This week, I want to talk about krill. Kodiak Island is known for its big animals. We have the largest brown bear, the largest Sitka black-tailed deer, one of the largest red fox subspecies, the largest halibut, and the largest whales, just to name a few examples, but in this post, I’ll discuss some of the most diminutive but extremely important animal species in our marine environment. That’s right, I’m talking about those tiny little zooplankton in the ocean.
Okay, you are yawning, but please keep reading. Euphausiid species, more commonly known as krill, are the food for everything from adult herring and Pollock to marine birds to blue and fin whales, the largest animals on earth; and perhaps more importantly, they are on the menu for the juveniles of most species of fish in the ocean.
I guess if I really wanted to start at the base of the food chain, I’d write about phytoplankton, but to be honest, phytoplankton species, important as they are, even make me yawn. I find zooplankton, and especially krill, much more interesting, because I can see these organisms swimming in the water, and I sometimes see piles of their dead bodies when they wash up on the beach. Unfortunately, I have no photos to show you, and I’m not artistic enough to draw a sketch, but picture a very small shrimp. Unlike shrimp, though, the gills of krill are exposed and hang below the carapace, and the exoskeletons are translucent, allowing a view of the internal organs.
Krill reproduce and grow in response to blooms of phytoplankton and warming water temperatures. When phytoplankton bloom in the spring, producing a food supply, euphausiids populations swell in response, subsequently providing food for nearly everything else in the ocean environment. We see schools of herring consuming krill, and sea gulls and other marine birds frantically diving into the ocean to pluck out the small organisms. Since krill are heavier than water, they must continually swim to keep from sinking. They form dense swarms that may look like balls or extensive layers that may be several meters thick. Baleen whales focus on these swarms, often gulping several hundred kilograms of krill at a time.
I’m sure you get the idea that krill, as well as other zooplankton, are a vital food source, either directly or indirectly, for most animals in the marine environment. Here on Kodiak, I think of krill as a sign of spring, because when their populations swell, the ocean is suddenly alive with the activity of diving birds, huge schools of herring, and whales spouting. Euphausiids, though, are very sensitive to changing environmental conditions, and if their populations fail, the rest of the marine ecosystem could, and undoubtedly would, follow. Small and unexciting as they may be, we need to understand zooplankton population structures and their physical and chemical needs and monitor the health of these populations in our oceans.
Without phytoplankton and zooplankton, the oceans would just be water. Those tiny organisms don’t seem as boring anymore, do they?