Ecological subsidies to rocky shore communities : setting the stage for community dynamics in the Northeast Pacific

Graduation date: 2007This dissertation focuses on the importance of pelagic subsidies in the Northeast Pacific to rocky shore community regulation. My results document the patterns of pelagic subsidy supply, determine if those subsidies are correlated with community structure, and examine if community regulation differs between areas of high- and low-subsidies. Understanding how consistent ocean features and currents affect the supply of subsidies to rocky shore communities, and how those communities are in turn regulated, will enable managers to more effectively implement conservation and management policies.\ud \ud In Chapter 2, my co-authors and I studied the spatial and temporal patterns of pelagic subsidies along the northern California and Oregon coasts. Intertidal invertebrate recruitment consistently changed from very high levels north of Cape Blanco (southern Oregon), to intermediate levels between Capes Blanco and Mendocino (northern California), to very low levels south of Cape Mendocino. Phytoplankton concentration and mussel growth was higher north of Cape Blanco than south of Cape Blanco. Importantly, the regional differences in phytoplankton concentration and mussel growth suggest that bottom-up inputs may also be affecting community structure within the region.\ud \ud In Chapter 3, my co-authors and I examined the correlations between ecological subsidies and the cover and density of mussel bed organisms. There was a strong correlation between our general measure of pelagic subsidies and the composition of the mussel bed community. However, cover of the main constituent of the mussel bed, Mytilus californiainus, was not correlated with subsidies. This study confirmed the association between subsidies and community structure that had been previously untested.\ud \ud In Chapter 4, using a comparative-experimental approach I addressed the effect of recruitment on early mussel bed succession. Invertebrates dominated succession in the high-recruitment region studied, while algae played a principle role in the succession pathway of the low-recruitment region studied. While recruitment appeared to underlie the regional differences in early mussel bed succession, the differing effects of competition and predation within each recruitment regime led to different successional regimes