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Christensen V.,University of British Columbia | Coll M.,Institute Of Recherche Pour Le Developpement | Coll M.,CSIC - Institute of Marine Sciences | Coll M.,Ecopath International Initiative Research Association | And 5 more authors.
Ecosystems | Year: 2014

Why are marine species where they are? The scientific community is faced with an urgent need to understand aquatic ecosystem dynamics in the context of global change. This requires development of scientific tools with the capability to predict how biodiversity, natural resources, and ecosystem services will change in response to stressors such as climate change and further expansion of fishing. Species distribution models and ecosystem models are two methodologies that are being developed to further this understanding. To date, these methodologies offer limited capabilities to work jointly to produce integrated assessments that take both food web dynamics and spatial-temporal environmental variability into account. We here present a new habitat capacity model as an implementation of the spatial-temporal model Ecospace of the Ecopath with Ecosim approach. The new model offers the ability to drive foraging capacity of species from the cumulative impacts of multiple physical, oceanographic, and environmental factors such as depth, bottom type, temperature, salinity, oxygen concentrations, and so on. We use a simulation modeling procedure to evaluate sampling characteristics of the new habitat capacity model. This development bridges the gap between envelope environmental models and classic ecosystem food web models, progressing toward the ability to predict changes in marine ecosystems under scenarios of global change and explicitly taking food web direct and indirect interactions into account. © 2014 Springer Science+Business Media New York.

Christensen V.,University of British Columbia | Coll M.,Institute Of Recherche Pour Le Developpement | Coll M.,CSIC - Institute of Marine Sciences | Coll M.,Ecopath International Initiative Research Association | And 4 more authors.
Marine Ecology Progress Series | Year: 2014

We performed a global assessment of how fish biomass has changed over the last 100 yr, applying a previously developed methodology using ecological modeling. Our assessment built on more than 200 food web models representing marine ecosystems throughout the world covering the period from 1880 to 2007. All models were constructed based on the same approach, and have been previously documented. We spatially and temporally distributed fish biomasses delivered by these models based on fish habitat preferences, ecology, and feeding conditions. From these distributions, we extracted over 68000 estimates of biomass (for predatory and prey fishes separately, including trophic level of 3.5 or higher, and trophic level between 2.0 and 3.0, respectively), and predicted spatial-temporal trends in fish biomass using multiple regression. Our results predicted that the biomass of predatory fish in the world oceans has declined by twothirds over the last 100 yr. This decline is accelerating, with 54% occurring in the last 40 yr. Results also showed that the biomass of prey fish has increased over the last 100 yr, likely as a consequence of predation release. These findings allowed us to predict that there will be fish in the future ocean, but the composition of fish assemblages will be very different from current ones, with small prey fish dominating. Our results show that the trophic structure of marine ecosystems has changed at a global scale, in a manner consistent with fishing down marine food webs. © Inter-Research 2014

Torres M.T.,Spanish Institute of Oceanography | Coll M.,CSIC - Institute of Marine Sciences | Coll M.,Ecopath International Initiative Research Association | Heymans J.J.,Scottish Association for Marine Science | And 3 more authors.
Ecological Modelling | Year: 2013

The Gulf of Cadiz (North-eastern Atlantic, Spain) is an exploited ecosystem characterized by high marine biodiversity and productivity. Over the last decade, the landings of fish stocks such as anchovy (Engraulis encrasicolus), sardine (Sardina pilchardus) and hake (Merluccius merluccius) have been declining and currently remain low. A food-web model of the Gulf of Cadiz has been developed by means of a mass balance approach using the software EwE 6 to provide a snapshot of the ecosystem in 2009. The goals of this study were to: (1) characterize the food-web structure and functioning, (2) identify the main keystone groups of the ecosystem, (3) assess the impact of fishing to the Gulf of Cadiz compared to that in other essential marine ecosystems in the coastal area of Spain: Cantabrian Sea (North-eastern Atlantic) and Southern Catalan Sea (Mediterranean Sea), and (4) examine the limitations and weaknesses of the Gulf of Cadiz model for improvements and future research directions. The model consists of 43 functional groups, including the main trophic components of the system with emphasis target and non-target fish species. The main trophic flows are determined by the interaction between detritus, phytoplankton and micro- and mesozooplankton. Rose shrimp (Parapenaeus longirostris), cephalopods and dolphins present important overall effects as keystone species on the rest of the groups. The exploitation of fisheries composed mainly of trawlers, purse seiners and artisanal boats is intensive in the Gulf of Cadiz with all fleets exerting high impacts on most living groups of the ecosystem. The findings highlighted that the Gulf of Cadiz is a notably stressed ecosystem, displaying characteristics of a heavily exploited area. The comparative approach highlights that the three ecosystems display similarities with regard to structure and functioning such as the dominance of the pelagic fraction, a strong benthic-pelagic coupling, the important role of detritus, and the high impact of fishery exploitation. © 2013 Elsevier B.V.

Albouy C.,IRD Montpellier | Albouy C.,University of Quebec at Rimouski | Velez L.,IRD Montpellier | Velez L.,James Cook University | And 8 more authors.
Global Change Biology | Year: 2014

Climate change is inducing deep modifications in species geographic ranges worldwide. However, the consequences of such changes on community structure are still poorly understood, particularly the impacts on food-web properties. Here, we propose a new framework, coupling species distribution and trophic models, to predict climate change impacts on food-web structure across the Mediterranean Sea. Sea surface temperature was used to determine the fish climate niches and their future distributions. Body size was used to infer trophic interactions between fish species. Our projections reveal that 54 fish species of 256 endemic and native species included in our analysis would disappear by 2080-2099 from the Mediterranean continental shelf. The number of feeding links between fish species would decrease on 73.4% of the continental shelf. However, the connectance of the overall fish web would increase on average, from 0.26 to 0.29, mainly due to a differential loss rate of feeding links and species richness. This result masks a systematic decrease in predator generality, estimated here as the number of prey species, from 30.0 to 25.4. Therefore, our study highlights large-scale impacts of climate change on marine food-web structure with potential deep consequences on ecosystem functioning. However, these impacts will likely be highly heterogeneous in space, challenging our current understanding of climate change impact on local marine ecosystems. © 2013 John Wiley & Sons Ltd.

Heymans J.J.,Scottish Association for Marine Science | Coll M.,CSIC - Institute of Marine Sciences | Coll M.,Ecopath International Initiative Research Association | Coll M.,IRD Montpellier | And 3 more authors.
PLoS ONE | Year: 2014

Background: Ecological attributes estimated from food web models have the potential to be indicators of good environmental status given their capabilities to describe redundancy, food web changes, and sensitivity to fishing. They can be used as a baseline to show how they might be modified in the future with human impacts such as climate change, acidification, eutrophication, or overfishing. Methodology: In this study ecological network analysis indicators of 105 marine food web models were tested for variation with traits such as ecosystem type, latitude, ocean basin, depth, size, time period, and exploitation state, whilst also considering structural properties of the models such as number of linkages, number of living functional groups or total number of functional groups as covariate factors. Principal findings: Eight indicators were robust to model construction: relative ascendency; relative overhead; redundancy; total systems throughput (TST); primary production/TST; consumption/TST; export/TST; and total biomass of the community. Large-scale differences were seen in the ecosystems of the Atlantic and Pacific Oceans, with the Western Atlantic being more complex with an increased ability to mitigate impacts, while the Eastern Atlantic showed lower internal complexity. In addition, the Eastern Pacific was less organised than the Eastern Atlantic although both of these systems had increased primary production as eastern boundary current systems. Differences by ecosystem type highlighted coral reefs as having the largest energy flow and total biomass per unit of surface, while lagoons, estuaries, and bays had lower transfer efficiencies and higher recycling. These differences prevailed over time, although some traits changed with fishing intensity. Keystone groups were mainly higher trophic level species with mostly top-down effects, while structural/dominant groups were mainly lower trophic level groups (benthic primary producers such as seagrass and macroalgae, and invertebrates). Keystone groups were prevalent in estuarine or small/shallow systems, and in systems with reduced fishing pressure. Changes to the abundance of key functional groups might have significant implications for the functioning of ecosystems and should be avoided through management. Conclusion/significance: Our results provide additional understanding of patterns of structural and functional indicators in different ecosystems. Ecosystem traits such as type, size, depth, and location need to be accounted for when setting reference levels as these affect absolute values of ecological indicators. Therefore, establishing absolute reference values for ecosystem indicators may not be suitable to the ecosystem-based, precautionary approach. Reference levels for ecosystem indicators should be developed for individual ecosystems or ecosystems with the same typologies (similar location, ecosystem type, etc.) and not benchmarked against all other ecosystems. © 2014 Heymans et al.

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