Feeling hot hot hot

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.

Coral Bleaching event in the Vava'u Group.....

A rapid survey team assessing the reefs on Tonga reports observations of the first stages of mass coral bleaching.  The SPREP (South Pacific Regional Environmental Programme) BioRAP (Biodiversity Rapid Assessment Programme) working in the northern Tonga group of islands called “Vava’u” reports about 1-3% of corals are bleached.  Some corals are white; others partly white, and others are neon colors like light blue or yellow. 

Due to increasing water temperatures, the NOAA Coral Watch program previously announced a bleaching watch for Tonga (February 2014).  The team, recorded seawater temperatures rising in the last week to about 30.5^o C, as well as the appearance of bleached corals.  Most of the bleaching observed was between 10 meters and the surface, however individually bleached coral colonies were observed up to depths of 30 meters in some places. A range of coral species was recorded as bleaching.

Corals bleach when increased seawater temperatures occur over a period of time; the corals, which are made up of skeletons, animals and single-cell plants, are placed under stress. When the algae (zooxanthellae or plant living within the animal), which give corals not only its color but also the ability to photosynthesize and feed, are released by the coral colony, the coral becomes bright white. As the coral has lost the plant component it loses them as a food source and is under extreme stress to survive.  Corals may recover from bleaching events if seawater temperatures decrease to within the limits of coral development. Bleaching events effect many different areas of the marine ecosystem including the reef fish as well as weakened coral reefs provide little protection for shorelines.

Area of bleaching coral within the Vava'u archipelago.

Most days have been sunny, with very light winds and small waves, but February 28th was cloudy and rainy when the team departed Vava’u.  The SPREP BioRAP team was surveying reefs and terrestrial ecosystems in the Vava’u group in support of conservation planning in Tonga.  The Kingdom of Tonga is located north and slightly east of New Zealand, and east of Fiji in the Pacific, and the Vava’u group of islands is at about 18.6500^o S.

The coral reef areas identified as bleaching sites will continue to be monitored and recorded for further analysis.

The marine team was based on the Waitt Institute Scientific Platform to conduct the marine surveys of Vava’u as part of the BioRAP programme with SPREP, Ministry of Lands, Environment, Climate Change,  and Natural Resources, Waitt Foundation and VEPA.