Development and short-term dynamics of macrofouling assemblages on fish-cage nettings in a tropical estuary

A study was conducted at a fish culture farm in the Jaha River estuary, Malaysia, to examine the structure and development of macrofouling assemblages on floating net-cages. The study was conducted during the dry (August–October 2001) and wet (December–February 2002) seasons. Biofouling on 1.6 cm mesh net panels (size 0.2 m × 2 m) suspended inside (P, T) and outside (O) experimental net-cages was monitored every week until net openings were completely occluded by macrofouling organisms (8 wk and 12 wk for dry and wet seasons respectively). Seven species (6 phyla) of sessile organisms and 23 species (3 phyla) of non-sessile associates were recorded. Macro-colonization of net panels began with the hydroid Plumularia sp. irrespective of season and treatment (P, T, and O), while other species only appeared after 1 or 2 weeks of immersion. Inside net-cages where water flow was slow (mean < 6 cm s−1 at 0.50–0.75 m depth); macroalgae (Polysiphonia sp.), anthozoans (unidentified anemone), barnacles (Balanus amphitrite), amphipods (Gammaropsis sp. & Photis sp.), and tanaids (Leptognathia sp.) were dominant on the net panels during the dry season. In the wet season, hydroid (Plumularia sp.), mussel (Xenostrobus mangle), and nematode abundance were however significant. With stronger water flow (mean ≈ 20 cm s−1) as occurring outside the net-cages, macrofouling assemblages for both seasons comprised mainly Plumularia sp. and Gammaropsis sp. The macrofouling assemblage showed a clear succession of species that occupied different layers of the net panels. The study shows that while organic enrichment and retarded water flow together enhance the development of macrofouling assemblages, salinity, depth, substrate (net) area and species competition specifically influence community structure, colonization, and depth distribution of the macrofouling organisms.