Since my last post before moving to southern California was all about looking for nudibranchs in Northern California, I thought I'd follow it up and write about my experiences looking for nudibranchs down here. In the spirit of being inclusive I'm going to be discussing sea slugs in general, not just nudibranchs, since I've had very good luck spotting non-nudibranch sea slugs down here.
Differences between northern and southern California tidepooling
Before we start with photos, I need to cover some basics. Southern California, for the purposes of this post, is defined as everything southeast of Point Conception west of Santa Barbara. For any geologists reading, this is the western end of the Transverse Ranges - the formidable wall that separates the LA basin to the south from the coast ranges, San Joaquin Valley, and Mojave desert to the north. Geologically speaking, the transverse ranges form a rather nice barrier as well. Politically and historically speaking, the boundary might be placed somewhat further North - but climatically speaking, everything north of Santa Barbara is much more similar to northern California. Coastal chaparral gives way to coastal scrub, redwood groves begin appearing, summertime temperatures are much cooler, and of course, wine country starts just over the hill from Santa Barbara. The mountains begin to look green year round instead of brown.
These changes are all associated with the marine climate and ocean currents of our coast. The California current is a north-to-south cold water current - the direct opposite of the Gulf Stream in the Atlantic. This cold current brings chilly water from Alaska far south, and for the most part, is pretty close to the coast - until it reaches Point Conception. At that point (no pun intended) it continues south instead of bending east towards Santa Barbara, essentially forming a gigantic eddy between Santa Barbara and San Diego. Warm water from the west coast of Baja is transported north, keeping the water here "warm". I'll level with you: the water temperature here in San Diego typically peaks around 70F - about 10 degrees colder than the coldest it ever gets in the Florida keys. It's just warm enough to swim without a wetsuit for a month or two, and even then, it's still pretty chilly. Last fall (September 2025) it peaked at about 74F, which was pretty nice for snorkeling.
Not a nudibranch, but an enormous sea slug - Navanax inermis, a headshield slug (Cephalaspidea). It's typical to see small, juvenile specimens 2-6 cm long in tidepools, but these colorful predators get up to 25 cm; this is about a 15 cm long individual I saw while snorkeling. You pretty much need to go snorkeling or diving to see the big ones.
Comparing San Diego to the Florida Keys is unfair, so let's pick a couple points at the same latitude on each coast. Half Moon Bay, California - the place where I first (very briefly) swam in the ocean - tops out around 60F in August, whereas in Virginia Beach (VA) on the Atlantic coast, the water gets up to 80F. Summer sea surface temperatures are similar to Half Moon Bay further north, throughout the Pacific Northwest (e.g. identical summer temps in northern Oregon). On the other hand, in San Diego, the water typically gets up to about 70F during late summer. Hilton Head in South Carolina is at about the same latitude, and water temperatures get quite a bit higher - 83F (though in Charleston, we were frequently getting 85-88F in July/August). The minimum temperatures on the "temperate" Atlantic coast are also a striking point of comparison - the minimum temperatures are the same as the maximum on the Pacific coast. There's much less seasonal variation here - maybe +/- 10F, whereas the gulf stream exerts a +/- 20-30F swing. The eastern North Pacific is cold and stable and the western North Atlantic is hot and unstable.
This is a long way of saying that there is a marked jump in marine climate from central to southern California. In addition to this, ambient air temperature is much, much warmer. The water in the tidepools gets warm real fast. As a result, it's very difficult to find nudibranchs during the day - don't even bother with small tidepools. I've seen a couple of tiny salt-and-pepper dorids in a tidepool in the mid-intertidal zone, where the water was about 5-10 degrees warmer. Nudibranchs do not tolerate wild temperature swings, nor do they like sunlight. Down here in socal, your best luck is going to be in tidepools down in the lower intertidal zone, or better yet, subtidal pools and channels at minus tides.
Nudibranch hunters under the winter stars. Well, planets - I believe those are Venus and Jupiter just after sunset.
That brings me to another major difference. The tides down here suck. They tend to be 1-2 hours earlier than in northern CA - primarily a result of the latitude. The tide variation is pretty similar to the bay area - highs around 6-7 feet, lows around 0-2 feet, with minus tides maxing out at about minus 1.7 on new moons. Our minus tides up north get a little lower, down to about minus 2 - but, pretty comparable. The timing is what is awful, though - at least for me. From April to September, minus tides are typically from 4-7am. If you're a morning person, I am jealous. If I get up after only 4-5 hours sleep and go tidepooling, I'll get a migraine even if I go take a nap (it happened last week). We do get daylight minus tides, late in the afternoon or trailing into the late morning hours, from October to March.
Northern and Southern California are also starkly different in terms of coastal access and beaches. Nine times out of ten your prospective tidepooling spot will be a state park, a popular beach, or a surf break. I have rarely had to fight hard for parking in Northern California (with one exception: Pillar Point/Mavericks on the annual winter solstice tidepooling event put on by California Academy of Sciences, but that's admittedly different). In socal, virtually ALL of the tidepooling spots will be below a residential neighborhood - and a very rich one at that. If you're from socal or lived here long enough, you probably won't mind having to walk a ways from your parking spot. On the same note, tidepooling down here has recently surged in popularity, and I've seen some distressing videos on social media of mobs of people flipping over every rock and throwing/hurting wildlife. I have tried to keep myself focused on some of the less popular tidepooling spots that are frequented by the real nerds, who try their utmost not to threaten the intertidal ecosystem and its denizens any more. I do flip rocks, on occasion - flat ones, only, and I try my best to gently place them back into position (I stepped on one last week that someone had flipped and got a huge bruise and some cuts on my knee when it rotated under my weight and clobbered me in the leg). And, owing to this recent surge in popularity, I will not divulge the location of any of my spots. I did a bit of research and trial and error to find these locations. If you have a similar 'doggedness' about you, you can earn it yourself.
Nearly flat-lying layers of marine sandstone of Cretaceous age exposed in San Diego County at a minus tide.
South of Point Conception, the rocks are almost completely sedimentary in origin. That means that there is very little in the way of leg-breaking craggy igneous and metamorphic rocks that tidepoolers from Big Sur, the Monterey Peninsula, or the Sonoma/Mendocino coasts might be used to. Those coastlines have locally chaotic topography owing to the bedrock - Salinian granite in Monterey, and Franciscan Complex metamorphic rocks in Big Sur and the coast north of Marin Co. The rocks down here are all typically deep marine sandstones and shales with nice bedding, with loads of concretions and surge channels formed along joints and fractures in the rock. There are some localities where the rocks are mostly large rounded cobbles, but they are few. You're more likely to slip by walking across nearly horizontal bedding planes covered in slippery algae than while climbing - though I've had pretty good luck down here so far. It also means that a little more walking might be required. Altogether, it's very similar to tidepooling on exposures of the Purisima Formation at Pillar Point and Fitzgerald Marine Preserve back at home up north. It also means that some of these sites are quite accessible for kids and adults with bad knees.
A California blue chromodorid (Felimare californiensis) cruising along in a cobble-filled tidepool.
One last word - nudibranchs in southern California also tend to be very small. On average, the nudibranchs I see are often half to 1/3 the size of members of the same species in Northern California. Large ones do exist, but they're usually spotted by divers or more ambitious tidepoolers who find them during 4am minus tides. Maybe I'm only finding the dumb babies during daylight minus tides. Nudibranchs are also less common. A good nudibranch day for me is finding more than two in one visit. Up in Northern California, for me, seeing less than thirty seems like a waste of a minus tide. Fifty is typical for a late afternoon minus tide, and I've seen over a hundred before on two or three minus tides.
The Big, Obvious, Easy to Find Nudibranchs
Depending upon the location, the Hopkin's Rose nudibranch, Okenia rosacea, is probably the most common and conspicuous nudi here in socal. They're not quite as common in Northern California. At some locations here, at a minus tide, you can spot several in the same visit. This species has also been placed in the genus Ceratodoris; it grows to a total of 3 cm. It inhabits the coast from Oregon to northern Baja and feeds on bryozoans.
A white spotted sea goddess nudibranch, Doriopsilla albopunctata; these can be much darker in color, like this one resembling a roasted marshmallow, in southern California.
Somewhat Less Common, Absurdly Colorful Nudibranchs
The wildly blue-colored California blue chromodorid, Felimare californiensis - one of my absolute favorites. These don't even bother to camouflage themselves, so if they're out - you WILL see them! In this photo lies a tip to finding them: it's having lunch. Chromodorids eat sponges, and our three local chromodorids (California, Porter's and MacFarland's) all eat our yellow and orange encrusting sponges that live down in the subtidal zone. This species lives from Monterey Bay, CA, to southern Baja California Sur (La Paz, specifically).
A California blue chromodorid crawls past an onimous looking maw in the pool below - not anything to fear, it's just the exposed siphon of a rock-boring clam - specifically, a scale-sided piddock, Parapholas californica.
My absolute favorite southern California nudibranch - the incredible MacFarland's chromodorid, Felimida macfarlandi. Ecologically speaking they are similar to the California blue chromodorid and also feed on sponges. I've found them by flipping rocks as well as looking for zones of encrusting sponges during minus tides. This species lives from Monterey Bay, CA, to northern Baja California Sur.
One last view of a MacFarland's chromodorid working its way through brownish algae.
That's not candy corn - that's a Festive Babakina, Babakina festiva - one of our most flamboyant nudibranchs from the California coast. This individual was about 2 cm long. I have only seen two: this one, and a rather bleached looking individual a few months later. This species lives from Marin County, CA, to central Mexico.
Another shot showing the whole body of Babakina festiva, and all of its candy corn-like cerata. These are thought to feed on hydroids, like other aeolids - but little data is available.
A closer look at the head end and the comically inflated rhinophores of Babakina festiva.
Southern California's most outrageous, and probably most famous, nudibranch - the Spanish Shawl nudibranch, Flabellinopsis iodinea. These make my favorite nudibranch - the opalescent nudibranch - seem rather conservative in comparison. These can apparently get to massive sizes of 70 mm. These consume hydroids and steal the stinging cells and store them in their cerata.
Tiny, Hard to Find Nudibranchs
When I photographed this little guy - maybe 6 mm long - in October 2024, this species hadn't even been named yet; for the longest time, it was simply known as "Doto sp. A", and closely resembles the hammerhead Doto, Doto amyra. It was just named about one year ago, as Doto urak. Like other Doto spp., this one feeds on hydroids.
Another shot of this little cutie. Species in the genus Doto live worldwide, and their taxonomy has been quite challenging because they are typically under 1 cm in length.
A rather unusual find - this is a Pacific corambe (Corambe pacificus), I think - it could also possibly be a Steinberg's Corambe. These are relatively small, typically about 1 cm long, flattened, oval, and lacy - they look nearly identical to encrusting bryozoans that live on kelp fronds. Most folks have luck searching bryozoans on kelp to find these - I've only found them when I could tell there was a white blob on some sort of greenish algae.
Another Corambe - this one is next to a teeny little snail. I've spent plenty of time looking for these on bryozoan-encrusted kelp fronds, but had no such luck.
A tiny, ~6-7mm long white-crusted aeolid, Tenellia albocrusta. These are tiny, cryptic little nudibranchs that are hard to find but not uncommon. They live from Alaska to Baja and feed on hydroids.
Here's another Doto - the seal Doto, Doto kya. I've only ever seen one of these - this one was in Laguna Beach. They're the only California Doto with dark pigmentation on them. This species feeds on hydroids.
A branched dendronotid, Dendronotus venustus. These are apparently more common than I've encountered - another specimen from Laguna Beach. If it wasn't obvious by now, most of my luck finding cryptic, tiny nudibranchs is by searching amongst the red algae - very few of our nudibranchs blend in with red algae, and so virtually everything stands out. This species feeds on hydroids.
A salt and pepper dorid, Aegires albopunctatus. These are actually quite common, but most of them are about 8-12 mm in total length, and can look like a little bit of dead, bleached algae so it takes a bit of an eye to find them like these other more cryptic and rare forms. This species feeds only on calcareous sponges.
Ancula pacifica - no common name. These little ones look similar to species of Polycera (see below) but are pale and clear, with a few orange spots and stripes. Most are under 1 cm, but they get to 2 cm in length. This species feeds only on 'entoprocts', hydroid-like sessile filter feeders that are in their own phylum.
Curiously, this species may actually be a junior synonym of the eastern North Atlantic form Ancula gibbosa - suggesting that there may be one worldwide, or at least northern hemisphere, population of this tiny nudibranch. It seems unlikely to me - and, there are some anatomical differences.
Baby Nudibranchs
By virtue of having a search image tailored for tiny nudibranchs, I seem to come across babies of large species much more frequently down here. Some of these can pose a challenge to identify, thanks to occasionally looking quite a bit different than the adults - sometimes more pale, other times more vividly colored - and often with fewer cerata.
A juvenile San Diego dorid, Diaulula sandiegensis - this one was about 1 cm long, and was difficult at first to ID until I realized that it's a juvenile San Diego dorid without any spots. It looks suspiciously like a ridge tailed dorid, but the rhinophores look totally different. Fortunately, there are a few examples of juveniles posted to iNaturalist that helped me out.
A baby sorceror's dorid, Polycera atra. These handsome little fellows are commonly found further north during dockfouling - I've seen a couple of babies in the tidepools down here. These get to about 2 cm long and feeds on one particular type of bryozoan.
A juvenile Fisher's aeolid, Orienthella piunca, about 1 cm long. There's not much data on this species - it is easily mistaken for the three-lined aeolid (O. trilineata), which does not frequently have orange rhinophores. Identifying these socal aeolids with reddish cerata can be challenging!
Another Fisher's aeolid (O. piunca) but this one doesn't have a median white stripe like most of the individuals photographed online have!
A juvenile, ~1 cm long MacFarland's dorid, Limacia macfarlandi.
Other sea slugs - Saccoglossans, Aplysiomorphs, and Cephalaspideans
Navanax is a genus of 'headshield slugs' (Cephalaspidea) that are closely related to the sea hares. Some of these, like bubble snails, still have a reduced shell. Navanax grow to 25 cm and their yellow spots transition to more numerous and fine yellow lines; as adults they have more yellow/white on them than black. They are voracious predators of nudibranchs - so if you see one, you're on the right track! These are much easier to spot than nudibranchs as they are a little more tolerant of warmer water and sunlight.
Critters That Look Like they Should Be Nudibranchs But Aren't
An unusual sighting: an umbrella snail, Tylodina fungina. These look like a cross between a limpet and a nudibranch, but they are neither. They are sometimes called false limpets, and are closely related to the headshield slugs (Cephalaspidea) and the aplysiomorphs (sea hares) as well as the pteropods ('sea angels'). All of these groups have a highly reduced shell; these are the least 'sluggy' of them.
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