Term Paper on "Effect of Red Tide on Manatees"

Term Paper 6 pages (1576 words) Sources: 1+

[EXCERPT] . . . .

Red Tides and Manatees

The Effect of Red Tide on Manatees

The manatee population of Florida has suffered devastating effects not only from the fishing and boating industry, but the re-occurrence of the red tides has killed large numbers in recent years, leading to much research and numerous efforts regarding manatee protection and algae controls.

Manatees are large marine mammals, with adults averaging in weight between one thousand and fifteen hundred pounds, and averaging twelve feet in length (Trouble pp). They inhabit coastal estuarine systems within the boundaries of the tropics (Trouble pp). Their migration in North Florida is seasonal and prompted mainly by changes in water temperature, while in South Florida, however, the need for fresh or low salinity drinking water is a second reason for migration (Trouble pp). Crystal River, a tributary near the middle of Florida's West Coast, flows for roughly seven miles into the Gulf of Mexico, and at its headwaters are several major springs, from which hundreds of millions of gallons of clear, seventy-two degree water flows year- round (Trouble pp). When winter begins, the waters of the Gulf turn colder, forcing two hundred or more manatees up the river to Kings Bay, seeking shelter in the warm fresh water (Trouble pp). During recent years, the number of migrating manatees has increased significantly, a fact that may be related to environmental problems that manatees are facing in other parts of the state (Trouble pp). For regional manatees, finding warm waters is a matter of survival because the cold Gulf can lead to respiratory illnesses, which is the most common natural cause of death among manatee (Trouble pp). Although many spend their summers in the Crystal River area, they also tend to widely disperse in the adjacent waters of the Gulf and are difficult to find (Trouble pp).

Between 1995 and 1996, about twenty percent of the Florida manatee population died from exposure to red tide, a toxic algae bloom that occurs naturally in the Gulf of Mexico, and to which manatees have been exposed to for many years (Trouble pp). Scientists believe that perhaps the blooms are more concentrated due to the increasing levels of pollution in Florida's coastal waters, and moreover, that the pollution may be reducing the manatees natural immune system and its resistance to disease (Trouble pp). Furthermore, many believe that the continuing construction and development in coastal areas and the loss of wetland habitat, which filters surface water runoff "(which had previously reduced pollution to coastal waters), and the resulting contamination and loss of the coastal grasses which are the manatee's food supply," have all contributed to forcing manatees into ever shrinking ranges (Trouble pp).

Blooms of karenia brevis, red tide, are noticeable to the public, both to boaters offshore and to onshore beach-goers, primarily because of the respiratory irritation, dead fish, and discolored water (Environmental pp). However, aside from these three general signs, there are more serious symptomatic effects both on offshore and near-shore marine ecosystems (Environmental pp). Many marine species, such as bay scallops, surfclams, oysters, tunicates, commercial and recreational species of fish, sea birds, sea turtles, manatees, and dolphins, tend to accumulate toxins either released by K. brevis cells or by feeding on K. brevis, or by feeding on toxic animals that have eaten K. brevis, or else they become sick and die when exposed to a red tide for an extended period of time (Environmental pp). Symptoms found in these species are related to K. brevis concentrations and release of neurotoxic substances called brevetoxins, and during a bloom, these brevetoxins are present in seawater and accumulate in filter feeders, and are distributed as aerosols in sea spray (Environmental pp). Skin and respiratory irritation in marine species as well as humans can result from exposure to these aerosols (Environmental pp).

Generally, the first indicators of K. brevis bloom are the offshore fish kill of bottom fish such as grouper, snapper, hogfish and eels, then as the winds and currents move the bloom into the near-shore water, other fish such as catfish, mullet and drums fall victim, leaving seabirds that consume the beached fish in danger of accumulated toxins as well (Environmental pp). It is estimated that one hundred tons of fish per day are killed during blooms off Florida's West Coast (Environmental pp). Signs of intoxication in exposed fish include violent twisting and corkscrew swimming, regurgitation of food, fin paralysis, loss of equilibrium, and convulsions, and fish may also become paralyzed and suffocate because brevetoxins promote central nervous system dysfunction (Environmental pp). Moreover, invertebrate species such as scallops and sponges, as well as sea turtles may be poisoned by K. brevis exposure (Environmental pp).

However, it is Florida's manatee population that is perhaps the most visible of the marine mammal species suffering from the impacts of K. brevis blooms (Environmental pp). In 1982 and 1996, the southwest coast of Florida experienced mass manatee mortality due to red tides - thirty-nine tides and over one hundred and fifty manatee deaths were reported for each year (Environmental pp). During both of these years, there were elevated salinity levels in Pine Island Sound where high K. brevis cell concentrations persisted during an unusual winter bloom (Environmental pp). According to a 1998 study, "manatees are at high risk from February to April if a bloom enters the near-shore waters of southwest Florida, if salinities of the estuarine system are greater than 29%, and if large numbers of manatees are dispersing into the bloom area," - in both 1982 and 1996 these circumstances were present (Environmental pp). There are basically three paths of toxicity for manatees, "aerosol inhalation, food ingestion, and seawater intake" (Environmental pp).

As blooms increase infrequency and intensity, marine mammal mortality figures can be expected to continue (Environmental pp).

Although estimates of Florida red tide vary, costs of $20 million dollars for episodes that last several months are often cited, leading scientists to work on ways of stopping red tide (Red pp). Recently, a project funded by the Florida Institute of Phosphate Research produced data to justify one possible solution, the use of Florida phosphatic clay (Red pp). Actually clay has been used for years in Japan, China and Korea to control or suppress red tide blooms (Red pp).

When added to the seawater, the clay particles attaches to each other and to microscopic organisms like the red tide algae, eventually growing into aggregate particles that settle to the ocean bottom. If they settle deep enough and are not resuspended or don't escape, the organisms die

Red pp).

Although studies done in Korea indicate that the clay does not build up on the ocean floor, experts warn that this may not be the case in other locations (Red pp).

The term "red tide" is used because when there is a high concentration of K. brevis causing the water to become discolored, usually red, however, the water may actually appear greenish, brownish, and even purple, or it may retain its normal color (When pp).

A great deal of research exists on the organism and its toxins, however, "relatively little exploration of exposure to and adverse health effect from K. brevis and the brevetoxins has been done in human and other animals" (Mini pp).

This organism is quite fragile and breaks up easily in the surf, thus, releasing brevetoxins into marine waters, and at air-sea interface these aerosols form and, upon exposure to ultraviolet light, may be modified into different mixtures of brevetoxins and/or other biologically active compounds (Mini pp). The first documentation of the importance of the Florida red tide toxins as an aerosol exposure was done in 1948, and more recent research has verified the occurrence of self-reported upper and lower respiratory symptoms associated with inhaling brevetoxin aerosols during red tide events (Mini pp).

When the neurologic activities of brevetoxins… READ MORE

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