Goldilocks and Coral. hmmmm?

Picky Picky Picky


Rick MacPherson writes in Coral and the Goldilocks Effect:

For as much as I love coral reefs, I've gotta admit that coral polyps are the prima donnas of the ocean. Most coral reefs are located between the tropics of Cancer and Capricorn--not much more than 30 degrees north and south of the equator. Not too far north nor too far south, but just right. Corals are also found farther from the equator in places where warm currents flow out of the tropics, such as Florida and southern Japan. Reef building corals grow best in waters with a temperature of between 21 and 29 degrees Celsius (70 and 85 degrees Fahrenheit). It is possible for soft corals to grow in hotter and colder places, but growth rates under these conditions are very slow. Again, they like it just right.

Tropical coral species are particularly fussy about temperature. As I've described before, when sea surface temperatures start to climb more than 2-4 degrees Celsius for an extended period of time, coral polyps get stressed and can expel their algal symbionts. Once the algae (zooxanthellae) are evicted, the translucent coral polyp appears white (or bleached). If temperatures remain elevated and the coral cannot reacquire new heat-tolerant algae, the coral may die.



But bleaching can result not just when conditions are too warm, but also when conditions are too cold. Some recent news from Heron Island on Australia's Great Barrier Reef describes how unusually cold weather has resulted in a winter bleaching event. Just the other day I described how the relatively rare phenomenon of sun-dried tides can cause mass coral bleaching and mortality. In a twist on that theme, if unusually low tides are coupled with chilly, windy (conditions that are just wrong for coral) a similar mass mortality can result. These images of bleaching are courtesy of Ove Hoegh-Guldberg's fantastic website Climate Shifts.

1. Where do coral reefs grow?

Coral reefs can be seen throughout the tropical and subtropical Western Atlantic and Indo-Pacific oceans, generally within 30 degrees N and 30 degrees S latitudes.

2. Why do you think that coral reefs only occur between certain latitudes, and then only within certain areas?

Studies have shown that most reefs grow well between the temperatures of 23-25 degrees C. The temperature is ideal year round in these locations, not too hot, and not too cold.

3. What major factors limit where coral reefs can found? List 5 major factors limiting the occurrence of coral reefs and describe HOW these factors limit the establishment or success of coral.

	Factor	Requirements	Why is it important?
	Temperature	18-30 C (64-86 F)	Stable temperature between 18-30 C is necessary for the survival of coral reefs.
	Salinity	33 - 36 parts per thousand
	Light	The maximum depth for actively growing coral is 70m	The need for light for coral reefs� symbiotic plant is thought to limit reefs building corals to shallow water.
	Wave action	Reef development is generally more abundant in area that is subject to strong wave action.	Waves carry food, nutrients, and oxygen to the reef.� Waves distribute coral larvae.� Waves prevent sediment from settling on the coral reefs.

Corals historically thrived in clear water, but recent bleaching events have revealed that water can be too clear! Corals need some nutrients and plankton for food, but not enough to promote algal overgrowth and rapid bioerosion rates.

The corals of the Florida reef tract provide clues to how “Goldilocks” these reef builders can be. The offshore reefs, where waters are clearest, have declined dramatically over the past several decades such that coral cover is now too low to sustain reef accretion. Only on patch reefs is coral cover at least in double-digit percentages.
Hallock, Pamela. " Goldilocks and the Three Biogenic Carbonate Minerals: What Determines “Just Right”?. College of Marine Science, University of South Florida

There is a greater variety of species in, on and around coral reef than anywhere else in the ocean. This is a link to Florida Coral Reefs

What would you do ? This is a "REAL LIFE " interactive about coral. Make decisions by yourself or with classmates



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