SEMINAR: MBF602 - Paul Jones - Friday 04/22/2011 @ 1pm in SLAB seminar room

["Paul Jones" <pjones@rsmas.miami.edu>]

Caribbean Cooking: Effects of thermal stress and elevated pCO₂ on growth and photo-physiology of Caribbean scleractinian corals

 

Climate models predict rising sea surface temperatures and reductions in oceanic pH as a result of increased atmospheric CO₂. Both of these factors are expected to threaten reef-building corals, yet few studies have investigated how reef corals will respond to the combined effects of both stressors simultaneously. To better understand how these factors interact we carried out a fully crossed analysis with replicate nubbins of two Caribbean coral species (Porites astreoides and Montastraea faveolata) exposed to two pCO₂ levels (380 and 800ppm) and two temperatures (27 and 31^oC); the four treatment conditions were also replicated threefold to control for tank effects. In addition, each treatment contained nubbins from M. faveolata colonies dominated by Symbiodinium in either clade C or D. Experimental conditions were maintained by direct bubbling with CO₂ gas and a computer-controlled heater-chiller system. The outdoor tanks were covered by a neutral density screen which exposed corals to approximately 50% ambient solar irradiance. Prior to the start of the experiment, coral nubbins were acclimated to ambient pCO₂ levels (380 ppm) and temperature (27^oC) for two weeks. Temperature and pCO₂ levels were then increased at a rate of 0.5^oC and ~40 ppm per day, with experimental conditions being reached after 10 days. Trial conditions were maintained for 5 weeks before being returned to ambient levels at the same rate. Monitoring of the corals continued during a recovery phase. Coral symbiont chlorophyll fluorescence was analyzed weekly using an Imaging-PAM (Walz, GmbH) to determine characteristics such as quantum yield of PSII, photosynthetic capacity and light limiting photosynthetic rate. Coral tissue samples were taken to determine algal symbiont densities, pigment concentrations, and Symbiodinium identity and quantitative composition (using real-time PCR). Buoyant weights and color-scaled photographs were also taken weekly to document temporal changes in mass, size, tissue pigmentation and health. Provisional results indicate that elevated temperature has a greater effect on photophysiology than elevated CO₂ alone. Once the temperatures were returned to 27^oC, elevated CO₂ did impair the corals recovery, suggesting a decreased resilience. Coral growth was also influenced more by temperature than CO₂. Corals in the elevated temperature treatments displayed decreased growth during experimental exposure, but increased growth (ie. higher than control temperature treatments) during the recovery period.

 

 

Paul Jones

Research Associate

Division of Marine Biology & Fisheries

University of Miami

Rosenstiel School of Marine & Atmospheric Science

4600 Rickenbacker Causeway

Miami, FL 33149

 

email:  pjones@rsmas.miami.edu

phone:  305-421-4226