Calcification accretion units, or CAUs, are used to assess the current effects of changes in seawater carbonate chemistry on calcification and accretion rates of calcareous and fleshy algae in the Hawaiian and Mariana Archipelagos, American Samoa, and the Pacific Remote Island Areas as part of the Pacific Reef Assessment and Monitoring Program (RAMP).

Laboratory experiments reveal calcification rates of crustose coralline algae (CCA) are strongly correlated to seawater aragonite saturation state. Predictions of reduced coral calcification rates, due to ocean acidification, suggest that coral reef communities will undergo ecological phase shifts as calcifying organisms are negatively impacted by changing seawater chemistry.

Deployed on the seafloor for a period of time, CAUs allow for recruitment and colonization of CCA and hard corals. By measuring the change in weight of the CAUs, the reef carbonate accretion rate can be calculated for that time period. Monitoring net accretion over successive deployments allows for the detection of changes in calcification rates over time.

The calcification rate data described here are from CAUs that have been deployed and retrieved at existing, long-term monitoring sites during NOAA Pacific Islands Fisheries Science Center (PIFSC), Coral Reef Ecosystem Program (CREP) led RAMP missions around American Samoa and the Pacific Remote Island Areas in 2010 and 2012, in accordance with protocols developed by Price et al. 2012. There are typically (but not always) five CAU sites established at each location CREP visits with five units deployed at each site.

CAUs are composed of two 10 x 10 cm flat, square, gray PVC plates, stacked 1 cm apart, and are attached to the benthos using stainless steel threaded rods. Calcareous organisms, primarily crustose coralline algae and encrusting corals, recruit to these plates and accrete/calcify carbonate skeletons over 2-3 year deployments. Due to the simple, low-cost design and analysis, statistically robust numbers of calcification plates can easily be deployed, recovered, and processed to provide estimates of net calcification.

This study provides information about Pacific-wide spatial patterns of algal calcification and accretion rates and serves as a basis for detecting changes associated with changing seawater chemistry due to ocean acidification. In conjunction with benthic community composition data (separate dataset), the calcification rates will aid in determining the magnitude of how ocean acidification affects coral reefs in the natural environment. The data can be accessed online via the NOAA National Centers for Environmental Information (NCEI) Ocean Archive.

Analysis of these data will expand scientists’ capacity for assessing coral reef resilience regarding the effects of ocean acidification outside of controlled laboratory experiments. These data can also be used in comparative analyses across natural gradients, thereby assisting efforts to determine whether key reef-building taxa can acclimatize to changing oceanographic environments. These data will have immediate, direct impacts on predictions of reef resilience in a higher carbon dioxide (CO2) world and on the design of reef management strategies.

This effort is a partnership between CREP and Drs. Nichole Price of Bigelow Marine Laboratory and Jen Smith of Scripps Institution of Oceanography, who have extensive knowledge of marine benthic algal community ecology.