SEAGRASS REGRESSION CAUSED BY FISH CULTURES IN FORNELLS BAY (MENORCA,WESTERN MEDITERRANEAN)

A three year monitoring programme (1988-1990) of embayment habitats do minated by the seagrasses Posidonia oceanica and Cymodocea nodosa was carried out in Fornells Bay (Menorca, Western Mediterranean), where gi lthead seabream (Sparus auratus) was artificially reared. Responses ra nging from shoot density decrease to total seagrass demise were observ ed. Posidonia oceanica was more drastically and quickly affected than Cymodocea nodosa. In 1990, a total of 2 ha of seagrass were significan tly degraded. Increased light attenuation, sedimentation rates, and gr azing pressure are proposed as the principal factors accounting for se agrass regression.