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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.

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Ichthyoplankton assemblages in the south central Tyrrhenian Sea are not known in spite of this being an intensely fished area. There are two large canyons in this region: Dohrn, in the Gulf of Naples, and Cuma, at the south end of the Gulf of Gaeta. In this study, we provide the first description of summer ichthyoplankton assemblages in the vicinity of the two canyons and present the physical features and Lagrangian particle tracking analyses at the time of the sampling. We identified fish larvae of 19 families and fish eggs of 8 families. The most abundant species was Engraulis encrasicolus, which was found at densities comparable to other known spawning grounds of the western Mediterranean. Mesopelagic species, such as Gonostomatidae and Myctophidae, were also abundant, especially at the Cuma Canyon. The notochord and standard length of the E. encrasicolus larvae ranged from 2.06 to 10.47 mm and was significantly smaller at the Cuma stations than at the Dohrn stations, suggesting the presence of sub-populations with different spawning phenologies. The passive particle tracking analyses and the examination of currents confirmed distinct circulation features between the two sampled regions and in relation to depth and proximity to the canyon heads. These results uncover previously unknown rich assemblages of fish eggs and larvae and have conservation and management implications given the proximity of these canyons to a marine protected area and to an intensely fished continental shelf.