Approche quantitative de la fonction de nourricerie jouée par les ...

Chapitre 4 : Impact of vegetation structure dynamics and usage on the nursery function of
West European tidal salt-marshes.
stops its colonisation, so that sub-adults are absent. A re-colonisation by older fish then
occurs. In terms of predation, the marsh provides the young stages with physico-chemical
protection because of the very strong constraints that any potential predators would face
(salinity, temperature, dissolved oxygen, etc.). The ability of some species to withstand these
conditions is a considerable evolutionary advantage. However, the shallowness and temporary
nature of these habitats obliges the fish either to be of small size or have good swimming
abilities, allowing them to actively swim out of the creeks before they dry out. The
colonisation process used by Thinlip mullet enables it to optimise the use of an unlimited food
resource, the benthic micro-algae. Two hypotheses could therefore be proposed in terms of
the frequentation of these marshes. Firstly, these food resources could allow the fish to build
up energy reserves needed for reproduction (ovogenesis). Secondly, the return to these
ecosystems after spawning in the sea could allow those fish exhausted by this stage in the life
cycle to recover essential energy reserves. The species colonising the marsh for one or other
of these purposes could be called Opportunistic salt marsh settlers. Here again the food
resources support the whole population.
Different kinds of salt marsh settlement and trophic utilization
Salt marsh
Salt marsh settlers species
Young-of-the-year salt marsh settlers species
They are present during the early stage up to one year at the most or accidentally during
their second year (nursery fonction sensu stricto ).
Juvenile salt marsh settlers species
They are present at age 0 and 1, before sexual maturity.
Opportunistic salt marsh settlers species
They colonise the salt marsh at any age (facultative strategy).
Resident settlers species
Feed there, but also use salt marshes as permanent habitats
Marine
Transient salt marsh Settlers species
Stay for shrot moments during transit between
riverine and marine systems
Figure 30: Conceptual diagram of settlement behaviours and food resource use o European saltmarshes
by different fish populations.
Figure 30 : Schéma conceptuel du comportement colonisateur et de l’utilisation des marais sales
européens par différentes populations de poissons.
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