Remember the bay's other filter feeders

Courtesy photo — The Capital
Dr. Erica Goldman of the Maryland Sea Grant

By Dr. Erica Goldman, science writer with Maryland Sea Grant

We mourn the loss of the bay's oysters, of their ecological prowess and of the way of life they made possible. We mourn the loss of the bay's great fisheries, of 100-pound sturgeon that once cruised the waters and of shad that migrated up the Chesapeake by the millions.

We don't mourn the less charismatic creatures — the sea squirts, worms, mussels, and more. The other filter feeders that lived in the crevices of oyster reefs, they too have declined in diversity and abundance, along with the health of the bay. But we don't miss them like we miss the oysters.

The oysters went noisily, amid conflict and gunfire.

The others, those creatures of the benthos, were the civilian casualties of the oyster wars, of urbanization and pollution. They left quietly, their absence as inconspicuous as their presence. We don't even know exactly what species once thrived in great numbers. We've only been keeping tabs recently, our records reflecting times of scarcity, not of bounty.

During a recent visit to the National Museum of Natural History, I was struck by a diorama showing the creatures of the Burgess Shale as they might have looked living in ancient seas. The display showcased a living reef structure, reconstructed from fossils found in the Canadian Rockies in the early 1900s. Every nook and cranny was filled with life, the bottom of the ocean carpeted by ancient starfish-like crinoids and wriggling with crustaceans.

Did the bay's historic oyster reefs once look like this? While historical reconstructions and maps of oyster reefs in the Chesapeake offer clues to the shape and extent of these structures, we know comparatively little about what animals lived with the oysters.

We may not know what the bay's ancient oyster reefs looked like, but we do know what reefs can do for us now. Large vertical reefs provide habitat for other species to live — several recent studies make this point clear. When restored oyster reefs are allowed to grow undisturbed, with oyster shells protruding high into the water column, other species settle on and around the reef in mind-boggling numbers.

Restored oyster reefs attract abundant and diverse life — sea squirts, barnacles, mussels, insect-like amphipods, crabs and more, according to a 2006 study by University of Maryland researchers Kennedy Paynter and William Rodney published in the Journal of Experimental Marine Biology and Ecology
. These researchers found that the density of animals was 10 times higher on a restored oyster bar than in an unrestored area — one notable filter feeder, the hooked mussel, proved 200 times more abundant.

Like oysters, the forgotten filter feeders — the mussels, sea squirts and more — remove algae from the water column. Like oysters, they lock up nitrogen, sequestering it in their body tissues. Like oysters, they help alter the flow of nutrients through the bay's food web in a way that could help improve the quality of the Chesapeake's polluted waters. And, along with oysters, they could help make a difference in the health of the bay.

Today, we've lost more than we ever knew we had. The Chesapeake is a changed place — a product of human engineering, intended or otherwise. The bay's ecology has been sculpted by years of harvest, use, and often abuse.

The bay of the future will also be shaped by acts of engineering. Its ecological state will reflect choices we make now to restore or deplete aquatic resources, including the bay's natural buffers.

We're trying as hard as we can to bring back the native oyster. We're even considering introducing a non-native one. But we rarely allow reefs to grow to great heights, undisturbed and protected from tongs, dredges, and boat anchors. In fact, when the oyster season opened in the beginning of October, sanctuary reefs in Virginia's Rappahannock River that had been untouched for some 10 years were again reopened to commercial harvest.

We rarely think about the other filter feeders that call an oyster reef home. They've become collateral damage in the oyster wars. We keep some track of their comings and goings through surveys, but they've largely fallen to the sidelines of any active restoration plans.

If our goal for the Chesapeake is cleaner waters and healthier fisheries, perhaps the forgotten filter feeders could lend a hand, assisting oysters with the monumental task of filtering the bay's murky water. For the Chesapeake's one species of oyster, there are dozens of other species that could help remove algae from the water column. Maybe the oyster will always reign supreme among filter feeders. But aren't the others worth a closer look?
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(Revised Oct 2007)