PS 10-123 - Community Structure and Species Dynamics in Oregon’s High Intertidal

Abstract: The intertidal is a highly dynamic community, requiring organisms to survive in an environment with a wide range of potential conditions. These environmental gradients, especially with regards to temperature stress, will only continue to become more extreme as climate change progresses, making studies of intertidal communities key to predict how species in less stressful environments may eventually respond to similar stressors. Despite the multitude of studies in the intertidal, the algae and barnacle-dominated high zone of the intertidal, defined as the highest region of coastline that still undergoes regular daily immersion, is not well understood in comparison to the rest of the region. Our study aims to understand how trophic interactions in this community may shape its overall structure. Specifically, we studied the influence (presence or absence) of three abundant molluscan grazer species (limpets) on primary space occupiers attached to the rock. In the field, we excluded grazers using a randomized block design at two sites in each of two regions. Treatments included all species present (control) or absent (total exclusion), and presence of each species alone (single grazer) the high intertidal; response variables were abundance of algae and sessile invertebrates from initial colonization of bare rock onwards.

Preliminary results show no significant impact of grazers on the abundance of primary space occupiers. These findings suggest that grazing is not a major determinant of community structure. Potential reasons for a lack of response include a failure of barnacle settlement, which facilitate algal colonization, or abiotic stressors. These data are consistent with other prior studies, which suggested that the dominant high intertidal macroalgae, fucoid algae, may be too large or tough for small, high intertidal grazers to control. Future studies therefore must determine whether stressors such as temperature, which have been shown to reduce the toughness of intertidal macroalgae, or the resumption of barnacle recruitment may alter this relationship, especially as climate change continues to intensify these factors.