The Tidepooler

Pacific and Steinberg’s Corambes: California’s Most Cryptic Nudibranchs

Many nudibranchs are famous for their flashy colors and flamboyant patterns, making them some of the most beautiful creatures on the reef or in the tide pools. These sea slugs, it seems, have no issue being seen by divers, tide poolers, or prospective predators who see their bright colors as a warning of foul taste or toxin. 

But not all nudibranchs take this approach. Instead, some nudibranchs have such excellent camouflage that few people even know of their existence, let alone have seen one in the wild. The Pacific and Steinberg’s corambes are possibly the most cryptic nudibranchs on the coast of California. With coloration that is nearly identical to the pattern of the kelp lace bryozoan (Membranipora membranacea) that they feed upon, these nudibranchs become almost invisible, living on their food source most of their lives. 

Because these two species are so incredibly alike in ecology, appearance, diet, and lifecycle, I have chosen to talk about them both in one post. 

Quick facts

• Both nudibranchs in the suborder Doridina (Dorids)
• Incredibly difficult to tell apart when observing in the field
• Both species feed solely on kelp lace bryozoan (Membranipora membranacea)
• Have some of the best camouflage around
• Both range from Baja California to Vancouver

Apparence

Because these nudibranchs are so similar in appearance, there is no harm in describing them together. Both Pacific and Steinberg’s corambes are characterized by white/transparent flat body, slightly humped in the center, with light colored lines crisscrossing the body that are interspersed with small blotches of red/brown coloring. There is some variation in coloration with certain individuals of both species exhibiting patterns that more closely resemble spots than lines. Their coloration is incredibly cryptic when they are on their only food source, nearly perfectly matching the patterns of this colonial animal. Unless you are looking for these animals, you would never notice them and even if you are looking, they are very difficult to spot. See this article for more information on appearance and body structure of these animals

The Pacific corambe has a notch toward the anterior of the mantle and characteristic rolled rhinophores. These are the only two visual differences between the two species as the Steinberg’s corambe lacks and notch and has smooth rhinophores that taper and are blunt at the ends. Branchial plumes, usually 2 to 4, that are used for respiration can be extended from under the mantle at the rear. Both these slugs lack oral tentacles and any kind of cerata or papillae. 

The typical size range of these two species is another notable difference, but they are both so small that this is not practical to distinguish the species when observing in the field. Neither of these slugs often exceed 1.3 cm in length with the Pacific corambe typically growing larger and having a longer lifespan than the Steinberg’s.

Diet

Both the Pacific and Steinberg corambes only have one shared food source: kelp lace bryozoan (Membranipora membranacea). These colonial animals are sedentary and have a tiny crown of tentacles used for feeding, similar to tiny anemones, except that their tentacles contain no nematocysts. Each individual lives in a rectangular cell which they build on the leaves of kelp and other algae. 

Both species of corambe feed on these creatures by sucking out the contents of the rectangular blocks through the frontal membrane. This leaves the “skeleton” of the animals intact, so as not to destroy their camouflage as they feed. 

Habitat and Range 

The Pacific and Steinberg’s corambes share the exact same range from Baja California to Vancouver, Canada. 

These slugs are rarely seen away from their food source, which grows primarily on California giant kelp as well as a few other species. Occasionally, they are washed off their bryozoan home into open water or crawl elsewhere, but this is seldom. They can often be found while snorkeling in shallow waters off the California coast, living on the bryozoan colonies that grow on the leaves of kelp forests. I saw most of the specimens in these photos while paddle boarding in open water near kelp paddies. 

If kelp is growing in the low-intertidal, you have a chance of seeing these slugs there. Corambes are also occasionally seen on pieces of detached kelp with bryozoan colonies that wash into the intertidal. 

Behavior 

Both Pacific and Steinberg’s corambes are among a group of camouflaged dorid nudibranchs that likely live their entire lives on their food source. Other nudibranchs that feed on sponges exhibit this behavior as well. Both of these corambe species live, eat, mate, lay their eggs, and likely die on this single habitat. 

Because their kelp lace bryozoan food source is seasonally abundant, there is some competition between these species for food and space. Paul M. Yoshioka discusses these competitive behaviors in his paper “Competitive coexistence of the dorid nudibranchs Doridella steinbergae and Corambe pacifica.” While I cannot get into the details here, these two species compete seasonally for food and thus impact who can reproduce— and by how much. Like all true nudibranchs, the Pacific and Steinberg’s corambes are simultaneous hermaphrodites, possessing both male and female reproductive organs throughout their lives. This means that any slug can mate with any other slug, although an individual cannot fertilize itself. 

Both these species begin to reproduce at around 50-60 days old. Eggs spirals take about 6 or 7 days to hatch, at which time the larva spend about 25 days in the plankton stage before settling on the bryozoan to develop into adults. 

Pacific or Steinberg’s Corambe

These two species are often visually indistinguishable from each other and share the exact same range in the eastern Pacific. They are very similar not only in appearance but also in behavior, diet, range, and ecology. As stated above, the only visual differences between the two species is the Pacific corambe’s notch toward the anterior of the mantle and characteristic rolled rhinophores in contrast to the uninterrupted mantle and smooth rhinophores of the Steinberg’s. 

However, these differences can be difficult to see in the field, especially without a powerful macro camera. Even researcher Paul M. Yoshioka remarked that smaller individuals could not identified as one species or the other in the lab and had to be removed from observation

In this post, I have done by best to identify the photos, but if you believe you see a misidentification, please contact me. See the resources below for more information on these two species. 

How to Find Pacific and Steinberg’s corambes

Just to be clear: these nudibranchs are hard to find. They aren’t the flamboyant Hopkins rose or Spanish shawls whose bright colors pop out in the tide pools. These corambes are cryptic and their camouflage keeps them hidden from predators, tide poolers, and snorkelers alike. 

But if you’re really determined, these nudibranchs can be found. The first step is to find some giant kelp that is encrusted with kelp lace bryozoan. Larger patches are better as the larger food source is more likely to attract slugs. Whether you are snorkeling, tide pooling, kayaking, or paddle boarding, this is your first step. 

Once you’ve found a probable habitat for corambes, it is easier to look for their eggs instead of the animals themselves. These tiny spirals are easier to pick out among the bryozoan. If you find a kelp leaf with eggs, spend some more time scouring it to look for the nudibranchs. Keep in mind that these nudibranchs are incredibly small, oval shaped, and very flat compared to other nudibranch species that are long and slender. See if you can pick out the Pacific corambe in this picture below with my hand and silicon ring for scale. Hint: it is the same individual in the picture above.

I searched for many months before I found one of these nudibranchs, so don’t give up if you don’t find any right away. Try different locations and different water depths for some variety. 

Resources

“Corambe pacifica.” The Sea Slug Forum, http://www.seaslugforum.net/find/corapaci. Accessed 19 June 2023

“Pacific Corambe.” iNaturalist, http://www.inaturalist.org/taxa/50032-Corambe-pacifica. Accessed 18 June 2023

“Steinberg’s Corambe.” iNaturalist, http://www.inaturalist.org/taxa/48388-Corambe-steinbergae. Accessed 18 June 2023

Yoshioka, Paul M. “Competitive Coexistence of the Dorid Nudibranchs Doridella Steinbergae and Corambe Pacifica.” Marine Ecology Progress Series, vol. 33, no. 1, 1986, pp. 81–88. JSTOR, http://www.jstor.org/stable/24825617. Accessed 18 June 2023.

Yoshioka, Paul M. “Life History Patterns of the Dorid Nudibranchs Doridella Steinbergae and Corambe Pacifica.” Marine Ecology Progress Series, vol. 31, no. 2, 1986, pp. 179–84. JSTOR, http://www.jstor.org/stable/24817574. Accessed 18 June 2023.