Grazing of inflorescences of the seagrass Posidonia oceanica (L.) Delile

An experiment using cages was designed to demonstrate herbivore consumption of Posidonia oceanica (L.) Delile reproductive structures, in a north-western area of the Mediterranean Sea. The percentages of mature inflorescences and those damaged by herbivores in caged vs, uncaged (control) vs. partially caged plants (artefact control) were compared. Inflorescences damaged by herbivores were 84.3 +/- 3.1% in the control and 79.5 +/- 3.2 % in partial cages. Significantly more mature inflorescences were found in caged (37.5 +/- 2.4%) vs. uncaged (10.1 +/- 2.9 %) and partially caged plants (6.7 +/- 0.9 %). The real contribute of herbivores to the loss of fertilised inflorescences of P. oceanica was approximately 27 %, as the differences between mortality in caged and in uncaged plants. These results suggest that herbivores could affect sexual reproduction in P. oceanica, but further investigation is needed to investigate biotic interactions in the meadows.