Abstract

The molluscan assemblages inhabiting the leaf and rhizome layers of Posidonia oceanica were studied in a deep water (–24/26 m) settlement of a highly heterogeneous substratum on an off-shore reef in the central Tyrrhenian Sea. This is one of the few works dealing with the rhizome layer and with Posidonia oceanica that has settled on hard substrata. The leaf assemblage only had a few species, less than other assemblages at a comparable depth in the same basin. This poorness may be due to the depth, but it may also be due to the high fragmentation of the meadow. However, the high percentage of carnivores is consistent with previous observations in deep water meadows. The rhizome assemblage is highly diverse both in terms of species and feeding guilds, which could be explained by the higher affinity for low light conditions of most molluscs and the greater habitat heterogeneity. The marked differences in the two taxocoenoses and the high diversification of the rhizome assemblage evidence that they should be included in studies on the potential diversity of Posidonia oceanica meadows. Failure to consider this layer seriously affects any evaluation of the biodiversity of this habitat, which is of great conservation interest.

Highlights

  • Posidonia oceanica (Linnaeus) Delile is a marine plant endemic to the Mediterranean Sea, where it is distributed quite evenly with the exception of the extreme western part near Gibraltar and the extreme eastern part (Egypt east of the Nile Delta, Palestine, Israel and Lebanon, where it is absent probably due to excessively high temperatures)

  • SUMMARY: The molluscan assemblages inhabiting the leaf and rhizome layers of Posidonia oceanica were studied in a deep water (–24/26 m) settlement of a highly heterogeneous substratum on an off-shore reef in the central Tyrrhenian Sea

  • This is one of the few works dealing with the rhizome layer and with Posidonia oceanica that has settled on hard substrata

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Summary

Introduction

Posidonia oceanica (Linnaeus) Delile is a marine plant endemic to the Mediterranean Sea, where it is distributed quite evenly with the exception of the extreme western part near Gibraltar and the extreme eastern part (Egypt east of the Nile Delta, Palestine, Israel and Lebanon, where it is absent probably due to excessively high temperatures). It is not present in the Sea of Marmara or the Black Sea due to their low salinity. It is estimated that it hosts around 400 plant species and thousands of animal species (Boudouresque et al 2006), and it is a nursery for several other marine animal species

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