You've probably heard eating fish and other seafood is good for your health. One of the main reasons is that seafood is an excellent source of two important omega-3 fats called EPA and DHA .
Authors
- Bethany Rose Dawson
PhD Candidate, School of Biological Sciences, Adelaide University
- Camille Mellin
Senior Lecturer and ARC Future Fellow, School of Biological Sciences, Adelaide University
- Evangeline Mantzioris
Program Director of Nutrition and Food Sciences, Accredited Practising Dietitian, Adelaide University
EPA and DHA are critical for the development and function of brains, eyes and healthy hearts . They also reduce chronic inflammation , which is linked to many chronic diseases . They can also reduce the risk of premature births and perhaps even some types of cancer .
While humans can produce EPA and DHA from ALA (an omega-3 fat found in plants) and it's possible to get them from foods such as linseed and walnuts, seafood is the main source for most people.
However, our new study shows many fish and other seafood will become less rich in omega-3s over time, due to rising ocean temperatures as the climate changes. In fact, we found omega-3 could drop by 50% under very high warming scenarios.
This is very bad news for human health but also for the health of other animals in the food web.
What is the food web?
Marine algae are among the only forms of life that produce EPA and DHA omega-3s . Examples of marine algae include seaweeds and diatoms (a type of phytoplankton).
Marine algae form the base of marine food webs - a term that means the feeding relationships of different species within an ecosystem. This means marine algae are crucial sources of micronutrients to all animals .
When animals, such as invertebrates like crabs and starfish, eat marine algae, they obtain EPA and DHA.
This is passed up the food chain as fish or other larger animals eat those invertebrates. Eventually, the EPA and DHA reaches humans through the seafood we eat.
However, if EPA and DHA levels get disrupted along the food chain, less of those crucial fatty acids are available for animals higher up - including humans.
What we did and what we found
Our systematic review aimed to understand how climate change may affect these essential fats.
We collected and analysed data from 489 separate experiments involving 132 marine species. These included algae, invertebrates and fish. Bringing together findings like this from many studies shows how marine life is changing globally.
We looked at two aspects of climate change - ocean warming and acidification. Since 1980, ocean temperatures have risen by 0.6°C and the number of heatwaves has doubled . By 2100, ocean temperatures could rise by 4.1°C .
The burning of fossil fuels is driving up CO₂ in the atmosphere, which causes ocean acidification. These environmental changes can have diverse effects on marine life .
We looked at what the research shows could happen in response to three levels of warming: low (0- 6°C hotter), medium (6-10°C hotter) and high (more than 10°C hotter).
Our systematic review found that warming of 0-6°C ( which can already happen during marine heatwaves ) led to 19% lower omega-3 fatty acids in fish in experiments lasting between 24 hours and six months.
That does not include the additional warming impact on the nutritional quality of food fish eat, which our study suggests would happen in the wild.
Under high warming scenarios (more than 10°C hotter), omega-3 reduced by 50% in fish, 34% in algae, and 51% in invertebrates.
Levels of saturated fats - which are less beneficial and abundant in many meats and dairy products - increased by up to 22%.
These disruptions along the food chain have the potential to reduce nutritional value throughout the entire marine ecosystem. This is a significant ecological and public health concern.
We found ocean acidification had less impact on fatty acids than warming, suggesting rising temperature is the dominant driver of this problem.
Why is this happening?
To survive, all living things need to maintain cell function under different environmental conditions.
Under warmer environments, cell membranes (which contain fats) become more flexible and fluid.
To counteract this, individual organisms can replace omega-3s with more rigid structural saturated fats.
These keep the membranes more stable - a process called homeoviscous adaptation .
Why is this a problem?
This is a problem globally. People in tropical regions often have poorer-quality diets and don't consume enough of these omega-3 fats . And people in developed countries are also not eating enough omega-3 fats.
This problem will be harder to solve if climate change reduces the omega-3 in seafood.
This is especially relevant considering fish stocks are already under pressure from overfishing and other human impacts .
The ecological consequences are also far-reaching, as omega-3s are important for growth, reproduction and immune function in marine organisms themselves .
What do we need to do?
To limit the worst of climate change, experts have called for urgent cuts to greenhouse gas emissions .
Our research highlights the importance of managing food security. It is crucial to make sure essential nutrients can still be provided to human populations in their traditional foods in the future, even as the climate changes.
There is a huge amount of food waste, with up to 80% of fish parts discarded during food processing . Given the projected declines in nutrition into the future, these wasted fish parts could be better utilised.
This might, for instance, include making fish oil products rich in omega-3 and other nutrients, or using these fish parts as nutritional aquaculture feed.
Camille Mellin receives funding from the Australian Research Council. She is affiliated with the South Australian Research and Development Institute (Aquatic Sciences).
Evangeline Mantzioris has received funding from the National Health and Medical Research Council. She has been appointed to the National Health and Medical Research Council Dietary Guideline Expert Committee.
Bethany Rose Dawson does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
