The outer bands of a hurricane are beginning to whip the water with wind and drizzle, but De Mutsert and Van der Ham steer their 20-foot motorboat into the bay. Calling instructions to each other in Dutch, they soon arrive at a small island of cordgrass and mangroves, one of their lightly oiled study sites.
At their first sampling point, in shallow, bathtub-warm water near the island, Van der Ham stands at the back of the boat, gripping the metal-edged planks at the mouth of a long, skinny net. It’s a kind of trawl used by many commercial shrimpers. “Except their nets are a lot bigger, and they’re a lot better at using them,” says Van der Ham as he untangles some wayward ropes.
After ten minutes of trawling, De Mutsert and Van der Ham muscle up the net, which is twitching with dozens of small, silvery fish—menhaden, croaker and spot. A few shrimp—some juveniles with jellylike bodies, some adults nearly eight inches long—intermingle with the fish. All of these species depend on marshlands for survival: they spawn at sea, and the juvenile fish and shrimp ride the tides into Barataria and other bays, using the estuaries as nurseries until they grow to adulthood.
When De Mutsert returns to the lab in Baton Rouge, she’ll debone her catches—“I’m really good at filleting very tiny fish,” she says, laughing—and analyze their tissue, over time building a detailed picture of the sea life’s growth rates, overall health, food sources and the amount of oil compounds in their bodies.
The fish and shrimp are members of an enormously complex food web that spans the Louisiana coast from inland freshwater swamps to the edge of the continental shelf and beyond. Freshwater plants, as they die and float downstream, supply nutrients; fish and shrimp that grow to adulthood in the marshes return to sea to spawn on the continental shelf; larger fish like grouper and red snapper, which spend their lives at sea, use coral reefs to forage and spawn. Even the Mississippi River, constrained as it is, provides spawning habitat for tuna where its water meets the sea.
Unlike the Exxon Valdez spill in Alaska, in which a tanker dumped oil on the surface of the water, the BP oil gushed from the seafloor. Partly because of BP’s use of dispersants at the wellhead, much of the oil is suspended underwater, only slowly making its way to the surface. Some scientists estimate that 80 percent is still underwater—where it can smother sponges and corals, interfere with many species’ growth and reproduction, and do long-term damage to wildlife and habitats.
“The oil is coming into the food web at every point,” says Cowan. “Everything is affected, directly and indirectly, and the indirect effects may be the more troubling ones, because they’re so much harder to understand.” Data from De Mutsert and others in the lab will illuminate where the food web is most stressed and suggest ways to protect and repair it.
As penetrating rain descends, De Mutsert and Van der Ham matter-of-factly don rain jackets and keep trawling, stopping just before sunset. Their samples secured, they finally make a break for shore, slamming over the growing whitecaps in the failing light, then maneuvering around tangles of floating, oil-soaked boom. Drenched to the skin, they pull into the dock.
“Yeah,” De Mutsert acknowledges nonchalantly. “That was a little crazy.”
But tomorrow, hurricane notwithstanding, they’ll do it all again.