Habitat structure and biological characteristics of a maerl bed off the northeastern coast of the Maltese Islands (central Mediterranean)

Forty stations within a 20 km² Maltese maerl bed were sampled by grab to gather data on sediment granulometry and the percentage mass, sphericity, and morphotype of rhodoliths. Two stations were monitored between July 1996 and April 1998 to study temporal variation in species diversity and abundance of the epi- and endo-benthos. Maerl was commonest at 51-90 m depth with 20-39% live rhodoliths in central parts of the maerl bed, while the peripheral parts had less than 20% live rhodoliths. The most abundant rhodolith morphotypes were branching forms and those with a rugged surface. The maerl bed proved to have high species diversity with 244 animal and 87 algal taxa recorded; molluscs, crustaceans, and annelids were the dominant taxa in the endobenthos, and bryozoans and sponges in the epibenthos. Community composition, rhodolith morphology and sediment characteristics at the two sites were related to differences in the hydrodynamic regime resulting from seabed topographical heterogeneity.