The effects of intermittent exposure to low-pH and low-oxygen conditions on survival and growth of juvenile red abalone

J. P. Barry,T. W. Kim,F. Micheli

doi:10.5194/bg-10-7255-2013

Abstract

Abstract. Exposure of nearshore animals to hypoxic, low-pH waters upwelled from below the continental shelf and advected near the coast may be stressful to marine organisms and lead to impaired physiological performance. We mimicked upwelling conditions in the laboratory and tested the effect of fluctuating exposure to water with low-pH and/or low-oxygen levels on the mortality and growth of juvenile red abalone (Haliotis rufescens, shell length 5–10 mm). Mortality rates of juvenile abalone exposed to low-pH (7.5, total scale) and low-O2 (40% saturation, mg L−1) conditions for periods of 3 to 6 h every 3–5 days over 2 weeks did not differ from those exposed to control conditions (O2: 100% saturation, 12 mg L−1; pH 8.0). However, when exposure was extended to 24 h, twice over a 15-day period, juveniles experienced 5–20% higher mortality in the low-oxygen treatments compared to control conditions. Growth rates were reduced significantly when juveniles were exposed to low-oxygen and low-pH treatments. Furthermore, individual variation of growth rate increased when juveniles were exposed simultaneously to low-pH and low-O2 conditions. These results indicate that prolonged exposure to low-oxygen levels is detrimental for the survival of red abalone, whereas pH is a crucial factor for their growth. However, the high individual variation in growth rate under low levels of both pH and oxygen suggests that cryptic phenotypic plasticity may promote resistance to prolonged upwelling conditions by a portion of the population.

Highlights

Marine ecosystems are under threat from ocean acidification as the excess burden of fossil fuel CO2 dissolves into the ocean (Orr et al, 2005; Hofmann et al, 2010)
Juvenile abalones (Haliotis rufescens, shell length 4–12 mm, 4–5 months of age) were acquired from the Abalone Farm Co. located in Cayucos, California, where many individuals collected over several years from Southern California abalone populations are reared at ambient temperature
These experiments indicate that repeated short-term (3–6 h) exposure of abalone juveniles to conditions documented during upwelling (Booth, 2011) has no detectable immediate effect on their survival

Summary

Introduction

Marine ecosystems are under threat from ocean acidification as the excess burden of fossil fuel CO2 dissolves into the ocean (Orr et al, 2005; Hofmann et al, 2010). Many studies of the biological effects of ocean acidification have focused on the predicted change of mean pH of ocean surface waters derived from IPCC climate scenarios (e.g., Bibby et al, 2007; Orr et al, 2005; Dupont et al, 2010; Byrne et al, 2011). It is assumed that many benthic animals living in nearshore marine environments either adapt to the local natural fluctuations of pH and dissolved oxygen (DO), or tolerate occasional short-lived exposure to potentially stressful conditions (Alenius and Munguia, 2012; Vaquer-Sunyer and Duarte, 2008).

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Conclusion