Pelicans, dolphins and manatees—all residents of Florida’s biologically rich Indian River Lagoon—are dying at a rate that's alarming local wildlife experts, reported Discovery News. What's more alarming is that nobody knows for sure what's killing them.
About 111 manatees, 300 pelicans and 46 dolphins have been found dead recently by locals. The Indian River Lagoon is a biodiverse estuary that is the native habitat of thousands of species of animals and plants. The experts don't know the the culprit, but they have suspects.
Environmental damage is the primary suspect, but it comes in many forms in the lagoon. An unprecedented algae super bloom colored the water a vivid green in 2011. The following year, a type of brown algae, previously seen in the waters off the Texas coast, appeared in the lagoon, turning the water brown. Algae removes oxygen from the water, harming many plants in the process. After the algae blooms cleared, more than half the sea grass meadows that line the lagoon floor were dead. Another brown tide has been seen this year.
The destruction of the sea grass meadows, a primary food source for the manatees, is another possible culprit. With the sea grass gone, the manatees have been eating other plants and algae to make up for the loss. Autopsies of the endangered animals revealed they'd eaten decently in the absence of the sea grass, but experts worry that the change in their diets indirectly led to their deaths when they became sick and drowned.
Many of the dead pelicans and dolphins found by locals were very underweight, suggesting death by starvation. Sea grass is where many Floridian fish species find shelter. Less sea grass means fewer fish survive to feed the dolphins and pelicans.
A third, and final, potential cause of the deaths is pollution. Estuaries are where rivers and oceans meet, making them the eventual dumping grounds for most of the pollution carried downstream. Fertilizer from farms upstream and contaminated water from an Army Corps of Engineers project at Lake Okeechobee are two sources of pollution in the water. High levels of mercury, a known dolphin killer, have been detected in the estuary.
Without certainty regarding the cause, stopping the deaths is difficult. The pelican deaths are slowing, reported the Tampa Bay Times and manatee deaths have slowed to about one every other week. Meanwhile, seven dolphins were found dead last week.