Invertebrate diversity on rocks in the reef tank

The rock surfaces in the reef tank are literally covered with life:

• Small colonies of small-polyped stony corals are growing rapidly on these rocks. Visible here are colonies of Pocillopora damicornis (top center, and also behind the feather duster worm, very pale or brownish color in this photo) and Seriatopora histrix (left center, brownish pink color) that have grown rapidly from tiny fragments glued to the rocks with underwater epoxy putty.
• Orange encrusting sponges are growing on the rocks at top right.
• The white antennae (right center) belong to a scarlet cleaner shrimp.

Cleaning symbioses on coral reefs: In the wild, cleaner shrimp make their living by picking parasites and necrotic tissue off fish. The shrimp typically rest upside down under ledges with their white antennae sticking out to advertise their cleaning services. Fish solicit cleaning by taking a particular posture near the shrimp that indicates the fish is not a threat. The shrimp swim out and climb all over the fish, picking it over for edible morsels, and even reaching into the gills or climbing into the mouths of large fish.

A variety of other shrimp and small fish species also provide similar cleaning services in coral reefs the world over. For example, students in our Florida Keys Marine Biology course in January 1998 observed cleaning being done by neon gobies, blueheaded wrasses, juvenile porkfish, and a juvenile french angelfish. The juvenile angelfish was cleaning a 6-foot barracuda directly beneath us as we snorkeled at the reef! It is not uncommon at coral reefs to see groups of large fish lined up at cleaning stations waiting to be serviced by cleaner shrimp or cleaner fish.

• Below the shrimp is an orange tunicate (sea squirt), which is a chordate closely related to vertebrates. Tunicates have tadpole-like larvae that swim, but adults are sessile animals that feed on microorganisms filtered from the water. Tunicates have two prominent openings, one for drawing water in, one for expelling water.
• Feather duster worms (lower left) are large polychete worms that live in leathery tubes of their own making. The large, feathery appendages emanating from the worms' heads trap tiny food particles from the water. Tiny cilia (small beating hairs) in grooves along the "feathers" transport the trapped food particles to the worms' mouths. Though most people initially think these flower-like creatures are plants, they most definitely are animals, as is demonstrated by their sudden disappearance into their tubes when they are disturbed!
• Out of focus in the background are growths of the green algae Dictyosphaeria and Ventricaria. They have extremely large bubble-like cells visible to the naked eye. In the case of Ventricaria, these cells can exceed 1' in diameter.
• The pink and purple colors on the rocks are due to growths of encrusting coralline algae.

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