by B. N. Sullivan
Gorgonian sea fans are a common sight on most tropical reefs, and some semi-tropical reefs. Sea fans actually are colonies of coral polyps attached to flexible tissue called gorgonin, which grows over time into intricately intertwined branches. The result is the characteristic fan-shaped colony.
The polyps feed by extending their tiny tentacles to entrap microscopic plankton that pass by. For this reason, sea fans are found most often in areas of the reef where there are mild to moderate currents, including tidal currents. The fan shape of the colony is adaptive for catching food.
Many species of sea fan are quite colorful. They get their color from microscopic organisms called zooxanthellae, a type of algae that lives in the tissues of corals. The zooxanthellae produce nutrients through photosynthesis, and these nutrients are used by the host corals.
The sea fans in the photo on this page are 'Hickson's Giant Fans' (Subergorgia hicksoni), one of the most common Red Sea fan species. The photo was taken at The Brothers Islands, a pristine marine preserve in an isolated area of the Red Sea. The image was captured during a deep dive on the southeast side of Little Brother, the smaller of the two 'brothers.'
We entered the water from a boat moored near the southern tip of the island, and headed counterclockwise along the island's edge as we began our descent. We rounded a bend and were astonished to see an entire deep slope, beginning at a depth of about 35 meters (115 feet), covered with rows and rows of these large sea fans.
As we descended toward them, I remember thinking that they looked almost like the backs of theater seats, all lined up and facing the same direction, into the current. The scene was almost too much to take in, and impossible to capture well with the camera. It's dark at that depth, and even the most powerful strobes only light an area a few feet wide. So, I had to settle for what you see here.