Oil spills perturb entire ocean food webs – Gulf of Mexico ecosystem may never recover

Desdemona Despair

Heidelberg, New York, 10 July 2017 (Springer Nature) – Oil spills not only have a direct impact on species and habitats, but may also set off a cascade of perturbations that affect the entire food web. These are the findings of new research published in an article in the special issue on Ocean Spills and Accidents in Springer’s journal Archives of Environmental Contamination and Toxicology (AECT).

Oil spills are well known to cause significant harm to some species and to local environments, but the sudden and unexpected occurrence of each accident, the unique way each ecosystem is affected, and an often poorly-prepared assessment capacity have constrained the understanding of the full consequences of such events.

In this study, researcher Jeffrey Short and his co-authors have discovered a major new ecological damage pathway following oil spills. The researchers found that the mass mortalities of seabirds and marine mammals associated with the 2010 Deepwater Horizon blowout in the Gulf of Mexico reduced predation on forage fish populations considerably.

The loss of top predators has resulted in large increases in the abundance of fish, such as menhaden, in the Gulf of Mexico in the years after the accident. These findings provide significant new insights into the nature of oil spills, and underscore the need to study not just those species obviously affected, but also the entire food web, during oil spill assessments.

“Our discovery suggests that the structure of food webs change after an oil spill, which may be much more damaging to fish and other aquatic fauna than the direct impacts of the spilled oil itself,” explained Short.

“While the direct effects of oil spills on ecosystems have been well documented, this new study following the Deepwater Horizon blowout in 2011 provides the first indication that oil spills can alter the nature of entire aquatic food webs,” said Peter S. Ross, editor-in-chief of AECT.

Contact

Stella Mueller | Springer Nature | Communications
tel +49 6221 487 8414 | [email protected]
For more information about the study: Jeffrey Short [email protected]
Peter S. Ross (Editor-in-Chief of AECT) [email protected]

Oil spill impacts may perturb entire food webs

By Alexander C. Kaufman
18 July 2017

(Huffington Post) – Jeffrey Short has been asking the same question for nearly three decades: What happened to the herring?

After the 1989 Exxon-Valdez oil spill off Alaska’s southern coast, the fish ― a vital link in the food chain and resource for the local economy ― began disappearing. Yet Short, a scientist stationed in Alaska for the National Oceanic and Atmospheric Administration, struggled to connect the dots between the spill and the herring population crash.

Now his latest study ― one of two published this month examining how the 2010 Deepwater Horizon disaster affects animal and plant life in Gulf of Mexico ― offers some clues. The spill, caused by a BP oil well that blew out and gushed 200 million gallons of crude for 87 days straight, killed thousands of mammals and sea turtles and more than 1 million birds.

Without those predators, schools of fish rapidly multiplied, straining an ecosystem not designed to handle populations of that size. The number of menhaden, a species of fish in the herring family known colloquially as bunker or pogies, roughly doubled in a year.

“It’s an astonishingly huge effect,” Short, who now runs his own environmental consultancy in Juneau, Alaska, told HuffPost. “The result of doubling that population put enormous stress on the rest of the food web because Gulf menhaden were already at carrying capacity of that habitat.”

As a result, the fish put pressure on their planktonic prey and began to starve, in turn becoming less nutritious to the remaining seabirds and other fish that rely on them as food.

“The seabirds, were they alive, would eat enormous numbers of juvenile menhaden,” Short said. “Instead they were dead, and didn’t eat them, accounting for a classic example of a population explosion by release from predation.” […]

“We suspect this may be the answer to the herring question,” Short said. “Diseases caused the population to crash and they never recovered. We think this is a pretty big deal.”

The ecosystem in the Gulf of Mexico also may never recover, Short said.

“So far, it looks like the Gulf menhaden population is permanently in what I’d call a hyper-abundant state, which means they’re continuing to be chronically under-nourished and consume a lot of the productivity in the ecosystem,” he said. “It’s not impossible, but it may be an irreversible effect.”

He added: “We think it’s by far the biggest ecological effect, on the surface at least, of the Deepwater Horizon … This is something that happens across many thousands of square kilometers, from Alabama almost to Texas.” [more]

New Studies Show How The 2010 Gulf Oil Spill Still Starves Fish At Sea And Plants On Shore

ABSTRACT: Gulf menhaden (Brevoortia patronus) exhibited unprecedented juvenile recruitment in 2010 during the year of the Deepwater Horizon well blowout, exceeding the prior 39-year mean by more than four standard deviations near the Mississippi River. Abundance of that cohort remained exceptionally high for two subsequent years as recruits moved into older age classes. Such changes in this dominant forage fish population can be most parsimoniously explained as consequences of release from predation. Contact with crude oil induced high mortality of piscivorous seabirds, bottlenose dolphin (Tursiops truncatus), waders, and other fish-eating marsh birds, all of which are substantial consumers of Gulf menhaden. Diversions of fresh water from the Mississippi River to protect coastal marshes from oiling depressed salinities, impairing access to juvenile Gulf menhaden by aquatic predators that avoid low-salinity estuarine waters. These releases from predation led to an increase of Gulf menhaden biomass in 2011 to 2.4 million t, or more than twice the average biomass of 1.1 million t for the decade prior to 2010. Biomass increases of this magnitude in a major forage fish species suggest additional trophically linked effects at the population-, trophic-level and ecosystem scales, reflecting an heretofore little appreciated indirect effect that may be associated with major oil spills in highly productive marine waters.

Anomalously High Recruitment of the 2010 Gulf Menhaden (Brevoortia patronus) Year Class: Evidence of Indirect Effects from the Deepwater Horizon Blowout in the Gulf of Mexico