A couple of weeks ago, Glen and I went to the San Juan Islands in the Salish Sea of Washington state for a week long Marine Naturalist Training Program, offered by the Friday Harbor Whale Museum. This was something of a departure for us, Glen especially: he describes himself as a terrestrial naturalist. This was also challenging because our class was full of people madly in love with whales, and not much else. I can understand that: whales were my gateway drug into learning about the natural world. But over 30+ years as an amateur naturalist, I’ve learned a few things. One is that whale sightings are few and far between, so it behooves us to keep our eyes open for whatever nature has to show us. Tonight’s feature was moon jellyfish.
It was a beautiful evening, near to dusk when we walked from our campsite overlooking Haro Strait and went over to the sandy beach where the kayaks launch. At the end of the day, most of the kayakers had returned back to port and the beach was quiet. A very high tide was lapping at the sand. The tidal verge was full of interesting things, but what really caught our eye was the huge raft of moon jellyfish, bobbing at the water’s edge, tangled up with seaweeds.
Moon jellyfish Aurelia aurita aka saucer jellies live near the coast of many oceans: Atlantic, Indian and Pacific and of course the Salish sea, where we were staying. They are made of a gelatinous gel and can be as big as 20 inches in diameter, though the ones we saw were about 8 inches. They can swim, using their central bell to pulse rhythmically, but in the strong currents around these islands and a high full moon tide, they had been caught and brought in to the shore, where if they get beached, they die.
They are carnivorous and feed on the tiny animals that live in plankton soup (zooplankton). The small larvae forms of mollusks, crustaceans, copepods and tunicates get caught up on the sticky arms of the jellyfish, where tiny flagella move these tasty bits to the mouthparts where they can be digested.
Moon jellyfish first emerge as adults around May. You can tell males from females: the females have a lovely pink color around the four horseshoe shaped discs at the top of the bell. The males have white discs: as the season progresses, the males release gametes from these discs into the water. The females pick up these gametes and transfer them to the pink gonads, where fertilization occurs. She broods her eggs for several days and then releases the larvae into the plankton soup. The adults then die and no more will be seen until the following spring, while the larvae float in the plankton, finally finding a rock to attach to and become a polyp. The following spring this polyp starts to transform, casts itself from the rock and begins to morph into an adult jellyfish. And the cycle repeats itself again.
We sat on the beach in the gathering dark, the moon jellies bobbing in the shallow water. As the sun began to set, a gaggle of Canada Geese joined us at the tide’s edge, nudging the jellies aside to pick out thin strips of eel grass, which they nibbled then sucked down like spaghetti. The sun sank in a smoke-haze sky, scarlet over Haro strait. We sat there until dusk, in the company of jellyfish and geese…
• photos by Glen Buschmann
• The Whale Museum at Friday Harbor: https://whalemuseum.org
• A live jelly cam at this link: http://www.montereybayaquarium.org/animals-and-experiences/live-web-cams/jelly-cam
• A great you tube of moon jellies: www.youtube.com/watch?v=xUNb08COAw8