Differential response to cold and warm water conditions in Pocillopora colonies from the Central Mexican Pacific

Abstract

Coral communities from the Central Mexican Pacific have suffered regional bleaching as a consequence of temperature anomalies stemming from El Nino Southern Oscillation events and local events. Due to these and other impacts, there is an urgent need to better understand the physiological response of reef corals to changes in their external environment. In this study, we measured lipid content and endosymbiont densities in colonies of the common, reef-building coral Pocillopora verrucosa in order to gauge their response to thermal stress, in particular, over a multi-month time span. Colonies were collected from different depths and different sites in the same area in three different periods. In coral colonies from the southern site, both markers varied temporally over the course of the year, though no variation was found between colonies from different depths. In colonies from the northern site, total lipid content varied significantly between depths and over time. The northern colonies which had been seriously affected by the cold water bleaching appear to be more sensitive to stress events than those from the southern site, which demonstrated an acclimatization response to the elevated temperatures to which they were exposed. And also different colonies were collected and acclimatized in laboratory aquaria and exposed to thermal stress (28 and 31 °C). Only colonies exposed to 31 °C experienced a significant decrease in total lipid content within their cells. Likewise, these colonies also demonstrated a statistically significant 82% reduction in density of endosymbiotic dinoflagellates (genus Symbiodinium). A better understanding of the ability of corals to acclimatize to different temperature regimes will allow managers to target particular reef ecosystems for enhanced protection under future periods of thermal stress, namely those expected to be brought on by global climate change.