Lessons from the Lab: The Secret Life of Barnacles

Have you ever stopped and really pondered about barnacles? Probably not, I know I hadn’t. While they don’t attest to be anything more than a nuisance, waiting cut up the soles of your bare feet, I think they warrant more attention than we give. For one, did you know that barnacles have an eye? That’s right, the barnacles are the proverbial ‘fly on the wall’ when you are at the beach! But don’t worry too much, a barnacle’s eye is not much like yours or mine, but rather is a patch of photosensitive cells (ocellus) that can detect the presence or absence of light.

barnacle-600x450

See if you can find the eye on this sagittal cross section of a barnacle. (credit: http://deepseanews.com/wp-content/uploads/2014/06/barnacle-600×450.jpg)

This cool fact is what spurred me to develop an eye related project in the lab. After some research, I found that barnacles actually exhibit anti-predatory behaviour when a sudden shadow is cast over them. Who knew they were so dynamic!? This shadow-reflex, whereby a barnacle withdraws its feeding appendage into its shell and closes up, is thought to serve as protective behaviour from fish or other invertebrates that may be attempting to prey on them.

Here we see barnacles withdrawn into their shell. (credit: http://mlo.stanford.edu/images/balanus.jpg)

Here we see barnacles withdrawn into their shell. (credit: http://mlo.stanford.edu/images/balanus.jpg)

I was particularly interested in seeing how different factors might affect the length of their shadow-reflex; in other words, their hiding time. The amount of time a barnacle hides for is important, if they hide for too long they miss out on feeding opportunities and if they don’t hide for long enough they risk being eaten! I chose to manipulate the salinity of seawater and see how it affected the hiding time in the barnacle, Balanus glandula (a common species found on the west coast of North America). I thought that decreased salinity (less salty than seawater) would cause hiding time to increase because it represents sub-optimal environmental conditions, so a barnacle would be less inclined to feed in it.

My experimental setup, minus the tray used to cast a shadow over the barnacles.

My experimental setup, minus the tray used to cast a shadow over the barnacles.

I cast a shadow over barnacles in tanks with different salinity conditions and found that my prediction was correct! Hooray! Barnacles did hide for longer at the lower salinity condition, which was exciting to see. I also looked to see if region barnacles were collected from (Bamfield or Vancouver), individual barnacle size, or group size affected how long they hid for, but I didn’t find any evidence of an effect.

So why did I choose to manipulate salinity? Well, climate change is predicted to bring more extreme weather patterns, namely precipitation. Freshwater contributions from rain and swollen rivers and streams can decrease the salinity along the coast, which is where barnacles call home. The findings of this experiment provide a stepping-stone to more sophisticated studies that can investigate more specific effects of salinity on barnacle function.

Personally, I would be interesting in seeing if there is a difference in hiding time between barnacles that live at different heights in the intertidal zone (lower, intermediate, and upper), since they are submerged in water for different lengths of time with each tidal cycle. I would guess that barnacles from the upper intertidal zone, that are able to feed the least, would be likely to have shorter hiding times than barnacles from the lower intertidal zone, that are able to feed almost all day long. Perhaps one day we can find out!

For more information, see these fine links:

http://deepseanews.com/2014/06/the-all-seeing-all-knowing-eye-of-upside-down-barnacles/

https://www.youtube.com/watch?v=-naBxQehN4o

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