Coral Reef 101: Introduction

There is no way to simply describe the complexity of the coral reef. It is composed of organisms who’s body plans, life histories, and associations with other organisms are alien to most people. I have found that many of those visiting the reef enjoy the colors, shapes and motion but have no idea what they are looking at. This will be a series of posts that will help you identify four types of organisms you might have overlooked or misunderstood while snorkeling or SCUBA diving and also help you understand a little about how they are organized. Pictures will be from various places in the Bahamas that I have taken over the past 5 years.

Coral Reef at Sandy Cay, Abacos, Bahamas.  Living hard corals make up the basic structure of the reef and provide substrate for other organisms to colonize when the coral animals die.

So let’s start with the basics. These organisms make up the large-scale structure of the reef: Gorgonians, hard corals, sponges, which are animals, and macroalgae, which are plants. The first 3 are primarily found as colonial animals, meaning that they originated from a microscopic larva that once settled onto the substrate, attached and started to reproduce by division. Macroalgae are generally more organized than the scum that you may be familiar with in your aquarium or on your boat bottom, but still do not have true roots, stems, leaves or vascular structures to transport water and nutrients within the plant as land plants and sea grasses do.

A coral reef at Long Island, Bahamas with areas devoid of living coral but overgrown by pink coraline algae, finger sponges, a large green sponge and feathery Gorgonians.
Former Elkhorn Coral reef at the northern end of Andros Island, Bahamas.  The Elkhorn Coral died about 20 years ago as a result of disease and has been overgrown by macro algae and Gorgonians. One small living colony of Elkhorn Coral (Acropora palmata) can be seen in the center of the photo.

We can find them all in the photo posted on the heading of the website. The numbers refer to 1-Gorgonians 2-hard coral 3-sponge 4-algae. You will typically see them all mixed together in varying proportions. Sometimes one organism or another will be dominant or absent. They are in a never-ending competition for growth space since they live their lives attached to the substrate.

Patch coral head at Highbourne Cay, Bahamas. #1–Gorgonians   #2bottom-center Mustard Hill Coral (Porites astereoides)  #2Center Great Star Coral (Montastraea cavernosa)  #2 two colonies right under the number Golfball Coral (Favia fragum) #2top  number is between 2 colonies of probably Mustard Hill Coral (which is not always yellow).   #3right-center Octopus Sponge (maybe Ectyoplasia sp.)  #3left bottom red and blue encrusting sponges.  #3top-left Stinker Sponge (Ircinia felix).   #4upper a mass of green filamentous algae above the number  #4lower  Pink coraline algae that has grown over bare dead coral.

There is a lot in that picture, isn’t there.  Don’t be overwhelmed!  Future posts will explain more about these four members of the reef community.



One thought on “Coral Reef 101: Introduction”

  1. Your photo and description is a fantastic guide. I keep coming back to it. Really appreciate you doing this.

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