Last week the Catlin Seaview Survey Shallow and Deep Reef teams embarked on an expedition to the Northern Great Barrier Reef, a UNESCO World Heritage Marine Site. This is a particularly memorable expedition for the project teams who are returning to the Great Barrier Reef where the Catlin Seaview Survey commenced our initial data collections in 2012.
On this occasion we have joined forces with the Waitt Foundation in an ambitious trip across approximately 700 kilometres, from Opal Reef (a bit more than half way up the reef), east of the Daintree National Park in North Queensland, to the far northern survey site, Saunders Reef located east of the Jardine River National Park on the Cape York Peninsula.
One of the aims of this survey is to document the impact of one of the most powerful cyclones to have struck the coast of Australia in recent years, Severe Tropical Cyclone Ita. In April 2014 T.C. Ita crossed Day Reef a site that we’d surveyed on our first trip to the reef in 2012. Using the visual information gathered on our initial “baseline” expeditions to the GBR, the Shallow Reef surveys will compare the state of the reef both before and after the cyclone.
Surveying such remote areas of the Great Barrier Reef is always a gamble because winds and tidal waves can rapidly change and prevent access to most of these reef systems. Fortunately, we have had fantastic weather for our first week in the field; winds haven't blown more than 20knots. Underwater, we have been impressed by the wilderness of these reefs on every dive. Here we have seen large schools of pelagic and reef fish, numerous sharks, including tigers, grey whalers, silver tips, and hammerheads.
Wave action, tidal surge and sediment transportation generated by cyclones can have significant effects on the structure of coral reefs across large spatial scales. However, predicting the impact of cyclones on reefs is a difficult task because wave and wind patterns are erratic and dependent on a range of factors. Having a visual baseline and reference point to show the before and after state of coral reefs (at a broad scale) following a cyclone event can help to us to understand the biological or physical attributes that may make reefs more resilient and able to withstand the impacts of cyclones or severe storms.
The unpredictable impacts of cyclones, coupled with other human-influenced stressors such as overfishing and agricultural runoff, can interact to cause greater impacts than if they occurred in isolation. Given the expected increase in cyclone intensity and frequency as a product of a warming sea surface, evaluating the impacts of cyclones on coral reefs is an important contribution to the understanding needed to inform the best management strategies and decisions to preserve reef integrity into the future.