Response to sudden increases in temperature (thermal shock) under laboratory conditions in the coral Pocillopora verrucosa

Abstract

Coral bleaching is an increasing worldwide phenomenon associated with climate change. Bleaching results from the interaction of biotic and abiotic variables including sudden changes in temperature. To evaluate the response to sudden changes in temperature (thermal shock) prior to bleaching, fragments of Pocillopora verrucosa were subjected to experimental thermal stress. The fragments were acclimatized at 27ºC during eight days and then exposed to thermal shock at two temperatures (28.5°C and 30.5°C) for 72 h. The stress response was evaluated quantifying the total lipid content, symbiont density, and tissue damage. Changes in the evaluated estimators were evident at 30.5°C when an initial increase in the amount of lipids was detected, followed by a decrease after 30 h; symbiont density diminished up to 84% at the end of the experiment relative to the initial density estimated. The control and 28.5°C treatments presented no differences. Damage to the polyp tissue was mainly observed as a thinning of the mesenteries and the gastrodermal layer. The study area is strongly influenced by internal waves that cause sudden changes in temperature, so understanding how corals respond to these daily fluctuations will allow us to estimate their survival potential and help future management and conservation efforts in this region.