Short-term responses to ocean acidification: effects on relative abundance of eukaryotic plankton from the tropical Timor Sea

Abstract

Anthropogenic carbon dioxide (CO2) emissions drive climate change and pose one of the major challenges of our century. The effects of increased CO2 in the form of ocean acidification (OA) on the communities of marine planktonic eukaryotes in tropical regions such as the Timor Sea are barely understood. Here, we show the effects of high CO2 (mean ± SD pCO2 = 1823 ± 161 μatm and pHT = 7.46 ± 0.05) versus in situ CO2 (504 ± 42 µatm, 7.95 ± 0.04) seawater on the community composition of marine planktonic eukaryotes after 3 and 48 h of treatment exposure in a shipboard microcosm experiment. Illumina sequencing of the V9 hypervariable region of 18S rRNA (gene) was used to study the eukaryotic community composition. Increased CO2 significantly suppressed the relative abundances of different eukaryotic operational taxonomic units (OTUs), including important primary producers, although the chlorophyll a concentration remained constant. OA effects on eukaryotes were consistent between total (DNA-based) and active (cDNA-based) taxa after 48 h, e.g. for the diatoms Trieres chinensis and Stephanopyxis turris. Effects of OA on the relative abundances of OTUs were often species- or even ecotype-specific, and the incubation selectively allowed for detection of the OA-sensitive OTUs that benefitted the most from incubation in a closed bottle, as containment effects on the community structure were evident after 48 h. Many OTUs were adversely affected by sudden decreases of seawater pH, suggesting high sensitivity to OA at the base of the tropical marine biodiversity and difficult-to-predict outcomes for food-web functioning in the future ocean.

The Role of Extracellular Carbonic Anhydrase in Biogeochemical Cycling: Recent Advances and Climate Change Responses

“…An early study by Tortell and Morel [ 64 ] demonstrated that HCO 3 − uptake in the equatorial Pacific Ocean is regulated by the ambient CO 2 concentrations, where phytoplankton assemblages did not express eCA under high CO 2 concentrations (750 µatm). Several studies observed a reduction in eCA activity as a response to high CO 2 concentrations (800 µatm) in diatom assemblages of the West Antarctic Peninsula [ 65 , 66 , 67 ] and more recently in the Timor Sea phytoplankton assemblages [ 18 , 68 ]. Contrarily, tolerance of highly variable CO 2 levels has been observed for diatom assemblages in the subarctic Pacific, indicating that the direct uptake of HCO 3 − dominates carbon uptake for these assemblages [ 69 ].…”

Comparative Sensitivities of Zooplankton to Ocean Acidification Conditions in Experimental and Natural Settings

“…We chose abundance as our response variable because abundance or its co-variate, biomass, is the most commonly measured variable in long-term monitoring studies, including those that have been used to detect changes due to ocean condition (e.g., Hays et al, 2005;Mackas and Beaugrand, 2010;McKinstry and Campbell, 2018). Moreover, abundance has been used to detect response to change in short-term studies of marine microbes (Currie et al, 2017;Rahlff et al, 2021).…”