Marine food web structures differ greatly from those on land; plankton build up organic matter through photosynthesis that is consumed by secondary consumers, tiny crustaceans called copepods. These are then consumed by tiny juvenile fish or other small pelagic fish, and there are still a few small fish steps before it ends up in a big tuna or a large shark. This is important because in each conversion, when one organism consumes another, about 90 percent of the biomass gets lost simply by respiration and metabolism of the organisms, so that the amount of biomass that goes into a fish population is very much reduced by a long food chain. Coastal marine systems are more productive than open ocean systems because there is a threefold input into the food chain because in addition to plankton, there are plants that grow on rock-like algae and unicellular algae, as well as shorter food chains.
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