Relationship between sediment distribution and Posidonia oceanica seagrass

Relationships between sedimentary features and the distribution and structu re of Posidonia oceanica meadows were investigated in the Gulf of Oristano (Sardinia) in a study site stretching from the mouth of the Tirso River in a more sheltered, inner sector of the gulf to an outer, more exposed sector near the rocky Cape San Marco. The results demonstrate that gradients in s ediment texture and composition can be related to meadow distribution and a real coverage. Wie suggest that this involves the mechanical trapping of fi ne particles by the plants, enhanced mud deposition due to dampening of wav e action in the meadows, and the admixture of bioclastic sediments linked t o increased production by epiphytes and invertebrates. Independent evidence of seagrass erosion was recorded in an unvegetated breach ill the meadow. The mass of fine sediment which would be resuspended in the wake of meadow destruction was estimated at 30-90 x 10(3) tonnes km(-2) an amount which co uld substantially influence water quality and ecosystem stability in the gu lf.