Abstract:
Seagrass beds have served as nursery grounds and suitable habitats for many
marine organisms. Specifically, the leaves have provided a good source of food and
nutrition for marine organisms. Sea urchin herbivory on seagrasses had already been
demonstrated to cause reductions in the biomass of seagrasses. This present study
investigated the amount and rate of reduction in the biomass of Thalassia hemprichii in a
grazing set-up, conducted over a period of one week in Paniquian Island, Puerto Galera,
Oriental Mindoro. Comparisons of biomass reductions and grazing rates were made
between two varying stocking set-ups of sea urchins. Single-grazer set-up (SGSU): 1
grazer/cage or 11 grazers/m2, and multiple-grazer set-up (MGSU): 2 grazers/cage or 22
grazers/m2, were established in cages, 0.3m x 0.3 m x 0.3 m dimensions. Also observed
were the grazing behavior of the sea urchins and the influence that their behaviors have
had on the amount and rate of seagrass biomass reduction. Results showed that at 0.05
level of significance, there was no significant difference between biomass reductions of
Thalassia hemprichii, but that there was significant difference between grazing rates of
Toxopneustes chlorocanthus. The averaged values from the three replicates, for each
stocking set-up, showed higher biomass reduction and grazing rate values for SGSU than
for MGSU. The study demonstrated that grazing behavior of the sea urchins,
Toxopneustes chlorocanthus had influenced the grazing capacities of these organisms.
