Objective 3. Linking symbiont composition and calcification rates to coral demography along an anthropogenic gradient.

Objective 3.

Linking symbiont composition and calcification rates to the demography of a susceptible and resilient coral species along a gradient of anthropogenically induced environmental degradation.

There is much variability in how different coral species are coping with elevated sea surface temperature (SST) and lower pH. In fact, species composition in many corals reefs is changing from dominance of susceptible reef builders such as Orbicella anularis to more resilient "weedy" species such as Porites astreoides. These changes in colony abundances are a consequence of how elevated temperature and low pH levels are affecting the vital rates (i.e. growth, survivorship and fecundity) of coral populations. We hypothesize that differences in vital rates between susceptible and resilient species are related to how elevated SST and lower pH affect the photosynthetic and calcification physiology of these species. Thus, in this aim we seek to link differences in photosynthetic capacity, as related to symbiont composition, and differences in calcification rates (aim 2) to the demographic performance (i.e. population growth rate) of a susceptible (O. anularis) and a resilient species (P. astreoides) in a degraded and a pristine reef. We will tag and follow the fate of colonies of different sizes of both species at the two sites, as well as measure their photosynthetic capacity, symbiont composition and calcification rates. This will allow us to construct and analyze a size-based matrix population model linking colony physiology to population dynamics.

Porites and Orbicella on the reef in La Parguera: