Gulf Spill’s Ecological Impact: “The Scariest Thing Is That We Don’t Know”

Biologists observe oil inside crab larvae, and don't know if they will survive

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By Nicole Heller, Climate Central

As an ecologist, a lot of people have been asking me for my perspective on the oil spill in the Gulf of Mexico. The short answer is that I am depressed and uncertain. And I am not alone — biologists I have talked to feel the same way. Anytime you dump massive quantities of poisons into an ecosystem it’s bad. Plants and animals are going to die. Everybody understands that – whether you are a biologist, a third grader, or an oil executive.

But what about the more nuanced questions like: How extensive are the impacts going to be? What are the long-term ramifications for individual species? Are there going to be irreversible damages, like extinction?

I am not sure anybody can answer these questions with much confidence right now. 

Shortly after the explosion of the Deepwater Horizon oil rig almost two months ago, I wrote about some potential consequences if the oil washed ashore and infiltrated the already degraded Louisiana wetlands.

Well, the oil did reach land by April 30th and has since pushed into delicate estuaries and wetlands. Coupled with a forecast of an intense hurricane season this year, I can only shake my head in worry, as worst-case scenarios of habitat destruction seem plausible. Heavy storm events are likely to push oil further into the coastal estuaries, killing plants and animals and resulting in rapid erosion of the coastline.

But what is going on out in the ocean, where most of the oil is right now? 

I talked to Dr. Erin Grey, a marine biologist and postdoctoral researcher at Tulane University in New Orleans. Grey is working on Blue Crab demographics. In her research, she is trying to understand the population growth and movement patterns of Blue Crabs in order to build computer models that can be used to set catch targets, with the goal of enabling sustainable fishing of the species. I asked Grey how the oil is affecting the Blue Crabs, which are a valuable species for the Gulf economy. In 2008, for example, the landed value of Blue Crabs was about $40 million.

Grey explained that Blue Crabs, like other valuable Gulf fish and shellfish, such as Menhaden and Brown Shrimp, have a life cycle in which the female goes out into the open Gulf to reproduce. Larvae stay out in the open waters for the first month or so before they come into the wetland estuaries to live. Peak breeding season for Blue Crab is in the late spring and summer. Thus, when the oil spill started on April 20th, adult female crabs and millions upon millions of new larvae were likely out in the open Gulf waters.

So what happens when those individuals encounter oil? Do their gills get coated, making breathing difficult or impossible? Do they eat the oil and the chemical dispersants (i.e. Corexit) and get poisoned, or prevented from getting sufficient nutrition to grow?

Biologists don’t know

“The biggest pulse of juveniles returning to the estuary would be expected in September or October. If we don’t see hundreds of millions come back then we will know,” Grey said.

It’s been reported that dispersants interact with the sheen of oil to create little droplets that are the size of the larvae’s food. And Grey’s group is finding what she thinks is oil inside the post-larvae stage crabs as they are re-entering the estuary.

Interestingly, these crabs are alive. But how is the oil getting into their bodies? Are they eating it? If so, does this mean that the water is not toxic to crabs? Or will they die soon? It’s not yet clear.

Grey hadn’t planned to study toxicology in her work, but of course like many scientists in the region, her work changed after April 20th. Now she is rapidly trying to learn about the effects of this oil spill on Blue Crabs.

“I looked but was unable to find many oil toxicology studies on Blue Crabs or studies on dispersants,” she told me.

A standard toxicology test, the LC50, would provide the concentration of oil or dispersant in the water that kills 50 percent of Blue Crab individuals. Grey said she has made some guesses using estimates from studies done after the 1989 Exxon Valdez spill in Alaska and other spills, and her colleagues at the University of Southern Mississippi are rapidly embarking on toxicology studies of the Blue Crab to foster additional understanding.

I guess we will just have to wait and see and learn as we go, which isn’t very satisfying considering that oil continues to spill into the ocean.

Silly me, I thought we were supposed to understand the environmental risks, and how to conduct cleanup efforts, before we gave permits for oil drilling.

(Republished with permission of Climate Central)

(Pelican Rescue Photo: FEMA; Crab Larvae Photo: Erin Grey)