Conservationists feel a growing unease about the mysterious deaths of starfish and oysters in our region. The scientific detectives are on the case, but the mystery has only been partially solved. When some of Earth’s oldest foundational life-forms can’t flourish, species teetering further up the evolutionary ladder would seem to be in a precarious place too.
It was in 2013 that a wasting disease was observed in west coast starfish, which started turning into “gobs of goo” in tidal rock pools. In 2016 biologists decided a virus was the cause, perhaps helped by ocean warming, and easily transmitted due to the close mutual proximity the creatures live in. Starfish (or sea stars, class Asteroidea in the phylum Echinoderm) eat each other as well as shellfish, and also absorb nutrients — and contaminants — directly from sea water through their skin.
They breed by ejecting ova and sperm out of gonads in their arms, resulting in external fertilization. Some species brood larvae in specialized body cavities. Some reproduce asexually and also regenerate their own tissue after losing arms in struggles with predators. They re-create skin, guts and a vascular system from specialized cells migrating to the wound site. It’s startling to think that animals with a 500 million year old repertoire of such survival skills could die out today from a puzzling virus. Pollution from oil, heavy metals and pesticides adds to the burden.
The oyster is another ancient species locally assailed by viruses, such as noro-virus from sewage coming from boats and septic tanks. To reproduce, the females (when they are female; individual oysters alternate genders) draw sperm in from the surrounding water through a siphon, and then expel larvae after ten days. So, like starfish, they must cluster in order to reproduce. They act as undersea architects, creating reefs where the larvae, after a phase of drifting and growing a shell, cement themselves on top of the shells of their dead ancestors, making enormous banks and holes for other species deep in the seaweed forests. Filtering sediment out of estuary water, they let light into the eelgrass beds, to the benefit of fish like herring which feed the salmon which feed the whales.
Worldwide, oyster reefs have always protected shorelines from erosion and storm surges, but they can no longer do so because 85% of known oyster beds have been lost to over-harvesting in the past 130 years. This is bad news for the starfish, crabs and other molluscs that eat oysters. The “Olympia” species native to our beaches are listed under the federal Species At Risk Act, and are now rarely seen. Commercial shellfish growers raise the imported Pacific or Japanese oyster. In nature oysters can live up to twenty years, but few survive commercial harvesting that long.
The world is our oyster, said Shakespeare. Maybe, but certainly the oyster’s world has been stolen by us. The oyster crops up in another familiar piece of literature: “The Walrus and the Carpenter”. In Lewis Carroll’s humorous 19th century nonsense poem scores of oysters are invited by the narrator to walk pied-piper-style (despite not having feet) along the beach until finally they are tricked, captured, and eaten with bread and butter — and many apologies.
“I weep for you,” the walrus said:
I deeply sympathize …
But answer came there none
And this was scarcely odd, because
They’d eaten every one.”
Nonsense it may be, but the poem tells a tale of sober science yet to come. Wild oyster beds were 85% over-harvested in 130 years? At that rate it won’t be long before we’ve eaten every one. That’s if they don’t die off from disease first.
Barbara Julian is a local writer and nature enthusiast who writes monthly about the various species making their home in Oak Bay.