STRUCTURE AND DYNAMIC OF BIOFOULING COMMUNITIES WITHIN AQUACULTURE AREA IN NORTHERN ADRIATIC SEA, CROATIA

Biofouling communities are composed of sessile, suspension-feeding macrofouling organisms. Their composition and abundance are spatially and temporally variable, and are also determined by environmental factors and surface properties of collector substrates, such as: age, texture, depth, complexity, inclination and position in the water column. The intensive development of biofouling communities within aquaculture farms has a substantial detrimental impact on shellfish production due to physical shell damage, disruption of opening and closing of shellfishvalves, competition for food and space, reduction of water flow, and increased weight of aquaculture installations.

The current investigation was conducted between April and January within aquaculture areas of Lim Bay in the north-eastern part of Adriatic Sea and Pomer Bay.

Ropes with five replicates of clay tiles (12×12 cm) were placed next to mussels polyethylene (pergolari) mesh sleeves suspended horizontally from longlines, at depths of 1 and 5 meters from the surface.. Tiles were retrieved every three weeks, starting from May to January. Biofouling organisms were inspected immediately after collection of tiles. The most dominant biofouling species found in the Lim and Pomer Bay correspond to those previously observed in the Eastern Adriatic Sea (Fig. 1). Their variable horizontal and vertical distribution clearly reflects the complexity of ecological processes even within a small spatial scale.

Higher abundance of species found in Lim with respect to Pomer is probably related to the poor water circulation and consequently higher availability of nutrients within highly enclosed narrow and elongated fjord-like Lim Bay. On the other hand, Pomer Bay is deeper, more connected to the open sea and subjected to continuous exchange of water mass. The hydrographic conditions may have favoured more frequent occurrence of Tunicate species in particular Botryllus, Phallusia mammilata and Diplosoma listerianum within Pomer Bay.

Considering a great spatial variability and abundance of biofouling macrofauna species, further monitoring of their occurrence and recruitment peaks is required in order to choose an optimal deployment period for collectors and reduce negative effects of biofouling on aquaculture facilities and production.