UC San Diego

Determining the ecological impacts of long-term change versus those caused by shorter-term variation is important for making predictions and managing ecosystems. Historical surveys offer potentially valuables baseline data for the evaluation of long-term change. This study is based on two historical ecological surveys at two rocky intertidal sites (Dike Rock and Ocean Beach) in San Diego, California. The historical surveys are notable in that they overlap with or predate a major oceanographic climate shift in Southern California in the late 1970s. Although the 2012 surveys showed that the invertebrate communities at both sites had changed since the historical surveys, the changes were dissimilar. While both sites lost and gained a few invertebrate species, notably losing the predatory whelk Nucella emarginata and gaining another in Mexacanthina lugubris, species abundances at Dike Rock increased while those at Ocean Beach decreased. This may be due to the different substrates at the sites: the sandstone of Ocean Beach may have been more impacted by a changing wave climate than the basalt of Dike Rock. Data on the percent cover of macroalgae at Ocean Beach demonstrated changes in seven out of ten morphological groups. However, the lack of dramatic changes overall indicates the resilience of rocky intertidal communities to human impacts and the effects of climate change