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Predicting Plankton - Hakai Institute

Predicting Plankton

Oceanographers can now predict the timing of the spring plankton bloom in Rivers Inlet to within two days.

It is spring in Rivers Inlet, once one of the largest sources of sockeye salmon in British Columbia. Old canneries dot the shoreline, a reminder of the historical bounty prior to the stock collapse in the 1990s.

Within the water column, tiny organisms are starting to grow and proliferate—the spring plankton bloom. These floating plants (phytoplankton) and animals (zooplankton) make up the base of the Rivers Inlet food chain. The peak of the plankton bloom each spring can vary by almost a month from year-to-year. And the timing of this boom-and-bust cycle has consequences.

At 40 km long and 3 km wide, Rivers Inlet is one of the largest fjords on the Central Coast of BC. Map by Keith Holmes

Species that rely on the plankton bloom for food, notably juvenile sockeye salmon, can be adversely affected when the timing changes. Scientists with the Rivers Inlet Ecosystem Study, a precursor of the Hakai Institute, sought to find out what affects the timing of the plankton bloom in the region.

The first step to understanding this ecosystem was to build a model of the fjord including wind direction, wind speed, cloudiness, water temperature, and river flow.

Each spring, light begins to penetrate the water as the dull gray of winter lifts. Winds begin to shift. River levels fluctuate as the snow melts. Visibility in the water drops dramatically as phytoplankton flourish.

A simplified Rivers Inlet food chain. Diagram by Josh Silberg

The scientists compared the modeled plankton bloom to the actual bloom measured from boat-based sampling, and then made appropriate adjustments to the model.

For instance, a single strong wind event flowing offshore at the right time could change the date of the bloom by up to a week. River flow was also found to be an important factor.

By the end of the four-year study, published in the ICES Journal of Marine Science, the model was fine-tuned to predict the annual plankton bloom to within two days of the actual timing.

“The links between physics, chemistry, and the planktonic components of the community are really critical to what happens in the rest of the food web,” says co-author Brian Hunt, a Hakai Institute oceanographer.

Understanding juvenile sockeye salmon’s food source is key to ensuring the recovery of this culturally and economically valuable species.

This study has now expanded into the Hakai Institute Oceanographic Monitoring Program led by Hakai Institute oceanographers Brian Hunt and Jennifer Jackson. Hunt adds, “We are keeping a finger on the pulse of British Columbia’s coastal marine ecosystems year round.”

Hakai Institute scientists collect a plankton sample. Photo by Grant Callegari

Wolfe et al. (2015). Impact of advection loss due to wind and estuarine circulation on the timing of the spring phytoplankton bloom in a fjord. ICES Journal of Marine Science. doi:10.1093/icesjms/fsv151.