The influenceof hexactinellid sponge (Pheronema carpenteri) spicules on the patchy distribution of macrobenthos in the porcupine seabight (bathyal ne atlantic)

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Abstract
The hexactinellid sponge Pheronema carpenteri occurs in high densities (1.5 m−2) over a narrow bathymetric range (1000–1300 m) in the Porcupine Seabight, to the southwest oflreland. The possible influence of sponge spicule mats, which may cover ⅓ of the seafloor, on macrobenthic communities is assessed. Three box core samples were collected from the high density sponge zone (1250 m) and three cores were taken at each of two comparative non-sponge stations (900 and 1500 m). Analysis of data on the abundance and taxonomic composition of major groups of the larger (> 1 mm) macrobenthos suggests that the presence of sediment surface sponge spicule mats substantially modifies the fauna at the 1250 m station. The numerical abundance of macrobenthos within this station increases in an almost linear fashion with the volume of spicules present in a sample; in a single sample with the highest spicule volume, abundance was nearly an order of magnitude higher than that expected in the absence of spicule mats. The possible nature of sponge-macrobenthos interaction and the wider significance of the results are considered further.