Habitats

FACTORS STRUCTURING THE DISTRIBUTION OF FISHERY RESOURCES

This research brings together the research activities whose goal is to describe and understand the mechanisms that control the distribution of resources in space and time. We focus on the study of physical controls (eg, sedimentary structure, temperature, currents) and biotic (benthic fauna and flora, phyto-and zooplankton, species interactions, large predators).

A. Physical and Hydrodynamic background of the Channel 

The Channel is a shallow epicontinental sea characterized by diverse coastline (sandy or rocky foreshores, beaches of sand or pebbles interspersed with bays, estuaries or estuaries harboring marshes, mudflats and other pre-salted). It is under strong influence in the west Atlantic. The tidal and hydrodynamic conditions are specific (the average amplitude of the strong tidal waters of 5 to 12 m with tidal current speeds vary). The study of residual tidal currents can highlight areas of retention, dispersion and advection very marked.

Sea bottom stress due to tidal currents determines an instantaneous sedimentary succession leading to rocky areas of strong currents, fine sediment locked up in bays and estuaries. While overall growth in the Atlantic waters to the North Sea is mainly determined by the tide in the Channel, the wind regime is not to be overlooked. For example, easterly winds blowing for several days can lead to reversal of the general circulation.

In summer, at the mouth of the Channel, the establishment of a thermocline separates the stratified waters in the western waters is brewed under which drains along a "coastal river to the north the Seine estuary, inputs of freshwater from rivers. The result is a marked temperature gradient between the western waters, under the influence Atlantic and eastern waters, continental influence. Thermal Warming Channel signal reflected regionally warming observed over the entire North-East Atlantic during the last decades.

B. Mecanisms structuring the distribution of fishery resources 

The factors that control the distribution of resources can act on the individual level, population, community or the whole ecosystem. At the individual level, we note in particular the mechanisms related to physiology (eg thermal or haline tolerance) or the existence of specific habitat (eg substrate type). The controls across multiple populations are: food availability (primary and secondary), habitat availability, transport and retention of planktonic stages (larvae), intra-specific competition (density dependence), predation pressure, synchrony between individuals (eg for spawning), learning or 'imprinting' (for the migration routes), structure in sub-populations and connectivity. The relationships between species (competition, predation) and the trophic environment (planktonic and benthic) play a key role on dynamic spatial and temporal scale communities. Finally, the scale of the ecosystem, species diversity and trophic relationships and habitat availability controls are paramount.

The life cycles of many species are spatially structured exploited by migration patterns that create a spatial segregation between developmental stages that occupy different habitats. These habitats were sensitive when they are at a crucial stage for the renewal of the population. This applies, for example, spawning areas which host the larval or nurseries that house juveniles. The choice of spawning grounds by breeding, and the return of spawning adults on which they are derived, have been demonstrated for many species, but the underlying mechanisms determining including the return of spawners remain largely unknown. The respective contributions of abiotic controls (eg nature of the sediment, chemical signals, temperature, transport) and biotic (eg learning, competition, density dependence, trophic interactions) and interactions between these controls remain to be identified for most people . In the Channel, the coastal areas of study are particularly suited to the study of these controls. The coastal areas, estuaries and bays are temporarily colonized by juveniles of various species at this critical moment in their life cycle. In these nurseries, juveniles are abundant benthic organisms for their nutrition and growth. The adult communities, strongly structured in space along a gradient from the coast to sea following the sedimentary characteristics. They are characterized by distinct trophic guilds may respond differently to anthropogenic pressures, environmental variations or changes in trophic resources.

Contact: Sandrine VAZ, Ifremer Boulogne-sur-Mer