Differences in neurochemical profiles of two gadid species under ocean warming and acidification

Matthias Schmidt,Kai-Uwe Ludwichowski,Hans-Otto Pörtner,Christian Bock,Sean Lando Levin Seegert,Daniela Storch,Heidrun Sigrid Windisch

doi:10.1186/s12983-017-0238-5

Abstract

BackgroundExposure to future ocean acidification scenarios may alter the behaviour of marine teleosts through interference with neuroreceptor functioning. So far, most studies investigated effects of ocean acidification on the behaviour of fish, either isolated or in combination with environmental temperature. However, only few physiological studies on this issue were conducted despite the putative neurophysiological origin of the CO2-induced behavioural changes. Here, we present the metabolic consequences of long-term exposure to projected ocean acidification (396–548 μatm PCO2 under control and 915–1272 μatm under treatment conditions) and parallel warming in the brain of two related fish species, polar cod (Boreogadus saida, exposed to 0 °C, 3 °C, 6 °C and 8 °C) and Atlantic cod (Gadus morhua, exposed to 3 °C, 8 °C, 12 °C and 16 °C). It has been shown that B. saida is behaviourally vulnerable to future ocean acidification scenarios, while G. morhua demonstrates behavioural resilience.ResultsWe found that temperature alters brain osmolyte, amino acid, choline and neurotransmitter concentrations in both species indicating thermal responses particularly in osmoregulation and membrane structure. In B. saida, changes in amino acid and osmolyte metabolism at the highest temperature tested were also affected by CO2, possibly emphasizing energetic limitations. We did not observe changes in neurotransmitters, energy metabolites, membrane components or osmolytes that might serve as a compensatory mechanism against CO2 induced behavioural impairments. In contrast to B. saida, such temperature limitation was not detected in G. morhua; however, at 8 °C, CO2 induced an increase in the levels of metabolites of the glutamate/GABA-glutamine cycle potentially indicating greater GABAergic activity in G.morhua. Further, increased availability of energy-rich substrates was detected under these conditions.ConclusionsOur results indicate a change of GABAergic metabolism in the nervous system of Gadus morhua close to the optimum of the temperature range. Since a former study showed that juvenile G. morhua might be slightly more behaviourally resilient to CO2 at this respective temperature, we conclude that the observed change of GABAergic metabolism could be involved in counteracting OA induced behavioural changes. This may serve as a fitness advantage of this respective species compared to B. saida in a future warmer, more acidified polar ocean.

Highlights

Exposure to future ocean acidification scenarios may alter the behaviour of marine teleosts through interference with neuroreceptor functioning
The present study focuses on metabolites and amino acids involved in energy metabolism and regeneration of the neurotransmitter γ-aminobutyric acid (GABA) in order to test whether compensatory mechanisms to a rise of environmental CO2 are visible on neurotransmitter level
Boxplots of those components influenced either by CO2 or interactively by CO2 in combination with temperature are shown in Fig. 3 (Boreogadus saida) and Fig. 4 (Gadus morhua)

Summary

Introduction

Exposure to future ocean acidification scenarios may alter the behaviour of marine teleosts through interference with neuroreceptor functioning. Exposure to projected CO2-induced ocean acidification (OA) scenarios alters the behaviour of some marine teleost species [1]. The electrochemical gradient of neurons in the central nervous system alters. This process is believed to affect functioning of γ-aminobutyric acid type A receptors (GABAA-R). An altered functioning of the most important inhibitory neurotransmitter within the central nervous system, with great regulatory importance for neuronal circuits may lead to profound changes in neuronal activity and energetic demand. Acid-base regulatory processes are suggested to be responsible for altered fish behaviour, but this does not concern all species. Some species have been found to be more resilient to environmental CO2 than others, with unclear physiological background [6,7,8,9]

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