Crab Shoes

Since our last week’s field trip out to Tower beach I have been trying to imagine what it is like to be a shore crab. I can easily sympathize with intertidal invertebrates. After all they deal with changing environments every minute of the day. One second you have to be careful of aquatic predators while frantically trying to find food, and the next you are out, hot and dry desiccating in the wind and sun desperately trying to protect yourself against sea gulls or land scavengers. I am certain that worded this way you too are sympathizing with those lovely creatures. However, empathy is far from sympathy and the exercise I was trying to achieve was to really put myself into a shore crab shoe not simply observe it from a distance.

Purple Shore Crab (Hemigrapsus nudus)

Evidently, I spent the first day of this exercise walking sideways. That alone was trickier than you may think and although you may argue that my eyes are not on stalks, my head is. Also, though it may have helped me running into less electric poles it was painful nonetheless for I had a sour neck for the 3 days that followed. Observing the range of eyestalks and eye separation across the crab taxonomy is wildly fascinating. Additionally, research shows that these adaptations are mainly due to surrounding bottom topography (1). In general crabs that live on flat bottoms have vision adapted to see more accurately along the horizon. Elongated eyestalks as well as narrower positioning of the eyes enables them to do so. In comparison crabs that live in rocky three-dimensional environments such as the Dungeness and Purple shore crabs that we observed on Tower beach have less need for vertical resolution. Instead their wider spread and short stalks allow them for better horizontal resolution. In the end I wondered if crabs too could get soar eyestalks…

 

Ghost Crab (Ocypodinae)

The second day, I spent it trying to simulate what having to feed myself with claws would be like. Conveniently I have lobster claw dive gloves at home for this purpose. The gloves are seven millimeter thick and only allow me to move both my index and thumb independently from the rest of my fingers. Again, I felt like I was cheating considering I had 3 as opposed to 2 parts claws. However, I quickly changed my mind when I realized the difficultly of the exercise. Eating peas was significantly harder.

On the third day I woke up with a soar neck and much more hungry than usual. By consequence I pulled the curtains and hid under my blankets. At that moment, I dearly hoped for all intertidal crabs that this is not how it feels to be in their shoes. At the thought of having to shed my spine and wait several days for the new one to harden again, I terminated the experiment.

I may not be any closer to feeling like a crab but I have gained many ideas for future research regarding these brave little ones. Also, if you are interested in yet another outstanding ability found in the Fiddler crab here is a link to an awesome study. http://www.sciencedirect.com/science/article/pii/S0141113607000712

Fiddler Crab (Uca sp.)

References

  1. Zeil, J., Nalbach, G., & Nalbach, H. O. (1986). Eyes, eye stalks and the visual world of semi-terrestrial crabs. Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology, 159(6), 801-811.
  2. Images were taken from Google Images.
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