First report on in situ biodeposition rates of ascidians (Ciona intestinalis and Styela clava) during summer in Sanggou Bay, northern China

Ascidians are globally important members of marine fouling communities. We measured in situ biodeposition rates of Ciona intestinalis and Styela clava, common biofoulers of aquaculture infrastructure, in Sanggou Bay, northern China, during September. Ascidian numbers were recorded within a scallop Chlamys farreri farming zone to assess biodeposit loading. Both ascidians were most abundant on lantern nets and scallop shells in August and September. The average densities of C. intestinalis and S. clava in the farming zone in September were approximately 329 and 22 ind. m-2, respectively, and their biodeposition rates were 32.1 and 121.2 mg dry material ind.-1 d-1, respectively. Total daily biodeposit production by ascidians in September within the scallop farming zone may amount to 13.24 g m-2, with daily organic matter, C, N, and P biodeposition rates of 1.88, 0.94, 0.11, and 0.98 × 10-2 g m-2, respectively. The predicted daily biodeposit production by C. intestinalis and S. clava within the scallop farming zone in the bay during September was 105.9 t dry material, 7.52 t C, 0.86 t N, and 0.078 t P. By comparison, drop-off to the sea floor was approximately 143.0 t of dry matter for an entire growing season, which would be a relatively small input if averaged on a daily basis. However, some of the drop-off is expected to occur as a short-duration pulse of material (e.g. during cleaning), which may be relatively important in terms of benthic effects. The results suggest that the biodeposition processes and drop-off of C. intestinalis and S. clava may play an important role in coupling material fluxes from the water column to the seabed