See full version: What is coral bleaching
In 2005, the U.S. lost half of its coral reefs in the Caribbean in one year due to a massive bleaching event. The warm waters centered around the northern Antilles near the Virgin Islands and Puerto Rico expanded southward. Comparison of satellite data from the previous 20 years confirmed that thermal stress from the 2005 event was greater than the previous 20 years combined. here
Not all bleaching events are due to warm water. [links]
A healthy, resilient reef can either resist a stressful event, like bleaching, or recover from it. When a coral bleaches, it is not dead. Corals can survive if water temperatures return to normal quickly.
Warmer water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching. When a coral bleaches, it is not dead. Corals can survive a bleaching event, but they are under more stress and are subject to mortality. here
Can coral survive a bleaching event? If the stress-caused bleaching is not severe, coral have been known to recover. If the algae loss is prolonged and the stress continues, coral eventually dies. Download this infographic: In English | In Spanish more
The Caribbean experienced widespread coral bleaching during the summer and fall of 2005. This NOAA Coral Reef Watch composite shows maximum Degree Heating Weeks thermal stress accumulations. View it as an animation. Image courtesy of NOAA Coral Reef Watch. more
As atmospheric temperatures have increased in recent decades, so has the temperature of the ocean’s surface waters. Corals are stressed when water temperatures are as little as one degree Celsius warmer for a week or more, especially when there are no winds to mix surface waters and provide relief from the strong sun and ultraviolet (UV) rays.
During the 1997-1998 El Niño/Southern Oscillation event, warming of ocean temperatures resulted in massive coral bleaching throughout the western Pacific and Indian Oceans. Approximately 16 percent of the world’s coral reefs were effectively destroyed. This was the largest single bleaching event ever recorded to date, and alerted the world to the dramatic impact that just one bleaching episode could have on the survival of reefs in many locations. more
In 2005, the world experienced another record-breaking bleaching event in the Caribbean. That summer, reefs throughout the Caribbean experienced the worst mass bleaching event on record in this region, with as much as 90 percent of corals bleached and 40 percent mortality (or greater) at many sites. To add to the devastation, diseases took advantage of weakened coral, especially in the U.S. Virgin Islands, causing increased mortality. Elkhorn and staghorn corals – which in 2006 became the first corals listed as ‘threatened’ by NOAA under the Endangered Species Act – bleached and succumbed to disease, as did other coral species. [links]
Under stressful conditions, corals can lose their symbionts. Some of the main causes for coral stress are: 1) surface water temperatures that are too hot or too cold; 2) changes in the water’s salinity; and 3) runoff from land carrying dirty, cloudy, or contaminated water into the reef. When the zooxanthellae get stressed out, they start producing damaging oxidizing substances (similar to the compounds that cause aging in humans), and the corals expel them. more
Coral reefs are complicated ecosystems, filled with many different types of corals and other organisms. The main structure of most reefs is controlled by stony coral colonies that grow into large, boulder-like formations. Healthy corals host tiny photosynthetic creatures called “zooxanthellae” (zoo-zan-thell-ee) in their skeletons. Corals and the zooxanthellae are symbiotic, meaning that the host organism (the coral) and the symbionts (the zooxanthellae) both benefit by cooperating and living together. However, the symbiotic pair live in a delicate balance.
Zooxanthellae are often responsible for giving the corals their color. When the zooxanthellae are expelled, the coral loses its source of pigmentation, and all that’s left behind is the coral’s white calcium carbonate skeleton: this white, symbiont-free coral is “bleached.” more
90% of their energy from their symbionts. Bleached corals are greatly weakened and susceptible to further stress. If corals are not promptly recolonized by zooxanthellae, they can die from starvation, or fall victim to disease. [links]
It is not just the corals that feel the devastating effects of global warming and pollution. 1,800 species of fish, 5,000 types of mollusks, and over a hundred species of sharks all rely on the Great Barrier Reef, inhabiting the waters, feeding, or finding protection within the incredible fauna. The diversity of the creatures in such a small part of the ocean is a natural wonder, and all these creatures are under threat. [links]
The coral reefs in the Caribbean have been significantly affected because of coral bleaching. According to The Guardian, the coral reefs in the region have all declined by over 50% in the last fifty years. Scientists predict that all the coral reefs in the Caribbean will be gone in the next twenty years unless we act now. [links]
Unfortunately, the effects of coral bleaching are already causing extreme and unrepairable damage to the reefs of the oceans. here
This is a rather worrying phenomenon and does sometimes happen naturally. However, human causes have made bleaching occur more rapidly and widespread bleaching events have killed a lot of reefs. In order to protect the coral reefs of the world, we must understand what causes the bleaching and what humanity has to do to protect the corals.
Because the temperatures of the oceans are rising, delicate ecosystems around the world are being threatened. Coral reefs are one of them. Because the temperatures of the water is going up, corals get stressed and the bleaching process occurs. more