It is a very long
and thin line that separates the terrestrial wonders of British Columbia
from the wonders hidden beneath the sea. And just as on land, there
are a myriad of forces at work there. The
edge of the continent slips below the sea's surface, in a gentle slope
called the continental shelf. At the edge of this shelf, the sea floor
plummets from about 200 meters below the surface to the ocean depths.
Most marine life exists in the relatively shallow water of the continental
have gouged long narrow fiords into British Columbia's coastline,
the sea floor may be three times deeper than on the continental
shelf. In many cases, the glaciers left large mounds of gravel and
rock at the mouths of these fiords, called sills. The currents moving
over these sills force nutrients upward, making the fiord mouths
productive feeding areas. Behind the sills, the water often lies
stagnant and almost lifeless.
The key to survival
in the ocean is light. Below about 40 meters, there is too little
light for plant life to photosynthesize, and in this surface layer
is found the first link of an amazing food chain. These are the
tiny organisms known collectively as phytoplankton. Some of the
plankton feed on the detritus of dead organisms. Others feed on
other phytoplankton. They may all be consumed by larger organisms
such as zooplankton, which are for the most part the larval stages
of more familiar marine animals such as crabs and shrimp.
Each group of
organisms provides food for other larger organisms; from phytoplankton
to mussel to Surf Scoter to Bald Eagle; from euphausiid shrimp to
herring, to salmon and Harbour Seal, and then to Killer Whale.
The deeper ocean
waters are relatively lifeless, but undersea landforms can alter
currents to force life-giving nutrients to the surface. The best
known of these are the shallower "banks", like the large
La Pérouse Bank off Ucluelet. These are productive areas for fish,
and important commercial fishing grounds. The abundant food also
draws thousands of pelagic seabirds like Sooty Shearwaters and Black-footed
Albatross. These species spend most of their lives at sea, coming
ashore only to nest. Many of them breed in the southern oceans,
and spend their "winter" in British Columbia waters.
The narrow coastal
strip produces the greatest abundance and diversity of life in the
oceans, and it is here that most people will experience the marine
world. Access to this world is made easy by the twice-daily movements
of the tides, which conveniently retreat from the shores to expose
whole communities of marine organisms.
Many of these
organisms occur in the zone between high and low tides, and are
well adapted to periods of several hours exposed to the sun and
air. A visit to a rocky shoreline will reveal mussels and limpets,
anemones and sea urchins, and bright orange and purple sea stars.
Tiny crabs and sculpins dart for cover as shadows pass over them.
Then the tide comes in again, drawing its liquid curtain across
this remarkable performance, until it is time to repeat the cycle
There are many
species that can be harvested from the mud and sand, like tasty
clams of several species. Beware, though, that occasionally there
is a bloom of algae that produces a toxin. The toxin does not harm
shellfish, but when passed to humans, it can cause death by paralytic
shellfish poisoning. The bloom is known as Red Tide, and fisheries
authorities should be consulted before any shellfish are harvested.