Relating species traits to environmental variables in Indonesian coral reef sponge assemblages

A key goal in ecology is to understand how species with given traits vary with changing environmental conditions. In the Spermonde Archipelago, Indonesia, we identified environmental gradients associated with significant variation in sponge species traits. These were ( 1) an on-to-offshore gradient, ( 2) a gradient from locally perturbed reef sites characterised by fluctuating sediment load concentrations and poor water transparency to locally pristine sites characterised by good water transparency and ( 3) a depth gradient. Species with a massive growth form were associated with inshore reef environments, whereas species with a cup growth form were linked to offshore reefs with a high coral cover. Weakly bioactive species and species with a globular, fan or fistulose growth form were associated with locally perturbed reef environments as indicated by fluctuating sediment levels and reduced water transparency, whereas strongly bioactive species and species with a massive-encrusting and tube growth form were associated with more pristine reef environments with good water transparency. With respect to depth, oviparous species and species with a cup and massive growth form were most strongly associated with deeper transects, whereas species with a ramose, massive creeping and massive-encrusting growth form were most strongly associated with shallower transects. Results of the present study indicate that environmental conditions and species traits interact to determine the composition of sponges across coral reefs.