Imagine a landscape of white rock pockmarked with thousands of holes. At night, out of each hole extends a hand with six or more fingers, writhing and snapping at anything that passes by. To complete this bizarre scene, visualize the hands covered with hairs. To touch these hairs could mean instant death, for some are very poisonous. Now imagine all of this covered in a layer of mucus. Each hand is connected to the other by a thin layer of tissue extending over the surface of the rock, so that this becomes one big mat of living tissue.
This science-fiction description is very close to the reality faced by minute planktonic organisms floating helplessly toward a coral reef in the warm tropical seas. The hands referred to are the coral animals, known as polyps, each with six or more tentacles armed with cells capable of shooting out threads tipped with poison or sticky mucus, or whip-like ends that can wrap around prey. No other animal group uses these unique weapons. Few other animals can remove tiny organisms from the water with such efficiency. Yet, as efficient as the colony of coral animals is, it can not be sustained by what it can trap in seas whose meager crop of plankton cannot meet it’s nutritional needs.
Though they are voracious and efficient carnivores, corals as well as gorgonians, anemones, and giant clams must rely on a very unique means of supplementing their nutrition. Each harbor within their cells a single-celled algae called zooxanthellae (pronounced zoo-zan-thell-y). The coral polyps and zooxanthellae have what is known as a symbiotic relationship. Coral polyps produce carbon dioxide and water as byproducts of respiration. The zooxanthellae cells use the carbon dioxide and water to carry out photosynthesis. Sugars, fats and oxygen are some of the products of photosynthesis which the zooxanthellae cells produce. The coral polyp then uses these products to grow and carry out cellular respiration. The tight recycling of products between the polyp cells and the zooxanthellae is the driving force behind the growth and productivity of coral reefs. As much as 90 percent of the organic material they manufacture photosynthetically is transferred to the host coral tissue.
Another byproduct of the symbiotic relationship with zooxanthellae is color. Several million zooxanthellae live and produce pigments in just one square inch of coral. These pigments are visible through the clear body of the polyp and are what gives many reef-building coral their beautiful color. As you begin to understand the complex ecosystem of the coral reef, it becomes clear how small physical changes such as ocean temperature, ocean acidification, poor fishing practices and land-based pollution can threaten the reefs’ ability to survive.
We invite you to come visit our coral reef exhibit, located in the Rocky Coasts Gallery, and watch this fascinating ecosystem close-up. Our philosophy is simple. If you see it, learn about it, and care about it, you will help protect it.
Blog, photo and video by Kevin Blakely, Zoo Keeper
