The diet and feeding rates of gastropod grazers in Singapore's seagrass meadows

A wide variety of organisms are known to graze on seagrasses and their associated epiphytes, and this plant-animal interaction can affect the health of seagrass meadows. Grazing patterns tend to vary across meadows and faunal groups, and little is known regarding how gastropod grazers influence meadows in the tropics. To better understand this interaction, we surveyed the gastropod diversity in five meadows in Singapore. Further, grazing potential (i.e. potential food sources and feeding rates) of common gastropod species was quantified through ex situ grazing experiments, while their diet compositions were elucidated using dual delta C-13 and delta N-15 stable isotope analyses. The surveys revealed a high diversity of 274 gastropod species/morphospecies while PERMANOVA and SIMPER analyses showed that communities differed significantly among sites but not among seagrass species. Diet composition analysis indicated that seagrass leaves were the main food source for most gastropod species examined while epiphytes were important for microsnail (shell size <5 mm) species. However, all the gastropod species tested fed on epiphytes in the ex situ experiments. These findings contribute new insights into grazing by marine gastropods on tropical seagrass meadows, and highlight the potential importance of both direct grazing and epiphyte removal on tropical meadows.