Measuring the Environmental Impact of the Gulf Oil Spill

 

November 2010

 

The oil spill in the Gulf of Mexico was the largest accidental release of oil in history with over 4.9 million barrels (=206 million gallons) released; however, accessing the actual environmental impacts will be very difficult. The largest environmental impact is likely to take place in the part of the world that is most unfamiliar to us and the least studied - the deep sea.

         The well associated with the Deepwater Horizon rig was nearly a mile (1.6 km) below the surface; everything below 1 km from the ocean’s surface is considered the deep sea. This environment is the largest most stable habitat on Earth; it is perpetually in darkness (no sunlight penetrates this region) and is always cold (only 1 to 2°C above freezing). The animals that live there are subject to enormous pressure (hundreds of pounds per inch) and also have to deal with vast amounts of empty space (prey items and mates are difficult to find). These difficult conditions have led to the evolution of some strange-looking organisms. Adaptations for this environment include flashing lures, fleshy black bodies, giant teeth and eyes, and generally odd body shapes and behaviors (see photos on page 4). The majority of animals that live here use bioluminescence (light generated from bacterial symbionts or by the animal itself) to communicate and to attract prey. The common perception that the deep sea is depauperate in terms of species richness and diversity is wrong. The most abundant vertebrate species in the world live in this habitat (lanternfishes, Neoscopelus spp.; bristlemouths, Cyclothone spp.) as do some of the rarest and most bizarre forms known. There are more than 2,000 fish species known from the deep sea (more than all the birds, amphibians and reptiles of North America). One hypothesis of the origin of deep-sea fishes is that the deep ocean is a refuge for the living remnants of primitive lineages that were outcompeted by more advanced forms in ecologically rich habitats like coral reefs. Giving credence to this idea is the fact that advanced spiny-rayed fishes (Acanthomorphs), which make up the majority of extant fishes, are generally absent from the deep sea despite their complete dominance of every other aquatic habitat. Therefore, despite the perception of the deep sea being an ecological desert, it is in fact very rich.

         When the decision was made to allow the release of chemical dispersants below the surface at the source of the oil spill a trade off was being made between two environmental disasters. Allowing all of the oil to come directly to the surface (by not using dispersants) would have meant potentially having the Louisiana shoreline and its fragile marsh and estuarine habitats threatened. Allowing dispersants to be sprayed a mile below the surface meant endangering the deep-sea habitat where the damage would go largely unseen. In the end, we have oil in both habitats. Dispersants had never before been used below the surface and little data exists about how these chemicals breakdown and how they interact with the deep-sea environment. The dispersants that were used, Corexit 9500 and 9527, degrade quickly in warm waters when exposed to sunlight: it is not known how these chemicals break down in the dark and cold deep ocean. There is also no way of dealing with subsurface oil: oil at the surface can be skimmed and burned, treated and broken down. Even if we could treat subsurface oil, it would be difficult to find. We have inadequate tools for discovering oil floating in the water column as either tiny suspended microdroplets or as dense deep-sea plumes. We frankly do not know how long oil combined with dispersants will remain in the environment. We do know that the combination of high atmospheric pressure and darkness certainly allows the oil to be maintained in the deep sea much longer than it can in warm surface waters.

         To study the impact of the oil spill on the Gulf environment, my lab and collaborators at Ohio State University (PI - Daniel Janies) have created a program called SpeciesMap. This program maps the known pre-spill distributions of fishes in the northern Gulf of Mexico (where there are about 600 species known) based on historical records from museum collections (including LSU’s) and the collections of state and federal agencies. These georeferenced data can be incorporated into a NOAA map of the oil spill, and it can be used to compare post-spill and pre-spill distributions (see map above). SpeciesMap provides the user a way to visualize where fishes were collected before the spill and compare collections post-spill to see if any species have been extirpated from certain locations or if they are less abundant than in the past. We can incorporate data about life history to see if spawning grounds have been affected or if migratory routes have changed. SpeciesMap is freely available on-line (http://speciesmap.org) and we have reached our goal of mapping all northern Gulf fishes (see map above for an example). For many species of northern Gulf fish we know little else besides their distributions. This program will help determine if the oil spill permanently changed this environment or if it will quickly rebound.

         My post-doctoral fellow, Matthew Davis, and I have also submitted an NSF proposal to study the deep-sea environment and how it was established. We are targeting three taxonomic groups: batfishes (Ogcocephalidae), cods (Gadiformes), and lizardfishes (Aulopiformes). These groups are notable because they are some of the few lineages that have representatives in the deep sea and in shallow waters. Because of that diversity we can study how the deep sea was invaded and what adaptations need to take place in order to accommodate that transition. The batfishes are a family of anglerfishes that have an unusual flattened body shape that make them look more like moldy crackers with eyes than they do fish (see image on top). This is a group I’ve been interested in ever since moving to Louisiana. Two colleagues, Hsuan-ching “Hans” Ho (Academica Sinica, Taiwan) and John Sparks (American Museum of Natural History) and I recently described two new species of pancake batfish from the Gulf of Mexico. These are the two newest species described from the region and one of them is only found off the coast of Louisiana and northern Texas. Amazingly, of the more than 1500 or so fish species found in the Gulf only 73 are endemics (found no where else). This new endemic species, that we call the Louisiana Pancake Batfish (Halieutichthys intermedius), has received a lot of press coverage because of its incredible beauty and because it was discovered in the region of the oil spill.

         The deep sea is home to an amazing diversity of rare and odd forms with many yet to be discovered and many other secrets to be revealed. As we learn more about the effects of the largest environmental disaster in U.S. history we should keep in mind how difficult measuring that impact will really be. The only thing we know with certainty is the fact that we still know very little.