Data for Researchers

Harmful Algae in the Strait

Plankton, including the microscopic “grass” of the sea (phytoplankton) and the tiny animals that feed on them (zooplankton), are composed of many different species. Some of these are harmful to marine life and humans, even though they are often only a small part of the total plankton community. In BC waters, Harmful Algae Blooms (HABs) regularly cause severe economic losses through finfish and shellfish mortality and shellfish harvest closures.

The most important species of harmful algae in BC waters are:

Alexandrium spp.

Many species from this genus produce a neurotoxin (saxitoxin) which causes paralytic shellfish poisoning (PSP) in humans and other mammals. There are numerous shellfish harvest closures every year in BC due to saxitoxin in shellfish flesh exceeding regulatory limits.

Chaetoceros convolutus and C. concavicorne

Two species with long setae (spikes) that can be harmful to fish gills when present in large numbers.

Dictyocha spp

A silicoflagellate which is toxic to fish.

Dinophysis spp

A dinoflagellate that produce toxins causing diarrhetic shellfish poisoning (DSP).

Heterosigma akashiwo

An ichthyotoxic raphidophyte, this species is an important source of salmon and herring mortality and probably the most prominent fish-killing algae in the world.

Pseudo-nitzschia spp

Some species in certain conditions produce a neurotoxin (domoic acid) that causes amnesic shellfish poisoning (ASP). Although it is not generally considered a problem in the Strait of Georgia, the CitSci program started to enumerate this species in 2018.

Rhizosolenia setigera

A centric diatom with long, needle-like spikes that can clog fish gills when present in large numbers.

Our Methods

Surface seawater samples for phytoplankton analysis are collected with a Niskin bottle (or directly by submerging the sample container) at each station, with additional water samples from 5 metre, 10 metre, and 20 metre depths being collected at one station (Busy) per patrol in the same manner as the nutrient samples. Once collected, samples are immediately preserved by adding Lugol’s iodine solution (final concentration in the sample 1–2%).

Samples are then visually examined by an analyst using a compound light microscope to characterize the types of phytoplankton present; the limitations of optical methods limit this to species larger than about 10 µm in size.

Phytoplankton analysis follows a method developed by the Harmful Algae Monitoring Program. Species are identified to the lowest taxonomic level possible based on morphology. The dominant species or group in each sample are enumerated (reported as cells mL-1), in addition to all species that are known or suspected to have a negative effect on finfish and shellfish in BC.

Mean Conditions in the Strait of Georgia

Mean near-surface conditions for the Strait of Georgia since 2015. This figure summarizes thousands of stations, the combined efforts of dozens of people over many years.

a) Fraser River inflow, b) Chlorophyll biomass (vertical bars show spring bloom timing from other programs, c) Alexandrium spp., d) Chaetoceros convolutus and concavicorne, e) Dictyocha spp., f) Dinophysis spp., and g) Heterosigma akashiwo

Note in particular the 2^nd row, which shows the seasonal and inter-annual changes in the the biomass of primary producers (phytoplankton) in the Strait, the ultimate source of organic material for all animal life in the Strait.

Sometime during March/April in each year the spring phytoplankton bloom occurs and the biomass increases tremendously before exhausting the immediately available nutrients. Since this very important event sometimes occurs between sampling times, or earlier than sampling occurred in some years, red markers are show to indicate the bloom time as estimated from continuous measurements of near-surface Chlorophyll from BC ferries.

Seasonal Variation

Here, concentrations of Dinophysis spp., Chaetoceros convolutus and concavicorne, Heterosigma akashiwo, Dictyocha spp., Rhizosolenia setigera and Alexandrium plotted here on maps at the location of the measurement, separated into 3-month intervals for each year. Multiple samples are available at each location in each of these intervals and the markers are semi-transparent to provide an indication of the different observed concentrations.

CHAETOCEROS AND CONCAVICORNE, AND DINOPHYSIS SPP.

RHIZOSOLENIA SETIGERA AND ALEXANDRIUM SPP.

HETEROSIGMA AKASHIWO AND DICTYOCHA SPP.

Time Series

Here we show concentrations of Alexandrium spp., Chaetoceros convolutus and concavicorne, Dictyocha spp., Dinophysis spp., Heterosigma akashiwo, Rhizosolenia setigera, and Pseudo-nitzschia spp. as time series at each location, for all years.

In these figures, data for each station are plotted horizontally at the time of sampling, at a vertical location that coincides with its location in the map at left. Some stations (e.g., from Cowichan Bay) have been offset vertically to avoid confusing them with other locations.

Locations which were sampled but at which no HA were seen are marked by small black dots. Otherwise concentrations are indicated by the size and colour of the markers.

Oceanographic conditions in the Strait are seasonally affected by freshwater inflow, and the blue line at the bottom indicates the flow of the Fraser River at Hope, which is the major source of freshwater to the Strait.