How does the gastrovascular system in perforate and imperforate corals affect physiological response to environmental stress?

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Coral reefs are under siege from global environmental stresses including increased sea surface temperature and ocean acidification. But we still poorly understand how corals react to these stresses. We need to understand the stress response if we are to effectively plan conservation efforts to save corals on our changing planet, including the location and design of marine protected areas. Corals are colonial organisms, composed of repeating units (polyps) all connected in a colony. Each polyp has a central, gastrovascular cavity that is directly involved in many physiological functions, such as digestion and gas exchange. Scientists have known for a long time that there are two types of colony ?blueprints? for coral species: one where the gastrovascular cavities of all of the individual polyps in a colony are connected by a plumbing system that is open all the time (perforate), and another type (imperforate) in which the gastrovascular cavities of only adjacent polyps are connected by a tiny plumbing system that is only open when the polyps are expanded. Thus, perforate coral species have the potential to share nutrition continuously between all polyps in the colony because the internal plumbing connections function like a primitive circulatory system, with cilia driving flow inside these tiny pipes. The spatial and temporal extent of circulation in imperforate species is more limited. This research will be the first systematic examination of how perforate and imperforate corals respond to environmental stress. The initial experiments will use temperature stress because global warming is causing increasing coral mortality through more frequent coral bleaching events. The researchers have formulated a mathematical model patterned after an electrical network (where each node on the network is a single polyp) that predicts how dissolved oxygen and pH (a measure of acidity that affects photosynthesis, respiration, and calcification) will vary inside and around a coral colony. The predictions of the physiological model will be tested for colonies ranging in size from two polyps to thousands. Understanding how tiny young colonies react to thermal stress is important because continued growth of healthy reefs requires that juvenile colonies prosper and grow, which may not happen above certain threshold temperatures. The performance of large colonies is important to understand, as they produce a disproportionate share of coral larvae. The research will use sophisticated sensors and techniques, some of them borrowed from human medicine. The researchers will make measurements of a number of variables inside the gastrovascular system of individual polyps, and over the surface of the colony, to quantify physiological functions under normal and stressful temperatures. They will also take tissue samples from the polyps to measure heat shock proteins, protective compounds made by all life forms on Earth when under stress. This research will produce a tested general predictive model that should be usable to predict physiological response to stress in almost every coral species. This project will involve undergraduate and graduate students, and a postdoctoral scholar, some of whom are from groups underrepresented in science. There will also be significant K-12 educational efforts including classroom visits, public demonstrations, and lesson plans that will be available on the award-winning VIMS Bridge web site. There is also the possibility that new technology will be developed during the research that will be useful to physiologists who work with marine organisms.