Dive Dry with Dr. Bill

040: Gorgonians or Soft Corals

Although southern California waters are not warm enough for coral reef development, we are blessed with their relatives the soft corals in our spectacular kelp forests. Soft corals or gorgonians are colonies of feeding polyps attached to the rocky floor of the kelp forest or on rocky reefs and overhangs. Evolutionarily they are related to sea anemones, hydroids and jellyfish as well as the reef-building hard corals.

There are three main species of gorgonians in our waters. The California golden gorgonian has golden brown branches with yellow polyps, while its close relative the brown gorgonian has darker brown branches with white polyps. Both of these are found from Pt. Conception to Baja California, reach heights of about three feet and are found to depths of 100 feet. The red gorgonian is very distinctive with slender bright red branches and white polyps. They are found from Monterey Bay to Baja down to depths of 200 feet. However, below 10-20 feet the color may not be obvious without artificial illumination since red light is filtered out first in water.

The branches which form the structural skeleton of soft corals are made of a hard, dark protein known as gorgonin. The soft tissues have small structures made of calcium carbonate embedded in them. This is the same material that reef-building corals use to build their hard colonies. The branches are usually aligned at right angles to the current to allow water to pass through them from which the polyps capture food.

Each feeding polyp is like a tiny sea anemone with eight tentacles. The tentacles have stinging cells that allow them to capture small organisms and food particles which pass nearby in the currents. Gorgonians share a common digestive system so when one polyps feeds, all benefit... a form of invertebrate socialism! If you touch one polyp, it often triggers it and others nearby to withdraw into the protective skeleton. I have inadvertantly done this when my video housing made contact with the polyps just as I was preparing to record them feeding. All I got on tape was the polyps closing up and retracting.

In most species each colony is a different sex... like having men's and women's dormitories at school (remember that far back?). Since each polyp is fixed to its branch, there is no visitation allowed! During periods of warmer water, the polyps cast their reproductive products into the water and the larvae drift in the plankton for about 30 days before settling. The new, slow growing colonies are not reproductively mature for several years but may live for 50 years or more.

Gorgonians are often fed upon by snails. I have yet to see a fish attack a gorgonian colony, perhaps because of the horny skeleton and sharp calcium carbonate structures in their soft tissues. They are often colonized by anemones known as zoanthids which grown on their branches, killing the soft coral's polyps. A bivalve or oyster-like mollusc is occasionally found attached to the branches too, using them as a support structure.

A few years ago I had an opportunity to dive the soft coral capital of the world, Fiji. In Fijian waters soft corals are often more dominant than their hard, reef-building coral relatives. The range of shapes was impressive: in addition to species like those in our waters there were intricate sea fans and sea whips many feet long. The range of colors far exceeded that of our local species. Drift diving past these formations was like floating over a collection of impressionistic paintings (since my uncorrected dive mask softly blurs everything I see).

Having dived in environments dominated by hard coral reefs and by soft corals, I enjoy the beauty of both. However, if my bouyancy control skills lapse temporarily, I prefer the latter. Landing on soft corals is much easier than tearing myself apart on the hard coral reef!

© 2003 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.

Image caption: brown gorgonian; red gorgonian; golden gorgonian
from above; feeding polyps of golden gorgonian

This document maintained by Dr. Bill Bushing.
Material © 2003 Star Thrower Educational Multimedia