KODIAK — Kodiak is in summer mode; salmon fishing is at its height, tourists are swarming town, there is a constant background sound track of lawn mowers, outboards and children playing, and the roads are dusty. Some people love and enjoy every moment of it while others complain about too much heat and too much watering the gardens. Just as people are divided on the pro’s and con’s of summer heat, so are the life forms in the ocean.
As you may remember from previous amazing nature columns, I am a plankton ecologist by training, even though that is not what I spend a lot of time doing anymore. However, sometimes I take the good old plankton net out on a boat and peek at the treasures it brings to the surface. Here are the many small organisms that make up the community of floaters and drifters. These form the food base for all the filter feeders and all the plankton feeders including the smelt, capelin, candle fishes and herring. Forage fish in turn are the bread and butter for anything enjoying Kodiak waters from king salmon over seals, sea lions and numerous sea birds to the whales. But there is something else in the plankton, which feeds on other plankton animals and gives my sample a gooey consistency: lots of jellies.
“Jellyfish may benefit from a warming ocean with fewer species that compete for food. While jellyfish have absolutely no brains, they are likely to outlast much more evolved and more intelligent life forms on this planet.” I wrote this eight years ago, when I chose jellyfish as the topic for this column for the first time. That was before I went to the National Marine Educators Association conference, at which I witnessed a group of Marine Science Educators spent a lot of time discussing that it confuses children if we call jellies jellyfish, because they are biologically very different from fish. Personally, I found this an insult to the bright minds of children, who in my experience are plenty capable of telling the difference between a jelly and a fish, whether the name has fish in it or not. However, I did adopt the recommended terminology of sea stars instead of starfish, so I guess I should also say sea jellies instead of jellyfish.
Sea jellies are a diverse group of animals called the cnidaria. All cnidaria have cnidocysts, cells with the capacity to produce and fire a poison. However, the vast majority of these poisons are so benign that humans don’t even feel them and only in a few cases are they strong enough to sting, as in the case of the lion’s mane jelly in Alaska. In the most extreme case the poison can kill, as in the infamous box jelly in Australia, which holds the record for possessing the most poisonous venom in the animal kingdom.
The over 11,000 species of cnidaria are divided into classes. Among these are the sea anemones, the hydrozoa and scyphozoa, which are what you think of as jellyfish, the cubozoa, which are the Australian box jellies, and some other, less common forms. The most conspicuous jelly in Kodiak waters is the lion’s mane, which is usually bright orange to red in the middle, but can be blue as well. If you have ever had the pleasure to have these jellies dropping out of a salmon net that is coming over the side on top of you, or picked their slimy tentacles out of its meshes, your fascination has probably most understandably turned into a loathing. Pretty when in the water, these jellies can give people a nasty rash that hurts and itches for days. The stinging cells can still fire when the jelly is dead or the tentacles torn off. In the same class of scyphozoans are also the moon jellies, transparent, saucer sized jellies with a white or orange four petal flower pattern inside. The moon jelly is harmless, its sting too benign for people to feel.
Both, lions mane and moon jellies have a most fascinating life cycle, in which subsequent generations have entirely different body shapes: Imagine your children looked like trees, and from their branches dropped babies that grow up into people, only to then have sex and give birth to trees. It sounds very weird, and so it is. The moon jellies in the ocean are male when the four-petal structure inside is white and female when it is orange. In late summer all the jellies somehow manage to form aggregations called a “smack”. There is a school of fish, a pod of whales, a gaggle of geese, a murder of crows and a smack of jellies. When the time is up, the males release sperm and the females release their eggs into the water. The rest is up to chance; only those eggs that encounter viable sperm will proceed to grow into larvae, which float in the plankton for a while before they find a suitable area and settle. Out of this larva grows a small polyp, which in time releases tiny jellyfish budded from its body. These little jellies grow bigger and develop gonads and the cycle starts again.
In my plankton sample, however, are many much smaller, delicate jellies, most of them only half an inch to two inches in size. These are in the class of hydrozoa. They also have the generational bimorphism, which is what scientists call that switch between two different shapes. Think of it this way: in one class the jellies are the dominant life form and they grow big and travel far, in the other group the polyp is the dominant life form and lives for a long time, but the jellies are small and delicate. To tell which class a jelly belongs to you have to look closely: If you imagine the jelly as an invert bowl, you need to look at the lip of the bowl. If there is a little ledge protruding inward like in a sugar bowl that has a lid or in the lid of a teapot, then it’s a hydrozoan, if that ledge is missing, it is a scyphozoan and will probably get bigger.
Later in the summer you will also be seeing little transparent gooseberries in the water. Take some time and look at these or better yet, get a glass with some seawater and then shine a black light on them. You will see rows of lamellae beating and reflecting the light in iridescent rainbow colors, and trailing long tentacles. Gooseberries are not in the phylum cnidaria and have no stinging cells at all; they are comb jellies. If you ask me “what they are for” (a question I get curiously often), let’s just say they are for beauty, for diversity and for being amazed by nature.
Switgard Duesterloh runs the Ocean Science Discovery Program, which invites school classes to hands-on place based Marine Science learning units. She is in the process of expanding the program to include more opportunities for summer learning experiences for kids, youth, families and adult travelers. For more info or to contact her about Amazing Nature email firstname.lastname@example.org.