Fri. Feb 23rd, 2024

A model for predicting the future of hopes ;ces du Saint-Laurent

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Images of the seabed were taken in the St. Lawrence off the coast of Chandler .

  • Joane Bérubé (View profile)Joane Bérubé

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Scientists see it as “the other problem” created by rising greenhouse gas emissions. The acidification of the St. Lawrence is a chemical phenomenon that is difficult to reverse, the effects of which on wildlife are beginning to be measured. Modeling will also make it possible to better assess its impacts on different species.

Principal researcher for Fisheries and Oceans Canada (DFO) at the Maurice-Lamontagne Institute, Diane Lavoie is working on this modeling. It allows us to see the extent of the phenomenon, but also to predict its scale according to seasonality and the different depths of the gulf and estuary. The projections allow us to glimpse the transformation of the St. Lawrence by 2030, or even 2100.

Its modeling is added to those of rising temperatures and falling oxygen. It therefore gives a more accurate portrait of the ongoing phenomena that influence the marine ecosystem on which the survival of molluscs, crustaceans, fish and marine mammals depends.

We, what we did was that we added in this system [the regional climate model], all the biochemistry!

A quote from Diane Lavoie, principal researcher for Fisheries and Oceans Canada

Sometimes the phenomena converge. On the surface, acidification will be favored by an increase in precipitation and a greater supply of fresh water. Sometimes they diverge. The increase in water temperature will have the effect of slowing down the decrease in calcium carbonate saturation.

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The circulation of ocean currents adds to the complexity. The Saint-Laurent is a very heterogeneous environment, recalls the specialist.

Scientific models predict, for example, that in the long term, the increase in acidification will be less in the depths of the Laurentian Channel, but more significant in the south of the Gulf, on the Magdalen Plateau and in the Shediac Valley, which are important fishing areas.

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The table shows the evolution of acidification in the gulf.

In 70 years, modeling shows an increase in acidification of around 40% in the deep waters of the southern Gulf, but the entire St. Lawrence will be more acidic.

If we only consider the temperature, a species of cold water, when it warms up, can move towards colder waters. In the case of acidification, there is no real refuge because it is global, underlines Diane Lavoie.

So, even though we often hear that the oceans are great carbon sensors, once in the water, carbon dioxide reacts with carbon molecules. water to form carbonic acid and leads to ocean acidification.

Each species will be affected differently, sometimes not at all.

The most important consequence of an increasingly acidic marine environment is undoubtedly the dissolution of calcium carbonate, the material that is used by different organisms to make their skeleton, their carapace or their external shell.

As [calcium carbonate concentrations] decrease, at some point, the water becomes corrosive, so these shells that are already formed will begin to dissolve, explains Diane Lavoie.

This is a potentially major impact for several Gulf species. Lobster, shrimp, mussels, oysters, so everything that we like to eat and which are very important commercial species, lists the one who has been studying the effect of climate change on the marine environment for several years.< /p>Open in full screen mode

A lobster in the bottom of the water (Archive photo)

< p class="StyledBodyHtmlParagraph-sc-48221190-4 hnvfyV">There are two types of calcium carbonate, aragonite and calcite, which are not used by all species in the same way. Aragonite, on the other hand, is much more soluble than calcite. So the aragonite will be affected much more quickly, comments Ms. Lavoie.

By 2080, the surface waters of the entire Gulf, fresher than now, will be undersaturated in aragonite, making the formation difficult or impossible typos.

The model indicates that aragonite is already below the solubility threshold on a very large proportion of the St. Lawrence seabed.

So, there are certain species that need it to, for example, build bones, carapaces that might already have difficulty building them. achieve. This is also the subject of work in progress. As for calcite, it is already below the saturation threshold in certain places in the estuary and on the Magdalen Plateau for a few months per year.

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Oysters less than a year old.

Acidification can also affect the survival rate of small larvae, explains Diane Lavoie. This can affect growth because while the organism is still trying to reform its shell, it puts less energy elsewhere, so it will be in worse condition. In the lobster for example, the claws could be smaller.

The researcher adds that according to certain studies, the nutritional quality of certain species of phytoplankton, at the base of the food chain, is lower. The fish are not spared. There are studies which have shown that it could have effects on their sensory capacities, therefore perhaps a reduction in the avoidance of predators, reports the researcher.

Diane Lavoie is collaborating in the study which aims to establish the acidification thresholds which could disrupt certain species, such as lobster, blue mussel and oysters.

The digital model is a tool that can help better understand changes in the habitat of several species such as crab, lobster or northern shrimp.

The research is oriented towards species that are already well studied, which allows it to use already existing data to determine acidification thresholds, such as as levels of calcite or aragonite, which would be harmful.

Once the thresholds have been determined, researchers will be able to use their projections to determine whether acidification will affect the species in question. What we can see with the model is the when, the where, the severity of the change, indicates the scientist.

To find out what the impacts will be on species, researchers look at their location in the water column at their different life stages depending on seasonal variabilities. Lobster larvae, for example, will be found on the surface at first. During this period, we will look at the surface. Then the larva will settle. There, we will see, what is happening at that moment, illustrates the scientist.

To get an accurate picture, research continues. Currently, says Ms. Lavoie, what we are really missing is the thresholds. What pH value for a given species for a given life stage.

When these thresholds are known, they will be put in conjunction with the projections of the digital model this which will make it possible to obtain a portrait of the vulnerabilities of the species analyzed in certain places, at certain times and to what degrees.

Research results are expected to be published in 2024.

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