Rearing performances of Spongia officinalis on suspended ropes off Southern Italian coast (Central Mediterranean Sea)

The availability of bath sponges has been recently reduced due to the depletion of natural banks due to the high fishing pressure together with some local epidemic events. At present, the commercial supply is far below the demand. The main purpose of this work was to estimate the rearing performance of Spongia officinalis var. adriatica, one of the most common Mediterranean commercial sponges, testing two different variants of culture on suspended ropes: a horizontal system placed close to the seabed, and a vertical system extended along the water column. The trials were carried out in Southern Italy (Ionian coast of Apulia, Central Mediterranean) from April 1997 to April 2000. Wild specimens of sponge were cut into pieces of different weight to test possible differences in growth and survival. During the study period, both systems resisted deterioration due to water movement and other ecological factors. In general, the growth performance (average weight, specific growth rate) did not significantly vary between the cultivation systems, nor were statistical differences in growth detected between the cuttings of different initial size. The mean growth observed was rather variable among sponge cuttings, even considering the same rearing condition and size range. The measured variations of hydrological parameters did not seem to affect survival, growth performance, or reproductive activity, which was detected almost all year round. Larger explants (about 50 g in wet weight) reached the commercial size after three years of rearing, thus identifying this initial size as the most suitable for cultivation purposes. At the end of the study period, the survival rate was 75%, with a more apparent decrease during the first year of rearing.