Coral bleaching is a phenomena that results from high ocean temperatures. Coral thrives in a narrow temperature window, unable to grow if the water becomes either too hot or too cold. Sometimes a worldwide or regional weather pattern of particularly high temperatures will cause coral bleaching, where the coral dies as a result, turning white rather than it’s natural color of tan, yellow, brown, or green.
According to this excellent blog post on the subject by Dr. Jeff Masters of Wunderblog, the entire globe (but mostly the Pacific) is currently experiencing an extended coral bleaching event.
The last coral bleaching event we experienced out at Glover’s Reef in Belize where our island is located was in 1998. This high temperature season culminated in Hurricane Mitch, one of the strongest hurricanes to date, that drastically altered our island. It does not appear that the current event is affecting us out at Glover’s Reef in Belize; the ocean temperatures have so far are remaining normal, which is approximately 80 degrees F.
Charles Darwin sparked more than one controversy over the natural progression of life. One such case involved the evolution of coral atolls, the ring-shaped coral reefs that surround submerged tropical islands.
Coral reefs are actually huge colonies of tiny animals that need sunlight to grow. After seeing a reef encircling Moorea, near Tahiti, Darwin came up with his theory that coral atolls grow as reefs stretch toward sunlight while ocean islands slowly sink beneath the sea surface. (Cooling ocean crust, combined with the weight of massive islands, causes the islands to sink.)
A century-long controversy ensued after Darwin published his theory in 1842, because some scientists thought the atolls were simply a thin veneer of coral, not many thousands of feet thick as Darwin proposed. Deep drilling on reefs finally confirmed Darwin’s model in 1953.
But reef-building is more complex than Darwin thought, according to a new study published May 9 in the journal Geology. Although subsidence does play a role, a computer model found seesawing sea levels, which rise and fall with glacial cycles, are the primary driving force behind the striking patterns seen at islands today.
“Darwin actually got it mostly right, which is pretty amazing,” said Taylor Perron, the study’s co-author and a geologist at MIT. However, there’s one part Darwin missed. “He didn’t know about these glacially induced sea-level cycles,” Perron told OurAmazingPlanet.
What happens when sea-level shifts get thrown into the mix? Consider Hawaii as an example. Coral grows slowly there, because the ocean is colder than in the tropics. When sea level is at its lowest, the Big Island builds up a nice little reef terrace, like a fringe of hair on a balding pate. But the volcano — one of the tallest mountains in the world, if measured from the seafloor — is also quickly sinking. Add the speedy sea-level rise when glaciers melt, and Hawaii’s corals just can’t keep up. The reefs drown each time sea level rises.
The computer model accounts for the wide array of coral reefs seen at islands around the world — a variety Darwin’s model can’t explain, the researchers said.
“You can explain a lot of the variety you see just by combining these various processes — the sinking of islands, the growth of reefs, and the last few million years of sea level going up and down rather dramatically,” Perron told OurAmazingPlanet.
For nearly 4 million years, Earth has cycled through global chills, when big glaciers suck up water from the oceans, and swings to sweltering temperatures that melt the ice, quickly raising sea level. This cyclic growth of ice sheets takes about 100,000 years.
The researchers also found that one of the few places in the world where sinking islands and sea-level rise create perfect atolls is the Society Islands, where Darwin made his historic observations.
Do you know which species is the largest fish? Why whale sharks, of course.
You’ll find out many amazing facts like that in a fascinating feature on the Mesoamerican Reef that ran in National Geographic Magazine in October. The article features some awe inspiring images like this one, shot by photographer Brian Skerry, off the coast of the Yucatan, just north of Belize.
Big Fish, Little Fish: Trapped under ice, lost at sea, chased by sharks, photographer Brian Skerry has had more than a few scares in 35 years of catching images of underwater wildlife. Despite appearances to the contrary, this close encounter with a whale shark was quite the opposite. Snorkeling off Mexico’s Yucatán Peninsula, amid some 400 of the world’s biggest fish, Skerry spotted a massive maw coming at him with a remora darting around inside the giant filter feeder. “It’s not something the shark would eat,” notes Skerry of the suckerfish. Neither is he. Nonetheless, he quickly moved out of the way.
Central America’s Mesoamerican Reef is half the length of its famous Australian counterpart but in many ways more remarkable. If you like coral reefs you’ll love this article.
The print edition of the article carried this wonderful map of the region (not available in the online version.) It highlights the coral reefs, mangrove forests and sea grass beds within the region. Check out where Adventure Island is!
Of the approximately 5,000 species of fish found along the coral reef, perhaps none are as feisty and territorial as the damselfish. Notoriously aggressive, these fish are known to nip at anything that comes between them and their food source. Likewise, these fish fiercely guard their egg clutches during spawning; quickly attacking anything that comes within close proximity. There are approximately 315 species of damselfish found worldwide, 14 species of which are found in the tropical waters of the Western Atlantic. Of those, the Sergeant Major is one of the better known and abundant species.
Found throughout temperate waters of the world, damselfish are palm-sized fish that rarely exceed six inches in length. They are brightly colored in shades of orange, red, yellow and blue, and are characterized with forked tails and a nostril on each side of the head. Attracted to the reef for protective habitat and food, damselfish feed on algal mats found among the coral, as well as other plant matter and small animals suspended in the water. With a tiny mouth lined with sharp teeth, damselfish are skilled at grinding their teeth on algae, resulting in an audible clicking sound.
It is during feeding time that the aggressive behavior of the damselfish becomes very apparent. Competing with parrotfish and surgeonfish for algae, the tiny, but quick damselfish are known to be formidable challengers, antagonizing their rivals until they leave the area. The Blue tang, however, is one of the few fish that has learned how to avoid the nips of the damselfish by feeding in large swimming groups.
Of all damselfish in the Caribbean, the Sergeant Major is one of the more plentiful and common species. This fish is larger than most damselfish (eight inches) and is named for five black bars on the side of its body that resemble the insignia of a rank in the military. The upper body of the Sergeant Major is yellow, occasionally with shades of blue, and the lower body is white with shades of gray, with a dark spot near the pectoral base. In addition to their aggressive feeding behavior, these fish participate in courtship rituals, in which nests are prepared. At this time, males also change colors and actively pursue females during the morning hours by continually circling and nudging them. Reproduction occurs during a five-month spawning period from April to August, which is linked to the lunar cycle. After approximately 200,000 eggs are laid on coral heads, the male protectively guards them until the eggs mature and hatch, after which time he returns to his normal coloration.
Fortunately, because of the curious and aggressive behavior of the Sergeant Major, and Damselfish in general, scientists continue to focus much attention on these fish. Currently in Belize and throughout the world, damselfish have a healthy population and are not threatened. However, just like all other living creatures in the sea, the damselfish is dependent on many factors, such as a healthy reef environment, for it to continue to thrive.
The huge fish, which can grow as large as 8.2 feet (2.5 m) and can weigh as much as 800 pounds, is considered of fine food quality. Atlantic goliath grouper were a highly sought after quarry for fishermen of all types. The grouper’s inquisitive and generally fearless nature makes it a relatively easy prey for spear fishermen. They also tend to spawn in large aggregations, returning like clockwork to the same locations, making them particularly vulnerable to mass harvesting. Until a harvest ban was placed on the species, its population was in rapid decline. The fish is entirely protected from harvest and is recognized as a critically endangered species by the World Conservation Union (IUCN).
Though rarely, the goliath grouper is occasionally spotted on Glover’s Reef, and when it happens it is always an awesome experience. Come dive with us on Long Caye.