Devastating transboundary impacts of sea star wasting disease on subtidal asteroids

Sea star wasting disease (SSWD) devastated intertidal sea star populations from Mexico to Alaska, but little detail is known about its impacts to specific subtidal species. We assessed the impacts of SSWD over 5 of the 6... [ view full abstract ]

Sea star wasting disease (SSWD) devastated intertidal sea star populations from Mexico to Alaska, but little detail is known about its impacts to specific subtidal species. We assessed the impacts of SSWD over 5 of the 6 basins of the transboundary US/Canadian marine ecosystem, the Salish Sea, a world-wide hotspot for temperate asteroid species diversity with a high degree of endemism. We also studied SSWD on Washington’s outer coast. We analyzed data on the three most common sea star species collected by trained volunteer scuba divers, before (2006-2013) and after (2014-2015) the SSWD outbreak, as well as scientific strip transect data for 8 common asteroid species and one genus collected by scientific divers in the San Juan islands during summer 2014 and 2015. In all 5 basins and on Washington’s outer coast the sunflower sea star (Pycnopodia helianthoides), the dominant species, and the giant pink sea star (Pisaster brevispinus) showed severe declines, while the leather sea star (Dermasterias imbricata) did not. Strip transect data showed increasing SSWD prevalence in P. helianthoides, mottled star (Evasterias troschelii) and Henricia sp. between May and August 2014, although the maximum prevalences varied among species. Transect counts showed severe decline of adult P. helianthoides and moderate declines of E. troschelii and Henricia sp. Rare subtidal species such as purple sea star (Pisaster ochraceus), P. brevispinus, sun star (Solaster stimpsoni) and rainbow star (Orthasterias koehleri) also seem to have declined, while counts of D. imbricata and Vermilion star (Mediaster aequalis) suggested increasing densities. Our findings are consistent with previous reports on severe P. helianthoides reductions from California to Alaska, which rises concern with respect to the conservation of this ecologically important species. These data also highlight differential susceptibility and impact of SSWD among asteroid species.