A major ocean warming [marine heatwave] event occurred along the WA west coast from November 2010 until March 2011 influenced by a very strong La Nina event [opposite to El Nino] that caused masses of tropical water to flow between Indonesia and NW Australia and maintained very high ocean temperatures as it moved south down the west coast of WA. This was the same La Nina event that caused the incredible rain and flooding in eastern Australia during the same period of time.
At the height of the “heatwave”, temperatures of 3.5 deg C over ambient levels were recorded. This provides a major “shock” to the marine environment and caused fish kills and extensive coral bleaching in areas not accustomed to the sudden onset of high temperatures. Tropical fish species ended up much further south than their usual predicted ranges. Graphics depicting the southward migration of this heatwave event can be seen at: http://www.fish.wa.gov.au/docs/pub/Highlights/marine-heatwave.php
In some cases, these are the warmest sea temperatures ever recorded for these regions and they appear to have been influenced by a much stronger than usual Leeuwin Current over summer, associated with the very strong La Nina event. The baseline information collected through SRFME and WAMSI over the last 10 years has allowed marine scientists to begin to quantify the magnitude and significance of the event and also begin to predict the ongoing implications for Western Rock Lobster recruitment, prawns, scallops, finfish etc. It further illustrates the importance of establishing marine scientific baselines and ongoing monitoring. The extent of the coral bleaching has been reported as high as 90% in some parts of the Mid West around places such as Shark Bay. Scientists will now continue to monitor the recovery as the La Nina event continues to break down. Some marine scientists are suggesting the marine heatwave “event” may be a likely indication of what to expect in the future with predicted increased climate variability affecting the marine environment, especially ocean warming, as we move into the future.
Photo: DEC Marine Science Monitoring Team evaluating the magnitude of the coral bleaching event in Shark Bay in May 2011