National Coral Reef Monitoring Program: Calcification Rates of Crustose Coralline Algae Derived from Calcification Accretion Units (CAUs) Deployed across American Samoa from 2010 to 2018

The calcification rate data described here are derived from Calcification Accretion Units (CAUs) that were deployed and retrieved at long-term climate monitoring sites during NOAA Pacific Islands Fisheries Science Center (PIFSC), Ecosystem Sciences Division (ESD) led National Coral Reef Monitoring Program (NCRMP) missions in American Samoa in 2015 and 2018, as well as pre-NCRMP missions in 2010 and 2012. CAUs are PVC settlement plates that facilitate the recruitment and colonization of crustose coralline algae, hard corals, and other reef calcifiers. Laboratory experiments show that CCA and coral calcification rates are strongly correlated with seawater chemistry, and shifts in carbonate chemistry conditions due to ocean acidification could lead to reduced calcification and accretion rates and ecological phase shifts in coral reef communities.

Coral reef calcium carbonate accretion rates can be estimated by measuring the change in weight of the CAUs between deployment and retrieval. Monitoring net accretion over successive deployments allows for the detection of changes in reef calcification rates over time. Five units were deployed on the seafloor at each CAU site for 3 years. The number of processed CAUs for a site may be less than the number deployed, either because the units were lost or damaged at sea and therefore not recovered, or in rare instances, due to errors during laboratory processing.

This study provides information about spatial and temporal patterns of reef carbonate calcification and accretion rates and serves as a basis for detecting changes associated with changing seawater chemistry due to ocean acidification. 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.