Spatially Explicit Modeling Reveals Cephalopod Distributions Match Contrasting Trophic Pathways in the Western Mediterranean Sea

Populations of the same species can experience different responses to the environment throughout their distributional range as a result of spatial and temporal heterogeneity in habitat conditions. This highlights the importance of understanding the processes governing species distribution at local scales. However, research on species distribution often averages environmental covariates across large geographic areas, missing variability in population- environment interactions within geographically distinct regions. We used spatially explicit models to identify interactions between species and environmental, including chlorophyll a (Chla) and sea surface temperature (SST), and trophic (prey density) conditions, along with processes governing the distribution of two cephalopods with contrasting life-histories (octopus and squid) across the western Mediterranean Sea. This approach is relevant for cephalopods, since their population dynamics are especially sensitive to variations in habitat conditions and rarely stable in abundance and location. The regional distributions of the two cephalopod species matched two different trophic pathways present in the western Mediterranean Sea, associated with the Gulf of Lion upwelling and the Ebro river discharges respectively. The effects of the studied environmental and trophic conditions were spatially variant in both species, with usually stronger effects along their distributional boundaries. We identify areas where prey availability limited the abundance of cephalopod populations as well as contrasting effects of temperature in the warmest regions. Despite distributional patterns matching productive areas, a general negative effect of Chla on cephalopod densities suggests that competition pressure is common in the study area. Additionally, results highlight the importance of trophic interactions, beyond other common environmental factors, in shaping the distribution of cephalopod populations. Our study presents a valuable approach for understanding the spatially variant ecology of cephalopod populations, which is important for fisheries and ecosystem management.Versión del editor4,411

Climate and Demography Dictate the Strength of Predator-Prey Overlap in a Subarctic Marine Ecosystem

There is growing evidence that climate and anthropogenic influences on marine ecosystems are largely manifested by changes in species spatial dynamics. However, less is known about how shifts in species distributions might alter predator-prey overlap and the dynamics of prey populations. We developed a general approach to quantify species spatial overlap and identify the biotic and abiotic variables that dictate the strength of overlap. We used this method to test the hypothesis that population abundance and temperature have a synergistic effect on the spatial overlap of arrowtooth flounder (predator) and juvenile Alaska walleye pollock (prey, age-1) in the eastern Bering Sea. Our analyses indicate that (1) flounder abundance and temperature are key variables dictating the strength of flounder and pollock overlap, (2) changes in the magnitude of overlap may be largely driven by density-dependent habitat selection of flounder, and (3) species overlap is negatively correlated to juvenile pollock recruitment when flounder biomass is high. Overall, our findings suggest that continued increases in flounder abundance coupled with the predicted long-term warming of ocean temperatures could have important implications for the predator-prey dynamics of arrowtooth flounder and juvenile pollock. The approach used in this study is valuable for identifying potential consequences of climate variability and exploitation on species spatial dynamics and interactions in many marine ecosystems

Transdisciplinary graduate education in marine resource science and management

In this article we consider the current educational needs for science and policy in marine resource management, and we propose a way to address them. The existing literature on cross-disciplinary education in response to pressing environmental problems is vast, particularly in conservation biology. However, actual changes in doctoral-level marine science programs lag behind this literature considerably. This is in part because of concerns about the time investment in cross-disciplinary education and about the job prospects offered by such programs. There is also a more fundamental divide between educational programs that focus on knowledge generation and those that focus on professional development, which can reinforce the gap in communication between scientists and marine resource managers. Ultimately, transdisciplinary graduate education programs need not only to bridge the divide between disciplines, but also between types of knowledge. Our proposed curriculum aligns well with these needs because it does not sacrifice depth for breadth, and it emphasizes collaboration and communication among diverse groups of students, in addition to development of their individual knowledge and skills.Keywords: experiential learning, transdisciplinary, professional skills, graduate educatio

Towards ecosystem-based management: identifying operational food-web indicators for marine ecosystems

Modern approaches to Ecosystem-Based Management and sustainable use of marine resources must account for the myriad of pressures (interspecies, human and environmental) affecting marine ecosystems. The network of feeding interactions between co-existing species and populations (food webs) are an important aspect of all marine ecosystems and biodiversity. Here we describe and discuss a process to evaluate the selection of operational food-web indicators for use in evaluating marine ecosystem status. This process brought together experts in food-web ecology, marine ecology, and resource management, to identify available indicators that can be used to inform marine management. Standard evaluation criteria (availability and quality of data, conceptual basis, communicability, relevancy to management) were implemented to identify practical food-web indicators ready for operational use and indicators that hold promise for future use in policy and management. The major attributes of the final suite of operational food-web indicators were structure and functioning. Indicators that represent resilience of the marine ecosystem were less developed. Over 60 potential food-web indicators were evaluated and the final selection of operational food-web indicators includes: the primary production required to sustain a fishery, the productivity of seabirds (or charismatic megafauna), zooplankton indicators, primary productivity, integrated trophic indicators, and the biomass of trophic guilds. More efforts should be made to develop thresholds-based reference points for achieving Good Environmental Status. There is also a need for international collaborations to develop indicators that will facilitate management in marine ecosystems used by multiple countries.JRC.D.2-Water and Marine Resource

Climate and demography dictate the strength of predator-prey overlap in a subarctic marine ecosystem

There is growing evidence that climate and anthropogenic influences on marine ecosystems are largely manifested by changes in species spatial dynamics. However, less is known about how shifts in species distributions might alter predatorprey overlap and the dynamics of prey populations. We developed a general approach to quantify species spatial overlap and identify the biotic and abiotic variables that dictate the strength of overlap. We used this method to test the hypothesis that population abundance and temperature have a synergistic effect on the spatial overlap of arrowtooth flounder (predator) and juvenile Alaska walleye pollock (prey, age-1) in the eastern Bering Sea. Our analyses indicate that (1) flounder abundance and temperature are key variables dictating the strength of flounder and pollock overlap, (2) changes in the magnitude of overlap may be largely driven by density-dependent habitat selection of flounder, and (3) species overlap is negatively correlated to juvenile pollock recruitment when flounder biomass is high. Overall, our findings suggest that continued increases in flounder abundance coupled with the predicted long-term warming of ocean temperatures could have important implications for the predator-prey dynamics of arrowtooth flounder and juvenile pollock. The approach used in this study is valuable for identifying potential consequences of climate variability and exploitation on species spatial dynamics and interactions in many marine ecosystems. Copyright: 2013 Hunsicker et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credite

Season and prey type influence size dependency of predator−prey body mass ratios in a marine fish assemblage

Marine and freshwater food webs are strongly structured by size-dependent predator−prey interactions. Predator−prey body mass ratios (PPMR) are important parameters in size-based food-web models, but studies evaluating the temporal stability of PPMR or its relationship to predator feeding modes are scant. Using a large data set of predator−prey pairs from a diverse fish community sampled in summer, fall, and winter, we showed that community-level PPMR varied with predator mass in a nonlinear (dome-shaped) manner. PPMR was higher in the summer relative to the fall and winter for all predator body size classes regardless of whether prey were fish or invertebrate. Further, the size dependency of PPMR was dome-shaped for invertebrate prey but positive and linear for fish prey. We empirically show that community-level PPMR is dynamic rather than fixed, which is in agreement with general expectations set by simulation studies of biomass spectra. However, we are presently unable to identify the specific processes underlying these patterns. Size-based models of marine ecosystems offer considerable promise over traditional taxa-based approaches, and our analyses provide insight into major patterns of variation in PPMR in a temperate marine system.Keywords: Feeding interactions, Food web, Body mass, Puget Sound, Trophic level, Demersal fish, Size spectr

Des maux du corps à la corporalité des mots : étude des effets d’un groupe danse pour patients douloureux.

International audienc

Community del15N data sets

<p>Data analyzed in:</p> <p>Reum, J.C.P, Jennings, S., Hunsicker, M.E. (In Press) Implications of scaled δ15N fractionation for community predator-prey body mass ratio estimates in size-structured food webs. Journal of Animal Ecology. </p> <p> </p

Assessing the potential for competition between Pacific Halibut (Hippoglossus stenolepis) and Arrowtooth Flounder (Atheresthes stomias) in the Gulf of Alaska.

Pacific Halibut (Hippoglossus stenolepis) support culturally and economically important fisheries in the Gulf of Alaska, though recent decreases in mean size-at-age have substantially reduced fishery yields, generating concerns among stakeholders and resource managers. Among the prevailing hypotheses for reduced size-at-age is intensified competition with Arrowtooth Flounder (Atheresthes stomias), a groundfish predator that exhibited nearly five-fold increases in biomass between the 1960s and mid-2010s. To assess the potential for competition between Pacific Halibut and Arrowtooth Flounder, we evaluated their degree of spatiotemporal and dietary overlap in the Gulf of Alaska using bottom trawl survey and food habits data provided by the Alaska Fisheries Science Center (NOAA; 1990 to 2017). We restricted analyses to fish measuring 30 to 69 cm fork length and used a delta modeling approach to quantify species-specific presence-absence and catch-per-unit-effort as a function of survey year, tow location, depth, and bottom temperature. We then calculated an index of spatial overlap across a uniform grid by multiplying standardized predictions of species' abundance. Dietary overlap was calculated across the same uniform grid using Schoener's similarity index. Finally, we assessed the relationship between spatial and dietary overlap as a measure of resource partitioning. We found increases in spatial overlap, moving from east to west in the Gulf of Alaska (eastern: 0.13 ± 0.20; central: 0.21 ± 0.11; western: 0.31 ± 0.13 SD). Dietary overlap was low throughout the study area (0.13 ± 0.20 SD). There was no correlation between spatial and dietary overlap, suggesting an absence of resource partitioning along the niche dimensions examined. This finding provides little indication that competition with Arrowtooth Flounder was responsible for changes in Pacific Halibut alHHsize-at-age in the Gulf of Alaska; however, it does not rule out competitive interactions that may have affected resource use prior to standardized data collection or at different spatiotemporal scales

Predatory role of the commander squid Berryteuthis magister in the eastern Bering Sea: insights from stable isotopes and food habits

Squid are an important component of many marine food webs, and they can impact other species through predation and competition. However, quantifying their influence on other food web components requires knowledge of their trophic position and trophic ontogeny, which are unknown in many ecosystems. The eastern Bering Sea (EBS) is a highly productive region that supports large commercial fisheries, and a modicum of knowledge exists on the ecological role of squid in this region. We combined stomach content and stable isotope analyses of muscle tissue (δ15N and δ13C) to identify the feeding ecology of the commander squid Berryteuthis magister in the EBS continental slope ecosystem. We also use a novel methodology to elucidate potential finer-scale variation in squid trophic ecology by reconstructing feeding chronologies of individual B. magister from concentric eye lens layers. Our analyses indicate that the position of B. magister in the EBS food web increases by approximately 1 trophic level between juvenile and adult stages. Also, in contrast to many squid species, we found that predation by B. magister is not constrained by prey body size and that B. magister are more likely to share prey resources with commercially valuable fishes, particularly walleye pollock Theragra chalcogramma, than to prey upon their juvenile stages. Further, the reconstructed feeding chronologies indicate substantial variability in squid feeding patterns that are not captured on the time scales of the conventional analyses. Together, the findings of this study contribute to a better understanding of the ecological role of B. magister and the trophic linkages and energy flow within the EBS food web