UC San Diego

The selective removal of large individuals from a population (size-selective harvesting) is one of the most wide spread anthropogenic impacts of species in the marine environment. Size-selective harvesting can have numerous direct and indirect effects on the population biology, life history, and ecology of the target species and surrounding communities. This dissertation examines the cascading effects of size-selective harvesting on an ecologically important member of the rocky intertidal community of California, the Owl limpet, Lottia gigantea. In the first chapter, I review what is known about the effects of size-selective harvesting across fish, marine invertebrates, and terrestrial vertebrates. In Chapter 2, I examine the effects of size-selective harvesting on the population biology and ecology of L. gigantea by comparing exploited field sites with well-protected field sites across a large portion of the California mainland portion of its geographic range. I show that populations where L. gigantea is size-selectively harvested differ significantly in terms of size, abundance, biomass, and reproductive output compared to populations of this species that are protected from human harvesting. These differences also lead to changes in the structure of mid- intertidal communities, primarily due to the scaling relationship between size and space occupancy in L. gigantea. In Chapter 3, I show that populations of L. gigantea are able to adjust a very important aspect of their life history (the timing of sex change) when subjected to size-selective harvesting. The relative size at which they change sex from male to female remains constant (0̃.75) across populations subjected to varying degrees of harvesting pressure. This is the first study to measure all of the necessary life history parameters that are needed to test the theoretical predictions for an invariant relative size at sex change within a species. In the fourth chapter, I use genetic methods to indirectly examine population connectivity of L. gigantea along the mainland coast of California. My results indicate that there are no significant barriers to gene flow between sampled field sites, suggesting that local populations of this species are demographically open