Experimental co-culture of low food-chain organisms, Sabella spallanzanii (Polychaeta, Sabellidae) and Cladophora prolifera (Chlorophyta, Cladophorales), in Porto Cesareo area (Mediterranean Sea)

The filter feeder polychaete Sabella spallanzanii (Gmelin) was co-cultured with the green seaweed Cladophora prolifera (Roth.) Kunz, in an off-shore experimental system. Both species have previously been experimented as bioremediator organisms for waste treatment deriving from aquaculture farms and can have a high economic value as a byproduct of polyculture. The present experiment has been conducted in an area 2 miles off the coast of Porto Cesareo (Ionian sea, Southern Italy). The growth was followed in some modules anchored to the bottom at two different depths (15 and 25 m depth). The results indicate differences among replicates located at different depths. Both organisms show a faster growth at the shallower levels. Within this level, polychaetes reached a mean biomass of 860 +/- 74 mg dw (average +/- SE) per worm, 30 times larger than that of the starting point, after a standstill in the first period, probably due to the manipulation activities. The major growth has been recorded during the winter. Algae have shown an increase of 34 g ww month(-1) (average +/- SE) in the shallower levels vs. only 11 g ww month(-1) (average +/- SE) in the deeper levels. The RGR calculated after 60 days was 115% in the shallower levels vs. about 60% in the deeper ones. A considerable decrease in growth rate was observed during the last period; this was probably due to the presence of increasing fouling community on the rearing cages surely affecting the light intensity