AT THE SMITHSONIAN

Phytoplankton: The “Biggest” Little Guys in the Ocean

February 8, 2010

When we recently heard about a "huge" find made by Sharyn Hedrick, a phytoplankton taxonomist at the Smithsonian Environmental Research Center (SERC) in Edgewater, Maryland, we wanted to see it—except, we couldn't. The phytoplankton, Amphisolenia quadrisipina, that turned up in Hedrick's lab, while really large by phyto standards, was only about 600 to 700 microns: just smaller than the tip of a needle.

Curious about what exactly these microscopic creatures do for the ocean, I recently spoke with Hedrick.

Tell me more about the type of phytoplankton, Amphisolenia quadrispina, you saw in samples sent from the Bay of Bengal. Why was it so different for you?

It was originally identified in 1907. . . and again in 1933. . ., but this is the first time I actually saw it in one of my samples. For a taxonomist its like hitting the Lotto. I’ve looked at samples from the coastal areas of Belize and Florida for over 20 years and never run across one. I believe they are rare; at least on the western side of the Atlantic. It is prolific in that area, I can tell you that. I don’t know who eats it, but it must be very large, I would say

When the average person thinks about marine life, phytoplankton probably aren’t the first thing that comes to mind. But they produce a good amount of the earth's oxygen—about half of the total amount produced by all plant life. Could you explain what they are, and what role they play in the ocean?

Phyto is a Greek word that means plant. So the phytoplankton group comprises all of the plant-like microscopic organisms in the water. If the planet was completely dissolved of phytoplankton, nothing in the river, or in the bay, or in the ocean would survive because these guys are the basis of the food chain. They’re eaten by all kinds of things, actually, but in the Chesapeake Bay area, they’re usually eaten by zooplankton, which are considered animals, and then by larvae to fish and larvae to crabs. Phytoplankton are what they survive on, and those things work their way up on the food chain until we end up having them on our plate. There are thousands of species, freshwater, brackish and salt water species, and each one is different even if only slightly. Diatoms, for instance, can’t propel themselves, so they’re at the whim of the tide current and the wind and they can’t do anything but go with the tide. Dinoflagellates have flagellas, which help them go in any direction they want. Through photosynthesis, phytoplankton also take carbon dioxide out of the water and release oxygen as a by-product. That’s a big job for them.

Can phytoplankton be dangerous?

Sometimes. People are generally familiar with water that turns green from large mats of stringy, slimy goo. That is caused usually by Spirogyra or Ulothrix phytoplankton in freshwater ponds, which can go from farm pond to farm pond on the feet of birds and geese. They are also with red tides or mahogany tides. This is caused by several different species depending on the area. That’s just the color of the chlorophyll that that species have. When I go out on the water everyone here can tell you I’m a fanatic with colors on the water and what kind of phytoplankton they mean. They think I’m nuts, but I’m usually right.

Here on the Chesapeake our main culprit is Prorocentrum minimum. It is a dinoflagellate. It's hazardous when the population reaches a non-sustainable level and starts to die off because the cells sink to the bottom, leaving oxygen-depleted waters, which in turn kill off fish. In some parts of the world this species is reported to have a poison that they excrete to kill off fish. There are only a handful of dino species that excrete poisons that affect people. A few years ago there was a large bloom of Dinophysis acuminata on the lower Potomac River that caused shellfish poisoning in people. The shellfish beds were shut down until the bloom was over. So these blooms can hurt the economy, too.

You studied marine biology at Bridgewater State College in Massachusetts. How did you become interested in phytoplankton?

I lived on Cape Cod while I was going to school at Bridgewater State College and one morning I got up and the news on the local Cape Cod station said there were 34 whales stranded down in Wellfleet, off the coast of Cape Cod, not very far from where I lived. So I called my professor and he called a couple of other people and we got permission to come down and see what we could do for the whales. But by the time we got down there they had already been euthanized. They landed in an marsh and there was no way they would let a backhoe in to move them. So, our job was to cut up the whales and let the pieces be carried out to the Bay, which was really so very tragic.

I was later curious about what the pieces of whale meat that were left in the tidal pond would do, and what kind of nutrients they would add. I got permission to go into the marsh and do a study in there. I worked in there a couple of months collecting samples and right away, as soon as I started looking at the samples, I realized, “Oh my God. There are all these diatoms in here, these are fantastic!” And my natural history professor gave me a book about them. I spent the next six months identifying phytoplankton, and that in turn got me my first job as a phytoplankton taxonomist: I went to work for the Philadelphia Academy of Natural Sciences. All because of those whales.

You have two short non-fiction stories published. One is called “Potheads,” about the stranding of the Pilot whales in Wellfleet on Cape Cod, where you first “fell in love” with diatoms. What’s the story behind the title?

That’s what those whales are called; that’s the common name. They have this huge melon on their head. If you look at a humpback whale they’re very smooth—they’re bumpy with knobs and barnacles, but there’s no shape to the head. It’s very flat. Potheads like the Pilot whales are different. If you can picture a cartoon whale, they have a big head and they stand there and smile. Potheads are just like that. They have a huge head and it's called a melon right on top, and supposedly it helps them with sonar and helps them navigate where they’re going. The name goes back to whaling days, they were named potheads a long time ago, long before the pilot whales came along.