by Angela Herring

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.”

Originally published in news@Northeastern on May 28, 2014