Exposure history determines pteropod vulnerability to ocean acidification along the US West Coast

N Bednaršek,S R Alin,S A Siedlecki,A J Hermann,R A Feely,P Mcelhany,G G Waldbusser,B Moore-Maley,H O Pörtner,T Klinger,N Tolimieri

doi:10.1038/s41598-017-03934-z

Abstract

The pteropod Limacina helicina frequently experiences seasonal exposure to corrosive conditions (Ωar < 1) along the US West Coast and is recognized as one of the species most susceptible to ocean acidification (OA). Yet, little is known about their capacity to acclimatize to such conditions. We collected pteropods in the California Current Ecosystem (CCE) that differed in the severity of exposure to Ωar conditions in the natural environment. Combining field observations, high-CO2 perturbation experiment results, and retrospective ocean transport simulations, we investigated biological responses based on histories of magnitude and duration of exposure to Ωar < 1. Our results suggest that both exposure magnitude and duration affect pteropod responses in the natural environment. However, observed declines in calcification performance and survival probability under high CO2 experimental conditions do not show acclimatization capacity or physiological tolerance related to history of exposure to corrosive conditions. Pteropods from the coastal CCE appear to be at or near the limit of their physiological capacity, and consequently, are already at extinction risk under projected acceleration of OA over the next 30 years. Our results demonstrate that Ωar exposure history largely determines pteropod response to experimental conditions and is essential to the interpretation of biological observations and experimental results.

Highlights

Observed declines in calcification performance and survival probability under high CO2 experimental conditions do not show acclimatization capacity or physiological tolerance related to history of exposure to corrosive conditions
Given their history of exposure to low Ωar conditions in their natural environment, we hypothesized that pteropods may be pre-adapted or have developed a physiological capacity to acclimatize to ocean acidification (OA) conditions, allowing these organisms to maintain critical biological processes regardless of the exposure history
Calcification was measured across a range of in situ Ωar conditions from which the individuals were collected, and survival was tested under experimental conditions in which the partial pressure of CO2 was elevated

Summary

Introduction

Observed declines in calcification performance and survival probability under high CO2 experimental conditions do not show acclimatization capacity or physiological tolerance related to history of exposure to corrosive conditions. Given their history of exposure to low Ωar conditions in their natural environment, we hypothesized that pteropods may be pre-adapted or have developed a physiological capacity to acclimatize to OA conditions, allowing these organisms to maintain critical biological processes regardless of the exposure history. To better understand acclimatization capacity in pteropods in the CCE, we conducted experiments to test the ability of individual pteropods to successfully maintain biological processes, including calcification and survival, following different histories of exposure to low Ωar in the natural environment. The study was designed to determine whether and how exposure history can cause differential responses of pteropods and whether acclimatization capacity becomes apparent through shifting tolerance thresholds under variable levels of Ωar conditions during different exposure histories

Methods

Results

Discussion

Conclusion