By: Bristol
Our oceans are home to a great many bizarre creatures, and nudibranchs are some of the most diverse and colorful. These carnivorous sea slugs live nearly everywhere in the ocean, are often poisonous, and come in a variety of exciting colors and shapes, often reminiscent of ribbon candy, or pokemon. If you search “nudibranch” on google, you’ll find images of incredibly colorful sea slugs, mostly found in the tropics. However, there is also a whole world of stunning nudibranchs in the colder waters of the world.
I am familiar with three of the nudibranch species found in Alaska. You have to be looking for them, usually, to see them; in the shallow water or in tide pools. In the low tide eelgrass of Kodiak Island we once found the unfortunately-named Flabellina trophina (someone please name their kid Flabellina), also called aeolid nudibranch or white-tipped nudibranch. This is a mostly transparent or whitish sea slug, maybe an inch and a half long, with little leafy structures on its back tipped with fluorescent white spots. Less commonly, there was Triopha catalinae, the orange-spotted nudibranch. These little guys are milky white with orange spots dotted along their backs. (For more nudibranchs found in Kodiak, go to https://www.afsc.noaa.gov/kodiak/facilities/kodiakspeclist.pdf and search for the Order Nudibranchia. All of them are beautiful.) My most recent nudibranch find was much less colorful but just as cool. I discovered them in Prince William Sound.
At the time, I was living out of a two-person tent on Naked Island and helping collect data on Pigeon Guillemots, a seabird related to Puffins. Each day we left camp bright and early to scour the island for them. As we left the beach one morning, I happened to lean over and see, not far below me, zillions of jellyfish-like things in the submerged eelgrass. They didn’t look exciting at first glance, but I hadn’t seen these before and was intrigued. One or two of them had come detached from the grass and came near the surface: little translucent venus fly traps with four silly-looked appendages like elongated balloons. Curiouser and curiouser. I filed away the observation until that evening when we returned to camp. In the tidepool guide, I found them: Melibe leonina, the lion’s mane nudibranch, or hooded nudibranch.
Hooded nudibranchs are pretty interesting, turns out. That venus flytrap-looking appendage was exactly that: an oral hood, or giant mouth, that it uses to catch little zooplankton and other tiny prey. The little inflated balloons are basically external gills called cerata, and the nudibranch can jettison them if it feels disturbed, in the hope that a predator will pursue the gills and not the nudibranch itself. Apparently it may also shed them if an inflatable raft goes by. Whoops.
The graceful motion the nudibranchs made as they fled from the terror of our raft is also notable: Although their main mode of transport is by gliding around on their foot, like slugs on land, they can also contort their bodies using their simple nervous system. This lets them arch and bend their way through the water, although it’s unclear if they have any control over their direction. (For a video of a hooded nudibranch swimming, go to https://www.youtube.com/watch?v=P9JbmGerCMU)
Now, I didn’t lift any of the little guys out of the water because in my experience, as a curious child in tide pools, that’s a great way to kill marine life. Unfortunately, because of this propensity to avoid meaningless death, I missed out on one of their cooler attributes. Hooded nudibranchs use various chemicals to deter predators. For whatever reason, the specific chemicals this species use smell great: like watermelon, strawberries, or flowers, depending on the person. For this reason (and because of how they like to stick to eelgrass in groups with their hood open) a group of hooded nudibranchs is called a bouquet.
For a great video of a hooded nudibranch being a hooded nudibranch, click here
The photos used here were taken by Kay Underwood of a nudibranch found in the waters of Kodiak Island. It was briefly placed in a blue bucket before being released safely.
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