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Underwater Photo of the Week - September 17, 2018

Fijian Seascape

POTW September 17, 2018


Hi Gang!

In diving circles, the South Pacific island nation is known for healthy reef communities that reveal eye-popping colors on almost every dive. While some of the attention-grabbing colors come from myriad tropical reef fishes, a mix of crinoids, and sea fans, it is the soft coral trees that we can’t take our eyes off of and that are so dominant in many dive sites that make the strongest impressions. 

This week’s POTW shares a beautiful Fijian seascape that is dominated by a mix of colorful soft corals. 

Despite an appearance that might make you think that corals are rocks or plants, all corals are living animals. Scientists separate corals into two classes; (1) the hard, or reef building corals, and (2), soft, or non-reef building, corals. Soft corals are also known as gorgonian corals and octocorals. 

Unlike hard, reef building, corals, soft corals lack significant amounts of limestone in their skeletons. So, when soft coral polyps come to the end of their lives, their remains do not contribute to the long-term structure of coral reefs the way that hard corals do. Even so, soft corals play fundamentally important roles in many rocky and coral reef communities by providing homes, places of attachment, shelter and food for a variety of fishes, snails, worms, basket stars, brittle stars, cowries, crabs, and other invertebrates. In addition to the soft corals featured in this week's POTW image, the invertebrates divers refer to as sea fans, sea whips, and sea rods are also types of soft corals.

Worldwide, there are at least 2,700 species of soft corals. The majority of soft corals are colonial organisms with a number of individual animals sharing the same stalk. Each polyp has an opening on the top of the body where food is taken in and waste is eliminated. Armed with stinging cells that help soft corals defend themselves and capture their food, eight tentacles form a protective ring around each polyp.

Soft corals have flexible skeletons comprised of a protein called gorgonin. Their skeletons contain very calcium carbonate, or limestone, but only in small blocks called spicules that provide structural support to the colonies.

The bodies of most coral polyps are clear and translucent. The brilliant colors are derived from the pigments produced by the millions of tiny algae known as zooxanthellae that live in the tissues of the polyps. 

Soft corals usually occur in current-swept areas. The currents bring prey and other nutrients to the immobile polyps.

The fish in the upper center of the frame is a colorful species of sea bass commonly referred to by several common names including coral trout, coral grouper, leopard coral grouper, and leopard coral trout. Ichthyologists know this colorful species as Plectropomus leopardus.

I hope you enjoy this week’s colorful POTW!

See you next week,



See you next week,