This thick, tough dark gray sponge grows in ledges and caves in shallow water surge channels on the windward seaward reef. These channels are subject to heavy wave action and surge, causing chunks to occasionally be ripped off their substrate and washed across the shallow interisland reefs, coming to rest on the lagoon slope as the cross-reef current dissipates. The sponge apparently requires considerable water movement to survive, so the colonies washed into the lagoon tend to slowly die and dissolve. The sponge is preyed upon by the nudibranch Glossodoris rufomarginata, which also is often washed across the reef into the lagoon, where it continues to feed on the dying sponges. Most of the photos below were taken of sponge colonies washed into the lagoon.
In its normal surge channel habitat, the dark gray sponge is often overgrown with algae, bryozoans and other encrusting organisms. The nudibranch grazers are common.
Created 20 May 2019
Updated 28 September 2023