Herbivory on Posidonia oceanica: Magnitude and variability in the Spanish Mediterranean

We examined the leaf age dependence, magnitude and variability of herbivore consumption of Posidonia oceanica (L.) Delile leaves in the Spanish Mediterranean. Two patterns of herbivore consumption along the life-span of P. oceanica leaves were found, namely a linear and a parabolic curve of cumulative leaf consumption versus leaf age, which are indicative of leaf- age-independent consumption rates and preference for mid-aged leaves, respectively. The fish Boops salpa contributed about 75% to the total herbivore consumption, and seemed to be responsible for the parabolic pattern of consumption with leaf age. Herbivory appeared 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 production. This percentage tends to increase in the northern populations of the Spanish Mediterranean as a result of the longer leaf life-span and associated higher cumulative consumption values, and the lower leaf production of these populations. It is concluded that, in spite of the low levels of herbivory on P. oceanica in the Mediterranean, this seagrass supports a high herbivore production due to its large primary production.