Keeping the Dominos from Falling in the Gulf’s Food Chain
Although images of oil-drenched pelicans and blackened marshes are fading from public consciousness, researchers are grappling with the long-term impacts of the BP oil disaster on the Gulf of Mexico ecosystem. One of the greatest concerns is the potential collapse of key links in the ecosystem’s food chain, and the ecological domino effect this could set off.
Those of us responding to the Gulf disaster are haunted by just such a collapse in Prince William Sound following the Exxon Valdez spill. The collapse of the herring fishery in Prince William Sound did not become fully apparent until four years after that spill. What then are the prospects for a similar jolt to the Gulf’s food chain, and how might we prevent such an event from happening?
This was the central question at a scientific symposium that just wrapped up in Sarasota Florida, sponsored by National Wildlife Federation, Mote Marine Lab, University of South Florida, and the National Oceanic and Atmospheric Administration.
Bringing together a diverse collection of 40 scientists, resource managers, fisherman, and conservationists, the gathering considered:
- How the spill might affect the Gulf’s food web
- Which parts of the system might be at particular risk
- How we might detect such impacts
- How we can keep these ecological dominos from toppling.
Over two days, experts sifted through information about how fish and other marine creatures responded to, and may have been impacted by the more than 200 million gallons of oil that spewed in the Gulf and the 2 million gallons of chemical dispersants that were used to break the oil into smaller globules. One major conclusion is that despite the enormous economic and ecological importance of the Gulf, there is an embarrassing lack of reliable baseline information about this ecosystem.
What we do know, however, is that the timing of the spill coincided with spawning activity in many Gulf species, and the epicenter of the spill is an area where much of this reproduction typically takes place.
Atlantic blue fin tuna, for instance, among the most magnificent of large predatory fish, breed in only two places on earth—the Mediterranean Sea and the Gulf. Eggs of this already dangerously depleted species were deposited into the Gulf’s waters during the height of the spill. Tarpon, an important game fish were spawning during this period too. And although tarpon are not typically associated with the northern Gulf, according to experts from the University of Miami up to half of the larvae deposited along the west coast of Florida may have been carried northward towards the oil plumes emanating from the blown out well.
Unfortunately for blue fins, tarpon, and other fish spawning during this period, oil is particularly toxic to eggs and larvae.
Although much of our discussion centered around the fate of top predators such as tuna, sharks, and billfish, the group was perhaps even more concerned about possible impacts on smaller, more humble fishes that serve as prey.
Menhaden, for example, exist in vast quantities and serve as a critical link in the food chain for many commercially and recreationally important fish species. These small fish are also harvested in enormous quantities by people, primarily for use in animal feed.
Should the spill cause a decline or possible collapse of important prey species like menhaden or mullet, the ecological and economic consequences could be catastrophic.
Another key lesson from the Exxon Valdez spill emerged during the symposium. Although the customary narrative suggests that herring populations unexpectedly collapsed four years after the spill, it turns out that there were warning signs only recognized in hindsight. Not only were these warning signs missed, but fisheries managers actually cranked-up harvest levels in the sound based on faulty assumptions about stock health. This intensified harvest exacerbated the spill-related declines and apparently contributed to the collapse.
Detecting early warning signs of possible food chain collapses in the Gulf will be essential for managers to ensure that recovery and restoration efforts of the Gulf ecosystem can be successful.
Symposium participants concluded that carrying out a rapid risk assessment to determine which components of the food chain might be most vulnerable is a priority research need. Such an assessment would enable targeted sampling and assessments to pick-up warning signals while there is still time to act. And heeding fisheries management mistakes made in Prince Williams Sound, symposium participants also urged that catch levels be managed cautiously over the next few years.
Realizing our vision of restoring the Gulf requires that we pay attention not just to what is immediately visible, but also to what is going on beneath the still teeming surface of the Gulf’s waters. Although it is difficult to forecast exactly what effect declines in one species may have on others, should the Gulf’s ecological dominos start to topple, the impact will affect not only fish and wildlife but people as well.
This is one game we can’t afford to play.