and yes not just us humans, but again our corals are under thermal stress with hot ocean water temperatures over a prolonged period of time. Other environmental issues that can cause coral bleaching is run off and pollution, extreme low tides which can cause an excessive amount of sunlight on the corals.
Just last week on a survey we noticed corals paling and bleaching in shallow waters on the reef flats and following on from the bleaching event recorded in February through April 2014, we are again watching closely.
Firstly lets just talk about the basics of coral reef formations and corals themselves:
Corals are made up from rock (limestone) which forms the skeleton and attachment for the coral, plant (zooxanthellae) that gives corals there colour as well as photosynthesizing and producing oxygen. The zooxanthellae and the polyp have a mutualistic relationship each providing benefits to the other.
The animal is a polyp that has tiny tentacles that extend out and catch passing particles which feed the coral. There can be thousands of small polyps on a single coral head and millions spread over a coral reef area.
 |
| Anatomy of a coral polyp © Encyclopaedia Britannica. |
Coral reefs provide many functions or services to people including food, enjoyment and recreation and protection from climatic events such as storms, tsunamis and waves. If a coral reef is not healthy and in balance these services can be affected. Keeping coral reefs healthy through managing fishing, reducing anchoring and pollution are some of the ways to keep our ecosystems in balance.
So what is bleaching?
 |
| This coral bleaching infographic by NOAA provides great simple information on the causes and impacts of bleaching. |
When oceans temperatures exceed the normal threshold for corals (between 23C and 29C) and maintain that heat for a period of time, corals will start to drop the zooxanthellae, the corals begin to look very bright in colour, this is known as paling. If the temperatures remain high, the coral then may further bleach turning itself bright white. At this stage corals still may recover if water temperatures reduce quickly and the algae returns.
If the corals remain bleached and the water temperatures remain high, coral mortality may become an issue. Once a coral has completely bleached it is at risk of no longer providing food or habitat for marine animals as well as protection for shorelines from storms and large waves.
 |
| Those bright hot red spots are all around the waters of Tonga at the moment. |
 |
| Chart showing possible bleaching stress between February and May 2015. |
How can you help?
VEPA is a supporter of the
CoralWatch program which can be used by divers and snorkelers to easily monitor changes in reef colour. Its free to do and we will input the data, so please if you would like to join in pop by the VEPA office located at the bottom of the Guttenbeil Plaza.
