The metabolic response of thecosome pteropods from the North Atlantic and North Pacific oceans to high CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and low O&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;

Amy E Maas,Zhaohui Aleck Wang,Gareth L Lawson

doi:10.5194/bg-13-6191-2016

Abstract

Abstract. As anthropogenic activities directly and indirectly increase carbon dioxide (CO2) and decrease oxygen (O2) concentrations in the ocean system, it becomes important to understand how different populations of marine animals will respond. Water that is naturally low in pH, with a high concentration of carbon dioxide (hypercapnia) and a low concentration of oxygen, occurs at shallow depths (200–500 m) in the North Pacific Ocean, whereas similar conditions are absent throughout the upper water column in the North Atlantic. This contrasting hydrography provides a natural experiment to explore whether differences in environment cause populations of cosmopolitan pelagic calcifiers, specifically the aragonitic-shelled pteropods, to have a different physiological response when exposed to hypercapnia and low O2. Using closed-chamber end-point respiration experiments, eight species of pteropods from the two ocean basins were exposed to high CO2 ( ∼ 800 µatm) while six species were also exposed to moderately low O2 (48 % saturated, or ∼ 130 µmol kg−1) and a combined treatment of low O2/high CO2. None of the species tested showed a change in metabolic rate in response to high CO2 alone. Of those species tested for an effect of O2, only Limacina retroversa from the Atlantic showed a response to the combined treatment, resulting in a reduction in metabolic rate. Our results suggest that pteropods have mechanisms for coping with short-term CO2 exposure and that there can be interactive effects between stressors on the physiology of these open ocean organisms that correlate with natural exposure to low O2 and high CO2. These are considerations that should be taken into account in projections of organismal sensitivity to future ocean conditions.

Highlights

Ocean acidification, a result of the dissolution of anthropogenically produced carbon dioxide (CO2) into seawater, is increasingly considered to be one of the most pervasive human changes to the marine system (Halpern et al, 2008; Doney et al, 2009; Gruber, 2011)
We collected two species of thecosome pteropods exclusively from the Atlantic, Limacina retroversa (Fleming, 1823), a subpolar species, which is absent from the North Pacific, and Diacria trispinosa (Blainville, 1821), which can be found in temperate and tropical regions of the Atlantic, Pacific, and Indian oceans
This study reveals that short-term exposure to low O2 and high CO2, similar to what would be experienced by individuals in the Pacific during diel vertical migration, does not influence the oxygen consumption of adult individuals of most of the thecosome pteropod species examined from either the Atlantic or Pacific

Summary

Introduction

A result of the dissolution of anthropogenically produced carbon dioxide (CO2) into seawater, is increasingly considered to be one of the most pervasive human changes to the marine system (Halpern et al, 2008; Doney et al, 2009; Gruber, 2011). As a consequence of the changing equilibria, there is a reduction in pH and the saturation state of calcium carbonate (CaCO3), including the biogenic forms of calcite and aragonite. As ocean acidification continues, the water becomes undersaturated and corrosive, meaning that in the absence of compensative biological action, conditions will favor the dissolution of the CaCO3 found in the shells and skeletons of calcifying organisms, with aragonite being more sensitive than calcite (Millero, 2007). Perturbations of seawater carbonate chemistry can affect the ability of some calcifying animals to create and maintain calcium carbon-

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