**1. Introduction**

Ecosystems on earth plays an important role in regulating climate and as well as a fundamental life-giving resource for human kind. Aquatic ecosystems are majority supported by photosynthetic organisms that fix carbon and produce oxygen, comprise the base of food web. Though, under sure circumstances, the abundance of various taxa reaches level that cause harm to humans and other organisms. These proliferations habitually are referred to as 'harmful algal blooms' (HABs), that includes a variety of species and consequences that humans perceive as adverse. HABs occur in all aquatic environments such as freshwater, brackish and marine and at all latitudes. We know in the nature algae are a normal part of the aquatic ecosystem, forming the actual base of the aquatic food web as they are large and very diverse group of organisms, the majorities are microscopic in size, except some macroscopic algae. Mainly the microscopic algae are most often as single cells, other than some can form chains and colonies. For the most part micro algae live in the water, whereas others live in or near to the sediment or attached on to some of surfaces for some time also for entire life cycle. Many of macro algae are also known as seaweeds they can be multicellular and complex. Algal blooms also acts as natural important component for many aquatic systems, generally spring blooms are triggered by some seasonal warming, increased availability of light and nutrient and

also water column stratification. These blooms are significant part for energy and material transport through the food web, as well plays an important role in the vertical flux of material out of the surface waters therefore these blooms are known to be prominent considering with those acknowledged as "harmful." These algae can form harmful algal blooms, when they assemble and grow in massive amounts damaging the ecosystem, or if the algal community shifts to species that makes some toxin compounds disrupting the normal food web and also harmful to human beings [1]. Problem of harmful algal bloom is wide and persistent, affecting numerous estuaries, coasts, and freshwaters system throughout the world, along with disturbing ecosystems, human health, social life style as well as dilemma for economy systems.
