The Oil Spill’s Growing Toll On Sea Life in the Gulf of Mexico

A prominent marine biologist says the impacts of the oil gushing into the Gulf of Mexico will persist for years, no matter when the flow finally stops. What’s more, scientist Thomas Shirley says that most of the damage remains out of sight below the surface, as creatures succumb to the toxic effects of the rapidly spreading tide of oil.

Thomas Shirley of Texas A&M University has spent most of his career studying the aquatic life of the Gulf of Mexico. Indeed, shortly before the Deepwater Horizon oil spill, Shirley was part of a team of 140 scientists from 15 countries that completed an all-species inventory of the Gulf, from phytoplankton to sperm whales. Despite decades of intensive oil drilling, the inventory showed that the Gulf of Mexico still harbored 15,700 species of sea life. In the area immediately surrounding the spill, Shirley and his fellow scientists tallied 8,332 species of plants and animals, including more than 1,200 fish (such as the Atlantic bluefin tuna), more than 1,500 crustaceans (including the blue crab), and 29 marine mammals (including bottlenose dolphins).

But the massive amounts of oil spewing from the ruptured Deepwater Horizon rig are already having a “devastating” effect on marine life in the

Thomas Shirley

Gulf, according to Shirley. The oil, coupled with the dispersants designed to break it up, will — at least in the foreseeable future — deal a serious blow to the foundation of this ecosystem: the tiny plants and animals known as phytoplankton and zooplankton. “When you start removing pieces of this big food web out there, what’s going to happen?” asks Shirley, who holds the endowed chair in biodiversity and conservation at the Harte Research Institute, which is dedicated to studying the Gulf of Mexico. “We don’t really know, but likely not good things.”

In an interview with Yale Environment 360 contributor David Biello, Shirley discusses how entire generations of shrimp, crab, oysters, and other commercially important marine life may be wiped out and take years to recover. Much of that devastation will remain invisible to us, as creatures from sperm whales to sea turtles may die from the effects of the oil and sink beneath the waves without a trace.

Shirley says that, despite the Gulf’s warm waters and indigenous population of oil-eating microbes, the impacts of this oil spill are likely to be felt for a long, long time — especially if a hurricane blows the oil deep into Gulf Coast wetlands. “If this oil spill ends up back in the marsh areas that are nurseries for a lot of these species, we will see very long-term effects,” says Shirley, who also studied the impacts of another famous oil spill — the Exxon Valdez off the coast of Alaska. “Twenty-one years later we still see effects [of the Exxon Valdez]. I predict long-term effects here.”

Yale Environment 360: Gven your recent survey of the marine biology of almost the entire Gulf, what’s your assessment of the damage to date?

Thomas Shirley: Well, I really don’t have hard data on damage. The only thing we have so far are body counts of the oiled birds, questionable data about the causes of deaths of many marine turtles and a few marine mammals. But, no doubt with this amount of oil in the water there have been many mortalities at all trophic levels — crabs, shrimp, fishes. Lots of things that are small and out of sight of most people, but are important in food webs.

e360: The estimates are now, if you take the high end of the government [estimate], roughly 40 million gallons of oil out there in the Gulf somewhere. What’s your assessment of what the impact on the whole ecosystem will be over time?

Shirley: It will be devastating. But again, most people are not aware of the workings of the ecosystem. And so, to most people all they will see is oiled birds or animals that wash up on shore. What I will see and be concerned about are losses in production of shrimp and crabs and fishes for next year and the year after.

e360: When you say “devastating,” what does that mean? Does that mean that the population is cut in half or the population is poisoned, or does it mean that there won’t be any shrimp next year?

Shirley: Well, within this [affected] region of the Gulf — and that’s now getting to be a sizeable portion of the Gulf — there will be losses of next year’s year-classes of shrimp and crabs. Those that would have been hatched and grown up this year will not be present next year. Some of them will have died as eggs or as larvae or juveniles. Others would never have been produced because each of the parents died or the parents used that energy to fight the toxicity of the oil and disperse it.

e360: What is killing the larvae and the parents? Is it the oil itself or is it some of these dead zones that might be developing?

If we start losing parts of the system, it’s not going to work quite as it’s supposed to.”

Shirley: Most likely [it] will be oil, particularly in the deep plumes, but at the surface also. Surface waters [are] where we have the highest productivity, and by that I mean primary production of phytoplankton is going to be affected. But right immediately under that is all the zooplankton, [and the] larval fish that depend upon the zooplankton for food, [and] the larval shrimp that depend upon them for food. Those are the things that are taken out by contact with the oil, and the oil that’s in solution now because of the dispersants, and these big plumes. Although both BP and NOAA [the National Oceanic and Atmospheric Administration] are as yet questioning the deep plumes, saying there is no data. I think the data are all there.

People are out there taking water samples even as we speak. And the water samples come up heavily laden with oil and gas. And, I think in the next few days we’ll have signatures of those oil samples that confirm that it’s from the Deepwater Horizon oil. Most people are not aware that zooplankton [engage in] vertical migration. [They] move up and down in the water column. In fact, there’s a whole series of different migrations. But they move up and down through the water column for hundreds of meters. And so these animals are moving through these plumes of oil and gas, and being exposed to it.

e360: What is going to bear the brunt as far as sea life goes? Is it the smaller organisms? Is it the larger organisms that perhaps bear the impact of bio-accumulation of some of these toxics?

Shirley: They all will. There’s not really bio-magnification of oil. There’s a bio-concentration that can increase in each particular organism. As they come into contact with more oil or consume it, they can build up oil in their tissues. But that is not magnified in the next trophic level. In fact, if you traced oil content into higher trophic levels, often as you go up the food web into larger and larger predators, there is often a decrease in the content of oil. It doesn’t mean that they’re not affected, either by contact or by food, but it’s not bio-magnified like you would see for metals or pesticides.

e360: What about spawning areas? How will they be impacted by the oil? Is it simply the fact that perhaps larval fish will try to eat the oil or is it more the physical coating, either of the fish itself or the surface?

Shirley: Well, all of those things and more. So some of it will affect food. Some of the fish will actually nip at little gas or oil droplets, and see that as potential food sources and consume that. That’s already been reported although not really quantified in any scientific experiments. But divers have already observed different species of fish biting oil droplets. It will affect their food and then through indirect effects. Some of the food that would have been present for them will not be present. Often, fish that have come into contact with oil have decreased sensory capabilities. So it affects either vision or taste or smell, and they are not as good at finding food. And then part of their energies are being used to combat this oil that they’ve taken into their system instead of using that energy for growth or later on for reproduction. So [there are] a lot of different ways oil can affect the organisms.

e360: Is there a difference between how it will impact in, say, the spawning areas versus the deeper sea or further out in the open ocean?

“One hurricane could change [everything]. If this oil ends up in marsh areas, it could have very long-term effects.”

Shirley: Not really. In spawning areas, you would simply have early life history stages, either gametes or larvae or juvenile concentration in those areas. And, frankly, we don’t know where all of those areas are for the different species. You know, for commercially important species we know pretty well where things happen, but not even all of those. But what we don’t know are all of the trophic links. So one of the things that we like to compare this to, if you ever take apart a watch and you have all these different gears and different mechanisms, little wheels up to big wheels, and they all work together to produce a nicely functioning watch. If you put the watch back together without those little parts, it’s not going to work. And we often don’t know what all those little wheels and spokes are. And in this case we’re talking about the different smaller animals, the zooplankton, and the different kinds of plankton. But they’re part of the mechanisms that contribute toward a functioning ecosystem. If we start losing parts of the system, it’s not going to work quite as it’s supposed to. We will be limping along, so to speak.

e360: And, you mentioned the commercially important species. So let’s go through some of them. I understand that it’s spawning time for the bluefin tuna. What does this mean? Does this mean that the Japanese aren’t going to enjoy Atlantic bluefin tuna sushi next year?

Shirley: Well, they’ve already taken out 80 percent of the stock and it’s not just the Japanese, it’s fishing fleets around the world, but the Japanese are the primary consumers. And the Gulf of Mexico is one of two spawning areas for the North Atlantic bluefin tuna. So, yes, I am fairly certain that the area around the Deep Horizon is not a spawning area. In fact, I’m sure that’s not the case. But the later life history stages may well be exposed. And the [satellite-] tagged tuna certainly utilize the Loop Current, and if they follow it around, there is a strong possibility they will be exposed to oil.

e360: Does that mean that we shouldn’t eat them or, like you said, since the bio-magnification isn’t a threat here, is it relatively okay to eat those bluefin?

Shirley: Oh, I think all of the fish that go to the market will be tested, and I think that our own sensory capabilities are much more sensitive even than any of the testing. So I think that most of the food from the sea that will be harvested will be tested and it will be okay.

e360: What about oysters and shrimp and the other commercially important seafood that contributes so much to the seafood of the entire United States?

Shirley: We have three species of shrimp that are commonly harvested; brown shrimp, white shrimp, and pink shrimp. And, of course, the American oyster and the blue [oyster]. Those are five prime products that most people think of when they think of the Gulf harvest of seafood. [The spill is] already closing down the exporters in that region. So there are widespread effects throughout the country. Over here in Texas, where we have our own oyster production, it’s very difficult to find oysters now. I know the rest of the country is also feeling the effects.

e360: How long do you think before all of these species, not just oysters, are back at commercial levels?

Shirley: Well, I think first of all we have to know how long the oil spill is going to continue, and we need to see where it finally ends up. One hurricane two weeks from now could change all of our considerations of the spill. If this oil ends up back in marsh areas that are nursery areas for the life history stages of some of the species, or the coast oyster reefs, which are typically back in bays and estuaries, it could have very long-term effects. But we’re working pretty much in the face of uncertainty right now, until we cap the well and know something about the volume of oil and learn about where it’s going to end up.

“We see portions of the damage but you have to realize that many more have died.”

I think most people are not aware that the Loop Current changes in intensity. Early in the year the Loop Current had a fairly low current speed. That will be picking up as we progress into the summer. And, that will be generating more eddies that spin off, some to the west, some to the east. And some of those eddies could very well carry this oil back to other Louisiana estuaries probably to the west or to the Texas coast. As the current picks up, it could carry this oil to other areas of Florida. We really don’t know where it’s going to end up yet. So there are all kinds of dire scenarios that might occur.

e360: You mentioned that most people’s picture of the oil spill is going to be the oiled birds. But obviously the sea turtles and marine mammals are the other charismatic megafauna impacted by the oil spill. What will be the effects on them?

Shirley: It probably will be severe because these are long-lived species that have a low reproductive output. Sea turtles have to be pretty old before they even start reproducing. The Kemp’s Ridley turtle, most of the population is in the Gulf — these things are eight to 10 years of age before they begin to reproduce. So if we lose large numbers of them as a result of this spill, well, then recovery will be slow. I think most people aren’t aware of how many marine mammals there are in the Gulf.

There’s a population of about 1,600 sperm whales that occurs in the northern Gulf of Mexico. And a big part of their range is where the spill is now — there and farther to the west. And these large sperm whales are vertically migrating. They dive to about 400 meters to catch their food, prey items [like] squid and fish. These [whales] are going to be diving through the plume. Their prey vertically migrate and their prey could well be exposed to oil.

So they could either lose food sources, they could consume the food that’s tainted and therefore take it in themselves, or they could have direct exposure to it as they continually dive. Individual whales dive many times during the day to get their food. And these are also long-lived. They have a time span that is roughly similar to humans in terms of when they begin to reproduce, and how many offspring they have. And, of course, they can live much longer than humans, so recovery is slow. We don’t know if sperm whales will be affected by the spill, but judging from other spills around the world like in [the] Exxon Valdez, I strongly think that will be the case.

e360: Will we even know? I mean, with sperm whales obviously they’re pretty much living their lives out of sight. And if and when they do die, they pretty much sink to the bottom. Will we even know if they’re being impacted?

Shirley: That’s the case for most things. We won’t know what’s happened to them. Most people think that the oiled birds wash up on shore. Only a tiny fraction wash up on shore. Most of them sink out of sight. Just about everything sinks. And we know this for a fact because oiled birds and oiled mammals were tagged and released, dead ones, dead bodies, carcasses were tagged and released and only a small fraction were recovered. So we know that what we see has a strong multiplier affect. We see a portion of the damage and you have to realize that many more of them have died. So, yes, for most whales you’ll never see them if they die.

e360: How long do these impacts continue? Does it stop when the oil spill stops? Does it go on for decades?

Shirley: Well, I would preface it by saying we’re in warmer water here in the Gulf of Mexico. The ecosystem is adapted to oil. There’s a large natural seep that occurs throughout the Gulf. There’s a chronic exposure to oil. There is something like 50 million gallons a year that’s lost from natural seeps from about 1,500 sites around the Gulf naturally. So, that means that there are microbes adapted to breaking down the oil. That means that recovery here would be much faster than in areas that don’t have this chronic exposure to oil. But if we look at other areas like Prince William Sound, now 21 years after the Exxon Valdez in which there were only 11 million gallons lost. And, all of that at the surface, not coming from 5,000 feet, no deep plumes.

There are still 21,000 gallons of oil [in Prince William Sound] that you can dip your hand into that smells and it’s liquid. You can touch it. You can feel it. It’s still killing animals. It’s among the most toxic portions of the oil. Why isn’t it cleaned up? Well, because it’s buried under intertidal rocks. But sea otters that dig down and dig out clams, they’re getting tainted food and they’re getting into this oil themselves. And any other organisms that live in the shallows of tidal zone. That’s just what we know about: 21,000 gallons that’s still there. So with many more times the volume of oil here in the Gulf, there will be oil residues. There will be oil tar balls. There will be mousse. There will be oil that persists.

And, I dare say that the litigation over this will persist for decades. It’s still ongoing in Alaska, so we know that the environment is still being affected. We know that many species have not recovered there yet, some sea bird species, some fish species. They’re gone. So 21 years later, we still see effects. So I would predict that there will be long-term effects here. Most of the oil will be gone. Most of the Gulf will recover well, and in a span of just a few years, but the effects of this oil spill will persist for decades.