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A Blue View: From the Bottom of the Food Chain

by John Racanelli, Chief Executive Officer

Published January 16, 2014

A Blue View is a weekly perspective on the life aquatic, hosted by National Aquarium CEO John Racanelli.

From the smallest plants and animals invisible to the human eye to entire ecosystems, every living thing depends on and is intricately linked by water.

Tune in to 88.1 WYPR every Tuesday at 5:45 p.m. as John brings to the surface important issues and fascinating discoveries making waves in the world today.

January 16, 2014: From the Bottom of the Food Chain

Click here to listen to John discuss the importance of plankton in the ocean's complex food chain!

The ocean food web is much more than the dramatic clash of sharks devouring marine mammals and large fish. While many of us know that the ocean food web is complex, it’s easy to focus on the apex predators at the top. But the view from the bottom up is an essential component in understanding the ocean and all of its inhabitants. Microscopic drifting organisms, called plankton, serve as the foundation upon which the ocean’s entire food web is built.

The very definition of these tiny drifters is formed from the Greek word planktos, meaning “wanderer.” And that’s exactly what these tremendously important animals and plants do, touching all the creatures of the sea as they flow along its ever-changing currents.

Plankton include both phytoplankton and zooplankton. Phytoplankton are tiny microscopic cells that include bacteria, plants, and algae found near the surface of the water where photosynthesis occurs. A single drop of water contains thousands of phytoplankton.

Crab Megalopa Larva Audubon Magazine

This is a crab megalopa larva (magnification x 40). Image via Audubon Magazine.

Not all zooplankton is tiny. After all, jellies are a type of zooplankton. But most zooplankton are microscopic, including the tiny larvae of crabs, jellyfish, corals, and worms as well as adult animals like tiny shrimps, copepods and krill. To understand the size of these small zooplankton, consider this analogy: to fill a coffee cup, it would take a quarter of a million copepods, small crustaceans that are the most common zooplankton in the ocean. A single gallon of water from the Chesapeake Bay can contain half a million zooplankton.

Zooplankton eat phytoplankton, and are themselves eaten by small fish and a few large species like the whale shark and baleen whales. Small plankton-eaters are, in turn, eaten by larger fish, and so on until you get to the apex predators: large squids, fish, marine mammals, and, yes, the voracious human species.

All levels of the food chain are critical to ensuring a healthy balance in the oceans, but as we grapple with issues related to sea level rise and ocean acidification, scientists are studying what these changes will mean for the base of this complex web—the consequences of which will affect literally every marine species in the world.

Sea Angel Audubon Magazine

These juvenile "sea angels" (magnification x 20) are only 5 millimeters long. Image via Audubon Magazine.

One very important ecosystem service that plankton provide: they produce as much as 70 percent of the world’s oxygen as a byproduct of photosynthesis, an essential function that impacts the very air we breathe. Ocean scientist and explorer Sylvia Earle estimates that one family alone—Prochlorococcus—is perhaps the most abundant photosynthetic organism in the world and provides the oxygen for one in every five breaths we take.

This is even more incredible when one considers that all of this activity is happening in just the upper layer of the ocean, the epipelagic zone, where sunlight can reach. Though this zone is just a drop in the overall makeup of the ocean, what plankton do there reverberates from the deepest parts of the ocean to the upper atmosphere.

Plankton are not normally visible, except when huge blooms show up as blue/green swirls of color when viewed from above. Scientists are able to monitor the distribution of phytoplankton from space by analyzing the reflected light from the water’s surface. The Climate, Ocean, and Sea Ice Modeling team at Los Alamos National Laboratory is at the forefront of the development of these computer simulations. This group is focused on understanding how global climate change may impact the world’s phytoplankton population.

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