Research

Controls on Coral Reef Calcification

Numerous laboratory and mesocosm experiments have provided valuable information on how coral calcification responds to changes in CO2 as well as other parameters such as light, temperature, nutrients, and heterotrophic feeding (Cohen and Holcomb, 2009). However, results from controlled laboratory and mesocosm experiments cannot be directly extrapolated to the coral reef ecosystem level where multiple parameters affect NEC simultaneously. As part of my doctoral research with Richard Feely and Chris Sabine at NOAA’s Pacific Marine Environmental Laboratory (PMEL), we determined that a previously published model of coral reef NEC that included CO2 levels, temperature, and coral cover was inadequate for predicting NEC rates on multiple reefs, indicating that additional parameters must play a critical role in determining coral reef NEC (Shamberger et al., 2011). Now, as a Postdoctoral Scholar at the Woods Hole Oceanographic Institution (WHOI), I am building on these initial observations and ideas working with Anne Cohen to investigate the relationships between NEC and CO2 on Pacific coral reefs with varying CO2 levels, nutritional status, community composition, and flow regimes. In addition, we are investigating the relative importance of coral calcification versus coralline algae calcification in the overall ecosystem response to ocean acidification. Also working with me on this project are chemical oceanographer Dan McCorkle and physical oceanographer Steve Lentz, both on the faculty at WHOI. Through this multidisciplinary collaboration, I am expanding both my field and laboratory skillset (see below) and my perspectives on the oceanographic, chemical, and biological processes that influence the coral reef response to climate change.

Coral Reef Sensitivity to Changing CO2

Coral reefs are highly biogeochemically active ecosystems with high rates of calcification, photosynthesis, and respiration that strongly alter the seawater CO2 system of coral reef waters. For my doctoral research at the University of Washington (UW) and PMEL with Richard Feely and Chris Sabine and our collaborators Fred Mackenzie, Marlin Atkinson, and Eric DeCarlo at the University of Hawaii (UH), I led several field expeditions to measure diel time series of CO2, NEC rates, and organic production rates of the barrier reef in Kaneohe Bay on the island of Oahu in Hawaii. To make these measurements, I monitored spatial and temporal changes in seawater total alkalinity (TA), dissolved inorganic carbon (DIC), salinity, and temperature by manually collecting water samples and deploying CTDs and automated water samplers from a small boat that I operated. I also performed TA and DIC analyses at PMEL and calculated the full seawater CO2 system using CO2SYS. I analyzed TA and DIC on separate systems at UH and PMEL but am now analyzing TA and DIC simultaneously on a VINDTA 3C system at WHOI. We found that NEC rates of the Kaneohe Bay barrier reef were high compared to what has been measured on other coral reefs despite comparatively high CO2 levels. I was also able to utilize the large natural variability in seawater CO2 on the Kaneohe Bay barrier reef to assess the reef’s sensitivity to changing CO2 levels and found that NEC was more highly correlated with CO2 than with temperature, light, organic production, or residence time of water (Shamberger et al., 2011). The relationship between NEC and CO2 has been investigated for only a handful of coral reefs in the world (Shamberger et al., 2011). In order to better quantify the variability that exists in the coral reef NEC-CO2 relationship, I am measuring NEC on coral reefs with a range of CO2 levels as part of my postdoctoral work at WHOI. In Palau we are measuring NEC on the barrier reef where CO2 is low and in restricted bays where the long residence time of water and biochemical processes such as calcification and respiration result in elevated seawater CO2. I utilize box models to calculate NEC and organic production rates in coral reef systems and my postdoctoral work has required modifying these calculations for different reef spatial configurations.

Natural Cycling of CO2 in Coral Reefs

In order to predict the effects of ocean acidification on coral reefs, it is necessary to first understand the natural CO2 cycling within coral reef ecosystems. My doctoral research utilized high frequency (hourly to every three hours) measurements of air and surface water CO2, salinity, and temperature over several years by an in situ CO2 mooring to determine the processes controlling CO2 in Kaneohe Bay lagoon and barrier reef waters on diel, seasonal, and annual time scales. I use a combination of Excel and Matlab to analyze these large data sets and can apply the same methods to data produced by any number of in situ CO2 system sensors. While photosynthesis and respiration control the diel cycle of CO2, net calcification elevates CO2 levels on seasonal and annual time scales in Kaneohe Bay relative to the open ocean and atmosphere (Shamberger et al., in prep). For my M.S. research with Fred Mackenzie at UH, I performed a bi-monthly time series study of the seawater CO2 system (calculated from TA and DIC data I collected and analyzed) and determined the processes controlling air-sea CO2 exchange in the lagoon waters of Kaneohe Bay. In agreement with my later doctoral work, we found that Kaneohe Bay lagoon waters are a net annual source of CO2 to the atmosphere due mainly to calcification (Fagan and Mackenzie, 2007; Massaro et al. 2012). We also found that Kaneohe Bay barrier reef waters are a net annual source of CO2 to the atmosphere of a similar magnitude as lagoon waters (Shamberger et al., in prep).