Physiological Responses of an Arctic Crustose Coralline Alga (Leptophytum foecundum) to Variations in Salinity.

Arley F Muth,Andrew J Esbaugh,Kenneth H Dunton

doi:10.3389/fpls.2020.01272

Abstract

In the Beaufort Sea, Arctic crustose coralline algae (CCA) persist in an environment of high seasonal variability defined by naturally low pH ocean water and high magnitude freshwater pulses in the spring. The effects of salinity on the CCA Leptophytum foecundum were observed through a series of laboratory and field experiments in Stefansson Sound, Alaska. We found that salinity (treatments of 10, 20, and 30), independent of pH, affected L. foecundum physiology based on measurements of three parameters: photosynthetic yield, pigmentation, and calcium carbonate dissolution. Our experimental results revealed that L. foecundum individuals in the 10-salinity treatment exhibited an obvious stress response while those in the 20- and 30-salinity treatments were not significantly different for three parameters. Reciprocal in situ transplants and recruitment patterns between areas dominated by CCA and areas where CCA were absent illustrated that inshore locations receiving large pulses of freshwater were not suitable for CCA persistence. Ultimately, spatially and temporally varying salinity regimes levels affected distribution of CCA in the nearshore Arctic. These results have implications for epilithic benthic community structure in subtidal areas near freshwater sources and highlight the importance of salinity in CCA physiology.

Highlights

Calcification of marine organisms is of broad and current interest in ocean climate change studies
Salinity and temperature treatments remained consistent over the 5-week treatment period (Table S1). pH values decreased in all treatments over each week, but the changes did not differ among treatments or between periods
While the 20- and 30- treatments were at equilibrium and 1.6, respectively, dissolution did not differ between salinities in respect to AT changes

Summary

Introduction

Calcification of marine organisms is of broad and current interest in ocean climate change studies. Lower pH levels, driven by carbon dioxide (CO2) uptake into ocean water, causes a reduction of calcium carbonate (and other forms e.g., aragonite and calcite) saturation levels leading to decreased calcification rates of species. Growth, and net calcification have been shown to occur when coralline algal species are exposed to lower than ambient pH conditions for short time periods Low salinities decrease calcification rates and slow productivity in CCA species (King and Schramm, 1982). Marine invertebrates are susceptible to freshening waters as juvenile oysters cultured under decreased salinity and pH conditions showed increased rates of mortality, but low salinities alone had the most impact (Dickinson et al, 2012)

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Conclusion