Biomass Pyramids of Organisms in the Ocean

Written by ethan shaw
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Biomass Pyramids of Organisms in the Ocean
Krill are zooplankton that are among the most abundant of ocean organisms. (Hemera Technologies/ Images)

A biomass pyramid is a model used to illustrate the transfer of energy through the rungs of a particular food web, also called trophic levels, by estimating the mass of organisms at each one. Nearly all life on the planet is powered directly by energy from the sun, though certain ecosystems in the deepest depths of the ocean harness hydrothermal energy in the absence of sunlight. Primary producers make up the bottom of the pyramid, being organisms that directly translate solar energy into forms usable to other living things. In the ocean, the "pyramid" isn't always that shape, given the large numbers of tiny creatures that consume the primary producers. However, in general, the available energy decreases up the system, limiting the numbers of higher-level organisms.

Bottom Foundation

In most parts of the ocean, the foundation of the biomass pyramid consists of photosynthetic organisms. These include the immensely numerous and diverse hordes of phytoplankton, which include microscopic algae and bacteria that engage in photosynthesis. Other examples of photosynthetic organisms at the bottom of the trophic system include seaweeds, which are not plants at all but algae.

Zooplankton and Others

The primary consumers of phytoplankton are zooplankton, which are animals that include a large number of organisms. Some are simple, single-celled organisms, but the zooplankton category also includes multi-celled creatures such as jellyfish. Larvae and juveniles of numerous larger marine organisms, including many fish, function as zooplankton before maturing into bigger forms with different food preferences. Many, like krill, can be staggeringly abundant. Certain mollusks and other invertebrates also feed directly on algae and other bottom-rang organisms through grazing and filter-feeding.

Middle Ranks

An array of animals consumes zooplankton, from tiny squid to enormous fish, in the form of giant filter-feeders such as basking sharks and baleen whales. Those huge filter-feeders can simplify a biomass pyramid, circumventing many middle rungs of secondary consumers. But along many other ecological routes, progressively larger organisms hunt other consumers of zooplankton, and thus up the rungs of the food chain and the biomass pyramid. An example is the 6-foot Humboldt squid, a formidable cephalopod of the eastern Pacific Ocean. These voracious hunters may travel in schools of better than a thousand animals, targeting smaller prey like fishes and other squid.

Biomass Pyramids of Organisms in the Ocean
Many larger marine organisms prey on others in the same trophic level. (Jupiterimages/ Images)

Top Ranks

The largest and generally rarest of the members of the oceanic biomass pyramid are the top predators, which from an energy standpoint, get a highly inefficient remainder of the solar power originally captured by phytoplankton. These include creatures such as the orca, a big, social dolphin that feeds on everything from tuna to baleen whales; large predatory sharks such as such as the great white; tiger and Pacific sleeper sharks; and sperm whales, which dive to great depths to hunt massive squid.

Biomass Pyramids of Organisms in the Ocean
The great white shark is an example of an apex, or top-level, predator in the oceans. (Comstock Images/Comstock/Getty Images)

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