Development of benthic monitoring methods using photoquadrats and scuba on heterogeneous hard-substrata: a boulder-slope community case study

Photoquadrats enable efficient and cost-effective quantitative estimation of epibenthic communities. Despite their utility, however, there has been limited use of photoquadrats for such purposes in temperate north-west Europe, where there is also a growing need for standardized approaches to marine monitoring. 2.A rapid photoquadrat-based methodology was trialled by scuba divers on a heterogeneous boulder-slope habitat in a Special Area of Conservation (SAC) in Northern Irish waters. To investigate the monitoring potential of the method, the benthic community was randomly sampled in the summers of 2009 and 2010. The community was represented at species level (community composition) and by functional group (community structure), and the data-extraction resolution was varied using different numbers of point intercepts per image (25, 50, and 100) to assess the balance of precision and efficiency with regard to detection of community change. 3.The method was efficient in situ and yielded sufficient sample images for estimation of local benthic community diversity (number of species). The community varied significantly, with six distinct sub-communities identified within the survey area. High spatial variability obscured detection of temporal changes in the overall community composition and structure. However, spatial variability was substantially reduced by testing only the dominant sub-community, in which significant changes were detected between 2009 and 2010.4. The ability of the photoquadrat to detect individual taxa was related to data resolution: the more point-intercepts sampled, the more taxa were discovered, but the data-extraction effort was greater. After considering the ability of the photoquadrat method to quantify number of species and to detect change in community structure, as well as its precision and efficiency, the inspection of 50 point intercepts per sample image was found to be optimal. These findings demonstrate the benefits of photoquadrat-based methods and highlight their potential as a standard approach to marine monitoring