The use of lepidochronology to assess the impact of terrigenous dischargeson the primary leaf production of the Mediterranean seagrass Posidonia oceanica

The impact of terrigenous discharges on the leaf production of the Mediterr anean seagrass Posidonia oceanica has been investigated. The shoot leaf pro duction has been estimated by using the lepidochronological technique (a re construction method based on the cyclic annual variation of the sheath thic kness), whose sensitivity as a tool to detect this kind of man-induced impa ct has also been tested. For this purpose, a number of 20 shoots were colle cted at each of the four sites investigated, represented by two impacted an d two control sites, located along the northern coast of the Ischia Island (Gulf of Naples, Italy). The annual leaf production per shoot of the year i n which the Impact occurred and that of the two previous years has been est imated. A decrease of the leaf production was observed in P. oceanica shoot s from the impacted sites after the terrigenous discharges, while such a tr end was not detected at the control sites. The decrease of the primary leaf production (around 20%) was mainly attributable to the decreased mean numb er of leaves produced per year, whereas mean leaf density and length remain ed constant. The results obtained in this study confirm that P. oceanica is a sensitive indicator of the environmental quality of coastal waters and t hat lepidochronology is a useful tool to provide evidence of the impact ind uced by terrigenous discharges on coastal zones colonized by this seagrass. (C) 2000 Elsevier Science Ltd. All rights reserved.