Abstract
AbstractPost‐settlement dispersal is a key process in the recruitment of bivalves. To assess the role of such secondary migrations and to identify potential associated triggers, we conducted an in situ sampling survey during the summer recruitment period on the bivalve assemblages of a coarse‐sediment temperate tidal habitat in the Chausey archipelago (Normandy, France). The dynamics of drifters were studied using three types of settler traps (for example, bedload, pelagic, and sinking transports), and we monitored both the abiotic (hydrological and hydrodynamic conditions) and the trophic (nano‐ and pico‐sized particulate organic matter [POM]; fatty acid composition of POM and sediment organic matter [SOM]) environmental parameters. Such an approach allows the discrimination of passive migration (due to sediment erosion by tidal currents and waves) from active migration (related to recruit behavior). Secondary migrations were observed in 25 bivalve taxa, and these mainly involved decreasing abundances of Mytilidae, Nuculidae, Semelidae, Mactridae, and Lucinidae individuals on the study site, highlighting the crucial role of these processes in highly dynamic coastal benthic assemblages. Surprisingly, the intense post‐settlement dispersal observed at the end of the recruitment season was not synchronized with periods of high hydrodynamic stress but to a change in the structure of phytoplanktonic assemblages, particularly the nanoeukaryotic component. Such a response by bivalve recruits to a trophic pelagic cue—triggering secondary migrations—could result from an increased demand for energy required for active migratory behavior.
Highlights
Most benthic marine invertebrates exhibit a bentho-pelagic life cycle with a larval stage dispersing into the water column (Thorson 1950) followed by settlement and metamorphosis into a post-larva in the benthic boundary layer (BBL)
Bivalve recruit migrations No bivalve recruits were found in the epibenthic traps for either of the experimental periods sampled (17 June and 27 August)
We show the ability of bivalves to undergo active migrations independently of hydrodynamic stress
Summary
Most benthic marine invertebrates exhibit a bentho-pelagic life cycle with a larval stage dispersing into the water column (Thorson 1950) followed by settlement and metamorphosis into a post-larva in the benthic boundary layer (BBL). Post-settlement mechanisms correspond to the terminal phase of recruitment, and they include mortality of early juveniles due to several causes (Hunt and Scheibling 1997), abiotic factors for intertidal species (Jenewein and Gosselin 2013). Another significant factor is the migration of recently metamorphosed post-larvae, called the secondary migration (Gu€nther 1992a, Olivier and Retiere 2006), but this has been little studied in coarse-sediment habitats
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