An Air Force C-130 sprays disperstants in the Gulf of Mexico. Photo courtesy Deepwater Horizon ResponseOne hundred days after BP’s blown out well began erupting oil into the Gulf of Mexico, a few things are clear.For one, damage to the Gulf Coast from BP’s oil will last for years, even decades. And that damage is largely happening out of view as a toxic mix of oil and chemical dispersant attacks the Gulf’s sensitive food web in unknown ways.”We think we’ve got it stopped, and I’m optimistic about that, but we’ve got this enormous puddle of oil out there,” said George Crozier, executive director of the University of South Alabama’s Dauphin Island Sea Lab. “The chairman of my research department has coined this phrase, which isn’t very helpful, but it’s catchy: ‘We don’t even know what we don’t know’.”While images of oiled sea turtles and pelicans are heartbreaking, scientists are concerned the more nefarious impacts to the Gulf are happening on the microscopic level far underwater, a consequence of the BP pumping three quarters of a million gallons of dispersant a mile below the surface in what amounts to an unprecedented science experiment in the nation’s fish basket.”The question is what’s happening at the bottom of the food chain,” he said. “Clearly the eggs and larvae of the commercial and recreation species, and the phytoplankton that they depend on, are all the most vulnerable stages of the food chain.”Crozier’s lab has a five-year record of sea life in the Gulf, taken from a testing station near Dauphin Island. He’s waiting for the results of their most recent surveys of plankton and other species, and he’s not expecting good news.”A lot of our eggs and larvae are in the top 100 meters, so as this cloud of toxins spreads upward, we’re making an assumption that its killing all of them,” he said. “I absolutely hate the use of dispersants at depth. I think that was the most huge of mistake in the process of containment.”Last week, a group of prominent marine researchers released a statement calling for the end of the use of dispersants in the Gulf, saying, “Corexit dispersants, in combination with crude oil, pose grave health risks to marine life and human health.”Corexit combined with oil, scientists say, is more toxic to fish and other marine life than either oil or dispersant alone.For example, coral larvae have a fertilization rate of zero when they come into contact with dispersant and dispersed oil compared to a 98 percent fertilization rate in the presence of just oil, the statement said.”My hunch is that oil-dispersant compounds are smaller and therefore more easily taken up by the larvae,” said Tulane’s Erin Grey, who was not among the researchers who signed the statement.But there is a lot that is still unknown about how dispersant and oil mixed will impact wildlife in the Gulf. For instance, does oil ingested or absorbed by smaller creatures concentrate in the creatures that eat them, moving up the food chain in a process called bioaccumulation?”Since the beginning of this disaster, we’ve had grave concerns and too many unanswered questions about the unprecedented amount of dispersants being applied. It’s become clear they’re doing more harm than good,” said Aaron Viles, campaign director for the Gulf Restoration Network.The third episode of the Gulf Restoration Network’s Gulf Tides series focused on dispersants in the Gulf:Researchers at Tulane have found orange droplets, which they suspect to be oil, dispersant or a mix of both, in post-larval blue crab in Gulf waters from Texas all the way to Florida.The Deepwater Horizon rig exploded, killing eleven people, just as the crab spawning season was getting underway and female crabs move out of coastal estuaries to release millions of fertilized eggs into the Gulf of Mexico.”If you look at the maps of the oil spill, they are out their floating around in that. So they are presumably being exposed to oil everywhere they are,” said Caz Taylor, an assistant professor in Tulane’s Ecology and Environmental Biology Department.As those eggs morph into larvae and then into tiny megalopae, they drift back into the coast. That’s where Taylor and her fellow researchers have been intercepting them.Looking at the megalopae under microscopes reveals that one out of every five has an orange droplet, Taylor said. The highest rate was near Pensacola, where about half of the megalopae had the droplets.”I believe that the oil is going to cause a lot of mortality in the larvae that are still out there, so we’re going to see a big drop in stocks in the next few years,” Taylor said.But the effects of the tainted oil don’t stop with the juvenile crabs.Scientists expect these undersea, toxic plumes to result in at least a near term – in the next few years – dip in the number of other popular commercial fish species like bluefin tuna.”Peak spawning of Atlantic bluefin tuna occurs from April-May and thus the timing of the spill is not the best for bluefin,” Jay Rooker, Professor & McDaniel Chair of Marine Fisheries at Texas A&M University, told the Gulf Restoration Network in an e-mail.That compounds an existing problem: populations of tuna are still much reduced despite over two decades of fishing restrictions, according to Rooker.And those tainted blue crab megalopae are food for numerous species, from adult crabs to bait fish like menhaden.”The worry is that whatever this is inside them will accumulate or magnify up the food chain. But we don’t know whether that will happen or not,” Taylor said.The unprecedented use of dispersants has been advertised as a trade-off: by breaking the oil into droplets and keeping it from reaching the surface, dispersants can limit the impacts to beaches and coastal wetlands and speed the biodegradation of the oil.But that’s just traded a visible impact for a largely unseen one, and it hasn’t helped that the oil skimming effort has been inadequate to collect or contain what oil was on the surface.”They’ve kept them out of sight and out of mind, and that’s a good thing for BP,” Crozier said. “I just don’t think it would have been as bad if they’ve had let it come to the surface so we would see it and skim it and burn it, or at least keep track of it. It’s just complicated things so where the whole package might have been a five to six year problem has turned into a decadal problem.”Even given all that, Crozier is optimistic the Gulf is resilient enough to recover in the long term, even from a disaster of this magnitude.What might not survive, however, are the businesses that depend on a healthy gulf – the fishers, restaurants and charter boat captains – that can’t wait for the Gulf to heal itself.Matthew Preusch is a volunteer with the Gulf Restoration Network.