Predictive modeling of dominant macroalgae abundance on temperate island shelves (Azores, Northeast Atlantic)
Volcanic oceanic islands typically rise steeply from the ocean floor and are surrounded by narrow shelves produced by swell erosion on the islands' flanks. This study focuses on mapping the distribution of six macroalgae that dominate infralittoral on-shelf hard substrate biotopes around the island of Faial (Azores, northeast Atlantic): articulated Corallinaceae, Codium elisabethae, Dictyota spp., Halopteris filicina, Padina pavonica, and Zonaria tournefortii. Semiquantitative data on their abundance, collected by SCUBA diving, ROV, and drop-down camera surveys, are intersected with a series of gemorphological and oceanographical explanatory variables collated from various sources that include multibeam surveys, satellite imagery, ooeanographic modeling. and GIS analysis. Ordered logistic regression models are used to find the combinations of major environmental variables that best explain the abundance variations observed. The predictive distribution maps obtained for the six macroalgae are combined to produce the first predictive map of macroalgal facies on an island shelf in the Azores. Depth- wise general and sectoral macroalgal zonation are also presented.