A Different Kind of Red Menace

by JR

Manatee Killing Red Tide

The idea of large areas of the ocean running red sounds like something out of a horror movie, as though Jaws were a cautionary documentary about bloodthirsty sharks instead of the original summer blockbuster. Instead, red waters are associated with an increasingly common phenomenon called a red tide or, more accurately, a harmful algal bloom (HAB). Harmful algal blooms in the Gulf of Mexico off the west coast of Florida are caused by the photosynthetic unicellular organism Karenia brevis, a type of dinoflagellate or marine plankton. While hardly the type of organism to inspire a week-long celebration on the Discovery Channel, the fact remains that K. brevis harmful algal blooms cause many problems. These HABs adversely affect animals and humans that are exposed to such blooms in Florida.

HABs of K. brevis are thought to begin by upwelling of nutrients promoting the growth of K. brevis near the surface of coastal waters [1]. What makes K. brevis so problematic is the organism’s ability to produce a unique type of neurotoxin, called brevetoxins. These brevetoxins are released when the cell is destroyed by factors such as wind or waves [2]. During a HAB event, the high concentrations of K. brevis cells make this release of brevetoxins a problem for marine species, as well as humans living near the coast. Even after a HAB event has ended, brevetoxins can remain in the water and later be released into the air through bubbles that rise to the surface, where they are incorporated into marine aerosols that can travel inland [2]. In a study done by Hardison et al, it was shown that K. brevis produced more brevetoxins under phosphorous (P) and nitrogen (N) limited conditions [1]. The production of brevetoxins in P-limited conditions was twice that of N-limited conditions on top of the observed increase in both conditions, prompting a need to measure the amount of brevetoxins rather than just the concentration of K. brevis [1].

K. brevis

Florida is a popular tourist destination, so HABs can negatively impact the Florida tourist industry, as red waters and the risk of negative effects from the toxins are hardly a draw for tourists. This has negative economic impacts in areas that depend on tourism and fishing, as, for example, the tourism industry in Florida is worth $57 billion [3]. In humans, one such negative effect is that inhaling airborne brevetoxins can cause respiratory irritation, such as coughs or bronchitis, the effects of which are more potent and therefore measurable in people who have asthma [3]. In a study done by Hoaglund et al, the costs of the respiratory illnesses were estimated to be $0.5-$4 million in Sarasota County, Florida alone, depending on severity [2].

Another human risk factor associated with brevetoxins is neurotoxic shellfish poisoning (NSP). Commercially, shellfish are monitored for brevetoxins, but this does not stop people from recreationally collecting and eating shellfish that might contain brevetoxins [4]. Shellfish are filter feeders, so they can consume the K. brevis cells during a HAB event, leading to the buildup of brevetoxins in shellfish tissues [5]. When these shellfish are eaten by humans, the brevetoxins can cause symptoms associated with NSP ranging from stomach upset to partial paralysis [4]. No deaths have been associated with either factor, but they are a cause for alarm nonetheless [2, 4].

Humans are not the only creatures affected by these HAB events. Fish kills in Florida are most commonly caused by HABs—a shocking 96% of them between 2003 and 2007 [6]. Fish can absorb brevetoxins across their gill membranes, or by consuming other fish that have similarly been exposed to the toxins, leading to the death of the fish [7]. These fish kills might seem advantageous to shore birds and other marine animals that feed on the fish, but brevetoxins can travel up the food chain. Furthermore, the presence of large amounts of dead fish choke up the water, resulting in a lack of oxygen for other species that live there [7].

As mentioned, brevetoxins present in living or dead fish can travel up the food chain. Van Deventer et al observed shore birds feeding on HAB-killed fish on beaches in central west Florida [8]. The researchers collected dead fish and tested them for brevetoxins, and they also collected shore bird carcasses to similarly test for brevetoxins [8]. The tested fish were found to have levels of brevetoxins that could be potentially lethal to small shore birds, and the shore birds also had brevetoxins present in their digestive tracts [8]. Although the researchers did not conclude that the shore birds died from consumption of fish killed during a HAB event, there is evidence that the fish were indeed the source of the brevetoxins found in the birds [8].

Another example of the dangers of brevetoxins to Florida wildlife can be found in manatees. Exposure to high levels of brevetoxins can be lethal to Florida manatees, but exposure at lower levels may adversely affect their immune systems, as well [9]. In a study by Walsh et al, the researchers took plasma samples from rescued manatees recovering at the Lowry Park Zoo in Tampa, Florida [9]. The researchers tested the plasma samples for brevetoxins, as well as various tests to determine the fitness of the manatees’ immune system [9]. The researchers found a relationship between increased brevetoxin levels and decreased lymphocyte proliferation, suggesting that brevetoxins may have a negative, immunosuppressant effect on the manatee immune system [9]. The Florida manatee is an endangered species, a status aggravated by human activity, and exposure to K. brevis HAB events further threatens a species already at risk.

Red tides caused by K. brevis may not be preventable, but understanding of its effects and monitoring can be useful in mitigating the negative effects of such events. A system piloted in Sarasota County and Manatee County, Florida called Integrated Ocean Observing System allowed lifeguards at eight public beaches to report different conditions on the beach, such as dead fish and respiratory distress of beach goers [3]. The data was then transferred to a server accessible by the public [3]. Similar databases in other areas at risk of HABs would be helpful to limit human exposure to airborne brevetoxins, as well as shellfish that may have accumulated brevetoxins in their tissues. Further, understanding of the risks can help with conservation of animal species at risk of exposure to K. brevis brevetoxins. Red oceans caused by algal blooms might not be as glamorous as waters blood-stained by shark attacks, but unlike uncommon shark attacks, algal blooms pose a common risk that should be no less urgent.

References:

1. Hardison, D.R., Sunda, W.G., Shea, D., and Litaker, R.W. (2013). Increased Toxicity of Karenia brevis during Phosphate Limited Growth: Ecological and Evolutionary Implications. PLoS One 8.

2. Hoagland, P., Jin, D., Polansky, L.Y., Kirkpatrick, B., Kirkpatrick, G., Fleming, L.E., Reich, A., Watkins, S.M., Ullmann, S.G., and Backer, L.C. (2009). The Costs of Respiratory Illnesses Arising from Florida Gulf Coast Karenia brevis Blooms. Environ Health Perspect 117, 1239–1243.

3. Kirkpatrick, B., Currier, R., Nierenberg, K., Reich, A., Backer, L.C., Stumpf, R., Fleming, L., and Kirkpatrick, G. (2008). Florida red tide and human health: A pilot beach conditions reporting system to minimize human exposure. Science of The Total Environment 402, 1–8.

4. Watkins, S.M., Reich, A., Fleming, L.E., and Hammond, R. (2008). Neurotoxic Shellfish Poisoning. Mar Drugs 6, 431–455.

5. Abraham, A., Wang, Y., El Said, K.R., and Plakas, S.M. (2012). Characterization of brevetoxin metabolism in Karenia brevis bloom-exposed clams (Mercenaria sp.) by LC-MS/MS. Toxicon 60, 1030–1040.

6. Gannon, D.P., McCabe, E.J.B., Camilleri, S.A., Gannon, J.G., Brueggen, M.K., Barleycorn, A.A., Palubok, V.I., Kirkpatrick, G.J., and Wells, R.S. (2009). Effects of Karenia brevis harmful algal blooms on nearshore fish communities in southwest Florida. Mar Ecol Prog Ser 378, 171–186.

7. Pierce, R.H., and Henry, M.S. (2008). Harmful algal toxins of the Florida red tide (Karenia brevis): natural chemical stressors in South Florida coastal ecosystems. Ecotoxicology 17, 623–631.

8. Van Deventer, M., Atwood, K., Vargo, G.A., Flewelling, L.J., Landsberg, J.H., Naar, J.P., and Stanek, D. (2012). Karenia brevis red tides and brevetoxin-contaminated fish: a high risk factor for Florida’s scavenging shorebirds? Botanica Marina 55, 31–37.

9. Walsh, C.J., Butawan, M., Yordy, J., Ball, R., Flewelling, L., de Wit, M., and Bonde, R.K. (2015). Sublethal red tide toxin exposure in free-ranging manatees (Trichechus manatus) affects the immune system through reduced lymphocyte proliferation responses, inflammation, and oxidative stress. Aquatic Toxicology 161, 73–84.