Oil's Legacy in the Open Sea

Two silver fish with big eyes facing one another
One of the many deep sea fish species collected from the Gulf of Mexico. The Argyropelecus aculeatus is one of the many hatchetfish species. (Danté Fenolio)

For those who study the deep sea, the Gulf of Mexico is a special place. A combination of geography and climate create a welcoming home for a diverse number of species unrivaled by any other place in the world. One study conducted over the last ten years revealed that there are roughly 900 species of fishes in Gulf’s deep sea, and 186 of those species had never before been seen in the region.

Travel back in time to 2010 and our understanding of the region was very different. There was a recognition that the Gulf was extremely diverse, but no one had ever attempted to catalogue every species in the deep sea. Then the Deepwater Horizon’s oil well ruptured. The heartbreaking oil spill that year was not only a tragedy for those aboard the oil rig, it was also devastating for the sea life across the entire gulf. It also revealed that there was almost no way to determine how far-reaching the oil’s impact would be due to this lack of information. Nonetheless, Dr. Tracey Sutton was undeterred.

A scientist at Nova Southeastern University, Sutton had recently participated in the Census of Marine Life, a 10-year global initiative to discover and catalogue ocean life. A phone call with National Oceanic and Atmospheric Administration contractor Melanie Schroeder prompted the two to coordinate an expedition plan in the Gulf using the same network of people and similar collection techniques as the census.  

scientists in life jackets await the retrieval of a big net off the back of ship
Scientists await a net as it is hauled back on deck. (Courtesy of DEEPEND)

From November to December 2010, NOAA’s Fisheries Research Vessel Pisces swept across the Gulf collecting samples from the deep-sea water column, including fishes, shrimps, and squids, and jellyfish. Researchers towed large nets to depths as deep as 4,900 feet (1,500 meters) beneath the sea surface. Once hauled back on deck, the nets could be emptied, their contents a treasure trove of deep sea creatures for scientists to collect and store for future identification. 

After a first successful expedition, follow-on expeditions were conducted over 10 months in 2011. It became the largest deep-sea survey of the water column conducted in oceanographic history. Then in 2015 a three-year expedition under the Gulf of Mexico Research Initiative’s DEEPEND Consortium, also led by Sutton, continued to survey the Gulf, this time with new tools like genetic testing.

The thousands of samples collected took years to sift through. From 2011 to 2015 experts specializing in fishes, cephalopods (octopuses and squids), jellyfish, and crustaceans meticulously combed through the unidentified deep-sea creatures from the 2010-2011 expeditions, often with the aid of a microscope and using crinkly, old identification books as their guide. In some cases, the distinction between one species and another was as subtle as an extra fin ray or light organ. They found dragonfishes, dreamer anglerfishes, flying fishes, vampire squids, glass (larval) eels, jellies shaped like alien saucers, bright red shrimps, and more. Every individual they identified was then tallied and records of each species’ numbers grew.

Then with the addition of genetic testing in the later expeditions, things became even more interesting. Identification with only the aid of an eye can only use physical characteristics of the body to make an identification— an essential requirement but also a limitation that can lead to mistaken identities. Ocean species often undergo dramatic transformations as they age, so many times a juvenile will look completely different than its adult self. The use of genetic testing revealed to the researchers on multiple occasions that two seemingly different animals were actually the same! It also revealed that taxonomists were historically making a distinction between two fishes that were actually one species.  

a orange colored crustacean with big antennae
A beautiful orange colored copepod from the deep sea in the Gulf of Mexico. (Danté Fenolio)

Beyond the amazing discoveries, however, a worrying trend was beginning to emerge. The motivation behind the massive survey effort was to understand how the deep-sea water column would respond to the Deepwater Horizon oil spill, and as the 2015 survey year progressed it became apparent that the numbers weren’t good. Many species populations were significantly smaller than the 2011 survey. Shrimp population numbers were down by about half, squid populations down two-thirds, and fishes were down about 75 percent. But the biggest decline came from two of the most important food sources of large marine animals. The “anchovies of the open sea,” a group called lanternfishes, decreased over 80 percent, and krill, the favorite food of large whales, decreased by over 90 percent.  Surveys in 2016, 2017, and 2018 all showed similar numbers to 2015.

Such a dramatic decrease across so many species clearly indicates a massive fallout from some environmental trigger. According to Sutton, the lack of pre-spill baseline data makes it difficult to definitively claim the declines were due to the spill, but the lack of any known major environmental driver of the same scale during the years between 2011 and 2015 indicates the spill was likely a contributor, if not the major cause of the declines. “The real problem is that we did not have any data from before the spill, and that is enormously important because we don’t have a baseline of what the Gulf should look like,” says Sutton. “We have to infer that 2011 was close to the baseline.” 

What remains clear is that the ocean remains full of secrets. While it’s understood that the Gulf is a unique habitat, it’s also understood there may be other places just as diverse as the Gulf yet to be discovered. Scientists have studied less than one percent of the world’s midwater ecosystems and, according to Sutton, the Gulf is now one of the best studied midwater habitats in the world, at least from a direct sampling and analysis perspective. It is possible that other regions of the ocean are just as diverse, we just haven’t explored them yet.

Such little understanding can mean catastrophic devastation in the wake of an industrial accident, like the chain of events following the Deepwater Horizon spill. But this type of environmental degradation is not unique to oil drilling in the Gulf. “Industry is plowing into ecosystems where we don’t have any science, in which case it is difficult or nearly impossible to determine the effect of that industry on that system,” says Sutton. “That may be the most important point of this research.”

February 2021