February 7, 2012
My post yesterday about the crab houses in the sand at Barr Al-Hikman turned out to be quite popular, so I thought I’d share some more pictures of crabs and crab houses and other crab life traces which I observed at Barr Al-Hikman. In addition to the Ocypode saratan “ghost” crab (thanks for the identification help, Tony Martin!), I observed at least two other species of crab at Barr Al-Hikman.
The first species is a dark red colored crab that I observed when walking out on some of the modern coral and carbonate deposits. These crabs were scuttling about everywhere, but if you came too close to them they would dart into small cracks and crevices in the carbonates and put up their big claw defensively.
The second species of crab which I observed is a very tiny, tan-colored crab. We actually pulled this poor little guy out of his home. On several of the beaches, we noticed small holes surrounded by small balls of sand. The field trip leaders informed us that these the little balls of sand are called “sand bubbles” and that they are produced by the tiny crabs that live in the little holes. The sand bubbles are made by the crabs when they emerge from their holes during low tide to search for bits of food that have been brought in by the recent high tide. After they search through a few grains of sand, the crabs roll the sand grains into a tiny ball so that they don’t search the same sand grains again. Smart behavior, if you ask me! Sand bubbles can leave some spectacular patterns and designs on the beaches, as show in this article.
We were curious to see one of the little crabs responsible for the sand bubbles, so we decided to dig one of the little crabs out of his (or her?) “safe” little home. We took a shovel and started turning over some sand. Before long, we found a little crab. After inspecting him for a minute or two, we returned him to the beach, where he quickly dug himself back into the sand. I feel bad that we disturbed the little guy and destroyed his home, but it was neat to see him!
I’m not normally that interested in biology. Generally, I find biology stuff such as vegetation annoying since it covers up the interesting rocks. However, I enjoyed meeting these two crabs: Mr. Red Crab and Mr. Little Crab. Can anyone identify these two crab species and tell me more about them?