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Climate Detectives Projects 2023-2024

Project title: DĂ©placement des populations de bivalves en mer du Nord

CollÚge Saint André   Auvelais   Belgium

Research question

Quels sont les impacts des changements climatiques sur les populations de bivalves en mer du Nord et comment cela peut il
avoir un impact sur les Ă©cosystĂšmes marins ?

Summary of the project

We studied the consequences of climate change on the evolution of bivalve populations. The presence of bivalves is essential to the proper functioning of marine ecosystems. Bivalves filter water and maintain its quality. They are a source of food for many organisms. With global warming affecting, water PH, salinity and temperature. These changes are causing problems for the shells of bivalves. Researchers aroud the world are interested in this and regularly set off to explore the world’s seas to learn more about bivalves, with the aim of discovering and demonstrating that they can be used as environmental archives. We want to understand why these marine animals move around, and consequently what will happen to our oceans in the future as a result of the changes happening to the species. We can carry out observations using satellite images such as sentinel-2 and -3, as well as Landsat, which would provide information on oceans, sea surface as well as water cover. We can also obtain information using virtual capture, marking and recapture (CMR) to identify individuals by their location. We haven’t found any other sufficient or interesting data that would help us find relevant information.
In order to carry out a statistical analysis of the causes of bivalve movement, we need to study several factors: Water ph, temperature and salinity. We’ll use this data to measure the rate of bivalve resistance to pH and temperature. Thanks to the various data we can find, notably from satellites and the CMR already mentioned. To carry out a spatial analysis, we need the geographical locations of the bivalves. Then, to help us in our research, we’d like to know the bivalves’ diet and feeding habits, to see if this might have influenced their movements. Finally, the population dynamics of the bivalves will help us observe changes in the number of individuals of this marine organism.

Main results and Conclusions

Quels sont les impacts des changements climatiques sur les populations de bivalves en mer du Nord et comment cela peut il
avoir un impact sur les Ă©cosystĂšmes marins ?

Over the past 100 years, the population of certain bivalve species has shifted northwards, mainly as a result of rising water temperatures and acidification.
According to a report by the Flemish Sea Institute (VLIZ), average temperatures in the North Sea have risen by 2 to 3°C. This increase weakens oxygen levels in the water. Oxygen-dependent bivalves will die, as they cannot migrate as easily as other organisms (e.g. fish).
In his book « The Sea Shore », C.M. Yonge states that bivalves thrive on sandy beaches, with a population of around 3.56 million shellfish per hectare of beach.
In terms of diet, bivalves feed on tiny prey that can be poisoned by various elements, such as micro-plastics, oil and acid rain, as a result of pollution. Water pollution can also reduce the availability of food.
Water acidification also plays an important role in bivalve migration. Our oceans absorb around 30% of the CO2 present in the air. Before the industrial revolution, the average pH of the oceans was around 8.2, and is now down to 8.1, representing a 30% increase in acidity. According to the IPCC’s Sixth Assessment Report, ocean pH could fall to around 7.8 by 2100. This would make the oceans 150% more acidic, affecting half of all aquatic life (particularly organisms using CaCO₃, such as bivalves).
Salinity in the North Sea is between 35 and 35.5 PSU. Researchers from various laboratories (CERFACS, LEGOS, LOCEAN and GAME) have noticed that over the past 30 years, surface waters in low-salinity regions are becoming milder and high salinity regions saltier: a recent evolution of the tropical water cycle, and a response to the increasing atmospheric concentration of greenhouse gases. In the North Sea, bivalves are not affected by changes in salinity.

What’s Next? Actions to make a difference and help lessen the problem

We have obtained the following possible solutions. A first idea: conduct surveys with shellfish farmers to assess their perception of the risk linked to acidification. Then, find strategies to regulate pH tested in the laboratory and then in real conditions in shellfish farming sites. Third point, use macro-algae found on the foreshore (coastal zone subject to tides, sometimes submerged and sometimes exposed) and consumed shellfish shells to make the environment more alkaline (basic) and locally remedy ocean acidification. We could also establish a monitoring system aimed at tracking the movements of bivalve populations and understanding the factors that influence them. Research on habitats, breeding cycles and predators can provide valuable data for developing management strategies. Also, protecting and rehabilitating the natural habitats of bivalves in order to encourage their presence in 2
suitable areas and limit their migration to undesired areas could help. This may involve restoring wetlands, creating artificial reefs or managing breeding grounds.
There is already a project led by Ifremer in France aimed at analyzing the impacts of acidification and warming of waters on the most cultivated bivalve species. The CocoriCO2 project has several goals : an observation goal (in particular by means of 12 pH sensors distributed along the French coast), analysis (2 experimental units), anticipation (survey among shellfish farmers to assess their perception of acidification) and find solutions to the problem (laboratory tests of the effect of brown macro-algae and alkaline products on pH). A project like this would be a perfect opportunity for Belgium to preserve the bivalves on its coasts.

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