecosystem functioning, we stress that species traits—especially functional rarity—should become an indispensable step in the development of conservation management plans.
... Freshwater ecosystems have high conservation significance for the crucial ecosystem functions and services they contribute, including providing key habitat for flagship aquatic species such as dolphins, gharials, and otters (Hammerschlag et al., 2019;Desforges et al., 2022;Acharya et al., 2022). Freshwater ecosystems occupy < 1% of the earth's surface, yet they support 12% of all known ...
... Particularly for marine mammals, many species are experiencing ongoing population growth and range expansion under legal protection and related policies (Magera et al. 2013;Valdivia, Wolf, and Suckling 2019). This ongoing recovery not only leads to restoration of species populations, but also potentially re-establishes or expands ecosystem benefits (Hammerschlag et al. 2019;Mayer et al. 2019;Roman et al. 2014). However, population recovery also has the potential to cause concerns about conflicts with established industries (Boustany et al. 2020;Cammen, Rasher, and Steneck 2019;Nie 2003;Reidy 2019). ...
... The increased abundance of resources benefits the remaining consumers, and thus, the abundance of their interactions is higher. However, it should be noted that this boost in abundance comes at the cost of losing consumer species and interaction richness, with possible detrimental consequences on ecosystem functioning (Hammerschlag et al., 2019;Ritchie & Johnson, 2009;Schmitz et al., 2010). ...
Ecosystem restoration is becoming a widely recognised solution to the biodiversity crisis. However, there is still a gap between restoration science and practice. Specifically, we lack a theoretical framework that would improve our understanding of ecosystems' recovery and allow us to optimise restoration design.
Here, we narrow this gap by developing spatially explicit metacommunity models and studying the recovery dynamics of communities during restoration.
We show that community response depends on how damaged the landscape is prior to restoration, with highly fragmented landscapes imposing greater challenges to community recovery. In such cases, recovery depends on the type of interaction and the structure of the interaction network.
Furthermore, we demonstrate that community recovery can be maximised with careful spatial planning. Specifically, when recovering communities composed of antagonistic interactions, restoration should target areas adjacent to the most species‐rich sites. In the case of mutualistic communities, the same strategy should be adopted in the short term, whereas in the long term, restoration should be extended to sites that improve the overall connectivity of the landscape.
Synthesis and applications: Our results highlight the importance of considering interactions between species and spatial planning in restoration projects. Moreover, they provide insights into improving the efficiency of restoration and, thus, can help guide the design of restoration projects.
... ecology and movement patterns of crocodylians are relatively less explored, with taxonomic and geographic gaps often jeopardizing their conservation [26,43,107]. Traditionally relying on mark-recapture and observation/count techniques [53,115], research on the spatial ecology of crocodylians has increasingly benefited from new technologies, among which telemetry tracking emerged as a promising tool for monitoring these large, yet secretive animals [29,52,57,65,91,96]. ...
Crocodylians are top predators that play key ecological roles in aquatic ecosystems. As in other groups of large predators, crocodylian populations are often impacted by habitat loss, habitat degradation or direct exploitation for commercial purposes or subsistence. Hence, understanding their spatiotemporal ecology can provide valuable information for conservation planning. We reviewed the published scientific literature on telemetry-tracking in crocodylians, combining the terms “telemetry”, “track” or “tag” and variations; “VHF”, “UHF”, “satellite”, “GPS”, “radio”, “acoustic” or “transmitters”; and “caiman”, “alligator”, “crocodile”, “gharial” or “Crocodylia”. Publications retrieved by our search were carefully reviewed for information on study length, geographic location, sample size, taxonomy, and telemetry technology used. We identified 72 research articles in indexed journals and 110 reports available from the IUCN’s Crocodile Specialist Group, published between 1970 and 2022. Publications included 23 of the 27-living described crocodylian species. We identified strong geographic and taxonomic biases, with most articles proceeding from the USA (21.2%) and Australia (14%), with Alligator mississipiensis and Crocodylus porosus as the main target species in studies conducted in these countries, respectively. Despite representing 22% of IUCN’s reports, Gavialis gangeticus was referred in a single indexed research article. VHF telemetry was the prevalent tracking method, followed by GPS and acoustic transmitters. Studies using VHF devices had generally shorter in length when compared to alternative technologies. Transmitter weight represented less than 2% of the body mass of the carrying individual in all studies. Although attachment site of transmitters was notified in all research papers, few described anaesthetic or clinical procedures during attachment (33%). Our review highlights the need to encourage publication of crocodylian telemetry studies in non-English speaking countries in Asia, Africa, and Latin America, where many endemic species are threatened. We also highlight the need of detailed information on methods and results to facilitate the choice and implementation of appropriate protocols in future telemetry-tracking studies.
... The absence of a holistic understanding of how freshwater biota access essential nutrients currently limits our ability to interpret trends in observational research from individual sites and draw out generic and transferable principles. It is vitally important that future research on nutrient enrichment does not ignore key biotic groups actively involved in nutrient cycling and metabolic responses to enrichment, such as the consumers (Small et al. 2009;Sutherland et al. 2013;Stewart et al. 2018;Hammerschlag et al. 2019). Current theory urgently needs revision to incorporate the growing evidence, including our own, that the organic nutrients are often the dominant (> 80%) fraction in natural freshwaters (Durand et al. 2011;Yates et al. 2019;Johnes et al. 2020;Wymore et al. 2021), and highly bioavailable to single-celled organisms, higher plants and consumers, which exhibit taxonspecific preferences for different DOM compounds and can thus simultaneously access different parts of the nutrient pool to support production (Brailsford et al. 2019a;Mackay et al. 2020;Tada and Grossart 2014;Canelhas et al. 2016;Rofner et al. 2016;Pisani et al. 2017). ...
... And additionally, the distinctions between scientific concepts in different disciplines may impede fast answers to this strongly interdisciplinary question. Although the problem of understanding the interactions between ecosystem structures, functions and services has been investigated from several aspects in the past (Barbier et al. 2011;Harrison et al. 2014;Liquete et al. 2016;Pascual et al. 2016;Erhard et al. 2017;Roche and Campagne 2017;Rodrigues et al. 2017;Hammerschlag et al. 2019;Rullens et al. 2019;Teixeira et al. 2019), many questions are still unanswered. Therefore, we try to illuminate some related aspects of this problem area for the investigated marine-coastal ecosystems: How can we connect ecosystem services and the empirical, ecosystem-based results achieved during the BACOSA project (see Chaps. ...
This part provides a general description of the abiotic conditions of the Baltic Sea, which gives the reader the basic background required for understanding the peculiarities of the system investigated. Being a microtidal brackish water system, large with respect to area and volume, but having just narrow connection to the adjacent ocean, pronounced, but relatively stable gradients in salinity are a unique feature making the Baltic something special. In addition, post-glacial history resulted in characteristic patterns of subsoil geology as well as prevailing coastal types, which are presented on a Baltic scale here before being treated in detail for the investigation area.
... Their migrations are thought to play an important role in marine communities and ecosystems by horizontally and temporally connecting habitats and transferring energy via the trophic cascade (e.g. Dulvy et al., 2000;Hammerschlag et al., 2019;Heithaus et al., 2008Heithaus et al., , 2012. Although their migration also supports their populations through energy intake, they have been threatened with extinction (Dulvy et al., 2014;Worm et al., 2013) due to overfishing (e.g. ...
Aim: Despite extensive studies of phenological shifts in migration by climate change and driving factors of migration, a few issues remain unresolved. In particular, little is known about the complex effects of driving factors on migration with interactions and nonlinearity, and partitioning of the effects of factors into spatial, temporal, and spatio-temporal effects. Here, we aim to elucidate migration pattern as well as its driving factors under climate change.
Location: Western North Pacific.
Taxon: North Pacific spiny dogfish Squalus suckleyi.
Methods: We first examined long-term changes in the timing and geographic location of migration by applying the Barrier model, a spatio-temporal model, to c. 5-decade time series data (1972–2019) for the presence/absence of spiny dogfish in the west- ern North Pacific. We then evaluated the spatial, temporal and spatio-temporal ef- fects of driving factors (fish productivity, sea surface temperature [SST], depth and magnetic field) on seasonal occurrence patterns using a machine learning model and an interpretable machine learning technique.
Results: The migration area did not change over c. 5-decades, whereas the migra- tion timing advanced by a month after 2000. The spatial effects of magnetic field and depth were consistently large and the spatial and spatio-temporal effects of SST increased in the migration season, even though the temporal effect of SST was con- sistently weak.
Main Conclusions: The migration area of spiny dogfish was stable over time because of the effect of magnetic field and a strong preference for submarine topography, whereas the migration timing advanced as a result of tracking a suitable location based on SST, which increased sharply after 2000. Therefore, temperature and other factors simultaneously influence migration under climate change, highlighting the im- portance of considering both biotic and abiotic factors and understanding the under- lying processes in predicting future impacts of climate change on species distribution.
... Cartilaginous fishes, such as sharks, rays, and skates, were included because of their importance for the ecosystem functional diversity (Pimiento et al., 2020). Additionally, numerous species from all four of these taxonomic groups are usually present at the top of food chains, where the impacts of plastic pollution may be biomagnified due to trophic transfer (Anbumani and Kakkar, 2018;Carbery et al., 2018) and any adverse impacts of plastic-wildlife interactions will have knock-on effects on ecosystem functioning (Benkwitt et al., 2022;Hammerschlag et al., 2019;Pimiento et al., 2020;Tavares et al., 2019). In general, many of these species are also of broader conservation concern (IUCN SSC Shark Specialist Group, 2007; UNEP/CMS Secretariat, 2015, 2014). ...
Southeast (SE) Asia is a highly biodiverse region, yet it is also estimated to cumulatively contribute a third of the total global marine plastic pollution. This threat is known to have adverse impacts on marine megafauna, however, understanding of its impacts has recently been highlighted as a priority for research in the region. To address this knowledge gap, a structured literature review was conducted for species of cartilaginous fishes, marine mammals, marine reptiles, and seabirds present in SE Asia, collating cases on a global scale to allow for comparison, coupled with a regional expert elicitation to gather additional published and grey literature cases which would have been omitted during the structured literature review. Of the 380 marine megafauna species present in SE Asia, but also studied elsewhere, we found that 9.1 % and 4.5 % of all publications documenting plastic entanglement (n = 55) and ingestion (n = 291) were conducted in SE Asian countries. At the species level, published cases of entanglement from SE Asian countries were available for 10 % or less of species within each taxonomic group. Additionally, published ingestion cases were available primarily for marine mammals and were lacking entirely for seabirds in the region. The regional expert elicitation led to entanglement and ingestion cases from SE Asian countries being documented in 10 and 15 additional species respectively, highlighting the utility of a broader approach to data synthesis. While the scale of the plastic pollution in SE Asia is of particular concern for marine ecosystems, knowledge of its interactions and impacts on marine megafauna lags behind other areas of the world, even after the inclusion of a regional expert elicitation. Additional funding to help collate baseline data are critically needed to inform policy and solutions towards limiting the interactions of marine megafauna and plastic pollution in SE Asia.
... Cartilaginous fishes, such as sharks, rays, and skates, were included because of their importance for the ecosystem functional diversity (Pimiento et al., 2020). Additionally, numerous species from all four of these taxonomic groups are usually present at the top of food chains, where the impacts of plastic pollution may be biomagnified due to trophic transfer (Anbumani and Kakkar, 2018;Carbery et al., 2018) and any adverse impacts of plastic-wildlife interactions will have knock-on effects on ecosystem functioning (Benkwitt et al., 2022;Hammerschlag et al., 2019;Pimiento et al., 2020;Tavares et al., 2019). In general, many of these species are also of broader conservation concern (IUCN SSC Shark Specialist Group, 2007;UNEP/CMS Secretariat, 2015. ...
Please cite this article as: L.C.M. Omeyer, E.M. Duncan, N.A.S. Abreo, et al., Interactions between marine megafauna and plastic pollution in Southeast Asia, Science of the Total Environment (2023), https://doi.
... The increased abundance of resources benefits the remaining consumers, and thus, the abundance of their interactions is higher. However, it should be noted that this boost in abundance comes at the cost of loosing consumer species and interaction richness, with possible detrimental consequences on ecosystem functioning (Ritchie and Johnson, 2009;Schmitz et al., 2010;Hammerschlag et al., 2019). ...
Ecosystem restoration is becoming a widely recognised solution to the biodiversity crisis. However , there is a gap between restoration science and practice. Specifically, we lack a theoretical framework which would improve our understanding of ecosystems' recovery and allow us to optimise restoration design. Here, we narrow this gap by developing spatially explicit meta-community models and studying the recovery dynamics of communities during restoration. We show that community response depends on how damaged the landscape is prior to restoration, with highly fragmented landscapes imposing greater challenges to community recovery. In such cases, we found that the recovery depends on the type of interaction and the structure of the interaction network. Finally, we demonstrate that community recovery can be maximised with careful spatial planning. When recovering communities composed of antagonistic interactions, restoration should target areas adjacent to the most species-rich sites. In the case of mutualistic communities, the same strategy should be adopted in the short-term, whereas in the long-term, restoration should be extended to sites that improve the overall connectivity of the landscape. Our results highlight the importance of considering interactions between species and spatial planning in restoration projects.
... And additionally, the distinctions between scientific concepts in different disciplines may impede fast answers to this strongly interdisciplinary question. Although the problem of understanding the interactions between ecosystem structures, functions and services has been investigated from several aspects in the past (Barbier et al. 2011;Harrison et al. 2014;Liquete et al. 2016;Pascual et al. 2016;Erhard et al. 2017;Roche and Campagne 2017;Rodrigues et al. 2017;Hammerschlag et al. 2019;Rullens et al. 2019;Teixeira et al. 2019), many questions are still unanswered. Therefore, we try to illuminate some related aspects of this problem area for the investigated marine-coastal ecosystems: How can we connect ecosystem services and the empirical, ecosystem-based results achieved during the BACOSA project (see Chaps. ...
The marine and coastal ecosystems of the Baltic Sea are exposed to an intensification and diversification of anthropogenic activities and related environmental pressures. Human interest in marine resources and space often overlap with environmental protection objectives, causing conflicts. Research can assist capacity building to enable knowledge-based decision-making in marine management and policy to help solve these issues. Three participatory systematic maps were carried out on marine and coastal ecosystem services (ES), monetary and non-monetary valuation methods applied to value them, and the interrelation of ES and human health and well-being in the Baltic Sea region. Policy advisors were engaged throughout the review process. The aim was to map existing scientific knowledge and identify knowledge gaps for the scientific community and to support the implementation and update of the key marine protection policies in the region. This chapter introduces the review methodology, provides an overview of knowledge gaps and missing links in ES research, and addresses future steps to connect the dots.
... And additionally, the distinctions between scientific concepts in different disciplines may impede fast answers to this strongly interdisciplinary question. Although the problem of understanding the interactions between ecosystem structures, functions and services has been investigated from several aspects in the past (Barbier et al. 2011;Harrison et al. 2014;Liquete et al. 2016;Maes et al. 2016;Pascual et al. 2016;Erhard et al. 2017;Roche and Campagne 2017;Rodrigues et al. 2017;Grizzetti et al. 2019;Hammerschlag et al. 2019;Rullens et al. 2019;Teixeira et al. 2019), many questions are still unanswered. Therefore, we try to illuminate some related aspects of this problem area for the investigated marine-coastal ecosystems: How can we connect ecosystem services and the empirical, ecosystem-based results achieved during the BACOSA project (see Chaps. ...
Coastal lagoons provide important ecosystem services, but are simultaneously highly vulnerable. We aim at a better understanding of the mechanisms of ecosystem service production in these ecosystems. Three case studies, based on results obtained during the BACOSA and SECOS projects, identify the impact of the functional organism groups bioturbating zoobenthos, phytoplankton and macrophytes on coastal lagoons. These empirical results are merged with a theoretical framework on the relations between ecological conditions and ecosystem services, consisting of an integrative matrix projection. RESPON (relative ecosystem service potential) points are estimated for the three case studies. All functional groups have an overall positive effect on ecosystem services, and a very high impact on integrity parameters such as biodiversity, trophic efficiency and nutrient retention. The highest scores are obtained for macrophytes, while phytoplankton only has a slightly positive impact. For bioturbation, a major lack of knowledge was identified; bioturbating zoobenthos with high biodiversity is assumed to favour “seafloor integrity”. Despite major difficulties such as lack of knowledge and highly different approaches, our analysis results in specific recommendations for management and future research. Management must consider the high connectivity of coastal lagoons with other ecosystems. Harsh impacts destroying benthic fauna communities have to be minimized. The promotion of submerged vegetation, which is an important provider of ecosystem services, must be implemented in the management of coastal lagoons.
... Nevertheless, the majority of conservation literature remains biased toward terrestrial organisms, with less than 20% of recent studies focusing on aquatic species 28 . Many potential threats to freshwater biodiversity have been evaluated 27 , but the effects of predators on aquatic biodiversity have received less attention, which makes it difficult to understand how aquatic species maintain diversity 29 . Streams with only apex predator (Lutra lutra) in taiga forest systems represent an ideal model that can be used to examine the influence of predators on the prey community in natural systems. ...
Predator–prey interactions are critical for understanding species composition and community assembly; however, there is still limited research on whether and how the prey species composition or community assembly in natural communities are mediated by predators. To address this question, we performed a field investigation to examine the influence of the presence of Lutra lutra on the diversity of fish communities of the Hunchun River Basin, Jilin Province, China. Our results indicate that L. lutra, as a potential umbrella species and generalist predator in the stream ecosystem, promotes the coexistence of a vast variety of fish taxa, which emphasizes the importance of top-down control in the ecological community. We suggest that L. lutra regulates the fish community assembly likely through the stochastic process. Although this was a pilot study regarding predator–prey interactions, the results highlight the effects of predators on the prey community assembly, and emphasize the role of predators on the maintenance of biodiversity and ecosystem function. Future conservation decisions involving ecosystem biodiversity should require the inclusion of predation intensity. The inclusion of scientific research and protection of umbrella species would thus constitute an additional and important step in biodiversity conservation.
... The global decline of populations of predatory fish (Christensen et al., 2014;Estes et al., 2011;Myers and Worm, 2003;Pauly et al., 1998) is commonly caused by overexploitation, changes in food web structure and function, as well as unfavorable environmental conditions (Christensen et al., 2014;Hammerschlag et al., 2019;Möllmann et al., 2021;Valdivia et al., 2017). In coastal areas, predatory fish are often caught for food and recreation, and are of high socioeconomic value (Hyder et al., 2018;Koemle et al., 2021). ...
The northern pike (Esox lucius) is an iconic predatory fish species of significant recreational value and ecological role in the Baltic Sea. Some earlier studies indicate local declines of pike in the region, but a thorough spatial evaluation of regional population trends of pike in the Baltic Sea is lacking. In this study, we collate data from 59 unique time-series from fisheries landings and fishery-independent monitoring programs to address temporal trends in pike populations since the mid-2000′s in eight countries surrounding the Baltic Sea. In a common analysis considering all time-series in concert, we found indications of an overall regional temporal decline of pike in the Baltic Sea, but trends differed among countries. Individual negative trends in time-series were moreover found in several regions of the Baltic Sea, but predominantly so in the central and southern parts, while positive trends were only found in Estonia and northern Finland. The mix of data used in this study is inherently noisy and to some extent of uncertain quality, but as a result of the overall negative trends, together with the socioeconomic and ecological importance of pike in coastal areas of the Baltic Sea, we suggest that actions should be taken to protect and restore pike populations. Management measures should be performed in combination with improved fishery-independent monitoring programs to provide data of better quality and development of citizen-science approaches as a data source for population estimates. Possible measures that could strengthen pike populations include harvest regulations (including size limits, no-take areas and spawning closures), habitat protection and restoration, and an ecosystem-based approach to management considering also the impact of natural predators.
... Thus, there is a continuing need to integrate satellite telemetry with individual physiology, metabolism, gene expression, and reproductive strategy to better understand the context of movement decisions (Hays et al., 2016). Investigating the ecological and economic consequences of seasonal shark presence/ absence (tourism, fisheries, indirect/direct predation effects; see Hammerschlag et al., 2019), overlap of potentially dangerous shark species with humans, climate change effects on shark movement and distribution, and population connectivity will be essential to create holistic and effective management decisions across scales (e.g. from local and regional to international) Hays et al., 2019). The effects of climate-driven environmental changes on shark movements and distribution are comparatively understudied, particularly with respect to future predicted changes (Vedor et al., 2021). ...
Satellite telemetry as a tool in marine ecological research continues to adapt and grow and has become increasingly popular in recent years to study shark species on a global scale. A review of satellite tag application to shark research was published in 2010, provided insight to the advancements in satellite shark tagging, as well as highlighting areas for improvement. In the years since, satellite technology has continued to advance, creating smaller, longer lasting, and more innovative tags, capable of expanding the field. Here we review satellite shark tagging studies to identify early successes and areas for rethinking moving forward. Triple the amount of shark satellite tagging studies have been conducted during the decade from 2010 to 2020 than ever before, tracking double the number of species previously tagged. Satellite telemetry has offered increased capacity to unravel ecological questions including predator and prey interactions, migration patterns, habitat use, in addition to monitoring species for global assessments. However, <17% of the total reviewed studies directly produced results with management or conservation outcomes. Telemetry studies with defined goals and objectives produced the most relevant findings for shark conservation, most often in tandem with secondary metrics such as fishing overlap or management regimes. To leverage the power of telemetry for the benefit of shark species, it remains imperative to continue improvements to tag function and maximize the outputs of tagging efforts including increasing data sharing capacity and standardization across the field, as well as spatial and species coverage. Ultimately, this review offers a status report of shark satellite tagging and the ways in which the field can continue to progress.
... Their size and longevity allow great whales to exert strong effects on the carbon cycle by: (i) storing carbon more effectively than small animals [7], (ii) ingesting extreme quantities of prey [7], and (iii) producing large volumes of waste products [8]. Considering that baleen whales have some of the longest migrations on the planet [9], they potentially influence nutrient dynamics and carbon cycling over ocean-basin scales [10][11][12]. ...
The great whales (baleen and sperm whales), through their massive size and wide distribution, influence ecosystem and carbon dynamics. Whales directly store carbon in their biomass and contribute to carbon export through sinking carcasses. Whale excreta may stimulate phytoplankton growth and capture atmospheric CO2; such indirect pathways represent the greatest potential for whale-carbon sequestration but are poorly understood. We quantify the carbon values of whales while recognizing the numerous ecosystem, cultural, and moral motivations to protect them. We also propose a framework to quantify the economic value of whale carbon as populations change over time. Finally, we suggest research to address key unknowns (e.g., bioavailability of whale-derived nutrients to phytoplankton, species- and region-specific variability in whale carbon contributions).
... Fishes are one of the most important components of the oceans as they have important ecological roles and provide a wide range of ecosystem services (Hammerschlag et al., 2019). Large migratory fishes such as tunas, mackerels, and amberjacks can function as valuable indicators of ocean health because they are either top predators (e.g. ...
Fishes are one of the most important components of the oceans and are exposed to several anthropogenic pressures, namely microplastic (MP), contaminants that are now ubiquitous worldwide. Taking advantage of the 2020 Circumnavigation Expedition carried by the NRP Sagres tall ship of the Portuguese Navy, fish samples from the southern Atlantic ocean were collected to evaluate possible MP contamination. In a total of 14 weeks of campaign, seven large migratory fishes of commercial interest were collected across the middle Atlantic Ocean and along the South American Atlantic coast. All individuals were contaminated with MPs, with an average of 18 ± 11 MPs/fish. In all fish sampled, both the gastrointestinal tract and gills presented MPs, indicating different contamination pathways including via their preys and from surrounding water, respectively. A total of 124 MPs were observed, where 72 % were fibers and 28 % particles, mostly of blue color (85 %), and with rayon and nylon as the most abundant polymers. This study is an important contribution to increase the scientific knowledge of MP contamination in mesopelagic fishes used for human consumption and collected in the open waters, reinforcing the need for further research regarding MP contamination in top predatory species from high trophic levels.
... Top predators provide important functions and services in marine ecosystems, including regulating food webs, supporting fisheries and generating tourism (Estes et al., 2016;Hammerschlag et al., 2019;Enquist et al., 2020). In addition, there is increasing evidence that marine predators may play a role in ocean nutrient and carbon cycling (Atwood et al., 2015;Schmitz et al., 2018;Martin et al., 2021). ...
There is increasing interest in assessing the impact of whales on nutrient and carbon cycling in the ocean. By fertilising surface waters with nutrient-rich faeces, whales may stimulate primary production and thus carbon uptake, but robust assessments of such effects are lacking. Based on the analysis of faeces collected from minke whales (n=31) off Svalbard, Norway, this study quantified the concentration of macro-and micronutrients in whale faeces prior to their release in seawater. Concentrations of the macronutrients nitrogen (N) and phosphorous (P) in minke whale faeces were 50.1 ± 10.3 and 70.9 ± 12.1 g kg⁻¹ dry weight, respectively, while the most important micronutrients were zinc (Zn), iron (Fe), manganese (Mn) and copper (Cu). By combining measured faecal nutrient concentrations with estimated prey-consumption and prey-assimilation rates, we calculate that the current population of approximately 15 000 individuals in the small management area (SMA) of Svalbard defecate daily 7 ± 1.4 tonnes (t) N and 10 ± 1.7 t P during summer. The molar ratio of N:P in minke whale faeces was 1.6:1, meaning that N was proportionally limiting, when compared to average elemental ratios of 16:1 in phytoplankton. In case of no N-limitation in surface waters at that time, the release of elemental P through defecation in surface waters has the potential to stimulate 407 ± 70 t of carbon per day during summer as new or regenerated primary production in the SMA of Svalbard. This amounts to 0.2 to 4 % of daily net primary production to this region. This study provides the first assessment of nutrient concentration in whale faeces prior to their dissolution in sea water. Further research, namely on the amount of N released via urine and seasonal changes in excreted nutrients, is needed to better assess the full potential of whale nutrient additions to dissolved nutrient pools in surface waters at regional and global scales.
... Assessing wildlife population abundance is fundamental for understanding ecosystem roles (Heithaus et al., 2008;Hammerschlag et al., 2019) and supporting conservation processes (Johnston et al., 2015;García-Barón et al., 2019). For instance, IUCN Red List assessments are highly dependent on population abundance estimates (IUCN, 2001). ...
There is a remarkable paucity of estimates of the numeric importance of sea turtles at foraging grounds. The Banc d'Arguin (BA) is a vast shallow marine area off the coast of Mauritania, known as a site of world importance for coastal migratory birds and other biodiversity, including extensive seagrass beds. We sampled foraging green turtles on the BA, and extensively tracked adult female green turtles from the Bijagós archipelago, the only significant nesting aggregation within 3000 km of the BA, to estimate the abundance of this foraging aggregation. Additionally, we used a demographic simulation to support our findings. Based on satellite tracking of adult females (n = 46), we estimate that 50 % of the nesting population from the Bijagós migrate to the BA post-nesting. We combine data on numbers nesting in the Bijagós with information on proportion migrating to the BA in the same years to conservatively estimate that 8285 adult female green turtles forage at this site. We also estimate that adult females represent only 5.6 % of the green turtles in the BA, implying that the number of turtles there is of the order of 150,000 individuals. Most of the BA enjoys effective protection as part of the Parc National du Banc d'Arguin where significant fisheries regulations are well enforced by a marine surveillance program. We show that the BA is one of the major foraging sites for green turtles nesting in the Bijagós and a site of critical importance for immature and adult green turtles in a global context.
... Fish stocking and overfishing in natural freshwater ecosystems are two widespread and long-term human activities that lead to alterations in ecosystem functions and services globally (Eby et al. 2006;Hammerschlag et al. 2019;Wang et al. 2022). In recent decades, China has increased its contribution to the largest global freshwater aquaculture production from 38.5% in 1980 to 63.6% in 2011 (Jia et al. 2013). ...
Freshwater lakes across the world have undergone dramatic changes in biological components and water quality over the past several decades. Previous studies focused on potential drivers mainly on nutrient enrichment in the catchment. However, the relative importance of climate change and the top-down cascade effects of fish stocking on water quality is not fully understood. Here, by compiling 155 lakes data with four periods of field investigation in subtropical lakes in China, we found no significant changes in water total nitrogen and total phosphorus in the past two decades. However, the phytoplankton abundance increased significantly, and the water clarity declined by 44.1%. We further found that carp stocking and climate change are potentially more important than nutrients driving water quality change, which is also evidenced in two lakes (Lake Donghu and Qiandao) with long-term monitoring histories. Specifically, carp stocking can decrease the water clarity directly by stirring up sediment and indirectly by trophic cascade along the food web. For climatic factors, mean annual temperature (MAT) has a positive effect on phytoplankton abundance, while mean annual precipitation has a negative one, with climates overall having little effect on water clarity. In addition, nutrient enrichment and climate change also have strong interactions with carp stocking, which may enhance the top-down effects on water quality. Our findings highlight that either MAT or carp stocking may become an overwhelming driver of water clarity decline, which provides new insights into the conservation strategy for water quality management in the subtropical lakes in China.
... It is difficult to make generalisations about the efficacy of sensory deterrents and their ability to deliver consistent bycatch reductions. The efficacy of each method is context dependent, varying with species, fishery and (Kiszka et al. 2015;Hammerschlag et al. 2019). The removal of apex predators can cause trophic cascades, leading to collapse or re-structuring of food webs (Daskalov 2002;Heithaus et al. 2008), threatening the livelihoods of commercial and small-scale fishers, coastal communities that depend on them and potentially having widespread conservation impacts. ...
Marine megafauna are critical for marine ecosystem health and their removal can cause food webs to collapse. Methods to reduce marine megafauna mortality can result in conflict between scientists, conservationists, fishers and fisheries management due to real or perceived effects on target catch, income and food security. Sensory deterrents have been used in attempts to mitigate bycatch and retain target catch quantity and quality. Here, we completed a systematic review of 116 papers, plus 25 literature reviews published between 1991 and 2022, to investigate potential for sensory deterrents to mitigate bycatch across four marine megafauna taxonomic groups (marine mammals, sea turtles, seabirds and elasmobranchs). Lights on gillnets are the only technology so far to result in significant bycatch reductions across all four taxonomic groups. It is difficult to make generalisations about the efficacy of sensory deterrents and their ability to deliver consistent bycatch reductions. The efficacy of each method is context dependent, varying with species, fishery and environmental characteristics. Further research is recommended for field studies assessing bycatch mitigation in all sensory deterrents, including combinations of deterrents, to assess effects on target and non-target species. The associated issues of habituation, habitat exclusion and foraging around fishing gear are important, although reducing mortality of vulnerable species should remain the highest priority for conservation and preserving ecosystems that fishers depend on. Multiple complementary measures will be required to achieve consistent bycatch reduction targets in many fisheries, of which sensory deterrents could play some part if implemented appropriately.
... Sharks have historically been portrayed as "man-eaters" and such stereotype has been supported by a generally sensationalist media coverage of shark-human incidents [28,29,40]. More recently, there has been a shift in the image of sharks to being essential for healthy aquatic environments [14,25]. Alongside this perception change, the non-consumptive use of sharks through the tourism industry has gained considerable popularity among wildlife tourists [37]. ...
Wildlife tourism can assist species conservation through community-involvement and education, while contributing to regional economies. In the last decade, shark diving has become increasingly popular among wildlife tourists worldwide, including cage-diving with white sharks (Carcharodon carcharias). In Australia, birthplace of the white shark diving industry, an adaptive management framework has been developed to minimise potentially detrimental effects on white sharks. We monitored the residency of 135 white sharks using acoustic tracking over eight years (2013–2021) at the Neptune Islands Group Marine Park to assess the efficacy of management regulations put in place in 2012, which limited the number of operating boats to three and a maximum of five weekly days of activity. A sensitivity analysis was conducted to investigate possible differences in shark residency as a function of number of acoustic receivers used and their corresponding distances to long-term monitoring stations. Similar residency patterns were observed independently of the number of receivers used or their deployment locations, suggesting that the monitoring design was adequate to monitor shark residency. White shark yearly residency decreased following the implementation of new regulations in 2012 and returned to baseline levels by 2013–2014. Our results highlight that white shark residency can recover from tourism-related changes and showcase how adequately-developed and -implemented regulations can enable the successful management and long-term sustainability of one of the oldest shark tourism industries. This adaptative framework (problem identification, development and implementation of policies, efficacy monitoring and performance evaluation) is broadly applicable to management of other tourism industries.
... Elasmobranchs generally play important roles in shallow-water ecosystems in reefs, bays, and estuaries in tropical and temperate oceans [1]. However, despite their environmental importance, the global abundance of oceanic sharks and rays has declined by 71% since 1970 due to an 18-fold increase in relative fishing pressure [2]. ...
The tiger shark Galeocerdo cuvier (Péron & Lesueur, 1822) (Carcharhinidae) is classified as near-threatened along the Brazilian coast, in line with its global categorization. Although Rio de Janeiro, located in southeastern Brazil, is internationally identified as a priority shark conservation area, many shark species, including tiger sharks, are landed by both industrial and artisanal fisheries in this state. However, there is a lack of detailed information on the species capture pressures and records for the state of Rio de Janeiro. Therefore, the aims of this study were to expand the tiger shark record database and to improve upon future conservation and management strategies. Tiger shark records from four coastal Rio de Janeiro regions were obtained by direct observation. The information obtained from fishery colonies/associations, environmental guards, researchers, and scientific articles, totaling 23 records, resulted in an approximately 5-fold increase in the number of tiger shark records off the coast of the state of Rio de Janeiro. A possible seasonality pattern concerning the size of the captured/observed animals was noted, emphasizing the need to consider the coast of Rio de Janeiro as an especially relevant area for at least part of the life history of tiger sharks.
Fisheries science uses quantitative methods to inform management decisions that reflect cultural preferences which, in turn, indirectly influence the states of ecosystems. To date, it has largely supported Eurocentric preferences for the commodification of marine organisms under the tenets of maximum sustainable yield, whereby abundances are intentionally maintained far below their historical baselines despite broader socio‐ecological trade‐offs. In contrast, Indigenous Knowledge Systems (IKS) adhere to the principle of “take only what you need and leave lots for the ecosystem,” implementing lower fishery removals to support socio‐ecological resilience. Despite the power imbalance favouring Eurocentric preferences in decision‐making, fisheries scientists increasingly recognize that the pairing of IKS and Western science, or Two‐Eyed Seeing, would lead to more holistic management goals. For recognition to transcend tokenism, meaningful collaborations and co‐governance structures underlying knowledge co‐production must carry through to legislated policy changes. Using recent co‐governance developments for fisheries management and spatial protections involving federal, provincial and Indigenous governments in Pacific Canada, we illustrate how the precautionary approach, including reference points and harvest control rules broadly applied in international fisheries, could be revised to make collaborative fisheries management compatible with IKS and improve biodiversity and fisheries protections. Our recommendations may create socio‐economic trade‐offs at different timescales for commercial fishers. Pre‐empting that challenge, we discuss IKS‐compatible economic approaches for addressing shorter term costs arising from reduced exploitation rates. Although our case study derives from Pacific Canada, the insights provided here are broadly applicable elsewhere in the world.
Almost half of all chondrichthyan species in the Mediterranean Sea are threatened with extinction, according to the IUCN Red List. Due to a substantial lack of access to data on chondrichthyan catches in the Mediterranean Sea, especially of threatened species, the implementation of conservation measures is extremely insufficient. This also concerns the Adriatic Sea. Here we present a detailed and up-to-date assessment of the species occurring in Croatian waters, as the last checklist of chondrichthyans in Croatian waters was conducted in 2009. Occurrence records from historical data, literature and citizen science information have been compiled in order to present a comprehensive list of species occurrences. We found 54 chondrichthyan species between 1822 and 2022, consisting of a single chimaera, 23 rays and skates, and 30 shark species. Here, four additional species are listed but are considered doubtful. Five species are reported here for the first time for Croatian waters that were not listed in the survey from 2009. Nearly one-third of the species reported here are critically endangered in the entire Mediterranean Sea, based on the IUCN Red List. Additionally, we revisited the Croatian records of the sandtiger shark Carcharias taurus Rafinesque, 1810 and discussed its potential confusion with the smalltooth sandtiger shark Odontaspis ferox (Risso, 1810). Our results thus provide novel insights into the historical and current distribution patterns of chondrichthyan fishes in the Croatian Sea and provide a basis for further research as well as conservation measures.
Dada a elevada diversidade nas estratégias de história de vida, os elasmobrânquios (tubarões e raias) tornam-se interessantes modelos para o estudo de relações entre a fisiologia e interações ecológicas no ambiente marinho. Embora os esforços para a conservação dos elasmobrânquios, que é atualmente o segundo grupo de vertebrados mais ameaçado do planeta, tenha estimulado um aumento no número de estudos sobre os padrões ecológicos e impactos antrópicos, pouco ainda se sabe sobre sua fisiologia. Assim, nesta tese de doutorado foram investigadas as variações fisiológicas sazonais e espaciais associadas ao estágio de vida e comportamento de tubarões de diferentes histórias de vida, utilizando múltiplas ferramentas não-letais para fornecer uma melhor compreensão dos padrões energéticos e reprodutivos, além de uma base fisiológica que ajude a prever os efeitos de distúrbios ambientais nos tubarões. O capítulo 1 aborda as variações inter- e intraespecíficas na ecologia nutricional de tubarões de diferentes estratégias de história de vida em um sistema insular oceânico protegido, o Arquipélago de Fernando de Noronha. Foram abordados também as variações nos padrões de dieta e condição nutricional e metabólica relacionados à reprodução de fêmeas de tubarões-tigre Galeocerdo cuvier (capítulo 2) e machos de tubarões-lixa Ginglymostoma cirratum e tubarões-galha-preta Carcharhinus limbatus (capítulo 3). Os capítulos 4, 5 e 6 abordam os efeitos da vida urbana na condição nutricional e padrões alimentares de tubarões com diferentes estilos de vida, o tubarão-lixa, o tubarão-galha-preta e o tubarão-tigre, respectivamente. Os resultados mostraram que a influência da urbanização na qualidade da dieta dos tubarões parece ser mais pronunciada em espécies sedentárias, como o tubarão-lixa, quando comparado com espécies mais ativas. Por fim, o capítulo 7 trouxe uma abordagem inédita na pesquisa de tubarões, combinando múltiplos marcadores fisiológicos com informações obtidas através de ultrassonografia e da telemetria acústica passiva para entender relações entre os aspectos fisiológicos e comportamentais de tubarões-tigre expostos ao turismo de alimentação. Os resultados demonstraram que o estágio de vida, a regulação endócrina e a condição nutricional influenciam e/ou são influenciadas pelo tempo que os tubarões passam interagindo com o turismo de alimentação. Em conjunto, os resultados mostraram que os biomarcadores nutricionais, reprodutivos e metabólicos utilizados nesta tese fornecem uma poderosa ferramenta para descrever padrões ecológicos complexos dos tubarões, especialmente quando combinados com outras tecnologias para rastreamento da movimentação e identificação do estágio reprodutivo dos tubarões.
Marine predators are globally threatened by anthropogenic stressors, but are key for ecosystem functioning. Their worsening conservation statuses indicate that current management is failing, requiring us to urgently reimagine their conservation needs to ensure their survival. Their life histories, threats, and resource needs are diverse. Consequently, spatial conservation areas targeting all species will overlook such heterogeneity, contributing to the problem. Here, we demonstrate that marine mammals, elasmobranchs and teleost fishes return drastically different spatial conservation priority areas, based on Marxan scenarios for 42 marine predator species in the Mediterranean Sea. None of the marine predators are sufficiently covered by the current marine protected area (MPA) system, with marine mammals being the least protected despite having the greatest designated MPA extent, highlighting disconnects between conservation goals and current management outcomes. To save marine predators, taxon specific ecological requirements and resulting spatial heterogeneity need to be accounted for in marine spatial planning.
Modern sharks have an evolutionary history of at least 250 million years and are known to play key roles in marine systems, from controlling prey populations, to connecting habitats across oceans. These ecological roles can be quantified based on their functional traits, which are typically morphological (e.g., body size) or behavioural (e.g., feeding and diet). However, our understanding of such roles of extinct sharks is limited by the inherent incompleteness of their fossil record, which consists mainly of isolated teeth. As such, establishing links between tooth morphology and ecological traits in living sharks could provide a useful framework to infer sharks’ ecology from the fossil record. Here, based on extant sharks from which morphological and behavioural characteristics are known, we assess the extent to which isolated teeth can serve as proxies for functional traits. To do so, we first review the scientific literature on extant species to evaluate the use of shark dental characters as proxies for ecology to then perform validation analyses based on an independent dataset collected from museum collections. Our results reveal that 12 dental characters have been used in the shark literature as proxies for three functional traits: body size, prey preference and feeding mechanism. From all dental characters identified, tooth size and cutting edge are the most widely used. Validation analyses suggest that seven dental characters – crown height, crown width, cutting edge, lateral cusplets, curvature, longitudinal outline and cross‐section outline – are the best proxies for the three functional traits. Specifically, tooth size (crown height and width) was found to be a reliable proxy of all three traits; the presence of serrations on the cutting edge was one of the best proxies for prey preference; and tooth shape (longitudinal outline) and the presence of lateral cusplets were among the best indicators of feeding mechanism. Taken together, our results suggest that in the absence of directly measurable traits in the fossil record, these seven dental characters (and different combinations of them) can be used to quantify the ecological roles of extinct sharks. This information has the potential of providing key insights into how shark functional diversity has changed through time, including their ecological responses to extinction events. This article is protected by copyright. All rights reserved.
Marine turtles are of the highest ecological concern in terms of conservation and restoration programs and marine territorial ordering. Marine resourceextracting industries have severe negative impacts on their populations and their habitats. Thus, private industries and decision makers require the best and most robust spatially explicit scientific knowledge for a sustainable and responsible operation and government administration. Therefore, the identification of marine turtle hotspots is a strategic milestone for ecosystem management and an integral ecological knowledge about any region. We identified and delimited marine turtle hotspots in the Gulf of Mexico and
Mesoamerican Reef. We analyzed satellite-tracked data of 178 individuals belonging to four marine turtle species. We used Brownian bridge movement models to estimate space use surfaces and map algebra to weight and merge layers of multiple species, life stages, and movement phases. The Yucatan Peninsula and central Veracruz in Mexico, along with the Florida Keys and Louisiana coast in the US, harbor the primary hotspots where marine turtles aggregate. We defined four primary hotspots used for migration in the western Gulf of Mexico, around the Yucatan Peninsula, a northern route following the
Loop Current, and a southern one towards Gorda Bank, Central America. This study is the largest assessment of marine turtle hotspots in Mexico and Cuba and supports strategies for reinforcing regional management actions for their conservation, as well as a stronger response and preparedness for tackling anthropic threats to these species. This milestone contributes to extending the knowledge frontiers about these species to a new level.
Animals need to move between different habitats to successfully complete their life cycle. Anthropogenic activities and infrastructure impact animal movement, especially in the aquatic realm, due to habitat alteration (including fragmentation), pollution, overexploitation, the spread of invasive alien species and climate change. Gaining knowledge on the complex phenomenon of fish movement is essential to understand the diverse ways in which anthropogenic activities may influence the spatial ecology of fish, which can inform management. The four main methods to study fish movement are through observation and interception, electronic tracking, otolith chemistry and environmental DNA. We discuss the strengths and shortcomings of these methods and suggest effective management can be aided by combining these and other methods. Often the weaknesses of one technique can be met by the strengths of the others. Also, cross-boundary collaboration is essential for the successful management of fish that move over jurisdictional boundaries to complete their life cycle. Data analyses on interdisciplinary datasets obtained at spatial scales relevant to the movement ecology of a given population can yield a more holistic understanding of fish movement. This knowledge may help for the appropriate selection of cost-efficient, evidence-based and effective management actions that balance the needs of fishes and human activities.
Graphical abstract
The assessment of the spatial overlap between eligible cetacean conservation areas (CCAs) and fishing grounds could be a strategic element in the implementation of effective conservation measures in the pelagic offshore areas. A multi-species bio-economic modelling approach has been applied to estimate the fishing traits in eligible CCAs in the Northern Ionian Sea (NIS, Central Mediterranean Sea) between 10-800 m of depth, adopting the Spatial MAnagement of demersal Resources for Trawl fisheries model (SMART). Four possible CCAs were defined according to the distribution of cetacean species, their bio-ecological needs, as well as socio-economic needs of human activities, identifying a Blue, Red, Orange and Green CCAs in the NIS. SMART spatial domain was a grid with 500 square cells (15×15 NM). The analysis was conducted for the period 2016-2019, considering the Otter Trawl Bottom (OTB) fleet activities in the study areas through the Vessel Monitoring System. The spatial extension of fishing activities, hourly fishing effort (h), landings (tons) and economic value (euros) for each CCA and the NIS were estimated as yearly median values. Fishing activities were absent in the Blue CCA, where the presence of the submarine canyon head does not offer accessible fishing grounds. The hourly fishing effort in the Green area accounted for about 22% (3443 h) of the total hourly effort of the NIS, while the Orange and Red areas were about 8% (1226 h) and 2% (295 h), respectively. The Green CCA corresponded to about 14% (36 tons) of the total landings in the NIS, whereas the Orange and Red areas represented about 9% (22 tons) and 6% (16 tons), respectively. The Green CCA accounted for about 13% (156 thousand euros) of the total economic value of the NIS, while the Orange and Red areas represented about 6% (69 thousand euros) and 4% (44thousand euros), respectively. Results showed no or negligible negative effects on trawl activities by potential spatial restrictions due to the establishment of CCAs highlighting the importance to consider spatially integrated information during the establishment process of conservation areas for cetacean biodiversity according to the principles of Ecosystem Based Management.
Abstract: Alien species invasion is one of the major causes of global biodiversity loss. As the top predators of the food web, invasive alien vertebrates have dominant impacts on native species population, community structure and ecosystem functions. Based on intensive and systematic literature review, we summarize the direct (e.g., predation, competition, reproductive interference and gene pollution) and indirect (e.g., disease transmission and habitat modifications) impacts of invasive alien vertebrates on native biota across population, community, ecosystem, and biogeography levels. We particularly focus on the impacts of invasive alien species on island ecosystems, protected areas and the regions along the “Belt and Road Initiative”, which are located in biodiversity conservation hotspots and are extremely sensitive to biological invasions. We finally summarize recent research progress and the directions of future studies on invasive alien vertebrates and potential conservation and management strategies in China.
摘要：外来物种入侵是造成全球生物多样性下降的重要因素之一。入侵脊椎动物作为食物链的上游类群，对生物多样性的危害尤为显著，但长期以来缺少对脊椎动物入侵危害的系统阐述。本文从直接影响（捕食危害、种间竞争和繁殖干扰、种间杂交和基因污染等）和间接影响（疾病传播、栖息地环境改变等）两个方面，分别在种群、群落、生态系统和生物地理格局等不同水平上，阐述外来入侵鱼类、两栖爬行类、鸟类和兽类等脊椎动物类群对生物多样性的影响机制，并以典型生物多样性脆弱区（岛屿生态系统和自然保护地）以及 “一带一路”倡议沿线为例，探讨外来脊椎动物入侵对生物多样性保护的挑战；最后，概述我国入侵脊椎动物对生物多样性危害的研究现状，并结合生态安全的国家需求以及国际科学前沿，展望我国外来脊椎动物入侵危害研究的未来发展方向。
The social-ecological systems framework (SESF) is arguably the most comprehensive conceptual framework for diagnosing interactions and outcomes in social-ecological systems (SES). This article systematically reviews the literature applying and developing the SESF and discusses methodological challenges for its continued use and development. Six types of research approaches using the SESF are identified, as well as the context of application, types of data used, and commonly associated concepts. The frequency of how each second-tier variable is used across articles is analyzed. A summary list of indicators used to measure each second-tier variable is provided. Articles suggesting modifications to the framework are summarized and linked to the specific variables. The discussion reflects on the results and focuses on methodological challenges for applying the framework. First, how the SESF is historically related to commons and collective action research. This affects its continued development in relation to inclusion criteria for variable modification and discourse in the literature. The framework may evolve into separate modified versions for specific resource use sectors (e.g., forestry, fisheries, food production, etc.), and a general framework would aggregate the generalizable commonalities between them. Methodological challenges for applying the SESF are discussed related to research design, transparency, and cross-case comparison. These are referred to as "methodological gaps" that allow the framework to be malleable to context but create transparency, comparability, and data abstraction issues. These include the variable-definition gap, variable-indicator gap, the indicator-measurement gap, and the data transformation gap. A benefit of the framework has been its ability to be malleable and multipurpose, bringing a welcomed pluralism of methods, data, and associated concepts. However, pluralism creates challenges for synthesis, data comparison, and mutually agreed-upon methods for modifications. Databases are a promising direction forward to help solve this problem. In conclusion, future research is discussed by reflecting on the different ways the SESF may continue to be a useful tool through (1) being a general but adaptable framework, (2) enabling comparison, and (3) as a diagnostic tool for theory building.
Trophic cascade theory predicts that predator effects should extend to influence carbon cycling in ecosystems. Yet, there has been little empirical evidence in natural ecosystems to support this hypothesis. Here, we use a naturally-occurring trophic cascade to provide evidence that predators help protect sedimentary organic carbon stocks in coral reef ecosystems. Our results show that predation risk altered the behavior of herbivorous fish, whereby it constrained grazing to areas close to the refuge of the patch reefs. Macroalgae growing in “riskier” areas further away from the reef were released from grazing pressure, which subsequently promoted carbon accumulation in the sediments underlying the macroalgal beds. Here we found that carbon stocks furthest away from the reef edge were ~24% higher than stocks closest to the reef. Our results indicate that predators and herbivores play an important role in structuring carbon dynamics in a natural marine ecosystem, highlighting the need to conserve natural predator-prey dynamics to help maintain the crucial role of marine sediments in sequestering carbon.
We summarise current understanding of consumer recycling in lake nutrient cycles and expand on it by integrating emerging knowledge from food web ecology. The role of consumer nutrient recycling (CNR) is initially framed in the wider context of lake nutrient cycling, which includes hydrodynamic and biogeochemical processes, and their responses to global environmental change. Case studies are used to demonstrate that effects of CNR on lake ecosystems range widely, from reduced nutrient cycling rates to exacerbation of eutrophication. CNR depends on consumer biomass, body size and diet, remaining relatively consistent through the year and becoming important as other fluxes seasonally ebb. Universal patterns in food web structure, for example, consumer–resource biomass ratios, body size scaling and relationships between trophic level and diet breadth, are used to demonstrate the predictability of CNR effects. Larger, mobile, top predators excrete nutrients at a lower rate but over a wider range, linking nutrient cycles across habitats. Smaller-bodied, lower trophic level consumers have strong localised nutrient cycling effects associated with their limited mobility. Global environmental-change drivers that alter food web structure are likely to have the greatest impact on CNR rates and should direct future studies.
The availability of iron controls primary productivity in large areas of the Southern Ocean. Iron is largely supplied via atmospheric dust deposition, melting ice, the weathering of shelf sediments, upwelling, sediment resuspension, mixing (deep water, biogenic, and vertical mixing) and hydrothermal vents with varying degrees of temporal and spatial importance. However, large areas of the Southern Ocean are remote from these sources, leading to regions of low primary productivity. Recent studies suggest that recycling of iron by animals in the surface layer could enhance primary productivity in the Southern Ocean. The aim of this review is to provide a quantitative and qualitative assessment of the current literature on pelagic iron recycling by marine animals in the Southern Ocean and highlight the next steps forward in quantifying the retention and recycling of iron by higher trophic levels in the Southern Ocean. Phytoplankton utilize the iron in seawater to meet their metabolic demand. Through grazing, pelagic herbivores transfer the iron in phytoplankton cells into their body tissues and organs. Herbivores can recycle iron through inefficient feeding behavior that release iron into the water before ingestion, and through the release of fecal pellets. The iron stored within herbivores is transferred to higher trophic levels when they are consumed. When predators consume iron beyond their metabolic demand it is either excreted or defecated. Waste products from pelagic vertebrates can thus contain high concentrations of iron which may be in a form that is available to phytoplankton. Bioavailability of fecal iron for phytoplankton growth is influenced by a combination of the size of the fecal particle, presence of organic ligands, the oxidation state of the iron, as well as biological (e.g., remineralization, coprochaly, coprorhexy, and coprophagy) and physical (e.g., dissolution, fragmentation) processes that lead to the degradation and release of fecal iron. The flux of dissolved iron from pelagic recycling is comparable to other sources in the region such as atmospheric dust, vertical diffusivity, vertical flux, lateral flux and upwelling, but lower than sea ice, icebergs, sediment resuspension, and deep winter mixing. The temporal and seasonal importance of these various factors requires further examination.
Animal movements can facilitate important ecological processes, and wide-ranging marine predators, such as sharks, potentially contribute significantly towards nutrient transfer between habitats. We applied network theory to 4 years of acoustic telemetry data for grey reef sharks (Carcharhinus amblyrhynchos) at Palmyra, an unfished atoll, to assess their potential role in nutrient dynamics throughout this remote ecosystem. We evaluated the dynamics of habitat connectivity and used network metrics to quantify shark-mediated nutrient distribution. Predator movements were consistent within year, but differed between years and by sex. Females used higher numbers of routes throughout the system, distributing nutrients over a larger proportion of the atoll. Extrapolations of tagged sharks to the population level suggest that prey consumption and subsequent egestion leads to the heterogeneous deposition of 94.5 kg d−1 of nitrogen around the atoll, with approximately 86% of this probably derived from pelagic resources. These results suggest that sharks may contribute substantially to nutrient transfer from offshore waters to near-shore reefs, subsidies that are important for coral reef health.
Historic hunting has led to severe reductions of many marine mammal species across the globe. After hunting ceased, some populations have recovered to pre-exploitation levels, and may again act as a top-down regulatory force on marine ecosystems. Also the harbour seal population in the international Wadden Sea grew at an exponential rate following a ban on seal hunting in 1960's, and the current number ~38,000 is close to the historic population size. Here we estimate the impact of the harbour seal predation on the fish community in the Wadden Sea and nearby coastal waters. Fish remains in faecal samples and published estimates on the seal's daily energy requirement were used to estimate prey selection and the magnitude of seal consumption. Estimates on prey abundance were derived from demersal fish surveys, and fish growth was estimated using a Dynamic Energy Budget model. GPS tracking provided information on where seals most likely caught their prey. Harbour seals from the Dutch Wadden Sea fed predominantly on demersal fish, e.g. flatfish species (flounder, sole, plaice, dab), but also sandeel, cod and whiting. Total fish biomass in the Wadden Sea was insufficient to sustain the estimated prey consumption of the entire seal population year-round. This probably explains why seals also acquire prey further offshore in the adjacent North Sea, only spending 13% of their diving time in the Wadden Sea. Still, seal predation was estimated to cause an average annual mortality of 43% and 60% on fish in the Wadden Sea and adjacent coastal zone, respectively. There were however large sources of uncertainty in the estimate, including the migration of fish between the North Sea and Wadden Sea, and catchability estimates of the fish survey sampling gear, particularly for sandeel and other pelagic fish species. Our estimate suggested a considerable top-down control by harbour seals on demersal fish. However predation by seals may also alleviate density-dependent competition between the remaining fish, increasing fish growth, and partly compensating for the reduction in fish numbers. This study shows that recovering coastal marine mammal populations could potentially become an important component in the functioning of shallow coastal systems.
Prey responses to predation risk can affect multiple phenotypic traits that have significant implications for population‐to‐ecosystem‐level properties. The general stress paradigm (hereafter GSP ) proposes integrating the principles of ecological stoichiometry and prey physiological plasticity in response to predation risk to provide an explicit mechanistic framework to evaluate the direct influence of predation risk on ecosystem functioning.
However, theoretical attempts evaluating the GSP have focused on only one component of phenotypic plasticity, neglecting the fact that multiple phenotypic responses can affect nutrient demand and consumption, and therefore, the overall animal effect on nutrient cycling rates and stoichiometry.
In this study, we used a dynamic state variable model to examine how variation in predation and starvation risk on a landscape of patch types that vary in food quality affects the behavioural and physiological phenotypic responses of prey and the linked nutrient and carbon recycling.
We found that the stress imposed by predation risk promotes prey carbon limitation, which leads to increased nutrient release and carbon uptake due to a stoichiometric mismatch between an animal's demand and food stoichiometry. Such effects can be altered by prey shifting spatially to carbon‐ or nutrient‐rich patches. However, the abilities of prey to cope with new physiological demands can be affected by absolute stress level or the predation risk distribution on a spatially implicit landscape of stoichiometric‐divergent patch type availability. Overall, starvation risk can act as a selective force favouring individuals that maximize their growth, thus reducing their nutrient release, but increasing their exposure to predation risk.
Our results provide an important connection between predator‐induced stress ecology and ecosystem functioning, linking organism nutrition and ecological stoichiometry to fitness outcomes, thus improving our understanding of how non‐consumptive predator effects can scale up to ecosystems.
A plain language summary is available for this article.
More than half the fish in the sea
As the human population has grown in recent decades, our dependence on ocean-supplied protein has rapidly increased. Kroodsma et al. took advantage of the automatic identification system installed on all industrial fishing vessels to map and quantify fishing efforts across the world (see the Perspective by Poloczanska). More than half of the world's oceans are subject to industrial-scale harvest, spanning an area four times that covered by terrestrial agriculture. Furthermore, fishing efforts seem not to depend on economic or environmental drivers, but rather social and political schedules. Thus, more active measures will likely be needed to ensure sustainable use of ocean resources.
Science , this issue p. 904 ; see also p. 864
There have been significant efforts recently aimed at improving the aerodynamic performance of aerofoils through the modification of their surfaces. Inspired by the drag-reducing properties of the tooth-like denticles that cover the skin of sharks, we describe here experimental and simulation-based investigations into the aerodynamic effects of novel denticle-inspired designs placed along the suction side of an aerofoil. Through parametric modelling to query a wide range of different designs, we discovered a set of denticle-inspired surface structures that achieve simultaneous drag reduction and lift generation on an aerofoil, resulting in lift-to-drag ratio improvements comparable to the best-reported for traditional low-profile vortex generators and even outperforming these existing designs at low angles of attack with improvements of up to 323%. Such behaviour is enabled by two concurrent mechanisms: (i) a separation bubble in the denticle's wake altering the flow pressure distribution of the aerofoil to enhance suction and (ii) streamwise vortices that replenish momentum loss in the boundary layer due to skin friction. Our findings not only open new avenues for improved aerodynamic design, but also provide new perspective on the role of the complex and potentially multifunctional morphology of shark denticles for increased swimming efficiency.
Sharks are a diverse group of mobile predators that forage across varied spatial scales and have the potential to influence food web dynamics. The ecological consequences of recent declines in shark biomass may extend across broader geographic ranges if shark taxa display common behavioural traits. By tracking the original site of photosynthetic fixation of carbon atoms that were ultimately assimilated into muscle tissues of 5,394 sharks from 114 species, we identify globally consistent biogeographic traits in trophic interactions between sharks found in different habitats. We show that populations of shelf-dwelling sharks derive a substantial proportion of their carbon from regional pelagic sources, but contain individuals that forage within additional isotopically diverse local food webs, such as those supported by terrestrial plant sources, benthic production and macrophytes. In contrast, oceanic sharks seem to use carbon derived from between 30° and 50° of latitude. Global-scale compilations of stable isotope data combined with biogeochemical modelling generate hypotheses regarding animal behaviours that can be tested with other methodological approaches.
Lipid and fatty acid (FA) analysis is commonly used to describe the trophic ecology of an increasing number of taxa. However, the applicability of these analyses is contingent upon the collection and storage of sufficient high quality tissue, the limitations of which are previously unexplored in elasmobranchs. Using samples from 110 white sharks, Carcharodon carcharias, collected throughout Australia, we investigated the importance of tissue type, sample quantity, and quality for reliable lipid class and FA analysis. We determined that muscle and sub-dermal tissue contain distinct lipid class and FA profiles, and were not directly comparable. Muscle samples as small as 12 mg dry weight (49 mg wet weight), provided reliable and consistent FA profiles, while sub-dermal tissue samples of 40 mg dry weight (186 mg wet weight) or greater were required to yield consistent profiles. This validates the suitability of minimally invasive sampling methods such as punch biopsies. The integrity of FA profiles in muscle was compromised after 24 h at ambient temperature (~20°C), making these degraded samples unreliable for accurate determination of dietary sources, yet sub-dermal tissue retained stable FA profiles under the same conditions, suggesting it may be a more robust tissue for trophic ecology work with potentially degraded samples. However, muscle samples archived for up to 16 years in −20°C retain their FA profiles, highlighting that tissue from museum or private collections can yield valid insights into the trophic ecology of marine elasmobranchs.
Coral reefs are among Earth’s best-studied ecosystems, yet the degree to which large predators influence the ecology of coral reefs remains an open and contentious question. Recent studies indicate the consumptive effects of large reef predators are too diffuse to elicit trophic cascades. Here, we provide evidence that such predators can produce non-consumptive (fear) effects that flow through herbivores to shape the distribution of seaweed on a coral reef. This trophic cascade emerged because reef topography, tidal oscillations, and shark hunting behaviour interact to create predictable “hot spots” of fear on the reef where herbivores withhold feeding and seaweeds gain a spatial refuge. Thus, in risky habitats, sharks can exert strong ecological impacts even though they are trophic generalists that rarely feed. These findings contextualize the debate over whether predators influence coral reef structure and function and move us to ask not if, but under what specific conditions, they generate trophic cascades.
Reef sharks may influence the foraging behaviour of mesopredatory teleosts on coral reefs via both risk effects and competitive exclusion. We used a “natural experiment” to test the hypothesis that the loss of sharks on coral reefs can influence the diet and body condition of mesopredatory fishes by comparing two remote, atoll-like reef systems, the Rowley Shoals and the Scott Reefs, in northwestern Australia. The Rowley Shoals are a marine reserve where sharks are abundant, whereas at the Scott Reefs numbers of sharks have been reduced by centuries of targeted fishing. On reefs where sharks were rare, the gut contents of five species of mesopredatory teleosts largely contained fish while on reefs with abundant sharks, the same mesopredatory species consumed a larger proportion of benthic invertebrates. These measures of diet were correlated with changes in body condition, such that the condition of mesopredatory teleosts was significantly poorer on reefs with higher shark abundance. Condition was defined as body weight, height and width for a given length and also estimated via several indices of condition. Due to the nature of natural experiments, alternative explanations cannot be discounted. However, the results were consistent with the hypothesis that loss of sharks may influence the diet and condition of mesopredators and by association, their fecundity and trophic role. Regardless of the mechanism (risk effects, competitive release, or other), our findings suggest that overfishing of sharks has the potential to trigger trophic cascades on coral reefs and that further declines in shark populations globally should be prevented to protect ecosystem health.
Marine protected areas are being implemented at an accelerating pace, and hold promise for restoring damaged ecosystems. But glaring shortfalls in staffing and funding often lead to suboptimal outcomes.
In simple, linear food chains, top predators can have positive indirect effects on basal resources by causing changes in the traits (e.g. behaviour, feeding rates) of intermediate consumers. Although less is known about trait-mediated indirect interactions (TMIIs) in more complex food webs, it has been suggested that such complexity dampens trophic cascades. We examined TMIIs between a predatory crab (Carcinus maenas) and two ecologically important basal resources, fucoid algae (Ascophyllum nodosum) and barnacles (Semibalanus balanoides), which are consumed by herbivorous (Littorina littorea) and carnivorous (Nucella lapillus) snails, respectively. Because crab predation risk suppresses snail feeding rates, we hypothesized that crabs would also shape direct and indirect interactions among the multiple consumers and resources. We found that the magnitude of TMIIs between the crab and each resource depended on the suite of intermediate consumers present in the food web. Carnivorous snails (Nucella) transmitted TMIIs between crabs and barnacles. However, crab –algae TMIIs were transmitted by both herbivorous (Littorina) and carnivorous (Nucella) snails, and these TMIIs were additive. By causing Nucella to consume fewer barnacles, crab predation risk allowed fucoids that had settled on or between barnacles to remain in the community. Hence, positive interactions between barnacles and algae caused crab –algae TMIIs to be strongest when both consumers were present. Studies of TMIIs in more realistic, reticulate food webs will be necessary for a more complete understanding of how predation risk shapes community dynamics.
The harvest and consumption of wildlife are integral to the livelihood, culture, and nutritional status of the Inuit of northern Canada. When wildlife populations are perceived to be vulnerable, harvest restrictions may be enacted to protect species conservation interests. Such restrictions may also have consequences for the nutrition and food security of Inuit communities. This study aims to estimate the harvest numbers of key wildlife species needed to sustain the traditional diet of Inuit. Using responses to the food frequency questionnaire that were collected from 806 men and 1275 women during the Inuit Health Study of 2007 – 08, we characterized annual country food consumption in five Inuit regions of northern Canada. Data on average edible yield of food species and Inuit population demographics were compiled and used to estimate the total number of harvested animals. Caribou (Rangifer tarandus) was the species consumed with the highest prevalence (> 90%) and in greatest amounts (29.6 – 122.8 kg/person/yr), depending on sex and region. The annual consumption rate for beluga whale (Delphinapterus leucas) was 5.9 – 24.3 kg per person, depending on sex and region, and that for ringed seal (Pusa hispida) was 4.1 – 25.0 kg per person. To sustain this consumption rate, it is estimated that a mean total of 36 526 caribou, 898 beluga whales, and 17 465 ringed seals are required annually. These results provide a baseline for food security and resource management in the Canadian Arctic to balance Indigenous subsistence needs and wildlife conservation.
Significance
Whether environmental conditions, harvesting, or predation pressure primarily regulate an ecosystem is still a question of much debate in marine ecology. Using a wealth of historical records, we describe how climate and fishing interact in a complex marine ecosystem. Through an integrative evidence-based approach, we demonstrate that indirect effects are key to understanding the system. Planktivorous forage fish provide an important role in the system, linking bottom-up and top-down processes such that fishing can indirectly impact the plankton and environmental effects can cascade up to impact demersal fish and predatory seabirds. Cascading trophic interactions can be mediated by opposing bottom-up and top-down forces; this combination has the potential to avert regime wide shifts in community structure and functioning.
