Ocean Watch

Monday, January 25, 1999

Plankton obscures
water but is basis
for ocean life

Recently, I took my visiting aunt on a submarine tour off Waikiki. As the sub moved through the blue water, we passed school after school of colorful fish, then spotted two green sea turtles.

"This is wonderful," my aunt said, pressing her face to the glass.

"It sure is," I answered, staring through my port. "Look at all this cool plankton."

She didn't know what I was talking about and when I pointed out the specks of marine life twirling in the water before us, she wasn't exactly thrilled.

She nodded politely, then turned her attention back to the bigger species.

OK, so plankton is hard to see and makes the water look cloudy.

But without plankton, there wouldn't be any other life in the ocean to look at.

Plankton is the term for all the tiny plants and animals that drift with ocean currents.

Most planktonic organisms are capable of some type of locomotion (which keeps them off the bottom) but they are too small to swim independently of currents.

The plants in plankton are the basis of all life in the ocean.

Like land plants, these one-celled marine plants make their own carbohydrates from sunlight and carbon dioxide.

Planktonic animals eat these microscopic plants, then become food for larger animals.

And so it goes up the food chain.

Most people already know the importance of plankton in maintaining the health of our oceans.

But here are some interesting facts about plankton you might not know:

The scarcity of plankton in Hawaii's surrounding ocean is responsible for the water's lovely blue color.

Because warm tropical waters bear far less plankton than cold water, blue light reflects directly off the water molecules.

However, in cold, nutrient-rich water, yellow light reflects off abundant plankton.

This combines with blue light from the water, making green- or gray-colored water.

Microscopic plants about 50 micrometers in size (about half the diameter of a human hair) make up from 50 to 80 percent of all organic matter in the ocean.

Crustaceans make up about 70 percent of animal plankton.

These creatures, which have stiff outer shells as skeletons, are sometimes called insects of the sea.

Some are microscopic; others are two or so inches long.

Among these large ones are krill, planktonic crustaceans that are eaten in great quantities by whales.

Planktonic snails called pteropoda (wing-footed) are found in dense swarms in most seas.

Instead of a foot, these snails have fins, allowing them to swim vertically.

To appreciate how hard it is for tiny pieces of plankton to remain suspended in the water, imagine a human swimming in fluid a million times more viscous than water.

The closest to this is thick molasses.

Plankton isn't always hard to see.

Once, while I walked on the south shore of New Zealand's South Island, a wave washed over my companion's boots.

When we looked down, the boots were wiggling with tiny creatures.

 

Even though plankton is sparse here, you can usually see pieces of it swirling through Hawaii waters.

It may not look as thrilling as reef fish or sea turtles, but it's the reason they're all there.