brevis blooms are not a new phenomenon, and fish kills that result from red tides caused by K. brevis in the Gulf of Mexico have been described in the scientific literature since 1960 or so and have been reported anecdotally for more than two centuries (Naar et al. 2002). In this regard, Backer and her associates (2005) emphasize that, "The human health effects from consuming shellfish with high concentrations of brevetoxins in their tissues have been well documented. However, there is very little information describing human health effects from environmental exposures. It is ironic that we know the least about the aspects of the Florida red tide problem that poses the greatest public health hazard in terms of number of people affected" (645). Today, K. brevis blooms are monitored closely in order to mitigate the foregoing health hazards that are related to the consumption of shellfish and shellfish harvesting is banned in those instances where the densities of K. brevis exceed 5,000 cells per liter of seawater (Landsberg and Steidinger 1998).
A study by Brand and Compton (2007) analyzed K. brevis samples that were taken from the region near the southwest coast of Florida between Tampa Bay and Sanibel Island during the period between 1954 to 2002 to identify corresponding spatial and temporal patterns. According to these researchers, "K. brevis was found to be approximately 20-fold more abundant within 5 km of the shoreline than 20 -- 30 km offshore. Overall, K. brevis was approximately 13 -- 18-fold more abundant in 1994 -- 2002 than in 1954 -- 1963" (Brand and Compton 232). During the period 1954 to 1963, K. brevis blooms took place mostly during the fall months; by contrast, during the period between 1994 and 2002, blooms were prevalent during the fall months as well as winter and spring (Brand and Compton 2007). In this regard, Brand and Compton speculate that the increased concentrations of nutrients in the ecosystem are probably responsible for this increased prevalence of bloom events due in large part to the increased presence of humans and associated activities in this region over the past 50 years (Brand and Compton 2007).
Effect on Other Marine Plants.
Although the HABs caused by K. brevis have been shown to represent a serious health threat to benthic organisms as well as other aquatic and terrestrial life, including humans, less is known about the effect on marine plants. It is reasonable to suggest, though, that K. brevis can contribute to a toxic environment that may harm or even kill various marine plant species. In this regard, Woofter et al. (2005) emphasize that, "Aquatic species are of particular relevance because K. brevis is a fragile dinoflagellete that readily breaks, releasing toxin directly into the water or upon contact with inert or living objects" (12).
Differences between Red Tide in the Gulf of Mexico and Elsewhere.
The term "red tide" is used to describe any type of harmful algal bloom (Bankoff 2002) and while the red tides created by K. brevis are the most commonplace in the Gulf of Mexico, there are at least 22 other known species of toxic dinoflagellates, some of which are also responsible for such HAB occurrences elsewhere around the world (Aguirre, Ostfield, Tabor, House and Pearl 2002). According to Russell (1998), "These blooms are extremely toxic, both to the marine life feeding upon them and to people who eat contaminated shellfish. Over the past decade, the number of such single-celled algal species has soared from 22 to 55 around the globe" (36). Many researchers attribute to explosion in the numbers of harmful algal species to increased human activities along coastal regions of the world. In this regard, Aguirre and his associates (2002) note that, "Outbreaks of certain species in this group, and of various species among the newly recognized toxic dinoflagellates, are strongly correlated with nutrient pollution in quiet, poorly flushed coastal embayments and estuaries" (230). Other regions besides the Gulf of Mexico that experience red tides (or so-called brown tides or even green tides) are characterized by elevated levels of human population and corresponding nutrient pollution that results from inadequately treated sewage and other sources of effluents (Aguirre et al. 2002). According to these researchers, "Some species, such as the toxic Pfiesteria complex and many toxic cyanobacteria, are known to thrive in degraded waters overenriched with nutrients. Other species, such as the toxic Pseudonitzschia complex, are most abundant in waters that have been enriched in nutrients from upwelling processes or from sewage and other anthropogenic nutrient additions" (Aguirre et al. 2002:230). Red tide events caused by other species have also been reported in the near-shore fishing zones off the Philippines (Bankoff 2002). Although the causes of red tides elsewhere in the world may be different, their bottom-line impact is much the same as that experienced in the Gulf of Mexico. For example, Harris (2002) reports that, "Among the most visible evidence of deterioration of the marine environment is the notable increase in frequency and scale of red tide occurrences along the coastal areas of China and South Korea over the past few decades. In particular, in the 1990s in the seas adjacent to South Korea, red tides not only occurred along seashores more frequently but also spread extensively to the open seas" (172). The adverse health consequences of these HABs are less well-known than those in the U.S., but the economic impact of these red tide events on these Asian nations was shown to be enormous (Harris 2002).
The research showed that Karenia brevis (formerly Gymnodinium breve) is a marine dinoflagellate that is responsible for creating the red tides that develop in the Gulf of Mexico. In addition, it was shown that K. brevis produces brevetoxins, the powerful toxins that cause neurotoxic shellfish poisoning. The research also showed that the brevetoxins produced by K. brevis represent a serious health threat to numerous aquatic wildlife species including fish, waterfowl, and marine mammals as well as terrestrial life including human beings. Finally, the research showed that harmful algal blooms or red tides are not unique to the Gulf of Mexico, but they have become more frequent and have tended to last longer than in years past, due in part to the increased levels of human activity along the coastal regions where they take place. Virtually all of the studies reviewed emphasized the need for additional research in this area and given the potential health and economic threat represented by red tides, such research should take place sooner rather than later.
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