For many of us, one pull toward a career in marine biology is the strong influence of aesthetics: the smell of salt spray on the wind during a storm, the roar and rumble of breaking waves, the colors of pink seaweeds and blue mussels in a tidepool…and nothing illustrates this aesthetic power better than nudibranchs.  Frequently, when students are asked about their favorite marine organisms, they say “nudibranchs” (well, then there are sharks and orcas, of course).  Drew Harvell delves into both this aesthetic attraction and the intellectual draw of nudibranchs, in terms of some of their remarkable natural history stories.  Enjoy!

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Dr. Megan Dethier, FHL Director
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A Nudibranch Life List

by Dr. Drew Harvell

I’ve listened to bird watchers talking about their life lists.  I never thought at all about my own life lists until one day last Fall on a minus low tide in Pacific Grove, California.  It was exciting to see not one, but four brand new nudibranchs.  The two I was most excited about were the speckled Triopha (Triopha maculata, Figure 1) and Hopkin’s Rose (Ceratodoris rosacea).  I worked on the congener of the speckled Triopha (Triopha catalinae, the clown nudibranch, Figure 2) for my PhD research at FHL, which was about the predator-prey battles between predatory nudibranchs and their sessile prey (bryozoans in this case).  So, finding this dark cousin to the white and orange clown nudibranch took me way back and delighted me.

I’ve hunted the Hopkins Rose in the wild for the last 2 years, since I winter in Pacific Grove.  After lots of searching, there it was near Ed Rickett’s Great Tidepool; a bright pink spot at the edge of a smaller tidepool.  What a breath-taking beauty with all that stunning rose ornamentation (Figure 3)!  The dreamy rose color is stolen from its prey, the rosy bryozoan, just as the fabulous pink of flamingo plumage is derived from algal pigments taken from its crustacean prey.  Hopkins Rose is a tricky one to place taxonomically, since the dorsal (back) ornamentations look like the finger-like cerata of an aeolid nudibranch (Super Family Aeolidea), but those vibrant almost-fuschia dorsal gills clearly mark it as a dorid (Suborder Doridae).  It was named by Frank McFarland for Timothy Hopkins, an early benefactor of Stanford’s Hopkins Marine Lab.

This ability to steal and re-use stuff from their prey is the hallmark of nudibranchs and their relatives.  Another San Juan Island example is the orange-red pigments which the common nudibranch Rostanga pulchra steals from its same-color sponge prey, Ophlitaspongia pennata (Figure 4).  The bright sponge pigment gives color to Rostanga and also its eggs, rendering both cryptic on top of their main prey species.  Those eggs hatch into long-lived larvae that swim in the plankton for over a month.  The tiny larvae then search out that one species of orange-red sponge to settle on; contact with the sponge actually induces their metamorphosis into the adult form.  The bright color marks a toxic chemical also stolen and used for the sea slug’s defense.

While we think of nudibranchs as bright and showy, other nudibranchs blend with their prey.  This is the case of our very common Corambe steinbergae, the cryptic predator on the lacy bryozoan and another player in my PhD dissertation (Figure 5).  Corambe is a fascinating beast and is similar to Rostanga in that it has a long-lived larva that will only metamorphose from its larval stage when it finds its one prey species, Membranipora membranacea.  Its entire survival depends on its sensory capability to find this one prey bryozoan species.

I didn’t think having a nudibranch life list was odd until several folks looked at me strangely and quietly said “You have a nudibranch life list?”  My friend Judy, a long-time birder immediately asked, “how many are on your life list?” as if I should have kept a tally and know immediately the new number.

I first counted up the ones I knew from my time as an undergraduate and graduate student at Friday Harbor Labs and all the time spent in the remarkably biodiverse waters of the Salish Sea, adjacent to FHL.  I can’t show all of these here, but conveniently at the Labs there is also a Conservation Biology class run by Dr. Jon Allen, and last summer his class collected a diversity of species as an example of the showy biodiversity in our waters.  I call Figure 6 (of the class collection) a nudibranch circus.  I love the shot because it encompasses 4 different families within the wider diversity of nudibranchs.  Among these is the masterful shag rug nudibranch that takes up, and uses for its own defense, miniature harpoon-like nematocysts from its anemone prey: the beautiful pink-tipped, green Anthopleura elegantissima.  I call this ability to steal and then sequester a structure from a different species a superpower; it is unparalleled in the animal kingdom to uptake and use organs from so far across the kingdom of life.  Also in the nudibranch circus photo is another aeolid, Hermissenda crassicornis (Figure 7).  The remarkable adaptations of nudibranchs and seven other marine invertebrates are the topic of my new book, The Ocean’s Menagerie, out this spring.

The concept of a nudibranch circus was born on our dives in Wakitobi, Indonesia where we sought to find and film nudibranch matches to the Blaschka glass collection (while we were also doing research on coral health).  This footage ended up in David O. Brown’s film Fragile Legacy and my book A Sea of Glass, about our work to restore Cornell’s Blaschka Glass Collection, and hunt for the living matches of jellies, octopus, sea anemones and nudibranchs.  We surfaced from one dive and a diver said, “WOW, it was like a nudibranch circus down there.”  The bright dots, stripes, and splotches of color and frilly gills of nudibranchs does remind one of a circus; I think of it as a biodiversity circus.  In addition to that dive, I saw an additional 30 nudibranch species on various tropical dives.

So all told, I reckon my life list of nudibranchs so far includes over 60 species – and I have the remarkably rich waters of the Salish Sea and high biodiversity at FHL to thank for such a strong start.  The Labs’ access to diverse habitats in a region of unusually high numbers of species of all kinds of invertebrates has been a life-long gift, fueling my passion for invertebrate natural history. There are 74 nudibranch species listed in Kozloff’s Marine Invertebrates key, of which 33 are dorids and 19 are aeolids, so I’ve barely scratched the surface with the roughly 30 species I’ve seen near Friday Harbor Labs.

Where next to go?  There are a lot more to be found in the rich waters of the tropical Pacific and Australia.  Terry Gosliner of Cal Academy estimates there are about 6,000 species worldwide and he says only half are named.  One big one still on my life list to see in the wild is the pelagic Blue Dragon (see my blog The Blue Fleet).

It’s been a privilege for my students and I to work for so many years in the invertebrate-rich waters of the San Juan Islands from our shore base at Friday Harbor Labs.  As a graduate student I benefited from financial support to work at FHL, and in turn my graduate students have repeatedly benefited from the Labs’ donor-based scholarship funds.  You can learn more about nudibranchs in our waters in my new book out this month, which is dedicated to FHL!

References:

Gosliner T.M., Valdés Á., and D. Behrens.  2018.  Nudibranch & Sea Slug Identification Indo-Pacific.  Second edition.  Jacksonville: New World Publications.  ISBN: 978-1-878348-67-8.

Harvell C.D.  2025.  The Ocean’s Menagerie: How Earth’s Strangest Creatures Reshape the Rules of Life.  Viking Penguin Random House.

Harvell C.D.  2016.  A Sea of Glass: Searching for the Blaschka’s Fragile Legacy in an Ocean at Risk.  Univ California Press.

Harvell C.D.  1985.  Partial predation, inducible defenses, and the population biology of a marine bryozoan (Membranipora membranacea).  PhD Dissertation, University of Washington.

Harvell C.D.  1984.  Predator-induced defense in a marine bryozoan.  Science: 224, 1357-9.

Kozloff E.  Keys to the Marine Invertebrates of Puget Sound, the San Juan Archipelago, and Adjacent Regions.  Seattle: University of Washington Press.

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