The differential effects of two dominant epiphyte grazers associated with surfgrass Phyllospadix torreyi in controlling epiphytic algae levels in seagrass beds

Surfgrass Phyllospadix torreyi is an ecologically important foundation species of intertidal habitats throughout the west coast of North America, acting as a nursery and carbon sink. Excessive epiphytic growth stimulated by anthropogenic nutrient uploading can inhibit their photosynthesis, negatively impacting these invaluable habitats. Therefore, there is a growing need to understand the roles played by epiphyte grazers- i.e. hermit crabs (Pagurus spp,.) and turban snails (Tegula spp.) in controlling epiphytic overgrowth in surfgrass beds. In this study, we experimentally examined the effectiveness of these two dominant grazers in the surfgrass ecosystem. Based on the morphological and potential behavioral differences, we hypothesized that hermit crabs and snails will have varying influence on epiphytic growth on surfgrass. Specifically, we predict that hermit crabs will have disproportionately larger effects on overall epiphyte loading, due their ability to forage effectively in surfgrass canopy where epiphytes accumulate faster. To investigate this, we conducted a five week mesocosm experiment where we reared surfgrass shoots with either hermit crabs, turban snails, or without any grazers. After terminating the experiment, surf grass was collected, the epiphytic algae were removed from each blade, and the dry weight of the grass and epiphytes were recorded. Our preliminary results suggest that hermit crabs graze at the canopy more frequently than turban snails, which were more often found grazing within the basal area of surfgrass shoots and on the substrate. Further data collection and analysis will examine whether variable grazing activities between the two dominant grazers have led to different epiphytic growth on surfgrass.