A significant bleaching event has been reported from the area of Lord Howe Island. Southern Cross University (SCU) researchers, who have been monitoring the coral reefs off of Lord Howe Island since 1993, have mapped the extent of the bleaching and damage to the corals and will be returning later in the year to assess the rate of recovery.
Above average sea temperatures during early 2010 have led to the first recorded major coral bleaching event here, with water temperatures exceeding 26 – 27 ˚C over the last few months, a couple of degrees higher than the usual summer sea temperature.
Lord Howe Island lies within a marine protected area, the Lord Howe Island Marine Park, and was declared a World Heritage site in 1982. This is a reef of particular importance being the southern-most tropical reef in the world. It features an unusual combination of tropical and temperate marine flora and fauna, including many species living at their distributional limits, reflecting the extreme latitude of coral reef ecosystems.
The diversity of marine life here includes:
· At least 500 species marine fish of which 400 are inshore species and 15 are endemic.
· More than 83 species of corals and 65 species of echinoderms of which 70 per cent are tropical, 24 per cent are temperate and 6 per cent are endemic.
· At least 235 marine benthic algae species of which 12 per cent are endemic
This bleaching event was caused by warm seawater carried south on the East Australian Current, coinciding with the hottest, driest, cloudless January on record. It has been far larger than the minor bleaching that took place during the mass coral bleaching of 1998, which severely damaged coral reefs around the world. Lord Howe Island was relatively unscathed in 1998 with few coral species becoming bleached and most recovering.
Although elevated sea surface temperatures are the main factor in coral bleaching this event seems to have been made more severe by there being little ocean swell during the hot weather, leading to poor water mixing resulting in a hotter lagoon with lower levels of water oxygenation.
Unlike the Great Barrier Reef, Lord Howe Island is relatively isolated from other reefs, this reduces the rate with which recruitment of organisms can occur to replace populations damaged by the event, and as a result, the reef may take decades to recover.
Professor Peter Harrison, from SCU’s School of Environmental Science and Management, said that this unusual bleaching event is further evidence that climate change is having a very real impact and that even cooler water, sub-tropical reef systems were not immune to these changes. He also noted that two of the major sites affected by the bleaching were within protected areas of the marine park, and pointed out that research from other tropical reefs showed that areas protected from fishing had better recovery rates from severe coral bleaching episodes.
Marine protected areas are being seen as increasingly important as they can help the recovery of reef systems adversely affected as climate change takes hold and affects the marine environment.