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Hiding in plain sight: Shellfish-killing phytoplankton in Washington State.
Teri L King1, Nancy Nguyen1, Gregory J Doucette2
1Washington Sea Grant, University of Washington, P.O. Box 488, Shelton, WA 98584, United States.
Harmful Algae
|July 25, 2021
Summary
Harmful algal blooms caused by Protoceratium reticulatum and Akashiwo sanguinea are linked to summer bivalve shellfish mortalities in Puget Sound. Yessotoxins (YTX) produced by these algae damage shellfish and necessitate early warning systems for mitigation.
Area of Science:
- Marine Biology
- Ecotoxicology
- Aquaculture Science
Background:
- Summer bivalve shellfish mortalities have been a persistent issue in Puget Sound for decades.
- Previous research attributed these losses primarily to spawning stress and bacteria, overlooking the role of phytoplankton.
- Recent observations indicate increasing occurrences of Protoceratium reticulatum and Akashiwo sanguinea blooms, coinciding with shellfish health declines.
Purpose of the Study:
- To investigate the role of specific phytoplankton species, Protoceratium reticulatum and Akashiwo sanguinea, in summer bivalve shellfish mortalities in Puget Sound.
- To assess the presence and impact of yessotoxins (YTX) produced by these phytoplankton on shellfish health and survival.
- To highlight the importance of early warning systems for harmful algal blooms (HABs) in mitigating aquaculture losses.
Main Methods:
- Monitoring of phytoplankton populations, specifically P. reticulatum and A. sanguinea, through the SoundToxins research and monitoring partnership.
- Measurement of yessotoxins (YTX) concentrations in shellfish tissues (e.g., blue mussels, Manila clams) and phytoplankton samples.
- Histological examination of affected shellfish tissues to identify cellular damage.
- Isolation and culture of P. reticulatum to determine toxin quotas.
Main Results:
- Blooms of P. reticulatum and A. sanguinea have increased in frequency and duration in Puget Sound.
- Yessotoxins (YTX) were detected in Puget Sound bivalve shellfish, with concentrations below EU human health limits but sufficient to cause mortality.
- A 2019 bloom of P. reticulatum coincided with Manila clam mortality, showing digestive gland damage and high YTX levels in clams and phytoplankton.
- A cultured P. reticulatum isolate exhibited the highest recorded YTX quota in the U.S. to date.
Conclusions:
- Protoceratium reticulatum and Akashiwo sanguinea blooms, producing yessotoxins, are significant contributors to summer bivalve shellfish mortalities in Puget Sound.
- YTX contamination poses a threat to shellfish health and survival, even at levels below human consumption regulatory limits.
- Early detection and warning of HABs are crucial for shellfish growers to implement mitigation strategies, such as early harvest or enhanced filtration, thereby reducing economic losses.
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