Photosynthetic responses of corals Mussismilia harttii (Verrill, 1867) from turbid waters to changes in temperature and presence/absence of light

Abstract

Responses of corals to climate change stresses are species and locality specific. As light is an important component of temperature-induced stresses, we experimentally tested the responses of a turbid water coral, Mussismilia harttii, to changes in temperature in the presence and absence of light. Chlorophyll fluorescence parameters were measured using a diving-PAM. Experiments were carried out at distinct temperatures. Polyps were kept in the dark or were continuously exposed to 300 µmol photons m-2.s-1 irradiance. No visible bleaching of coral samples was seen in temperatures between 26.5 and 35.0 ºC, but most polyps at higher temperatures showed signs of tissue necrosis. There was a reduction of Fv/Fm as temperature increased, with a further drop in the presence of light, indicating a synergistic effect of these factors. We suggest that the photodamage to M. harttii endosymbionts triggered by temperatures of 33.0 ºC and 35.0 ºC results from a decline of the repair process, as well as the effect of light on the PSII. Recovery data for polyps kept in 31.0 ºC showed that this temperature (depending on time of exposure) seems to be borderline; temperatures higher than 31.0 ºC lead to long-term damage or death of M. harttii.