Date of Award

Fall 10-12-2019

Document Type

Thesis: Open Access

Degree Name

MS Marine Science

Department

Environmental and Ocean Sciences

Committee Chair

Jeff Crooks, PhD

Committee Member

Nathalie Reyns, PhD

Committee Member

Drew Talley, PhD

Committee Member

Theresa Talley, PhD

Abstract

Even though the introduction of the Pacific Oyster, Crassostrea gigas, to the west coast of North America, happened roughly a century ago, it has only been in the past 15 to 20 years that C. gigas has started to become an established and conspicuous species along Southern California’s coast. The establishment of C. gigas in Southern California has the potential to heavily influence many native species, as it has done globally. In Southern California, this invasion is particularly relevant for the native Olympia Oyster, Ostrea lurida. The Olympia oyster has both historical and present-day threats to its population, due to overfishing, pollution, and exotic species introductions. Understanding the distribution and demography of both species at the relatively early stage of C. gigas establishment is important for future management of both species.

In order to address this, sampling was conducted along the rip rap of the San Diego River, near its connection with the Pacific Ocean. Transects were laid down at the high, mid and low intertidal, and quadrats along these transects were sampled quarterly for one year. Densities, biomass, Condition Index, length frequencies, and Von Bertalanffy growth constants were used to look at the growth of the two species over this time period. For C. gigas, growth lines were also used as a tool to estimate age and growth. This work demonstrated that O. lurida densities were in fact much greater than those of C. gigas, but that these native oysters had greater numbers in the low intertidal and diminished as tidal height increased. Crassostrea gigas numbers also decreased with increase tidal height, although less dramatically than O. lurida. Even though there is a large size difference between the two species, growth rate constants found using the Von Bertanlaffy growth model (k) in the low- and mid-intertidal combined were found to be very similar, indicating similar growth rates. Further analysis of growth rates of C. gigas across tidal zones, using growth lines, demonstrated that the growth rate decreased as tidal elevation increased.

This study on the demography on native and invasive oysters in San Diego provides a foundation of baseline scientific information against which future change can be assessed, and can also inform future research directions, such as investigations of how each species interacts independently with their environment and with one another.

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