woman standing beside a lagoon holding parts of a dead crab, a number of people look on

Perceived Biodiversity loss in Mansons Lagoon

Around 30 people trekked around the Spit into Mansons Lagoon, during the July 12 ‘Gumbooting the Lagoon.’ While Jane Newman, from the Cortes Island Museum, explained the site’s human history, marine biologist Deb Cowper and FOCI’s Autumn Barrett-Morgan introduced everyone to intertidal life forms. One of the many topics that arose was the loss of marine life.  

Examining a healthy sand dollar – Photo by Autumn Barrett-Morgan

After the tour, Cortes Currents asked Cowper further explanations. 

“I haven’t come and done any firsthand studies or seen any data sets that people have been monitoring over time. I can’t give a definitive answer that such and such a population is in decline or what the trends are, “ she began.  

Then Cowper proceeded to make some personal observations. The parts of the shoreline usually covered by water looked pretty healthy, but there appeared to be less biodiversity and numbers in the more exposed upper region. This appeared to also be true in the inner lagoon. 

This Moon snail was probably feeling ‘a bit freaked out’ about being picked up, but healthy – Photo by Autumn Barrett-Morgan

“There’s probably no one ‘smoking gun’ here. You could talk about impacts of people trampling or collecting. You could talk about shifting climate, that’s probably a really big one.  You could point to a number of different things and without proper studies, it would be kind of wrong on me to try and figure out exactly what was the cause,” explained Cowper. 

Tokin Wakefield has observed the lagoons crab population virtually disappear during the 40 years she has lived by the edge of the lagoon. She and Cowper discussed the species during the gumboot tour. 

“They used to be everywhere And now we can hardly find them in the inner lagoon,” said Wakefield.

Underside of a healthy sea star, which is clinging to the pebbles. Deb Cowper is pointing it its mouth. – Photo by Autumn Barrett-Morgan.

Cowper also noted that, while it could be coincidental, she saw a much higher proportion of sea stars with wasting disease.

“They seemed to be more on the rebound before the heat dome.  This year I was surprised that probably a quarter of the individuals that we saw were impacted, which is concerning that it seems to be happening again,” she said. 

No one picked up the sea stars have wasting disease (the cloudy white bits). It is advanced in the purple sea star – Photo by Roy L Hales

While some species are recovering better than others, Cowper said she has not seen as much biodiversity in the lagoon since last year’s heat dome. 

While thousands of barnacles perished in the heat dome, there is also “lots of the spat of the little babies on the rocks.” So she expects to see a full recovery providing there isn’t another heat dome. 

“When the barnacles have a critter in them, they’ve got the little trap doors closed, but these guys are all empty. These animals have died. They were essentially baked in their shell.” explained Cowper. – Photo by Roy L Hales

The number of sea stars is so reduced that Cowper suggested they need imported plankton born replacements.   

“I’m quite worried about the sand dollars though, I really expected to see more this year.  Last year, I saw an absolutely beautiful crop of sand dollars before the heat dome. I saw the devastation immediately afterwards, but it really doesn’t seem to have rebounded that I can just see from our tour today. That’s a bit of a concern.”

She added, “If we’ve got a lot of those heat dome type episodes as climate change progresses, I think we might be in trouble and see lots of shifts in the ecosystem.”

Providing heat domes are once in a lifetime events, or not particularly frequent, she expects the Marine life to rebound.

A part of Mansons Lagoon where Deb Cowper said there used to be a large sand dollar population. The greenish tinge is algal growth that has grown up on the dead ones. There are still a few live sand dollars. – Photo by Roy L Hales

“What we’re all very concerned about, and I think what we’re witnessing unfold, is that climate change is going to bring these significant changes at a far greater rate and the frequency of those is going to ultimately impact species attempts to recover,” explained Cowper.

“Different species on the intertidal zone have a different range of tolerance. Those who are really adapted and do well, or live in a habitat like those gaper clams (fairly well  protected and deep, where it’s cool), they will continue to do reasonably well. But those species that are not as tough to do with changing temperatures in particular, salinity perhaps, and so on, they will quite likely shift in terms of their distribution. They might well lose numbers and potentially lose their foothold on this area.”

Everyone walked through the sandy area and was instructed to be careful to not trample the Eel Grass (north side of the Spit at low tide) – Photo by Roy L Hales

Top image credit: Deb Cowper showing the tour fragmentsd of a dead crab from the lagoon – Photo by Roy L Hales

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