The Persian Gulf is a semi-enclosed marine system surrounded by eight countries, many of which are experiencing substantial development.

International audienceThe Bay of Biscay (North-East Atlantic) has long been subjected to intense direct and indirect human activities that lead to the excessive degradation and sometimes overexploitation of natural resources. Fisheries management is gradually moving away from single-species assessments to more holistic, multi-species approaches that better respond to the reality of ecosystem processes. Quantitative modelling methods such as Ecopath with Ecosim can be useful tools for planning, implementing and evaluating ecosystem-based fisheries management strategies. The aim of this study was therefore to model the energy fluxes within the food web of this highly pressured ecosystem and to extract practical information required in the diagnosis of ecosystem state/health. A well-described model comprising 30 living and two non-living compartments was successfully constructed with data of local origin, for the Bay of Biscay continental shelf. The same level of aggregation was applied to primary producers, mid-trophic-levels and top-predators boxes. The model was even more general as it encompassed the entire continuum of marine habitats, from benthic to pelagic domains. Output values for most ecosystem attributes indicated a relatively mature and stable ecosystem, with a large proportion of its energy flow originating from detritus. Ecological network analysis also provided evidence that bottom-up processes play a significant role in the population dynamics of upper-trophic-levels and in the global structuring of this marine ecosystem. Finally, a novel metric based on ecosystem production depicted an ecosystem not far from being overexploited. This finding being not entirely consistent over indicators, further analyses based on dynamic simulations are required

No abstract

Inverse analysis was used to model the food webs of two intertidal mudflat ecosystems: Aiguillon Cove (AC) and Brouage Mudflat (BM) (south-western Atlantic coast, France). The aim of the present study is to describe and compare the functioning of these two ecosystems. The method of inverse analysis has been adapted in order to take into account, in a single calculation, two seasons: spring/summer (mid-March to mid-October) and autumn/winter (the rest of the year). Gathering all available data on the two sites, the most important gaps in knowledge were identified with the help of sensitivity analyses: they concerned mainly the exports of material by grazing fish (such as mullet Liza ramada), resuspension of microphytobenthos, and fluxes linked to microfauna which is poorly known for the two systems. The two sites presented the same overall type of functioning (net import of detritus, export of living organic material and higher faunal activity during spring/summer). In both ecosystems, primary production was dominated by the microphytobenthic production, of which a great part was exported via water-column advection and biotic vectors (grazing fish), while many secondary producers also used detritus as a food resource. Each system also had its own characteristics, one BM being much more seasonally driven than the other AC. It appeared essential to take the seasons into account, as variations in microphytobenthos production and in meiofauna, macrofauna and biotic vectors led to great differences in the food-web organisation Résumé

No abstract

Mesozooplankton can be considered the most important secondary producers in marine food webs because they hold an intermediate position between the phytoplankton assemblage and the upper trophic levels. They also are a robust indicator of climatic and hydrological conditions. We conducted an analysis of the interannual variability of the spring mesozooplankton assemblage, as sampled by the PELGAS fisheries survey in the southern part of the Bay of Biscay (Northeast Atlantic Ocean) between 2003 and 2013. We examined hydrology and trophic drivers to explain the variability. Our results revealed that the subsurface temperature, the subsurface salinity, the biomasses of subsurface pico-, nano-, and microphytoplankton, and the copepod assemblage exhibited a recurrent spatial pattern that was driven mainly by freshwater and nutrient inputs from the main rivers. The mesozooplankton assemblage was dominated by copepods (82%), composed of coastal, neritic, and oceanic copepod genera that paralleled the various hydrological fronts converging in the southern Bay of Biscay. The copepod community displayed high temporal-variability; there were three periods of abundant adult copepods throughout the southern Bay of Biscay. The copepod community was structured primarily around the drive for resource control, especially by the microphytoplankton biomass (24.3% of the total variability), and to a lesser extent by hydrological features (13.7% of the total variability). Highlights ► Spring mesozooplankton was studied over a decade in the southern Bay of Biscay. ► Hydrobiological features of habitats displayed relatively stable spatial patterns. ► Spatial structuration of habitats was mainly driven by continental outflow. ► Mesozooplankton abundance decreased from 2007 to 2009 but recovered afterward. ► High percentage of gelatinous organisms and low percentage of copepods occurred in 2006. ► In springtime, the copepod dynamics was mainly governed by resource availability.

Marquis, E., Niquil, N., Vézina, A. F., Petitgas, P., and Dupuy, C. 2011. Influence of planktonic foodweb structure on a system's capacity to support pelagic production: an inverse analysis approach. – ICES Journal of Marine Science, 68: 803–812. Coupled plankton/small pelagic (SP) fish systems were analysed to assess how foodweb structure influences the export of carbon to pelagic fish during the spring bloom in the Bay of Biscay. The investigation of carbon export flows through inverse analysis was supplemented by estimating the carrying capacity for pelagic fish production by applying linear programming. A planktonic foodweb dominated by microbial pathways had the highest trophic efficiency owing to the tight coupling between planktonic trophic levels and predation pressure on mesozooplankton by fish. Moreover, the magnitude of the gap between carrying capacity and estimated carbon export was related to the size structure of primary producers, with the picophytoplankton-based foodweb having the smallest gap and the microphytoplankton-based one the largest gap. Planktonic foodwebs dominated by small autotrophic cells channelled most of their available carbon to pelagic fish production, whereas foodwebs dominated by large phytoplankton were better suited to benthic communities with a large loss of carbon through sedimentation. Although the total carbon available to higher trophic levels does not vary with the size of the main primary producers, the potential export to SP fish depends on the structure of the planktonic foodweb.

International audienceIn order to investigate the parameters controlling the heterotrophic protists (nano-microzooplankton) on the continental shelf of the southern Bay of Biscay, plankton communities and their physico-chemical environment were studied 4 times in February, April, June and SeptembereOctober 2004 at three stations in the euphotic zone in the Bay of Biscay. The abundance and carbon biomass of heterotrophic protists (ciliates, heterotrophic dinoflagellates and nanoflagellates) as well as all the others groups of plankton (picoplankton, nanophytoplankton, diatoms, autotrophic dinoflagellates, metazoan micro-zooplankton and mesozooplankton), the environmental parameters and the primary and bacteria production were evaluated at each sampling period. Microzooplankton grazing experiments were undertaken at the same time. Ciliates and heterotrophic dinoflagellates accounted for the main major component of nano-and microzooplankton communities in term of biomass. The total carbon biomass of heterotrophic protists was highest in spring and lowest at the end of summer. The development of heterotrophic protists started after a winter microphytoplankton bloom (principally large diatoms), the biomass was lower in June and was low in September (through inappropriate prey). The carbon requirement of microzooplankton ranged from 50 to more than 100% of daily primary, bacterial and nanoflagellate production. The heterotrophic protist community was predominantly constrained by bottom-up control in spring and at the end of summer via food availability and quality