"ZONATION AND DISTRIBUTION PART I"
zonation-describes the different zones or areas of the marine environment
To describe relationships in the marine environment, we must be able to define where different groups of organisms live in the ocean. Marine ecologists have divided the ocean into two major zones: the pelagic zone includes all the waters of the ocean, and the benthic zone includes the ocean bottom. The pelagic zone is further divided into the littoral, neritic, and oceanic zones. The littoral zone includes the supratidal zone (or spray zone). The littoral zone also includes the intertidal zone, which occurs between the highest and lowest tides in an area. The final area of the littoral zone is the subtidal zone, which is always covered by seawater, and extends into the neritic zone. The neritic zone is the nearshore ocean environment, that which occurs above the continental shelf and is often called the coastal waters. The oceanic zone, by far the most extensive, is all the rest of the ocean beyond the continental shelf. The benthic zone extends from the intertidal, to the continental shelf, to the continental slope, to the deep ocean floor. The material that covers the ocean floor can range from mud or silt to large rocks.
Life in the ocean is not evenly distributed. Organisms are much more abundant is nearshore waters than in oceanic waters. Scientists often use the term biomass to indicate the total mass of all organisms in an area. Biomass is usually given as grams/m2 or grams/m3. Although the oceanic zone comprises 90% of the ocean's area, the neritic zone has ~ 40 times more biomass than the oceanic zone. The greater abundance of biomass in coastal areas is due primarily to the abundance of phytoplankton in this zone. Phytoplankton are the basis of most food chains in the ocean; they are at the "bottom" of the food chain. Phytoplankton are more abundant closer to shore because there are more nutrients (inorganic molecules needed to survive) here. Most organisms live closer to shore because this is where most of the food is.
II. Organisms in Groups
Ecologists may study the interaction of one individual organism with its environment, but more often, they study the interactions within groups of organisms. Groups of organisms are organized into distinct levels:
Using the butcher paper and large markers, make a map of the ocean floor like the one shown in Figure 1. Make sure that the map is large enough to paste many 3"x5" pictures of marine organisms about onto it. Discuss the major zones of the ocean and label them on your map. Hang your giant map at the front of the classroom.
Hand out the organism cards to the students (2 per student for a class of 25). On the back of each card is a brief description of the animal and its habitat. Have each student come up to the front of the class and tape their organism onto the appropriate area of the map.