Biochemical Composition of Caribbean Gorgonian Corals and Their Symbiosis Under Ambeint and Stressful Conditions
Gorgonian corals are the dominant benthic fauna on Caribbean reefs. Unlike scleractinian corals, gorgonian abundance on these reefs has remained stable or has increased. Therefore, to predict how climate change will affect the reef community, it is essential to understand gorgonian physiology under ambient and stressful situations. Under ambient conditions, eight gorgonian species hosted different clade B Symbiodinium, and in two gorgonian species in which the bacterial microbiomes were investigated, two distinct communities were found. In the eight gorgonian species, skeletal content varied from 75-96%, with those having more tissue also having more Symbiodinium density within their branches. The composition of organic matter also varied with the greatest amounts of lipid and proteins in the Pseudoplexaura species, and also large protein content in Pterogorgia anceps, carbohydrate in the Eunicea species and Plexaurella dichotoma, and refractory material in the Eunicea species and Antillogorgia americana. The biochemical differences explained how a subset of the gorgonian species coped with injury and elevated temperature. Lesion recovery took 2x longer in Eunicea flexuosa than in Pseudoplexaura porosa, and both species exhibited different immune responses. Lesion recovery led to lower Symbiodinium density in injured branches of both species, but Symbiodinium photochemistry, the prevalence of dominant bacterial groups and bacterial community structure did not change. Although the prevalence of some bacteria varied post-injury, both gorgonian species healed without signs of disease. When exposed to elevated temperature, the Symbiodinium genotypes and density did not change in branches of Eunicea tourneforti, E. flexuosa and P. porosa. Conversely, at elevated temperatures, in the Eunicea species, physiological modifications occurred in both the hosts and their symbionts (protein and antioxidants), while in P. porosa, the changes primarily occurred in their symbionts (chlorophyll content and photochemistry). Due to the low amounts of tissue resources, in the Eunicea species, their acclimation may not include changes in Symbiodinium photosynthesis, while the larger tissue content and hence resources in P. porosa may allow changes in Symbiodinium parameters. The ability to successfully deal with stressors like injury and elevated temperature may partly explain why gorgonian corals continue to thrive on Caribbean reefs.
Coral, Microbiome, Octocoral, Symbiodinium, Symbiosis, Zooxanthella, Biology
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