The Food Chain Gang

The ocean is vital to our life. Very few people, particularly local fishermen, would argue with this statement. As humans, the ocean may not be our primary source of food, but it provides nourishment directly and indirectly to every living thing. In the ocean, nearly all life is dependent on plants, since it is plants, with help from the sun, that have the ability to convert water, carbon dioxide and nutrients into sugar, protein, and other sources of nutrition. Animals therefore are dependent on plants, since animals cannot harness nutrition through this process of photosynthesis. In simple terms, plants produce and animals consume. This is the fundamental concept of food chains. Most of us couldn't escape our first science class without learning about food chains. It's no wonder such importance is given to this process, since food chains form the basis of life in the sea and on land. A food chain is comprised of a series of organisms in which each participant is food for the next member of the series. The first link, or producers, in most marine food chains are plants, such as phytoplankton and diatoms. All subsequent links in the food chain are considered consumers. Each step along a food chain is known as a trophic level. The most basic trophic level is comprised of producers, plants and algae that make their own food.

Reef Brief is a weekly column published in the San Pedro Sun
In the ocean there is a multitude of food chains that overlap and intersect with each other, forming complex food webs. Most marine organisms eat a variety of foods so that if one link in a chain is depleted, alternate food sources can be consumed. All animals are considered consumers, with those consuming only plants called herbivores, and those consuming other animals called carnivores. Those organisms that digest the bodies of dead plants and animals, as well as the wastes of both, are known as decomposers. The abundant diversity of life in the sea has formed a delicately balanced network of predators and prey, all of which are dependent upon each other for survival. It's one thing to learn food chains from a textbook, and quite another thing to see how it works in nature. This was the case for me, when I studied the feeding behavior of Finback whales in Quebec, Canada. The Finback is one of the largest creatures in the world (reaching lengths of over 50 feet); thus I assumed that it had to feed on fairly large fish to obtain sufficient energy. It turns out, the Finback has a relatively short food chain involving only krill that feed on phytoplankton. In an impressive display of vigor, these whales leap out of the water, gulp large quantities of water and zooplankton (krill) and force water out through the baleen or food-catching brushes located in its mouth. Like most other whales, the Finback instinctively knows that more energy can be acquired by consuming huge amounts of these tiny and bountiful crustaceans than eating larger and less abundant fish. In other words, in the ocean, there are many small primary producers (krill), and as the food chain advances, there are progressively fewer larger organisms (fish), until at the end of the chain, there are only a very few extra large top consumers (whales).Thus, all marine organisms are involved in one or more food chain, transferring energy from the smallest of organisms to the largest. And all animals, even whales, are ultimately dependent on sunlight and photosynthesis for survival.

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