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). Sedi ment chemistry, microbial and meiofaunal assemblages were investigated from March 1997 to February 1998 on monthly basis at two stations: the first wa s located under the mussel farm, while the second nas at about 1-km distanc e and served as control. Benthic response to changes in the biodepositional regime was investigated in terms of biochemical composition of the sedimen tary organic matter, phytopigment content, bacterial abundance and composit ion and meiofaunal community structure. A large accumulation of chloroplast ic pigments, proteins and Lipids nas observed under the mussel farm. Such c hanges in the sedimentary conditions reflected the accumulation of faeces a nd pseudo-faeces and led to the creation of reducing conditions. Microbial assemblages beneath the mussel cultures increased their densities and displ ayed, when compared to the control, a larger cyanobacterial importance asso ciated to a strong decrease of the picoeukaryotic cell density. Farm sedime nts displayed significant changes in meiofaunal density: turbellarian, ostr acod and kinorhynch densities decreased significantly, while copepods remai ned constant or increased possibly profiting of the enrichment in microphyt obenthic biomass associated to mussel biodeposits. The comparative anal? si s of the mussel biodeposition and fish-farm impact on sediments beneath the cultures revealed that mussel farms induced a considerably lower disturban ce on benthic community structure. (C) 2000 Elsevier Science Ltd, All right s reserved.