This microscope image shows the carcass of a small crustacean (possibly a deep-sea amphipod) that was caught in the spines of one of the newly discovered carnivorous sponges, Cladorhiza evae.
Killer sponges sound like creatures from a B-grade horror movie. In fact, they thrive in the lightless depths of the deep sea. Scientists first discovered that some sponges are carnivorous about 20 years ago. Since then only seven carnivorous species have been found in all of the northeastern Pacific. A new paper authored by MBARI marine biologist Lonny Lundsten and two Canadian researchers describes four new species of carnivorous sponges living on the deep seafloor, from the Pacific Northwest to Baja California.
A far cry from your basic kitchen sponge, these animals look more like bare twigs or small shrubs covered with tiny hairs. But the hairs consist of tightly packed bundles of microscopic hooks that trap small animals such as shrimp-like amphipods. Once an animal becomes trapped, it takes only a few hours for sponge cells to begin engulfing and digesting it. After several days, all that is left is an empty shell.
MBARI researchers videotaped the new sponges on the seafloor, then collected a few samples for taxonomic work and species-reference collections. Back in the lab, when they looked closely at the collected sponges, the scientists discovered, as Lundsten put it, “numerous crustacean prey in various states of decomposition.”
Sponges are generally filter feeders, living off of bacteria and single-celled organisms sieved from the surrounding water. They contain specialized cells called choancytes, whose whip-like tails move continuously to create a flow of water which brings food to the sponge. However, most carnivorous sponges have no choancytes. As Lundsten explained, “To keep beating the whip-like tails of the choancytes takes a lot of energy. And food is hard to come by in the deep sea. So these sponges trap larger, more nutrient-dense organisms, like crustaceans, using beautiful and intricate microscopic hooks.”