Optimising sampling strategies in coral reefs using large-area mosaics

Abstract

Adequately sampling benthic cover in marine ecosystems is a challenge with most methods encompassing only a small portion of the area for which cover is estimated. Recent advances in photogrammetric techniques are providing opportunity to map expansive areas of reef. This study aimed to evaluate the adequate level of sampling for traditional quadrat-based designs at ecologically relevant scales. We used large-area (~250 m2), high-resolution (0.911 - 0.143 mm/pixel) mosaics to assess the precision and reproducibility of quadrat-based benthic sampling and identify the most efficient strategy (size and number of quadrats). There was a strong relationship between the percent cover of benthic classes and the level of sampling effort required to adequately sample them. As expected, larger quadrats were found to be more efficient when sampling effort was expressed in number of quadrats. This study aims to identify the optimal level of sampling (least effort that would result in a given target precision) to characterize coral reef benthic communities (whatever they are) within each site. As such, the sites selected were intentionally very different and together represented the broad scale of heterogeneity found in shallow coral reef communities. Abundance data can be used in combination with the relationships presented here to determine the optimal sampling protocols for management approaches to coral reef monitoring.