Food availability and energy status of the cold-water coral Desmophyllum dianthus from the Comau Fjord, Chile

The rising CO2 content in the atmosphere causes chemical changes in the oceans and a reduction in the pH value. Especially calcifying organisms, such as cold water corals, are expected to be negative affected by this chemical change. Several laboratory studies have shown that cold water corals are less affected by the effects of ocean acidification than previously thought, but there are only a few in-situ studies available so far. The cold water coral Desmophyllum dianthus is ubiquitous in the Comau Fjord in Chile along a natural vertical and horizontal pH gradient. None of the parameters measured so far limits the occurrence or growth of the coral. The reason why D. dianthus is able to adapt so well to environmental conditions is still unknown. Many studies have already suggested that the reason for this adaptability depends on the energy status. In order to obtain information on how the growth of D. dianthus could change in the course of ocean acidification, the protein concentrations of D. dianthus in austral autumn and austral winter as well as at six stations along a pH gradient at a depth of 20m were determined in this study. In addition, corals were cross-transplanted between the stations at the head and the mouth of the fjord. The measured protein concentrations were finally linked to the available phytoplankton biomass and growth. The results revealed seasonal differences between the protein concentrations as well as differences during a season along the stations. Additionally, a positive correlation of protein concentrations and pH values was found. No differences between protein concentrations and growth were found between the transplanted corals, but this was expected as there was no large difference in pH values between the stations. The available phytoplankton biomass, measured using chlorophyll-a-fluorescence, showed seasonal differences with higher values in austral autumn compared to austral winter. A positive relationship between the phytoplankton biomass and the pH values along the stations could be established. No relationship could be established between the protein content and the phytoplankton biomass. The results of this study lead to the conclusion that D. dianthus has enough energy available to withstand the conditions of ocean acidification, but it is not reflected by the phytoplankton biomass.