Investigation of the impacts of heatwaves and hypoxia on commercial shellfish species and development of monitoring and mitigation tools

In 2022, Fisheries and Oceans Canada (DFO), in partnership with the Council of the Haida Nation, embarked on a 2-year research project to address climate change impact knowledge gaps for Pacific oysters and Pacific razor clams. The project aims to examine the impacts of acute stressor events in marine environments, including heatwaves and hypoxia (low or depleted oxygen) which are increasing in duration and frequency due to climate change. Of particular concern are heatwaves, which can lead to various detrimental impacts, most notably mass die-offs of shellfish. However, the impact of heatwaves and hypoxia is poorly understood. To address these knowledge gaps, DFO is undertaking research to examine the impacts of singular (heatwave/hypoxia) and coinciding (heatwave+hypoxia) on stress response, energetics, condition index, and survival in two shellfish species of commercial and First Nations interest. This project contributes to climate change vulnerability assessments for Pacific oysters and Pacific razor clams and experimental mitigation techniques to address these climate impacts are ongoing.

Read the Summary Link to Full Case Study

Understanding and Assessing Impacts

Acute stressor events in marine environments are increasing in duration and frequency due to climate change. Of particular concern are heatwaves, which can lead to various detrimental impacts, most notably mass die-offs of shellfish. In July 2021, as a recent example, a heatwave in western Canada caused a mass die-off of shellfish along the coast of British Columbia. In addition to thermal stress, warming events cause oxygen limitation due to forced rises in organismal metabolic rates and oxygen demand and parallel reductions in water oxygen concentration, thereby magnifying challenges to survival. According to the literature, under current climate change projections, dissolved oxygen in the oceans is also forecast to decline and an increased incidence of hypoxic events is predicted for coastal areas. However, the impact of heatwaves and hypoxia on marine species is poorly understood and mitigation techniques remain largely nonexistent. In recent years, cultured Pacific oysters have demonstrated a high susceptibility to summer mortality. Mortality rates typically range from at least 30% but can extend to near total loss. Recent research has shown mortality in the field to typically occur when summer temperatures reach >19–20°C. There is also growing awareness that heatwaves are a contributing factor, but an in-depth investigation is still required. Likewise, the role of oxygen limitation during these events is poorly understood. Similarly to Pacific oysters, declines in population abundance due to decreased recruitment of juveniles and increased mortality of adults have been observed in natural populations of Pacific razor clams.

For additional climate information, look at the Resources section of this example (below). 

Identifying Actions

While climate change stressors are likely contributing to these declines, research on the topic for the species is acutely lacking. In 2022, Fisheries and Oceans Canada, in partnership with the Council of the Haida Nation, embarked on a project to address these knowledge gaps for two species of commercial and cultural importance: Pacific oysters and Pacific razor clams. The project objectives included:

  •  Examine the impacts of singular (heatwave/hypoxia) and coinciding (heatwave+hypoxia) short-term acute stressor events on stress response (gene expression), energetics (oxygen consumption), condition index, and survival in two shellfish species of commercial and FN interest (Pacific oysters, Pacific razor clams);
  • Develop genetic marker sets that may be used for monitoring stress levels in shellfish populations;
  • Test genetic marker sets in natural settings during summer months;
  • Monitor temperature and oxygen conditions at two field sites over two summers and correlate with shellfish mortality;
  • Pilot test the use of aeration to maintain/improve oxygen levels as a mitigation strategy for heatwave/hypoxia events; and
  • Contribute data to climate change vulnerability assessments for Pacific oysters and Pacific razor clams.

Implementation

A combination of controlled laboratory experiments and field testing/monitoring will assess species vulnerability, develop genomic monitoring tools for field populations, and test a potential mitigation strategy for aquaculture/wild recruitment environments. Controlled experiments were carried out in the Fisheries and Oceans Climate Change and Ocean Acidification Laboratory (FOCCOAL) housed at the Pacific Biological Station. Singular (heatwave/hypoxia) and coinciding (heatwave+hypoxia) short-term (5–10 days) stressor events were simulated using temperatures and/or oxygen levels representative of a recent (e.g. 2021) heatwave and/or hypoxic events occurring in coastal British Columbia. Laboratory-based stress/condition responses were characterized according to complementary biomarkers including changes to the transcriptome (RNA-seq), oxygen consumption, reproductive status, and condition index. RNA-seq data was used to develop a genetic marker set that may be used for monitoring stress response in the field. This genetic marker set was applied to field trials during which animals were deployed at field sites for the summer months (May-August). During this time, gene expression (RT-qPCR), condition index, and survival was monitored regularly (i.e. twice per month). If a natural heatwave/hypoxic event occurs during the field trials, opportunistic samples will be taken during and after the stressor event. Temperature and oxygen conditions were continuously monitored during this period via the deployment of oxygen and temperature loggers. Finally, the project pilot tested the use of artificial aeration (i.e. maintenance of normoxia/hyperoxia) during laboratory trials as a potential mitigation strategy for heatwave events. This approach is based on research findings that suggest hyperoxia can increase thermal limits in bivalve species and on the use of artificial aeration in finfish mariculture as a method of limiting stress in animals during hypoxic events.

Outcomes and Monitoring Progress

Results from year one of the project are still being assessed. The expected outputs are:
1. Testing of potential methods for mitigation of heatwaves.
2. Development of candidate gene set for monitoring stressor responses in Pacific oysters
3. Development of candidate gene set for monitoring stressor responses in Pacific razor clams
4. Compile dissolved oxygen monitoring data for the field site located in the Salish Sea.

Next Steps

If laboratory-based mitigation experiments show promise, pilot testing at field sites will form the basis for future investigation. The results from these experiments will inform future proposals examining the impacts of oceans and warming on shellfish. Candidate gene sets developed in this project will also be applied to future monitoring of shellfish populations experiencing climate change.

Resources

Additional Resources:

Additional Climate Information:

Using climate change projections enables better adaptation decisions, as it allows you to better understand how the climate may change. To learn how to choose, access, and understand climate data, visit ClimateData.ca’s Learning Zone.  

Visit ClimateData.ca and click “Explore by Variable” for future climate projections related to temperature and precipitation, which can be used to inform adaptation planning.