Mollusks

 

Turban snails, mussels, and barnacles on an intertidal rock at McClures Beach.

The phylum Mollusca is large and diverse, encompassing ten different classes of animals. The animals are most commonly recognized as one of three different types: the bivalves, the univalves, and those without shells (or with very small internal shells, ex. slugs). Bivalves are mollusks with two shells such as clams and oysters. Univalves are animals with one shell such as a snail. Mollusks without shells include squid, banana slugs, and octopi.

Some mollusks are terrestrial, occurring in most environments on earth, while others live in the water for some or all of their life. Many of the most popular mollusks are marine species because they are pretty and some are caught for food or jewelry. Some of the qualities that define a mollusk are definite organs (mainly heart, gonads, and kidneys), a complete digestive tract, and a muscular foot. Although their bodies are not segmented, they do have two definable parts: the head and the foot. Their shells are made of calcium carbonate. The shells are very decorative on the inside for many marine species, and the outside for many snails. Most mollusks have at least two stages of life and their second stage (or adult phase) is often marked by bearing a shell.

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Chitons

Polyplacophora are more commonly referred to as chitons. They look ancient, like a trilobite of the ocean. Their body is an elongated dome with eight overlapping plates and they are usually as big as a quarter. Making their living on algae, they are commonly found in intertidal areas as they cling to the rocks, but usually they are camouflaged very well with cryptic coloring.

 

A colony of mussels.

Bivalves

Those animals with two shells are conveniently all lumped together in class Bivalvia. They don’t have a formal eating structure, so they filter food by siphoning it from the water with gills between their two valves. Their organs, including their nervous system, are all located between the two shells and they have a muscular foot that can stick out. This foot is used for locomotion, attaching to rocks, or both. Bivalvia is diverse and includes animals like the oyster, which give us pearls by covering bits of sand that come into their system with the calcium carbonate that they use for their shells. The waters surrounding Point Reyes are a popular spot for collecting clams, mussels, and oysters. Check our Fishing page and Marine Life Protection Act page for more information on where collecting bivalves is permitted, harvest limits, and for information about the annual mussel quarantine.

Tusk Shells

The class Scaphopoda are known as tusk shells and found in marine environments world wide. They look like elephant tusks that are 15cm long, and they feed on the bottom of the sea. Most likely, these animals occur at our Seashore, but the chances of seeing them are extremely unlikely.

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A banana slug.

Gastropods

Gastropoda is the most widespread class within Mollusca. It is estimated to have as many as 75,000 species and undoubtedly many of its species occur at Point Reyes. The gastropods are univalve animals and can be terrestrial, freshwater, or marine and include snails, abalones, limpets. Their name is from Greek roots with gaster referring to stomach and poda referring to feet. This makes sense because their major two body parts are their head region (with most of their organs) and their muscular foot. This separation also comes from a process which also defines a gastropod called torsion. Torsion occurs during their development into an adult; their internal organs twist 180 degrees and results in the separation of its organs from its foot. Although the gastropods have some similarities, they are for the most part extremely varied and because they all live in very different places, they eat very different things.

The banana slug is one of the most commonly spotted Gastropods at Point Reyes.

 

Black abalone (Haliotis cracherodii).

The abalone is by far most famous specimen of Gastropoda at Point Reyes. It is a beautiful marine snail that at one time was extremely abundant along the coast. Black abalone is one of seven abalone species found in California's intertidal waters. Commercial fisheries for black abalones began in 1968, and by the 1990s, landings had plummeted to almost zero. But fishing wasn't the only culprit. Black abalone populations have been severely depleted by withering syndrome. This disease, caused by a bacterial infection, halts the abalone's production of digestive enzymes. No longer able to digest food, the abalone must consume its own body mass. The disease was first recognized in the mid-1980s and has since decimated black abalone populations by up to 99% in some regions. As a result, black abalones have been classified as critically endangered by the International Union for the Conservation of Nature. As a result of the deplete populations, there are currently (as of 2020) very stringent restrictions on the collection of abalones in northern California. Learn more about withering syndrome in the Multimedia section below and about regulations for harvesting abalone on California Fish and Wildlife's Ocean Sport Fishing Regulations website.

Cephalopods

Most intelligent and softest are the easiest way to describe the cephalopods. The creatures of Cephalopoda have lost their shells, and compensate with a far more developed brain. Also, they have an overdeveloped muscular foot, which is turned into arms or tentacles. Its flagship members are octopus, squid, cuttlefish, and nautilus. Besides being able to make a living in difficult places, they are able to defend themselves in unusual ways. Most are able to change color and texture rapidly to match surroundings, and are also able to shoot an ink cloud to make a getaway.

Point Reyes Seashore has the red octopus (Octopus rubescens), but like may inhabitants of the sea, it is almost never seen. They do live in intertidal areas, but spotting one is extremely rare and if you do, it is safest to not touch the animal. Another common cephalopod is the common squid, but don't expect to see this one either. They only will come towards the shore area to breed and then die.

Text for this page was primarily written by Kristen Truchinski.

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Multimedia Presentations

From 2007 to 2012, Pacific Coast Science and Learning Center Science Communication Interns produced a series of podcasts, videos, and audio-slide shows exploring science from Bay Area national parks. Two of these The Natural Laboratory multimedia products focused on mollusks—one on Olympia oysters and one on the Humboldt squid. Listen to the podcasts below. Visit our Multimedia Presentations: The Natural Laboratory Audio Podcasts page for additional podcasts.

 

• The Natural Laboratory Podcast: Searching for the Endangered Black Abalone in Northern California

  
  

  A The Natural Laboratory podcast produced by the Pacific Coast Science and Learning Center in 2012 in which Cassandra Brooks interviews Amy Henry, an intern looking for black abalones in the Golden Gate National Recreation Area and Point Reyes National Seashore.

  Credit / Author:

  Cassandra Brooks / Pacific Coast Science and Learning Center

  Date created:

  02/15/2012

  Audio Transcript

  [Introduction]

  [intro music]

  This is the Natural Laboratory, a podcast exploring science for Bay Area National Parks. I'm Cassandra Brooks.

  [intro music fades and is replaced by upbeat guitar-led music for duration of the podcast]

  Black abalone is one of seven abalone species found in California's intertidal waters. This small abalone, with a smooth dark shell, has succumbed to the same fate as most abalones: overfishing. Commercial fisheries for black abalones began in 1968, and by the 1990s, landings plummeted to zero.

  But fishing wasn't the only culprit. Black abalones have gotten sick—really sick—with withering syndrome. This disease, caused by a bacterial infection, halts the abalone's production of digestive enzymes. No longer able to digest food, the abalone must consume its own body mass.

  The disease was first recognized in the mid-1980s and has since decimated black abalone populations by up to 99% in some regions. As a result, black abalones have been classified as critically endangered by the IUCN.

  Southern California populations have been especially hard hit by withering syndrome, yet little is known about the status of Northern populations.

  [Darren Fong Interview]

  Darren Fong: We got a request from the federal agency—National Marine Fisheries Service—for information about the status and trends of, uh, black abalone in our park and we actually had no information to provide them because we never did any surveys for that species within our park.

  Cassandra Brooks: That's Darren Fong, Aquatic Ecologist with the Golden Gate National Recreational Area. Per request, Fong set out with interns Amy Henry and Kari Eckdahl looking for black abalones in the Golden Gate National Recreational Area and Point Reyes National Seashore. Here's Amy Henry.

  [Amy Henry Interview]

  Amy Henry: Well, no large-scale survey has been done of black abalone north of San Francisco Bay before, or even in the Bay Area. Black abalone have never been particularly common in this area, but no one has ever been out and surveyed these sites before. So, although we know that they're rare, we don't know how rare. So, the data and information that we're collecting is going to provide information for future studies, for the studies of these endangered species, and will lead to better legislation and how to protect them.

  CB: So far, they've found black abalones, but not very many of them, and none with withering syndrome. But these surveys are just the first step.

  Part of their challenge is getting down to the rocky—and sometimes treacherous—intertidal, where the abalones live.

  AH: So, the sites that we've been surveying have been identified using Google Earth and a project, a few years back, called the Coast Biophysical Inventory. This project identified areas of rocky coastline where abalone possibly could live. So, basically, all that we know going to a site beforehand is that it's rocky. So, we've interviewed park rangers from the local area to find out about the best trails to get down to sites. Sometimes this requires a rope to climb down crumbly steep cliffs, sometimes we get there and it doesn't look like good abalone habitat at all and we are sorely disappointed.

  We're also working at very early in the morning hours. The timing of our surveys have to be going with the low tides, and they have to be negative tides, below zero tide. And some of these will occur at 4:30 in the morning. We've woken up at 3 am before and taken a hike out in the dark with flashlights where we think there are spooky creatures behind every turn.

  CB: To Amy and Kari, all the early mornings and scrambling over cliffs have been worth it.

  AH: The Park Service really has a mission that you can get behind. You can really support and know that the work you're doing is for the benefit of all the citizens of America and California and to protect it for future generations. And even for our small little piece of protecting black abalone, it's a really beautiful creature that I never appreciated before, never knew much about before. And, hopefully, because of our work, we'll be able to show it to our children in the future and say, "We had a piece in protecting this animal from going extinct."

  CB: With the Pacific Coast Science and Learning Center, I'm Cassandra Brooks.

  [music fades]

 

• The Natural Laboratory Podcast: Fishing for the Humboldt Squid

  
  

  A The Natural Laboratory podcast produced by the Pacific Coast Science and Learning Center in 2009 in which Casandra Brooks interviews four marine biologists from Stanford University's Hopkins Marine Station who are studying the Humboldt squid in central California's coastal waters.

  Credit / Author:

  Cassandra Brooks / Pacific Coast Science and Learning Center

  Date created:

  11/24/2009

  Audio Transcript

  The Natural Laboratory Podcast Transcript: Fishing for the Humboldt Squid

  Introduction

  This is the Natural Laboratory, a podcast exploring science for Bay Area National Parks. I'm Cassandra Brooks.

  [music]

  Today, I am out with scientists and educators off Monterey Bay searching for the Humboldt squid (Dosidicus gigas), also known as the Jumbo squid. Or in Mexico, where the fish are caught commercially, they call them “Diablo rojo”—the red devil.

  These voracious deep-water predators, which can grow to up to ten feet long and swim 24 kilometers per hour, are new arrivals to the central California coast. Scientists from Stanford University's Hopkins Marine Station are studying the squid, trying to understand why they've moved into the northeast Pacific coast and what affect they might have on the local ecosystem.

  I join the Stanford crew for a fishing adventure, along with scientists with the National Marine Fisheries Service, local fishermen and educators with the Monterey Bay National Marine Sanctuary.

  Interview with Erik Larsen

  Erik Larsen: So I'm Erik Larsen, captain of the research vessel Fulmar and we just left Monterey heading to a point about four miles southwest of cypress point off of Carmel and we are going to stop the boat and set up for some squid jigging in about 700 meters and see what happens.

  Today it's a little windy and a little bit of swell, 6- to 7-foot swell, supposed to get to 25 knots of wind, but right now, it's not too bad, a little lumpy, of course that's just me talking (he laughs).

  Interview with William Gilly

  Cassandra Brooks: I'm standing on the back of the boat with professor William Gilly, who is spearheading the Humboldt squid tagging program as part of Hopkins tagging of Pacific predators program.

  We are perched on the side of the boat, holding sturdy fishing rods outfitted with large spiked glow-in-the-dark jigs. We drop the jigs a couple hundred feet down in the water and wait, hoping to trick a squid into biting.

  Humboldt squid feed in frenzies, snatching anything they can find in the water, including a variety of different fish species, but occasionally other squid that get in the way.

  They seize prey with long tentacles covered with rings of prickly serrated teeth, which they use to bring the prey up to their mouth where they devour it with their large sharp beak.

  If the squid are down here and actively feeding, they're sure to latch onto the jig.

  Gilly's research team uses satellite tags to record an animal's movements underwater in space and time. Once affixed to a squid, the tag tells the researchers how deep the animals are diving, where they are traveling to and where they prefer to live. Historically, the Humboldt squid were seldom found further north than Baja California, Mexico.

  Then with the 1997/98 El Nino, the squid came en masse and have maintained a fairly regular presence since then.

  Cassandra Brooks: So, why do you think they are here?

  William Gilly: Well I guess there is stuff for them to eat. [chuckles] It's not clear why they seem to be expanding their presence to more northern latitudes, maybe there are too many in the south and they need growing room. But they seem to be establishing themselves in areas that in recent history have been not subject to their presence. Like, Monterey Bay, and they seem to be getting established off the Olympic Peninsula in Washington, a lot around Vancouver and the Queen Charlotte Islands.

  CB: Does it seem like they are here to stay?

  WG: Well they have been here more or less stably since 2002 and unless something changes to make what they are eating go away, I think they will probably be here for a while. That's my guess

  Interview with Julie Stewart

  CB: Julie Stewart is a graduate student in Gilly's lab who is looking at oceanographic properties that may correlate with the squid's seasonal invasions and migrations.

  CB: So, you think it's a combination of climate change and ecosystem changes?

  Julie Stewart: I think so, there has to be, they have to be able to get here to begin with, so climate change is providing a route, but once they are here, they have to be able to stay here. Physical oceanographic conditions have to be correct and they have to be able to find food, they have to be able to avoid predators and to be able to reproduce. Which is a big thing.

  The big question is establishment. Is this thing able to establish itself, what is it eating, what is it doing?

  If these squid are going somewhere else to spawn and each generation is re-invading and re-establishing itself then that's an interesting question, but right now we just don't know.

  CB: So, the satellite tags will actually give you information as to whether they are just migrating here to feed and then returning back south?

  JS: That's the goal.

  Interview with Danna Staaf

  CB: To find out if the squid are reproducing here in California, Danna Staaf, a graduate student in Gilly's lab, has been searching for squid babies, or what she calls paralarvae.

  CB: So, we were just out here doing a plankton trawl.

  Danna Staaf: That's right. That's one of the main ways we use to look at where the squid babies are and what the squid babies might be eating. It gives you an ecosystem perspective of what's available for them.

  We are up here in California in cold water, which is not where they spawn, at least not where we think they spawn. We know that Humboldt squid spawn in warm waters off Mexico, and Central America and further south than that, but we have not yet found any baby Humboldt squid in California. But we keep looking, because as waters get warmer and conditions change, they might well start spawning here. We want to be the fi rst to know. I do think it's too cold for them (it's too cold for me!).

  Conclusion

  We continue fishing for the rest of the day, but didn't find any adult or larvae Humboldt squid.

  Gilly and his team aren't sure why there were scarce today, but they'll be out again soon fishing in nearby waters.

  For the Pacific Coast Science and Learning Center, I'm Cassandra Brooks.

 

Additional Reading

Leskiw, D. 2020. Holding Fast, Or Failing? There are dozens of confounding elements working against abalone recovery on the California coast. Earth Island Journal 35(1): 18–25. Available at https://earthisland.org/journal/index.php/magazine/entry/holding-fast-or-failing-abalone-california/ (accessed 26 August 2020).