Bruce A. Menge1, Francis Chan1, Karina J. Nielsen2, and Tess L. Freidenburg3. (1) Oregon State University, (2) Sonoma State University, (3) California State University, East Bay
Background/Question/Methods Detection of the impacts on ecosystems of climate perturbations such as El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and North Pacific Gyre Oscillation (NPGO) can provide insight and understanding into long-term ecological changes that might be expected with climate change. Although these perturbations are primarily measured in the oceans, our understanding of their influence on key ecosystem processes in temperate coastal ecosystems is limited. Recent results based on analysis of time series datasets of up to 20 yr length suggest that two key ecological subsidies in the northern California Current System (NCCS), phytoplankton abundance (food for filter-feeding ecosystem engineers) and mussel recruitment (potential mussel population replenishment), increased by up to 5 orders-of-magnitude in the year 2000. Further, these changes were linked to patterns of variation in the NPGO, a 10-15 year climatic cycle related to variation in winds over the North Pacific. Did these changes lead to changes in intertidal community structure? Results/Conclusions Analysis of long-term data on community structure indicates that no persistent monotonic change in abundances of strong interactors, including mussels, barnacles and sea stars, occurred between 1990-2008. Since prior research has indicated that an important precondition for successful mussel colonization is facilitation by dense covers of barnacles, we analyzed our 20-year data set on barnacle recruitment to evaluate if similar temporal shifts in recruitment magnitude had occurred. In contrast to mussel recruitment, barnacle recruitment did not vary with climate patterns. Further analysis suggested that patchy increases in mussels in the low zone occasionally occurred but only one year after dense barnacle recruitment. A field experiment demonstrated that increases in mussels occurred only when predation on barnacles was prevented. Thus, despite the climatically-driven increase in mussel recruitment, barnacle recruitment was insensitive to climate variability, and neither facilitation by adult barnacles nor temporally persistent predation were altered. We conclude that although some components of rocky intertidal ecosystems exhibit high sensitivity to climatic variation, other components have been less sensitive. With the resulting lack of change in species interactions, this differential sensitivity of major habitat-forming species disrupts the sequence of events that could lead to major disruption of community structure.
