At a certain time of year, an unusual, alien-like phenomenon moves in the shallow waters of Vancouver Island.
In the Facebook group, Field Naturalists of Vancouver Island, someone shared a special sighting of swimming polychaetes in the waters off East Sooke. Louise Page, who teaches invertebrate biology and marine biology at the University of Victoria, identified the giant swimming worms to likely be Nereis brandti, also known as the “giant piling worm” or “giant clam worm.”
“Nereis brandti is huge, growing up to a foot in length,” said Page. “They typically live buried in the sand during the year.”
Page noted the video posted in the Facebook group, which featured multiple worms, was “fascinating behavior,” as they tend to only come up once per year to mate.
“This behaviour, which is called swarming, is triggered by a lunar cue. They all swim up into the water column, males and females at the same time, same place, and have a big orgy up there,” said Page with a laugh. “They release eggs and sperm, and very rapidly, little larvae develop and start to feed on phytoplankton.”
Typically the worms mate during spring or summer, when there is lots of phytoplankton for the larvae to feed on. After metamorphosis, they will usually feed on kelp, but some species also feed on other animals.
These curious worms, which resemble giant centipedes, develop multiple pairs of appendages, which stem off body segments. Each segment contains a little kidney and gonads, and eventually when the larvae become mature enough, they lose the appendages and become animals that burrow in the sands.
From here, the cycle continues, and eventually they too will swim up to mate in the water column on a particular lunar cue. Some species live for one year, others live for multiple.
“Swimming up into the water column is dangerous behaviour. They are subject to a lot of predators,” said Page. “It is important that they all swim up at the same time. For some species, this is a fatal activity, once they rupture they die … others will go back and burrow.”
The worms are also attracted to light, which could be another reason they swam towards the camera flash in the video posted on social media.
She said giant clam worms belong to the family called Nereididae, and different species of these underwater worms can be found throughout the world’s oceans at all depths.
Some, fascinatingly enough, live near deep ocean hydro-thermal vents and don’t feed at all. They live on hot, toxic fluids seeping out of the Earth’s crust.
“When these worms were first discovered, it was amazing. They were huge, about one metre long. When we dissected them, they didn’t have a gut, just massive tissue inside,” said Page. “It was worked out that this massive tissue had bacteria in it. Those bacteria have an amazing metabolic pathway where they can oxidize the hydrogen sulphide.”
Essentially, the worms were feeding on bacteria rather than sunlight.
“It’s the same cycle land plants use to create carbohydrates. The worms utilize sulphide to create organic carbon,” said Page. “When these worms were first discovered, we thought perhaps they could be first kinds of animals on the planet, but that has been discredited. These worms have invaded the deep sea from shallow water habitats.”
Shallow water Nereididae play an important role in the food chain. Being primary consumers, they keep the system powered as food for larger fish and other secondary consumers.
For those interested in learning more about marine annelids, Page will offer a presentation on April 12. The free seminar highlights interesting photos of various marine worms. To register, visit pacname.org/regional-chapters/british-columbia.
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