Something in a Florida Lagoon Is Killing Manatees, Dolphins & Pelicans -- But No One Knows What

Since this time last year 51 dolphins, 111 manatees and up to 300 pelicans have been found dead in Florida's Indian River Lagoon, but no one can figure out what the mysterious killer is, according to a report by Wired.

Whatever is causing the animals to perish works so fast, the report stated, that some of the manatees still have food in their mouths, although it wasn't their typical food. Interestingly enough, other dead wildlife animals seems to be starving.

Indian River Lagoon (Photo: US Fish and Wildlife Service)

So far, the only thing those that investigating the case can tie together is that it all seems to center around the lagoon, which Wired noted more than two decades ago was called an "estuary of national significance" by the Environmental Protection Agency.

Several agencies -- St. Johns River Water Management District, Florida Fish and Wildlife Conservation Commission, Hubbs–SeaWorld Research Institute and NOAA Southeast Fisheries Science Center -- are evaluating various facets of these unusual deaths related to the lagoon.

According to St. Johns River Water Management District, in 2011 a "superbloom" of algae occurred, killing about 60 percent of the system's seagrass, a primary source of food for the manatees and of importance for fish as well. A second brown tide boom occurred in August 2012.

Seagrass coverage can be seen declining dramatically in the area in the last few years. (Image: SJRWMD)

Wired reported that the widespread manatee death began last July, reached a height this spring and seems to have tapered from there. The pelicans began dying in February, and then the dolphin die off started.

“They’re in good body condition from what we can tell, no other diseases or signs of trauma,” Veterinarian Martine DeWit with FWC said, according to Wired of the manatees.

The food in some of the manatee's digestive tracts, DeWit said, is unusual for them though:

Instead of sea grass, pathologists are finding macroalgae, mostly Gracilaria, in the manatees’ digestive tracts. This type of seaweed is normally not toxic. But, “on microscopic examination of the tissues, we found some inflammation in the wall of their gastrointestinal system,” DeWit said, noting that the changes were only minor. “Our first thought is it has to be something associated with the algae – something in the sediment, absorbed by the algae, or a compound of the algae itself.”

Unlike the manatees, Wired noted researchers saying the dolphins and the pelicans look like they starved.

(Photo: Hubbs-SeaWorld Research Institute via Wired)

But when the investigators seek out toxins, infections or other suspects, they find nothing:

Whether the skinny dolphins are the result of depleted or shifting fish stocks, parasites, toxins, disease, or something that simply makes it hard for them to catch fish, is unknown. What scientists do know is that the number of dolphin mortalities during the first half of a normal year is around 17. With roughly 700 dolphins living in the entire lagoon, this year’s mortality rate is already approaching 10 percent of the population.

Biologist Megan Stolen with Hubbs-Sea World Research Institute told Wired "the entire lagoon is changing" and that to figure out the problem, they are "[looking] at the whole picture."

It is still an option that all these deaths are unrelated to each other but all "the result of a multi-pronged ecological catastrophe," as Wired put it:

Connecting crashing seagrasses with vegetarian manatees, fish-eating mammals and fish-eating birds is not easy. Complicating the picture is that other seagrass-eating species, such as sea turtles, appear unaffected. Other fish-eating species, such as cormorants and herons, are mostly unperturbed. The bull shark population scavenging the dolphin carcasses doesn’t appear to be in trouble. And though the dolphins and pelicans both eat fish, they’re not necessarily eating the same fish.

This year again a brown algal bloom is starting to spread. At this time, some scientists are trying to figure out what brought on the 2011 and 2012 blooms.

"The lagoon’s health had been improving, and then out of the blue came this unforeseen superbloom,” William Tredik with the Indian River Lagoon Protection Initiative said to Wired. “The algal blooms seem to have been the catalyst for a lot of other things, but we don’t have all those links figured out yet.”

Watch this Tampa Bay Times video about the mass deaths:

Read more details about the lagoon's history and current work being done to figure out what is killing some of the wildlife in Wired's full article.

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