If you have spent time underwater, you have probably seen sponges. Whether warm water or cold, sponges abound. Some are even found in freshwater. New species, in both shallow and deep water, are discovered every year. This one, probably a branching vase sponge (Callyspongia vaginalis, for those who care) is common in the Caribbean.
Sponges attract some attention because of their colors and shapes, but for the most part they seem uninteresting, motionless if not for wave and current action. To the casual observer, they just sit there, doing nothing. But in fact they are pumping huge volumes of water, constantly filtering.
Here, I released a harmless green dye near the outside of the base of the sponge. Thirty seconds later the dye was streaming out through the inside of the sponge.
Pretty cool, right? But it also reminds us that all the tiny stuff that we humans dump in the water finds its way into the marine food web.
Also visible in the photo: the long bristly arms of a brittle star, the small discs and tentacles of zoanthids (relatives of sea anemones and jelly fish) that live on the outside of the sponge, and a goby (maybe a Yellowline Goby). Sponges, after all, form the basis of a tiny community of their own.
Biologist Bill Streever (above left) is the award winning and bestselling nature writer behind Cold, Heat, and In Oceans Deep. His wife, marine biologist Lisanne Aerts (above right), is an award winning photographer. They live aboard their cruising sailboat Rocinante, currently in South America. When not busy fixing the boat, they sail, dive, hike, row a dinghy, paddle kayaks, and look at the world through the twin lenses of science and history. Billstreever.com