"ZONATION AND DISTRIBUTION PART II"
nutrients:-organic molecules that help organisms grow
Once your map is complete, it will become apparent that most of the marine life is concentrated nearshore. Although some very large animals live in the oceanic zone, their numbers are small in comparison to the size of it. Ask the students to describe the trend they see.
This trend is due mainly to the abundance of light and nutrients in the coastal zone. It is much shallower than the oceanic zone, sunlight penetrates all the way to the ocean floor. This is important because phytoplankton, which are at the bottom of almost all food chains, require this light for photosynthesis. In photosynthesis, sunlight is captured by the plant and the energy particles in sunlight (photons) are used to drive a chemical reaction that produces sugar. This sugar is the food for the plant. Why don't we see an abundance of life in the upper layers of the oceanic zone also? Because light is not the only important factor. Phytoplankton also require inorganic and organic nutrients like iron and nitrogen. These compounds are most abundant nearshore, because of runoff from the land. Without these nutrients, phytoplankton do not grow as well.
As we said above, phytoplankton are at the bottom of the food chain. This means that herbivores eat them, other animals eat the herbivores, and so on. The more phytoplankton that are available, the more herbivores there will be to eat them, and the more herbivores there are, the more carnivores to eat them. Ultimately, if there are lots of phytoplankton, there will be lots of organisms else too.
Because phytoplankton are so important, scientists have lots of ways of measuring their abundance. One fairly new method uses images of the ocean taken from satellites in space. Satellites take a picture of the ocean and send it back to earth electronically, like a television signal. These satellites have sensors in them that can detect the specific pigments that phytoplankton use for photosynthesis (the most common pigment is chlorophyll). They then convert the concentration of these pigments into a color. When a scientist looks at a satellite image of the ocean, he or she can tell how much phytoplankton is in the water by the color. Red usually means a lot of phytoplankton and blue/purple means very few phytoplankton. These colors are of course not the actual color of the phytoplankton, but instead are a "false color" used to relay information.