Seawater pH Predicted for the Year 2100 Affects the Metabolic Response to Feeding in Copepodites of the Arctic Copepod Calanus glacialis.

Peter Thor,Ella Guscelli,Agneta Fransson,Claudia Halsband,Allison Bailey,Elena Gorokhova,Adrianna Ianora

doi:10.1371/journal.pone.0168735

Peter Thor, Ella Guscelli + Show 5 more

Open Access

https://doi.org/10.1371/journal.pone.0168735

Copy DOI

Abstract

Widespread ocean acidification (OA) is transforming the chemistry of the global ocean, and the Arctic is recognised as a region where the earliest and strongest impacts of OA are expected. In the present study, metabolic effects of OA and its interaction with food availability was investigated in Calanus glacialis from the Kongsfjord, West Spitsbergen. We measured metabolic rates and RNA/DNA ratios (an indicator of biosynthesis) concurrently in fed and unfed individuals of copepodite stages CII-CIII and CV subjected to two different pH levels representative of present day and the “business as usual” IPCC scenario (RCP8.5) prediction for the year 2100. The copepods responded more strongly to changes in food level than to decreasing pH, both with respect to metabolic rate and RNA/DNA ratio. However, significant interactions between effects of pH and food level showed that effects of pH and food level act in synergy in copepodites of C. glacialis. While metabolic rates in copepodites stage CII-CIII increased by 78% as a response to food under present day conditions (high pH), the increase was 195% in CII-CIIIs kept at low pH—a 2.5 times greater increase. This interaction was absent for RNA/DNA, so the increase in metabolic rates were clearly not a reaction to changing biosynthesis at low pH per se but rather a reaction to increased metabolic costs per unit of biosynthesis. Interestingly, we did not observe this difference in costs of growth in stage CV. A 2.5 times increase in metabolic costs of growth will leave the copepodites with much less energy for growth. This may infer significant changes to the C. glacialis population during future OA.

Highlights

Widespread ocean acidification (OA) is transforming the chemistry of the global ocean, and the Arctic is recognised as the region where the earliest and strongest impacts of OA are expected [1,2,3]
We found significantly increasing metabolic rates and decreasing ingestion rates with decreasing pH in copepodite stage IV (CIV) but interestingly not in CV
They were distinguished from C. hyperboreus and C. finmarchicus copepodites on the basis of size [9], the presence of red pigmentation in the antennules, a characteristic distinguishing C. glacialis from C. finmarchicus [25], and the lack of lateral spikes on the distal prosome segment, a characteristic of C. hyperboreus

Summary

Introduction

Widespread ocean acidification (OA) is transforming the chemistry of the global ocean, and the Arctic is recognised as the region where the earliest and strongest impacts of OA are expected [1,2,3]. Previous studies have shown that while naupliar development and growth may not be significantly affected at OA levels down to pHT 7.47 [13], unchanged development was upheld by increasing physiological buffering at decreasing pH: gene expression was significantly altered in groups of genes coding for such important functions as DNA repair and transcription (Bailey et al submitted) It seems that pH stress is countered by altered gene expression patterns to maintain unchanged developmental rates. Long term incubations of females have shown no effects at pHF 7.24 on metabolic rate, gonad maturation rate, or mortality [17] This suggests that responses to OA may vary among developmental stages in C. glacialis. We measured metabolic rate and RNA/ DNA ratio (an indicator of biosynthesis [22]) concurrently in fed and unfed individuals subjected to two different pH levels representative of present day and the “business as usual” IPCC scenario (RCP8.5) prediction for the year 2100 [23]

Methods

Results

Discussion