Fouling and predation of oyster crops in San Quintin Bay, Baja California, Mexico, and a review of the facilitative effects of non-indigenous species on native species

The oyster aquaculture systems of San Quintin Bay (Baja California, Mexico) were investigated as a model to analyze the effect of fouling and predatory pests on a commercially important non-indigenous species. Introduced oysters (Crassostrea gigas) provide novel and unique habitat for fouling communities, and also provide a novel food source for native predatory whelks. However, fouling and predation are also the main pest management concerns of the artisanal oyster farmers. The first chapter of this dissertation documents the recruitment and succession patterns of the oyster fouling communities. Recruitment is highly variable, correlating with changes in water temperature. Throughout succession invasive ascidians dominate, both in terms of diversity and cover, eventually overgrowing the majority of the shell, and requiring manual removal. Chapter 2 details the impact of native predatory whelks ( Macron trochlea), which were a previously unknown source of oyster mortality. Feeding rates, preferences, and behavior are documented, showing that whelks are active predators of juvenile oysters. Combining knowledge of fouling community variability, whelk predatory behavior, oyster growth rates, and oyster farming techniques, I develop feasible rearing suggestions to decrease pest impacts due to fouling and predation.;As exemplified in the model system, non-indigenous species have diverse effects on both native and other non-indigenous species. In contrast to the extensively documented detrimental effects of non-indigenous species through competition and predation, facilitative interactions have been mostly overlooked, particularly the facilitative effects of non-indigenous species on native species. In the concluding chapter of this dissertation I address this information gap by providing evidence from terrestrial, marine, and freshwater systems that non-indigenous species can result in an increase in the abundance or biomass of native species. Several mechanisms of facilitation are detailed and exemplified, including habitat creation/modification, trophic subsidy, pollination, competitive release, and predatory release. These interactions can be classified into one of three types of facilitation (novel, substitutive, or indirect), each of which is conceptually defined. These findings help predict how, when and why native species are facilitated, helping invasion biologists and managers determine how to minimize detrimental impacts of non-indigenous species while capitalizing on their beneficial effects.