Date of Award

Fall 1-14-2022

Document Type

Thesis: Open Access

Degree Name

MS Marine Science


Environmental and Ocean Sciences

Committee Chair

Jeff Crooks

Committee Co-Chair

Drew Talley

Committee Member

Theresa Talley


Many marine ecosystems are facing the growing threat of biological invasions. These invasions can have a variety of different impacts on ecosystems and their inhabitants. The Pacific oyster, Crassostrea gigas, is currently in the relatively early stages of invasion in San Diego estuaries. Crassostrea gigas is a large, filter-feeding bivalve that forms dense oyster beds on hard substrate. These oysters are known to outcompete native counterparts and drastically alter habitats where they are present. Crassostrea gigas is an ecosystem engineer that, through shell creation and formation of a dense oyster matrix, impacts ecosystems in a variety of direct and indirect ways. However, the impacts of this ecosystem engineer at an early stage of invasion are not well-understood. To investigate the effects of C. gigas in a relatively recently-invaded site, this study examined the relationships between oyster beds and macrofaunal assemblages in Los Peñasquitos Lagoon, San Diego, California, USA. Mudflat areas with oyster beds had markedly higher total abundance, species richness, and biomass of resident macrofauna, with bivalves (not counting the oysters themselves), amphipods, and decapods tending to have higher densities and biomass in oyster beds. Interestingly, for the range of oyster beds examined here, there were minimal associations between the amount of actual shell material present and macrofaunal properties, suggesting that there may be a threshold associated with bed impacts. Overall, the findings of this study align with similar conclusions of other global studies in suggesting that C. gigas as invaders and ecosystem engineers have potentially large impacts on the biodiversity, and that this should be an important consideration in considering management of this non-native bivalve and coastal ecosystems.


An extraordinary amount of thanks to the University of San Diego, Grand Valley State University, the University of California Santa Cruz, Southwest Wetlands Interpretive Association, and other organizations whom so generously and patiently provided assistance and support through use of their facilities and equipment over the years and obstacles which have allowed for the completion of this research. Additional gratitude to Dr. Eric Snyder (GVSU), Keith Fink, Tanner Barnes, and all of the important people who have helped see various aspects of this research to their completion. Of course, I am humbled to thank Dr. Jeff Crooks, Dr. Drew Talley, and Dr. Theresa Talley whom I am fortunate to call dear friends and already know that there are not words enough that can express the gratitude a man given a 2nd chance at life may have. Lastly, but not least of which, thank you to my family and my loved ones without whom I would have never found the personal strength to forge onward.