Meeting Abstract
Scleractinian reef corals live within a few degrees of their upper thermal limit. They exist in an obligate symbiosis with single-cell dinoflagellates in the family Symbiodiniaceae, however, thermal stress from episodic or seasonal ocean warming facilitates the breakdown of the coral-algal partnership (i.e., coral bleaching) that can lead to coral mortality. Algal symbionts (all formally classified in the genus Symbiodinium, now recently reclassified into many different genera) exhibit diverse functional traits that are integral to coral host nutrition, defense, and physiology, and effect the performance of reef corals during (and following) temperature stress. Here, we examine how Symbiodiniaceae contribute to the thermal tolerance of four coral species in Kāne‘ohe Bay, Hawai‘i (Montipora capitata, (Porites compressa, (Pocillopora acuta, and (Pavona varians) that differ in key functional traits: skeletal morphology, tissue thickness, and Symbiodiniaceae fidelity and transmission mode. Twelve genotypes per coral species (n=5 genotype-1) were placed into ambient (ca. 28°C) or high (ca. 31°C) temperature treatments for 2 weeks, and then held at 28°C for one month for a period of physiological recovery. DNA was assayed at three time points (prior to heat stress, after high temperature exposure, and after recovery period) and treatment effects on microbial community assemblages were identified through amplicon sequencing of ITS2, and Symbiodiniaceae performance was assessed through PAM fluorometry, cell counts, and Chl-a. Our across species comparison of coral physiological performance with microbial communities offers clarity on the impact of Symbiodiniaceae in holobiont thermal tolerance as global climate change and ocean warming continue to threaten coral reefs.
