Brown Tubular Sponge

Agelas schmidtii

The brown tubular sponge is a large demosponge known for its distinctive mound shape, often reaching up to a meter across. It features several dozen vertical tubes, each narrowing towards the top and ending in a large opening called an osculum. These tubes can grow up to 16 cm long and 8 cm wide, with walls strengthened by spongin fibers and calcareous spicules. The sponge is typically brownish orange or brick red, with deep grooves and shallow cup-shaped depressions on the sides. These depressions are home to dark reddish-brown zoanthids, a type of colonial coral that lives symbiotically with the sponge. The sponge is commonly found in the Caribbean Sea, Greater Antilles, Puerto Rico, northern Brazil, and the northern Gulf of Mexico, thriving on reefs at depths of 15 to 45 meters where strong currents and clear waters are present. As a filter feeder, the brown tubular sponge draws in water through small pores near its base, capturing food particles with flagellated cells called choanocytes. It primarily feeds on bacteria-sized particles, which make up 80% of its diet. The water exits through the osculi after the particles are filtered. Divers encountering this sponge can expect to see its unique tubular structure and the symbiotic zoanthids that inhabit its surface. The sponge's resilience and elasticity make it an interesting subject for observation. The brown tubular sponge produces a secondary metabolite known as sceptrina, which has antimicrobial properties.