ABSTRACT
The oceans and estuaries of the world support an enormous number of organisms, ranging from the smallest microbes to the largest mammals. This chapter focuses on the major taxonomic groups of organisms living in estuarine and marine environments. It examines the physical, chemical, and biological factors affecting the abundance, distribution, and diversity of the organisms. Viruses are obligate parasites that infect marine organisms contributing to widespread disease and mortality. Viruses can have significant impact on microbial food webs and ecosystem processes in the marine environment. The depth to the anaerobic zone in seafloor sediments is a function of physical–chemical properties and biological processes occurring in the water column and sediments. Physical, chemical, and biological factors influence the functional morphology, behavior, and distribution of benthic fauna. Organisms inhabiting estuaries must adapt to a highly fluctuating environment where perturbations in physical, chemical, and biological conditions are great.
