Harmful Algae in the Strait of Georgia, 2015-2023

Study Extent

Sampling was carried out throughout the Strait of Georgia in a coordinated fashion on scheduled dates, approximately 1–3 times per month between February and October from 2015 to 2023. All sampling was conducted during the daylight hours of the maxima and minima periods of the fortnightly tidal cycle, with gaps for weekends and holidays. Sampling sites included both nearshore and open water locations.

Sampling

Surface seawater samples for phytoplankton analysis were collected at each station with a bucket. Additional samples were collected at 11 stations from 5, 10, and 20 m using Niskin bottles. Once collected, samples were immediately preserved in Lugol’s iodine with a final concentration in the sample of ∼1–2% (Throndsen, 1978). All water samples were resuspended, and a 1 mL aliquot was settled on a Sedgewick-Rafter slide (Throndsen, 1995) for at least 5 min prior to identification. The entire slide was examined with a compound light microscope (OMAX Lab Binocular) at 100X magnification.

Method steps

1. Phytoplankton analysis followed a method developed by the Harmful Algae Monitoring Program (HAMP, Haigh et al., 2004). Species were identified to the lowest taxonomic level possible based on morphology (Hasle, 1978). The dominant species or group in each sample was enumerated (reported as cells mL–1), as well as all species known or suspected to have a negative effect on finfish and shellfish in BC (Haigh and Esenkulova, 2011). Since this method does not generally permit reliable identification of nanoplankton, HA species <10 μm (e.g., Chrysochromulina, Prymnesium) were not identified. In addition, a biomass index estimation was employed, and percentages of total biomass in five main groups (diatoms, dinoflagellates, raphidophytes, other phytoplankton, and microzooplankton) were estimated (Haigh et al., 2004).

HA that were identified and enumerated in this study were Alexandrium spp., Chaetoceros convolutus, and C. concavicornis (combined), Dictyocha spp. [Octactis speculum, which prior to 2017 was described as Dictyocha speculum (Chang et al., 2017) was included in the counts], Dinophysis spp. (Phalacroma spp. were included in the counts as this genus is closely related to Dinophysis and share the same negative effects), Heterosigma akashiwo, Margalefidinium fulvescens [prior to 2017 described as Cochlodinium fulvescens (Gómez et al., 2017)], and Rhizosolenia setigera.

1. Chaetoceros convolutus
   rank: species
2. Sundstroemia setigera
   rank: species
3. Alexandrium species
   rank: genus
4. Cochlodinium fulvescens
   rank: species
5. Heterosigma akashiwo
   rank: species
6. Dictyocha species
   rank: genus
7. Noctiluca scintillans
   rank: species
8. Pseudo-nitzschia species
   rank: genus
9. Chaetoceros concavicornis
   rank: species

Sampling Sites in the Strait of Georgia