Angels in the plankton
One of my fondest memories in while submerged in waters of the Northwest was an encounter with an angel. I was snorkeling around San Juan Island when I shifted my focus from the awesome seaweed and invertebrate life on the rocky outcrop, to the plankton mere inches in front of my face. There floated one of the loveliest and most graceful creatures I had ever encountered (it would be a few years yet before I cast eyes upon my wife). The sea angel (Clione limacina) gets up to 3″ long, though the one I shared the water with was smaller. During late winter, sea angels populations can explode in the plankton, though chance encounters can happen any time.
It seems I’m not the only one smitten with Clione. It has apparently reached cult status in Japan where sea angel figurines have even been packaged and sold with beer.
Of course, Clione‘s not the only angel in the plankton. Sea angels actually like to eat sea butterflies (Limnacina helicina). In fact, the sea angel’s species name is the same as the sea butterfly genus (limnacina). This is one of the many cases where taxonomists (people who identify things) name name creatures in a way that tells us something about them or their relationship to their environment.
Like the sea angels, sea butterflies are also planktonic gastropods, though in the case of butterflies you can actually see the shell through their clear tissue. Their wings (a snails foot that has evolved into two large parapodia [translation: near foot]) can beat rapidly, and since they have to compensate for the added weight of their shell, their wings have to keep busy when they’re close to the surface. They are minute fishermen (only 1/2″ long),
stringing up mucus nets 4 times their size to capture tiny copepods and other microscopic plankton. When the net is full, they reel it in, gobble it up and spit out a new one.
While on the Bremerton Marina docks recently, I was able to get a few blurry shots of a winged sea slug (Gastropteron pacificum). It only reaches half the size (1.5″) of a large sea angel, but is such a pleasure to watch swim. It’s opaque, darker color and graceful swimming make it easier to spot from the surface than a sea angel. When not swimming, it often curls up on the bottom to rest.
All these species are not directly related, though they’ve evolved away from their snail, sea slug (nudibranch), limpet, and chiton cousins. They have left the sea floor to take advantage of the bounty of the plankton. Here’s to the angels in our lives! JEff
Jeff Adams is a Washington Sea Grant Marine Water Quality Specialist, affiliated with the University of Washington’s College of the Ocean and Fishery Sciences and based in Bremerton. You can follow his Sea-life blog, email to jaws@uw.edu or call at 360-337-4619.
