Florida Keys News
Wednesday, December 14, 2016
Mercury study raises questions about bay

SOUTH FLORIDA — Record levels of mercury found in bottlenose dolphins in the coastal Everglades may indicate a problem throughout the ecosystem’s sea life, according to researchers.

A study published late last month showed that dolphins in Everglades National Park and Florida Bay had higher levels of mercury in their system than ever before recorded. These levels were also higher than those found in any other bottlenose dolphin population in the world.

The high mercury levels can be associated with a combination of natural and manmade sources, according to this recent study. Mercury, which is a neurotoxin, has the potential to impact the long-term viability of these dolphins, causing problems with their immune and reproductive systems.

Some fish species in the coastal Everglades presumably also contain high mercury levels, although that angle was not explored in this study, researchers said.

“Absolutely, it’s very likely,” Florida International University ecologist Jeremy Kiszka told the Free Press last week when asked if mercury might also affect other marine animals in the same area. 

Kiszka explained that “bioaccumulation” happens as mercury moves up the food chain from smaller fish to large predators, which means that bottlenose dolphins most likely have been eating fish that contain higher than normal levels of mercury, as well. 

Kiszka was part of the research team that conducted the bottlenose dolphin study. Aside from FIU, it included scientists from the University of Liege in Belgium, the University of Groningen in Netherlands and the Tropical Dolphin Research Foundation in Virginia.

This could be a cause for concern to anglers eating their catch, as mercury can have toxic effects on the nervous, digestive and immune systems of humans, and on lungs, kidneys, skin and eyes, according to the World Health Organization.

Everglades National Park has a warning in place for anglers harvesting certain fish in the southern Everglades and northern Florida Bay. They warn that bass have been found with high mercury levels and should not be consumed more than once a week. Spotted seatrout, gafftopsail catfish, bluefish, crevalle jack and ladyfish are also listed.

“Authorities are well aware [of the high mercury levels in fish],” Kiszka said while referencing past work by other ecologists. “But we need a lot more information.”

Kiszka and the rest of the research team found that mangroves were the probable main culprit for the high mercury levels in bottlenose dolphins. When mangrove leaves, which contain mercury, drop into the brackish Everglades water they interact with bacteria, which converts the chemical into highly toxic methylmercury.

Aside from mangroves, the study found that nearby farming and industrial smokestacks likely also play a role in the high mercury levels.

South Florida is home to huge agricultural tracts situated in drained former swampland. Agriculture runoff seeps into the water table and eventually makes its way into the bay.

Florida Power & Light’s Turkey Point nuclear plant, located in Homestead on Biscayne Bay, includes two 400-megawatt oil/natural gas-fired generation units, which could release mercury when oil is being used. 

“We have to reduce the impacts from these sources [to help fix the issue],” Kiszka said.

The team that conducted this most recent study hopes to continue and expand their work. They would like to focus on alligators, fish and sharks, among others, and see if their mercury levels are similar to dolphins found in the coastal Everglades and the Florida Keys.

“If this is found to be true, how will it affect the long term viability of these animals?” Kiszka proffered.

bbowden@keysnews.com

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