Recently published research in the Journal of Comparative Pathology associates the dramatic bird die-off of 2018 to the unusual Bisgaard Taxon 40 bacteria. According to Audubon Florida, researchers believe that brevetoxin, a neurotoxin produced by red tide, may weaken seabirds and make them susceptible to deadly bacterial infections. Another possibility is that the mortality is caused by some combination of the two toxins, says Dr. Marianne Korosy, Director of Bird Conservation at Audubon Florida.
Red tide is created by blooms of Karenia brevis, a marine dinoflagellate that occurs naturally in coastal waters, but which is fed into toxic blooms by nutrient runoff, among other factors.
"In 2018, there were fairly high levels of red tide," says Korosy. "The sort of general thought process was that the brevetoxin that's produced by red tide probably weakened the birds and made their immune systems weak so that they were exposed to infection by other bacteria that were in the environment. And that's where this Bissard 40 possibly is an opportunistic bacteria and that invaded their systems and was present in their carcasses. So it's a combination of factors, red tide, and then that allowing an opportunity for other more virulent pathogens to invade their bodies and cause mortality."
Korosy says it was difficult to track bird deaths in 2018 — just as they are difficult to track today.
"There's nobody putting together, tallying the total mortality of these events for birds," says Korosy. "And the other thing is that the county has raking machines. They were removing bird carcasses from the beaches shortly after dawn. So those numbers of birds are lost to us, we don't have a tally of those either."
The death of dozens of Royal Terns found dead in Southwest Florida this year has already been linked to red tide.
"I'm not sure if they've done the analyses. But that's certainly what suspect because the Royal turns feed farther offshore. So they're bigger, they're bigger terns, they feed offshore, and that's where the red tide is right now," she notes.
Joanna Fitzgerald is director of the von Arx Wildlife Hospital at the Southwest Florida Conservancy. They’ve taken in over 100 sick royal terns in the month of February alone--more than all of 2020, combined. So far, they’ve released about 50.
"What we do at our facility with every patient is we actually have an integrated approach to wildlife medicine," Fitzgerald says of how they care for the birds. "So we do Eastern and Western medicine. All of them were getting fluids, with the Chinese herbs, and a supplement that supports the liver. Since you know if there are any toxins, we want to help the liver be able to detoxify the body."
Korosy says releases from Lake O could be feeding the toxic red tide blooms: "It's my understanding is that the experts believe that the heavy nutrient load in the water released down the Caloosahatchee River and into Gulf Mexico is exacerbating the red tide. In other words, causing larger blooms. That are distributed over a wider area and have a much longer duration."
Korosy advises folks to be mindful of their own actions to keep red tide-feeding nutrients out of the water, because when nutrients from agriculture, septic tanks, and elsewhere flow through Southwest Florida’s canals and rivers, they become food for the red tide. "People can do things locally, minimize the amount of fertilizer they apply to their lawns during summer months. There are some local governments that have implemented ordinances that restrict fertilizer applications in the summer. I don't know that that's in case in Collier County, but it is something that can be looked at."
Fitzgerald calls for more baseline studies of the birds, identifying how much brevetoxin a healthy bird can maintain in their system.
"I feel mainly that we just need to continue to raise the level of awareness of what is going on and continue to fund the research. there's just so much more research needs to be done," ssays Fitzgerald.
Fitzgerald also sees how the birds can act as alarm clocks for humans.
"So many of these animals are, I don't know if you necessarily want to say canary in the coal mine. But similar to that a lot of what we see going wrong with the environment we see at these wildlife hospitals, not just ours, but throughout the country," she says. "And we need to pay attention to those because it's, in my opinion, signaling the possibility of further degradation in the environment. I not only care about the animals, most people care, because it also affects humans, you know what I mean? There's a relationship, we're visiting the same beaches that these animals are visiting."
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