Microbial and meiofaunal response to intensive mussel-farm biodeposition in coastal sediments of the Western Mediterranean

We studied the impact of organic loads due to the biodeposition of a mussel farm in a coastal area of the Tyrrhenian Sea (Western Mediterranean). Sediment chemistry, microbial and meiofaunal assemblages were investigated from March 1997 to February 1998 on monthly basis at two stations: the first was located under the mussel farm, while the second was at about 1-km distance and served as control. Benthic response to changes in the biodepositional regime was investigated in terms of biochemical composition of the sedimentary organic matter, phytopigment content, bacterial abundance and composition and meiofaunal community structure. A large accumulation of chloroplastic pigments, proteins and lipids was observed under the mussel farm. Such changes in the sedimentary conditions reflected the accumulation of faeces and pseudo-faeces and led to the creation of reducing conditions. Microbial assemblages beneath the mussel cultures increased their densities and displayed, when compared to the control, a larger cyanobacterial importance associated to a strong decrease of the picoeukaryotic cell density. Farm sediments displayed significant changes in meiofaunal density: turbellarian, ostracod and kinorhynch densities decreased significantly, while copepods remained constant or increased possibly profiting of the enrichment in microphytobenthic biomass associated to mussel biodeposits. The comparative analysis of the mussel biodeposition and fish-farm impact on sediments beneath the cultures revealed that mussel farms induced a considerably lower disturbance on benthic community structure. Copyright (C) 2000 Elsevier Science Ltd.