Meeting Abstract
Scelaractinian corals form the basis of one of the most diverse ecosystems on the planet, coral reefs. However recently these ecosystems have been in decline due to die offs of corals as a result multiple stressors, including increasing sea surface temperatures, disease outbreaks and nutrient enrichment. Corals are dependent upon symbiotic dinofagellates, Symbiodinium, for their nutritional needs. Despite this, theory suggests that Symbiodinium may suppress host immunity to maintain symbiosis. To explore the consequences of symbiosis on host immunity, we conducted an experimental manipulation of symbiont density using nutrient enrichment. Cores of the Caribbean coral Orbicella faveolata were pre-treated with nutrient enrichment for one month to increase symbiont density. Following this period both nutrient enriched and control corals were exposed to immune challenge using a mixture of lipopolysaccharides and Poly I:C. Following the experiment, samples were analyzed using RNAseq and symbiont density was quantified using qPCR. Analysis of host gene expression revealed different effects of nutrient enrichment and symbiont density. As expected, increases in symbiont density appeared to have a negative effect on host expression of immune-related transcripts. In contrast, nutrient enrichment alone, and in combination with immune challenge, increased expression of several putative immune transcripts. Our results suggest an important ecological trade-off for corals: while increased symbiont density may provide an energetic benefit to the host, this likely comes at the cost of reduced host immunity. Further study of this trade-off is essential to understand the potential consequences of increasing disease prevalence on reef ecosystems.
