Water, as we all
know, is a liquid, and moves freely in response to the force of the
Earth's gravity. It also moves in response to other gravitational
forces, specifically those of the Moon and the Sun. But it is only
in the enormous oceans that we see this movement.
Marine Life at Botanical Beach
in the Juan de Fuca Provincial Park
of the oceans are known as tides, and they follow an enormously complex
influence is the gravitational pull of the moon, so the tidal cycle
follows very closely the movement of the moon in its orbit. But
this major effect can be compounded by the tilt of the Earth, so
that there are higher tides in areas that are tilted more closely
to the Moon; this results in seasonal differences in the tides.
The tides are also affected by the lesser gravitational pull of
the much more distant Sun, so that the highest tides occur on the
New Moon, when the Moon and the Sun are on the same side of the
Earth. A second smaller tide occurs because the landmasses on the
side of the Earth opposite the Moon are pulled towards the Moon
more than the water. The whole is further complicated by local geographic
eccentricities on land and on the sea floor. The daily tidal fluctuation
in British Columbia ranges from about two meters in the south to
over seven on the North Coast. Despite all the complications, however,
the tides follow quite predictable patterns, and a tide book is
a worthwhile investment on any visit to the coast.
The tides have
been having their way on the planet for eons, and thus have had
their effects on the evolution of life. Just as there are plants
and animals which have adapted to live beneath the waves, and in
the many diverse habitats on land, so, too, there are thousands
of species which live in the life zone which is affected twice daily
by the tides.
As the tide
recedes to its daily low point, this life zone is exposed to the
elements, and the plants and animals there must survive until the
next high tide. They are also exposed to the curious eyes of the
intertidal explorer. Even an average tide will reveal wondrous things
along the shore, or clinging to dock pilings, but it is the lowest
tides of the year, in the summer, which expose the richest diversity
habitats have their species of interest, from muddy bays to wave-washed
beaches, and rugged rocky outcrops. But it is these rocky shores
that offer the best viewing opportunities, with relatively easy
access, and many small pools left behind by the receding tide.
in the intertidal area fall into a few basic groups. While there
are a few grasses to represent the flowering plants, most "seaweeds"
are algae, and are grouped generally as either red, or green, or
brown algae. The long whip-like stipes of Bull Kelp (Nereocystis
luetkeana), a brown alga, with their hollow bulbous tips, can be
seen in masses in the water, and often cast up on the beach. If
you think it looks funny, don't be too critical; you have probably
eaten an extract from kelp that keeps your ice cream smooth and
Held fast to
the rocky substrate are masses of rockweed (Fucus species), whose
mucous covered fronds retain moisture, and provide cover for small
marine animals. The bright green seaweed you see may be sea lettuce
(Ulva species). The occasional translucence of this alga is understandable,
because each frond is only two cells thick.
In the tidepools,
small sculpins dart into protected places. The most common is the
Tidepool Sculpin (Oligocottus maculosus), whose colour is best described
as "camouflaged". This and a few other small fish are
the only vertebrate animals likely to be encountered in the intertidal
By far the vast
majority of the life in the intertidal zone consists of species
of invertebrate animals. These "spineless" wonders range
from the well-armoured crabs to the limp-wristed but beautiful sea
slugs, or nudibranchs.
Some of the
most obvious of the invertebrates do not look much like animals
at all. Almost any tidepool will reveal numbers of Giant Green Anemones
(Anthopleura xanthogrammica). The waving fronds are minutely raspy,
and help to guide prey items toward the animal's central mouth.
The tentacles then close around the prey, and it is digested. The
Aggregating Anemone (A. elegantissima) appears like a collection
of olivaceous jelly-like blobs. When they open, however, they reveal
tentacles of exquisite pink and blue. Their "aggregation"
results from their reproduction by cloning. The Frilled Anemone
(Metridium senile) prefers deeper water, but it's prominent white
"flowers" are often seen on dock pilings.
some areas is the Ochre Sea Star (Pisaster ochraceus), which, true
to its name, is orange. Except when it is purple. Sea stars (they
are not fish) move along the bottom until they find suitable prey
like limpets or mussels. Their strong suction feet will open the
toughest shell, and the stomach is then inserted into the prey,
and digests the prey. These animals are in turn sometimes the prey
of Glaucous-winged Gulls, which will patiently sit while a sea star
in the mouth relaxes sufficiently to be swallowed whole.
In the tidepools,
and under beach wrack and rocks, are found dozens of the little
Purple Shore Crab (Hemigrapsus nudus). They scurry sideways in search
of cover, and although small, are capable of inflicting some pain
with their little pincers. The tidepools are home, too, to Hermit
Crabs (Pagurus species). Unlike their cousins, who shed their shells
and grow new ones, the Hermit Crabs borrow the shells of various
deceased snails, moving into larger ones as their growth dictates.
are festooned with mussels. California Mussels (Mytilus californiensis)
are more often found on exposed shores, while the smaller Blue Mussels
(M. edulis) prefer more protected waters, often with lower salinity.
More difficult to pick out on the rocks are the chitons, molluscs
with segmented shells that look a little like oversized sowbugs.
The various species range in size from 5 to 30 cm.
like molluscs, but in fact they are crustaceans, like shrimp. When
submerged by the tide, their hard shells open, and delicate fan-like
fronds sieve the water for food. At low tide, they shut tightly
to preserve moisture.
On a very low
tide, it may be possible to find the amazingly soft-bodied sea cucumbers,
and sea slugs, or nudibranchs. Some of these are the most exotically
coloured animals in these waters. Many are quite small, growing
to 6 or 8 cm, but a careful search of tidepools can be rewarding.
are not devoid of life, but much of it is buried below the surface.
There are many species of clams, some native, and some introduced,
and most make their existence by filtering nutrients from the water
in the sandy safety of their burrows. The granddaddy of all the
clams is the Geoduck (Panopea abrupta), which is pronounced "Gooey-duck".
It may reach twelve pounds in weight after a life span of 150 years.
Despite living 1 or 2 meters under the sand, they are harvested
The taking of
clams and mussels and other shellfish for human consumption is legal,
but there are regulations about the numbers and sizes of each species
that may be taken. WARNING: It is also imperative that shellfish
lovers watch for Red Tide warnings. Red Tide is an algal bloom that
produces toxins in filter-feeding organisms like shellfish, and
these toxins are concentrated and passed on to humans, causing the
potentially fatal Paralytic Shellfish Poisoning.
The beach is
also home to beach fleas, which are not fleas at all, but would
give them a jump for the money. On exposed beaches, the California
Beach Flea (Megalorchestia californiana), with its striking red
antennae, is common, while on more protected beaches, the smaller
Beach Hopper (Traskorchestia traskiana) replaces it. Both feed on
decaying kelp and other beach wrack, and retreat to burrows during
most of the day.
A walk along
the beach may also turn up the shells of Sand Dollars (Dendraster
excentricus). The living animal, related to the sea urchins, moves
just under the sand, filtering detritus out of the water.
intertidal zone can be done anywhere there is access to the shore,
and at any time of the year. Daytime low tides occur only from spring
through fall, however. And a word of caution here:
the water that receded with the tide, will return. Be extremely
careful not to become stranded offshore by an incoming tide; the
next low tide could be 24 hours away. Be especially careful, too,
on exposed coasts. Many people have lost their lives when swept
off rocks and beaches by large waves. Occasional "rogue"
waves are not a maritime myth; they can and do occur.
some respect for the creatures you have discovered. Avoid stepping
on them, even barnacles where possible. Leave the creatures where
you have found them. They will not survive "at home",
and sea stars will not dry out aesthetically. Return animals to
their tidepools, and replace any rocks that you have lifted.