Temperature and community consequences of the loss of foundation species: Surfgrass (Phyllospadix spp., Hooker) in tidepools

By ameliorating environmental conditions, mediating species interactions and regulating resource availability in ecosystems, habitat-forming, foundation species underlie the structure and function of many ecological communities. Current and predicted human-induced changes to ecosystems require a mechanistic understanding of how foundation species enable the persistence of diverse, functioning ecological communities. By manipulating the abundance of a putative foundation species of rocky intertidal tidepool communities, the seagrass Phyllospadix spp. (surfgrass), this study assesses how surfgrass affects the thermal environment and structure of tidepool communities over a period of two years. Surfgrass removal pools experienced temperatures up to 10 °C higher than control pools during low tide. Changes in community composition of sessile organism accompanied this change in thermal regime. Over two years, removal pools saw a significant decline in the abundance of coralline crusts and bare space and an increase in the abundance of foliose red algae while control pool communities remained stable. At the level of functional groups, community similarity metrics showed pool communities became more variable in space in response to surfgrass removal, demonstrating that pool communities diverge dramatically in the absence of surfgrass. In removal pools, recovery of surfgrass was limited with less than 25% of pre-removal abundance after two years. However, removal pool communities shifted toward species compositions that favor surfgrass recruitment and suggest a mechanism by which surfgrass recovery may be enhanced over the long-term. Surfgrass clearly play a foundational role in tidepools by reducing pool temperatures and act to stabilize tidepool communities.