HERBIVORY ON POSIDONIA-OCEANICA - MAGNITUDE AND VARIABILITY IN THE SPANISH MEDITERRANEAN

We examined the leaf age dependence, magnitude and variability of herb ivore consumption of Posidonia oceanica (L.) Delile leaves in the Span ish Mediterranean. Two patterns of herbivore consumption along the lif e-span of P. oceanica leaves were found, namely a Linear and a parabol ic curve of cumulative leaf consumption versus leaf age, which are ind icative of leaf-age-independent consumption rates and preference for m id-aged leaves, respectively. The fish Boops salpa contributed about 7 5% to the total herbivore consumption, and seemed to be responsible fo r the parabolic pattern of consumption with leaf age. Herbivory appear ed to be a minor factor in the control of P. oceanica production since it only accounted, on the average, for about 2% of its leaf productio n. This percentage tends to increase in the northern populations of th e Spanish Mediterranean as a result of the longer leaf life-span and a ssociated higher cumulative consumption values, and the lower leaf pro duction of these populations. It is concluded that, in spite of the lo w levels of herbivory on P. oceanica in the Mediterranean, this seagra ss supports a high herbivore production due to its large primary produ ction.