A PRODUCTION-MODEL FOR POSIDONIA-OCEANICA BASED ON TEMPERATURE

The leaf growth and plant population dynamics of the Mediterranean sea grass Posidonia oceanica were investigated in relation to relevant env ironmental factors, such as temperature and irradiance. Two stands, lo cated at 5 and 22 m in a continuous P. oceanica bed off Lacco Ameno (I sland of Ischia, Gulf of Naples), were studied over 1 year. The aims o f the study were: (1) to investigate the influence of temperature on t he spatial and temporal growth pattern of P. oceanica, using an ad hoc simulation model of the monthly plant production; and (2) to identify the most efficient descriptors of plant growth, and therefore to achi eve a simple method by which shoot production could be estimated. Irra diance is low at 22 m in the Lacco Ameno meadow, with the minimum valu e lower than 80 mu E m(-2) s(-1) in winter. Temperature also different iates the two water bodies in summer. The two stands differ for their structure (e.g. leaf area index), for plant production, and for some p henological features (e.g. leaf width). The best biological descriptor s of plant production were identified and an equation was derived to e stimate plant growth; the equation is based on the growth of the leaf of Rank 2, which describes the growth pattern of the whole plant. Sign ificant correlations between temperature and the production descriptor s were found. A numerical model of yearly leaf growth was devised. The model was validated by predicting the growth pattern of several Medit erranean P. oceanica beds and comparing with observed values. It was a lso applied to simulate plant growth for the Lacco Ameno bed in preced ing years, at both 5 and 22 m depths. (C) 1997 Academic Press Limited.