Chapter 8 - Types of Aquatic Organisms

Abstract

This chapter provides an overview of several types of aquatic organisms (their survival, habitats, and taxonomic principles). Traditional taxonomic schemes distinguish organisms on the basis of their behavior, metabolic characteristics, and morphology. Recently, molecular techniques have been used for taxonomic purpose. Three major groups of organisms have been proposed at the broadest level of classification: the Eukarya (eukaryotes), the Bacteria, and the Archaea. Organisms can be classified by their mode of obtaining nutrition and by the habitat they inhabit in addition to their evolutionary relatedness. Organisms that use CO 2 as their primary carbon source are autotrophic; those that use organic carbon are heterotrophic. Autotrophic organisms include those that obtain energy from light (photoautotrophic) and chemicals (chemoautotrophic). Heterotrophic organisms include predators, detritivores, and organisms that live on dissolved organic compounds. Organisms can also be classified by their direct interactions (competition, mutualism, exploitation, commensalism, amensalism, and neutralism) with other organisms. Freshwater habitats contain representatives of most of the groups of organisms on Earth. Some of them may have evolved directly from marine ancestors and others that are secondarily aquatic may have evolved from terrestrial species.