New killer sponges found in the deep sea

Four new species of meat-eating sponges have been discovered deep in the waters off California, a new study says.

There are about 8,500 species of sponges, a type of simple, mostly stationary invertebrate, and the vast majority passively filter their food on the seafloor. 

But in the past two decades, scientists have found seven species of carnivorous sponges that attack prey and the new discoveries bump that number to 11, said Lonny Lundsten, a biologist at the Monterey Bay Aquarium Research Institute.

While studying thousands of hours of video filmed by a robot in waters about 1,800 feet (548 m) deep, Lundsten became an expert at recognising unusual life-forms. So when he spotted some unusual-looking sponges, the scientist immediately used the robot to collect live samples to take back to the lab.

There, he found the sponges had tiny prey animals trapped on equally tiny hooks on the sponges’ bodies, according to the study, published recently in the journal Zootaxa.

Hooked on crustaceans

Most deep-sea sponges filter feed by slurping bacteria and other single-celled organisms, creating a small current to force as many of these organisms past their body as possible. The cells, known as choanocytes, have long, tiny, rat-like tails that they whip around to create the current.

The strange sponges Lundsten spotted, however, didn’t have choanocytes – they had hooks, just like the seven other known species of carnivorous sponges. The microscopic hooks are located at the ends of tiny hairs that branch out from the tree-like sponges, a very different appearance from the porous sponges you use in the bath.

Lacking a mouth to chew its prey, the sponge instead relies on specialised cells that travel through its body carrying special enzymes, which slowly break down the prey. After several days, all that remains of the crustacean is an empty shell.

The four species Lundsten discovered, Asbestopluma monticola, Asbestopluma rickettsi, Cladorhiza caillieti, and Cladorhiza evae showed up mostly near undersea volcanoes and deep-sea vents in the northeastern Pacific.

Some like it hot

The newfound sponges’ harsh habitat may partly explain their killer lifestyle, Lundsten pointed out. Near volcanoes and vents, little life floats by, even the single-celled variety – so having (and constantly beating) choanocyte tails would be a waste of energy. 

Being carnivorous, on the other hand, means the invertebrates don’t have to expend as much effort to find food.

The deep-dwelling sponges likely also have another food source in the bacteria that live near the deep-sea vents on the ocean floor. 

“It just goes to show how little we know about life at the bottom of the ocean,” Lundsten said. “It’s the largest habitat on the planet, and we’re still discovering new species all the time.”