1 – The oceans

Publisher Summary Ecology is the study of relationships between organisms, and their surroundings. This study is fundamental to an understanding of biology because organisms cannot live as isolated units. The activities which comprise their lives are dependent upon, and closely controlled by, their external circumstances, by the physical and chemical conditions in which they live, and the populations of other organisms with which they interact. All life on earth constitutes a single ecosystem divisible into innumerable parts. This chapter is concerned with the marine ecosystem, occupying a larger volume of the biosphere. Living processes involve energy exchanges. Energy for life is drawn primarily from solar radiation, transformed into the chemical energy of organic compounds by the photosynthetic processes of plants. Seawater covers approximately 71% of the earth's surface, an area of about 361 million square kilometers. The major currents of the oceans are caused by the combined effects of wind action, and barometric pressures on the surface, and density differences between different parts of the sea. In an aquatic environment very simple and fragile forms of life can exist because the water affords them support, flotation, transport, and protection thereby permitting very simple reproductive processes, and minimizing the need for structural complications, such as locomotors organs, skeletons or protective coverings. There are broadly two ways in which organisms live in the sea—they float or swim in the water, or they dwell on or within the sea bottom. Correspondingly the two major divisions of the environment are the Pelagic and the Benthic. The Pelagic Division comprises the entire water body forming the seas and oceans. The sea bottom and the seashore together make up the Benthic Division which comprises three major zones, the Littoral, the Sublittoral and the Deep Sea Zones.