Trophic Subsidies Research Articles

Trophic Biomarkers Indicate Coastal Surf Zone Hydrodynamics Affect Resource Assimilation by Mytilus californianus Mussels

Surf zone hydrodynamics influences the delivery of coastal phytoplankton and detritus food subsidies to shore. Variation in surf zone hydrodynamics can cause phytoplankton concentrations to be higher at dissipative than reflective surf zones, altering both the quantity and quality of food for intertidal suspension-feeders. To assess if surf zone-dependent food availability influences suspension-feeder diets, we out-planted Mytilus californianus mussels for a 5-month common garden experiment at sites with dissipative and reflective surf zones at Cape Arago, Oregon. Stable isotopes, gravimetric lipid weights, and fatty acid trophic biomarkers of extracted abductor muscles were used to examine possible diet differences between mussels grown at dissipative and reflective sites. Both δ15N‰ and δ13C‰ values varied significantly between dissipative and reflective surf zone types, but there was no difference in gravimetric lipid weight between surf zone types. The multivariate fatty acid composition of mussels from dissipative and reflective sites differed; mussels at dissipative sites had a higher proportion of fatty acids indicative of diatoms in their diet (e.g., 16:1ω7, 20:5ω3), whereas mussels at reflective sites had a higher proportion of fatty acids indicative of dinoflagellates (e.g., 22:6ω3). Aspects of our stable isotope and fatty acid data suggest trophic subsidies to mussels were influenced by surf zone hydrodynamics.

Winter bird gets the worm: consumption of earthworms (Lumbricidae) by striated caracaras (Phalcoboenus australis) in invasive Yorkshire fog (Holcus lanatus) in the Falkland Islands (Malvinas)

Biological invasions can drive ecosystem change and alter predator ecology by providing trophic subsidies that mitigate the effects of seasonally pulsed resources. Striated Caracaras (Phalcoboenus australis) are near threatened, non-migratory falconids who inhabit the southern coasts of South America and the Falkland Islands (Malvinas) and feed on seasonally migratory colonial seabirds. Here we report the first multi-day observation of caracaras foraging extensively for earthworms (Lumbricidae) and beetle larvae (Coleoptera) in introduced Yorkshire fog (Holcus lanatus) on New Island, Falkland Islands. Our results suggest that invertebrates may be a more important winter resource than previously thought, and that caracaras benefit indirectly from introduced grasses in the Falklands, a relationship that merits special consideration when identifying ecological restoration plans.

Evidence for long-term seamount-induced chlorophyll enhancements

Seamounts are ubiquitous global features often characterized by biological hotspots of diversity, biomass, and abundance, though the mechanisms responsible are poorly understood. One controversial explanation suggests seamount-induced chlorophyll enhancements (SICE) subsidize seamount ecosystems. Using a decade of satellite chlorophyll data, we report substantial long-term chlorophyll enhancements around 17% of Pacific seamounts and 45% of shallow (< 100 m) seamounts, with the highest probability of detection at shallow, low-latitude seamounts. SICE is shown to enhance chlorophyll concentrations by up to 56% relative to oceanic conditions, and SICE seamounts have two-fold higher fisheries catch relative to non-enhancing seamounts. Therefore, seamount-induced bottom-up trophic subsidies are not rare, occurring most often at shallow, heavily exploited seamounts, suggesting an important subset of seamounts experience fundamentally different trophic dynamics than previously thought.

Environmental factors influencing primary productivity of the forest-forming kelp Laminaria hyperborea in the northeast Atlantic

Rates and drivers of primary productivity are well understood for many terrestrial ecosystems, but remain poorly resolved for many marine ecosystems, particularly those within in coastal benthic environments. We quantified net primary productivity (NPP) using two methods as well as carbon standing stock within kelp forests (Laminaria hyperborea) at multiple subtidal habitats in the United Kingdom (UK). Study sites spanned 9° in latitude and encompassed a gradient in average temperature of ~ 2.5 °C. In addition to temperature, we measured other factors (e.g. light intensity, water motion, nutrients, sea urchin density) that may influence productivity. Although estimates of NPP were highly variable between sites, ranging from 166 to 738 g C m-2 yr-1, our study-wide average of 340 g C m-2 yr-1 indicated that L. hyperborea forests are highly productive. We observed clear differences between NPP and carbon standing stock between our cold northernmost sites and our warm southernmost sites, with NPP and standing stock being around 1.5 and 2.5 times greater in the northern sites, respectively. Ocean temperature was identified as a likely driver of productivity, with reduced NPP and standing stock observed in warmer waters. Light availability was also strongly linked with carbon accumulation and storage, with increased light levels positively correlated with NPP and standing stock. Across its geographical range, total NPP from L. hyperborea is estimated at ~ 7.61 Tg C yr-1. This biomass production is likely to be important for local food webs, as a trophic subsidy to distant habitats and for inshore carbon cycling and (potentially) carbon sequestration. However, given the strong links with temperature, continued ocean warming in the northeast Atlantic may reduce primary productivity of this foundation species, as optimal temperatures for growth and performance are surpassed.

Dietary fatty acids of spiders reveal spatial and temporal variations in aquatic-terrestrial linkages

Stream and riparian food webs can be strongly linked by inputs of aquatic emergent insect prey to terrestrial predators. However, quantifying these linkages and understanding how they vary in time and space is challenging. We investigated the dynamic width of a riverine trophic subsidy zone by determining the relationship between perpendicular distance from a river and dietary contributions of aquatic insect prey to web-building spiders' diets. To assess this relationship, riparian web-building spiders at two river sites were sampled during four seasons and analysed for the fatty acids 16:0, 16:1ω7 and 20:5ω3, their total ω3-fatty acid content and their ω3:ω6 ratio to evaluate trophic subsidies reaching them from an adjacent river. River-derived fatty acids generally declined with increased distance from the river, indicating a diffusion of aquatically derived subsidies into the riparian zone. While the river was only 16 m wide at its broadest, river-derived trophic subsidies were detected up to four times that distance from the river edge. Spiders at a downstream section of the river, characterised by generally higher emergence rates of aquatic insects, contained higher proportions of aquatic indicator fatty acids compared with spiders located upstream, where emergence rates were lower. Similarly, proportions of aquatic indicator fatty acids in spiders were lowest during winter when aquatic insect emergence rates were lowest. The fatty acid 20:5ω3 (eicosapentaenoic acid; EPA) held the best promise as a biomarker of aquatic-derived tropic subsidies and could be developed as a useful tool for riparian research and management.

Freshwater Inflow Variability Affects the Relative Importance of Allochthonous Sources for Estuarine Fishes

Estuaries are influenced by seasonal and inter-annual variability in marine and freshwater intrusion. This variability affects the abundance and distribution of resources and consumers and may drive estuarine food web dynamics. This study tests for relationships among environmental variables and estuarine consumer δ13C, and assesses whether freshwater-derived sources increase in relative contribution to estuarine consumers during high freshwater inflow events. Data were collected seasonally from 2010 through 2016 for Patos Lagoon, Brazil, and included rainfall and river discharge in the drainage basin, and salinity, chlorophyll-α, and phytoplankton abundance in the estuarine zone of the lagoon. Similarly, stable isotope data (δ13C, δ15N) were collected seasonally for autochthonous sources and consumers (detritivorous and zooplanktivorous fishes) in the estuarine zone, and allochthonous sources of freshwater and marine origin. Mixed-effect models assessed relationships among consumer δ13C and environmental variables, and Bayesian mixing models (MixSIAR) estimated the relative importance of autochthonous and allochthonous sources for estuarine consumers. Hydrology affected estuarine consumer δ13C, corresponding to greater contributions of marine-derived organic material during periods with high freshwater inflow, especially for detritivorous juvenile mullet. This unexpected finding is likely due to high freshwater inflows delaying recruitment of juvenile mullet from coastal areas into the estuarine zone such that data from seasonal sampling reflected marine rather than local feeding and active transport of marine-derived sources into the estuarine zone. In addition to transporting freshwater-derived organic material, high freshwater inflow events may have other important indirect effects on the dynamics of trophic subsidies to estuarine food webs which require further study.

Maladapted Prey Subsidize Predators and Facilitate Range Expansion.

Dispersal of prey from predator-free patches frequently supplies a trophic subsidy to predators by providing more prey than are produced locally. Prey arriving from predator-free patches might also have evolved weaker defenses against predators and thus enhance trophic subsidies by providing easily captured prey. Using local models assuming a linear or accelerating trade-off between defense and population growth rate, we demonstrate that immigration of undefended prey increased predator abundances and decreased defended prey through eco-evolutionary apparent competition. In individual-based models with spatial structure, explicit genetics, and gene flow along an environmental gradient, prey became maladapted to predators at the predator's range edge, and greater gene flow enhanced this maladaptation. The predator gained a subsidy from these easily captured prey, which enhanced its abundance, facilitated its persistence in marginal habitats, extended its range extent, and enhanced range shifts during environmental changes, such as climate change. Once the predator expanded, prey adapted to it and the advantage disappeared, resulting in an elastic predator range margin driven by eco-evolutionary dynamics. Overall, the results indicate a need to consider gene flow-induced maladaptation and species interactions as mutual forces that frequently determine ecological and evolutionary dynamics and patterns in nature.

Nearshore seascape connectivity enhances seagrass meadow nursery function.

Diverse habitats composing coastal seascapes occur in close proximity, connected by the flux of materials and fauna across habitat boundaries. Understanding how seascape connectivity alters important ecosystem functions for fish, however, is not well established. For a seagrass-dominant seascape, we predicted that configuration and composition of adjacent habitats would alter habitat access for fauna and trophic subsidies, enhancing nursery function for juvenile fish. In an extensive Zostera marina seagrass meadow, we established sites adjacent to (1) highly complex and productive kelp forests (Nereocystis luetkeana), (2) unvegetated sand habitats, and (3) in the seagrass meadow interior. Using SCUBA, we conducted underwater observations of young-of the-year (YOY) rockfish (Sebastes spp.) recruitment across sites. Using generalized linear mixed effects models, we assessed the role of seascape adjacency relative to seagrass provisions (habitat complexity and prey) on YOY recruitment. YOY rockfish collections were used to trace sources of allochthonous vs. autochthonous primary production in the seagrass food web, via a δ13 C and δ15 N isotopic mixing model, and prey consumption using stomach contents. Overall, seagrass nursery function was strongly influenced by adjacent habitats and associated subsidies. Allochthonous N.luetkeana was the greatest source of energy assimilated by YOY rockfish within seagrass sites. In seagrass sites adjacent to N.luetkeana kelp forests, YOYs consumed higher quality prey, which corresponded with better body condition relative to sites adjacent to sand. Moreover, kelp forest adjacency enhanced YOY rockfish recruitment within the seagrass meadow, suggesting that habitat complexity is a key seascape feature influencing the nursery function of nearshore habitats. In general, to promote seascape connectivity, the conservation and restoration of nursery habitats should prioritize the inclusion of habitat mosaics of high structural complexity and productivity. We illustrate and emphasize the importance of using a seascape-level approach that considers linkages among habitats for the management of important nearshore ecosystem functions.

Trophic ecology of ghost crabs with diverse tastes: Unwilling vegetarians

Food webs on ocean-exposed sandy beaches are almost entirely underpinned by trophic subsidies from the sea. Ghost crabs (Ocypode spp.), which are highly mobile invertebrate consumers that display a diversity of feeding modes, form an important consumer on numerous beaches around the world. However, little is known of their trophic structure and the role they play as vectors for spatial subsidies through movement of marine derived nutrients inland. The aim of this study was to determine the trophic ecology of the Golden ghost crab (Ocypode convexa) and understand what its role is in terms of marine connectivity along the mid-west coastline of Australia. Based on stomach content (percentage frequency (%F) and percentage volume (%V)) and stable isotope analyses (mixing models using ẟ13C and ẟ15N), the dietary composition of O. convexa was typically dominated by brown algae, and complemented by marine and terrestrial vascular plants and arthropods (various insects and amphipods). However, feeding assays revealed that the species had a clear preference for fish and invertebrate carcasses when the choice was offered, indicating a proclivity for the more nutritionally valuable animal flesh when available. Thus, ghost crabs are likely to be unenthusiastic consumers of vegetables, and are likely to feed on algae and macrophyte matter only when animal carrion or live animal prey is sparse. Consistent intake and assimilation of marine matter by ghost crabs, and their likely predation by higher level consumers, such as foxes (e.g. Vulpes vulpes) and birds (e.g. Corvus coronoides), support the concept that they form a vector for cross-boundary fluxes of marine carbon to inland ecosystems, although it needs to be recognized that ghost crabs also derive part of their nutritional requirements from terrestrial sources.

Isotopic Variation of Macroinvertebrates and Their Sources of Organic Matter Along an Estuarine Gradient

Spatiotemporal patterns in the basal resources fueling the macrobenthic food web of a temperate coastal embayment subject to a low-turbidity riverine discharge (Gwangyang Bay, Korea) were evaluated using carbon and nitrogen stable isotopes. This study examined trophic links of macrobenthic food web with primary production in diverse wetland habitats along the riverine–estuarine–coastal marine continuum. δ13C and δ15N values of macrobenthic assemblages collected along the salinity gradient of the main channel and their putative sources of organic matter (i.e., riverine particulate organic matter (RPOM), Phragmites australis, microphytobenthos (MPB), phytoplankton, and Zostera marina) were determined. A permutational analysis of variance test showed seasonal uniformity in the isotopic niches of the macrobenthic community within different channel locations. In contrast, isotopic nestedness calculated for the microbenthic community emphasized clearly different trends in its isotopic niches among locations. The δ13C values of phytoplankton, suspended and sedimentary organic matter, and macrobenthic community displayed a consistently positive relationship with salinity, characterizing an important contribution of local phytoplankton to the nutrition of macrobenthic community. The isotope mixing model revealed that Phragmites-derived organic matter contributed considerably to the nutrition in the estuarine channel, whereas MPB and Zostera provided trophic subsidies to the deep bay and offshore communities. The nutritional importance of RPOM was minimal at all sites. Overall results suggest that phytoplankton production is a major nutritional contributor to the macrobenthic community in the main channel and that trapping POM originated from neighboring wetlands leads to a longitudinal isotopic niche shift in the macrobenthic community.

Influences of angler subsidies on the trophic ecology of European barbel Barbus barbus

European barbel Barbus barbus is a recreationally important riverine fish that is widely introduced outside of its natural range. Contemporary angling practises for B. barbus involve the use of baits based on marine fishmeal (MF). MF is isotopically distinct from freshwater prey via highly enriched δ13C and thus its dietary influence on B. barbus can be tested via differences in fractionation factors (Δ13C). Correspondingly, stable isotope data from 11 riverine B. barbus populations tested how their trophic ecology varied across populations according to MF from angling. Δ13C of fish with macroinvertebrate prey resources varied within and between populations (range 0.90–10.13‰) and indicated that, within populations, up to 71% of B. barbus had relatively high dietary contributions of MF. These contributions were significantly and positively related to fish length, with MF influences increasingly apparent as fish length increased. Population isotopic niche sizes increased as the dietary influence of MF in that population increased. These results indicated that whilst MF from angling can act as a strong trophic subsidy, its influence varies spatially and with fish length, with its use as a food resource by B. barbus generally involving dietary specializations of larger-bodied individuals.

Coastal marine ecosystem connectivity: pelagic ocean to kelp forest subsidies

AbstractThe movement of trophic resources between and among ecosystems, referred to as cross‐ecosystem subsidies, is a common phenomenon. In the marine environment, both adjacent and distant ecosystems are connected by oceanographic forces that transport nutrients, organisms, and other materials. Kelp forest ecosystems are one example of an open marine system that both exports and receives trophic subsidies. Though rocky reefs are rich in kelp‐based energy produced internally, kelp forest organisms also rely on phytoplankton, and the influx of holoplankton and meroplankton from adjacent open ocean habitats. In this paper, we seek to clarify the identity of holoplanktonic and meroplanktonic subsidies, quantify their energetic and nutrient contributions to the kelp forest, and further explore the impacts of these subsidies for individual consumers and for kelp forest communities. We reviewed six individual subsidy organisms that are commonly advected to kelp forests on the West coast of North America, and show that these organisms from the pelagic ocean represent important resource pulses for kelp forest consumers. In addition, we summarize the characteristics of subsidies, consumers, and recipient ecosystems that provide insight into the dynamics of subsidy influx and impacts to recipient systems. Finally, we provide suggestions as scientists move forward with efforts to quantify the impacts of cross‐ecosystem subsidies. Trophic subsidies are a major force shaping both marine and terrestrial communities and ecosystems. Quantitative information about these subsidies and their impacts on food webs will not only improve our understanding of these ecosystems, but also improve food web models, and predictions of ecosystem response to change.

Grazers extend blue carbon transfer by slowing sinking speeds of kelp detritus

Marine plant communities such as kelp forests produce significant amounts of detritus, most of which is exported to areas where it can constitute an important trophic subsidy or potentially be sequestered in marine sediments. Knowing the vertical transport speed of detrital particles is critical to understanding the potential magnitude and spatial extent of these linkages. We measured sinking speeds for Laminaria hyperborea detritus ranging from whole plants to small fragments and sea urchin faecal pellets, capturing the entire range of particulate organic matter produced by kelp forests. Under typical current conditions, we determined that this organic material can be transported 10 s of m to 10 s of km. We show how the conversion of kelp fragments to sea urchin faeces, one of the most pervasive processes in kelp forests globally, increases the dispersal potential of detritus by 1 to 2 orders of magnitude. Kelp detritus sinking speeds were also faster than equivalent phytoplankton, highlighting its potential for rapid delivery of carbon to deep areas. Our findings support arguments for a significant contribution from kelp forests to subsidizing deep sea communities and the global carbon sink.

Connectivity increases trophic subsidies in fragmented landscapes

Landscape corridors mitigate the negative effects of habitat fragmentation by increasing dispersal. Corridors also increase biodiversity in connected habitat fragments, suggestive of metacommunity dynamics. What is unknown in this case is the mechanisms through which metacommunity dynamics act. Working in a large-scale fragmentation experiment, we tested the effect of corridors on the movement of prey species and subsequent effects on predator nutrition (which we call trophic subsidies). We enriched plants of central patches with 15 N, then measured δ15 N in green lynx spiders, the most abundant insect predator, in patches that were either connected to or isolated from the enriched patch. We found that corridors increased prey movement, as they increased spider δ15 N by 40% in connected patches. Corridors also improved spider body condition, increasing nitrogen relative to carbon. We suggest a novel mechanism, trophic subsidies, through which corridors may increase the stability or size of populations in connected landscapes.

Aquaculture-derived trophic subsidy boosts populations of an ecosystem engineer

Environmental management of coastal aquaculture is focused on acute impacts of organic and nitrogenous wastes close to farms. However, the energy-rich trophic subsidy that aquaculture provides may create cascades with influences over broader spatial scales. In a fjord region with intensive fish farming, we tested whether an ecosystem engineer, the white urchin Gracilechinus acutus, was more abundant at aquaculture sites than control sites. Further, we tested whether diets influenced by aquaculture waste altered reproductive outputs compared with natural diets. Urchins formed barrens at aquaculture sites where they were 10 times more abundant (38 urchins m-2) than at control sites (4 urchins m-2). Urchins were on average 15 mm larger at control sites. In the laboratory, urchins fed aquafeed diets had 3 times larger gonad indices than urchins fed a natural diet. However, their reproduction was compromised. Eggs from females fed an aquafeed diet had 13% lower fertilisation success and 30% lower larval survival rates at 10 d compared with females fed a natural diet. A reproductive output model showed that enhanced numbers of 10 d old larvae produced by the dense aquaculture-associated aggregations of G. acutus will supersede any detrimental effects on reproduction, with larval outputs from aquaculture sites being on average 5 times greater than control sites. The results show that aquaculture waste can act as a trophic subsidy in fjord ecosystems, stimulating aggregations of urchins and promoting the formation of urchin barrens. Where finfish aquaculture is concentrated, combined effects on the wider environment may produce ecosystem-level consequences.

Living on a trophic subsidy: Algal quality drives an upper-shore herbivore's consumption, preference and absorption but not growth rates.

The transfer of seaweeds from subtidal bottoms to nearby intertidal rocky shores is a common but often overlooked phenomenon. Freshly detached seaweeds often represent critical trophic subsidies for herbivores living in upper-shore rocky intertidal areas, such as the marine snail Diloma nigerrima. This species relies on three species of seaweeds for food and displays feeding strategies to deal with a resource that is scarce and at times unpredictable. This study focused on the nutritional quality of freshly detached algae (Durvillaea antarctica, Lessonia spicata and Lessonia trabeculata) and measured Diloma nigerrima’s algal consumption rates in trials with and without choice. Absorption efficiency and growth of individual snails fed on each alga were also measured. Durvillaea antarctica had the highest nutritional quality and was the most consumed algae in both single and multiple-choice trials. Absorption efficiency was also highest for D. antarctica but growth rates of snails fed with this species were similar to those fed with the other algae. Combined, these results suggest that D. nigerrima has the ability to discriminate among seaweeds based on their nutritional quality. A potential increase in oxygen uptake when D. nigerrima is consuming the preferred food item is also proposed as a plausible hypothesis to explain the mismatch between snails’ preference and growth rate. These results aim to guide further studies on trophic subsidies and their role in coastal systems.

Fish presence and inter‐patch connectivity interactively alter the size of emergent insects in experimental enclosures

AbstractStructural habitat complexity (SHC) and functional habitat connectivity (FHC) are the basic components that make up the physical architecture of an ecosystem, and can have substantial impacts on predator–prey interactions. These structural components influence animal behaviors such as inter‐patch movement, foraging, and competition, and can impact community structure/dynamics in terrestrial and aquatic ecosystems. The effects of SHC and FHC on predator–prey dynamics within an ecosystem may also have important cascading effects on neighboring ecosystems by altering the movement of individuals across ecosystem boundaries. For example, when aquatic insects emerge as adults, they enter terrestrial ecosystems where they become an important food resource for terrestrial predators. Using a multiple patch, predator enclosure design in ponds, we tested whether altering intra‐patch plant stem densities (SHC) and inter‐patch distances (FHC) would influence the impact a predatory fish has on the biomass, quality, and trophic composition of emergent insects. As expected, fish significantly reduced emergent insect biomass (33% ± 7.6, mean ± SE). Intra‐patch stem densities (SHC) did not significantly alter fish effects; however, inter‐patch distance (FHC) did significantly alter the impact of fish on the size of some emergent insects. Damselflies that emerged in treatments with fish present and shorter inter‐patch distances were significantly larger, 4.1 ± 0.1 mg/m2 compared to 3.3 mg/m2 ± 0.1 in the long/fish treatments. In fish treatments, this effect on damselfly size resulted in greater reductions in total emergent insect biomass in long inter‐patch distance treatments (47.3% ± 6.9) compared to short inter‐patch distance treatments (20.5% ± 12.4). Our results suggest that physical components of a habitat, such as inter‐patch distances, have important impacts on predator–prey dynamics within habitats. These altered predator–prey dynamics can then have cascading effects on adjacent habitats by influencing the abundance, trophic composition, and quality of exported trophic subsidies.

Trophic ecology of glass sponge reefs in the Strait of Georgia, British Columbia

Sponges link the microbial loop with benthic communities by feeding on bacteria. Glass sponge reefs on the continental shelf of western Canada have extremely high grazing rates, consuming seven times more particulate carbon than can be supplied by vertical flux alone. Unlike many sponges, the reef building species Aphrocallistes vastus has no microbial symbionts and removes little dissolved organic carbon. To determine how reef sponges therefore get enough food to sustain such substantial grazing we measured stable carbon and nitrogen isotope signatures of water, sediment and sponge tissues. To ensure samples were temporally associated, we also studied the duration particles were retained in tissues in controlled feeding studies using microscopic beads and 13C-labeled bacteria. Although fecal pellets were expelled from sponges within 24 hours of feeding, intact bacteria were still found in tissues and sponge tissues retained elevated 13C levels for at least 14 days. These independent lines of evidence suggest that carbon in reef sponge tissues may reflect food consumed from days to weeks earlier. Stable isotope analysis suggests that heterotrophic bacteria ingested by the sponges comes from a confluence of trophic subsidies: from terrestrial and oceanic sources, and also potentially on sediment-borne bacteria resuspended by tidal currents.

Global significance of seagrass fishery activity

AbstractSeagrass meadows support fisheries through provision of nursery areas and trophic subsidies to adjacent habitats. As shallow coastal habitats, they also provide key fishing grounds; however, the nature and extent of such exploitation are poorly understood. These productive meadows are being degraded globally at rapid rates. For degradation to cease, there needs to be better appreciation for the value of these habitats in supporting global fisheries. Here, we provide the first global scale study demonstrating the extent, importance and nature of fisheries exploitation of seagrass meadows. Due to a paucity of available data, the study used a global expert survey to demonstrate the widespread significance of seagrass‐based fishing activity. Our study finds that seagrass‐based fisheries are globally important and present virtually wherever seagrass exists, supporting subsistence, commercial and recreational activity. A wide range of fishing methods and gear is used reflecting the spatial distribution patterns of seagrass meadows, and their depth ranges from intertidal (accessible by foot) to relatively deep water (where commercial trawls can operate). Seagrass meadows are multispecies fishing grounds targeted by fishers for any fish or invertebrate species that can be eaten, sold or used as bait. In the coastal communities of developing countries, the importance of the nearshore seagrass fishery for livelihoods and well‐being is irrefutable. In developed countries, the seagrass fishery is often recreational and/or more target species specific. Regardless of location, this study is the first to highlight collectively the indiscriminate nature and global scale of seagrass fisheries and the diversity of exploitative methods employed to extract seagrass‐associated resources. Evidence presented emphasizes the need for targeted management to support continued viability of seagrass meadows as a global ecosystem service provider.

Biphasic predators provide biomass subsidies in small freshwater habitats: A case study of spring and cave pools

Summary There is increasing attention on how biomass exchanges determine linkages between ecosystems. However, there is limited information on the factors determining the direction and overall magnitude of energy flow, especially in systems where primary producers are limited. In this study we compared two aquatic ecosystems (cave and spring pools) using the biomass exchanges driven by a biphasic predator, the fire salamander (Salamandra salamandra). Between 2013 and 2014, we monitored 21 fire salamander breeding sites (12 cave pools and 9 spring pools) and we quantified the larval biomass input–export. The balance between input and export was related to different abiotic and biotic variables. Salamandra salamandra larvae constituted a major component of the animal biomass in both cave and spring pools, and were the most abundant top predator. Light was the most important parameter in constraining predator biomass; biomass export was lowest in the sites that received less light. In cave pools, the biomass balance was negative, while it was positive in spring pools. Our study demonstrates that cave pools are a system with much lower productivity than springs, and their functioning strongly depends on the input of external resources. Predator occurrence may constitute a major trophic subsidy in poorly productive environments. Gradients of abiotic variables such as light incidence can constrain population size of predators and determine a large variation in their biomass balance.