Photo: Len Gilday
Shores
Oyster are Pretty Awesome Creatures
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.
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.
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.
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 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.
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.