Helen of Troy

INTRODUCTION

Algae are widely present in freshwater environments, such as lakes and rivers, where they are typically present as microorganisms visible only with the aid of light microscope. Although relatively inconspicuous, they have a major importance in the freshwater environment, both in terms of fundamental ecology and in relation to human use of natural resources (Bellinger and Sigee, 2010).

Phytoplanktons are a key food item for aquaculture because this industry utilizes phytoplankton for the feeding of the animals being farmed. In mariculture, the phytoplankton is naturally occurring and is introduced into enclosures with the normal circulation of seawater. In aquaculture, the plankton can be either be collected from a body of water or cultured, through the former method is seldom used. Phytoplankton is used as a food stock for the production of rotifers, which are in turn used to feed other organisms. Phytoplankton is also used to feed many varieties of molluscs including pearl oysters, and giant clams (Conte and Cubbage, 2001).

Phytoplankton population in a pond is usually comprised of numerous species of microscopic plants that live in horizontal band or zone near the water surface. The densest population is usually located in a horizontal band extending from about two to three inches below the surface to a depth of 18 to 20 inches. The depth of the band depends on numerous factors including pond turbidity, light penetration and available plant nutrients (Conte and Cubbage, 2001).

The clarity of a pond depends on the presence or absence of suspended materials such as microscopic clay particles and phytoplankton. In the absence of this a pond will appear almost crystal clear. When the algal species in the phytoplankton community reproduce, the phytoplankton will reach a density that can be characterized as a slight cloudiness or turbidity in the water. What is being observed is not the individual algal cells, but light reflecting off millions of microscopic, single- and multiple celled microscopic plants when the phytoplankton can be observed it is called an algal loom often, the phytoplankton population can become so dense that it will produce a deep opaque color at the pond surface (Conte and Cubbage, 2001).