SCCF: Wildlife impacts reveal red tide’s persistence
The Sanibel-Captiva Conservation Foundation reported that over the past two weeks, the Clinic for the Rehabilitation of Wildlife treated an adult laughing gull and a ruddy turnstone, both admitted for suspected red tide/toxicosis. They died within 24 hours. An adult great egret and two juvenile double-crested cormorants were also admitted and were still in care as of May 13.
Wildlife impacts from brevetoxicosis are currently being reported without the local presence of a red tide bloom. The SCCF reported that one of the more confusing aspects of red tide — which is caused by high concentrations of the single-celled algae called Karenia brevis — is that it is sometimes found at “background” or very low levels.
“It can seem counterintuitive that animals are experiencing symptoms when K. brevis cell counts read as ‘not present’ or at ‘background concentrations,’ but multiple explanations for this exist,” SCCF Policy Associate Allie Pecenka said.
The first is the process of bioaccumulation, or the amount of toxins from K. brevis increasing in organisms as they move up the food chain. The toxins accumulate in the tissues of small fish and invertebrates like oysters and crabs during the feeding process and are ingested by predators at higher trophic levels. The toxin can also settle on plants, where it can remain long after a red tide event has passed and be further ingested by marine life.
“The largest predators tend to hold the highest levels of toxins, which build up faster than they can be broken down. This process explains why we may see the impacts of brevetoxicosis on wildlife later in the winter after animals have been ingesting the toxin for months on end,” she said.
Another reason impacted wildlife can be seen in communities not experiencing an active bloom is due to the nature of animals as they tend to move around. Seabirds cover vast distances, so an animal could be feeding far offshore in the Gulf of Mexico where a bloom is present, and then return to shore where it begins to exhibit symptoms. Since blooms require wind and currents to travel, an impacted bird is able to travel to areas where a bloom cannot. It means possibly seeing impacts from blooms that never interact with the coastal communities.
WHEN, HOW RED TIDE BLOOMS
The SCCF reported that red tide in Florida is a phenomenon caused by high concentrations of Karenia brevis, a dinoflagellate that occurs naturally in the Gulf. When present at trace levels, the organism has minimal impacts on the environment. However, when counts of K. brevis cells begin to rise and form a bloom, the harmful effects intensify.
The Florida Fish and Wildlife Conservation Commission (FWC) considers red tide to be at a “low-background” level if there are 0-1,000 K. breviscells per liter, with “very low” falling between 1,000 and 10,000 cells.
The SCCF reported that these background reports of K. brevis represent the naturally occurring concentrations of the organism present in the Gulf year-round, posing no threat to the coastal environment. While organisms may begin to be impacted from “very low” concentrations, once K.brevis cells per liter surpass 10,000 — moving into low, medium or high levels — harmful effects to the environment become increasingly likely.
“It’s important to understand that FWC’s red tide reporting system is excellent at identifying the presence of K. brevis close to our coastal communities, but it’s limited to reporting at specific sampling sites,” Pecenka said. “The associated data should not be regarded as a complete snapshot of existing red tide blooms in the Gulf, nor their potential for impacts to our region.”
The SCCF reported that red tide blooms typically initiate off Southwest Florida’s coast between late summer and early fall. In general, harmful algal blooms are fed by warm water temperatures and high levels of nutrient-rich runoff from increased rainfall. The conditions tend to compound between August and November, providing optimal conditions for K. brevis growth.
HISTORY AND INTENSIFICATION
The SCCF reported that while anecdotal accounts of red tide date as far back as the 16th century, the extent, severity and duration of blooms are now far more intense than they were historically.
“Research has shown that red tides are exacerbated by human activity; namely increased nutrient loading into waterways from agriculture and human development,” she said. “High levels of nitrogen and phosphorous from these sources feed the growth of an algal bloom, leading to the longer, stronger red tides we face today.”
When conditions conducive to growth are met, preexisting K. brevis cells begin to multiply 10-45 miles offshore to form a bloom. After initiating, blooms grow larger and more intense and may travel throughout the Gulf based on wind and current patterns.
The SCCF reported that when a bloom moves inland and is intensified by human-caused nutrient loading, the risk for a large-scale, long-lasting harmful algal bloom with devastating consequences becomes tangible.
“The negative impacts to our communities and environment from a large-scale red tide event are undeniable,” Pecenka said. “The lasting effects from a single event can have massive ramifications on the health of our ecosystems, economies and individuals within affected communities.”
“As we improve local water quality, the overall health of the Caloosahatchee system will reduce the potential for large-scale harmful algal blooms that harm our local ecosystems, communities and economies,” she added.
K. brevis cells release a toxin that attacks the nervous system of animals. The neurotoxins, called brevetoxins, are often fatal to fish, birds, sea turtles and marine mammals and can have adverse impacts in humans.
Report wildlife behaving erratically — unable to stand or fly, displaying tremors, apparent weakness or confusion — to CROW’s Wildlife Hospital by calling 239-472-3644 ext. 222.