Sponges recycle carbon to give life to coral reefs

In a new research, scientists have determined that sponges recycle carbon to give life to coral reefs.

The research was conducted by Jasper De Goeij, the student of marine biologist Fleur Van Duyl from the Royal Netherlands Institute for Sea Research.

Traveling to the Dutch Antilles with his student, Anna De Kluijver, De Goeij started scuba diving with the sponges to find out how much carbon they consume.

The duo collected sponges, placed them in small chambers and exposed the sponges to 5- bromo-2'-deoxyuridine (BrdU).

"The BrdU is only incorporated into the DNA of dividing cells," explained De Goeij, so cells that carry the BrdU label must be dividing, or have divided, since the molecule was added to the sponge's water, and cells can only divide if they are taking up carbon.

But when De Goeij returned to the Netherlands with his samples, he had problems finding the elusive label.

Discussing the BrdU detection problem with his father, biochemist Anton De Goeij, De Goeij Senior offered to introduce his son to Bert Schutte in Maastricht, who had developed a BrdU detection system for use in cancer therapy.

Maybe he could help De Goeij Junior find evidence of cell division in his sponges.

Taking his samples to Jack Cleutjens's Maastricht Pathology laboratory, De Goeij was finally able to detect the BrdU label in his sponge cells.

Amazingly, half of the sponge's choanocyte (filtration) cells had divided and the choanocyte's cell division cycle was a phenomenally short 5.4 hours.

"That is quicker than most bacteria divide," said De Goeij.

The sponge was able to take up the colossal amounts of organic carbon that De Goeij had measured, but where was the carbon going: the sponges weren't growing.
 
De Goeij tested to see if the cells were dying and being lost, but he couldn't find any evidence of cell death.

When he and his Pathology Department colleagues went back and looked at the samples, De Goeij realised that choanocytes were shedding all over the place.

Then, De Goeij remembered the tiny piles of brown material he found next to the sponges in the aquarium every morning.

The sponges were shedding the newly divided cells, which other reef residents could now consume.

"Halisarca caerulea is the great recycler of energy for the reef by turning over energy that nobody else can use (dissolved organic carbon) into energy that everyone can use (discarded choanocytes)," explained De Goeij.