Does Kwilákm Have Two Species of Oyster?

Photo: Len Gilday


Does Kwilákm Have Two Species of Oyster

Discover Kwilakm » Story » Shores

Pacific Oyster

(Magallana gigas)

Oysters on the seabed at low tide.
Photo: Will Husby

The Pacific oyster is Kwilákm’s common oyster and a relative newcomer to our shores. Pacifics were introduced into aquaculture operation beginning in 1925 following the collapse of the Olympia oyster fishery.

Pacific oysters, originating from Asian waters and relatively tolerant of warmer waters, are expected to adapt to our warming climate. However, as seawater absorbs carbon from the atmosphere and oceans become more acidic, crabs, seastars, sea urchins and oysters are finding it difficult to build their calcium carbonate shells.

The Olympia oyster

(Ostrea lurida)

Olympia Oyster
Olympia Oysters rarely grow larger than 6 cm. in size. Photo: Puget Sound Restoration Fund

Olympias, known to its fans as “Olys”, are BC’s only native oyster. They are small, only four to six cm across, fitting neatly in the hand. They are rounder and more delicate looking overall than Pacific oysters. A typical Olympia oyster is not even a quarter the size of its bigger, non-native cousins.

Olympia oysters are not easy to discover. They generally live lower in the intertidal than Pacific Oysters, making them less visible to the casual observer.

By the 1930s, BC’s Olympic oysters were nearly wiped out through a combination of over-harvesting, shore side development (that disturbed soils, releasing fine sediments which smothered oyster beds) and poisons such as vessel anti-fouling paint and the tons of toxic chemicals dumped by paper mills directly into nearshore waters. In 2003, BC’s native Olympia oyster was added to the Canadian Species at Risk Act as a species of “Special Concern”.

Are any Olympias remaining in Kwilákm?

The Olympia Oyster Field Guide, a knowledgeable guide available from the Puget Sound Restoration Society (PSRS), offers this advice about searching for Olympia oysters: “Olys are wonderfully cryptic critters. They are not showy oysters; they do not jump out at us as we amble along the beach or even muck and poke about. In fact, they bear very little resemblance to the archetypal oyster that we have in our mind’s eye as our ‘oyster search image.’One has to be searching for Olympia oysters to find them.”

Researchers assume that small populations of Olympia oysters are currently stable at low levels in the Salish Sea. Do Olys still hang on in the Bay? Good question: much remains to learn about our oysters. Please be careful when wandering our beaches. Return rocks to where you found them to protect the homes of small creatures. Collecting or harvesting Kwilákm oysters is not allowed.

Oysters in Kwilákm

Photo: Will Husby


Oysters in Kwilákm

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Oysters Are Important

Oysters are a foundation species, meaning they play a strong role in structuring their whole marine community. Oysters offer shelter for invertebrates and small fish that live among the shells of live oysters; inside shells of dead oysters; or in the spaces between oyster shells in oyster beds. During low tides, when the beach is hot and dry, oyster beds trap moisture, provide shade, creating cool, moist refuges for intertidal creatures such as marine invertebrates and crabs.

Oysters Do Well in Quiet Bays

Oysters prefer the brackish waters of estuaries. You can see them right where Terminal Creek drains into the sea in this most protected part of Kwilákm (see map).

Map: Will Husby

Oyster Habitat

Click on the ZONES below to view on the map.

OYsters and barnacles
Photo: Len Gilday

If you walk these shores at a low tide, you will see thousands of oysters wherever the shoreline has boulders and cobbles for oysters to settle on.

A community of oysters
Oysters, along with mussels and barnacles, build dense colonial communities such as this one, seen here at a low tide on Mother’s Beach. Bright green sea lettuce and bladderwrack hold fast to the colony. The brown spherical bladders aid in photosynthesis by helping keep the brown algae afloat when the tide comes in. The colony’s cracks and crannies provide the moist shelter small creatures need to survive on a hot dry beach. Photo: Len Gilday

Longtime resident John Rich believes Kwilákm’s current population of Pacific oysters may be higher than at any time over the seven decades he has been exploring these beaches: “When I was a child in the 1950s, it was rare to find an oyster on the beach in Snug Cove or Kwilákm. There were a few, and when we found them, we sometimes opened them up to eat them raw.”

Kwilákm translates as “clam bay” in the Squamish language. Clams must have been a significant source of food for First Nations people living along these shores. What do researchers know about the role oysters may have played shaping local First Nations’ diet and culture?

The Olympia oyster, BC’s only native oyster was vastly reduced in numbers over the past century, principally by over harvesting and pulp mill pollution. Find out more about BC’s Olympia oysters, affectionately known to fans as the “Oly”. Who are they and could any remain in Mannion Bay?

The Pacific oyster, now BC’s common oyster, is a relative newcomer, purposely introduced into aquaculture operations in 1925 after the collapse of the Olympia oyster fishery. Farmed Pacific oysters escaped into the wild to become BC’s overwhelmingly dominant oyster species, including at Mannion Bay.

Harvesting Mannion Bay’s shellfish is both illegal and unhealthy.

Oyster Harvesting: Health and Safety

Photo: Len Gilday


Oyster Harvesting: Health and Safety

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Harvesting bivalve shellfish in Mannion Bay is both unsafe and against the law. Sewage contamination and biotoxin closures are shown on the map based on the BC Centre for Disease Control‘s Shellfish Harvesting Status Map.

Map: Will Husby


Click on the legend zones below to view on the map.

The area in yellow is closed year round to all shellfish harvesting due to natural contamination from toxins present in various species of plankton that oysters and other shellfish feed on. For information about toxic biotoxins see Plankton.

The area in pink is closed due to septic contamination. Sewage can originate from pleasure boats that lack holding tanks and moor overnight in Kwilákm; from Snug Cove’s live-aboard boats; and from poorly maintained private septic systems located on lands around the Bay. The Snug Cove Sewer System, which serves about 100 connections, and does not include Deep Bay or Snug Point residences, pipes partially treated sewage to release just off Dorman Point. From there, tide and current can sweep the sewage around Snug Point to settle in Kwilákm.

Diseases associated with sewage contamination include ear infections, diarrhea, and hepatitis. Monitoring water quality is critical for public health. During the swimming season, Vancouver Coastal Health tests water off Bowen’s beaches for the presence and quantity of fecal coliform bacteria.

Fecal coliform is an indicator the water that has been contaminated by sewage. When beaches are officially closed to swimming, you’d best stay out of the water.

What can we do? When private septic systems bordering Terminal Creek or Kwilákm are poorly maintained, they can leak raw or partially treated sewage and excess nitrogen into the sea. If you have your own septic system, set up a service contract for your system and commit to a regular schedule of maintenance with an inspection and pump out as needed.

Paralytic Shellfish Poisoning

How do oysters fit into this story? Because oysters feed by filtering microscopic organisms from the water, impurities and bacteria present in the water will stay behind in the oyster’s tissue and build up over time. As a result, bacteria can be 100 times more concentrated within the oyster’s tissue than in the surrounding water.

Red tide is a common name for harmful algal blooms which result from large concentrations of aquatic organisms. Harmful algal blooms happen when algae grows so much in an area of the ocean that it discolours the water with a reddish or reddish-brown colour. Water draining from the land and containing sewage and fertilizer can transport nutrients to the sea and stimulate bloom events. Red tides commonly bloom in late summer and early fall when the water is warm.

Red tide in the bay
Red tide in the Bay. Photo: Bob Turner

Bivalve shellfish (clams, oysters, and mussels) concentrate the poisons in their body. Paralytic shellfish poisoning (PSP) occurs when humans or other mammals (including your pet) eat bivalve shellfish contaminated with large concentrations of poisonous aquatic organisms. According to the BC Centre for Disease Control, PSP symptoms can include: tingling and numbness spreading from lips and mouth, dizziness, nausea, vomiting, and paralysis. Time between ingestion and onset is between 30 minutes and three hours. Respiratory failure and death can occur within 12 hours.

Oysters and People

Squamish Nation canoe arrives in Snug Cove, Bowen Island-

Photo: Will Husby


Oysters and People

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Kwilákm Translates as “Clam Bay.”

Clams must have been a significant source of food for First Nations people living along these shores. What do researchers know about the role oysters may have played shaping local First Nations’ diet and culture?

First Nations and Olympia Oysters

Anywhere clams and oysters were abundant, First Nations ate large numbers of them. Over thousands of years, great piles of discarded shells, called “middens,” built up by the shore where people harvested and processed large numbers of shellfish. Some BC coast shell middens can be 9 metres deep; run for over a kilometre; and span over 10,000 years of continuous occupation. Shell middens contain a detailed record of what food was eaten or processed. Was Kwilákm once heaped with piles of discarded shells and other debris that could open a window on First Nations life around Kwilákm? 150 years of industry and development may have erased any signs of First Nations’ middens or settlements.

Becky Wigen, retired curator of the bone lab, University of Victoria’s Department of Archeology, has devoted decades to analyzing bone and shell from BC archeological sites. She doubts oysters were abundant in Kwilákm: “I have a feeling the oyster population was just not big enough in most places to be worth collecting in large amounts. They are, after all, not a very big shellfish.”

How important were Kwilákm’s oysters to First Nations’ diet and culture? Given the absence of evidence, we may never know the full story.

John Rich on the beach
John Rich has been exploring Kwilákm his whole life. Photo: Len Gilday

“When I was a child in the 1950s, it was rare to find an oyster on the beach in Snug Cove or Kwilákm. There were a few, and when we found them, we sometimes opened them up to eat them raw. Through the 1970s, oysters were picked from the flats in the Bay by residents and others who came to haul away buckets of them. It’s my recollection that by the 1980s there were not a lot of oysters left. When we walked down to the deep tidal flats last year, I was surprised to see the large number of fairly young oysters on the beach. Obviously there has been oyster spawning in recent years. Our current population of oysters may be higher than any time in the last 50 years.”

Oyster are Pretty Awesome Creatures

Photo: Len Gilday


Oyster are Pretty Awesome Creatures

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To discover some of the marvelous things oysters can do, look further in this section.

Oysters are a foundation species, meaning they play a strong role in structuring their whole marine community by providing shelter for invertebrates and small fish.

Oysters filter seawater for their diet of plankton and organic particles suspended in the water. One adult oyster can filter up to 200 litres of seawater per day. Large numbers of oysters, each filtering tiny particles, improve water quality.

Oysters and Climate Change: Shellfish absorb carbon from the ocean to grow their shells. Researchers have determined 12% of the weight of an oyster shell is carbon. By locking up carbon, oysters are doing their bit to the fight against climate change. To find out more about how ocean-warming and ocean-acidification is likely to affect Mannion Bay.

Oyster anatomy diagram
Cross-Section of An Oyster. Diagram:Will Husby

Filter Feeding

Oysters feed by filtering seawater for plankton and organic particles suspended in the water. One adult oyster can filter up to 200 litres of seawater per day. A survey in 2021 of Deep Bay shores during a low tide by citizen scientist Bob Turner estimated a population of between 15,000 to 20,000 Pacific oysters. Given the mix of juvenile and adult oysters, and that part of the day the oysters are out of seawater, this could translate into filtration of 15 million litres of seawater or 6 Olympic-sized swimming pools per week. Oyster filtration removes sediment and excess nutrients and keeps algal blooms in check.

Example of oysters filtering water
Figure: Chesapeake Bay Oyster Recovery Project

Clear water is a benefit to aquatic vegetation, which depends on sunlight penetrating the water to carry out photosynthesis. Better conditions for underwater plants such as eelgrass and seaweeds mean more high-quality habitat for juvenile salmon, stickleback perch, crabs, and others.

Oyster Life Cycle

Oysters are hermaphrodites. That means they are rather fluid about what sex to be. The oyster’s sex may change from year to year, normally during the winter.

Oyster life cycle
Diagram: Will Husby

A medium-sized female Pacific oyster can, in one season, discharge 50 to 200 million eggs into the water. The male oyster gives off sperm and fertilization occurs in the water. For several weeks, the larvae freely swim about as plankton, then settle down on oyster shells, rocks, or another hard surface. Once oyster larvae attach to a surface such as an oyster shell, they are known as spat. The spat will become an adult in two to three years and can live up to 30 years. As generation after generation of spat grow into adult oysters, they form dense, complex clusters known as oyster beds.

Oysters and Climate Change

Shellfish absorb carbon from the ocean to grow their shells. Researchers have determined 12% of the weight of an oyster shell is carbon. By locking up carbon, oysters are doing their bit to the fight against climate change while also reducing ocean acidification. How oysters will fare in future ocean conditions is uncertain. Oyster larvae are vulnerable to ocean acidification during the initial period of shell formation. Moreover, rising water temperatures are predicted to further impair oysters’ ability to reproduce.

Oyster Beds

Oyster Reef at Mannion Bay
Super low tides have revealed the existence of oyster beds near Mother’s Beach. Photo:Will Husby

Oyster beds are natural breakwaters, protecting shorelines from storm surge and erosion. During a storm, dense colonies of oysters, both living and dead, act as a natural breakwater, absorbing wave energy before it hits the shore, and preventing erosion.

Diagram:Will Husby

The climate crisis is increasing the intensity and frequency of winter storms. Scientists predict these trends will continue in the future. Protecting and encouraging Kwilákm’s oysters will help protect against storm surges.

The Terminal Creek Sand Flats

Sand worm tunnel in the sand on the bottom of the ocean.

Photo: Will Husby


The Terminal Creek Sand Flats

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Sand flats
A view from the south end of the Causeway across the sand flats at a very low tide in June 2021. The low tide exposes a high rim of beach sand and gravel, a middle zone of clay bed and boulder (see Clay Bed) and lower and broad sand flats deposited by Terminal Creek that extend underwater into Kwilákm . The flow of Terminal Creek has carved a channel to the deeper waters of Kwilákm. Photo: Len Gilday

The stream mouth of Terminal Creek, Bowen’s largest stream, flows across these tidal flats at a low tide. Terminal Creek drains one-third of the land on Bowen Island and carries not only its waters to the sea but also mud and sand. The mud is carried out to sea and settles in deep water, while the heavier sand is deposited near the shore. As a result, an extensive sheet of sand fills the river mouth area, creating a unique habitat for clams and other burrowing invertebrates.

Aerial view of sand flats

An aerial view of the sand flats taken at a very low tide in 2011. The Terminal Creek water pond behind the Causeway spills into a channel that is carved across the sand flats. The sand has been eroded by Terminal Creek from its watershed over thousands of years and carried to the sea where it has been deposited. The sand flats slope gently underwater out into Deep Bay, visible in this photo, where they have built a thick accumulation of sand. Geologists call the combined sand flats and the submarine sand pile a stream delta.

Sand flats exposed at low tide.
Sand flat exposed at low tide. The sand flats are extensively pock marked with small sand volcanoes that mark the siphon holes of clams or the burrows of animals such as ghost shrimp. The freshly erupted gray sand is distinct from a darker algal coating that covers the rest of the bottom at this location. Photo: Bob Turner
Sand volcanoes
Submerged sand flats with clam and shrimp holes. The density of the holes reflects the intense burrowing and rich life hosted by these shallow sands. Photo: Bob Turner
Seagulls harvesting sea stars
Gulls, harvesting sea stars at low tide. The sand flats at a low tide are a rich feeding ground for bird life. Photo:Will Husby

Purple Stars

Photo: Will Husby


Purple Stars

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Ocre Stars
Photo: Will Husby

Purple stars are probably the most common sea star in Kwilákm. They may be purple, orange, brown, reddish, or even yellow. Look for small white spines that form patterns across their backs. Most purple stars have five stout, tapering arms, but they may have four or seven. The best places to find them are in crevices in rocky shores and between and under cobble rocks at low tide.

Orca stars on a rock
Two purple stars crammed into a crevice to hide from predators such as gulls and to reduce water loss until the tide returns. Photo: Will Husby

Sea stars are a keystone species in some communities, where they balance prey population structure and species diversity. In Kwilákm they help control mussel population, which can expand quickly and exclude other species.

Purple stars are predators that hunt mussels, barnacles, snails, limpets, and chitons. Mussels seem to be their prey of choice.

Once a purple star finds its prey, it grips its shell with its tube feet and pries it open. The star then pushes its stomach outward through the crack. Its digestive juices dissolve the prey’s tissues and the extruded stomach absorbs the liquified prey. Complete digestion can take 2 to 3 days.

Ochre stars feeding
Purple stars feeding: note how their central bodies are hunched upward as they extrude their stomachs into their prey below. Photo:Will Husby

Purple stars look as if they cannot move or do so with glacial slowness. In fact, the underside of the purple star is covered by hundreds of tiny tube feet that it uses to move and to capture prey.

Starfish tube feet
An upside down star displaying its many tube feet. Photo:Will Husby

The tube feet are an intriguing feature of sea stars and their kin. They are powered by an ingenious water-pressure mechanism called the water vascular system.

Figure: Will Husby

Each tube foot consists of an ampula located inside the sea star’s body and attached to a single tube foot. When the muscles surrounding an ampula contract, more water is forced into the tube foot, which lengthens. Bands of small muscles in the outer wall of the tube foot contract to point the lengthening tube foot in different directions. When the ampula muscles relax, they expand, drawing water out of the tube foot so that the tube foot shortens.

Figure: Will Husby

Each tube foot is tipped with a disc that secretes a sticky substance used to attach to rocks or prey. When the sea star wishes to release its hold, the disc secretes a second chemical that breaks the bond of its glue.

Any one tube foot on a sea star can act independantly in responding to smell, touch, or light, but coupled together, many tube feet can synchronize their motion to produce a bouncing motion—their version of running. Researchers are still working out exactly how a sea star accomplishes this synchronization, given it has no brain and a completely decentralized nervous system.

Purple stars are known to live up to 20 years in the wild. During this time they must evade marauding gulls, their only known predators, who hunt them down for food at low tide.

Seagull with a sea stars in its mouth
A gull harvesting a young purple star near Mothers Beach. Photo:Will Husby

Because gulls cannot chew or dismember sea stars, they are limited to eating only small specimens of a radius of six cm or less.

Purple sea stars can breed at the age of five, and they spawn during the summer. The sexes are separate, even though indistinguishable externally. A large female can produce 40 million tiny eggs, which are fertilized by sperm released by males. The tiny larvae float around in the plankton for several months before they settle to the sea floor and become adult sea stars.

Sea Star Wasting Disease

From 2013 to 2015 many Bowen Islanders noticed a sudden decrease in the number of sea stars, including purple stars along the intertidal shores of Kwilákm. Many of the stars were damaged, with missing arms and ugly wounds.

Dying purple sea star
A dying purple star: Photo: Oregon State University

Many scientists believe that sea star wasting disease is caused by the “Sea star associated densovirus.” A sea star wasting disease epidemic swept the Pacific west coast in 2013 to 2015. A large proportion of the purple stars found along the coast died. The incidence of wasting was higher in tide pools than on exposed rock surfaces. The major die- off was followed by an unusual increase (up to 300x) in recruitment by young seastars. As a result of this recovery, today the population of purple sea stars on Bowen shores is similar to that before the onset of the wasting disease.

Nearshore Forests

Photo: Will Husby


Nearshore Forests

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Even seasoned nature watchers can be surprised that there are many ways that adjacent vegetation supports and enhances the lives of many marine creatures and ecosystems.

Nearshore forests play an important role in protecting shoreline properties from the impact of storms and high tides.

The diagram below highlights the many benefits of intact shoreline forest to marine ecosystems and to owners of shoreline property.

Click on the Labels to show details for each feature of the Nearshore Forest cross-section below:

Figure: Will Husby
Comfort and Safety

Vegetation shelters homes from strong winds and reduces possibility of shoreline erosion.

Reduces Impact of Precipitation

Vegetation slows descent of rainfall, reducing speed of surface runoff, thereby reducing slope erosion.


Vegetation and roots increase water seeping into soil, recharging groundwater.

Slope Stability

A matrix of roots holds soil and absorbs rainwater, reducing erosion and slumping.

Evapotranspiration Dries the Soil

As trees and shrubs breathe and photosynthesize, they draw in soil moisture and release large amounts of water vapour through their leaves, increasing soil stability.

Wildlife Habitat

Trees and dead snags provide nesting and roosting habitat for many species of sea birds.

Shade Microclimate

Overhanging branches near beaches create an ideal shaded environment for spawning forage fish eggs.

Food Source for Filter Feeders

Each autumn, tons of leaves fall onto shorelines and shallows along the shore.

Important Salmon Food Source

Wind-blown insects from seaside forests can account for up to half of the stomach contents of juvenile chum and Chinook salmon.

Wave Action

Waves pulverize leaves into fine particles – food for near-shore clams and mussels and providing good for diving birds.

Rotate your device to view diagram.

Managing Shoreline Erosion

Climate change in our region is resulting in more frequent and more severe winter storms, plus slowly rising sea levels. Recently, this has resulted in significant new erosion of beaches and shorelines. Scientists predict the trend will continue.

Modified Shoreline Landscape

Shoreline properties and homes adjacent to Kwilákm, built on soft shores of clay, sand, and gravel, may be threatened by storm erosion.

Illustration: Will Husby

Many homeowners who try to protect shorelines build hard structures to hold back the sea. These measures can have unintended consequences that damage marine life and in some cases increase erosion by reflecting wave energy at the beach and nearshore area surrounding the hard structure. 

Storm Damage

Illustration: Will Husby

Many landowners successfully protect their shoreline properties using natural materials, slopes, and plantings.

To learn more, see the Green Shores webpages located on the Stewardship Centre for British Columbia website.

Green Shores Landscape

Illustration: Will Husby

Deep Bay Brickyards

Photo: Will Husby


Deep Bay Brickyards

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Brick debris on the shore
A pile of discarded broken bricks along the south shore of Deep Bay near the Causeway marks the site of the former Mannion brickworks and ship loading docks. Photo: Bob Turner

The shores of Kwilákm once rang with the sounds of mining and industry. In the late 1800s, two major quarry operations mined the steep clay banks near what is now the Lagoon, and manufactured tons of red bricks that were used in the buildings of Vancouver. Piles of discarded broken bricks still can be found on the shores of Kwilákm.

Broken bricks covered in barnacles
The broken bricks have been colonized by a rich variety of green rockweed, white barnacles and blue mussels. Photo:Will Husby

As historian Irene Howard writes in “Bowen Island 1872 – 1972”(available to borrow from the Bowen Library), brickmaking was an important industry in the Lower Mainland during the early days of the building of the city of Vancouver, and the 60 to 80 acres of blue clay underlying Kwilákm and Snug Cove (link to Clay Beds) was a valuable resource. The clay was exposed in steep banks, easily quarried by hand, and then formed into molds, air dried, and baked in wood-fired kilns to make bricks. Ships were loaded with the bricks during a high tide, and transported to Vancouver. This industry preceded construction of the Causeway, when what is now the Lagoon (link to Lagoon section) was a narrow inlet of the sea.

SS Rothesay at Port
S.S. Rothesay in 1899 at the Mannion Brickyard in Deep Bay during the late 1800s. Photo: Courtesy of Bowen Island Museum and Archives.
City Hall, Vancouver
The City Market building on Main St. in 1928, was built in 1889 of Bowen Island bricks, and served as Vancouver’s City Hall from 1898 to 1929. Photo: Courtesy of
City of Vancouver Archives #CVA 1376-88.

One clay quarry and brickyard was on the north side of what is now the Lagoon and owned by David Oppenheimer, an entrepreneur and mayor of Vancouver from 1888-1891. The other brickyard, operated by Joseph Mannion, was near the south end of the Causeway. After closure of the Mannion brickyard, the flat floor of the clay pit became the site for Playing Field #1 and a popular band shell for the Union Steamship Company resort.

Old clay pit at Cardena Rd.
The #1 playing field of the Union Steamships Company resort was built on the flat floor of the Mannion clay quarry. Photo: Courtesy of Bowen Island Museum and Archives
View of the lagoon
A view across the Lagoon and Causeway to the south shore of Kwilákm and former site of Joseph Mannion’s clay pit and Brickyard. Photo: Bob Turner
View of the lagoon
A flat bench, now the site of private residences on the north shore of the Lagoon, is the former site of the Oppenheimer clay pit and brick yard. Above the steep bluffs underlain by clay is the Deep Bay residential neighbourhood. Photo: Bob Turner


Photo: Will Husby



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One clue that there is more life at Kwilákm’s beaches than meets the eye is the litter of dead clam shells.

These shells, many bleached white to reveal their composition of calcium carbonate, are often concentrated in tide line debris on a beach, or scattered across the muddier sections of beach. But where do all these clams live?

Dead clams on the beach
A litter of dead clam and oyster shells on Sandy Beach. Photo: Bob Turner.
Map: Will Husby

Clams Map

Click below to highlight each area on the map.

Clams are members of a family of invertebrates (animals without an internal skeleton) called bivalves that live within two shells connected by a hinge and pulled together by muscles attached to the shells.

Clam shells on the beach showing the inside and outside of the clam shells.
Two varnish clam shells showing the two shell sections joined by a hinge. Photo: Will Husby

Ancient clams date back in the geological record to the Cambrian Era 500 million years ago. Clams have a powerful muscular foot used for burrowing and live in or on sandy or muddy bottoms below shallow water.

Clam with foot extended
A cockle with its foot slightly extended Iower left. Photo: Will Husby

Burrowing clams differ from other bivalves such as oysters and mussels that live on and attach themselves to hard surfaces.

Clams live just beneath the sand or mud surface, where they are protected from wave action and many predators.

Clams are filter feeders that collect food particles from seawater. This food is largely bits of plants, bacteria, and algae that occur on surfaces or float in seawater. They do this by drawing in and expelling seawater through two tubes, the siphons or neck of the clam.

Horse clam with neck extended
A clam with its neck extended. Photo:Will Husby

These tubes can reach to the sand surface, and are used both to breathe as well as eat. The sand flats just offshore Sandy Beach are pockmarked with volcanoes that are the tops of many clam siphons.

Underwater sand volcanoes that are clam holes
Small sand volcanoes pepper the seafloor just offshore Sandy beach and mark the top of clam burrows and ghost shrimp burrows. Photo: Bob Turner.

Water is drawn into the clam by the movement of millions of hairs (cilia) on gills. Other hairs on the gills filter food from the passing water and transport the food to the mouth of the clam.

Most of Kwilákm’s clam shells are from shallow burrowing species that live within the top metre of sediment. Clams live underground to avoid predatory sea stars, snails, crabs, otter, mink, seals, and marine birds. They have two shells (valves) that are small, round to oval, with both shells of equal size. Some surface-burrowing species, such as cockles, have raised radial ribs on their shells that strengthen the shell against predators and damage.

Kwilákm may have deeper-burrowing species such as razor clams, but their shells are rarely seen. They burrow to greater depths for greater protection, and use longer siphons to reach the surface. Their shells are more elongate, smooth, and flattened to allow more rapid movement through the sediments.

Razor clam
Razor clam with its large digging foot extended (top right). Photo: wildsingapore is licensed under CC BY-NC-SA 2.0

Clams move with a blade-like muscular foot that is pointed for digging. The foot digs with a back and forth movement, creating a burrow. During digging the foot is extended; it grabs the burrow wall by expanding its foot, allowing it to grab and pull the rest of the animal downwards. At the same time, the clam quickly closes its shell, forcing water into the burrow and fluidizing the sediment, making movement through it easier. Both foot and siphons can be withdrawn inside the shells for protection.

It is interesting to compare the shells of different clams, as well as with oysters, to understand their differing defensive strategies against predators.

Clam collection
A comparison of (from left to right) oyster, cockle, butter clam, littleneck clam and mahogany clams. Oysters have thick armoured shells as they cannot move to escape attack. Cockles and other clams bury themselves to avoid predators. Photo: Bob Turner

Oysters have very thick shells, often with sharp spikes to deter predators. Oysters stand their ground and use armament to protect themselves. Clam don’t stand their ground, but rather hide in the sand or mud below the surface. The shallowest burrowing clams, the cockles, are most vulnerable to predators that dig them up. To protect themselves, they have thick rounded and strengthened shells with deep ridges that allow the two shells to lock together when closed. Cockles need this protection because their round shape means that they are slow diggers. Deeper burrowing clams have more streamlined shells that allow them to dig faster to escape predators, and so their shells can be thinner. Examples are butter clams and littleneck clams.

Clam shells grow at the edges, though increases in thickness take place everywhere. Clams reproduce by dispersing both eggs and sperm into seawater. Fertilized eggs develop into larvae that swim briefly and disperse widely before settling permanently on the bottom. Because of their sedentary lives, clams don’t need to draw much oxygen from water to live. During a low tide when their host sediment is dry and without water, clams can almost shut down their need for oxygen.

Oyster catcher on the beach
Oystercatcher eating a clam across from Sandy Beach. The oystercatcher’s long, strong bill allows it to probe into sand and mud looking for buried clams. Photo: Will Husby

The Curious Clay Beds of Kwilákm

Exposed clay beds at low tide.

Photo: Will Husby


The Curious Clay Beds of Kwilákm

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Clay beds
Much of the flat shore area seaward of the Causeway is the eroded top of the clay bed that underlies the area from Deep Bay neighbourhood to Snug Cove. Thin layers of beach sand and offshore sand cover parts of the clay surface. Photo: Bob Turner

Kwilákm has an unusual geology. A thick bed of clay, found only in a few other places on Bowen Island and around Howe Sound, underlies the Kwilákm and Snug Cove area. The clay bed has had a profound influence on the shape of the bay and European settlement of Bowen Island.

Clay is geological material made up of very fine mineral grains. This clay bed was formed on an ancient seafloor during the Ice Age from glacial flour carried to the sea by glacial meltwaters. The soft clay banks have been easily eroded by storm waves, causing retreat of clay banks and creating the broad tidal flats of Kwilákm near the Causeway. The gently sloping surface of the clay bed made it an ideal site for the Union Steamship Hotel, Snug Cove village, and later on, the Kwilákm and Snug Point neighbourhoods.

The clay bed was even mined for brick making in the 1800s (see the Deep Bay Brickyards story), fuelling Bowen’s early economy.

A cut away view of the underground near the Causeway from the Deep Bay neighbourhood (north) to Snug Point (south). The clay layer underlies beach deposits along the shore, and overlies bedrock. Retreat of the two clay banks has created the broad clay flats. Figure: Bob Turner/Will Husby
This map shows that the clay bed forms the foundation of the Deep Bay neighbourhood, the Lagoon area, and downtown Snug Cove. Figure: Bob Turner/Will Husby

Clay Beds Map

Click below to highlight each area on the map.

The clay bed contains scattered pebbles and boulders, and so along the intertidal shoreline of Kwilákm where the clay is exposed, these stones litter the clay surface. As the ocean waves have eroded the soft clay, these hard stones are left behind. These stones cover the surface so completely in places that they disguise the clay bed beneath. Whenever you see cobbles and boulders in the intertidal zone near the Causeway, you can guess that they are likely eroded from the clay bed.

The strange Ice Age origin of the Clay Bed

The clay bed formed near the end of the Ice Age when sea level was 150 m higher than it is today and the lower elevations of Bowen Island and all of the Vancouver region were seafloor. At that time (13,000 years ago) Ice Age glaciers were melting back up Howe Sound, releasing a great flow of melt waters into the Sound, and icebergs were breaking apart from the glacier front. The melt waters carried huge volumes of glacial flour, rock ground to fine silt by the eroding action of the moving glacier. This glacial flour mud settled out on the sea floor of Howe Sound, creating a thick layer of mud. Pebbles and boulders eroded and carried by the glacier became a part of icebergs that broke free from the glacier front and floated down Howe Sound. As the icebergs melted, these pebbles, and boulders were released, falling down into the muddy seafloor, forming a mix of mud, pebble, and boulder. If you take a close look at the clay bed, you can see all three of these components.

Kwilákm then and now: a) 13,000 years ago sea level was 150m higher and the Deep Bay area was seafloor that was accumulating mud, pebbles, and boulders from the retreating snout of a floating glacier; b) today the Ice Age clay layer forms the land of our Bowen Island neighbourhoods, and our shorelines. Figures: Bob Turner/Will Husby
When the ancient sea level fell to its present position about 5,000 years ago, the clay bed formed part of Bowen’s eastern shoreline. Ancient Terminal Creek flowed across the clay bed to the ocean, cutting a ravine in the clay. At the shore, the banks of the ravine were exposed to wave attack, causing erosion and retreat of the soft clay. Over time, retreat of the clay banks due to wave erosion left behind a gently sloping eroded floor of clay, referred to as the clay flats. Figures: Bob Turner/Will Husby.
Clay bed exposed in bank
Secrets of the clay bank! If you peek under the overhanging vegetation on the shoreline clay bank near Mother’s Beach you can see the clay bed with a matrix of clay (ancient seafloor mud) that contains boulders dropped to the ancient seafloor from floating icebergs. Photo: Bob Turner
Rock clay hoodo
The clay bed is viewed during a low tide along the northern shore of inner Mannion/Deep Bay east of Mother’s Beach. Here the clay bed (olive grey, foreground) is well exposed by the erosion of winter waves. A rock boulder (right) which has eroded out of the clay bed while protecting the clay below it, forms a ‘hoodoo’ feature. Oysters (left) are also abundant on the clay layer. Photo: Bob Turner
Honeycomb in clay bed
The clay in the clay bed is very compact and some clams and other organisms bore holes in clay, creating a honeycomb textures. Photo: Bob Turner
A large rock covered in oysters, mussels, and barnacles resting on sea bed at low tide.
A boulder eroded from the clay bed rests on top of the brown clay bed. The boulder surface is host to oysters and barnacles. Some oysters below the boulder are attached directly to the clay. Photo: Len Gilday

Blue Mussels

Photo: Will Husby


Blue Mussels

Discover Kwilakm » Story » Shores

Blue mussels are some of the bay’s most common observable sea creatures. They can be found in tight-packed aggregations at low tide on rocky shores, and on rocks almost anywhere along the edges of Kwilákm. They are an important food source for many sea and land creatures. Only strong predators are able to wrest them from their beds and break their hard shells.

Illustration: Will Husby

Blue mussels can live from 18 to 24 years.

Mussel Bed Bowe Island
The shell is black, blue-black or brown, tear-drop shaped and has concentric lines marking the outside. Photo:Will Husby

Mature blue mussels range from 5 to 10 cm—fitting easily into your hand. They grow quickly, taking from one to five years to reach maturity.

They occupy a broad variety of microhabitats, from the high intertidal where they are exposed to air and sunlight for many hours per day, to deeper subtidal regions where they are seldom exposed to the air. They thrive in a broad range of salinity, from lightly salted brackish water near the mouth of Terminal Creek to more salty oceanic seawaters found elsewhere in Atl’ka7tsem/Howe Sound.

Mussels living in intertidal zones tolerate extremes in temperature. In winter at low tide they are exposed to temperatures below freezing. In a normal summer the hot sun can shining on their black shells can be very hot. Studies show that adult mussels can tolerate temperatures up to 29oC for short periods.

Blue mussels resist drying up during low tide by tightly closing their shells, trapping a small amount of seawater within. If exposed to the air for a long time they open their shells slightly, breathing by passing air over their moist Gills.

Mussels are filter feeders, sucking in plankton and tiny particles of seaweeds and other organic materials that are suspended in seawater. They suck water in through their wide, fringed intake syphons and pump filtered water and their feces out their smaller excurrent syphons. Their fecal pellets, numbering in the millions, sink to the bottom, forming a fine grained sediment providing food and shelter for many bottom-dwelling sea creatures.

Figure: Will Husby

Like clams, blue mussels have a fleshy foot that they use to move about. But to protect themselves from being smashed about by waves, or being pried off rocks and eaten by crows, starfish, and sea birds, blue mussels deploy strong, silky byssal threads to attach to rocks, pilings, or other mussels. These threads are made by byssus glands, located within the mussel’s foot.

A mussel bed is held in place by thousands of byssal threads produced by the tightly-packed mussel. Individual mussels can move slowly by extending a byssal thread, using it as an anchor and then shortening it.

Mussel Armageddon

In June 2021, British Columbia, including Bowen Island, experienced an unprecedented heatwave. It peaked on June 28 and 29. Record temperatures of over 42oC were set in coastal areas on June 28. Unfortunately, these extreme air temperatures occurred on cloudless days and during extremely low tides. As a result, many intertidal creatures, including mussels, were killed, the result of being exposed to very long periods of intense sunlight which heated exposed rocks and the sea creatures living on them to temperatures in the upper 40oC. Dr. Christopher Harley, a marine ecologist, estimated that a billion intertidal marine creatures, including many blue mussels, were killed by the high heat.

Dead mussels
Open, dead mussel shells are part of a mussel bed near Sandy Beach. Photo: Will Husby

Fortunately many mussel beds in deeper water and/or in shaded areas along the shore survived the heat wave. Hopefully they will thrive and their offspring will repopulate the devastated areas.

Mussels as Pollution Fighters

Scientists at Plymouth Marine Laboratory in the United Kingdom have launched a series of trials using blue mussels to clean up microplastic pollution.

Their experiments show that a cluster of 300 blue mussels (weighing 5 kg) could filter out over 250,000 microplastic particles per hour. The microplastics are then either ejected out their excurrent syphons within ‘pseudofeces’ or in their normal fecal matter. Even when their feces contain buoyant plastic, they rapidly sink out of the water. This means sediments containing microplastics could be dredged up taking microplastics out of the system entirely.


Photo: Will Husby



Discover Kwilakm » Story » Shores

Because Bowen’s shores are so rocky, beaches are limited to pockets at the heads of bays. But islanders value them as places to access and enjoy the natural, wild beauty of Atl’ka7tsem/Howe Sound. It is here that we are most likely to encounter the water’s teeming wildlife, enjoy the salty aroma of ocean waters, and savour the refreshing coolness of a swim on a hot summer’s day.

Kwilákm has two significant beaches: Sandy Beach and Pebbly Beach, and one small pocket beach: Mothers’ Beach (see map).

Map: Will Hubsy

Beaches Map

Click below to highlight each area on the map.

How Beaches are Formed

The beaches of Kwilákm are associated with small streams (Terminal Creek for Sandy and Mother’s Beaches and a small unnamed stream for Pebbly Beach). For thousands of years, these streams have have eroded sand and gravel deposited by Ice Age glaciers across Bowen Island and carried them to the shore where they are deposited. Wave action holds the coarse sediment close to shore and spreads it laterally, while fine muds drift away to settle off shore in deeper water.

Figure: Will Husby

Because waves and tides tend to move sand and gravel out to sea, our beaches require a constant supply of new sand and gravel. Sandy Beach and Mother’s Beach receive new sand and gravel eroded from the banks of Terminal Creek. Pebbly Beach receives new materials from a small un-named stream and from gravels eroded by rain and waves along the shore.

A local geologist has observed that is likely that the construction of the Causeway in the 1920s changed the dynamics of beach building in Kwilákm.

Before the Causeway was built, Terminal Creek flowed directly into the Bay, regularly adding new sand and gravel to Sandy and Mother’s Beaches. Now Terminal Creek dumps its load of sand and gravel at the head of the Lagoon, filling the Lagoon rather than the Bay. As a result, little new sand is added to Sandy and Mother’s Beaches. Eventually both may be eroded by wave action and disappear.

Life on the Beach

Many who visit beaches for recreation conclude that beaches are lifeless deserts. The sand and gravels are hot and dry in summer, cold and damp in winter, and tide and wave action will wash any small plant or creature out to sea. But any small child who has spent time exploring a beach will tell you otherwise. In fact, Kwilákm’s beaches are teeming with life forms, each specially adapted to the beach zone it inhabits.

The beaches of Kwilákm can be divided into four zones. Each has different conditions that affect life within it. Each is a great place to explore for signs of life when visiting a beach.

Illustration: Will Husby

Upland Zone

Located above highest storm level. Vegetation casts cool shade on other zones of the beach, providing relief from direct sun.

Dry Zone

Located above high tide level except during storms. Conditions are hot and dry in summer and cold and damp in winter.

This zone often includes a wrack line, composed of decaying seaweeds and marine creatures washed ashore by wave action

Dry Beach Creatures

Tiger Beetle
Grasshoper Nymph
Sand Wasp

Log Zone

Consists of logs thrown onshore by winter storms, located at high edge of the beach

High Tide Line

This is the upper level of tides that come ashore twice daily. High tide levels vary over the month depending on the moon’s gravitational pull.

Low Tide Line

This is the lower level of tides that retreat from shore twice daily. Low tide levels vary over the month depending on the moon’s gravitational pull.

Wrack Line

This is a zone of seaweed and floating debris washed ashore by waves at high tide. This area of nutritious decaying seaweed attracts a whole community of tiny specialized creatures adapted to make use of this abundant food source.

Sand Flea
Yellow Jacket

Subtidal Zone

This is the area below the low tide zone. It is exposed only during very low tides that occur only a few times each year. Creatures living here have few adaptations to being exposed to the air.

Pipe Fish
Ghost Shrimp

Tide Pools

These are depressions in the beach where water from the retreating tide remains. It is home for many kinds of hardy marine creatures that can handle high water temperatures and low oxygen levels until high tide brings in fresh seawater.

Sea Star
Sun Star
Rock Crab

Intertidal Zone

Located between the high tide and low tide lines. Each day at low tide, the sea floor and creatures living here are exposed to the hot drying sun in summer and cold air in winter. Most intertidal beach creatures burrow into the sand to avoid these harsh conditions

Burrowing Creatures

Peanut Worm

Rotate your device to view diagram.

Beaches Are Ever-changing

Bowen’s beaches appear to be stable, never-changing entities of mud, sand, gravel, and pebbles. However, a keen observer can see that they are in a state of constant change.

The materials that make up beaches are constantly rearranged by winds, tides, and waves. Changes in beaches can be most clearly seen seasonally.

Figure: Will Husby

Summer is when Bowen’s beaches increase in size. Winds are less strong, producing smaller widely-spaced waves that move sand and gravel from deeper water landwards and deposit it on the beach front.

Figure: Will Husby

Winter is a time of storms. Waves are larger and taller, and tend to move the sand accumulated on a beach seaward, leaving behind cobbles and boulders. Winter beaches are smaller. Some even disappear completely.


Photo: Will Husby


Discover Kwilakm » Story » Shores

This zone consists of two segments: dry land (beaches and forest) adjacent to the water and the intertidal zone that is flooded by high tide twice each day.

The exposed bedrock of the cobble/boulder shoreline and shallows provides ideal habitat for barnacles,  mussels and rockweed.

Twice daily the tide comes in and twice daily it goes out again. The difference between high and low tide can be as much as five metres.

High Tide
Low tide

High and low tide seen from the Causeway. Sea level may change up to five metres in heigh and the sea may retreat as much as 100 metres. Photos: Bob Turner

Low tides expose many marine creatures . This is when land animals like crows join foraging gulls turning over rocks for crabs and digging holes looking for succulent clams.

The bay’s small beaches not only attract human bathers in the summer months, they are year round resting places for resident water birds and weary migrants who stop by to forage for a meal.

Least Sandpiper on Sandy Beach. Photo:Will Husby