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find out what do the terms 'algal bloom' and red-tides signify ?

Blooms are commonly called red tides, but scientists prefer the term "harmful algal blooms" (or HABs). The term red tide erroneously includes many blooms that discolor the water but cause no harm, and also excludes blooms of highly toxic cells that cause problems at low (and essentially invisible) cell concentrations. Therefore, harmful algal bloom is a more appropriate descriptor. Among the thousands of species of microscopic algae at the base of the marine food chain are a few dozen which produce potent toxins.  These species make their presence known in many ways, ranging from massive "red tides" or blooms of cells that appear to discolor the water, to dilute, inconspicuous concentrations of cells noticed only because of the harm caused by their highly potent toxins. Blooms of non-toxic micro- and macroalgae (seaweeds) also cause harm due either to indirect effects of biomass accumulation (such as anoxia or habitat alteration) or to physical features (such as spines which lodge in fish gill tissue).

HABs have one unique feature in common – they cause harm, due either to their production of toxins or to the manner in which the cells’ physical structure or accumulated biomass affect co-occurring organisms and alter food-web dynamics.


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