The ocean has become so acidic that it literally dissolves the crab shells ...

A new study reveals an alarming fact: the acidity of the Pacific Ocean has become so great that it dissolves the shells of crab larvae. This phenomenon is happening much earlier than researchers feared, demonstrating once again the critical state of our oceans and its potential consequences on the entire chain of life.

This study was conducted by an international team of researchers and funded by the National Oceanic and Atmospheric Administration (NOAA). NOAA studies in particular the acidification of the oceans and the impact of pH changes on the coasts.

The acidity of the water only increases

You should know that the world's oceans absorb about 30% of the carbon dioxide released into the atmosphere. This means that as the levels of CO2 in the atmosphere have increased, so too have the levels of CO2 in seawater, which in turn leads to an increase in the acidity of the water.

Now, researchers have found that ocean acidification along the west coast of the United States is increasing faster than that seen in the rest of the globe . This is particularly evident in coastal regions (up to 200 meters deep), which have a lower buffer capacity while at the same time providing substantial habitats for ecologically and economically important species. It is for this reason that the researchers focused on this area during their study, studying a species emblematic of the region: the sleeping crab.

And, according to the results, the acidity of the water has become so high that it goes so far as to dissolve the shells of newly hatched sleeper crabs.

Crabs will weaken… faster than expected

Researchers have found that the lower pH levels in their habitat affect the larvae by dissolving parts of their shells and damaging their sensory organs (which they typically use to navigate their environment).

This particular fact is already very worrying. However, scientists have been more alerted to the prematurity of this phenomenon. Indeed, the acidity of the water should not affect the crabs so quickly.  "We have discovered dissolution effects on crab larvae that are not expected to occur until much later in the century," said Richard Feely, study co-author and lead NOAA scientist.

This can only generate many problems for crabs: an inability to defend themselves against predators, poor buoyancy and loss of orientation due to the loss of their sensory organs, and difficulty moving around. Indeed, the consequences of the dissolution of the crab larvae are absolutely dramatic for their development towards adulthood.

“If these larval crabs need to divert energy to repair their exoskeletons, and are smaller, as a result, the percentage that makes it to adulthood will be at best variable, and likely go down in the long-term,” added Bednarsek to NOAA. “[...] if the crabs are affected already, we really need to make sure we start to pay much more attention to various components of the food chain before it is too late.”

This infographic shows the location of the crab larvae sampling, examples of ocean acidification impacts, and photos of a larval crab (left) and an adult crab (right). Credits: Nina Bednarsek / SSCWRP.

Ocean acidification is a danger to all

This discovery not only has an impact on crabs and the Pacific ecosystem: it could also affect the economies of cities in the Pacific Northwest, which fish and sell crustaceans (in these areas, the sleeper crab is an essential part of commercial fishing).

Unfortunately, that is not all. Becoming aware of these lesions of crabs is just one of the many symptoms demonstrating the critical state of our oceans. Ocean acidification is now threatening the entire food chain (as all species are interconnected and vital). "If the crabs are already affected, we really need to make sure that we pay much more attention to the different components of the food chain before it's too late," said Bednarsek.

In addition, as the ocean becomes more acidic because it absorbs more carbon dioxide from the atmosphere, this lowers the pH of the water. Then, the fact that the pH is lower, according to NOAA, modifies the ribs by releasing an excess of nutrients which can give rise to overgrowth of algae and thus participate in the increase in temperature and salinity of the water. Consequently, crustaceans and corals have a harder time forming a solid shell because they depend on carbonate ions, which are less abundant in more acidic waters. In the front line of sight, there are therefore not only crabs, but also oysters, clams and plankton, which all need the same carbonate ions to strengthen.

Ultimately, therefore, the entire ocean cycle is considerably weakened. NOAA stresses that it is absolutely vital to reduce our overall carbon footprint to decrease the carbon dioxide absorbed by the sea and try to at least slow the increase in ocean acidification.


Exoskeleton dissolution with mechanoreceptor damage in larval Dungeness crab related to severity of present-day ocean acidification vertical gradients

Bednaršek et al - Science of The Total Environment,

doi: 10.1016/j.scitotenv.2020.136610.

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