Salish Sea Marine Survival Project

65 HOW DO HARMFUL ALGAE IMPACT JUVENILE SALMON? QUESTIONS ADDRESSED DATA CONCLUSIONS Are there harmful algal blooms (HABs) in the Strait of Georgia and do they affect wild salmon? Does direct mortality of juvenile salmon increase as prevalence and intensity of harmful algae increase? Are zooplankton impacted by competition between primary producers of high and low (i.e., harmful algae) nutritional value? Thousands of water samples collected 2015-2018 by the PSF Citizen Science Program provided information on harmful algal blooms in the Strait of Georgia and associated water quality. Behavioural and histopathological observations of juvenile Chinook captured during blooms. Comparison of phytoplankton community composition with the zooplankton caught by the intensive SSMSP zooplankton sampling program. Phytoplankton community composition is strikingly different year to year and may have significant impacts on the food web. HABs, of both toxic and mechanically harmful species, are common in the Strait. There was a correlation between algal blooms, and both feeding activity and conditions of juvenile salmon in Cowichan Bay. BACKGROUND The harmful algae program was developed during 2014 with a pilot study in Cowichan Bay. This program was fully implemented in 2015-2018 with collections of phytoplankton samples taking place throughout the Strait of Georgia via the PSF Citizen Science Oceanography Program. Samples have been regularly collected from ~80 stations from February to November from surface waters (0 m) and at depths (5, 10, 20 m) from 10 priority stations. Phytoplankton data collected include: biomass estimation, identification and enumeration of dominant species, % of constituent groups (diatoms, dinoflagellates, silicoflagellates, raphidophytes, nanoplankton, zooplankton) and identification and enumeration of harmful algae. Water quality data collected concurrently with the phytoplankton samples is being used to determine the conditions that appear to promote the development of harmful algal blooms (HABs). Chinook caught by purse seine in Cowichan Bay during HABs have been examined at the histopathology lab at Pacific Biological Station in Nanaimo to determine if exposure to harmful algae affected body tissues. SUMMARY OF RESULTS TO DATE Multi-year in situ phytoplankton data clearly showed that phytoplankton dynamics in the Strait are a sensitive measure of oceanographic changes. Phytoplankton biomass and composition were strikingly different between years 2015-2018, and appear to be closely associated with nutrients and environmental parameters (Table 1). There is a clear synchrony in phytoplankton dynamics across the Strait, however there are significant differences among locations. This could have direct significance for young Chinook in specific rearing areas. Data collected allow evaluation of the relationship between harmful algal occurrence and environmental parameters. Two species of HABS, Heterosigma and Alexandrium, were associated with relatively colder temperatures (i.e., abundances of these HABs were higher in 2018 compared to the warm years of 2015- 2017). Heterosigma also was associated with high stratifi- cation and low salinity (fresher) waters. Shown below are "windows of opportunity" for two taxa, showing occur- rence at specific temperature/salinity ranges (Figure 1). YEAR CONDITIONS IN THE N.E. PACIFIC SPRING BLOOM SUMMER PHYTOPLANKTON COMMUNITIES HABs 2015 Year of the "Blob" and strong El Nino extremely early dominated by diatoms calm, some mechanically harmful blooms 2016 El Nino transitioning to La Nina normal diatoms, dinoflagellates, lot of silicoflagellates toxic blooms, mechanically harmful blooms 2017 La Nina normal diatoms, dinoflagellates, silicoflagellates toxic blooms, mechanically harmful blooms Table 1. Oceanographic conditions and phytoplankton communities during SSMSP

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