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Excerpt from
The Jade Coast by Rob Butler
Chapter 6.
Eelgrass Meadows and Saltmarsh
The Nuts and Bolts of Eelgrass Meadows and
Saltmarshes
Eelgrass meadows straddle the
intertidal and subtidal regions whereas saltmarshes lie
between the terrestrial and intertidal. Sea temperature,
salinity and clarity of water limits where eelgrass meadows
will grow. Distinct zones of different vegetation outline the
level of sea submergence in the saltmarsh but the amount of
moisture, salinity and nutrients in the sediments also dictate
their distribution.
Sea and sun
Sea temperature and sunlight
trigger photosynthesis in eelgrass meadows that sends a chain
of events rippling through the entire ecosystem. Sunlight
warms the beaches at low tide in spring and chills them in
winter that modifies the surrounding sea temperatures. The
amount of sunlight reaching the eelgrass plants determine how
far down the beach they can grow. There is an important
conservation message here: turbid waters caused by events such
as oil spills, sewage, and plankton blooms can reduce the
growth of eelgrass. And, as we will see, without eelgrass the
entire ecosystem would collapse.
Sediments and nutrients
The roots of eelgrass do much more
than just anchor the plant in soft sediments. The shower of
leaf litter from the floating canopy create oxygen-depleted
sediments about the roots where sulfur bacteria thrive2.
Their presence maintains the acidity of the sediments so that
nitrogen mineralization is made available to microbes more
quickly than if the bacteria were absent. Without the
microbes, the eelgrass meadow ecosystem becomes impoverished5.
Saltmarshes develop where high
tides inundate low-lying land. Little is known about marsh
soils in our region. The lower elevations are often saturated
with moisture. The type of soil is important because the finer
soils have the greatest supply of nutrients. The lower reaches
of saltmarshes that are submerged frequently by high tides are
often oxygen-poor just below the surface. The by-products of
decomposition in these soils are sometimes toxic to some
organisms making an already harsh environment more rigorous
for its inhabitants.
Salinity
Eelgrass is tolerant of a wide
range of salinities but it does best where the water is
brackish. The open ocean has a salinity of about 35 parts salt
per thousand parts water and eelgrass grows best in water with
a salinity between 10 and 30 parts per thousand. Any animal
living in the intertidal zone has to cope with changes in
salinity which some can do by moving in and out of the
intertidal portion of the beach. But for plants, salinity is
an invisible barrier to many plants. Few terrestrial plants
can tolerate saline conditions that sap plants of precious
moisture. So the competition for space goes to the salt-loving
halophytes that are adapted to a life in the salt zone. Many
saltmarsh plants store water in fleshy stems or roots, and
grow tiny leaves covered with fine, glaucous hairs to reduce
evaporation loss.
Eelgrass and Saltmarsh Food Webs
The Players
The producers inhabiting small estuaries
are phytoplankton, marine algae and eelgrass. They produce
food energy through photosynthesis. The grazers include
such animals as the chink shell that grazes algae on eelgrass
fronds, and the brant goose that eats eelgrass fronds. Among
the filter feeders are many small invertebrates that
cling to eelgrass fronds and clams that live in the mud. The
predators include invertebrates such as the
Dungeness crab, birds such as the great blue heron, and fish.
In other words, very dissimilar animals eat very similar food.
The producers that inhabit large
saltmarshes are glasswort and grasses such as spike grass and
wild rye. The grazers are ducks such as the American
wigeon and northern pintail.
The Producers in the Eelgrass Meadow and Saltmarsh
On sunny summer days, a green sheen
of eelgrass shimmers in a mirage that stretches for kilometers
along the shore of the great beach in Boundary Bay near
Vancouver. At low tide, the eelgrass looks like a meadow
uncovered by the sea. Beach walkers will be familiar with the
long sinuous green leaves of eelgrass sprouting from sandy
beaches near the low tide. There are 48 species of seagrass in
the world of which five species live on our coast. Three of
these are surfgrasses (Phyllospadix) found in rocky
habitats exposed to Pacific surf. Two species of eelgrass that
occur in our region are the widespread Zostera marina
which grows along the entire Pacific Coast, and a recent
invader, the diminutive Zostera japonica presently
established on beaches to the south and including the Strait
of Georgia. Particularly, large beds of eelgrass are found in
Humboldt Bay, Netarts Bay, Willapa Bay, Grays Harbor, Padilla
Bay, Boundary Bay, Tofino Inlet, Skidegate Inlet and Izembek
Lagoon, Alaska. About 9% of Puget Sound below mean lower low
water is covered by eelgrass3.
Eelgrasses are vascular plants that
share features common to many terrestrial plants. They produce
flowers, albeit tiny and inconspicuous ones, and they have
root-like underground rhizomes. The long narrow leaves slow
the movement of water and the tangles of rhizomes stabilize
sediments that enrich the area around the plant. The long,
swaying leaves also conceal tremendous numbers of animals that
use the bed as a refuge and nursery. However, as we will see,
eelgrass provides much more to the ecosystem than just the
breakdown products of its leaves.
One of the reasons that eelgrass
habitats in tropical and temperate environments are so rich in
species is that they provide many places for other plants and
animals to grow. The leaves of eelgrass grow at an astonishing
rate of about 5 mm each day and can reach up to 10 mm per day
under ideal conditions. These leaves support a microcosm of
epiphytic plants and animals, as well as provide food for
grazing animals and, supply detritus that feed invertebrates
in the eelgrass beds and on nearby beaches.
Eelgrass in Alaska survives ice
conditions but eelgrass in Washington and California cannot.
Generally, eelgrass grows best when the surrounding sea is
about 22oC. Thus, increasing sea temperatures in
late winter triggers eelgrass reproduction as early as
February4. Flowers can appear as early as March and
as late as July. The growth of eelgrass leaves begins in the
warmth of July and extends into November. A host of other
plants and animals establish communities on or between the
leaves of eelgrass.
Imagine how different we would feel
if our lives were dependent on scum. At first glance, it is
difficult to believe that this unappealing mass can be
important - but it is the cornerstone to the life in eelgrass
beds. Without the leaves of eelgrass, myriads of tiny plants,
bacteria and diatoms that cling tenaciously to the leaves
would be buried in mud or carried away by currents and tides.
Within days, meter long leaves of eelgrass turn a
two-dimensional mudflat into a three dimensional garden of
plants and animals suspended in a watery environment rich with
plankton. The weight of this growth on the leaves of eelgrass
can exceed the weight of the leaves by themselves over
two-fold6!
The fundamental steps in the growth
of plants and animals that cling to the leaves are the growth
of the diatom and bacteria coating on eelgrass leaves, the
entrapment of detritus, and the growth of tiny algae. Without
the ability of these tiny organisms to rapidly colonize
eelgrass leaves much of the life of the eelgrass ecosystem
would not survive. Entire life cycles of these epiphytic
plants and animals are adapted to the 3 to 8 week life span of
its life support system - the leaves of eelgrass. At first
glance, the eelgrass appears to be getting the worst of the
deal but the relationship between epiphytes and eelgrass has
evolved to be of mutual benefit. Eelgrass provides the
epiphytes with a free ride suspended in waters rich in
nutrients and close to the surface of the water where the sun
shines brightest. And in return, the epiphytes exchange
carbon, nitrogen and phosphorous with the eelgrass.
Suspended gardens
One of the first plants encountered
in eelgrass meadows (other than eelgrass, of course) is a red
alga Smithora naiadum that clings to the edges of
eelgrass leaves and is conspicuous because of its reddish
purple hue. It is widespread throughout our region. Also
abundant is a carnivorous amphipod that resembles an exuberant
miniature preying mantis. Jellyfish and tiny sea anemones
cling to eelgrass in summer. One of the most remarkable
creatures of eelgrass meadows is the hooded nudibranch. This
creature is a predatory sea slug that reaches 10 cm in length
and devours small amphipods and other crustaceans with the aid
of a hood. It resembles a flaccid mass of jelly in the hand,
but in the water the hooded nudibranch quickly fills out its
hood and delicate-looking sacs. It uses the hood as a
flotation device whereby it drifts to the surface to catch
small crustaceans with its tentacles. This animal wouldn’t
stand a chance on exposed rocky shores. Eugene Kozloff refers
to the hooded nudibranch in his superb book Seashore Life
of the Northern Pacific Coast as one of the “top ten” of
curiosities brought to marine biologists, or described over
the telephone. Nearly as intriguing is Phyllaplysia taylori,
a yellow-green sea slug bearing longitudinal black streaks. A
third sea slug in eelgrass meadows is the tiny
Aeolia papillosa
that Kozloff aptly described as resembling a shaggy little
mouse. Its diet is largely if not exclusively, anemones. Often
crawling about the leaves of eelgrass is an isopod that takes
on the colour of its background. A conspicuous group of
clingers on are the sponges and hydroids. A tiny sessile
jellyfish measuring up to about two centimeters and the
graceful kelp crab reside in eelgrass meadows. The jellyfish
eats plankton and small crustaceans, and the crab scavenges
dead animals often in association with broken-back and
coon-striped shrimp.
Grazers
The early 1990s, I began a study of the birds
of Boundary Bay that opened my eyes to the importance of
eelgrass beds to their survival. Autumn on the Jade Coast is a
time when waterfowl are on the move. From Alaska, central
British Columbia and Alberta, ducks and geese stream along the
coast by the millions. I drove my truck on to a dike that
skirts along the top of the beach of Boundary Bay. A leaden
sea reflected a silvery sky and there were ducks as far as I
could see. Wigeon, pintails, teal and mallards were tipping
and sieving the shallows for food. Scaup and scoters were in
deeper water. Along the beach scampered thousands of Dunlin
and plovers. I pondered how I would ever estimate the number
of birds that day. The ducks were milling about but few were
flying. The shorebirds were more mobile but generally stayed
within view. By counting groups of 50 or 100, I could
gradually tally the number on the beach. Over the next few
hours, I alternated short drives with counts of flocks an
eventually tallied nearly 100,000 ducks and 30,000
shorebirds.
The most conspicuous grazers of
eelgrass meadows and saltmarshes are ducks and geese. Eelgrass
meadows are one of the great storehouses of ducks in winter
along the Pacific. About 100 000 ducks congregate each winter
on Boundary Bay, 50 000 gather in each of Grays Harbor,
Padilla and Samish Bays, 200 000 amass in Willapa Bay, and 124
000 collect in Humboldt Bay. Many small estuaries also harbour
ducks, geese, swans and many other waterbirds. The most
numerous species are the American wigeon, northern pintail and
mallard. These herbivorous ducks arrive in eelgrass meadows in
large numbers beginning in late August and continue to arrive
as late as November from breeding grounds in western Canada
and Alaska. Wigeons are strictly herbivorous and set upon the
leaves of eelgrass, especially the introduced species
Zostera japonica whereas the pintail and mallard prefer a
more varied diet of seeds and plant stems found in saltmarshes
and nearby farms.
A conspicuous species that is
dependent on eelgrass is the brant. This sea-going goose eats
eelgrass while on the Pacific Coast. Brant return each year
to the same eelgrass meadow where they mostly graze the leaves
and stems to fuel long migrations to the arctic and back.
However they might also arrive in March to take advantage of
herring eggs deposited on eelgrass and other beaches.
Following breeding, about 150 000 brant spend the winter on
the Pacific coast in Baja California. They gather in one of
the world's largest eelgrass meadow in Izembek Lagoon at the
base of the Aleutian Island chain. From there, the brant
launches trans-Pacific flights of over 5 000 kilometers to
Mexico. The flight is demanding - by the time they settle in
Mexico the Brant will have lost about one-third of their
weight.
Far less conspicuous than the
grazing waterfowl in eelgrass beds are grazing invertebrates.
The chink shell is a widespread, and easily found snail in
Puget Sound and the Strait of Georgia eelgrass meadows. It
measures about 5 mm in height. Even more conspicuous than the
snail are its tiny yellow egg masses described aptly by Eugene
Kozloff as "little yellow life preservers". Also abundant is
one of my favourite denizens of the eelgrass meadows, the
bubble snail, whose bulging body can hardly be contained in
its dainty shell. It lays its yellow eggs in bands resembling
narrows strands of decaying gauze along the leaves of
eelgrass. Where the bubble snail is abundant, the tidal wrack
becomes littered with its paper-thin shells. Grazers also
find food on the mudflats. A film of greenish algae covering
mudflats in spring and summer feeds large numbers of
herbivorous horn snails. It was introduced with the Japanese
oyster earlier this century.
Grazers in the saltmarsh include
mice and voles from neighbouring grasslands and forest. The
most ubiquitous species is the deer mouse that roams the
saltmarsh largely at night. It nests under driftwood and below
ground. About all you see of the Townsend's vole is a fleeting
glimpse as it torpedoes along its runways in the grass and
down its burrow. Voles live much of their lives underground
but on wet wintry days, a rising watertable can force them
above ground.
Detritus-Feeders
Winter storms tear apart the leaves
of eelgrass and batter the dried saltmarsh plants. The dead
leaves and stems scatter about the beach and tumble into the
saltmarsh to become food for animals that live on plant
detritus. Many worms inhabiting eelgrass meadows and
neighbouring beaches go unnoticed but play an important role
in converting the detritus into animal protein. The top few
centimeters of some mudflats are crawling with marine worms,
crustaceans, and amphipods. If you look closely to the mud on
a warm day, it will appear to be moving as these marine
invertebrates jostle in the soupy mud. Their vulnerability to
predators resorts them to a life in the roots and sand away
from prying eyes. Several species of lugworms that live in and
around eelgrass meadows are also abundant in estuaries. An
abundant polychaete worm in eelgrass meadows is Notomastus
tenuis that lives by eating sediments. One of the most
important group of detritus-feeders that live on the substrate
beneath the eelgrass canopy and on neighbouring mudflats are
the crustaceans, notably the copepods, amphipods, isopods and
shrimps. These little animals are high on the list of entrees
of many fish. Copepods are seldom longer than on millimeter
but they are very numerous and haute cuisine for gunnels,
herring, salmon and seaperch. They become abundant in spring
and early summer when the water warms. Also important, are the
amphipods that devour algae and detritus. The best-known
amphipods are the beachhoppers that leap and scurry when wave
washed algae is turned aside. More will be said about them in
the chapter on boulders and sand beaches. The genus
Corophium contains several important species that consume
detritus from eelgrass, epiphytes, marine algae and animal
remains. Food is removed from water by the waving motions of
abdominal appendages and legs fringed with tiny hairs. Even
more abundant than Corophium are tiny mysid shrimp that
race through the water resembling miniature 'motorboats'.
“Deep down here by the dark water lived Old
Gollum,
a slimy creature. I don’t know where he came
from,
nor who or what he was. He was Gollum - as dark
as darkness,
except for two big round pale eyes in his thin
face.”
-J. R. R. Tolkien, The Hobbit
The ghost shrimp lives a
Gollum-like existence in muddy burrows often in association
with eelgrass meadows. It seldom is seen at the surface but
their telltale volcano-shaped burrow entrances belie their
presence. A small fish, the arrow goby, has taken up residency
in the burrows of ghost shrimps, along with other shrimps,
worms and small crabs.
The smallest of the North American
sandpipers is abundant in Pacific saltmarshes. The least
sandpiper weighs in at about 20 grams. Least sandpipers often
accompany migrating western sandpipers, which they closely
resemble. Both species stop at saltmarshes and mudflats on
their migrations in April and May on their way north to the
breeding grounds, and again on their southbound journey from
July through October. The least sandpiper eats copepods, small
clams, polychaete worms and other invertebrates along the
margins of salt marshes and roosts in the saltmarsh during
high tide. In southern British Columbia individual birds
linger for an average of about five days before departing on
their southward migration. The edges of saltmarshes sometimes
are riddled with holes made by the purple shorecrab. Little is
known about the habits of this crab in saltmarshes but it
likely preys upon invertebrates and scavenges dead animals
brought in by the tide.
Burrowing Filter Feeders
So far, we have been looking mostly
at creatures on the mud or in eelgrass beds and saltmarshes.
It’s now time to get dirty! In the oozing, smelly mud below
the eelgrass canopy are several species of clams, worms and
arthropods that feed on plankton. The most conspicuous clam is
the basket cockle that lies on or near the surface of the
beach where its short siphons can extend into the seawater.
The bent-nosed clam is often very abundant here too but lies
submerged in the ooze. Both species are also found on
neighbouring sandflats and mudflats. Whoever named the
inconspicuous macoma must have had an odd sense of humor. The
bright pink shells attract the eye of even the least
observant. This dainty clam seldom grows larger than one
centimeter across. It lives in muddy situations where it is an
important component of the diet of several shorebirds
including the western sandpiper and dunlin that flock to our
mudflats in great numbers. The geoduck, which is pronounced
‘gooey-duck’, and Pacific gaper lie as much as a meter below
the surface. They spurt water from their retractable siphons
if disturbed during low tides often to great delight of
unsuspecting beach walkers. All of these clams slurp in
plankton and expel wastes through siphons.
Surface Dwellers
“Two men look out through the same bars.
One sees the mud, and one the stars.”
-Frederick Langbridge
The abundance of clams, shrimps, worms and
other invertebrates that dwell in the mud attract predatory
crabs, ducks, gulls, shorebirds, and even some whales. The
Dungeness crab is a conspicuous invertebrate scavenger and
predator of the eelgrass meadow. In California, female crabs
molt in late summer and are mated before the shell hardens.
Eggs are brooded until December or January when hatching
occurs. The larvae are then carried offshore to mix with other
plankton, where they go through several development changes to
become swimming ‘megalopa’ in April and May. Between one and
two years later, the megalopae moult into juvenile crabs in
coastal areas and finally become adults in two and six years.
Dungeness crabs seldom stray inshore of the subtidal eelgrass
meadows. Female Dungeness crabs gather in nursery areas along
the subtidal edge of eelgrass meadows in the southern Fraser
River estuary where their densities can reach up to three to
four crabs per square meter, a testament to the abundance of
food in these eelgrass beds.
Along with the predatory crabs, the
rising tide also brings the sunflower star to hunt clams
within the eelgrass meadows. In Puget Sound the chief prey is
the butter clam. Watching sea stars is like watching paint dry
with one exception. The sunflower star is the sprinter of the
starfishes, visibly scurrying at breakneck speed (for sea
stars) of about 1.6 meters per minute along the bottom in
search of prey. Although very slow for us, it is curiously
rambunctious for a sea star. Hidden behind the gentle exterior
of the sunflower star is a ferocious hunter feared by bivalves
and sea cucumbers alike. Pity the unfortunate clams that falls
prey to Pycnopodia. The many-rayed star settles over
its victim and systematically lifts sand and gravel out of the
way. Small clams and urchins are swallowed whole whereas
larger victims are forced open by applying unrelenting
hydrostatic pressure force from its many tentacled feet to
overcome the adductor muscle of the clam. Once the valves have
parted, Pycnopodia everts its stomach between the
shells and digests the clam alive.
The glaucous-winged gull,
California gull and mew gull are abundant predators in
eelgrass beds in British Columbia and Alaska whereas the
western gull predominates south through Oregon and California.
The Glaucous-winged Gull eats ghost shrimps, Dungeness crabs,
basket cockles, and fish among other items. Shrimp are
snatched from their burrows, crabs are caught by turning over
eelgrass and sea lettuce, and cockles are broken from their
rugged shells by dropping them to the beach from the air.
Things in Southeast Alaska are big.
Big mountains, big glaciers, big distances, and big stories.
The Stikine River roars through the mountains of British
Columbia and southeast Alaska before emerging across a big
delta. The sand and mud delta lie largely untouched by humans
within the Tongass National Forest. From the air, the Stikine
draws in thousands of Central American shorebirds on their
migrations to Alaskan breeding grounds. In 1991, we knew very
little about how important the Stikine was to shorebirds in
the chain of migration mudflats linking the tropics to the
arctic tundra.
The third of May 1991 dawned clear and bright
when I boarded the plane in Petersburg. Onboard was Chris
Iverson from the US Forest Service. We were about to make a
low altitude flight across the Stikine delta in search of
flocks and then I would be dropped at a site where I would
rendezvous with Robert Clair from the Forest Service and my
colleague Terry Sullivan.
The plane roared out of Petersburg and swung
south past the icy blue floating glaciers calving from LeConte
Glacier. This territory was unchanged since John Muir hiked
the canyons of the Stikine in 18xx. Wolves and bears lived
along the shores, and the meadows of sedge spread out on the
flats for many kilometers. The air had spring freshness.
There is something exciting about spending time
in the wilderness dependent on your survival skills and
exploring an area where few scientists have trodden. I could
see Robert and Terry in the boat off to the starboard side and
I could hardly wait for the plane to put down so I could get
ashore. We slid on the water surface on a soft landing,
unloaded the gear into the boat and headed for a small cabin
on Little Dry Island.
That evening, we rigged up our equipment to
detect radio transmitters that I had attached to sandpipers on
the Fraser River delta in British Columbia a few days earlier.
The receiver hissed through headphones as I began to scroll
through the radio frequencies. An ever-so-faint chirp of a
radio seemed to peep in the headphones, but I wasn’t certain.
Quickly I climbed on to a high point and heard the chirping
once more but this time it was loud and clear. On the beach
before me was a sandpiper carrying a tiny radio transmitter
that I had glued to its feathers nearly 1000 kilometers away.
This confirmed our suspicions that the birds on the Fraser
also stopped on the Stikine delta. We later detected several
other radios on birds from the Fraser over the next few days.
The cerulean blue sky along the seashore that
evening was streaked with wisps of smoky grey clouds. To the
south, a grey rain was moving toward us. About 100,000
shorebirds were anxious to depart. I could hear it in their
rallying calls. The high tide had pushed a large flock close
to the marsh edge and their twittering calls periodically
erupted in din of chirps as flocks rose from the beach. Some
flocks began to form into long lines in the air and began to
climb higher in the sky. I followed with my binoculars their
silhouetted shapes against the reddening sky until the dots
became specks and the specks merged with the sky. Their next
stop would be the Copper River delta. In my imagination, I
flew with them.
We spent a few days catching, weighing and
banding sandpipers at Little Dry Island and then decided to
divide the team into two groups. Robert and I would move to
the north to Mallard Slough while the others remained at
Little Dry Island.
It was late afternoon before the tide was high
enough to float the boat. Slowly we poled our way into deeper
water before starting the motor and speeding off to the
northwest. It was important to get there while the tide was
high in Mallard Slough so that we could reach the camp. If we
missed the high water, we would be stuck overnight on the
mudflat.
The jade green waters sped by as we made our
way along the delta and soon Robert slipped the boat into a
riverine channel. We crept up the delta to a small cabin
overlooking a mudflat alive with thousands of shorebirds.
Robert and I decided that we should take advantage of the
opportunity to band some of the birds. Now the expression
‘biting off more than what one can chew’ springs to mind on
occasions such as the one we about to experience. We thought
we would be lucky to catch a few birds and so we hastily
erected three sets of aluminum poles with fine mist nets
strung out in a row. If we caught 20 birds, it would have been
a good day of banding. On cure, the flock wheeled and collided
headlong into our nets. The nets were festooned with over a
hundred flailing sandpipers. Robert and I had removed many
shorebirds from nets but this was going to be a daunting task.
The fine threads of mist nets clings to the bird’s feathers
without harming them. But it would require a minute or two to
remove each bird.
It is at times like this that one hopes for
Divine inspiration but seldom are prayers answered. So we
began the task of removing the birds one by one and placing
them into large boxes. Our backs were straining, our eyes felt
as though they were permanently crossed, and our throats were
parched by the time all the birds were free from the nets. Now
the tedious job of weighing, banding, measuring and recording
was to begin. We quenched our thirst and went to work. By
setting up a system, we were able to band and release all the
birds within a few hours of capture. Not ideal, but the job
was completed with no casualties. With the last bird on its
way, we fell back on our bedrolls to rest. We were hungry but
dinner would have to wait.
Beaches on the Jade Coast support shorebirds at
all times of year. One of the first shorebirds to be
encountered on mudflats in winter is the dunlin, a species
with a circumpolar distribution. Our subspecies, Calidris
alpina
pacifica
breeds in western Alaska. It undergoes a feather molt in late
summer and returns to our mudflats in September through to
November often in huge flocks to forage on worms and clams
during low tide. It feeds both during the day and night. Worms
are pulled from the mud and quickly swallowed. The abundance
of small invertebrate decomposers and small filter feeders
found on mudflats are the chief prey of over 50 species of
shorebirds along the Pacific Coast. The most numerous
shorebird in spring and summer is the western sandpiper. Large
numbers spend the winter on mudflats in California but only a
few western sandpipers remain in northern regions. The western
sandpiper breeds in western Alaska and spends the winter along
the southeast Atlantic Coast, around the Gulf of Mexico and
along the Pacific Coast from California to Peru. In April,
hundreds of thousands migrate north through our mudflats and
estuaries. They return on their journey to the south in July
through September. Western sandpipers eat many small worms and
the amphipod Corophium on mudflats and in estuaries.
Few species of bird on the Jade
Coast is as handsome as the black-bellied plover. Its
plaintive cry "keeer" is a fixture of windy, open mudflats
they occupy. In winter, the plover's colouration is a drab
brown, black and white that it exchanges for a handsome black
under parts in spring and summer - a sight to behold.
Black-bellied plovers hunt their prey by scanning the surface
of the mud until they detect the slight movement of
invertebrates at the mud surface and scamper to catch it. An
important prey species of plovers are marine worms but they
also eat small bivalves. Sometimes gulls will take up the
chase when a plover flies off with a large morsel. Studies in
Britain showed that black-bellied plovers defended stretches
of beach against other plovers9. These territories
included drainage channels on mudflats where they spend most
of the time foraging. On windy days, channels provided
territorial plovers with protection from windy blasts that
deterred other plovers from staying on the beach. The winds on
our mudflats seldom gust as high as those in some British
estuaries but plovers depart our mudflats on blustery days to
eat earthworms and insects or rest in nearby fields8.
Where the mud is particularly soft, the short-billed dowitcher
and long-billed dowitcher are sometimes numerous. Dowitchers
have long bills with sensitive touch receptors in their tips
that they use to probe for worms, crustaceans, fish eggs,
small snails and clams. The seasonal ebb and flow of tides and
day length strongly affect the Great Blue Heron’s breeding
cycle along the Jade Coast. The lengthening days of spring
bring warm sunshine onto the eelgrass meadows stirring the
growth of leaves and their epiphytes. This sudden growth spurt
provides food and shelter for millions of gunnels,
sticklebacks and sculpins waiting in deep water offshore to
breed. Their arrival attracts large numbers of herons to
eelgrass meadows. Once each female catches enough fish during
the low tides to begin to make eggs, she chooses a mate at the
colony and the nesting season begins. Herons require about 100
days to lay and incubate eggs, and raise their chicks8.
Adults and young depart the nesting colonies between June and
August to spend the summer and autumn catching fish in
eelgrass meadows. By autumn, the days are noticeably shorter
and a chill settles into the eelgrass meadows. Fish that were
abundant a few months earlier dwindle in number in the
eelgrass meadows and herons begin to search elsewhere for
food.
Swimming Predators
Large filter feeding invertebrates
such as clams, mussels and cockles are the mainstay of large
numbers of sea ducks in winter. The mild, ice-free climate and
high daytime tides allows them to feast on invertebrates in
eelgrass meadows and on nearby mudflats throughout the winter.
Between 10 and 20% of the world’s seaducks spend the winter
along the Jade Coast. Among the most numerous and widespread
diving ducks are the bufflehead, greater scaup, common
goldeneye, surf scoter, white-winged scoter, and long-tailed
duck. Scaup sometimes rest on shore and feed in shallow water
but the other species seldom come ashore. Bufflehead and
goldeneye are usually found in shallow water and scoters and
the long-tailed duck feed in the deepest water, sometimes tens
of meters in depth. However, there is much overlap in the
water depths used by all species. All of these ducks are
absent from the Pacific coast between March and September when
they breed in western Canada and Alaska.
Winter days along the Jade Coast
have certain sameness to them. Abrupt shifts in weather are
unusual and the birds come and go between feeding and loafing
areas along the shore. The tides flood the beach for most of
the day providing diving ducks with access to intertidal
invertebrates on the seafloor. In February, an event begins to
stir that will bring a sudden jolt of energy into coastal
ecosystems. Schools of Pacific herring begin to enter eelgrass
meadows from deep water to spawn and hordes of loons, gulls,
seaducks and sea lions arrive to gorge on them in one of the
most spectacular shows in the Jade Coast. Beginning in
February in the south and continuing until the third week of
July in the north, herring swim into the shallows to lay eggs
on vegetation and the beach. Eelgrass meadows are favoured
places although spawning is not exclusive to this habitat.
Spawning has been recorded for more than 250 km of shoreline
in British Columbia. In Alaska, the eggs form a thick soup
along some shores. The amount of spawn varies between years
and in good years over 100,000 loons, gulls, and ducks gather
for the feast. One estimate put the amount of spawn eaten by
75,000 scoters at 103 tonnes12. Each female herring
lays from 9 000 to 38 000 eggs depending on their age and
size. The sticky eggs adhere to eelgrass, kelp, rockweed and
rocks in a gelatinous mat. Males release their sperm in the
water creating white clouds in the spawning areas. The eggs
hatch in about 10 days depending on the sea temperature but
many provide food for marine invertebrates. The contribution
of this energy to the marine ecosystem is immense. On the west
coast of Vancouver Island, an estimated 16 million turban
snails and 9 million leather stars were estimated to eat 1021
tonnes of herring eggs and a further 235 tonnes of herring
eggs were consumed by gray whales13. For several
weeks each spring, herring beaches are a cacophony of
screaming gulls, barking sea lions, and rumbling fishing boats
all pursuing herring. Larval herring begin to feed on
invertebrate eggs, copepods and diatoms, and fall prey to
jellyfish and small fish. They grow rapidly so that about one
month after hatching, young herring are 2.5 to 4 cm long. At
this age, copepods remain their principal food but their diet
widens to include barnacle and mollusc larvae, bryozoans,
rotifers and small fish. They form into schools for the summer
and in the fall move offshore into deeper waters. Herring
fatten through the summer, fast in winter and rely on stored
oils to fuel the development of eggs and sperm. Large numbers
gather to feed at the mouth of the Fraser River estuary in May
and June. Herring are one of the mainstays of many fish, birds
and mammals on the Pacific Coast. Its eggs are consumed during
the spawn from late winter to early spring in eelgrass meadows
and other intertidal areas, and the first year-class of fish
is consumed year-round while at sea. The significance of
herring in the lives of many coastal species has not been
fully realized. The sudden appearance of this bountiful food
supply could very well prepare many birds and marine mammals
for breeding and migration. Tonnes of eggs also provide food
for snails, crabs and scavenging invertebrates.
Soon after the herring depart,
other fish arrive to breed in eelgrass meadows. As part of my
doctoral research, I hauled a beach seine net through eelgrass
meadows to estimate their seasonal abundance. The nets capture
a large number of fish that would go undetected otherwise. We
would pull the net ashore and quickly empty the catch into
buckets of water. The nets writhed with rigid sticklebacks,
wiry pipefish, wiggling gunnels, angry sculpins and sleek
shiner perch. For many fish, the abundant food and protection
from predators provided by eelgrass meadows make them
nurseries of choice for their growing young10. The
abundance of small fish in eelgrass meadows following the
arrival of spawning herring might be more than coincidental.
Herring spawn might be an important additional source of
nutrients for invertebrates that are the prey of small fish in
the eelgrass ecosystem. The shiner sea perch leave subtidal
waters for the shallows of eelgrass meadows in spring to give
birth. Female perch carry up to 35 young in their distended
bellies. Young perch are born largely in June and July. Once
they have given birth, females mate with the males sporting
black courtship colours for the occasion. The sperm stored in
her ovary, waits about six months before penetrating the ovary
wall and fertilizing the eggs in late autumn. Meanwhile the
recently born young grow quickly in the warm waters, hidden
from most predators in the tangle of eelgrass leaves where
they remain until their departure for deep water in autumn.
Copepods are important in the perch diet early in life, and
mussels, marine worms, shrimps, and barnacles are eaten later
in life. Birds, mammals, and fish eat the shiner sea perch.
Herons, eagles, cormorants, kingfishers, mergansers, mink,
otters, rockfish, dogfish and salmon eat sea perch.
Lurking among the eelgrass beds and
sporting red bellies and spines that lock into position, is
the three-spined stickleback. Much has been written about
stickleback behaviour in freshwater, but less is known about
the ones that inhabit eelgrass meadows. Sticklebacks are
small fish less than 4 centimeters from snout to tail. They
dine on copepods, amphipods, euphausids, barnacle and clam
larvae, crustaceans, insects and young fish. Sticklebacks are
well armed with strong scales along their flanks and sharp
spines on their back but this doesn’t stop the great blue
herons from eating large numbers of sticklebacks. Nor does the
stickleback armory stop kingfishers, mergansers and
buffleheads from making them a meal.
One of the oddest fishes in
eelgrass meadows and a personal favourite is the bay pipefish.
Measuring less than half a centimeter in depth and up to 33
centimeters in length, the pipefish looks like a fish that has
been stretched out of shape. Not only is it odd looking, but
it also has an unorthodox breeding behavior. Male pipefish
have pouches specially for tending the growing young.
Posterior to the anus of the male is a ventral slit which
forms the brood pouch. Sometime in about June, males court
females by showing off with body shakes and head nodding. An
interested female impressed by this show, entwines herself
around his rigid S-shaped body and transfers the fertilized
eggs into his pouch. He cares for the young until they become
independent at about 20 millimeters in length. If this sounds
strangely familiar, it is because pipefish are closely related
to the sea horses of warmer seas in which the males also tend
for the young in special pouches. The bay pipefish has no
teeth so it catches its copepod and amphipod prey by sucking
water and prey into the mouth by inflating the cheeks.
Some species of fish use eelgrass
meadows as places to grow after hatching in other habitats.
One very abundant group of fish in eelgrass meadows that fall
into this category is the gunnels. They are sometimes mistaken
to be eels because of the similarity of body shapes. The
largest species is the penpoint gunnel. Some monsters reach
nearly half a meter in length. The common name refers to a pen
nib-like anal spine. Two other abundant species of gunnel are
the crescent gunnel and the saddleback gunnel. Both of these
species seldom reach 30 cm in length. Gunnels are not easily
seen because of their cryptic markings. However, they can be
caught in large numbers in beach seine nets hauled through
eelgrass meadows in spring and summer. Gunnels lay eggs in the
subtidal in winter and swim into eelgrass meadows in spring to
feed on small crustaceans molluscs and other marine
invertebrates. Herons and cormorants eat large numbers of
gunnels. To get a better understanding of the magnitude of
fish in an eelgrass meadow we can look at estimates of how
many are eaten by herons. I estimated that 200 herons eating
gunnels and other small fish would consume less than one-tenth
of a percent of the 12,600,000 fish in a 31-hectare eelgrass
meadow on Sidney Island in June 1987 and 198814.
Now try to imagine how many copepods and amphipods are eaten
by 12 million gunnels.
Eelgrass beds are important
nurseries for the English sole that begins its life as an egg
in inshore waters where it hatches to become floating larvae.
Young soles are pelagic for 6 to 10 weeks and then move
inshore to feed on copepods, barnacle larvae and other small
invertebrates. They can be spotted as they scurry from
underfoot in a cloudy trail of mud. Adult English Soles spend
most of their life in subtidal and pelagic waters. English
soles are mobile souls that travel along much of the Pacific
Coast. The major diet is clams, marine worms, small
crustaceans and starfish.
The staghorn sculpin is one of the
most noticeable fish in eelgrass meadows. Young sculpins
follow the edge of the tide in search of marine worms, clams
and other invertebrates and older, larger individuals lurk in
the eelgrass where they eat small crabs, shrimps, fish and
invertebrates. Sculpins are an important part of the diet of
the mergansers, western grebe and kingfisher, and river
otters. Sculpins and flounders enter eelgrass meadows by
following the tides searching the mudflats for invertebrates
in the mud. When the tide is low, invertebrates move down
their burrows or bury in the mud, and hordes of shorebirds
probe the beaches for them. The common loon frequents the
edges of eelgrass meadows where it dives for fish, amphipods,
crabs, and shrimp. Often in the vicinity of eelgrass beds are
flocks of western grebes, especially in Puget Sound and
southern Strait of Georgia. Staghorn sculpin, gunnels and
shiner sea perch are eaten by these fish-eaters.
To
complete the survey of swimming predators is the largest
species to frequent eelgrass meadows and mudflats - the gray
whale. Gray whales eat amphipods, isopods, marine worms, clams
and herring eggs. Their habit of sucking up food and expelling
mud and sand through the baleen plates leaves tell-tale pits
in the muddy bottom that become pools when the tide ebbs.
The gray whale undergoes one of the longest migrations
of the mammals. The 9 000 km migration along the Pacific coast
begins in the breeding grounds in Baja California and ends in
the Bering, Chukchi and western Beaufort seas. Over 20 000
whales pass along the coast each spring reaching peak
abundance in March in California, April in British Columbia,
and May in Alaska. Some individuals remain along the coasts of
California to British Columbia and return with southbound
migrants in autumn and others remain year-round. Following a
summer of fattening, they return to the lagoons of Mexico to
give birth and breed. About a century ago, grey whales were
hunted heavily by the whaling industry. Now, with protection,
their numbers are increasing and we are witnessing a slow
reoccupation of their former haunts. For many slow
reproducing species, recovery to former abundance requires
many decades. Among the species bouncing back from years of
persecution are the trumpeter swan, bald eagle, humpback whale
and grey whale.
Aerial Predators
“Swift as the wind they fly, speeding along the
breakers
with directness of a runner down a course, and
I read fear in their speed.”
- Henry Beston, The Outermost House, 1928.
There is indeed something frantic
in the way sandpipers feed along the mudflats. They probe and
peck at invertebrates in the mud with knowledge that soon the
tide will return to cover their foraging sites. Large flocks
of shorebirds busying themselves at finding food leave them
exposed to the sleek and agile peregrine falcon and merlin.
Both falcons catch their prey by rapid flight and quick turns
that once seen will remain etched in your memory.
Winter on the Jade Coast is often cool and
damp, and the wind often blows cold from the eastern facing
valleys along flat beaches frequented by shorebirds. I have
walked these beaches on countless occasions dressed in a parka
to keep out the wind to seek out falcons. Often it is the
frantic frightful flights of shorebirds that alert me to the
presence of a falcon. The shorebirds spring from the mudflat
in a desperate bid to gain a height advantage to an incoming
falcon. Peregrines are much more successful in their chases
if they can surprise the shorebirds while they have their
heads down foraging along a beach than once the flock takes to
the air. But this day was extraordinary.
It was a mid summer afternoon when I pooled the
boat ashore on a small sandy beach in southeast Alaska. I had
come to search the beaches for shorebirds that migrated north
along this coastline in big numbers but were thought to be
scarce in summer. Either they took another route, or they flew
out of sight at high elevation.
Sand and mud beaches are uncommon habitats in
southeast Alaska and so I thought that if any shorebirds were
around, they should gather in a relatively few locations.
The sun was bright and the clear water lapped
the shore in a steady rhythm. The beach was about one
kilometer long and I did not expect to see many shorebirds. I
was correct. The marine chart showed another bay across a
narrow forested neck of land that I reached in a few minutes.
The shore was a mixture of sand and gravel and through my
binoculars, I could make out a small flock of sandpipers
pecking the shore for amphipods. This was the first flock I
had seen in several days and so I moved closer to see what
they were up to. Suddenly the flock wheeled and rose quickly
from the beach as a peregrine streaked into their midst. I had
not seen the falcon coming. The shorebirds bunched into a
tight flock in the air and hastily departed the beach. I
tracked them through my binoculars as they climbed high into
the southeast sky and were lost from sight.
The falcon’s pursuit sometimes begins high in
the air from which a spectacular dive on partly closed wings
is launched. The aim of this approach is to snatch an
unsuspecting shorebird from the ground or as it takes flight.
A second approach is to use stealth and speed during low level
pursuits to fly down the prey. The latter approach was used on
the flock in Alaska – unsuccessfully I might add.
As a rule, prey outnumbers
predators. The greatest amount of the sun’s energy held in
eelgrass leaves becomes food for trillions of invertebrates
which are eaten by thousands of shorebirds, and become prey to
a handful of falcons. In the saltmarsh, a few rough-legged
hawks, common barn owls and northern harrier hunt thousands of
mice and voles that nibble at tonnes of vegetation. The
harrier is a characteristic saltmarsh species of the saltmarsh
- more so than the other rough-legged hawk and barn owl.
Harriers are numerous in winter and a few nest in tall
grasslands at the edge of saltmarshes along the Jade Coast.
The languid marine waters of the
eelgrass meadow allow many delicate animals and plants to live
out lives in relative serenity. But where the seawater mixes
with freshwater emanating from land, animals and plants able
to cope with sudden shifts of salinity replace those
preferring marine conditions in eelgrass meadows. The waters
of estuaries are sometimes rich with nutrients streaming from
the land but special adaptations are required to survive in
this changing ecosystem, and this is the subject of the next
chapter.
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