Growth and Respiration of the Cold-Water Corals Tethocyathus endesa and Caryophyllia huinayensis in the Fjord Comau, Chile Wachstum und Respiration der Kaltwasserkorallen Tethocyathus endesa und Caryophyllia huinayensis im chilenischen Comau-Fjord

Abstract

The ongoing anthropogenic carbon dioxide (CO2) release into the atmosphere is leading to a concurrent increase of CO2 in the oceans, resulting in a reduction of pH through ocean acidification. Though cold-water corals are thought to be highly vulnerable, previous studies have shown that some of them may be resilient to lower pH values. Chile's Comau fjord shows a pronounced horizontal pH gradient, partly reaching such low pH values as they are predicted for most oceans by the end of the century, offering the opportunity to conduct in situ experiments investigating the effects of reduced pH regimes. Two coral species that are abundant and ecologically important in the fjord Comau, Tethocyathus endesa and Caryophyllia huinayensis, were used in a reciprocal cross-transplantation experiment in 2014 - 2016 between sites of high and low pH to investigate the influence of different pH regimes on the corals. An interspecific comparison of the respiration rates, mass and calyx surface area increase in 2015 - 2016 and the mortality of the two species was carried out. Results for the respiration rates of T. endesa and C. huinayensis were similar between the species, but were strongly elevated compared to studies from previous years. The transplant from low to high pH showed a higher carbonate accretion rate for T. endesa, suggesting that higher pH regimes may be favoured by this species. Results for the calyx surface area increase corresponded to the results in mass increase for both species, though C. huinayensis even showed negative results. The physical environment at the investigated sites was compared through pH, oxygen and temperature data. Sites of low pH showed similar pH and oxygen values that were lower than those at the site of high pH at rising tide. Furthermore, the mass increase was intraspecifically compared between the two years. T. endesa showed a reduced mass increase in the second year at the site of low pH, whereas C. huinayensis showed similar results for all treatments in both years. As ocean acidification will require long-term adaptions, this suggests that C. huinayensis may be able to adapt to different pH regimes better than T. endesa and over a longer period of time