Last updated: July 23, 2019
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Algal blooms were observed along the coastal waters of the Gulf of Mane and Pacific Northwest. A study shows that the Dinoflagellates Alexandrium fundyense and Alexandrium catanella were responsible for the formation of these blooms. (Isabella et al.., 2006). Cases of blooms covering vast area of coastal waters have been witnessed in the Gulf of Mexico and the east coast of Florida while in Europe recent blooms phenomena have been described in countries like Greece and France (Isabella et al., 2006).The Gonyaulax Dinoflagellates blooms and produce saxitoxin, that have been observed off the west coast of North America, and Alexandrium off the northeast coast which accumulates in shellfish. Eating contaminated shellfish causes paralytic shellfish poisoning (PSP).The PSP causes respiratory failure and death within 12 hours. Another toxin that accumulates in shellfish is brevetoxin, produced by the Dinoflagellates Karenia brevis (Isabella et al., 2006) Brevetoxin also causes respiratory irritations in humans especially in beach zones where many people engage themselves in recreational activities such surfing Karenia bloom produces toxicity that causes asthma –like breathing symptoms .These conditions are more experienced mainly along the Gulf coast of Florida..A toxin produced by the Dinoflagellates Dinophysis causes Diarrhetic shellfish poisoning (DSP), which results in digestive upset but which is not fatal. Ciguatera is another form of Dinoflagellates toxicity in tropical areas caused by eating fish contaminated by toxins of the Dinoflagellates Gambierdiscus toxicus.The Dinoflagellates Dinophysis species produces diarrheic shellfish poison (Kim et al., 2010).The effects of climate change are particularly noticeable in these shallow ecosystems whereby increased temperatures during the warm months warm enhances the reproduction of Dinoflagellates into large number that blooms resulting into red tides which pose ill health effects due to the production of toxins.(shah et al. ,2008)When these Dinoflagellates bloom, their toxins accumulates in clams, mussels and oysters that ingest them. Outbreaks of PSP in mussels and oysters caused by Alexandrium, Gymnodininium catenatum Graham and Pyrodinium bahamense (Satoshi et al., 2007)Urban and storm run-off often contains high concentrations of nutrients, oxygen consuming wastes, pathogens and toxic substances such as pesticides, heavy metals and oils are some of the causes of these blooms (Hossain et al., 2012).These enrichment of aquatic ecosystem such as the coastal waters may lead to eutrophication, which associated with sewage and /or sewage effluent discharge into the streams that feed aquaculture ponds.Variation in Dinoflagellates species distribution and abundance are mostly influenced by the changes in environmental conditions such as dissolved oxygen, salinity, nutrients and temperature (Vajravelu et al., 2017)Research studies have shown that salinity influence the growth potential and toxin production of harmful Dinoflagellates (Errera &Campbell,2012)However, many Dinoflagellates species are photosynthetic in that they occupy the starting point of the food chain of the aquatic environment helps in assessing the fisheries yield.This study aimed to improve on the understanding of environmental factors that control Dinoflagellates species that blooms causing red tides in order to be able make predictions  about the abundance ,seasonal dynamics and the potential hazards associated with the toxic algal blooms in the coastal waters of Kilifi creek ,north coast Kenya.2.1 Classification of Dinoflagellates speciesDinoflagellates exhibit a wide divergence in morphologically and size. They range in size from 1µm to >1mm.(Faust & Gulledge, 2013).The presence of the cell structure(theca) act as a major tool in differentiating them with other phytoplankton that causes algal blooms.(Faust & Gulledge, 2002).Cell, shape and surface ornamentation such as the presence of pores spines and ridges are the features that are mainly used in identification of Dinoflagellates species.(Faust & Gulledge,2002) Dinoflagellates have different cell type which is also as distinct feature in the process of identifying and classifying them. These cell type include the desmokont which has two dissimilar flagella inserted apically whereas dinokont has dissimilar flagella inserted ventrally (Faust & Gulludge, 2002)Some species of Dinoflagellates are armored in that they have the theca which is the outer covering cell structure and other species do not have the theca. This also can be used as a feature in identifying the different type of the Dinoflagellates species.2.2 Harmful algal blooms and its economic impactsRed tides are conditions when a Dinoflagellates population increases to such huge numbers that it discolors the water. This “bloom” may be caused by nutrient and hydrographic conditions, although the environmental conditions which result in red tides are not completely understood. For Dinoflagellates red tides, the water is discolored red or brown due to as high as 20 million cells per liter. (Isabella et al., 2006).Some red tides are luminescent; most in southern California create dramatic nighttime displays of bioluminescence in the wakes breaking on the beach. A synopsis of the putative mechanisms responsible for these red tides is kindly provided by Prof. Wolfgang Burger, a geologist and former Interim Director of SIO:They have been increasing in worldwide. The impacts of these blooms are felt in many ways ,for example ,marine life is greatly affected when exposed to the toxins whereby the top predators may end up dying affecting the trophic levels within the marine ecosystem.( Calabretti et al., 2017)In Florida, massive fish killing of up 100tonns due to toxins produced by the blooms have been estimated during active red tides.(Bibak & Hossein,2013)2.3 Ways to Control Harmful Algal BloomThe following are some of the mitigation measures that could be employed in controlling the spread of blooms in coastal waters.2.3.1 Mechanical ControlIn this method involves physical removal of algal cells from the water through filtration, skimming, Ultrasound and electrolysis (Bibak & Hosseini, 2013).Flocculation  method have been highly considered as one of the only HAB control method technologies  with a partially  successful  track record  in the marine environment(Bibak & Hosseini,2013).This method flocculation involves the treatment of blooms with flocculants  clays which scavage  particles ,including algal cells from sea water and carry them to  bottom sediments .In protection of recreational users of freshwaters temporally, pumping of surface algal scum from inshore areas has proven to be an effective mechanism (Bibak & Hossein, 2013).2.3.2 Chemical ControlThis method involves the use chemicals to kill or reduce the density of HABs cells. Copper sulfate, sterol surfactants, Sodium hypochlorite, magnesium hydroxide and others have been tried for control of HABs organisms (Bibak &Hosseini, 2013) Researchers observed that most chemicals tried have been too expensive and too non-specific causing damage to non target components of the marine ecosystem. Therefore, this method has been effective in treating blooms in drinking waters supplies and other enclosed systems. Ponds uses blue dyes to limit penetration of the wavelengths of light required for photosynthesis and thus reduce the growth of algae which results to algal blooms when reproduction is in large number.2.2.3 Biological ControlBiological control of algal blooms could include enhancement of existing predators, isolation of novel species and genetic engineering .Biological control organisms include species that feed, infect, or decompose HAB species (Bibak &Hosseini, 2013).Copepods and ciliates  can be used to graze on algae and Dinoflagellates  and some  viruses ,parasites  and bacteria that have a control mechanism tend to be abundant in marine ecosystem  which sometimes are host-specific  and have high  reproductive output.For example  Diatom is used to control  red tides  due to  Chanttonella red tides that occurs when diatoms are scarce  in surface water