Mariculture for bacterial and organic waste removal: a field study of sponge filtering activity in experimental farming

Culture experiments in the field were performed on
western Mediterranean populations of Ircinia variabilis
and Agelas oroides. To evaluate culture and
filtering performances among polluted and unpolluted
sites in shallow waters, farming experiments
were carried out in a harbour, a small tourist nautical
base and a pristine biotope. Sponge explants
were cultured onto nylon ropes, and in situ clearance
rate tests were performed on farmed sponges
to assess filtering ability under diverse farming conditions.
At the harbour site, sponge survival and
growth were similar to that observed in the two
unpolluted sites until early summer, when a rapid
increase in explant mortality occurred in response
to extreme variations in environmental conditions.
Filtering experiments revealed high retention and
clearance rates of I. variabilis and A. oroides at all
sites. The highest rates were observed at the polluted
site, reflecting the optimal metabolic performance
of explants in the first phase of culture under
stressful conditions. Our results highlight the
feasibility of sponge microcosms and the ability of I.
variabilis and A. oroides to clear large volumes of
water of organic and bacterial loads in polluted sites.