Promoting pinto abalone (Haliotis kamtschatkana) recovery in the Salish Sea: the effects of fluctuating temperature and elevated CO2 on survival, growth, and radula morphology

Overharvesting of pinto abalone (Haliotis kamtschatkana) in the Salish Sea between 1959 and 1994 caused severe population declines. This led to the Washington Department of Fish and Wildlife classifying pinto abalone as a “species of concern.” The Puget Sound Restoration Fund (PSRF) is committed to help pinto abalone recover by outplanting juveniles at specific sites around the Salish Sea. Survival of outplanted individuals is different at each site, but it is not clear why. Differences in water chemistry parameters, such as temperature and pH, could explain the differences in survival, either through differences in the mean conditions or through short term exposure to more extreme conditions. Future ocean warming and acidification could make fluctuations in water chemistry parameters more severe. The goal of my thesis was to simulate in lab the outplanting of abalone post-sets in fluctuating temperature and elevated CO2 conditions. I utilized an ocean acidification system to create atmospheres that affect seawater pH. I hypothesized that temperature fluctuations and high dissolved CO2 (low pH) will negatively affect survival, growth, and shell and radula morphology. Fluctuating temperatures yielded lower survival and greater growth, determined by mean shell length, compared to constant temperature. High CO2 yielded comparable survival and smaller growth than low CO2. Traditional morphological analysis of the radula found that fluctuating temperatures caused the radula to grow in a more compact manner, with smaller teeth formed closer together. Geometric morphological analysis found that radula tooth orientation was not affected by any of the treatments. This is the first study to find any effects of water chemistry on abalone radula morphology. Overall, the presence of a single stressor was detrimental to pinto abalone post-sets. However, the combination of stressors performed similarly to the absence of stressors. This indicates that fluctuating temperature can mitigate the negative effects of high CO2, possibly by increasing metabolic rate. In support of pinto abalone recovery efforts, PSRF can utilize my findings to evaluate water chemistry parameters at their outplant sites. I recommend that pinto abalone be outplanted in areas around the Salish Sea that are characterized by near constant temperatures, around 10°C, and low dissolved CO2 (high pH around 8.2). Due to yearly, seasonal, and weekly changes in water chemistry conditions, constant conditions do not exist. Outplant sites with the smallest fluctuations in water chemistry parameters should be used. In addition, ocean warming and acidification are expected to occur in concert. My findings indicate pinto abalone post-sets should be able to survive and grow under future climate scenarios, when outplanted into both temperatures that fluctuate on weekly scales, from 10°C up to 14°C, and acidification within 0.2 pH units when these conditions occur together, not separately.

Diehl E. J., 2022. Promoting pinto abalone (Haliotis kamtschatkana) recovery in the Salish Sea: the effects of fluctuating temperature and elevated CO2 on survival, growth, and radula morphology. MSc thesis, Western Washington University, 62 p. Thesis.

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