Inducers of settlement and metamorphosis of the shrimp Hippolyte inermis Leach in Posidonia oceanica.

Larvae of the caridean shrimp Hippolyte inermis persist in the plankton of the Mediterranean up to about one month. Since they need to reach appropriate coastal areas for their recruitment in seagrass meadows, we hypothesized that leaves of Posidonia oceanica or, alternatively, algae present in their epiphytic biofilms, might be physically recognised as target substrates and trigger larval metamorphosis and settlement. Chemical cues could improve the finding of suitable habitats for settlement. Thus, the effects of leaves of P. oceanica and biofilms of the diatom Cocconeis scutellum parva, seasonally abundant in the leaf epiphytic stratum, were investigated along with the effect of volatile organic compounds (VOCs) extracted from the epiphytic diatom. The physical induction with P. oceanica accelerated larval settlement, stimulating an earlier and faster metamorphosis of larvae. C. scutellum parva produced a weaker effect on settlement; however, diatom's VOCs had evident influence and accelerated metamorphosis and settlement. We concluded that such chemical cues as the VOCs produced by epiphytic diatoms, reinforce the effect of physical cues for the identification of suitable settlement locations for this shrimp.