Reef corals as flexible multi-partner symbioses: symbiont shuffling as a response to temperature variation

Wildlife Conservation Society, Bronx NY

Investigators

Abstract

Reef corals are first and foremost symbioses between invertebrate animals and dinoflagellate algae. Recent scientific and public concern over the eventual fate of corals and coral reefs in the face of continued climate change and global warming has led to the suggestion that corals may face widespread regional-scale extinction as early as 2030. However, because the dinoflagellate symbionts of reef corals are extraordinarily diverse, the possibility exists that reef corals may switch or shuffle symbionts in response to changing temperatures, and thus mitigate the effects of climate change. This study investigates this possibility by examining the effects of natural temperature variation on symbiont community distributions over a variety of spatial and temporal scales. In doing so, it investigates the paradoxical (in)stability of coral reefs while addressing one of the most pressing and significant questions in coral biology, ecology and conservation: do reef corals possess a novel symbiotic mechanism for mitigating future environmental change? To answer this, a multi-national, multi-year program will be established to monitor changes in these symbioses over time, and uses a threefold approach to investigating the role of temperature in regulating symbiont community structure. It will: (1) undertake latitudinal surveys of corals in three countries from two oceans that vary in their host and symbiont diversity; (2) survey and experimentally manipulate a model system in US domestic waters where temperature regimes vary over small spatial scales (meters); and (3) make seasonal comparisons of labeled coral colonies from four countries in three oceans. Using established and reliable molecular techniques that use Restriction Fragment Length Polymorphisms (RFLPs) in 28S-like rRNA genes as markers for the >15 symbiont genotypes will also enable the discovery of new symbiont taxa. Preliminary data from Australia indicate that high latitude coral hosts contain different symbionts from their tropical conspecific counterparts, supporting the hypothesis that different temperatures may favor different symbionts, and providing baseline data for comparison with other locations. Similarly, data from the 1997-98 El Nino event in Panama provide additional evidence indicating that different symbiont taxa vary in their susceptibilities to temperature stress. This suggests that different thermal optima may indeed promote shuffling of symbionts in response to temperature gradients.To date, no surveys of symbiont diversity have explicitly collected data to assess the effects of temperature on symbiont distributions. Together, the multiple approaches and scales (including experimental work) proposed here represent the first test of the hypothesis that corals may adapt to different temperatures by modifying their symbiont communities. This knowledge contributes to our understanding of the environmental and biogeographic controls on symbiont diversity and their significance for reef coral ecology and conservation. It also provides critical data for an assessment of the potential for long-term symbiont community change in the face of a globally warmer climate.