algae

Easy way to track phytoplankton

U. WASHINGTON (US) — It’s now much easier to pinpoint biological hot spots in the world’s oceans where some inhabitants are smaller than, well, a pinpoint.

Researchers have built a device that can count and classify microscopic algae called phytoplankton that range in size from one to hundreds of microns—the smallest being 1/100th the size of a human hair.

But as tiny as they may be, communities of the phytoplankton south of Vancouver Island, British Columbia, are big players when it comes to carbon, taking up 50 percent of the carbon dioxide going from the atmosphere into the oceans there.

“We thought that had to be a mistake at first,” says Francois Ribalet, a postdoctoral researcher in oceanography at the University of Washington and lead author of a Proceedings of the National Academy of Sciences paper on the discovery.

Phytoplankton, like plants on land, take up carbon from carbon dioxide during photosynthesis to build cells. Phytoplankton anchor the oceanic food web so where one finds a lot of phytoplankton, one usually finds a healthy collection of fish and animals.

The colors red, orange and yellow indicate marine areas with abundant microscopic algae, some of which would have gone undiscovered using typical discrete sampling methods. The biological hotspot depicted in the North Pacific in this video, for instance, was between places the ship stopped to sample. It was revealed only because of new UW technology able to continuously sample and quickly analyze seawater while a ship is underway. (Credit: Francois Ribalet)

If not eaten, phytoplankton die and sink, carrying their carbon with them. Worldwide, ocean phytoplankton consume as much carbon dioxide as the Earth’s forests and land plants combined.

“Being able to readily detect and track blooms of these small-celled phytoplankton is critical for understanding their impact in the oceans and global carbon cycle,” Ribalet says.

SeaFlow, a device being developed by Jarred Swalwell, a research engineer, is making that task easier.

The instrument is a flow cytometer that measures the size and pigment composition of each single phytoplankton present in a sample at a rate of thousands of cells per second.

Typically biologists with traditional cytometers looked for phytoplankton using tablespoon-sized samples of water collected 10 to 50 miles or more from each other.

SeaFlow can sample seawater continuously, making it possible to analyze samples every three minutes or two samples per mile traveled, says Jarred Swalwell, an oceanography research engineer and the device’s lead developer.

That’s because the instrument taps into the system found on board most oceanographic research vessels that supplies running seawater to shipboard labs for keeping specimens alive.

SeaFlow collects more samples in a day than most scientists gather on an entire cruise, Swalwell says.

Its sensors and banks of computers sort the characteristics of phytoplankton communities to determine what’s present.

A prototype of the device revealed the biological hotspot off Vancouver Island and, for the first time, a marine ecotone, something oceanographers knew must exist but had no way to locate before now.

Ecotones are areas where different habitats overlap, where a prairie and forest meet, for example, or a river and estuary intersect.

They are rich with species because plants and animals from both ecosystems might be found there, as well as those adapted specifically to this hybrid environment.

The ecotone discovered by Ribalet and colleagues is a 40-mile-wide region where ocean water rich with nitrates meets coastal water rich with iron and where not just one, but five oceanic phytoplankton communities were detected taking full advantage of the carbon and nutrients concentrated there.

“This was just unexpected diversity,” Ribalet says. “It flies in the face of the textbooks.”

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