Scalloping and Red Tide

Wilderness Medicine Elective, first trip of the year:

This past weekend was the first event of the year for the 4th year medical student wilderness medicine elective. As a part of working towards my Fellowship in the Academy of Wilderness Medicine (FAWM) certificate, I am an advisor and preceptor to the medical student elective. This elective allows students who have an interest in wilderness and austere medicine to learn by doing and teaching their peers. The introductory trip of the year was to Homosassa, FL to go scalloping while learning about seafood toxidromes, allergies, and the health effects of red tide. 

The day started by meeting our course director and captain for the day, Dr. Naughtin, at McRae’s boat ramp on the muddy Homosassa River. After some introductions and loading up the boat we made our way down river through the salt marshes and into the Gulf of Mexico. After a couple mile cruise north along the coast, the water quickly cleared up and we located a patch of seagrass at around 5ft depth. In the surrounding area hundreds of boats were out doing the same thing during the short open season for bay scallops. While putting on our snorkeling gear we had a quick debrief before entering the crystal-clear water. Along the bottom of these grass beds throughout the Gulf coast are Bay Scallops (Argopecten irradian). These bivalve mollusks are about 3 inches across, brown, with a round but ruffled shell. They have a mantle that lines the opening to the sides of the shell with many bright blue eyes. The muscle inside the scallop that holds the two sides of the shell together is the scallop meat that is bought in the market. Now with our target species identified, we are ready to scour the seabed for these tasty ruffles filter feeding atop the seagrass. 

One surprise before starting our harvesting is that one of our medical students announced that she did not know how to swim. This is a hands-on elective, so it was time to learn. She started the day hanging on the dive ladder and floating while the other students went off to start gathering scallops. The goal for the day was to hit the bag limit, 10 gallons of unshucked scallops per boat. Scalloping started slow, but our crew quickly started to get an eye for recognizing the scallops between the tall grass and our pair of 5-gallon buckets started to rapidly fill. During this time, our previously landlocked student was learning to tread water. The weather was perfect and by 2pm we were finishing up when our newly swimming student wanted to collect a scallop on her own before we left. She spotted a scallop, dove down to the bottom, collected her mollusk and swam back to the boat. This was quite an achievement for someone who just 4 hours prior had never swam before.

We cruised back to the coast and reentered the salt marshes on our way back upstream to the marina. On the way we stopped at Dr. Naughtin’s favorite local scallop shucker, pictured below, to have our shellfish cleaned and picked up in a few hours. Near the boat ramp we stopped at the monkey island, where a local had a few pet monkeys on a small outcropping in the middle of the river. We took this opportunity to discuss some of Florida’s history and the wild rhesus macaque monkey populations in the Ocala National Forest near Silver Springs. This wild troop of monkeys originates from the film set of a Tarzan movie in the 1930s and they have created a small population since that time. While waiting for the scallops to be cleaned we did our student presentations over Cajun food. We had student lectures on seafood toxidromes, seafood allergy management, and the health, economic, and environmental impacts of red tide which will be further discussed below. After dinner, we scooped up all 7lbs of our freshly cleaned scallops (after trading Mr. D his favorite beverage for expedited processing). We couldn’t have asked for better weather and marine conditions for our first excursion of the year and I look forward to learning more with this wild group of medical students over the next year!

Red Tide

Red tide is an algal bloom found around the world but becoming more common and impactful here in Florida, especially along the Gulf Coast. Red tide is made up of dinoflagellates of the species Karenia Brevis, which creates a neurotoxin called Brevotoxin. Brevotoxin is a lipid soluble polyether that works on voltage gated sodium channels. This compound has been found to do direct damage to DNA, causing issues in the immune system as well as nerve damage and inflammatory cytokine reactions. It is heat and acid stable as well as odorless, colorless, and tasteless. These properties make it dangerous as a contaminant in seafood as it is difficult to detect. Red tide can also be aerosolized into 8-9uM particles as waves crash onto the beach; this creates a pathway for brevotoxin to be an inhalational toxin and can be found in the air up to 1 mile inland. Red tide is most often seen in the news for the impressive die-offs in marine creatures as the toxins build up in the food chain to neurotoxic levels in larger species such as fish, sea turtles, dolphins, and seabirds. K. brevis is the only dinoflagellate that has been found to also produce the antidote to its own toxin. The antidote, Brevenal, has been isolated from red tide and in early sheep studies has had the ability to reverse symptoms of brevotoxin.

What causes these events?

Though it would be easy to entirely attribute red tide to human influence, red tides have been documented in Florida as a naturally occurring event for hundreds of years. However, these events have been increasing in frequency, especially in the last 10 years. Blooms appear to happen when there is an increase in temperature of the water with decreased movement, increased dissolved CO2, and increased nutrient burden. Many of these factors can be linked to human activity. Climate change secondary to greenhouse gas emissions has increased water temperatures as well as created acidification of the oceans leading to increased dissolved CO2 in the water. In addition, increased development along the coast of Florida has led to the destruction of the natural estuaries and mangroves that had previously filtered excess nutrients from rain run-off. The amount of run off is also increasing as paved surfaces do not allow water to seep through the ground and be filtered through Florida’s limestone and into the aquifer. This runoff carries nutrients from trash, fertilizer, and industry into the estuaries creating an environment ripe for algal blooms. Florida in the last 100 years has rerouted water from Lake Okeechobee that would normally flow down and across the Florida Everglades, into canals for irrigation of the sugar cane industry and to control flow to allow for cross-Florida highways. This initially seemed harmless, however now agricultural waste and fertilizer has a direct conduit to the Gulf of Mexico rather than spending weeks crossing the Everglades in a slow flow state where excess nutrients are absorbed. Here in Tampa Bay in 2021 we are experiencing one of the worst red tides in recent history following the leakage of phosphate mine waste from holding ponds at Piney Point on the SE side of the bay. Pinellas county is having a tremendous economic impact as the tourism industry is hard-struck, and workers are working around the clock to remove the hundreds of tons of dead sea life washing ashore.

Clinical manifestations in humans

Consumption of seafood contaminated by red tide is one of the most common methods of intoxication. Shellfish that feed by filter feeding plankton such as dinoflagellates can build up high levels of toxins. Symptoms of this are characterized by a syndrome called Neurotoxic Shellfish Poisoning (NSP) including circumoral paresthesias, GI distress, and ataxia in the hours following ingestion. Aerosolized red tide along the coastline is a respiratory irritant that causes an immune reaction in the lungs with cytokine release and can be dangerous for those with respiratory disease such as asthma. Recent studies have shown that in counties with red tide warnings in effect, there is a statistically significant increase in visits to the Emergency department for GI distress, asthma exacerbations, and bronchitis.

Treatment

GI symptoms are self-limiting, and care can be supportive with oral rehydration and antiemetics. Neuro symptoms typically do not last for more than a few days. Asthma exacerbations are the most life threatening manifestations of brevotoxin intoxication and is treated in the same manner as a typical asthma exacerbation with beta agonists, steroids, cromolyn, and--in extreme cases--intubation. In the future, brevenal (the naturally produced antidote), may be a treatment but at this time is not an approved modality.

Recommendations and prevention

It appears that Red Tide will be a common occurrence along the Gulf Coast of Florida in the years to come, so how can we avoid the toxidrome? It is important that during summer months that you check https://tidesandcurrents.noaa.gov/hab/gomx_condition.html?region=swfl before going to the beach or spending time near the water. If levels of red tide are elevated, you should stay away from the water, especially if you have asthma or other respiratory disease. If you must be near the water and you have asthma, it is recommended to wear a face mask to decrease inhalation of aerosolized red tide. It is also important to avoid ingestion of local seafood, especially shellfish in counties that have active red tide to avoid Neurotoxic Shellfish Poisoning.

1. Review of Florida red tide and human health effects

Lora E. Fleming a,b,*, Barbara Kirkpatrick c, Lorraine C. Backer d, Cathy J. Walsh c, Kate Nierenberg c, John Clark b, Andrew Reich e,f, Julie Hollenbeck a, Janet Benson e,f, Yung Sung Cheng e,f, Jerome Naar g, Richard Pierce c, Andrea J. Bourdelais g, William M. Abraham h,i, Gary Kirkpatrick c, Julia Zaias a, Adam Wanner h, Eliana Mendes h, Stuart Shalat j, Porter Hoagland k, Wendy Stephan l, Judy Beanm, Sharon Watkins e,f, Tainya Clarke b,i, Margaret Byrne b, Daniel G. Baden

2. Literature review of Florida red tide:

implications for human health effects

Barbara Kirkpatrick a,∗, Lora E. Fleming b, Dominick Squicciarini b, Lorrie C. Backer c, Richard Clark d, William Abrahamusb, Janet Benson e, Yung Sung Chenge, David Johnson d, Richard Pierce a, Julia Zaias b, Gregory D. Bossart b, Daniel G. Baden f

3.The human health effects of Florida Red Tide (FRT) blooms:

An expanded analysis

Porter Hoagland a,⁎, Di Jina, Andrew Beet a, Barbara Kirkpatrick b,c, AndrewReichd, Steve Ullmann e,Lora E. Fleming c,f, Gary Kirkpatrick b

Article written by Dr. Vincent Costers, PGY-2 of the USF Emergency Medicine program

Post edited by Michael Weaver