Resistance of rocky intertidal communities to oceanic climate fluctuations

A powerful way to predict how ecological communities will respond to
future climate change is to test how they have responded to the climate of
the past. We used climate oscillations including the Pacific Decadal
Oscillation (PDO), North Pacific Gyre Oscillation, and El Niño Southern
Oscillation (ENSO) and variation in upwelling, air temperature, and sea
temperatures to test the sensitivity of nearshore rocky intertidal
communities to climate variability. Prior research shows that multiple
ecological processes of key taxa (growth, recruitment, and physiology)
were sensitive to environmental variation during this time frame. We also
investigated the effect of the concurrent sea star wasting disease
outbreak in 2013–2014. We surveyed nearly 150 taxa from 11 rocky
intertidal sites in Oregon and northern California annually for up to 14
years (2006–2020) to test if community structure (i.e., the abundance of
functional groups) and diversity were sensitive to past environmental
variation. We found little to no evidence that these communities were
sensitive to annual variation in any of the environmental measures and
that each metric was associated with < 8.6% of yearly variation in
community structure. Only the years elapsed since the outbreak of sea star
wasting disease had a substantial effect on community structure, but in
the mid-zone only where spatially dominant mussels are a main prey of the
keystone predator sea star, Pisaster ochraceus. We conclude that the
established sensitivity of multiple ecological processes to annual
fluctuations in climate has not yet scaled up to influence community
structure. Hence, the rocky intertidal system along this coastline appears
resistant to the range of oceanic climate fluctuations that occurred
during the study. However, given ongoing intensification of climate change
and increasing frequencies of extreme events, future responses to climate
change seem likely.