Most Common Harmful Algal Bloom Species example essay topic

Throughout the world's coastal oceans, observations of harmful algal blooms, referred to as red tides in older literature, are being reported with increasing frequency. Often, these events are accompanied by severe impacts to coastal resources, local economies, and public health. Harmful algal blooms - accumulation of microscopic species of algae or larger, multi-cellular species - appear to be more disturbing than ever before, and may be increasing over time. Some species persist in the same geographic regions each year, while others are more sporadic, leading to the unexpected deaths of local fish, shellfish, mammals, and birds. Most harmful algal blooms are caused by both the microscopic species of algae, referred to scientifically as phytoplankton and the microphytobenthos, as well as other larger macro-algae. A bloom occurs when an alga rapidly increases in numbers to the extent that it dominates the local planktonic or benthic community.

Such high abundance can result from explosive growth, caused, for example, by a metabolic response to a particular stimulus (for example, nutrients or some environmental condition like a change in water temperature), or from the physical concentration of a species in a certain area due to local patterns in water circulation. Defining an algal bloom and characterizing the species that cause them presents a serious challenge. At one point, all harmful algal blooms were referred to as "red tides" because of the color the algae impart while suspended in the water, but this term has since been discredited because not all harmful algal blooms are red. Some may be brown, yellow, or green, and some may not discolor the water at all. Color is imparted through cellular concentrations of pigments like chlorophyll or lower abundance pigments.

Examples of harmful algal blooms that are commonly associated with water discoloration are blooms of many species of cyanobacteria, generally visible as floating green scums or colonies in coastal environments; two "brown tide" species, Aureococcus and Aureoumbra, that turn coastal lagoons dark chocolate brown; the dinoflagellates Alexandrium spp., Gymnodinium breve, and Noctiluca spp., that turn water red; and blooms of macro-algae (Smayda 1997). There are species that cause algal blooms in which there is no visible color change to the water. Such species include the chlorophyll-free dinoflagellate Pfiesteria piscicida, several Dinophysis species, and benthic micro-algae, like Gambier discus that grows on the surfaces of larger macro-algae in tropical waters. Pfiesteria and Dinophysis impart toxicity at very low densities, generally less than 1,000 cells per liter (Smayda 1997). In comparison, macro-algae are considered harmful due to dense overgrowth that can occur in localized areas, such as coral reefs of the tropics or coastal embayment's receiving excessive nutrient loading. Accumulations can be so high as to cover the bottom of a region, excluding other biota as well as creating an environment in which high oxygen consumption and the associated anoxic conditions accompany decomposition of the accumulated or displaced biomass.

Harmful algal blooms can have serious detrimental effects on the environment. The effects can range anywhere from damage to cells and tissues of an organism to the organism's death and can be caused by a number of different methods. Production of toxins, predation, particle irritation, induced starvation, and localized anoxic conditions are a few of mechanisms by which algal blooms can negatively impact the environment. Because of the wide range of these mechanisms, harmful algal blooms can affect many living organisms of the coastal ecosystem, from zooplankton, to fish, to even people.

Only a few harmful algal bloom species actually produce toxins that are poisonous to people and marine animals. The most well-known harmful algal bloom toxins are generically referred to as ciguatera fish poisoning (CFP), neurotoxic shellfish poisoning (NSP), paralytic shellfish poisoning (PSP), diarrheic shellfish poisoning (DSP), and amnesic shellfish poisoning (ASP). Pfiesteria piscicida also produces two toxic fractions, dermonecrotic and neurologic toxins that impact fishes and humans. Cyanobacteria also produce similar toxins that have common characteristics with several of these broad categories, including neurotoxin and hepa toxins.

Common symptoms of exposure to these toxins include gastrointestinal, neurological, cardiovascular, and hematological symptoms. The terms "fish" and "shellfish" are associated with these illnesses because the toxins are found in high concentrations in the fish and shellfish that ingest the harmful algae. The harmful algae then affect humans and marine mammals when they in turn consume the infected fish or shellfish. There are harmful algal blooms that produce toxins with no identifiable effects on humans but do however have overwhelming impacts on coastal living resources. For example, the flagellate Hetero sigma akashiwo is thought to produce an ichthyotoxin that kills fish, resulting in significant threats to penned fish in mariculture operations (Taylor and Horner 1994).

Predation is another way that several harmful algal bloom species can impact the coastal biota. Predation occurs when one organism captures or feeds on another organism. One common example of a predatory harmful algal bloom is the dinoflagellate Pfiesteria. Pfiesteria is not toxic all of the time, however. The exact conditions that lead to the toxic outbreaks of Pfiesteria are completely known or understood. For the most part, scientists agree that a high concentration of fish must be present to prompt the shift of Pfiesteria cells into toxic forms.

Pfiesteria outbreaks are common in shallow, poorly flushed estuaries in which schools of oily fish frequent. It is believed that compounds secreted by these fish stimulate the toxic stage of Pfiesteria (Burkholder and Glasgow 1997). There is mounting evidence that this dinoflagellate produces several toxic "fractions" that aid in prey capture. Two of these toxic fractions are produced after the P. piscicida is exposed to these fish secretions.

The first fraction has neurotoxin-like properties that affect the fish's neurological system. The second has dermonecrotic, or skin killing characteristics. The neurotoxin-like materials cause lethargy in the fish, and, when present in high enough numbers, death. The dermonecrotic compounds actually lead to shedding of the fish's external skin layers, eventually causing lesions and conceivably derived infections from fungi and other pathogens found in the surrounding water (Burkholder and Glasgow 1997). Fish kills coincident with Pfiesteria are likely to be a result of direct exposure to toxic compounds produced by the dinoflagellate, secondary infections associated with lesions, or a combination of both. Fish mortality is then followed by dinoflagellate ingestion of the dead fish tissue.

Particle irritation is yet another way in which harmful algal blooms can impact the coastal environment. Several harmful algal bloom species, in particular two spine-forming diatoms (Chaetoceros cavicorn is and C. convolutes), also cause significant problems for coastal fish that are commonly produced in mariculture operations. The deaths of fish and crustaceans occur because large numbers of these spiny phytoplankton become trapped in the animals' gills, leading to mucus accumulation and respiratory failure, hemorrhaging, and bacterial infection. Harmful algal blooms can also cause organisms to starve through nutritional and size mismatch (Smayda 1997). Organisms that ingest these harmful algal blooms are often unable to ingest enough high-quality food to survive. The brown tide organism Aureococcus reduced ingestion of nutritious algae in bay scallop larvae by interfering in the scallops' ciliated esophagus.

In adult suspension-feeding bivalves, the alga hinders the activity of lateral cilia in the gill, the main organ of particle capture, which ultimately reduces the bivalves' growth. Other harmful algal bloom species may be too small, too big, taste badly, or, as in the case of Prorocentrum minimum, alter the absorption capabilities of the organism's digestive system. Bloom densities of P. minimum actually kill juvenile oysters and bay scallops, perhaps by interfering in the shellfishes' ability to produce digestive enzymes or by causing atrophy of their digestive tissues (Smayda 1997). Excessive accumulations of algae, whether as a micro- or macro-algal bloom, are often followed by high decomposition rates of the accumulated material.

The decomposition is accompanied by oxygen consumption, stripping local waters of available oxygen and leading to hypoxic conditions in which there is too much oxygen or anoxic conditions in which there is not enough oxygen. Most marine biota cannot survive without oxygen, resulting in mass mortalities of fish and shellfish. Crustacean deaths occur because large numbers of algal cells become trapped in the creatures' gills, causing respiratory failure, hemorrhaging, or bacterial infection (Smayda 1997). Species of the diatom genus Chaetoceros, for example, become lodged in the gills, where their spiny filaments destroy the hosts' tissue. The most common harmful algal bloom species found in the Gulf Coast area is the dinoflagellate, Gymnodinium breve. Unlike many other bloom species, Gymnodinium has been well documented throughout history.

The earliest recorded fish kill, later credited to a Gymnodinium bloom, was in 1844 off the west coast of Florida. Since that time, persistent outbreaks have occurred along the west Florida and Texas coasts. In the late 1940's, scientists become aware of a number of relationships associated with this toxic species and the effects produced by its bloom. High cell densities of this toxic dinoflagellate discolor surface waters with a typical red coloration, producing what has historically been referred to as "red tide".

However, before actually seeing this "red tide", beach-goers tend to experience respiratory problems. These respiratory problems occur because Gymnodinium cells and their released toxins are inhaled as an aerosol. The toxic aerosol can affect humans at much lower concentrations than are required for the human eye to actually see discoloration in the water (Horner et al. 1997). Gymnodinium also produces brevetoxin, which is lethal to fish and results in massive fish kills that wash up and decompose on local beaches. Fish kills can occur before the water is visibly discolored, at concentrations of ~0.5 million cells per liter.

Exposure to this brevetoxin can also cause marine mammal mortalities; in 1996, more than 150 manatees were killed just south of Tampa Bay. Within the Gulf of Mexico region, these blooms are considered a natural phenomenon, and have not been attributed to any human factors. It appears that Gymnodinium bloom dynamics are most closely coupled to physical processes (Tester and Steidinger 1997). A resident population exists in the Gulf of Mexico at all times, with background concentrations of 1 to 1,000 cells per liter.

Initiation, transport, and retention of the bloom are all strongly affected by the extent of the northward diffusion of an offshore, clockwise current known as the Loop Current, its spin-off eddies, and its intrusions onto the west Florida shelf. Blooms may possibly originate around the fronts caused by the flow of the Loop Current along the outer southwest Florida shelf, around 40 to 80 miles offshore (Tester and Steidinger 1997). These fronts are characterized by various organic and inorganic nutrient and light systems that prove conducive to the growth of Gymnodinium. Once growth of the algae has begun, it may take up to 8 weeks for the cells and their associated toxins to develop in concentrations high enough to begin killing fish (Tester and Steidinger 1997).

Gymnodinium blooms are some of the largest recorded, covering areas of hundreds to thousands of square miles. For example, a bloom off the coast of Florida in 1964 covered an area of 14,000 square kilometers, from Apalachee Bay to Piney Point (Tester and Steidinger 1997). The timing of Gymnodinium blooms along Florida's western coast is well known, with incidences likely throughout the year but with most occurring in late summer and fall (Tester and Steidinger 1997). The persistence of a bloom depends on many factors including physical, biological, and chemical conditions and can range anywhere from a few months to more than a year; the longest bloom ever recorded began in September 1994 and ended in April 1996 in an area from Tarpon Springs to the Florida Keys (Mote Marine Lab 1998 on-line). Blooms are more common along the west coast of Florida, which has reported blooms during 23 of the last 24 years, than along the coast of Texas, which has experienced only three major blooms, in 1935, 1986, and 1997-1998 (Pinkerton 1998).

The results of these blooms can be both physically and economically devastating to a region. In April 1963, a bloom that occurred from Tampa Bay to Marco Island resulted in the deaths of more than 150 tons of fish, including a 700-pound grouper (Mote Marine Lab 1998 on-line). The red tide off the coast of Texas and Mexico between October 1997 and January 1998 was responsible for killing more than 14 million fish (Pinkerton 1998); this estimate was later increased to 21 million. These blooms and others like them have had harsh impacts on several industries, including fisheries (both fish and shellfish) and tourism. Blooms have also affected numerous other wildlife species, including manatees and birds.

In addition to the 1996 bloom that killed the manatees, a bloom in the Caloosahatchee River area of Florida in 1982 resulted in the deaths of 39 manatees illustrating the serious impact that these recurrent natural events can have on an endangered species. A red tide off the coast of the Florida panhandle in the fall of 1999 is believed to be responsible for more than 65 bottlenose dolphin mortalities since August 1999, when normally only one or two dolphin mortalities are observed. In Florida, there is strong community awareness and a commitment to reduce the impacts of these nearly annual events on the western coast. Researchers from academic, federal, state, and local organizations, as well as industry and citizen groups, all work to both monitor and alleviate the potential effects of harmful algal blooms. Researchers have been able to chart the progression of a bloom from initiation to senescence using remote sensing as well as sampling cruises. Observations like these are being used to develop a forecasting ability for the transport of offshore blooms into coastal regions.

With this information, coastal communities will be able to potentially limit the impacts of landfall of these toxic populations and the linked fish kills that are left on recreational beaches. Harmful algal blooms are not new phenomena, with written references dating back to Biblical times. Dinoflagellates have been found in the fossil record for millions of years, and cyanobacteria were the first photosynthetic life forms on Earth. In the words of Dr. Don Anderson, who researches algal species at the Woods Hole Oceanographic Institute in Massachusetts, "There are more toxic algal species, more algal toxins, more fisheries resources affected, more food-web disruption, and more economic losses from harmful algal blooms than ever before" (Anderson 1997).

The interest in harmful algal blooms stems, for the most part, from increased public awareness of the negative impacts to marine resources - standings and deaths of marine mammals, birds, and sea turtles; increased monitoring efforts and improved methods of detection; and the establishment of linkages between initial exposure and subsequent symptoms displayed by organisms exposed to a harmful algal bloom species. Understanding the ecology and oceanography of these species, and their affects on other organisms, including people, continues to be a challenge for researchers.

Bibliography

Anderson, D.M. 1997.
Bloom dynamics of toxic Alexandriumspecies in the northwestern United States. Limnology and Oceanography, 42, 1009-1022. Burkholder, J.M. and H.B. Glasgow Jr. 1997.
Pfiesteria piscicida and other Pfiesteria-like dinoflagellates: Behavior, impacts, and environmental controls. Limnology and Oceanography, 42, 1052-1075. Horner, R.A., D.L. Garrison, and F.G. P lumley. 1997.
Harmful algal blooms and red tide problems on the U.S. West Coast. Limnology and Oceanography, 42, 1076-1088. Mote Marine Laboratory. About red tide. Visited April 2003.
web Pinkerton, J. 1998 (on-line).
Red tide may be a killer we must learn to live with: Detection, warning may be most we can hope for in fighting algal blooms. The Houston Chronicle. Visited April 2003.
web Smayda, T.J. (1997).
What is a bloom? A commentary. Limnology and Oceanography, 42 (5), 1132-1136. Tester, P.A. and K.A. Steidinger. 1997.
Gymnodinium breve red tide blooms: Initiation, transport, and consequences of surface circulation. Vali ela, I., J. McClelland, J. Hauxwell, P.J. Behr, D. Hersh, and K. Foreman. 1997.