Crabby but crabtivating: hermit crabs and ocean acidification

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Searching through the intertidal at Tower Beach at low tide. Photo Credit: Kelly Borkowski.

Walking along Tower Beach, you might not realize how many different invertebrates are right below your feet. Giant isopods, small-but-mighty barnacles, common shore crabs, blue mussels, and periwinkle snails.

You pick up what you think is an unsuspecting periwinkle snail, but when you turn the shell over, you find a small bristly claw instead of a slimy muscular foot. You just found a hairy hermit crab!

Otherwise known as Pagurus hirsutiusculus, these hermit crabs are found in intertidal ecosystems from California to Alaska. Fluctuations in conditions, incredible competition and intense predation are just some of the challenges they see on a daily basis in the intertidal zone. It already sounds like these guys have it pretty bad, but there’s more…

As many of us know, greenhouse gas emissions cause many changing conditions in the marine environment, one of which being ocean acidification. Acidification causes many negative effects on the physiology of marine animals, including hermit crabs.

But what about the effects of acidity on their behaviour?

I was interested to explore how the foraging behaviour of hermit crabs was impacted by low pH, because this behaviour is very important in their ecosystems. These crabs help cycle nutrients from the decaying matter they eat back into the food web. Therefore, if they can’t find food, they can’t complete these connections.

To test this, I trekked down to Tower Beach and searched for some of these sneaky little critters. In the lab, I split them into two pH treatment groups: one pH similar to the ocean and one acidic pH. After a couple days, I put the crabs in another tank one by one and measured the time it took for each of them to reach a mussel (food!) on the opposite side.

Comparing results between treatments, I found that yes, hermit crabs in the acidic pH were slower at finding food! This result is important because it can help us predict these crabs’ behaviour as the ocean acidifies, and how this will impact their ecosystems.

Why did the crabs in the acidic treatment respond this way?

Firstly, in the acidic pH, more of the crabs’ energy will go towards maintaining their acid-base balance, therefore less will be left over for other activities such as locomotion.

It has also been found that the abilities of their olfactory antennae are reduced in low pH, therefore making it harder to smell their food.

Whatever the reason, acidification might impair their ability to locate food, posing a threat to their survival and the balance of their ecosystems. This is why it is so important to explore the effects of ocean acidification on the behaviour of marine animals!

Hairy hermit crabs are small and inconspicuous, but their ecosystems would not be the same without them!

So next time you wander down to Tower Beach, remember, there is more than meets the eye, and not every periwinkle shell necessarily contains a periwinkle snail!

Here are some scientific articles that inspired my experiment:

https://www.sciencedirect.com/science/article/pii/S0003347211002405

https://www.sciencedirect.com/science/article/pii/S0022098111005120

Here is a link to the hairy hermit crab species information:

http://linnet.geog.ubc.ca/efauna/Atlas/Atlas.aspx?sciname=Pagurus%20hirsutiusculus&ilifeform=102

Also, here is a cool video of some hermit crabs exchanging shells.

Claire Gimple, University of British Columbia, 3 April. Blogpost.

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