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Researchers soak up data from Mission 31

A giant barrel sponge living in the back­yard of the underwater research vessel Aquarius may be one of the planet’s oldest living crea­tures. Top­ping more than 2,000 years of age, these marine organ­isms filter large quantities of water from the sur­rounding reefs every day—providing useable energy to the fauna nearby.

Occa­sion­ally called the “Red­woods of the Reef” due to their large size and long lifes­pans, these ani­mals play a crit­ical role in the healthy func­tioning of coral reefs. For instance, they filter excess nutri­ents that can be harmful to coral reefs and remove dis­solved organic matter from the water column, con­verting it to a form that can be used by other species in the ecosystem.

And while their lifes­pans can reach into the mil­lennia, sci­en­tists have found that the cells they use to filter the water—called choanocytes—are shed and replaced with new ones every four to six hours.

“Sponges bring in a lot of energy from their sur­round­ings, yet their growth rate is almost zero,” said Allison Matzelle, a graduate student working in the lab of Brian Helmuth, a professor of marine and environmental science and public policy. “Instead of investing this energy into growth, a lot of it is used for the constant gen­er­a­tion and shedding of choanocytes.”

A better understanding of the bio­log­ical and envi­ron­mental mech­a­nisms at play during this process, Matzelle explained, would provide a better idea of what may happen to sponges—as well as the rest of the ecosystem—as a result of continuing envi­ron­mental change.

And that’s exactly what she hopes to obtain as the leader of a research project being carried out in con­junc­tion with Mission 31, a month-​​long underwater expe­di­tion beginning on June 1 and led by Fabien Cousteau, grandson of the legendary underwater explorer Jacques Cousteau.

For her dis­ser­ta­tion, Matzelle is building an energy budget model for the mussels that live off the coast of Mass­a­chu­setts. She’ll be pur­suing a sim­ilar project for Mis­sion 31, but here it’s more com­pli­cated. Mus­sels are extremely abun­dant; she can col­lect them in the field, bring them into the lab, and handle them during experiments. For a centuries-​​old sponge, that’s simply not the case.

“So the goal,” Matzelle said, “is to develop a non-​​invasive way of understanding the energy budget of these animals, where all of the exper­i­ments take place in their natural environment.”

Instead of collecting sample indi­vid­uals and creating controlled envi­ron­ments like she does with the mussels, Matzelle will figure out how best to measure phys­i­o­log­ical processes such as feeding, fil­tra­tion, and res­pi­ra­tion without removing the animals or altering their surroundings.

“I want to see how the phys­i­o­log­ical per­for­mance of these animals changes with fluc­tu­a­tions in the envi­ron­ment,” she said. “How do they respond to changes in tem­per­a­ture, water quality, and food avail­ability?” These processes are not only critical to the survival of the sponge, but also affect the amount of energy available to the rest of the reef.

Over the duration of the mission, Matzelle will take continuous water samples to measure a range of things, from the sponges’ pumping, feeding, and res­pi­ra­tion rates to the amount of energy they absorb from and release to the environment. She’ll also be gathering regular water quality data and hopes to come up with an effective, non-​invasive way to visualize the actual rate of sloughing. But that last task will be harder to do without harming the organism or its surroundings.

“These animals are critical to the functioning of the reef. A sig­nif­i­cant amount of energy trans­ferred through food webs could actu­ally be coming from these sponges,” Matzelle said. “They’re really impor­tant to the rest of the coral reef ecosystem.”

– By Angela Herring

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