Pelagic Resources Research Articles

Dissolved Organic Carbon Reduces Habitat Coupling by Top Predators in Lake Ecosystems

Increasing input of terrestrial dissolved organic carbon (DOC) has been identified as a widespread environmental phenomenon in many aquatic ecosystems. Terrestrial DOC influences basal trophic levels: it can subsidize pelagic bacterial production and impede benthic primary production via light attenuation. However, little is known about the impacts of elevated DOC concentrations on higher trophic levels, especially on top consumers. Here, we used Eurasian perch (Perca fluviatilis) to investigate the effects of increasing DOC concentrations on top predator populations. We applied stable isotope analysis and geometric morphometrics to estimate long-term resource and habitat utilization of perch. Habitat coupling, the ability to exploit littoral and pelagic resources, strongly decreased with increasing DOC concentrations due to a shift toward feeding predominantly on pelagic resources. Simultaneously, resource use and body morphology became increasingly alike for littoral and pelagic perch populations with increasing DOC, suggesting more intense competition in lakes with high DOC. Eye size of perch increased with increasing DOC concentrations, likely as a result of deteriorating visual conditions, suggesting a sensory response to environmental change. Increasing input of DOC to aquatic ecosystems is a common result of environmental change and might affect top predator populations in multiple and complex ways.

The trophic niche of Arctic charr in large southern Scandinavian lakes is determined by fish community and lake morphometry

The influence of interspecific interactions and habitat characteristics on the ecological niche of species’ populations is a controversial issue in ecology. We explored the niche use of Arctic charr (Salvelinus alpinus L.) in seven relatively large and deep lakes in southern Norway. We aimed to investigate how the presence of potentially competitive fish species, such as whitefish (Coregonus lavaretus L.), perch (Perca fluviatilis L.) and brown trout (Salmo trutta L.), and the lake morphometry affects the littoral reliance and niche breadth of Arctic charr. Stable isotope (δ13C and δ15N) analyses showed that Arctic charr relied less on littoral food resources than brown trout and perch but had largely overlapping niche with whitefish. Arctic charr showed narrower niche use (i.e. less individual variation in δ13C and δ15N) than the other fish species in all seven lakes, particularly in communities where both littoral and pelagic competitors were present. Our results demonstrate that Arctic charr rely much less on littoral resources (<50%) in large and deep lakes in southern Scandinavia than in small, shallower subarctic lakes, and that interspecific interactions with both littoral and pelagic resource competitors can lead to niche compression of this generalist salmonid fish.

Ecological clustering within a diverse minnow assemblage according to morphological, dietary and isotopic data

Summary The ecological role of an organism is a complex interaction between many factors, such as morphology, behaviour and physiology, which can act as functional constraints upon how an organism engages with the environment. We examined the ecological roles, guild structure and ecological convergence among 15 sympatric minnow species (Cyprinidae) in the New River (North Carolina, U.S.A.). Minnows often dominate fish species diversity and biomass in North American streams. We evaluated the ecological relationships among minnows using popular methods that correspond to different aspects of minnow biology: geometric morphometrics (landmark‐based PCA), gut content analysis and stable isotopes (13C, 15N, 2H). We then tested for clustering (i.e. guilds) and convergence among minnows using these traits. Important shape variation among species was primarily associated with mouth orientation and caudal peduncle morphology, implicating the importance of trophic and activity patterns. Minnows clustered into five guilds based on body shape. Gut contents revealed three discrete guilds: pelagic‐ and benthic‐oriented invertivory and benthic herbivory. Stable isotopes revealed only two discrete guilds: algivory and invertivory; however, all minnows preferentially assimilated invertebrates. Minnows thus exhibit dynamic ecologies based largely on utilisation of the benthic–pelagic resource axis.

Human dietary assessment in the Pre-colonial Lesser Antilles: New stable isotope evidence from Lavoutte, Saint Lucia

Dietary assessment of Late Ceramic Age inhabitants (~AD 1200–1500) from Lavoutte, Saint Lucia, Lesser Antilles was undertaken on human skeletal remains using stable carbon and nitrogen isotope analysis of bone collagen (δ13Cco and δ15N), and bone and enamel bioapatite (δ13Cap and δ13Cen). The isotope data were interpreted in the context of regional food webs, intra-population dietary variation was assessed relative to individual demographic variables and the results were compared to contemporaneous populations at multiple scales. Moderately enriched δ13Cco and elevated δ15N point to substantial contributions from both non-marine and marine protein sources, including nitrogen-enriched pelagic resources. The lack of correlations between δ13Cco and δ13Cap (or δ13Cen) suggests distinct isotopic differences between protein and energy sources. The smaller range and variance of δ13Cco and δ15N values relative to δ13Cap and ∆13Cap-co indicate greater inter-individual heterogeneity in dietary energy sources relative to protein sources. Intra-population dietary variation was not, however, correlated with either age or sex, consistent with communal-based food consumption practices. From a broader perspective, the collagen isotope results are comparable with several islands in the Lesser Antilles but are distinct from others, indicating a large degree of regional variation in dietary protein sources, while the bone (and enamel) apatite results are more variable and overlap with many islands in both the Greater and Lesser Antilles indicating wider variation in average (whole) diets. The relative enrichment in δ13Cap and higher ∆13Cap-co values are strongly indicative that C4 (e.g., maize) or CAM plants were important dietary components. Overall, the isotopic evidence suggests that the Lavoutte population consumed mixed diets including substantial contributions of both C3 and C4/CAM plant resources, as well as terrestrial and marine protein sources.

Effects of water clarity and other environmental factors on trophic niches of two sympatric piscivores

Summary Water clarity can have a profound influence on aquatic ecosystem structure and processes via its effects on physical habitat (e.g., thermal regime, macrophyte density) and behavioural responses of biota (e.g., predator avoidance, reaction distances, foraging efficiency). Changes in foraging efficiencies under varying water clarity conditions are well documented for many freshwater piscivores in laboratory studies, but the influence of visual foraging conditions on interspecific trophic dynamics is poorly understood in wild populations, especially within water clarity ranges that are realistic for north‐temperate boreal lakes. Here, we used stable isotopes of nitrogen (15N/14N) and carbon (13C/12C) in fish muscle tissue to investigate how resource partitioning between two sympatric visual piscivores is related to water clarity and other habitat variables in 28 small (100–200 ha) Boreal Shield lakes. One of the species is adapted for foraging in low subsurface illumination (walleye, Sander vitreus) and the other in high subsurface illumination (smallmouth bass, Micropterus dolomieu). Trophic niche dimensions of the dark‐adapted predator did not respond significantly to differences in water clarity. In contrast, total isotopic niche space of the light‐adapted predator decreased significantly with increasing water clarity through greater use of pelagic resources and a narrower range of trophic levels, although these relationships were weak. Niche overlap ranged from 0 to 65%, but was not significantly related to water clarity. Rather, indices of prey availability appeared to be much stronger predictors of trophic interactions. Both species occupied more similar food‐web positions when yellow perch (Perca flavescens) abundance was higher, and had more similar niche size and trophic evenness with decreasing prey fish species richness. Results indicate that the trophic ecology of predators adapted to foraging in low light conditions is less influenced by water clarity than that of predators adapted to foraging in high light conditions. However, prey availability, rather than the environmental conditions in which foraging occurs, may be a more important driver of resource partitioning among generalists even when light conditions favour one species’ foraging strategy over another.

Seasonal depletion of resources intensifies trophic interactions in subarctic freshwater fish communities

Summary Climate change in recent decades has resulted in an increase in both the density and diversity of consumers in subarctic freshwater ecosystems. Despite this, harsh winter conditions in the region limit productivity and may serve as a bottleneck driving trophic interactions within the fish community, potentially determining the outcome of climate change for resident biota. However, due to the difficulties in sampling during winter months, few studies have assessed seasonal variation in the ecological interactions between native and range‐expanding species in subarctic regions. We examined seasonal variation in activity, diet (stomach content) and resource use (δ13C and δ15N stable isotope ratios) of two fishes: the resident cold‐water‐adapted European whitefish (Coregonus lavaretus L.) and the range‐expanding cool‐water‐adapted ruffe (Gymnocephalus cernua L.) in lakes with low and high consumer density. Results were contrasted with seasonal availability of benthic and pelagic resources and indirect measures of individual fitness, that is condition, growth and estimated lipid content (muscle elemental C : N ratio) of both species. The effects of fish density were apparent in both the diet and resource use of whitefish, which altered their diet and displayed reduced stomach fullness during winter in high‐density lakes. This was associated with an overall reduction in whitefish growth, condition and estimated lipid content in high‐density lakes, which was especially pronounced during winter. Ruffe utilised a greater proportion of profundal resources than whitefish in both summer and winter, potentially exploiting a vacant niche. Ruffe maintained condition and lipid reserves throughout the winter, highlighting the potential for further northward range expansion of the species. Winter acts as a seasonal bottleneck in subarctic lakes, but assumptions that this bottleneck primarily selects against warmer‐water‐adapted invasive species such as ruffe may be too restrictive. The effects of seasonal resource depletion on fish condition and invertebrate density were most severe in lakes with a high density of fish, and in these conditions, the cold‐water‐adapted resident whitefish was most adversely affected.

Modelling the strategy of mid-water trawlers targeting small pelagic fish in the Adriatic Sea and its drivers

Mid-water pair trawling (PTM) targeting small pelagic resources represents a key fishing activity in the Adriatic Sea. This fishery is experiencing a long period of crisis due to resource depletion and the lack of appropriate market strategies, and vessels spend most of the time searching for fishing schools. The searching strategy largely depends on the interaction between vessels: the captains of the PTM units take their decision also checking the position and the fishing status of other vessels. Understanding this strategy represents a key step towards a more effective resource management, since strategies directly determine the pattern of fishing effort. A Conditional Logit model has been devised to analyze fishermen's strategy as a non-cooperative game. This category of games is characterized by the existence of (at least) one equilibrium point – a Nash Equilibrium – in which each player plays his strategy, that is a Best Response to the strategies of the other players. This equilibrium point was estimated for the different scenarios defined by environmental (sea surface temperature and atmospheric pressure) and economic (fuel and fish prices at market) variables. Vessel Monitoring System data were used to capture fleet activity, while different datasets were collected to reconstruct environmental and economic drivers. Results indicate a good predictive power of the model, and suggest that the equilibrium strategy that guides units’ behaviour is invariant with respect to environmental conditions, whereas it is largely influenced by economic factors. These latter, via strategies, may determine important consequences on the resources in terms of exploited areas and the impact of fishing activity. In particular, a low fuel price when fish price is high leads to higher values of CPUE, and then to a more efficient but also impacting fishing activity.

Fishery management, development and food security in the Western and Central Pacific in the context of climate change

In the coming decades, fishery resource managers and policy-makers in Pacific Island countries and territories (PICTs) will be increasingly challenged by the need to ensure food security in the context of a changing climate, increasing human pressure on the marine environment, and limited understanding of marine ecosystems and associated resources. These decision-makers must address a pressing and overarching question – how will pelagic resources and pressures on such resources change over time and space? Answering this question requires ongoing inquiry into critical dimensions of pelagic species and systems, for both the commercial tuna species that are managed by Regional Fishery Management Organizations (RFMOs), as well as nearshore pelagic fishes that support many small-scale fisheries and are managed at national and local levels. Research priorities include generating further insight into life history and physiology, oceanographic context, movement and migration, food webs, ecosystem dynamics and stock status. Concurrently, socioeconomic research is needed to tailor fisheries management strategies to local, national and regional conditions; and improve understanding of incentive structures among players in RFMOs such as the Western and Central Pacific Fisheries Commission. PICT-based scientists and managers are ideally situated to generate new fisheries-relevant data; however, investments are needed to expand the capacity for research, management, and sustainable fisheries development within PICTs. Such capacity building can be accelerated through collaboration between PICTs, RFMOs, and scientific centers of excellence in Distant Water Fishing Nations. Without increased capacity development, this region will be adversely affected by the impacts of climate change and less able to take advantage of opportunities for economic development.

Stable isotopes confirm a coastal diet for critically endangered Mediterranean monk seals

Understanding the ecology and behaviour of endangered species is essential for developing effective management and conservation strategies. We used stable isotope analysis to investigate the foraging behaviour of critically endangered Mediterranean monk seals (Monachus monachus) in Greece. We measured carbon and nitrogen isotope ratios (expressed as δ13C and δ15N values, respectively) derived from the hair of deceased adult and juvenile seals and the muscle of their known prey to quantify their diets. We tested the hypothesis that monk seals primarily foraged for prey that occupy coastal habitats in Greece. We compared isotope values from seal hair to their coastal and pelagic prey (after correcting all prey for isotopic discrimination) and used these isotopic data and a stable isotope mixing model to estimate the proportion of coastal and pelagic resources consumed by seals. As predicted, we found that seals had similar δ13C values as many coastal prey species and higher δ13C values than pelagic species; these results, in conjunction with mean dietary estimates (coastal=61 % vs. pelagic=39 %), suggest that seals have a diverse diet comprising prey from multiple trophic levels that primarily occupy the coast. Marine resource managers should consider using the results from this study to inform the future management of coastal habitats in Greece to protect Mediterranean monk seals.

CATCH RATE AND CATCH COMPOSITION OF MINI PURSE SEINE IN BUALEMO, BANGGAI DISTRICT

Small pelagic fishery is the largest potential commodity in the waters of Tomini Bay which reached 64% of the total fish resources. Mini purse seine (soma pajeko) is the major fishing gear that used to utilize small pelagic resources in Tomini Bay. One of the main fishing grounds of mini purse seine vessels in Tomini Bay is in Bualemo and the surrounding waters. The aim of this research was to describe mini purse seine fishery in Bualemo especially about the aspects of the catch rate and catch composition. From the analysis of the daily catch data, there was a fluctuation of the average of catch rate each month. The catch of mini purse seine in Bualemo was dominated by two main species that is malalugis/mackerel scad (Decapterus macarellus) and bigeye scad (Selar crumenophthalmus). The large amount of the young fish (juvenile) caught by mini purse seine caused by the vessels operated around FADs and the mesh size that was less selective.

Dual fuels: intra-annual variation in the relative importance of benthic and pelagic resources to maintenance, growth and reproduction in a generalist salmonid fish.

Ecological systems are often characterized as stable entities. However, basal productivity in most ecosystems varies between seasons, particularly in subarctic and polar areas. How this variability affects higher trophic levels or entire food webs remains largely unknown, especially in these high-latitude regions. We undertook a year-long study of benthic (macroinvertebrate) and pelagic (zooplankton) resource availability, along with short (day/days: stomach content)-, medium (month: liver δ(13)C and δ(15)N isotopes)- and long-term (season: muscle δ(13)C and δ(15)N isotopes) assessments of resource use by a generalist fish, the European whitefish, in a deep, oligotrophic, subarctic lake in northern Europe. Due to the long ice-covered winter period, we expected to find general benthic reliance throughout the year, but also a seasonal importance of zooplankton to the diet, somatic growth and gonadal development of whitefish. Benthic and pelagic resource availability varied between seasons: peak littoral benthic macroinvertebrate density occurred in mid-winter, whereas maximum zooplankton density was observed in summer. Whitefish stomach content revealed a reliance on benthic prey items during winter and pelagic prey in summer. A seasonal shift from benthic to pelagic prey was evident in liver isotope ratios, but muscle isotope ratios indicated a year-round reliance on benthic macroinvertebrates. Whitefish activity levels as well as somatic and gonadal growth all peaked during the summer, coinciding with the zooplankton peak and the warmest water temperature. Stable isotopes of muscle consistently depicted the most important resource, benthic macroinvertebrates, whereas short-term indicators, that is, diet and stable isotopes of liver, revealed the seasonal significance of pelagic zooplankton for somatic growth and gonad development. Seasonal variability in resource availability strongly influences consumer growth and reproduction and may also be important in other ecosystems facing pronounced annual weather fluctuations.

Trophic flexibility by roach Rutilus rutilus in novel habitats facilitates rapid growth and invasion success

Stable isotope and gut content analyses, in conjunction with backcalculated length-at-age estimates of growth, were employed to examine the relationship between trophic ecology and growth rate of a successful invader, Rutilus rutilus, in eight lakes in Ireland. The data revealed that R. rutilus was a trophic generalist in Irish lakes. It utilized a greater proportion of pelagic resources in mesotrophic lakes than in eutrophic lakes, potentially due to a greater density of benthic macroinvertebrates in eutrophic systems. The species was characterized by a large dietary and isotopic niche width and high temporal and spatial variations in diet. Growth rates were typical of those found in the native range of the species and were unrelated to either lake productivity or fish's diet. A generalist trophic ecology confers significant advantages on an invasive species, allowing it to exploit a variety of novel resources and fluctuations in prey availability.

Lake morphometry and resource polymorphism determine niche segregation between cool‐ and cold‐water‐adapted fish

Climate change is increasing ambient temperatures in Arctic and subarctic regions, facilitating latitudinal range expansions of freshwater fishes adapted to warmer water temperatures. The relative roles of resource availability and interspecific interactions between resident and invading species in determining the outcomes of such expansions has not been adequately evaluated. Ecological interactions between a cool-water adapted fish, the perch (Perca fluviatilis), and the cold-water adapted European whitefish (Coregonus lavaretus), were studied in both shallow and deep lakes with fish communities dominated by (1) monomorphic whitefish, (2) monomorphic whitefish and perch, and (3) polymorphic whitefish and perch. A combination of stomach content, stable-isotope, and invertebrate prey availability data were used to identify resource use and niche overlap among perch, the trophic generalist large sparsely rakered (LSR) whitefish morph, and the pelagic specialist densely rakered (DR) whitefish morph in 10 subarctic lakes at the contemporary distribution limit of perch in northern Scandinavia. Perch utilized its putative preferred littoral niche in all lakes. LSR whitefish utilized both littoral and pelagic resources in monomorphic whitefish-dominated lakes. When found in sympatry with perch, LSR whitefish exclusively utilized pelagic prey in deep lakes, but displayed niche overlap with perch in shallow littoral lakes. DR whitefish was a specialist zooplanktivore, relegating LSR whitefish from pelagic habitats, leading to an increase in niche overlap between LSR whitefish and perch in deep lakes. Our results highlight how resource availability (lake depth and fish community) governs ecological interactions between native and invading species, leading to different outcomes even at the same latitudes. These findings suggest that lake morphometry and fish community structure data should be included in bioclimate envelope-based models of species distribution shifts following predicted climate change.

Ecological speciation in postglacialEuropean whitefish: rapid adaptive radiations into the littoral, pelagic, and profundal lake habitats

Understanding how a monophyletic lineage of a species diverges into several adaptive forms has received increased attention in recent years, but the underlying mechanisms in this process are still under debate. Postglacial fishes are excellent model organisms for exploring this process, especially the initial stages of ecological speciation, as postglacial lakes represent replicated discrete environments with variation in available niches. Here, we combine data of niche utilization, trophic morphology, and 17 microsatellite loci to investigate the diversification process of three sympatric European whitefish morphs from three northern Fennoscandian lakes. The morphological divergence in the gill raker number among the whitefish morphs was related to the utilization of different trophic niches and was associated with reproductive isolation within and across lakes. The intralacustrine comparison of whitefish morphs showed that these systems represent two levels of adaptive divergence: (1) a consistent littoral–pelagic resource axis; and (2) a more variable littoral–profundal resource axis. The results also indicate that the profundal whitefish morph has diverged repeatedly from the ancestral littoral whitefish morph in sympatry in two different watercourses. In contrast, all the analyses performed revealed clustering of the pelagic whitefish morphs across lakes suggesting parallel postglacial immigration with the littoral whitefish morph into each lake. Finally, the analyses strongly suggested that the trophic adaptive trait, number of gill rakers, was under diversifying selection in the different whitefish morphs. Together, the results support a complex evolutionary scenario where ecological speciation acts, but where both allopatric (colonization history) and sympatric (within watercourse divergence) processes are involved.

Living in the Ballona Wetlands of the Southern California Coast: Paleoenvironmental Reconstruction and Human Settlement

Over twenty years of archaeological research in the Ballona wetlands, California, USA, has provided the opportunity to reconstruct how settlement responded to landscape change in this dynamic environment over the last 8000 years. Analyses of stratigraphy, radiocarbon dates, and paleoecological indicators (foraminifera, ostracods, molluscs, diatoms, silicoflagellates, and pollen) from core samples indicate that sea level rise caused the Ballona to shift from a bay at the mouth of the Los Angeles River to a lagoon by about 7500 cal BP. As the lagoon gradually filled with sediment, the landscape also changed, providing abundant resources for human exploitation from the middle Holocene to the early historic period. The archaeological record reveals that human settlement responded also to long-term climatic fluctuations and changes in the course of the Los Angeles River. Settlement was most widespread between 4000 and 1500 cal BP, when the wetlands were most productive. The inhabitants of the Ballona chose to abandon most of the area between 800 and 400 cal BP, when climatic conditions deteriorated rather than to intensify exploitation of nearby pelagic resources as some neighbouring populations did. People returned to the Ballona after 400 cal BP, when climatic conditions ameliorated, but with a markedly different settlement structure than before.

Intensive fishing has not forced dietary change in the South American fur seal Arctophoca(=Arctocephalus)australis off Río de la Plata and adjoining areas

ABSTRACTSouth American fur seals (Arctophoca australis) inhabiting the Río de la Plata plume and adjoining areas are known to forage upon a wide range of prey (i.e. pelagic, demersal and benthic species).Since the 1960s, trawlers have operated in the area, targeting primarily demersal and benthic species. Carbon and nitrogen stable isotope ratios from 54 adult male fur seals dead stranded along the coast of southern Brazil from 1994 to 2011 were analysed to investigate whether the intensification of fishing in Río de la Plata and adjoining areas since the mid‐1990s has reduced the availability of benthic and demersal prey to the growing population of South American fur seals.No significant correlation between δ13C or δ15N values and stranding year was found, thus revealing that fur seals maintained a steady diet over 17 years.Reconstruction of the isotopic landscape of the study area using potential prey of fur seals showed a spatial segregation, with prey from southern Brazil typically enriched in 13C and depleted in 15N compared with those from northern Argentina. Most adult male fur seals relied mainly on small pelagic fishes and squid captured on the continental shelf, whereas medium pelagic and demersal–benthic prey played a minor role in the diet.It is concluded that South American fur seals rely on pelagic resources (i.e. small pelagic fish and squid) more strongly than previously thought and that their diet does not reflect the varying abundance of demersal–benthic resources in the area.As long as small pelagic fish remain under‐exploited in the area, competition between fisheries and fur seals is not expected. However, it is difficult to foresee how changes in the structure and dynamics of the ecosystem caused by fisheries may affect South American fur seal conservation in the long term. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Carbon and nitrogen stable isotopes reveal the use of pelagic resources by the invasive Ponto-Caspian mysid Limnomysis benedeni

The Ponto-Caspian mysid shrimp Limnomysis benedeni has rapidly invaded freshwater systems throughout Europe and is now found in extremely high abundances in invaded systems. However, very little is known about the trophic ecology of this mysid in invaded ecosystems, in particular the relative degree of herbivory, carnivory and detritivory of this potentially omnivorous species and where it derives its energy, i.e. via carbon fixed by algae inhabiting benthic or pelagic habitats or through allochthonous inputs. Here, we investigate the trophic ecology of L. benedeni in a recently established population in North-Western Germany using stable carbon and nitrogen isotopes. Our results suggest that in contrast to its previous classifications as a benthic or bentho-pelagic herbivore, L. benedeni is an omnivorous species, which can derive the bulk of its carbon from pelagic resources. Its trophic niche in different invaded ecosystems will be determined by multiple, system-dependent factors which have to be considered in order to predict the mysids’ invasion potential.

Spatiotemporal Variation of Juvenile Common Carp Foraging Patterns as Inferred from Stable Isotope Analysis

AbstractOntogenetic diet shifts from zooplankton to macroinvertebrates represent an important transition for many fishes during early life stages. However, some fishes have plastic feeding habits that allow them to take advantage of abundant prey resources or display diet specialization instead of undergoing distinct diet shifts. In this study, we evaluated ontogenetic changes in energy sources (based on the carbon isotope signature, δ13C) and trophic position (based on the nitrogen isotope signature, δ15N) for age‐0 Common Carp Cyprinus carpio from eight natural lakes in eastern South Dakota. In general, Common Carp trophic position decreased and energy sources shifted from pelagic to littoral prey resources from July to August. As anticipated, substantial inter‐ and intrapopulation variation existed in Common Carp isotope signatures. Common Carp trophic position increased with increasing fish TL in three lakes but decreased with fish TL in two systems. Intrapopulation variation in trophic position was related to Common Carp relative abundance during July, indicating that individuals may have specialized on different energy resources as a result of intraspecific interactions. The δ13C values decreased with increasing fish size in two populations during July, suggesting a shift toward pelagic resources; δ13C increased with fish size in six populations during August, suggesting a shift toward littoral resources. Our results indicate a high degree of trophic variation in juvenile Common Carp populations, indicative of a foraging generalist. Year‐class strength may increase trophic specialization of individuals but without negative effects on fish growth, suggesting that diet plasticity is an important factor contributing to the success of this invasive species.

Commercially-cultured oysters (Crassostrea gigas) exert top-down control on intertidal pelagic resources in Willapa Bay, Washington, USA

The capacity of filter feeders to reduce seston and phytoplankton concentrations in the water column has important implications for restoration and management of coastal ecosystems. We directly measured changes in chlorophyll a concentration on commercially stocked intertidal oyster beds (Crassostrea gigas) in Willapa Bay, Washington, USA by recording water properties near small drifters as they tracked parcels of water across tide flats. Chlorophyll declined 9.6% per half hour in water passing on-bottom adult oysters and 41% for longline adult oysters, whereas chlorophyll concentrations increased as water flowed across tide flats without adult oysters. Field filtration rates, which were fit to exponential declines in chlorophyll and accounted for oyster density and water depth, averaged 0.35Lg−1h−1 (shucked dry weight) for on-bottom aquaculture and 0.73Lg−1h−1 for longline culture, compared to values of 2.5–12Lg−1h−1 reported from laboratory studies of C. gigas. Field filtration rates may be lower than laboratory rates due to unfavorable field conditions (e.g., low initial chlorophyll concentrations) or masked by resuspension of benthic microalgae. In addition to distinctions among on-bottom, longline, and no-oyster habitats, Akaike's Information Criterion analysis showed temperature, initial chlorophyll concentration, and depth related to chlorophyll decline. This research corroborates mathematical models suggesting that benthic suspension feeders are exerting top-down control of pelagic production in this estuary, with strong patterns in chlorophyll emerging across extensive tideflats populated by C. gigas despite low field filtration rates.

Trophic status and condition of Hyalinoecia longibranchiata from two regions of contrasting oceanic productivity

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 477:147-159 (2013) - DOI: https://doi.org/10.3354/meps10160 Trophic status and condition of Hyalinoecia longibranchiata from two regions of contrasting oceanic productivity David O. Cummings1,2,*, Raymond W. Lee3, Scott D. Nodder4, Stephen J. Simpson1, Sebastian P. Holmes1,5 1School of Biological Sciences, University of Sydney, Sydney, New South Wales 2006, Australia 2Cardno Ecology Lab, Cardno NSW/ACT Pty Ltd, Level 9 The Forum, 203 Pacific Highway St Leonards, New South Wales 2065, Australia 3School of Biological Sciences, Washington State University, Pullman, Washington 99164, USA 4National Institute of Water and Atmospheric Research Ltd (NIWA), Wellington 6021, New Zealand 5Water & Wildlife Ecology Group (WWEG), The School of Science & Health, University of Western Sydney, Penrith, New South Wales 1797, Australia *Email: david.cummings@cardno.com.au ABSTRACT: The Chatham Rise and Challenger Plateau are 2 regions of New Zealand’s Exclusive Economic Zone with very different levels of productivity. The Chatham Rise is a physically dynamic region that sustains one of New Zealand’s largest mid-deep water fisheries, whilst the Challenger Plateau is a region of low hydrodynamic activity and productivity. These contrasting regions of pelagic productivity are likely to influence the trophic status of their benthic communities, where downward coupling of pelagic resources to the benthos occurs. Populations of the benthic quill worm Hyalinoecia longibranchiata (Onuphidae) were sampled at a range of depths on the Chatham Rise and the Challenger Plateau. Stable isotope signatures, δ13C and δ15N, and nutritional condition indices (DNA:dry weight, protein:DNA, RNA:DNA and C:N) of the quill worms were measured to: (1) determine whether regional-scale differences in surface productivity are reflected in the trophic status and condition of the quill worms; and (2) ascertain the extent to which other factors (e.g. depth, distance from the mainland) may affect this. Analysis revealed that H. longibranchiata collected on the Chatham Rise were more enriched in δ13C and in better condition than those collected on the Challenger Plateau. The isotopic enrichment observed at the Chatham Rise is likely to arise from differences in the quality and quantity of the organic inputs to the benthos. Overall, regional productivity had a much greater influence on the trophic status and condition, reflective of the degree of pelagic–benthic coupling, rather than any depth or spatial considerations. KEY WORDS: Bentho-pelagic coupling · Chatham Rise · Quill worms · Benthic nutrition · Challenger Plateau · Condition Full text in pdf format PreviousNextCite this article as: Cummings DO, Lee RW, Nodder SD, Simpson SJ, Holmes SP (2013) Trophic status and condition of Hyalinoecia longibranchiata from two regions of contrasting oceanic productivity. Mar Ecol Prog Ser 477:147-159. https://doi.org/10.3354/meps10160 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 477. Online publication date: March 12, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.