National Coral Reef Monitoring Program: Erosion data from bioerosion monitoring units (BMUs) deployed at coral reef sites in the Northern Mariana Islands, Wake Island, and Guam from 2014-03-25 to 2017-06-16 (NCEI Accession 0184292)

Ocean Acidification (OA) is expected to reduce the calcification rates of marine organisms, yet we have little understanding of how OA will manifest within dynamic, real-world systems, nor how to accurately measure said manifestation. The term bioerosion refers to the biological destruction of hard structures, such as coral skeletons. On coral reefs, this process is the antithesis of coral calcification. If rates of bioerosion are higher than calcification, healthy reef habitats can erode into rubble and sand.

The erosion rates provided in this data set were collected from bioerosion monitoring units (BMUs) retrieved at existing long-term monitoring sites during NOAA Pacific Islands Fisheries Science Center (PIFSC), Coral Reef Ecosystem Program (CREP) led NCRMP missions around the Northern Mariana Islands, Wake Island, and Guam.

This archive package contains BMU data from permanent long-term monitoring sites in the Northern Mariana Islands and Guam that were analyzed at NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML), as part of the NOAA National Coral Reef Monitoring Program (NCRMP). BMUs are constructed from clean coral skeletons and left on the reef for a period of 3 years. This set of data is the third run of BMUs that has ever been produced during what was a testing phase of best practices, and as such, the protocol established at the time was shortly thereafter amended in order to give a more thorough picture of bioerosion rates. Early analysis procedures at this stage utilized a benchtop 3D scanner (HDI Advance R2, 3D3 Solutions) for initial scans (pre-deployment), while post collection analyses (including those in this submission) were analyzed by a larger Computed Tomography device (CT scanner, Siemens). The current protocol utilizes the CT scanner for both pre and post-scans, for reference.

BMUs are CT scanned for changes in density, volume and mass in which rates of bioerosion can be assessed using Amira analysis software (FEI). Annual erosion and accretion rates can be determined from these data in terms of loss of reef structure volume as well as mass in grams of calcium carbonate. Accretion rates given in this data set were determined by finding the volume of non-original carbonate material found on the external surface of the BMUs divided by the number of years the BMU was deployed on the reef. These rates can detect accretion signals when calcifying organisms, such as corals or algae, have grown on their exteriors. Rates of macroboring were determined by changes in the internal volume of the BMUs (e.g., that removed by bore holes) divided by the number of years the BMU was deployed on the reef. Macroboring can occur from eroders such as, clionaid sponges, annelids and other macroboring fauna.
Discrepancies between volumetric measurement methods for this dataset (3D scanner and CT scanner) caused incidences where positive grazing volumes and rates are shown. This is caused by subtle differences between the accuracies of these two methods in assessing volumes combined with the measurement error involved in the analysis of the BMUs in Amira software.

Additionally, due to the methodological differences in assessing densities pre-versus-post deployment (pre-weight divided by 3D scanned volume versus CT-calculated density via Hounsfield Unit regression, respectively), these two sets of values are incongruous with one another.