MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14589

ABSTRACT: Top-down and bottom-up processes can mediate the structuring of biological communities. Several studies have provided separate support for those processes in pelagic and benthic compartments of reef systems, but studies focusing on whole-reef processes are less common. Here, we sampled three ‘reef compartments’ in the Alcatrazes Archipelago in Southeastern Brazil (i) benthic cover of colonial organisms, (ii) solitary organisms, and (iii) reef fish (i.e., pelagic) to identify the groups responsible for spatial community structure among reefs. A dynamic mosaic structure best defines the assemblages at each compartment, with substantial changes observed among sites over two consecutive years and at two depth strata, separated by a sharp thermocline. Changes in benthic cover of colonial organisms are largely due to the extent of the blooming of Sargassum canopies, algal turfs, and zoanthid Palythoa caribaeorum. Solitary organisms show a consistent monotonic change in the abundance of sea urchins, ascidians, and snails. Fish assemblage structure was different among reefs. However, we observed that large invertivore fish tended to concentrate in warmer water above the thermocline and small fish of different feeding habits in deeper and colder water in all reefs. We observed a potential strong link between the reefscape and solitary organisms, by a negative relationship between the abundance of urchins and the cover of Sargassum spp., suggesting top-down control. A second link, is indicated by a positive relationship between low-lying cover, composed of articulated turf and P. caribaeorum, and larger invertivorous fish, suggesting bottom-up control through the provision of favorable foraging grounds.