On a shelf at my home, I have a small jar that contains a smear of crude oil. I dug it up on the shore of a small island in Alaska’s Prince William Sound in May of 2009, on a reporting trip for a story about the legacy of the Exxon Valdez oil spill. That crude oil is more than 25 years old now, and its existence is a reminder of just how long lived the effects of a major oil accident can be. Years after the spill has been stopped, after the press has gone home, the crude oil released into a river or a sea will affect the biology of almost anything it touches—just as it continues to weigh on the people who live and work in the area fouled by crude.

That’s worth remembering as we observe the 25th anniversary of the Exxon Valdez spill today. On Mar. 25, 1989, a tanker captained by Joseph Hazelwood ran aground on Alaska’s Bligh Reef, spilling nearly 11 million gallons (42 million liters) of crude oil into Alaska’s near-pristine Prince William Sound. The oil spread out to more than 1,300 miles (2,100 km) of coastline, choking bird and sea life, and permanently damaging the region’s ecology. Even now, you can still find some of that oil on remote beaches in the Sound, preserved by the cold. As of 2010, just 12 of the 32 monitored wildlife populations, habitats and resource services affected by the spill were considered fully recovered or very likely recovered. The once-prosperous Pacific herring fishery still remains closed after the population of the fish crashed in the years following the spill. While much of the Sound has rebounded, it will never be the same—even a quarter century later.

The Exxon Valdez disaster was the biggest oil spill in U.S. history—until April 2010, when BP’s Deepwater Horizon drilling rig was destroyed in a well blowout, leading to an oil gusher that lasted 87 days and resulted in more than 200 million gallons (757 million liters) of crude flowing into the Gulf of Mexico. While much of the oil was either cleaned up in a response operation that cost billions of dollars or was broken down by bacteria in the warm Gulf waters, the ecological damage from the spill was major, and almost four yeas later, scientists are only beginning to gauge the cost to marine life.

Here’s one example: in a new study published in the Proceedings of the National Academy of Sciences, researchers from the National Oceanic and Atmospheric Administration (NOAA) and several universities assessed the impact of Deepwater Horizon oil on developing embryos of bluefin tuna, yellowfin tuna and amberjack, all commercially important fish species that spawn near the site of the accident. The research team exposed embryos taken from breeding facilities to polycyclic aromatic hydrocarbons (PAHs), a toxic agent released by crude oil. In each tested species, PAH exposure—at levels the researchers said was realistic for the Gulf spill—was linked to abnormalities in heart function and defects in heart development. As the paper concluded:

Losses of early life stages were therefore likely for Gulf populations of tunas, amberjack, swordfish, billfish, and other large predators that spawned in oiled surface habitats.

The PNAS study isn’t the first to blame the BP oil spill for lingering problems with Gulf marine life; a study published earlier this month linked the spill to dwindling numbers of bottlenose dolphins Louisiana’s Barataria Ba. Nor will it be the last. But that hasn’t slowed the rush to keep drilling going in the Gulf of Mexico, a rush that BP has now been allowed to rejoin after initially being barred from participation in lease sales in the region. The British company won 24 out of 31 bids entered in an Interior Department offshore drilling lease sale held last week, paying more than $41 million for the right to explore oil and gas in the region. Altogether 1.7 million acres (.69 million hectares) off the coast of Louisiana, Mississippi and Alabama were opened up for new drilling. Despite evidence of the risks, nothing seems likely to stop operations in the Gulf.

As long as there is offshore drilling and marine transport of oil, the risks of accidents will exist. Just two days before the 25th anniversary of the Exxon Valdez spill, at least 168,000 gallons (636,000 liters) of oil spilled from a barge in Galveston Bay in Texas. The spill is blocking the bustling Houston Ship Channel, one of the busiest seaways in the U.S., and threatens an environmentally sensitive bird sanctuary nearby. Given the small size of the spill, it won’t have the kind of major aftereffects seen in the Valdez and the BP dissters. But it’s one more reminder that as long as our economy remains so dependent on oil, there will always be the risk of another catastrophe that could linger on and on.

[Update: BP sent along a statement in response to the PNAS study—I’m including it below:

The paper provides no evidence to suggest a population-level impact on tuna, amberjack or other pelagic fish species in the Gulf of Mexico. The oil concentrations used in these lab experiments were rarely seen in the Gulf during or after the Deepwater Horizon accident. In addition, the authors themselves note that it is nearly impossible to determine the early life impact to these species. To overcome this challenge, it would take more information than what’s presented in this paper.

It’s worth noting that the researchers mention in the paper how difficult it is to sample live but fragile yolksac larvae of big pelagic species like the bluefin tuna in the wild, which is the embryos used in the study were collected from breeding stations on land, not the Gulf itself.]

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