Abstract
Composition, trophic structure, and species-substrate relationships of molluscan assemblages inhabiting different hard bottom habitats (Sabellaria alveolata reef, photophilic bottoms, Phyllophora crispa sciaphilic assemblage, and coralligenous bioconstruction) were studied in two different sites of the Tyrrhenian Sea. In particular, molluscs from the Sabellaria alvevolata (Linnaeus, 1767) reef and coralligenous concretion were investigated, testing the hypothesis that bioconstructions increase the diversity and abundance of associated biota compared to the surrounding habitats. A total of 3134 individuals belonging to the classes of Polyplacophora (5 species, 24 individuals), Bivalvia (39 sp., 2734 ind.), and Gastropoda (53 sp., 376 ind.) were identified. These three taxonomic groups showed different distribution patterns in the studied habitats. Multivariate analyses revealed significant inter-habitat differences in the composition of mollusc assemblages, especially between bioconstructions and the other habitats. S. alveolata and coralligenous host the highest rich molluscan fauna when compared to the neighboring hard bottom habitats characterized by photophilic and sciaphilic assemblages. The first ones were dominated by bivalve suspension feeders, mainly represented by sessile and sedentary organisms, which act as bio-constructors, bio-eroders, or simply inhabit the several microhabitats provided by the bioconstructions, while the second ones host a rich molluscan fauna dominated by gastropod grazers and predators. The present study increases the comparative knowledge of molluscan assemblages inhabiting habitats of littoral plans of the Mediterranean Sea, providing pivotal information regarding biodiversity of coastal zones.
Highlights
In marine ecosystems, any structure built by living organisms that rises from the bottom toward the surface may be defined as bioconstruction, which strongly modifies the local environment through physical and ecological processes [1]. corals and calcareous algae are usually indicated as the builders of biotic reefs, barnacles, molluscs, encrusting bryozoans and tubeworms play key roles in the creation of complex biogenic structures, especially in the Mediterranean Sea [2]
The present paper provides quantitative data on molluscan assemblages from relevant coastal habitats which are widespread in the Mediterranean Sea
M. galloprovincialis is well-known as the food competitor of S. alveolata, contributing to the regression of the bioconstruction [9], while the high abundance of H. arctica and the occurrence of other species of suspension feeders, such as Parvicardium spp. and Venerupsis corrugata, are indicators of the softness of the reef that is made of poorly adherent sand grains
Summary
Corals and calcareous algae are usually indicated as the builders of biotic reefs, barnacles, molluscs, encrusting bryozoans and tubeworms play key roles in the creation of complex biogenic structures, especially in the Mediterranean Sea [2]. Ingrosso et al [3] reviewed the most important biogenic habitats along the Italian coasts, and found that a total of seven different formations develop. Diversity 2019, 11, 74 in infralittoral and circalittoral bottoms. Despite their ecological and economic importance within the Mediterranean basin, the knowledge of biology and ecology of bioconstructions is far from comprehensive. The knowledge of some algae-dominated habitats is still lacking, as in the case of Phyllophora crispa (Hudson) P.S. Dixon, 1964 sciaphilic assemblages in central
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