Barrel sponge

Photo: Albert Kok · CC BY-SA

Among the largest invertebrates on Caribbean reefs, giant barrel sponges can exceed 1.8 metres in diameter and are estimated to live for more than 2,000 years — earning them the nickname 'redwoods of the reef.' They are filter-feeders, pumping thousands of litres of water daily through their structure to extract bacteria and dissolved organic matter, playing a major role in reef nutrient cycling. The whorled interior of mature barrels provides shelter for arrow crabs, brittle stars, and banded coral shrimp. Their massive presence on the River Taw's deck indicates the wreck's water quality and current exposure are ideal for sponge growth.