Coral_polyps_Tom_Reynolds

Cool and Colorful

Published June 29, 2016 in CONSERVATION, MARINE LIFE

“In all my years of diving I have not yet seen such healthy reefs as those at Wakatobi,” says Simon Bowen, who visited the resort and Pelagian dive yacht in April 2016. While coral reefs in many regions have experienced great stress as a result of fishing activity, pollution and rising ocean temperatures, the corals around Wakatobi Resort remain in excellent condition. We certainly can take some of the credit for this. Our proactive conservation measures have helped us both maintain the reefs in near pristine condition and even restore a number of reefs that had shown the impacts of human activity 20 years ago. And then there’s Mother Nature, who really set the stage.

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Zooxanthellae algae are pigment cells that take up residence inside the coral’s tissue. It is an innate mixture of these cells that give coral its generous display of color. Photo by Marco Fierli, marcof8.com

Roommates with benefits

Before we delve into various reasons why Wakatobi’s reefs remain vital and colorful, let’s first take a brief review of the biology of the corals. Most divers know that corals are actually animals—they just happen to be glued to the reef. Coral polyps are carnivores that can extend tentacles to snare passing morsels, but they are also farmers. The actual coloration of coral is most often not from the polyp itself but from the tiny photosynthetic algae referred to as Zooxanthellae that lives within the coral. These tiny plants are probably the most important drivers of life in the reef system.

The actual coloration of coral is most often not from the polyp itself but from the photosynthetic algae known as Zooxanthellae, living within the coral.

New studies have revealed that zooxanthellae are a highly diverse group of organisms, which might include several hundreds of species. They may be very coral-specific or two or three species may even share a single coral host. The relationship between corals and zooxanthellae is one of mutual benefit. The coral provides the algae a protected environment, safe from the saturation of light and predation and allows the zooxanthellae to utilize the coral’s metabolic waste products to fulfill their dietary needs.

The perfect symbiotic relationship between the zooxanthellae algae and coral polyp facilitates a recycling of nutrients even in nutrient-poor waters. As much as 90% of the organic material photo-synthetically produced by the zooxanthellae algae is transferred directly to the host coral tissue. Drawing courtesy

The perfect symbiotic relationship between the zooxanthellae algae and coral polyp facilitates a recycling of nutrients, even in nutrient-poor waters. Image courtesy of Royal Society Biological Sciences

In return, the algae produce oxygen and help the coral eliminate its waste. Most importantly, zooxanthellae supply the coral with glucose, glycerol and amino acids, which are the products of photosynthesis. The coral uses these products to make proteins, fats and carbohydrates and to produce its calcium carbonate, which is vital for making its skeleton. This perfect symbiotic relationship between the algae and coral polyp facilitates a recycling of nutrients even in nutrient-poor tropical waters. In fact as much as 90% of the organic material photo-synthetically produced by the zooxanthellae is transferred directly to the host coral tissue.

Coral polyps eat tiny floating animals known as plankton, which they catch in their tentacles. Photo by Wayne MacWilliams

Coral polyps eat tiny floating animals known as plankton, which they catch in their tentacles, the flowery extensions of the polyp. Photo by Wayne MacWilliams

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As much as 90% of the organic material photo-synthetically produced by zooxanthellae algae is transferred directly to the host coral tissue. The Turbinaria coral seen here at the dive site Roma, grows well in the sun-lit depths. Photo by Glen Cowans

Too hot for comfort

Every species of coral has its comfort zone. Those that live in the extreme tropical zones of Tropical Atlantic/Caribbean, Pacific and Indian Ocean tend to do best when water temps hover between 23°– 29° C (73° – 84° F). Things can become problematic for corals when ocean temps heat up beyond this comfort zone. An additional 1° C rise in water temperature above seasonal norms may cause heat-stressed corals to shed their internal crops of symbiotic algae (the algae responds to the higher temps by producing toxic compounds). In addition to eliminating a primary food source, this biological eviction causes the corals to lose their colors, revealing the stark-white calcium-based structure beneath and the appearance of having been bleached.

While soft corals don’t help to build the rocky structure of the reef, they play an important role in reef ecosystems as hiding places for fish and filters for organic material. Photo by Karin van de Wouw

Soft corals play an important role in reef ecosystems as hiding places for fish and invertebrates, and filters for organic material. Photo by Karin van de Wouw

Bleaching is not necessarily a death sentence for a coral reef. The coral polyps can survive for a period of time without their algae crops by feeding on plankton captured by their tentacles, but this isn’t a balanced diet. If the polyps go for too long without their zooxanthellae partner, the bleaching may prove fatal to some or all members of a coral colony. Yet, a timely drop in water temperature often allows corals to recover from a bleaching event, and in time the colors will return as life gets back to normal. Fortunately, bleaching has never been and continues to not be an issue for Wakatobi Resort perhaps due to our location in Southeast Sulawesi. Our geographical positioning may have something to do with it as we are located outside the cyclone belt and not affected by cyclone activity; additionally, we do not experience extreme seasonal changes.

La Niña vs El Niño

Much of the world’s coral bleaching events such as those that recently hit portions of Australia’s Great Barrier Reef, the Maldives, some areas of Malaysia and Thailand, are being contributed to climate change and/or El Niño, which has caused higher than normal ocean temperatures.

“I expected to see at least some bleaching during my ten days snorkeling at Wakatobi, but I saw none.”

Wakatobi on the other hand was instead treated to somewhat of a La Niña effect, which made the waters here 1-2 degrees cooler than average for much of the past year. This cooling has caused guides and some guests to slip into a slightly thicker wetsuit, but conditions remain far from chilly, with most sites showing temperatures in the 24° to 27° C (73° to 80° F) range in the shallows, and a few degrees cooler at depth. And the corals seem to thrive at these temperatures.

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