By conservative estimates, harmful algal blooms (HABs) cost the United States $50 million per year (Hoagland, P. et al. Estuaries, 2002, 25:819-837). Such estimates are based upon direct economic impacts on tourism, fisheries, etc., and do not account for irremediable costs such as those caused by mass marine mammal mortalities (Landsberg, J. H. Rev. Fish. Sci., 2002, 10:113-390; Landsberg, J. H. and Steidinger, K. A. “A historical review of Gymnodinium breve red tides implicated in mass mortalities of the manatee (Trichechus mantus latirostris) in Florida, USA”, 1998, pp. 97-100, in B. Reguera et al. Eds, Proceedings of the 8th International Conference on Harmful Algae, Xunta de Galicia and Intergovernmental Oceanographic Commission of UNESCO, Vigo, Spain). Worldwide, algal toxins of all types may be responsible for as many as 60,000 human intoxication events per year (Van Dolah, F. M. et al. Hum. Ecol. Risk Assess., 2001, 7:1329-1345).
Nearly all coastal regions of the United States are impacted by HABs for various intervals in time and intensity. Perhaps no coastal environment has a frequency of HABs equal to that of the Florida Gulf Coast, caused by the non-peridinin dinoflagellate Karenia brevis (Davis) cf. Hansen and Moestrup (Gymnodinium breve). Although red tides have been observed in the Gulf of Mexico since the Spanish Conquests and reports of catastrophic fish mortalities go back to 1844, the identity of K. brevis, initially named G. breve, as the causative agent was not determined until the bloom of 1946 to 1947 (Gunther, G. et al. Ecol. Monogr, 1948, 18:311-324). In certain years, red tides have occurred during 12 months of the year, although they are most often encountered in the late summer and early fall, correlating with heavy rainfall (Landsberg, J. H. Rev. Fish. Sci., 2002, 10:113-390).
Efforts to control HABs have been hampered by limited research on the subject, particularly with respect to the monitoring and prediction of HABs. Historically, blooms have occurred primarily during the fall and winter months. Over recent years, however, the Florida red tide specifically, and HABs in general, appear to be more prevalent and wide-spread (Chretiennot-Dinet, M., Oceanis, 2001, 24:223-238; Hallegraeff, G. M., Phycologia, 1991, 32:79-99). Massive fish kills, marine mammal mortalities, human poisonings due to the consumption of tainted shellfish and complaints of respiratory irritations among beach-goers are associated with these blooms (Kirkpatrick et al., Harmful Algae, 2004, 3:99-115; Van Dolah et al., in Toxicology of Marine Mammals, Taylor & Francis, Inc., 2002, Vos et al. (Eds.), p. 247-269). These harmful effects are attributed to a suite of polyketide secondary metabolites known as brevetoxins, which are part of a larger family of dinoflagellate-derived polyketide toxins that pose a threat to human health. Brevetoxins are polyether ladder type compounds having two parent backbone structures, brevetoxin A and brevetoxin B, each with several side-chain variants. Examples of other harmful polyketide toxins include ciguatoxin, okadaic acid, and the related kinophysistoxins, pectenotoxins, yessotoxin, and the azaspiracids. The mechanism of synthesis of brevetoxins is unknown but is hypothesized to be the result of enzymes similar to polyketide synthetases. Recently, two polyketide synthetase genes were described from K. brevis (Snyder et al. Mar. Biotechnol., 2003, 5:1-12; Snyder et al. Phytochemistry, 2005, 66(15): 1767-80).
A myriad of approaches have been taken to address the problem of HAB monitoring and prediction, including satellite ocean color sensing (Stumpf, R. P. Hum. Ecol. Risk Assess., 2001, 7:1363-1368), photopigment analysis (Millie, D. F. et al. Limnol. Oceanogr., 1997, 42:1240-1251; Millie, D. F. et al. J. Phycol., 2001, 37:35; Oernolfsdottir, E. B. et al. J. Phycol., 2003, 39:449-457), and toxin analysis (Pierce, R. H. and Kirkpatrick, G. J. Environ. Toxicol. Chem., 2001, 20:107-114). Additionally, molecular methods are being developed to detect a variety of HAB species, including Alexandrium sp. (Adachi, M. et al. J. Phycol., 1996, 32:1049-1052; Godhe, A. et al. Mar. Biotechnol., 2001, 3:152-162), Gymnodinium sp. (Godhe, A. et al. Mar. Biotechnol., 2001, 3:152-162; Peperzak, L. et al. “Application and flow cytometric detection of antibody and rRNA probes to Gymnodinium mikimotoi (Dinophyceae) and Pseudo-nitzschia multiseries (Bacillariophyceae), 2000, pp. 206-209, in G. M. Hallegraff et al. Eds., Harmful algal blooms, IOC-UNESCO, Paris, France), Pseudonitzschia sp. (Peperzak, L. et al. “Application and flow cytometric detection of antibody and rRNA probes to Gymnodinium mikimotoi (Dinophyceae) and Pseudo-nitzschia multiseries (Bacillariophyceae), 2000, pp. 206-209, in G. M. Hallegraff et al. Eds., Harmful algal blooms, IOC-UNESCO, Paris, France), Pfiesteria sp., and Pfiesteria-like organisms (Litaker, R. W. et al. J. Phycol., 2003, 39:754-761) as well as K. brevis (Gray, M. et al. Appl. Environ. Microbiol., 2003, 69:5726-5730; Loret, P. et al. J. Plankton Res., 2002, 24:735-739).
Nucleic acid sequence-based amplification (NASBA) is an isothermal method of RNA amplification that has been previously used in clinical diagnostic testing. Recently, a real-time NASBA assay was developed for the detection of ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) large-subunit (rbcL) mRNA from K. brevis (Casper et al., Applied and Environmental Microbiology, 2004, August, 70(8):4727-4732; Casper et al., Harmful Algae, 2006, 6(1):112-118). The rbcL mRNA was selected as the target because cellular levels of mRNA are typically high and RNA degrades quickly in the environment, resulting in detection of viable K. brevis populations only. NASBA RNA amplification occurs at 41° C. (European Patent No. EP 0329822, Davey et al.). RNA is amplified by use of an enzyme cocktail including T7 RNA polymerase, avian myeloblastosis virus reverse transcriptase, RNaseH, and two target-specific oligonucleotide primers. A NASBA-based assay for K. brevis polyketide synthesis mRNA has been used to successfully detect and quantify K. brevis in cultures and field samples collected from the coastal waters of southwest Florida (U.S. Pat. No. 7,422,857, Paul, J., issued to the University of South Florida).
Approaches to direct HAB intervention can be grouped into three categories: mechanical, physical/chemical, and biological control. Mechanical control involves the use of filters, pumps, and barriers (such as curtains and floating booms) to remove or filter HAB cells, dead fish, or other bloom-associated materials from impacted waters. Physical/chemical control involves the use of chemical or mineral compounds to kill, inhibit, or remove HAB cells. Biological control involves the use of organisms or pathogens (such as viruses, bacteria, parasites, zooplankton, or shellfish) that can kill, lyse, or remove HAB cells.
There exists a continuing need for a mitigation system that is effective in controlling and managing an HAB and harmful algae. An important criterion for any effective HAB control system is that the benefits of using the intervention outweigh collateral damage such as threats to public health and environmental impacts.