Does geology matter? The effects of substratum and substrate properties on temperate rocky intertidal communities

Rock substrates and their properties are key components of the physical environment for many marine benthic communities. Each rock represents a unique geologic origin and time. The organisms inhabiting them also have their own histories and different organisms arrived on the evolutionary scene at different times. Thus, organisms have been interacting for different periods of time on substrates and their ecology is couched in this geologic context. Ecological research rarely includes this historical perspective, even through proxies (Chapter 1). In the rocky intertidal, the role of substratum in community ecology is surprisingly understudied for communities that have been hotbeds for conceptual advances in ecology. Using methods in field ecology, geomorphology, and petrology, I determined if: (1) substrate type affects community structure, diversity, and spatial and temporal variation in the rocky intertidal, (2) surface complexity is an important substrate feature for intertidal organisms, (3) mineralogy affects species or community structure, (4) substrates and their properties elicit differential responses by intertidal species.;On a local scale (Chapter 2), a sedimentary island comprised of distinct sandstone units presented a broad range of surface complexity to intertidal organisms. Body size of the dominant territorial limpet Lottia gigantea was substrate-driven, which can greatly impact this organism's sex ratio as well as algal communities and space competitors in the rocky intertidal. On a regional scale (Chapter 3), multiple rock types that were monitored exhibited differences in community structure, diversity, and biomass. These effects were small and driven by a small proportion of species. Surface complexity was not the primary factor in structuring communities and other properties such as mineral composition and susceptibility to erosion were also important. Natural and artificial substrates supported distinct communities. Variation in limpet body size and abundance was affected by substratum, but recruitment was not (Chapter 4). These relationships partly explained spatial and temporal variation in the intertidal. Results from these studies demonstrate the importance of substratum and can be incorporated into coastal conservation. This is especially important in the face of global climate change since intertidal communities will be subject to changing geologic settings.