ABC News 31 Jan 11;
Warm sea surface temperatures have bleached coral on the Ningaloo Reef.
The Department of Environment and Conservation says satellite technology has found temperatures at the reef have increased by about three degrees and in the past fortnight the water has been above 29 degrees, which is the trigger for bleaching to occur.
Coral bleaching occurs when algae, which lives in a symbiotic relationship with the coral, leaves because it is too warm.
That leaves the coral's white skeleton to be exposed.
The warmer temperatures are expected to last another three weeks because of ex tropical cyclone Bianca and other cyclonic conditions.
The DEC believes less than 20 per cent of the coral in the 300 km long Ningaloo Reef has been bleached.
Hot seas bleach Ningaloo Reef
Narelle Towie PerthNow 31 Jan 11;
ABNORMALLY hot sea temperatures at Ningaloo Reef are bleaching the area's coral, environmental officers say.
Ocean surface temperatures at the reef have been 3C higher than average since October and peaked at 29C in the past two weeks - the 'trigger level' for bleaching.
The Department of Environment and Conservation detected the patches of bleached corals using satellite imaging.
“By continually monitoring the reef, we can look at changes over time and determine the significance of temperature-induced bleaching events,” DEC marine science leader Chris Simpson said.
Coral bleaching is a phenomenon where algae, which gives coral its colour, is expelled from inside the reef's tissue because of stress, leaving just the white skeleton of the coral behind.
Bleaching events are usually caused by long periods of warm sea surface temperatures but they can also be associated with exceptionally low ocean temperatures, disease or pollution.
“Initial reports related to sea surface temperature indicate that water temperatures in the Ningaloo area have been elevated to levels that may cause bleaching in some coral species,” Dr Simpson said.
“These temperatures are not expected to drop for at least two to three weeks because of the cyclonic activity over the Pilbara and Kimberley restricting flushing and causing heating of lagoon waters."
Dr Simpson said Ningaloo Reef had experienced minor coral bleaching events caused from both elevated and lowered sea surface temperatures in the past 20 years with no apparent long-term effects.
Inner reef areas, particularly in bays such as Bills Bay that had restricted water flow, were particularly prone to coral bleaching.
“While this is of concern, there is some good news. Ningaloo has an exceptionally high diversity of corals with more than 300 species and it is this diversity that will provide some resilience to bleaching as different corals have different tolerance levels to bleaching.
“So there still will be many colourful displays of coral all along its 300km length.”
Dr Simpson said current surveys in Bills Bay showed species of the fine branching corals that had the lowest resistance to coral bleaching had started to bleach in some areas.
“We estimate that the bleaching in most areas is considerably less than 20 per cent of the live coral at this stage,” he said.
“Coral reefs can recover from bleaching events although it can be a decade or two before full recovery occurs.
“One of the important things for recovery is the presence of ‘source’ reefs to generate new larvae along with good water quality, suitable substratum for new coral recruits and strong herbivorous fish populations to prevent algae colonising the reef.”
DEC is asking for all Ningaloo Marine Park visitors to be on the lookout for coral bleaching. If bleaching is spotted, people are asked to note the location of the coral and, if possible, take a photograph.
If you spot coral bleaching contact the DEC’s marine park coordinator in Exmouth on 9947 8000.
