Date of Award

Winter 1-31-2021

Document Type

Thesis: Open Access

Degree Name

MS Marine Science

Department

Environmental and Ocean Sciences

Committee Chair

Nicholas C. Wegner

Committee Co-Chair

Mary Sue Lowery

Committee Member

John R. Hyde

Abstract

In 2001, white abalone, Haliotis sorenseni, became the first marine invertebrate to be listed under the U.S. Endangered Species Act. Allee effects due primarily to overharvesting and disease resulted in individuals being too far apart for successful fertilization. Despite the fishery closure in 1996, H. sorenseni still shows no signs of recovery. Today, the White Abalone Recovery Consortium (WARC), a group that includes federal and state agencies, aquaculture organizations, academic institutions, and public aquaria, is working to recover this endangered species back from the brink of extinction.

In order to better understand the metabolic demands and hypoxia tolerance of the endangered white abalone, H. sorenseni, this thesis measured aspects of metabolic physiology via closed respirometry techniques, in comparison with red abalone, Haliotis rufescens. The relationship of mean oxygen consumption rate of both H. sorenseni (n = 29) and H. rufescens (n = 27) to environmental dissolved oxygen level showed a logarithmic best-fit function. This curve shape reveals that abalone are slightly oxy-conforming at high dissolved oxygen levels and become increasingly conforming at lower oxygen saturations. Hypoxia tolerance as estimated by determining the P90, P75, P50, and P25 (values in which oxygen consumption was 90%, 75%, 50%, and 25% of resting metabolic rate), did not show a significant difference between the species. There were, however, higher levels of variability in P90, P75, P50, and P25 for H. sorenseni in comparison to H. rufescens, suggesting potential fitness differences between H. sorenseni cohorts spawned in captivity. Additionally, there was no significant relationship between abalone length (mm) (a useful metric of abalone size used both in the field and laboratories) and P50. Although no differences between species were detected with hypoxia tolerance, H. sorenseni had significantly lower resting metabolic rates (RMR) than H. rufescens for most of the size range tested (total mass 7.7 to 85.0 g). Higher temperatures had a significant effect on P90, P75, P50, and P25 for H. sorenseni, revealing the potential compounding effects of high temperatures and low oxygen on the species.

These metabolic data can help inform outplanting procedures of the endangered H. sorenseni such as determining favorable environmental dissolved oxygen and temperatures for outplanting site selection, as well as selecting fit captive bred abalone for outplanting. Higher variation in P90, P75, P50, and P25 values for H. sorenseni individuals highlights the need to investigate phenotypic and genetic fitness of all cohorts raised in the White Abalone Recovery Program. As the first marine invertebrate listed under the Endangered Species Act, increasing knowledge for successful outplanting of H. sorenseni is vital in recovery of the species.

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