Secondary hardground-communities in the northern Gulf of Trieste, Adriatic Sea

Secondary hardground-communities in the Bay of Panzano were investigated with respect to their taxonomic composition, distribution and to the taphonomic processes, which may influence their preservation potential. Every hardground category (mainly serpulid aggregates, various mollusc shells andChaetopterus tubes) at the investigated soft-bottom is attractive for potential epigrowth.

All epigrowth organisms are suspension feeders; serpulids are quantitatively by far the most important. “Constructors” (barnacles, bryozoans, oysters, serpulids) enlarge the hardground, have a considerable preservation potential and show limited taphonomic disintegration. In contrast, soft-bodied epigrowth (anemones, ascidians, sponges) and thin-walledChaetopterus tubes have a poor fossilisation potential. Vagile colonizers (ophiurids, echinoids, decapods, holothurians) show also strong taphonomic disintegration, but their species composition is partly reconstructable from fragments embedded in the sediment and provides indirect evidence for ascidians and sponges.

The density of overgrown secondary hardgrounds decreases distinctly with decreasing distance from the river mouth due to changing types of available hardgrounds, a markedly change of sedimentary facies and bottom trawling.