2016 |
Brosset, P., et al. "Linking small pelagic dietary shifts with ecosystem changes in the Gulf of Lions." Mar. Ecol.-Prog. Ser.. 554 (2016): 157–171.
Résumé: Since 2008, a severe decrease in size and body condition together with a demographic truncation has been observed in the sardine (secondarily in anchovy) population of the Gulf of Lions (NW Mediterranean Sea). In parallel, sprat biomass, which was negligible before, has increased tenfold. All of these changes have strongly affected the regional fisheries. Using trophic and isotopic data from contrasting periods of low versus high growth and condition, we investigated potential changes in diet and interspecific feeding interactions through time. Evidence of resource partitioning was found between sprat and both anchovy and sardine in 2004 and 2005. Since 2010, the isotopic niches of the 3 species have tended to overlap, suggesting higher risk of competition for food resources. Moreover, the wider trophic niche of sprat indicates higher variability in individual diets. Anchovy and sardine diet varied through time, with a high proportion of large copepods or cladocerans in periods of high growth and condition (1994 and 2007, respectively) versus a dominance of small copepods in the present (2011-2012). Furthermore, an important reduction in prey diversity was also identified in the diet of both anchovy and sardine during the most recent period. Our results support the hypothesis that changes in small pelagic fish growth, size and body condition and ultimately biomass could be due to bottom-up control characterized by changes in food availability and increasing potential trophic competition.
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Kirkman, S. P., et al. "Spatial characterisation of the Benguela ecosystem for ecosystem-based management." Afr. J. Mar. Sci.. 38.1 (2016): 7–22.
Résumé: The three countries of the Benguela Current Large Marine Ecosystem (BCLME), namely Angola, Namibia and South Africa, have committed to implementing ecosystem-based management (EBM) including an ecosystem approach to fisheries (EAF) in the region, to put in practice the principles of sustainable development in ocean-related matters. There is also recognition of the need for marine spatial planning (MSP) as a process for informing EBM with regard to the allocation and siting of ocean uses so that ecosystem health is ensured and trade-offs between ecosystem services are appropriately dealt with. Marine spatial planning is both an integrated and an area-based process, and this paper produces a spatial characterisation of the BCLME for achieving a common basis for MSP in the region, focusing on the oceanography, biology and fisheries. Recognising spatial variation in physical driving forces, primary and secondary production, trophic structures and species richness, four different subsystems are characterised: (1) north of the Angola-Benguela Front, (2) from the Angola-Benguela Front to Luderitz, (3) from Luderitz to Cape Agulhas, and (4) from Cape Agulhas to Port Alfred on the south-east coast of South Africa. Research and monitoring requirements of relevance for MSP and EBM in the region are identified, focusing on understanding variability and change, including with regard to the boundary areas identified for the system. To this end, 14 cross-shelf monitoring transects are proposed (including seven that are already being monitored) to estimate fluxes of biota, energy and materials within and between the subsystems. The usefulness of models for understanding ecosystem variability and changes is recognised and the need for fine-scale resolution of both sampling and modelling for adequate MSP as input to EBM for the often-conflicting interests of conserving biodiversity, and managing fisheries, recreation, offshore oil and gas exploration and exploitation, offshore mining and shipping routes, is emphasised.
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2015 |
Reygondeau, G., et al. "Progressive changes in the Western English Channel foster a reorganization in the plankton food web." Prog. Oceanogr.. 137 (2015): 524–532.
Résumé: Growing evidence has shown a profound modification of plankton communities of the North East Atlantic and adjacent seas over the past decades. This drastic change has been attributed to a modification of the environmental conditions that regulate the dynamics and the spatial distribution of ectothermic species in the ocean. Recently, several studies have highlighted modifications of the regional climate station L4 (50 degrees 15.00'N, 4 degrees 13.02'W) in the Western English Channel. We here focus on the modification of the plankton community by studying the long-term, annual and seasonal changes of five zooplankton groups and eight copepod genera. We detail the main composition and the phenology of the plankton communities during four climatic periods identified at the L4 station: 1988-1994, 1995-2000, 2001-2007 and 2008-2012. Our results show that long-term environmental changes underlined by Molinero et al. (2013) drive a profound restructuration of the plankton community modifying the phenology and the dominance of key planktonic groups including fish larvae. Consequently, the slow but deep modifications detected in the plankton community highlight a climate driven ecosystem shift in the Western English Channel. Crown Copyright (C) 2015 Published by Elsevier Ltd. All rights reserved.
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2014 |
Neira, S., et al. "Analysing changes in the southern Humboldt ecosystem for the period 1970-2004 by means of dynamic food web modelling." Ecological Modelling. 274 (2014): 41–49.
Résumé: A 22-group Ecopath model representing the southern Humboldt (SH) upwelling system in the year 1970 is constructed. The model is projected forward in time and fitted to available time series of relative biomass, catch and fishing mortality for the main fishery resources. The time series cover the period 1970 to 2004 and the fitting is conducted using the Ecopath with Ecosim (EwE) software version 5.1. The aim is to explore the relative importance of internal (trophic control) and external (fishing, physical variability) forcing on the dynamics of commercial stocks and the Southern Chilean food web. Wide decadal oscillations are observed in the biomass of commercial stocks during the analyzed period. Fishing mortality explains 21% of the variability in the time series, whereas vulnerability (v) parameters estimated using EwE explain an additional 20%. When a function affecting primary production (PP) is calculated by Ecosim to minimize the sum of squares of the time series, a further 28% of variability is explained. The best fit is obtained by using the fishing mortality time series and by searching for the best combination of v parameters and the PP function simultaneously, accounting for 69% of total variability in the time series. The PP function obtained from the best fit significantly correlates with independent time series of an upwelling index (UI; rho = 0.47, p<0.05) and sea surface temperature (SST; rho = -0.45, p<0.05), representing environmental conditions in the study area during the same period of time. These results suggest that the SH ecosystem experienced at least two different environmentally distinct periods in the last three decades: (i) from 1970 to 1985 a relatively warm period with low levels of upwelling and PP, and (ii) from 1985 to 2004 a relatively cold period with increased upwelling and PP. This environmental variability can explain some of the changes in the food webs. Fishing (catch rate) and the environment (bottom-up anomaly in PP) appear to have affected the SH both at the stock and at the food web level between 1970 and 2004. The vulnerability setting indicates that the effects of external forcing factors may have been mediated by trophic controls operating in the food web.
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2010 |
Llope, M., et al. "Overfishing of top predators eroded the resilience of the Black Sea system regardless of the climate and anthropogenic conditions." Global Change Biology. 17.3 (2010): 1251–1265.
Résumé: It is well known that human activities, such as harvesting, have had major direct effects on marine ecosystems. However, it is far less acknowledged that human activities in the surroundings might have important effects on marine systems. There is growing evidence suggesting that major reorganization (i.e., a regime shift) is a common feature in the temporal evolution of a marine system. Here we show, and quantify, the interaction of human activities (nutrient upload) with a favourable climate (run-off) and its contribution to the eutrophication of the Black Sea in the 1980s. Based on virtual analysis of the bottom-up (eutrophication) vs. top-down (trophic cascades) effects, we found that an earlier onset of eutrophication could have counteracted the restructuring of the trophic regulation at the base of the food web that resulted from the depletion of top predators in the 1970s. These enhanced bottom-up effects would, however, not propagate upwards in the food web beyond the zooplankton level. Our simulations identified the removal of apex predators as a key element in terms of loss of resilience that inevitably leads to a reorganization. Once the food web has been truncated, the type and magnitude of interventions on the group replacing the apex predator as the new upper trophic level have no effect in preventing the trophic cascade. By characterizing the tipping point at which increased bottom-up forcing exactly counteracts the top-down cascading effects, our results emphasize the importance of a comprehensive analysis that take into account all structuring forces at play (including those beyond the marine system) at a given time.
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Shannon, L. J., et al. "Comparing data-based indicators across upwelling and comparable systems for communicating ecosystem states and trends." ICES J. Mar. Sci.. 67.4 (2010): 807–832.
Résumé: Shannon, L. J., Coll, M., Yemane, D., Jouffre, D., Neira, S., Bertrand, A., Diaz, E., and Shin, Y-J. 2010. Comparing data-based indicators across upwelling and comparable systems for communicating ecosystem states and trends. – ICES Journal of Marine Science, 67: 807-832.
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