Crabs in acidic water: How I set out to see if green shore crabs can smell when in decreased pH water.

What is Olfaction, and Why Study it!?

Olfaction is a process by which species are able to smell things in the environment. Humans do this by inhaling through our noses, but there are many varieties of ways and differences in sensitivities between organisms in terms of smelling. Olfaction is an important process to all organisms, either to find food, evade predators, navigate the environment or a combination of these.

What does ocean acidification have to do with this?

Recent studies are finding that some marine organisms may not be able to smell under acidic conditions. Now, it’s probably at this point where I should explain to you what ocean acidification is if you’re not already aware.   You’ve probably heard that humans have been raising atmospheric carbon dioxide through fossil fuel emissions since the industrial revolution, but what you may not have known is that this also leads to more CO2 getting into the ocean. When carbon dioxide in the atmosphere is dissolved into the ocean, it causes a decrease in pH of seawater (ie. acidity increases).

How ocean acidification works.  Image source: oceanacidification.org.uk

How ocean acidification works. Image source: oceanacidification.org.uk

Studies involving reef fish as well as sharks have been showing that under acidic conditions, these organisms have a decreased capacity to smell. In the case of reef fish, this may be a predator that they are unable to detect, or in sharks, their prey. As acidity of seawater is predicted to decline further over the next century, the consequences this has to olfactory systems of marine organisms is largely unknown. Additionally, little research has looked at other marine species such as invertebrates, so I thought I’d do an experiment with crabs to see how they cope with acidic waters.

My study

The olfactory experiment setup. Crabs were under tupperwares, with crushed mussels at the other end of the tank.   The tupperware was lifted and crabs were timed how long it took to locate the food.

The olfactory experiment setup. Crabs were under tupperwares, with crushed mussels at the other end of the tank. The tupperware was lifted and crabs were timed how long it took to locate the food.

I acclimated green shore crabs (Hemigrapsus oregonensis) to ambient and elevated

acidic seawater for four days, then ran two experiements: (1) I tested to see how easily they are able to seek out food items (in this case, crushed mussels) and (2) how easily can they locate shelter.

I wanted to look at both these factors, as if I saw crabs were less able to seek out food when acclimated under increased acidity, this may be just because they were disoriented. The addition of a shelter seeking experiment allowed me to see whether crabs could still move and navigate the environment properly when exposed to increased acidic waters.

What I found

Interestingly, I found that crabs acclimated under increased acidity were able to seek out food items just as fast as crabs left at ambient acidity. Additionally, there was no difference in time to seek out shelter between the groups, indicating acidity did not impact movement or vision in crabs.

The shelter-seeking experiment.  Note the hole cut in the red cup for the crabs to hide in.

The shelter-seeking experiment. Note the hole cut in the red cup for the crabs to hide in.

These results suggest that crab olfactory systems may not be impacted by future acidic conditions in the ocean; however, more research is needed to fully understand this relationship.

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For more information, contact the author:

Steve.healy2@gmail.com

@SteveHealy4 on Twitter

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