Ever wonder why the murky, green waters of the northern latitudes are different than clear, blue waters of the tropics?

The murky green waters of Boston Harbor contain lots of life!

Or why New England had such large cod populations when the colonists arrived? Or why coral comes in so many beautiful colors?

Vibrant colors of a tropical reef

One reason: plankton! Well... so if plankton is such a big deal, why doesn't the Aquarium have a plankton tank? Well, one could argue that we do. Every tank in the aquarium is interconnected with plankton.

What are plankton? 
Like the term “cat,” plankton is an umbrella term used to describe a diverse set of organisms. The name plankton is derived from the Greek word planktos, meaning wanderer or drifter. Any creature carried by the ocean currents is considered plankton, from microscopic bacteria and algae to gelatinous siphonophores that grow in colonies longer than a blue whale.

Phytoplankton like diatoms, dinoflagellates, and coccolithophores are photosynthetic. They not only provide the base of the ocean food web, they also provide up to half of the oxygen that we rely on to breathe on land! But not all plankton photosynthesizes. Zooplankton feed on other organisms. Some plankton, called holoplankton, spend their whole life at the whim of ocean currents. These creatures
include copepods, brine shrimp, and sea jellies. Other plankton, called meroplankton, grow out of their drifting phase and embrace a more benthic or pelagic form. Lobsters, crabs, urchins, sea stars, barnacles and many fish all start their life as plankton!

Plankton…. They’re Kinda a Big Deal 
Phytoplankton are the base of the food web. These organisms convert the sun’s energy, along with carbon dioxide and water, into chemical energy and oxygen through photosynthesis. Because they are the first link between the sun’s energy and the rest of the food web, they are referred to as “primary producers”. This chemical energy, in the form of carbohydrates, is the fuel that helps to power the rest of the food web.

A right whale skim feeds on copepods. Watch video of a right whale feeding in Cape Cod Bay!

As the major primary producer of marine environments, phytoplankton provides the fuel for the rest of the system. Though some of the food webs they fuel are complex, some of them are relatively simple! One such food connection can be found right off the coast of New England. Phytoplankton feeds zooplankton, which feeds whales. From one of the smallest organisms to the biggest in only two
steps!

That water off New England is also very different from the sparkling turquoise waters you might see in the tropics—because of plankton. You see, the cold, nutrient rich water travels up to the surface of the ocean and hits sunlight, sparking a bloom of phytoplankton. The nutrients and blooms cause the waters here to appear murky and green. Tropical waters, however, have very few nutrients and thus phytoplankton blooms can’t occur. Without the phytoplankton and nutrients, the water is super clear. This abundance of phytoplankton supports the food web that is responsible for the iconic fisheries of New England. (Check out some of the tiny planktonic animals that appear in Boston Harbor!)

Cod is a cold water fish with iconic status in this region

Corals, along with some other marine animals like upside-down jellies and giant clams, rely on photosynthetic organisms most commonly referred to as zooxanthellae. Zooxanthellae help create food for their host. The zooxanthellae, mostly planktonic dinoflagellates (see the sketch above), are ingested by the host, encased in a membrane to protect then and then they go to work. The carbohydrates they create fuel the corals (and give them beautiful colors) while the zooxanthellae get a home and needed nutrients. Everybody wins!
So from the cool dark depths of our Gulf of Maine exhibits to the sparkling Giant Ocean Tank, these marine ecosystems are teeming with life that can all be traced back to the humble plankton. Keep that in mind the next time you visit the Aquarium and see our 600-lb fur seal lounging on the deck! (Pick up your timed ticket and print at home and you'll breeze right into the Aquarium!)

This post comes to us from Aquarium educator Kim McCabe.