Loss of coralline algal diversity due to ocean acidification


Loss of coralline algal diversity due to ocean acidification

Due to the acidification of the oceans, marine fauna is in serious danger. The lowering of the marine pH creates the phenomenon of coral bleaching; the calcium carbonate that makes up shells, molluscs, crustaceans and even coral, decreases in relation to the increase in acidity, thus losing the algae that live above the surface of the organism, leading it to death.

Although many organisms suffer from this increasing acidification, some photosynthetic organisms benefit from it. One case is represented by diatoms; that is microscopic algae belonging to phytoplankton. For these organisms, the increase in CO2 in water increases their ability to carry out their own photosynthesis processes.

These processes can be carried out if in the presence of certain environmental conditions.

Loss of coralline algal diversity due to ocean acidification

The study: Major loss of coralline algal diversity in response to ocean acidification, published on the Global change biology, explained: "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 favored 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 favored 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."