Seawater carbonate chemistry and coralline algal diversity

• Main Authors: Peña, Viviana, Harvey, Ben P, Agostini, Sylvain, Porzio, Lucia, Milazzo, Marco, Horta, Paulo Antunes, Gall, Line Le, Hall-Spencer, Jason M
• Format: Dataset
• Language: English
• Published: PANGAEA 2021
• Subjects: Alkalinity; total; standard deviation; Aragonite saturation state; Benthos; Bicarbonate ion; Calcite saturation state; Calcium carbonate; Calcium carbonate mass; Calculated using seacarb after Nisumaa et al. (2010); Carbon; inorganic; dissolved; Carbonate ion; Carbonate system computation flag; Carbon dioxide; CO2 vent; Coast and continental shelf; Community composition and diversity; Coverage; standard error; Entire community; Event label; EXP; Experiment; Field observation; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Location; Marine habitat; Mediterranean Sea; North Pacific; OA-ICC; Ocean Acidification International Coordination Centre; Partial pressure of carbon dioxide; Pacific; Ocean acidification
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.939815; https://doi.org/10.1594/PANGAEA.939815

Calcified coralline algae are ecologically important in rocky habitats in the marine photic zone worldwide and there is growing concern that ocean acidification will severely impact them. Laboratory studies of these algae in simulated ocean acidification conditions have revealed wide variability in growth, photosynthesis and calcification responses, making it difficult to assess their future biodiversity, abundance and contribution to ecosystem function. Here, we apply molecular systematic tools to assess the impact of natural gradients in seawater carbonate chemistry on the biodiversity of coralline algae in the Mediterranean and the NW Pacific, link this to their evolutionary history and evaluate their potential future biodiversity and abundance. We found a decrease in the taxonomic diversity of coralline algae with increasing acidification with more than half of the species lost in high pCO2 conditions. Sporolithales is the oldest order (Lower Cretaceous) and diversified when ocean chemistry favoured low Mg calcite deposition; it is less diverse today and was the most sensitive to ocean acidification. Corallinales were also reduced in cover and diversity but several species survived at high pCO2; it is the most recent order of coralline algae and originated when ocean chemistry favoured aragonite and high Mg calcite deposition. The sharp decline in cover and thickness of coralline algal carbonate deposits at high pCO2 highlighted their lower fitness in response to ocean acidification. Reductions in CO2 emissions are needed to limit the risk of losing coralline algal diversity.