Impacts on ecosystems and fisheries

Canada’s marine ecosystems are undergoing significant changes. These changes are related to a combination of climate change, natural variability, and other human pressures, such as fishing. Climate change is impacting our oceans and coastal communities, and we are seeing its results on all three of our coasts.

On this page:

• Biological impacts and interacting effects
• Shifting distributions of marine species
• Invasive species
• Impacts on Arctic mammals
• Our ongoing research

Climate change affects the long-term trends in ocean temperature and changes seasonal cycles of warming and cooling. This can affect the amount of food and oxygen available to marine plants and animals. For example, phytoplankton are small plants that form the base of the ocean food web and grow primarily in the upper ocean where sunlight is available. They are highly dependent on a supply of nutrients from waters far below the ocean surface. This vertical nutrient supply can be impacted by increasing ocean temperature because it makes it more difficult to pump nutrients to the ocean surface. Changing temperature can also impact the timing of phytoplankton blooms (large masses which can change the colour of seawater, e.g. red tides), which can subsequently impact overall productivity of the marine ecosystem.

Biological impacts

The biological impacts of changing ocean conditions can vary. Some species may actually fare better in future conditions, while others will not be able to adapt to the new conditions fast enough. If they can’t adapt or migrate to new habitats that are suitable, then some species may even go extinct.

Ocean acidification can make it difficult for many species to survive and thrive, and can have a variety of impacts on marine animal and plant life. There may be both direct and indirect effects on species of ecological and/or economic importance and we still have much to learn about these biological and ecological impacts.

Some marine organisms of economic importance like oysters, mussels and lobsters use calcium carbonate to form their shells or exoskeletons. As the ocean becomes more acidic, it takes more energy to build calcium carbonate shells or skeletons. In some cases, shells and animal exoskeletons may break down or corrode, and for some organisms, it may be impossible to build their shells or exoskeletons altogether. For some species, only parts of their life cycle (e.g. very early stages) may be particularly sensitive.

Other ecologically important organisms, such as some species of microscopic animals called zooplankton, also use calcium carbonate to build their shells. For example, pteropods (small swimming snails) are suffering damaging effects of ocean acidification in the open ocean. As the amount of available carbonate and the pH of oceans continue to decrease, the shells of pteropods begin to dissolve. As zooplankton are a main food source for many species (e.g. juvenile salmon and whales), these animals may struggle to find food and may change their diets. When organisms at the base of the food chain are at risk, the entire food web may also be at risk. The sensory capacity of fish may also be affected, making it more difficult for them to find food or to prevent being eaten themselves by predators.

Some organisms are sensitive to very small changes in pH while others aren’t so there may be ‘winners’ and ‘losers’ in a future ocean environment. For example, some species of marine plants, such as seaweeds and sea grasses, may benefit from increased levels of CO₂ in seawater because they need CO₂ for photosynthesis, just like plants on land. In other cases, a very small pH change can have harmful effects on marine life, impacting reproduction, growth and survival. Alternatively it is possible that some species may have the capacity to adapt over time by changing their diets, or moving to more favorable/less acidic environments, while some populations may suffer, decline or disappear. Harmful algal blooms occur when dense aggregations of microscopic simple plants (phytoplankton) grow out of control and produce toxic or harmful effects on fish, shellfish, marine mammals and birds. In the future, the frequency and toxicity of these harmful blooms are expected to rise in due to warmer acidified seawater conditions, which may also then impact human food security.

Other stressors, such as increased ocean temperatures and low oxygen conditions, may further compound these impacts. This means that aquatic organisms will encounter many changes in their environment at the same time. Higher temperatures and lowered oxygen levels add pressure to habitats that are already affected by other human impacts. How successful they are may depend on how much food is available. Changes lower down in the food web will impact larger species as well, since they depend on the smaller, more directly affected species as a food source.

Increased carbon dioxide in the atmosphere will also lead to higher water temperatures because of the greenhouse effect. Ocean acidification also occurs alongside hypoxia (low oxygen levels in the water) because of increasing water temperatures and higher amounts of nutrients coming from land sources, like agriculture. Species intolerant of hypoxia would need to avoid low oxygen waters to survive. For example, cod are expected to avoid waters at oxygen levels below 28%. Coastal areas close to large cities and agricultural centers are subject to pollution and excessive nutrients in the water; these nutrients can increase plant life communities to a level that kills animals from a lack of oxygen (eutrophication).

Shifting distributions of marine species

Changes in maximum ocean temperatures are leading to shifts in the distribution of many species.

Animals can respond in a range of ways to warmer waters. If an organism is not at the maximum temperature that it can tolerate, then higher temperatures may be beneficial because they may experience increased growth rates and allow the species to reproduce at a smaller size. Survival may increase if animals grow faster through critical life history stages. However, if the water is too warm for an organism to tolerate, animals that are able will move to and/or survive better in cooler waters, which were more similar to their original habitat before the temperature shift occurred.

If climate change alters the environment where a species lives, it may change its location to find more suitable conditions elsewhere. Certain species may change their location to follow food sources or to remain at the optimal water temperature for their survival. These re-locations can impact local species as the new arrivals compete for food and can also bring diseases or parasites.

Climate change can also increase the range for some species to include areas where new habitat becomes suitable while the old habitat is still in use. In this case, some individuals move into the new areas, while other individuals remain in their original region. Ranges may also get smaller in situations where parts of the old area no longer support the species and there is no new suitable area to live in.

Invasive Species

In some cases, climate change can allow unwanted species to establish themselves in new areas. In other cases, such as when sea ice melts, some species need to move to survive.

Plants or animals that enter a new environment where they hadn’t been before and become established are called invasive species. Organisms can be introduced in new areas through human activities, such as the movement of ships. It can also happen because habitats change and become more suitable for new species. For example, warming waters or changing ocean chemistry can provide a new location range for these species to then live in. These new species can become problematic. They dominate their new environment and out-compete local organisms. Invasive species can take advantage of “disturbances” in an ecosystem to become established.

Let’s look at three examples:

• the Arctic was a harsher region for species from other parts of the world to live because of the cold temperatures
  • as the Arctic waters warm, certain species migrate there and are able to grow and reproduce
• eel grass beds help maintain coastal beach structure and provide nursery areas for lots of young fish and shellfish but because of green crabs, originally from Europe, they are being uprooted
  • while some populations of green crabs are unable to survive in colder northern waters, an increase in temperature might allow them to become even more invasive
• marine tunicates, or sea squirts, are simple animals that have been found in areas where they weren’t found before
  • many types of sea squirts have invaded and spread around Prince Edward Island
  • they grow in clumps or like mats on solid surfaces, such as docks and boats, and are very hard to remove
  • they are problematic for the local mussel aquaculture industry causing productivity losses
  • as an attempt to prevent further spread of this species, movement of shellfish has to be controlled

Impact on Arctic mammals

Marine mammals experience a range of impacts due to climate change. Ocean acidification, shifts in habitat, or invasive species affect some species that large mammals rely on for food. These threats combine to make life more difficult for many large mammals.

In the Arctic, air temperatures are increasing about three times faster than the global average. As a result, dramatic reductions in Arctic sea ice cover are already evident and well documented. This makes animals that live in the Arctic particularly vulnerable to climate change. Many Arctic and sub-Arctic species use ice as a critical habitat during key stages in their life cycle. Some species such as ringed seals use fast-ice, the solid ice connected to shore. Others, such as harp seals and walrus, use the drifting ice or what’s called pack ice. Bowhead whales and narwhals rely on sea ice for their habitat and to support the food they eat. Seals rely on the marine environment for foraging. They must haul out on land or ice to rest, for breeding and moulting, or as a platform to access feeding areas. As the temperature warms and storms become more severe, sea ice is less widespread, lasts for shorter periods, and is not as thick as it was before.

Our ongoing research

We are monitoring and studying the effects that changing ocean conditions are having on Canada’s ecosystems and commercial fisheries.

We do research and/or modelling to:

• identify which marine species or stocks are the most vulnerable to changing climate and ocean conditions
• address knowledge gaps associated with climate change impacts and the vulnerability of fisheries and coastal ecosystems
• identify changes in habitats and species distributions

Access our completed research studies and ongoing monitoring activities.