Gargantuan Gastropods

All summer long, the tabloids and gossip columns are full of Malibu celebrity sightings, but here's a really big celebrity (or possibly a sea-lebrity) that's been overlooked: Aplysia vaccaria, the California black sea hare, a mild-mannered sea slug that has the distinction of being the world's largest gastropod. Eat your heart out, Orlando Bloom. Unless otherwise noted, all photos are © 2016 S. Guldimann.

Were you aware, dear reader, that the Malibu coast is currently playing host to large numbers of the world’s largest gastropod? While that sounds alarming like the plot of a 1950s B movie, this celebrity among slugs is a peaceful vegetarian, despite a passing resemblance to that movie monster favorite, The Blob.

Although it bears a distinct resemblance to Hollywood's favorite invertebrate horror,  A. vaccaria is mostly harmless. Image: Wikipedia

While the California brown sea hare, Aplysia Californica, is a regular tidepool resident in Malibu, this year, its much larger relative, Aplysia vaccaria—the black sea hare—is turning up in large numbers. No one at the Malibu Post can remember seeing more than one or two black sea hares. It's unclear if the vast number showing up this year is related to the unusually warm water or if other factors are in play.

Brown sea hares are smaller and usually a lighter color than their giant relative. Both species graze on kelp, which they chew up with a rasp-like tongue called a radula. Sea hares get their name from their rabbit ear-like appendages—actually scent organs called rhinophores.

Brown sea hares can grow to be impressively large for a slug, often measuring more than 15 inches from nose to tail.  A. vaccaria, however, can grow to be more than three feet long and weigh as much as 30 pounds. That’s one big slug. The largest specimens rarely turn up in the intertidal zone, but this year’s Malibu crop of A. vaccaria is still impressive, resembling a football in size and shape.

This unfortunate slug was left high and dry by the receding tide. However, sea slugs have adapted to the extreme conditions of the intertidal zone and can survive several hours out of water even in bright sunlight during low tide. The holes in the rock near this slug's head measure about an inch across, giving an idea of the creature's size.

Sea hare eggs look exactly like noodles, but probably would not be pleasant to eat. Both California species contain toxins from their algae diet that make them inedible to almost everything except lobsters—the garbage crew of the sea—and green anemones, which appear to be immune. There's a type of Australian sea hare that is so toxic that dogs have died after coming into contact with it. California sea hare species are much less potent, but it's a good idea not to handle them and to keep dogs away from them. Brown sea hares can release a purple dye that is a skin irritant. Black sea hares appear to depend on their terrible toxic taste for defense.

Sea hares are usually observed grazing on seaweed in tidepools during low tide, like this California brown sea hare, or waiting for the tide to rise while stranded, blob-like, on the beach, but they can also "fly" through the water with their wing-like parapodia—literally "foot wings."

There's actually a third giant gastropod on the loose in Malibu: the giant limpet, which is really another type of sea snail and not a true limpet at all. This species, Megathura crenulata, is the only known member of its genus, making it a monotypic genus. 

M. crenulata can grow to be nearly a foot in length. It may not be much to look at, but compounds in the blood of this primitive snail apparently hold promise as a cancer treatment. According to a 2011 article in the Journal of Immunology Research, "Keyhole limpet haemocyanin (KLH) appears to be a promising protein carrier for tumor antigens in numerous cancer vaccine candidates." 

After a sort of gastropod goldrush in the early 2000s that ran the risk of pushing this rare animal to the edge of extinction, M. crenulata is now being raised via aquaculture techniques.

Megathura crenulata, the only known member of its genus, lives only off the coast of California. The blood of this primitive snail species has become a key ingredient in vaccine research, but the burgeoning demand for the giant limpet blood could push this poorly understood and increasingly rare species to extinction. 

Here's a side view of M. crenulata, suggesting a very old person shuffling along under a large umbrella, and revealing the creature's true snail nature. Sea hares also have a shell, but it is internal and vestigial.

Sea hares are also important for medical research. According to the Aquarium of the Pacific's sea hare page, the California brown sea hare may not have a lot of brain wattage, but it has "the largest neurons in the animal kingdom, making it possible to identify individual nerve cells that are responsible for specific behaviors. They have been and are being used extensively in studying memory, behavior, and learning."

Humans may not find sea hares or giant limpets lovely to behold, but there's more to Malibu's giant gastropods than meets the eye. 

A football-sized specimen of A. vaccaria waits for the incoming tide on the beach at Little Dume.

The Hunting of the Snark

Shadows or sharks? During autumn in Malibu there's a good chance it's sharks. All photos @ 2014 S. Guldimann

"We have sailed many months, we have sailed many weeks,

   (Four weeks to the month you may mark),

But never as yet ('tis your Captain who speaks)

   Have we caught the least glimpse of a Snark!

"We have sailed many weeks, we have sailed many days,

   (Seven days to the week I allow),

But a Snark, on the which we might lovingly gaze,

   We have never beheld till now!

—Lewis Carroll, The Hunting of the Snark

I was looking for sharks, not Snarks, and pursuing them with cameras and snorkels, but my high-tech hunting aids were of no more use to me than thimbles and forks were to Carroll's unlucky Bellman and his Snark hunting crew.

One morning a little more than a week ago, the shallow water at Point Dume was full of leopard sharks, sleek, swift, dappled shadows, weaving amongst the swimmers' ankles. They were joined by their smaller cousins the smooth-hound sharks and by the aptly, if inelegantly, named shovel-nosed guitar fish, and there were dozens of them. 

It's a sure sign that autumn has arrived when the small sharks and rays begin to aggregate in the shallow warm water, but you only get a good look at them when conditions are calm and the water is clear. Conditions were perfect last week, as clear as glass and as warm as bathwater.

 I wrote about the phenomenon for the Malibu Surfside News, but the sharks proved elusive and, while I prowled the shallows every day for a week, GoPro camera in hand, I couldn't get a good photo for the article. The sharks remained as elusive as, well, Snarks.

"Just the place for a Snark!" the Bellman cries repeatedly in Carroll's Hunting of the Snark. It was, too. For sharks, if not Snarks. Or it would have been if there were any sharks to see. Leopard sharks congregate in warm, shallow water like this Point Dume cove in autumn, where they give birth to their young and feast on sand crabs. Although leopard sharks looks every inch a shark and can grow to more than five feet in length, they are harmless to humans, and eat primarily crabs, worms, clams and small fish like anchovies and grunion. 

I started my search in the shallow water near the reefs, traveling along the sandbars and around the new trenches of rocks revealed by the recent series of big waves. Those waves have removed large amounts of sand and completely changed the underwater landscape, but the big outcroppings of volcanic breccia—a tough, erosion-resistant stone, form fairly permanent landmarks. Between these reefs are areas that can shift swiftly between sand and cobble, depending on conditions.

 I saw plenty of sculpin, despite the fact that the sculpin's goal in life is not to be seen. This is a tiny tidepool sculpin, Oligocottus maculosus.

I also saw sea anemones, which have already begun to colonize the barren stretches of rocks and cobbles revealed by the recent wave action.

Here's a small secretive shrimp, hiding in the spiral skeleton of a sea shell. But still no sign of leopard sharks.

Like the Bellman and his crew, I hunted early and late. A little too late on this occasion. Once the sun moves behind the cliffs the water suddenly turns dark and mysterious. It's like swimming in ink. There could be all kinds of things down there, and you would never see them until it was too late...

A shark! Is that a shark?

It's not a shark. It's a California corbina, Menticirrhus undulatus—a large surf fish that belongs to the croaker family. Just like the leopard sharks, corbina like to eat sand crabs. They often congregate among the sharks and seem entirely unconcerned by their presence. They appeared to have the sand crabs all to themselves on this particular day. There wasn't a shark in sight...

A shark! (or at least the tail of a shark). 

And then a couple of sleek, spotted leopard sharks, slithy as Carroll's celebrated slithy toves, slide swiftly by. Alas, that was about as close as I got to documenting the quarry of my Snark hunt...

"There is Thingumbob shouting!" the Bellman said,

   "He is shouting like mad, only hark!

He is waving his hands, he is wagging his head,

   He has certainly found a Snark!"

They gazed in delight, while the Butcher exclaimed

   "He was always a desperate wag!"

They beheld him—their Baker—their hero unnamed—

   On the top of a neighbouring crag,

Erect and sublime, for one moment of time,

   In the next, that wild figure they saw

(As if stung by a spasm) plunge into a chasm,

   While they waited and listened in awe.

"It's a Snark!" was the sound that first came to their ears,

   And seemed almost too good to be true.

Then followed a torrent of laughter and cheers:

   Then the ominous words "It's a Boo—"

Then, silence. Some fancied they heard in the air

   A weary and wandering sigh

That sounded like "-jum!" but the others declare

   It was only a breeze that went by.

They hunted till darkness came on, but they found

   Not a button, or feather, or mark,

By which they could tell that they stood on the ground

   Where the Baker had met with the Snark.

In the midst of the word he was trying to say,

   In the midst of his laughter and glee,

He had softly and suddenly vanished away—

   For the Snark was a Boojum, you see.

Suzanne Guldimann

9 October 2014

It was a Boojum...

Between the Tides

October low tides this week, generated by the full moon, reveal the hidden world of tide pools at Point Dume. 

It's a strange and perilous world inhabited by ethereal and alien beauties and swift and deadly predators. The afternoon low tides generated by the full moon on Friday offered an opportunity to explore that hidden world, which  exists between the tides along Point Dume's rocky shore.

Volcanic rock, which weathers more slowly than the surrounding matrix of sedimentary stone, forms an elaborate network of pools along the shore from Paradise Cove to Point Dume. The entire area is now a Marine Protected Area. It's also an Area of Special Biological Significance. It's easy to see why: the rocks and colorful seaweeds hide an amazing variety of species, including crabs, snails, fish, anemones, urchins, starfish, octopus, barnacles, mussels, chitons, nudibranch, and a host of other organisms, that range from the mundane to the extraordinary.

Anthropleura elegantissima, the aggregating anemone, lives up to its Latin name, with elegant but deadly tentacles that it uses to paralyze small prey. The green color is generated by symbiotic algae. 

A great egret forages for supper among the tide pools.

Life in the intertidal zone is challenging. Organisms face pounding surf, periods of exposure during low tides. They are also impacted by pollution, and in some places are being loved to death by humans, who inadvertently trample habitat and disturb or remove plants and animals.

According to the OC Marine Project, a study conducted by Richard Ambrose, and J.R. Smith, in 2004,  "found that rocky intertidal sites within Santa Monica Bay were subjected to an alarming number of visitors at high use sites (25,000-50,000 visitors per year per 100 m shoreline)."

Point Dume's tide pools are still fairly pristine, due mostly to the fact that the visitors have to walk to the location, unlike areas that are located close to Pacific Coast Highway and easy parking. Humans enjoy exploring the tide pools for fun and education, but birds, like the great egret, above, and other coastal species depend on the intertidal zone for survival.

For thousands of years, humans also depended on the rocky shore for survival. One has only to climb to the top of the Point Dume headlands to find the evidence: scattered all over the cliffs are the shattered remains of sea shells. Bits of mussels and clam shells are everywhere. Abalone shell fragments, still iridescent and beautiful even after hundreds of years, are a reminder of a vanished era when the Chumash made their home here. Abalone where abundant then. They were plentiful even when I was a child. Today, the shards that surface from the ancient Chumash settlement are almost the only reminder that this species flourished here once. It's a sobering reminder of just how fragile the balance really is.

Ochre stars, which are more often orange or purple than anything that could be called ochre, and a colony of mussels occupy the rocks off Point Dume. These tide pools, located at the eastern edge of the headland, are constantly battered by powerful surf, but they are also protected from terrestrial predators, because they are only accessible by during the lowest tides.