Monitoring colony colour and zooxanthellae (<i>Symbiodinium</i>spp.) condition in the reef zoanthid<i>Palythoa tuberculosa</i>in Okinawa, Japan

Abstract

Abstract Colony colour, as assessed using waterproof colour cards, is an accurate, economical and rapid way of field monitoring coral bleaching. This technique, however, has never been applied to zoanthids, nor have variations in colony colour been directly correlated with microscopic observation of Symbiodinium condition. In this study, we examined 12 colonies of the common reef zoanthid Palythoa tuberculosa at two sites (Odo and Miyagi) in Okinawa, Japan, for one year to observe the relationship between colour card scores, Symbiodinium morphological condition and sea surface temperature (SST); Symbiodinium types within the study specimens were also examined. Colonies became paler during periods of rapid SST increase and significant correlations between P. tuberculosa colony colour and internal zooxanthellar condition were found for 5 out of the 12 colonies monitored. Results were more pronounced at the Odo site (significant correlations for four out of six colonies) as compared to the Miyagi site (a significant correlation for one out of six colonies). Internal transcribed spacer ribosomal DNA (ITS-rDNA) sequencing results showed no changes in Symbiodinium types among colonies, or between summer and winter. Due to their wide distribution, abundance and ease of identification, zooxanthellate zoanthids are good candidates for monitoring bleaching events on coral reefs.