Seasonal fluctuations in photochemical efficiency of Symbiodinium harbored by three reef-building corals that differ in bleaching susceptibility

Abstract

Coral Reefs ecosystems are the most vulnerable to climate change. In view of this, it is important to evaluate the rate at which reef-building corals develop functioning adaptations to climate change. In order to explore whether reef-building corals develop adaptation to climate change, chlorophyll a fluorescence, Symbiodinium abundance and types were monitored for two years in an established coral nurseries with three corals species that differ in bleaching susceptibility. The species were Poccilopora verrucosa, Porites cylindrica and Acropora formosa. Internal transcribed spacer two (ITS-2) regions of nuclear ribosomal DNA genes (rDNA) was used in monitoring the Symbiodinium types associated with the studied coral species. Pulse Amplitude Modulated (PAM) fluorometry method was used to determine seasonal changes in chlorophyll a fluorescence. In this study, it was found that A. formosa, P. verucosa and P. cylindrica maintained their Symbiodinium types; C3u, C1h, and C15 respectively throughout the seasons. A. formosa and P. verucosa responded significantly to seasonal fluctuation in both solar radiation and sea surface temperature by regulating their Symbiodinium cells densities and photochemical efficiencies except P. cylindrica. However, such seasonal fluctuations in these environmental parameters are not accompanied by acquisition of foreign Symbiodinium types from the environmental pool to boost their survival. This is a reflection of seasonal environmental stability that may cause low rate at which coral develop functioning adaptation to climate change.