Decorator Crab (Microphrys bicornuta) on Asparagopsis taxiformis algae
Music, Video, and Aquarium
2010 Morphologic Studios
This week’s video features an aquascape comprised of the beautiful purple macro algae Asparagopsis taxiformis. However, if you pay close attention to the left 1/3 of the screen, you’ll notice something… moving with claws… Nestled amongst the algae is a perfectly camouflaged decorator crab (Microphrys bicornuta). Keep paying attention… at 26 seconds into the clip you’ll notice a tiny isopod crustacean float by in the current and descend helicopter-style right onto the crab’s back. The unsuspecting isopod has no idea that it has landed upon an algae covered beast. Furthermore, it appears that the crab is not aware of the unexpected visitor until the isopod begins to explore its decorated exoskeleton. 50 seconds into the clip the isopod meets its fate with a few swift snatches of the crab’s claws. Without missing a beat, the crab continues scavenging amongst the rocks and algae. And life on the reef goes on…
Decorator crabs are amazing creatures in that they pick up pieces of their surrounding habitat and place them on their carapace (back, exoskeleton) in order to blend into their surroundings. Decorator crabs that live amongst sponges decorate with sponges, those that live amongst zoanthids use zoanthids, and so on. This instinctual logic is truly remarkable. The crab in the video has attached small pieces of the Asparagopsis upon itself, and as a result is all but indistinguishable from its surroundings.
Asparagopsis taxiformis has it’s own interesting back story. This algae is native to the Pacific ocean, but since the advent of inter-continental canals (Panama, Suez), it has made its way around the world by stowing away in the ballast water of ships. Subsequently the most frequent places to find this algae is along the rocks of harbors, marinas, and other locations where boats frequent. It prefers rocky coastlines subject to heavy surf conditions. In Hawaii this algae is known as limu kohu, and has long been traditionally used as a flavoring to meats and fish.
Asparagopsis taxiformis has a seriously complicated sex life. The form you see in the video is the ‘gametophytic’ stage. Gametophytes are either male OR female that subsequently release either male or female gametes (akin to sperm and eggs). When the male and female gametes successfully meet, they develop into a ‘tetrasporophyte’ which look nothing like the algae you see in the video. In fact, the tetrasporophyte phase of A. taxiformis is frequently encountered as ‘red hair algae’ in reef aquariums where it can become a nuisance. The Tetrasporophytes then release ‘tetraspores’ that will develop into the sexually active gametophyte stage seen here.