In 2023, a major El Niño on top of many decades of increasing global temperatures due to climate change brought the worst-ever marine heatwave to the Florida Keys. The water temperature exceeded 30 Celsius (the bleaching threshold where corals get stressed and start losing their symbiotic algae), earlier than ever, and reached temperatures higher than ever seen before in the Florida Keys. The killer temperatures lasted until October, which created an enormous "cumulative stress" on the corals (See picture). Even hardy, resilient species like sea fans, fire corals, and finger corals bleached and died, their flesh sloughing off their skeletons like meat from bones in an overcooked stew.
When I took my FGCU Marine Ecology class snorkeling there in October we saw a surreal scene of devastation. Dead but still-standing sea fans were covered in fuzzy algal turf. The few corals still alive were bleached to snow white, fluorescent pink, or yellow (see album).
The one part of the reef ecosystem that still seemed to be OK then was the fish. Even though the corals were dead and dying, the reef fish were still abundant in the no-fishing zones where we snorkeled. Sadly, in November 2023, not long after my class snorkeling trip, the fish in the keys also began to suffer. It was a mysterious ailment dubbed "spinning disease," that caused them to swim in an erratic, disoriented manner. It started happening to all sorts of fish species, from tiny pinfish to huge sharks and rays. The afflicted fish often die. This is particularly disturbing because it's affecting critically endangered species like the smalltooth sawfish. There are thought to be only a few hundred sawfish left in Florida, and more than 20 have already been found dead from this in the keys.
Naturally, people want to know what's causing the spinning disease, so just about every marine biologist and environmental management organization in Florida is trying to figure it out. People have tested for red tide (turns out it's not that), common pollutants like nutrients, pesticides, herbicides, and heavy metals (none of those seem to be much higher than normal), and diseases and parasites (none that we can find so far). Some people have speculated that recent water releases from Lake Okeechobee to the Caloosahatchee and St. Lucie estuaries caused it, but it couldn't have been that because: a) the spinning disease started months before the water releases and b) the water release areas are hundreds of kilometers north of the keys. That's not to say that pollution hasn't caused or contributed to this, though. The Florida Keys have been having problems for years with chronic and recurring sewage leaks and spills, including a broken pipe detected in October 2023 that leaked 106,533 gallons of sewage near the epicenter of the spinning disease on Big Pine Key. The info below on the spill is from the Florida Department of Environmental Protection's Public Notice of Pollution website, which also has information on thousands of other spills throughout the state.
Incident Location: (link)
Incident Description: During a verification inspection of the low pressure system force mains, the mechanics determined that the low pressure grinder system (LPS) force main was not passing a pressure test. Upon further investigation, staff discovered that the 1 1/4" HDPE force main had been augured through by a contractor while installing a fence post on private property. The force main was repaired, a portion of the fill was excavated and replaced and the area was cleaned up, washed down and lime was applied. Repair is complete and yard is restored.
Wastewater Type: Untreated
Cause: Contractor
Spill Volume: 106,533
Volume Recovered: 25
Waterbodies Impacted: N
Clean-up Status: Complete
Clean-up Actions: Vacuumed/pump truck, Applied lime, Washed down area, Raked and disposed of debris
Agencies Notified: Gary Hardie FDEP, State Watch Office
The continuing influence of sewage leaks and spills on marine water quality in the Florida Keys is indicated by elevated levels of an artificial sweetener called sucralose detected in recent FDEP monitoring. There's no natural source of sucralose, so if you're finding it in the water that means that there are wastewater inputs nearby, or that wastewater was spilled in the past and hasn't fully dispersed.
The other link to man-made pollution is the freakishly hot weather, which is signficantly hotter than normal due to the global problem of carbon dioxide pollution increasing the atmospheric greenhouse effect. In addition to contributing to hotter temperatures via the greenhouse effect, the elevated level of carbon dioxide in the atmosphere lead to higher levels of carbonic acid in seawater, lowering its pH. This phenomenon is called "ocean acidification" and has already made the ocean 25% more acidic, on average, than it was 150 years ago. Experiments show that hotter temperatures, more acidic waters, and higher nutrient pollution levels all stress corals individually, and that their combined effects are even worse, hence the post-apocalyptic state that Florida reefs are in now.
Anyway, back to the spinning disease. My FGCU colleague Dr. Michael Parsons, who specializes in studying harmful blooms of microscopic marine algae, has strong suspicions that it's linked to a type of single-celled dinoflagellate algae called Gambierdiscus.
Unlike the Karenia brevis dinoflagellate algae that causes red tide, Gambierdiscus is benthic. Benthic means mostly found on the bottom, growing as an "epiphyte" on seagrass, seaweed, rock, etc. It attaches kind of loosely, though, so if there's a lot on the bottom you'll also find some in water samples. During this spinning disease event, Dr. Parsons has been finding Gambierdiscus at levels 10 to 50 times higher than ever seen before in the keys. Gambierdiscus makes multiple types of neurotoxic chemicals that can harm other marine life, as well as people who eat contaminated seafood. The best-known toxin that Gambierdiscus makes is "ciguatoxin," which accumulates in the marine food chain from small algae-eaters to big predator fish, and can then be passed on to people who eat the fish and develop a serious illness called "ciguatera." The weird thing in this case, though, is that Dr. Parsons and the other harmful algae researchers working in the keys have not been finding much ciguatoxin in these Gambierdiscus or in the affected fish, and there haven't been any reports of people in the keys getting ciguatera from eating the fish. (I still wouldn't recommend eating any seafood from the keys now, though.) With ciguatoxin, you'd also expect it to affect just the species in the food chain that were getting exposed via their diet, and the spinning disease seems to be affecting all species of fish- bottom feeders, plant eaters, predators, planktivores, etc. That is leading Parsons and other to suspect that the spinning disease is caused by one of the OTHER toxins that Gambierdiscus makes- maitotoxin.
Maitotoxin is the one of the deadliest biologically-produced toxins known to science. Unlike ciguatoxin, maitotoxin is water-soluble, so fish can be directly exposed through the water rather than through their diet. The maitotoxin hypothesis is consistent with observations by fishermen in the keys that spinning fish often recover back to normal after 17-25 minutes in a tank with water from an unaffected area. Parsons suggests that rescue tanks could be set up to put some of the most endangered species of fish in to recover, but you'd need a pretty big tank for a 5 meter (16 foot) long smalltooth sawfish. Because the maitoxin molecule is huge and complicated, you need sophisticated equipment to detect and measure it, and not many labs in Florida are capable of doing that. Dr. Allison Robertson at the Dauphin Island Sea Lab in Alabama is able to do it, though, and she HAS detected maitotoxin in the recent samples Parsons has sent her from the keys. So far we just know that maitotoxin is present in the affected area- not how much there is. Parsons and Robertson are working on more quantitiative analysis now, comparing the concentration of maitotoxin in the spinning-disease area with its concentration in unaffected control areas. If the incidience of spinning disease closely corresponds with the concentration of maitotoxinin the water, and the concentration of maitotoxin in the water closely corresponds with the abundance of Gambierdiscus on the seafloor, that would be strong circumstantial evidence for the maitotoxin theory, which could be confirmed by experimental tests.
If it is maitotoxin produced by Gambierdiscus that is causing this, that will lead to more questions, such as "What's going on in the environment that's causing there to be so much Gambierdiscus and maitotoxin?" and "What can we do to stop it?" As for what's causing the Gambierdiscus increase, we already have a rough hypothesis based on what has been seen with Gambierdiscus in other parts of the world: It increases after man-made and natural disasters that damage reefs. Something about a degraded reef ecosystem seems to create ideal conditions for toxic Gambierdiscus. Maybe it's disruption of the normal microbial and grazer community that keeps Gambierdiscus in balance. Maybe it's increased availability of nutrients, seaweeds, and dead coral skeletons to grow on. Maybe it's all of the above. While we're waiting for more complete answers and the next phases of research, I have some suggestions:
1. Don't eat seafood from the Florida Keys until this is over, unless you're trying to do neurotoxicity experiments on yourself.
2. Get SERIOUS about keeping nutrient pollution out of South Florida waters-
a. Support wastewater treatment system upgrades, maintenance, and monitoring.
b. Tell the FDEP to bring the hammer down on those responsible for sewage leaks and spills.
c. Fertilizer also contributes to nutrient pollution, so stricter fertilizer regulations for the keys could help. If I was king of the keys I'd ban fertilizer year-round with no exceptions for golf courses.
d. Lobby the state and the feds to complete the everglades restoration projects they've been working on for decades that are supposed to improve the quality of the water passing through the Everglades to the keys.
3. Stop denying that climate change and ocean acidification are happening and start doing your part to reduce carbon dioxide pollution.
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