Award: OCE-1243958

In Fall 2011 and during 2012, we documented the extent of a widespread and severe mass mortality of rocky shore invertebrates along the north-central California coast in the northeast Pacific Ocean, following a harmful algal bloom (which occurred in August 2011). Formerly abundant intertidal populations of the ecologically important purple sea urchin (Strongylocentrotus purpuratus) and the predatory six-armed sea star (Leptasterias sp.) were extirpated from approximately 100 km of coastline; some purple sea urchins survived at depth subtidally. Other invertebrates, including the ochre sea star (Pisaster ochraceus) and gumboot chiton (Cryptochiton stelleri), also experienced elevated mortality. The severity and spatial scale of effects suggest the potential for long-term population, community, and ecosystem consequences. Continued surveys in 2013 and 2014 showed that purple sea urchins are recolonizing the coastline from which they were extirpated, albeit spatially patchily and mostly in low numbers; the six-armed sea star has yet to return to most sites. (The ochre seastar, one of the most important predators in this community, subsequently experienced a second mass mortality in 2014 attributed to seastar wasting disease. A few individual seastars survived, and this project has begun to identify the genetic basis of resistance to this disease.) Genetic analyses are revealing the diversity and geographic origins of the new colonists. As predicted, sea urchins, which produce vast numbers of long-lived planktonic larvae are recovering much faster and have much more local genetic dievrsity than other species that produce fewer offspring and with less dispersal potential. Understanding the cause and extent of, as well as recovery from, large scale disturbances may provide insight into marine rocky intertidal population dynamics, community dynamics, and potential short- and long-term consequences of future environmental change. Last Modified: 12/08/2016 Submitted by: Richard K Grosberg