Functional diversity associated with infralittoral cobble beds in the Maltese Islands

Abstract

Cobble beds represent a transitional habitat between the epibiotic assemblages found on hard substrata and the infauna typical of soft sediments. The aim of the present study was to characterise these habitats in terms of functional diversity by comparing cobble beds from nine sites around the Maltese Islands, and the different stratigraphic layers within each bed. Functional diversity allows an understanding of the whole ecosystem functioning based on the distribution and range of what organisms do in ecosystems. Samples were collected using SCUBA diving. Four replicates were taken from every station using a circular metal corer with an area of 0.1 m2. Most cobble beds were stratified into three layers: an upper cobble layer, an intermediate transitional layer composed of small pebbles and granules, and a basal sediment layer of sand and silt. In the laboratory the biota was sorted out from each sample and identified to the lowest possible taxon. Each taxon was then assigned to a trait in each of eight a priori defined functional groups (feeding mechanism; feeding apparatus; mobility; habitus; microhabitat; environmental position; body protection and reproductive strategy). Multivariate analysis showed a significant difference between sites and layers in feeding mechanisms, feeding apparatus, habitus and microhabitat and on this basis, three groups of cobble beds were distinguished: non-harbour cobble bed, harbour cobble bed and the Manoel Island B cobble bed.