Calcification accretion units (CAUs): A standardized approach for quantifying recruitment and calcium carbonate accretion in marine habitats

Abstract

Abstract Standardized metrics that quantify a component of ecosystem functioning are essential for evaluating the current status of coastal marine habitats and for monitoring how ecologically important ecosystems are changing in response to global and local environmental change. Calcification accretion units (CAUs) are a standardized tool for quantifying net calcium carbonate accretion, early successional community structure, recruitment of algae and sessile invertebrates and other response metrics that can be determined from image analyses in coastal marine habitats. CAUs are comprised of paired‐settlement tiles that are separated by a spacer. This design mimics the presence of different representative habitats that are common in most marine systems such as exposed benthic surfaces, cryptic spaces inaccessible to grazers and shaded overhangings. The protected space between the tiles facilitates recruitment and inclusion of cryptic taxa in community assemblage estimates. After a period of deployment, CAUs are photographed for image analysis and then decalcified to quantify calcium carbonate accretion rates. The CAU methodology provides a cost‐effective, standardized protocol for evaluating structure and function in marine benthic habitats. We illustrate how CAU data can be used to compare accretion rates and the relative proportion of carbonate polymorphs in ecosystems across the globe. Here we provide a comprehensive standard operating procedure for building, deploying and processing CAUs, to ensure that a consistent protocol is used for accurate data collection and cross‐system comparative studies.