Stories of the Tides
Often times, field guides are great for identifying unknown intertidal plants and
animals. However, interesting stories about these organisms are left out. The following
compilation of information comes from stories shared verbally and in written text. These
stories are great to tell during guided inquiry and even in the classroom before a fieldtrip to
the tidepools. Knowing the information or having it handy to share with students will make
the tidepools come alive.
Phylum Porifera - filter feeding colonies
Sponges
Sponges may look like simple plants, but many are
surprised to find out that they are animals. They are
relatively simple, but can grow in all shapes and sizes
depending on where they live. Sponges growing in calm
water tend to have more tube and volcano like structures.
In the intertidal however they will often grow very flat due
to high surf action. Sponges use many tiny holes called ostia to suck in seawater and shoot it
out larger volcano openings called oscula. While the water is within the sponge it filters out
all of the tiny organic particles, like bacteria, to feed and other nutrients needed for growth.
That would be like humans surviving off of air alone!
Phylum Cnidaria - animals with stinging cells called nematocysts. These nematocysts work
like high-powered barbs at the end of coiled ropes that shoot off when touched. These allow
the animal to take hold of its food or defend itself. Nematocysts found in the intertidal will
most likely not hurt you. Feel free to touch anemones, but it would be wise not to taste them.
Giant green anemones – Anthropleura xanthogrammica
There are many varieties of anemones in the
tidepools, and while they all have special characteristics
that separate them by species, they share some really cool
characteristics that make them similar. Most anemones
found in the intertidal are green. One may ask why? Green
anemones actually have tiny plants that live in their
tentacles and columns. The algae plants have chlorophyll
pigments that cause the anemone to turn green. The
relationship between the anemone and algae is symbiotic, which means that both organisms
benefit. Animals, even aquatic ones, require oxygen to breath. Respiration turns this oxygen
into carbon dioxide, which the algae then take up and use for photosynthesis, which gives off
oxygen as a waste. By hosting the algae within, the anemone has easy access to the precious
oxygen. In addition to providing readily available carbon dioxide, the anemone’s body makes
it a great home with built in stinging cell protection.
If you search the underside of rocks or shady cracks you might be able to find white
anemones. These are animals without algae in their bodies. It is not unhealthy; it just does not
rely on symbiosis to get any of its oxygen.
Cloning anemones/aggregate anemones - Anthopleura elegantissima
When these anemones find themselves living alone
on a bare rock, they will clone in order to reproduce. The
anemone will pull itself apart for about two days until it
rips in half. It will continue this process of cloning until it
runs out of room. If it runs into another group of
aggregate anemones that have been busy cloning as well,
war will erupt between the two colonies. The anemones
along the battle line will produce what are often called
“war clubs,” tentacles that swell up on the ends with
nematocysts. These two colonies will fight back and forth until there is a space between
them with no anemones inhabiting it. This is why you can see dividing lines between all of
the groups of aggregate anemones on the rocks during low tide.
Often times these anemones cover themselves with small rocks; these rocks are used
in a similar way to sun block, protecting them from the sun and helping them retain water at
low tide.
Brooding anemones – Epiactis prolifera
Brooding anemones come in different hues of
colors including bright red. Their bodies are flattened at
the base with radialy arranged lines. Unlike the giant
green and aggregating anemones, this animal relies on
motherly tactics to raise their young. The anemone’s
larvae swim out of their mom and position themselves
along the flattened base. They stay there until they grow into tiny anemones and are ready to
leave the home base. When you flip over a rock look for smaller anemones nearby the
mother anemone.
Phylum Mollusca – animals with a belly-foot
Black turban snail – Tegula funebralis
Looking for snails in the tidepools can sometimes be tricky. Don’t be surprised if you
pick one up and it’s actually a crab! Hermit crabs are notorious for using black turban snails’
old shell as their home. Snails are part of the “belly-foot” family, meaning that they eat,
move, and stick to rocks with their strong, fleshy body. Most snails are vegetarians and feed
on algae or seaweed. The white circle on the top of the shells is actually the oldest part of the
snail. It can live to be more than 20 years old, which is when it is no longer black on top.
Sometimes you will see coralline algae, limpets or smaller snails on the backs of black turban
snails as well.
Purple olive snail – Olivella biplicata
Just like the black turban snail shells, purple olive snail shells in the intertidal are
often found with hermit crabs within them. Purple olive snails live in sandy beaches about
an inch or so underneath the sand. If a sandy beach is nearby the tidepools you will likely
see a hermit crab making one of these beautiful shells into their home.
Miwok Indian tribes of the northern California coast and Chumash Indian tribes of
southern California’s channel islands used these beautiful shells as money for trade and
decorations on clothing and jewelry. Imagine begin able to go out and collect dollar bills on
the beach! If you look closely on the shell you will see very fine lines showing the pattern of
growth. The oldest part of the snail is at the very top of the spiral. The snail puts on tiny
layers each year as it grows more and more. Sometimes people ask how old many of the
creatures of the tide pools are. This is a rather difficult question to answer, but we can get
some sense by looking at the number of lines on the purple olive snail. Some snails you pick
up will have varying patterns. Some of the lines are very straight while others are very
jagged. The jagged lines may indicate a rough point in the snail’s life where maybe they
were attacked or lived through a rough winter. The smooth lines indicate an easy year for the
snail. By reading the lines we get a story of this snails long-lived life experiences.
Chitons
Chitons have remained virtually unchanged for over
500 million years! There’s one thing that you must remember
in the search for chitons: “eight plates are great!” Just like
terrestrial pill bugs, chitons have hard plates that protect their
body’s “belly-foot” and let them conform to uneven surfaces.
A chiton can be motionless and uninteresting to the untrained
eye, but if you manage to find one that lets loose from the
rock, you’ll discover something interesting and familiar. When removed from the rock,
chitons will curl into a crescent moon shape in order to protect the soft foot inside.
The Katy chiton is often found exposed during the
day, feeding on algae while most chitons are found in crevices
and under rocks. Other chitons may remain in the same place
for a long time while Katy chitons graze during the day. The
gumboot chiton is especially interesting. Unlike smaller
species found in the intertidal, the gumboot can be easily
dislodged and examined. In the gill chamber beside the belly
foot of the gumboot is a small white parasitic worm that has
found a safe home.
Nudibranchs
Keep your eye out for these small creatures. Often overlooked, over one hundred and
seventy nudibranchs can be found along Pacific Northwest shores. They are essentially
snails with out shells, but often much more colorful than our common garden slugs. They
come in a variety of colors including lemon yellow, bright red, orange and even purple!
Many nudibranchs are often missed though because they can be translucent in color making
them nearly invisible. The name nudibranch actually means “naked gills”. Some species use
finger like cerata on their backs for breathing and digesting food! The cerata can also be
used for defense. Many nudibranchs feed on the tentacles of sea anemones to steal their
nematocysts. Because they have special mucus to protect them, they are not harmed by the
harpoon-like stinging cells. The nudibranchs simply gobble them up and sort the stinging
cells for all of the cerata. The nudibranchs are then armed with the weapons of their prey!
Other nudibranchs lacking cerata have gill plumes located on their lower end. Like every
little brother or sister nudibranchs are picky eaters and feed almost exclusively on colorful
sponges.
Limpets
It’s impossible to find two limpets that look
identical. Their variety in colors and patterns make
searching for them an adventure with something new under
each rock. Limpets rely on their powerful suction power to
protect them from predators and pounding waves. In fact
pounding waves only allow the limpet to hold tighter onto a
rock. These simple creatures also have the ability to sense
when an enemy, usually a sea star, is around. When the situation arises, they can glide away
with their shell hiked up like a big southern bell skirt. The alternative is to just let go of the
rock and fall out of harms way.
Most limpets are vegetarians and graze on thin layers of algae that grow on rocks.
Their sandpaper-like tongue extends to the rocks and conveys the broken up food particles
into their mouth. Limpets have a designated home territory where it cruises around during
high tide. When the water recedes, some species even nestle into a “home-scar”, which over
time they have carved into the rock.
Mussels
You will most likely find mussels living in large
clumps. Where a young mussel chooses to settle will
determine the length of its life. Too high and it will die from
dehydration, too low and it will get eaten. Most choose a
place that already has adults present. Once a young barnacle
has found the right spot, it attaches itself with strings made
of protein called byssus. These byssal threads are elastic
bands secreted by a gland that provide it with limited movement. They are also what allow us
to wiggle them like a loose tooth. When the tide comes in the animal replenishes itself with
oxygen rich water while it collects plankton for its meal. It does this by siphoning water and
pulling it over its gills, which collect oxygen and food simultaneously.
Phylum Echinodermata – animals with penta (5) radial symmetry
Ochre stars – Pisaster ochraceus
You might know this animal as a starfish, but this is
a misconception because the sea star is most definitely not a
fish. Also called an ochre star, the common sea star can be
divided into five equal parts, and can even regenerate lost
arms. Following the path of a sea star can become very
confusing because it can move in whatever direction one of
its arms points it in. Not having a head or tail allows it to switch directions without turning
around. The underside of the animal is covered in tube feet, which move it along at three
inches a minute. The tube feet at the very tip of each arm don’t suction, but are light sensitive
to the animal can move out of direct sunlight. Aside from locomotion, the sea star’s tube feet
allow it to hold onto a rock, which protects it from harsh waves.
The stomach of a sea star is exerted from the animal’s underside when it’s time to eat.
It can slip into crevices to find and pry apart delectable morsels like mussels, limpets, and
snails. The stomach juices dissolve smaller animals outside of the sea stars body, and the
resulting liquid is then absorbed. So you could say that the sea stars like to literally eat out
for every meal!
Sunflower star – Pycnopodia helianthoides
With the ability to move up to 40 inches per minute,
the sunflower star navigates the subtidal and intertidal with
up to 24 arms and over 15,000 tube feet! The sunflower star
is hungry predator, eating crabs, sea cucumbers, snails,
chitons, and sea urchins. When the tide is low, you can see
these soft skinned, colorful creatures hanging out in shaded
areas of the pools. If the sunflower stars are in the sun, you can see small light sensors (they
look similar to the tube feet, but smaller) on the ends of their arms that will navigate them out
of the sun to avoid the dangers of drying up in a shallow tidepool.
Purple sea urchins – Strongylocentrotus purpuratus
The spiky purple spines and tube feet of the sea
urchin serve numerous purposes. The hard spines help
attach food and protect the animal from predators. The sea
urchin can also rise up onto the ends of the spines and walk
away like they are on stilts. Their tube feet allow them to
pass bits of food down to the mouth, which lies on the
underside of the animal. In addition to being an aid in food
digestion, tube feet are also the site of gas exchange: instead of using lungs or gills for the
uptake of oxygen, sea urchins use their tube feet.
Purple sea urchins prefer areas with strong wave
action. To protect themselves from especially harsh waves,
they can carve individual holes in the rock in which they
settle. The holes may take generations to dig, but it provides
for excellent protection from waves and predators. It also
makes eating easy, as each wave delivers it meals of algae,
seaweed and plankton. In some cases a sea urchin can grow
bigger than its home, make it stuck for life in the rock.
Many animals find sea urchins to be irresistible. Sea stars, sea gulls, and sea otters find them
to be a tasty treat. It’s easy to pick out a sea otter that regularly eats purple sea urchins
because of their purple stained teeth. Even people find the gonads of the animal to be a
delicacy!
Humans can use sea urchins as an indicator of ocean water health. Since they are one
of the first organisms to show signs of stress in less than perfect water conditions, the loss of
urchins from an area is a good indicator that something may be wrong with the water.
Phylum Arthropoda – animals with segmented legs (including crustations
Hermit crab – Pagrus spp.
Pick up a snail shell in the rocky intertidal and you’d
be surprised that it is actually a hermit crab! Not having a
home of its own, a hermit crab will spend its lifetime
searching for the perfect lodging. Its keen sense of smell
leads it to the shells of dead gastropods. As their soft
vulnerable body grows, it requires bigger and bigger shells. In
a hermit crabs busy life of finding new mobile homes and food, it’s hard to find time to mate.
When a male finds a female in which he is willing to fight over, he carries her around until it is
time for her to molt. At this point, they both release almost completely from their homes and
mate. Two appendages on the left side of her body, called “swimmerets” hold the fertilized
eggs until the young are released from the shell and into the water. Through evolution, hermit
crabs have lost some legs, but kept the dominant two pairs that are used to grab shells and
secure the animal into new homes.
Purple shore crab – Hemigrapusus nudus
The purple shore crab is one that you will always be able to find. It is distinguished
by the reddish-purple spots on its claws. Don’t be fooled though, the main body color can
vary greatly. Purple chore crabs feed primarily on seaweed and algae, but will occasionally
enjoy a dead animal carcass every now and then. Their main predators are shorebirds and
some fish. As crabs grow, they must molt their shells that are too small. During this time they
are especially vulnerable as prey. Crabs are distinctly male and female. You can tell the
difference by the shape of their underside. The male’s abdomen is V shaped while the
female’s is U shaped.
Phylum Chordata – animals with a backbone
Tidepool sculpins – Oligocottus maculosus
These small fish are very adapted to the tidepools;
they hug the bottom of the pools and are able to use their
fins to scoot around. When the tides are high, the sculpins
leave their home pools to search for food in the upper
intertidal pools. When the tides begin to fall, they return
to their home pools! It is unknown how they are able to
return to their specific pool, but it is hypothesized that it is
through the use of smell. Returning to a home pool is a safety mechanism for the sculpin,
assuring that they will not get stuck in a water-less pool too high in the intertidal. Tidepool
sculpins also have the ability to camouflage to their pools to help them hide from any hungry
birds above.
Black oystercatcher – Haematopus bachmani
Oystercatchers forage at low tides on a variety of
intertidal animals, but especially on mussels and limpets. As
a mussel gapes open when splashed by a rising tide, they are
vulnerable to oystercatcher predation. The bird must deliver
a quick, sharp stab between the two shells and sever the
adductor muscles so that the mussel doesn’t close down on the oystercatcher’s beak. Once
inside, the oystercatcher will withdraw the meat and swallow, yum! With limpets, a true
treat, oystercatchers will jab at the edge of the shell in order to dislodge the limpet from a
rock. The oystercatcher will then shake out the meat and swallow it in one gulp. Look for
empty limpet shells that have a nick out of their edge. This is a sign an oystercatcher has
eaten them.
Algae – not true plants because they don’t produce flowers or seeds
Bull kelp – Nereocystis luetkeana
Bull Kelp grows tall in Pacific Northwest subtidal
zones creating diverse kelp forest communities underwater.
Think of all of the species this plant provides homes for!
Bull kelp grows annually starting as a new plant each year
on the sea floor reaching up to the sunlight rich surface. At
the end of the growing season the 70-foot long plants will
wash ashore, entangled from the waves. However you are
likely to find bull kelp washed up as the growing season continues. The root like holdfasts
are strong and will often have rocks still attached with their strong grip. The long stem,
called a stripe, extends up to a large bulb float. This hollow float was used by coastal Native
American tribes as a bowl or cup to carrying water. The stripes were also dried and used for
fishing line. It was also pickled and eaten by early pioneers. They can also make a great
jump rope!
Laver or nori – Porphyra perforata
This red seaweed catches the sunlight beautifully on a clear day showcasing its
iridescent qualities. This plant dries up quickly in the high tide zones, but can easily rehydrate once the tide comes back up. This is the same plant used to make sushi nori, which
is baked into sheets, and is cultivated worldwide as food. Pick a small piece and taste it!
Rockweed – Pelvetiopsis limitata
Rockweed is the Northwest’s most commonly
seen algae. It grows on rocks in the intertidal instead of
stretching up from the ocean’s floor like its much larger
cousin bull kelp. The button-like holdfast keeps the algae
from drifting away from its rocky substrate. Rockweed
holds moisture extremely well so it can withstand drastic
changes in temperature. Tannins, a chemical released by the algae, prevents it from being
eaten by hungry tidepool creatures. The small bumps on the swollen ends of rockweed are
sites of reproduction. It chooses the perfect time at low tide to release the eggs and sperm
from the bulbs. The developing plant must eventually attach to a rock and grow a new
holdfast.
Coralline Algae - Corallina, Callirarthron and Bosiella spp.
Don’t fool this plant, or any other plants in Oregon’s rocky intertidal for coral. While
these algae may look like a hydrocoral, it’s actually coralline algae, which means that it is a
plant and not an animal. In the water they are vibrant pink, but above water for long periods
of time they turn white. What you are seeing when it’s white is the calcium carbonate that
comprises their cell walls. Calcium carbonate is the same stuff that you bones are made of.
Take off a piece and try crumbling it in your fingers, its tough! It provides structure and
tough enough to withstand storms and repels grazing animals.