Latitudinal variation in long-term stability and resilience of North American rocky intertidal communities

The potential for marine communities to be resilient to extreme environmental conditions (e.g., warm, hypoxic, or acidic water events, powerful storms, and altered ocean current patterns) has received a substantial amount of attention in recent years, as the urgency to mitigate for and protect against the resulting impacts grows. At the interface between land and sea, temperate rocky intertidal shores are the most accessible of marine habitats and hold high value for harvest, leisure, and scientific research, particularly for studies of anthropogenic impacts. We used data from the Multi-Agency Rocky Intertidal Network (MARINe) long-term monitoring program to examine patterns of resilience within rocky intertidal communities along the west coast of North America. We applied a multivariate community similarity approach to assess resilience—here defined as the ability to resist change or recover to a reference state. In particular, we explored: 1) the regional association between resilience and periodic warm water events (2 El Niños and the 2013-15 warm water “blob”), 2) the relationship between community resilience at the site scale and three attributes of biodiversity: richness, diversity and evenness, 3) the role of protection (inside/outside MPAs), and 4) the relationship between resilience and presence of the mussel, Mytilus californianus, an important “foundation” species that provides structure and habitat for many other organisms. We found differences in resilience associated with region and protection status. Resilience was linked to high species richness and perhaps counterintuitively, low evenness, although this result makes sense given the importance of foundation species in this system. The ability to distinguish resilient from non-resilient sites, and the factors likely responsible for such patterns have significant implications for resource management and conservation.