By Jeff Marliave, Vancouver Aquarium vice president of marine science
With the hot, calm weather this August, red tides returned to the Lighthouse Park region at the mouth of Howe Sound, and the bloom came with a vengeance. Elspeth Bradbury, of the Lighthouse Park Preservation Society, photographed the red tide at Caulfeild Cove on August 9. The red tide was cleared out of Caulfeild Cove by the weekend, but streaks of red tide were seen up into Howe Sound through the next week, appearing like blood poisoning streaks on a person’s leg.
There has not been regular, concerted research on red tides since the UBC Oceanography program of the 1970s, so it can only be speculated as to where and how the bloom got started in Caulfeild Cove. Red tide cells had been found dormant during winter in mud on Spanish Banks in the past. Nobody can say for sure whether or not the soft mud seabed surrounding Caulfield Park might have been overwintering habitat for the seeds of this year’s bloom in Caulfeild Cove.
Red tides are, of course, poisonous, and are the reason for shellfish contamination closures, indicated by signage that can be seen at most government docks around the Lower Mainland this summer. Clams, mussels, and oysters will feed on the red tide algae and accumulate the toxins in their pigmented tissues. Different shellfish clear the toxicity from their tissues at different rates. Mussels become much more toxic than other shellfish, but also clear the toxicity more rapidly. Different sea creatures react differently to red tides. In the El Nino summer of 2009, videotape was captured of sunflower seastars tumbling downslope to escape a red tide that was downwelling along shoreline west of Point Atkinson – that video can be viewed here, and is the second video titled “Sunflower Star Fish Landslide at Howe Sound.”