Wednesday, March 13, 2024

Nudibranch hunting in northern California: snapshots from winter tidepooling in Half Moon Bay, CA

This post has more to do with the coastal part of the title and less to do with the paleo part - I'll be doing more of these, since I figure there's probably some interest from readers regarding live, rather than dead, marine critters.

 I found Opalescent nudibranchs like this one on my own for the first time.

I've always enjoyed tidepooling since I was a young kid - and once I left foggy northern California to go to Montana, an extremely land-locked state, I realized how lucky I was to have world-class tidepools just a half hour drive from my parent's house. I didn't have the opportunity in New Zealand (tidepools, yes, but no car) and here in South Carolina, we don't have any water clarity - and, to be honest, a pretty depauperate marine invertebrate fauna in comparison to the Pacific coast. Since our very belated honeymoon a few years ago to the Bahamas and our subsequent Caribbean Spring Break snorkeling trips, I've gotten more and more interested in it, and in 2022 Sarah and I bought Olympus TG6 cameras, recommended to me by Dr. Maureen Berg, a biologist at UC Berkeley who spends a bit of time tidepooling at some of my favorite spots - but with much higher success at finding nudibranchs. Until about three years ago, I had only ever seen one or two nudibranchs in the wild - I was thoroughly unimpressed when I was a kid, seeing a couple of yellow gelatinous blobs. While paddling a canoe in Drake's Estero with Dick Hilton in 2011 (just a month after Sarah and I got married, and a few months before we left for NZ), Dick noticed an opalescent nudibranch on a frond of giant kelp - and I was mesmerized. I had seen photographs, but never one in person - I couldn't believe how beautiful the little creature was. I really got hooked only a few years ago: on a visit to Fitzgerald Marine Preserve (Moss Beach, CA) on a good minus tide with Sarah (and about 200 of our closest friends - new years, 2022), we found about a dozen nudibranchs - all of them some of the 'boring' ones - sea lemons, Monterey dorids, an orange peel dorid, and a few San Diego dorids. That visit was the one where I decided I needed an underwater camera. In December 2022 and 2023 I visited a spot in Half Moon Bay a friend of mine recommended - I'll keep the location a secret for the time being (sorry!) since it's much less frequented. But, it's a good one: tons and tons of nudibranchs.

Winter solstice sunset in Halfmoon Bay, California.

Why nudibranchs, by the way? I've never fully understood what the obsession is among tidepoolers with finding nudibranchs. And, I say this while admitting that I've totally gotten obsessed with nudibranchs as well, without really understanding why. I have some hypotheses, however. For starters, most of them are really quite beautiful - whereas others are more modest blobs of color. Some are rather cute - some of the dorids resemble the "sea bunny" nudibranchs of the Indo-Pacific. They're highly diverse: we've got 180 species along the California coast*, so there's many to go out and find. They're also challenging to find - many folks get out and expect them to just be coming out of the woodwork, and many get bored and impatient. You need to really relax, use your eyes, and look for little tiny blobs of color (for the colorful ones anyway). When you do find one, it's a huge rush! They are, in my opinion, some of the tiniest but most satisfying critters to find. There are many more cryptically colored species that are far more common (and larger) than nudibranchs that I've never seen before in person - and honestly, I've probably passed over a bunch of live baby abalones in search of nudibranchs.

*For comparison, there are a few dozen species in the Humann et al. Reef Invertebrates guide for the Caribbean, and only about two dozen here in South Carolina. For an apples:apples comparison, has about 100 species even for Florida and the northern Caribbean and Bahamas, 17 for the Georgia Bight (northern Florida through the Outer Banks of NC), and 144 for the California coast. I've intuitively known that the California coast is exceptional in terms of nudibranch diversity - but most marine species have a diversity hotspot in the Indo-Pacific (the Caribbean, for a number of reasons, has high diversity for many groups, but is a fraction of the Indo-Pacific). In the Phillipines, there are over double the species versus the California coastline. I suspect the unusually high species diversity is driven by the highly productive kelp forest and rocky shore habitats - and there's probably a bunch of ecological and phylogenetic papers out there on the subject that I haven't read.

Giant kelp, Macrocystis pyrifera. This is not from tidepooling, but is from a rather brave attempt at snorkeling in Monterey Bay in a wetsuit that was way too thin (I made it 45 minutes before I started shivering uncontrollably) - the water was a balmy 54 degrees F, about 10 degrees colder than what I'm used to in the summer at Lake Tahoe.

One last note before we dive in: I may be labeled as a marine mammal paleontologist, and it may be the majority of what I study, but I am really a marine vertebrate paleontologist and I try to keep myself well-rounded by collecting and identifying some of the more humble fossils which can round-out the ecological context of the 'giants' that I study - from little tiny shark and ray teeth to fish bones, clams, and even shrimp claws. We have a rather unique and iconic ecosystem on the Pacific coast, beautifully showcased by exhibits at the Monterey Bay Aquarium - which captivated me as a young kid. At some point in the past ten years it clicked that I was studying organic detritus of an ancestral version of this ecosystem. During the pandemic, Sarah surprised me with an early Christmas gift, knowing I couldn't fly home to California, and bought for me a Third Edition copy of Ed "Doc" Rickett's famous book "Between Pacific Tides". So for me, tidepooling - and future snorkeling in the kelp forests of San Diego (later this year, stay tuned!) - is a way for me to connect with this same ecosystem.

I don't always get good results shooting horizontally, but I do love trying to get "landscape" shots - or should I say, "tidepoolscape" shots. Here we see some sunburst anemones (Anthopleura sola), coralline algae, ?eelgrass, and brown tegula snails (Tegula brunnea).

 A bank of aggregating anemones (Anthopleura elegantissima) in one of my favorite individual tidepools. Each of these is about the size of a US quarter (~2.5 cm). This is actually at a completely different spot, if I'm being honest - but the same day. These anemones are smaller relatives of the famous giant green anemone (A. xanthogrammica) and also live a little higher in the intertidal zone. Because they reproduce rapidly and clonally they produce enormous colonies like this. They get up to 8 cm wide and live from 0-20 meters from Alaska to Baja California.

My only successful "over/under" shot as a photographer with my Olympus TG6 - chiefly because this camera doesn't have a big bubble lens for shooting this sort of photo. This one is taken in a tidepool that at low tide is perfectly still. More aggregating anemones, Anthopleura elegantissima.

Actually since we're on the topic of other spots, I also tried dock fouling in Princeton harbor in Half Moon Bay - I saw tons of these incredible tube worms. These are Giant Feather Duster worms, Eudistylia polymorpha. This species is a large polychaete that lives from Alaska to California from the intertidal zone down to about 400 meters. It's a large filter feeder, constructing a tube up to about 25 cm long and with a filter feeding apparatus up to about 5-6 cm wide.

 Some more giant feather dusters, Eudistylia polymporpha.

OK, now onto the photos from the tidepooling spot. Here's a six-armed sea star, Leptasterias aequalis. These sea stars only get to 5 cm in diameter (2"), and each of these were only about 2-3cm wide. This sea star lives from Washington state to southern California within the mid-intertidal zone.

First nudibranch: a pink champagne colored shag rug nudibranch, Aeolidia papillosa. These live from the low tide line down to (apparently) 900 meters; they feed on anemones, and at least in shallow water, prefer aggregating anemones (Anthopleura elegantissima), a couple of other species of Anthopleura, Metridium, and Epiactis, and Urticina. I've read that this nudibranch can take on the color of its prey - so perhaps it feeds on reddish proliferating anemones (Epiactis prolifera), which were somewhat common at this location.

A rather large (~3-4 cm) Hilton's Aeolid (
Phidiana hiltoni). These nudibranchs are less flamboyant than the opalescent nudibranchs, but are still stunning in their own right. I saw several such examples for the first time in my life on this one evening - including this individual. This is an aggressive nudibranch that has routinely been observed attacking other nudibranchs - it feeds on other nudibranchs and also hydroids. This species ranges from southern California to Marin County, which is the northernmost limit of its range, and from the intertidal zone down to about 60-70 meters.

 A tiny little baby
blue topsnail, Calliostoma ligatum! These are arguably beautiful snails as adults, but the juveniles are really quite vividly colored. These 'archaeogastropods' are in the family Trochidae and are just one of the highly diverse fauna of herbivorous gastropods on the Pacific coast (contrasting with virtually none here on the South Carolina coast). C. ligatum feeds predominantly on kelp but also opportunistically on microfauna (bryozoans, hydroids) and diatoms, inhabits rocky shores and kelp from 0-30 meters along the Pacific coast from Prince William Sound, Alaska, to San Diego.

An orange peel dorid, Acanthodoris lutea. This species feeds chiefly on one species of bryozoan! Its' bright orange coloration is a warning to predators against its toxicity from feeding on bryozoans. This species lives from Cape Arago, OR, down to northern Baja California, from the intertidal zone down to depths of 50 meters.

A tiny opalescent nudibranch, Hermissenda opalescens! These are my single favorite nudibranch species. I saw a bunch of these on my own on this tidepooling visit - and this little one was the first I ever found by myself. This individual measured about 15 mm long, but the species can get up to 50 mm (2"). This species lives from northern California to the Vizcaino Peninsula of Baja CA; at the northern part of its range it overlaps with a similar species, Hermissenda crassicornis, the range of which extends up to Alaska - they are hard to distinguish and were formerly considered one species. This species feeds predominantly on cnidarians, including hydroids and anemones, but also feeds on tunicates; it lives from the low tide line to about 30 meters.

Sea lemon butt! The gills (branchial plumes) of a noble dorid sea lemon (Peltodoris nobilis). These are some of the larger true nudibranchs from the Pacific coast, attaining incredible sizes of about 20 cm; they eat sponges, and live from Alaska to Baja California along rocky shores from 0-230 meters. Half Moon Bay, CA.

A tiny brittle star! This was my first time ever seeing a brittle star on the west coast. I saw them as a little kid in Hawaii, and I've seen several in the Caribbean more recently, but not at 'home'. This one is the western spiny brittle star, Ophiothrix spiculata. This is a juvenile - the disk can get to 2cm across with arms up to 15 cm long (actually, shockingly large - ~1' diameter!). Like other brittle stars, this species is a detritivore inhabiting rocky shores and hard substrates from the low tide line to 2000 meters and ranging from Half Moon Bay to Peru - meaning that this was found at the very extreme limit of its range.

A rather fat and self-satisfied looking San Diego dorid (Diaulula sandiegensis). These large dorids can grow to 4" (~100mm) and feed on just a few species of sponges; while first described from San Diego, they range from British Columbia to Baja California. They live on rocky shores from 0-35 meters depth.

My first ever Hopkin's Rose nudibranch, Okenia rosacea! Also, the only one I've ever seen in person. It was very, very easy to spot.

Okenia rosacea are dorid nudibranchs that get to 3 cm in length. They feed predominantly on one species of bryozoan, Integripelta bilabiata - which also gives them their brilliant pink color! They're hard to miss, to be honest. This species inhabits rocky shorelines from 0-10 meters and lives along the Pacific coast from Oregon to Baja California.

And a closeup of the face of the Hopkin's Rose - now you can actually tell where the rhinophores (often mistaken as the eye stalks seen in terrestrial gastropods) are the deep dark frilly tentacles at the upper left.

My first tidepool shrimp! A broken back shrimp - Heptacarpus. Perhaps stout coastal shrimp, Heptacarpus brevirostris. This species lives from the Aleutians to Santa Cruz, CA, and lives from the low tide line to 128 m down, typically in rocky shore habitats. These guys are hard to spot because they're typically nocturnal - I came across this one at sunset and it was getting pretty dark.

A great portrait of a San Diego dorid, Diaulula sandiegensis. Even these guys can look pretty up close.

California cone snail! Californiconus californicus are the coldest water members of the highly venomous family Conidae. Most species are tropical in distribution, with the highest diversity in the Indo-Pacific. Whereas other species of conids have highly specialized diets, Californiconus is a generalist predator feeding on fish, mollusks, and worms. Since the California cone snail is the only conid on the cold California coast, a generalist habit is likely required. Californiconus lives from 0-30 meters on rocky shores and sandy flats, and ranges from Bahia Magdalena in Baja California Sur north to San Francisco - meaning that I photographed these little guys at basically the northern limit of their range.

 My first adult Opalescent nudibranch I found on my own! (Hermissenda opalescens). I personally think this is the most beautiful out of the three species in this genus. The thick-horned nudibranch, Hermissenda crassicornis, lives further north in northernmost California through Alaska.

This was by far my best Hermissenda encounter, so I took the most photos of this beautiful individual.

This, and the image above, are perhaps my two favorite shots from the entire trip.

Another California Cone snail.

A festive dorid nudibranch - Tritonia festiva. These nudibranchs feed on the polyps of soft corals and can get up to 10cm in length. They have a circum north Pacific distribution, living from California to Alaska and also in Japan and Korea. These inhabit rocky shores from 0-50 meters.

 A kelp crab (Pugettia productus) doing... something? to a red rock crab (Cancer productus) shed exoskeleton. Kelp crabs are supposed to be herbivorous, and shed exoskeletons don't exactly have much of anything nutritional on them. Honestly, no idea what the hell is happening here!

These colorful dorid nudibranchs are perhaps the most common totally flamboyant species - Clown nudibranchs, Triopha catalinae. These apparently get to 15 cm in length and live from the Aleutians to the Sea of Cortez in Mexico, from 0-35 meters along rocky shores and kelp beds. They feed only on bryozoans. Half Moon Bay, CA.

Portrait of the clown nudibranch's head.

And a closeup of the gills.

 My first ever live gumboot chiton, Cryptochiton stelleri - they really, really look like a rock (and feel like one too). Honestly, they're firm with a little give, like a car tire. Unlike most chitons, the little armor plates that make up the shell are completely covered in soft tissue. They're also difficult to spot. I assume the soft tissue covering lends them the name "Cryptochiton". I've found three or four of the armor plates (called "butterfly shells") since my early 20s, and I found a few dead individuals that had puckered up considerably - having never seen a live abalone, I thought it was the body after separating from the shell! I didn't know of the existence of this giant chiton until I was in my 30s. So, there's a third meaning for me personally for "Cryptochiton". This is the world's largest chiton, growing to 36cm/14" and a weight of nearly five pounds! They feed on algae, and are nocturnal (perhaps explaining the rarity of sightings for me). They are preyed upon rarely owing to their massive size, but lurid rocksnails (Paciocinebrina lurida) might consume parts of their mantle and they are consumed occasionally by ochre stars (Pisaster ochraceus), giant Pacific octopus (Enteroctopus dofleini), and sea otters (Enhydra lutris). They live from central California north to the Aleutians and west to Japan, and inhabit rocky shores from the low tide line to 18 meters. Ed Ricketts wondered why Native Californians did not eat the species, and wrote about experimenting with cooking some in Between Pacific Tides: "After one experiment the writers decided to reserve the animals for times of famine; one tough, paper-thin steak was all that could be obtained from a large Cryptochiton, and it radiated such a penetrating fishy odor that it was discarded before it reached the frying pan".

Another Orange Peel dorid.

A lovely, somewhat larger opalescent nudibranch (Hermissenda opalescens).

 Just before it got dark I saw this large yellow blog, mistaking it at first for a sea lemon - when I approached, I realized it was actually a scallop! A rare first sighting for me: a juvenile (2-3cm wide) giant rock scallop (
Crassodoma gigantea) - a rather unique species of scallop that is mobile only as a juvenile and cement themselves to rocks like an oyster. Rock scallops are thick-shelled sessile scallops (Pectinidae) that end up living much more like oysters than the typically highly mobile scallops (which can swim) - they pick a spot and settle at about 4 cm diameter (~40 days old). They can grow to 15 cm width in the intertidal zone and up to 25 cm below the low tide line; they live down to 80 meters depth. This species lives on rocky coasts from British Columbia to Baja and the subtropical west coast of Mexico. Isolated thick scallop shells found on California beaches are immediately identifiable based on a deep purple patch near the hinge joint of the shell - giving this species another nickname - the purple hinge rock scallop. In the second picture you can see the dozens of jewel-like baby blue eyes that line the edge of each shell.

A similar color scheme to the clown nudibranchs but far more extravagant - Cockerell's dorid, Limacia cockerelli. This very showy sea slug is modestly sized at 25 mm maximum length, and lives from Vancouver to San Diego. This species lives from 0-35 meters, and in the southern part of its range is seen less frequently as it is typically subtidal. It preys exclusively on a single species of bryozoan.

Another, somewhat larger clown nudibranch (Triopha catalinae).

And a headshot of the clown nudibranch.

Three-colored topsnail, Calliostoma tricolor. This species presumably feeds on diatoms, hydroids, and other microinvertebrates like other Calliostoma topsnails; this individual is at the northernmost limit of its range, as it inhabits the coast from San Francisco to northern Baja California. These are supposedly entirely subtidal (5-20 meters deep) - so a rare find near the low tide line - and there are only a handful of records of this species in tidepools in the area - making this pretty little snail one of the more unusual sightings for me. There are only 356 observations for the entire species on iNaturalist.

Another shag rug nudibranch, Aeolidia papillosa - but less fun coloration than the pink one.

Black and white dorid (Acanthodoris rhodoceras). These little dorid nudibranchs are the closest nudibranchs we have to the Indo-Pacific "sea bunnies" that pop up on social media all the time. This species lives from Cape Arago, Oregon, to the Sea of Cortez in Mexico. They are thought to feed predominantly on bryozoans and attain a maximum length of 30 mm. Little data is published on their depth, but at least 0-15 meters from what I've read online. 

 An ominous looking kelp crab, Pugettia productus. These are emblematic of tidepools and kelp forests on the Pacific coast; the carapace can get up to about 8 cm across. Despite their prickly occurrence and temperament, these are mostly herbivorous crustaceans that feed on algae, and kelp in particular! They live from Alaska to northern Mexico at depths of 0-75 meters.

A brave Hermissenda opalescens heading off into the red algae.

That's all for now! No more tidepooling until May when we drive back to the Pacific coast. Many family and friends - land lubbers, extinct, and little colorful subtidal ones - are waiting for us.

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