Objective 2. The role of symbiont composition and photosynthetic capacity on coral calcification rates.

Objective 2.

The role of symbiont composition and photosynthetic capacity on coral calcification rates.

Calcification rates of corals have been shown to vary in conjunction with the photosynthetic activity of their algal endosymbionts in what has been termed light enhanced calcification. Symbiotic dinoflagellates of the genus Symbiodium consist of 8 phylogenetic clades (A-H) and multiple subclades that vary significantly in their photosynthetic capacities. This phylogenetic and functional diversity is thought to determine their distribution within and among coral hosts. In Montastrea annularis for example, symbiont composition varies with depth and position within a single colony, as well as among individuals at different depths, with Clade A more prevalent on the tops of colonies and Clade C dominating on the sides or at depth. Symbiont distribution also correlates with bleaching susceptibility, with Clade C generally thought to be the most susceptible to bleaching and Clades A and D being most resistant. We propose to measure photosynthetic efficiency and calcification rates in two species of live corals, Montastrea annularis and Porites astreoides from degraded and pristine sites using a combination of pulse amplitude modulated fluorometry (PAM) at the coral polyp scale (mm) and microscopic PAM and live cell imaging techniques at the individual symbiont scale (µm) to simultaneously determine symbiont functional diversity and intracellular signaling under different environmental conditions. We hypothesize that symbiont functional diversity will correlate with variations in internal pH, free Ca2+, and nitric oxide in the interstitial spaces, and calcification rates, and that these characteristics will vary between different environments, representing tradeoffs between clade composition and calcification rate. Performance of different holobiont (algal symbiont and coral host) combinations along an environmental stress gradient will elucidate consequences and tradeoffs of different host and symbiont partnerships and shed light on coral responses to global climate change.

To look at our chemical approach to prevent bleaching in corals, check out the eposter HERE.

Zooxanthellae in juvenile Porites astreoides: