Within the marine environment, microorganisms form one of the most important marine symbioses in the world: the symbiosis between corals and photosynthetic single-celled algal symbionts within the genus Symbiodinium. In nutrient poor waters of the tropics, this symbiosis maintains the coral?s high productivity, allowing corals to flourish and provide the foundation of the reef ecosystem. However, corals and associated ecosystems are under increasing stress due to climate change and other anthropogenic effects. Given the importance of this symbiosis to corals and the reef ecosystem, understanding the mechanisms governing the establishment and long term maintenance of this symbiosis is essential. Different coral species harbor different species of Symbiodinium and symbiont performance varies among symbiont species. In most corals, this symbiosis is reestablished each generation. Such flexibility could allow corals to respond to environmental changes between generations. However, the final host symbiont assemblage is not established at the onset of the symbiosis. Instead multiple symbiont types are initially taken up and a winnowing process occurs over time producing the adult symbiont assemblage. Understanding this early ontogeny in symbiotic species is critical to understanding how this symbiosis functions. This project focused on the early establishment of the symbiosis in two endangered corals (Orbicella faveolata and Acropora palmata), an octocoral (Briareum asbestinum) and a jellyfish (Cassiopea spp.). When newly settled recruits of each host species were placed in the field, each host initially acquired a diverse group of symbionts, including many symbiont types not found in the adult host. Within Orbicella faveolata recruits, symbionts differed from those within local and parental host populations irrespective of settlement location. However, across sites, symbionts within juveniles were similar, regardless of larval source. Thus symbionts are acquired from a local pool that can vary over time with selection possibly leading to more resiliency. In contrast, Briareum asbestinum?s offspring established symbioses with the symbiont type that was dominant in parental colonies, regardless of the environment in which the offspring was reared. This suggests that in this host species, host-symbiont specificity is a genetically determined trait. These species may not be able to respond to rapid, climate change-associated, environmental changes by means of between-generation switching of symbionts. Furthermore, as the symbiosis is established, symbiont type and the presence of multiple symbiont species affected host performance, symbiont density and composition. For example, O. faveolata growth and photobiology, but not survivorship, varied with symbiont type. The symbiont type leading to slower host growth used light more efficiently. These findings suggest that symbiont light use (i.e., photophysiology) and host carbon acquisition (i.e., host growth) are decoupled, but did not distinguish the source of this difference. Additionally, the relative abundance of symbiont species significantly influenced symbiont acquisition rate of carbon and nitrogen and the translocation of those nutrients to the host. These results provide evidence of competitive interactions among symbionts and/or host regulation of nutrient supply within mixed species Symbiodinium assemblages. Further studies are needed to tease apart these complex ecological interactions among symbionts and between the host and symbionts. Finally, in culture, growth patterns varied among Symbiodinium types and across light and temperature regimes. Not surprisingly, all symbiont species grew fastest at the natural environmental temperature (26oC) vs. a cooler temperature (18oC) demonstrating that Symbiodinium species regulate growth according to environmental conditions. Metabolites differed among these species and were affected by their physiological response to growth in different temperatures and light regimes. In the presence of multiple symbiont species, symbiont acquisition and relative abundance also varied with light environment. Previous studies using relatively low resolution markers failed to detect coevolution among host-symbiont lineages. A higher resolution phylogenetic analysis, using five host genes and four symbiont genes within the gorgonian family Gorgoniidae, support these findings and suggest that, at least over evolutionary time scales, these symbioses are flexible. A potential response to increasing sea surface temperature is range expansion. The coral Oculina patagonia, a species that is expanding northwards in the Mediterranean Sea, showed reduced symbiont diversity at the expansion front. Thus coral range expansion may be accompanied by reduced symbiont diversity, possibly resulting in limited adaptability of range-expanding coral. Throughout this project, we have collaborated with the Aquarium of Niagara (AON) on various projects, including articles for the quarterly newsletter, informational displays and lesson plans. We reinstituted the docent program, developing a training program and training docents who now volunteer at the AON. This collaboration is ongoing. In addition we provided numerous presentations to schools and educators on coral reefs and trained 61 undergraduates, 20 graduate students, 4 high school students, 2 post-docs, 1 high school teacher and provided field research experience to additional 59 students. The BURR Culture collection also provided cultures of Symbiodinium to researchers around the world. Data from this work has been deposited in BCO-DMO and will continue as manuscripts are published. Last Modified: 08/25/2016 Submitted by: Mary Alice Coffroth
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