Reef health updates summer 2018-19

Reef health updates summer 2018-19 © GBRMPA

Each summer we keep a close eye on the Great Barrier Reef as this time of the year presents the highest risk to the ecosystem from thermal stress, rainfall and floods, cyclones and storms, and outbreaks of crown-of-thorns starfish.

At this stage, the ongoing outbreak of coral-eating crown-of-thorns starfish and possible marine heatwaves are the biggest concerns for the Reef this summer.

Our climate is changing year-by-year and this is causing changes in the Reef ecosystem it's under pressure which makes the Reef more vulnerable to possible impacts particularly over summer.

With a changing climate, we can't rule out the risk of some level of bleaching we'll keep watch on the Reef over summer and encourage anyone out on the water to report reef condition through our Eye on the Reef app.

Update 5: 18 January 2019

Sea surface temperatures remain around average or below average for this time of year throughout the Marine Park, with the exception of the Far Northern management area of the Marine Park (above Princess Charlotte Bay) where temperatures are 0.5 1.5 degreesC above average.

While rainfall and cooler conditions brought some reprieve to parts of the Marine Park, the Far Northern, Northern and Central management areas (from approximately Townsville northwards) are currently on bleaching watch.

Localised instances of minor bleaching have been reported from all regions of the Marine Park since the start of summer, particularly in the northern half of the Reef.

Forecast models still predict above average sea surface temperatures through February and March for the entire Great Barrier Reef.

Regional and local weather conditions over the remainder of summer continue to be critical in determining the outcome for the Reef this summer.

Update 4: 11 January 2019

Tropical cyclone Penny peaked as a Category 2 system in the Coral Sea on 3 January 2019 before downgrading to a tropical low and turning back towards the Queensland coast. The system entered the Marine Park and crossed the coast around the Bowen region on 9 January 2019.

Heavy rainfall (and associated cloud cover) affected parts of Eastern and Central Queensland. This helped to cool sea surface temperatures over most of the Marine Park down to average or slightly below average, and decreased the current risk of coral bleaching across much of the Reef.

As a result much of the Marine Park is currently no longer on bleaching watch, apart from the Far Northern management area (above Princess Charlotte Bay).

While this cooling effect has provided relief in many areas in the Marine Park, a close watch for bleaching and other impacts will be maintained.

Heat waves across Queensland during December 2018 saw a rapid accumulation of thermal stress in sea surface temperatures. As a result corals in some parts of the Reef, particularly in the Northern and Far Northern regions, may still be experiencing the impacts of that heat stress, despite the recent short period of relief from above average temperatures.

Regional and local weather conditions over the remainder of summer continue to be critical in determining the outcome for the Reef this season.

Update 3: 4 January 2019

Since our last update on 20 December 2018, another tropical low crossed into the Marine Park from the Coral Sea before crossing into the Gulf of Carpentaria in late December 2018.

Once in the Gulf, the system strengthened and changed direction back towards the Cape. On 1st January 2019, this low pressure system became Tropical Cyclone Penny (Category 1) and crossed the coast on the Cape between Weipa and Thud Point, before quickly downgrading to an ex-tropical cyclone. After crossing over the Cape and back through the Marine Park as a tropical low, the system moved back into the Coral Sea and Tropical Cyclone Penny was reborn on 2nd January 2019.

The tropical low brought heavy rain to Cape York Peninsula and the Wet Tropics region, resulting in minor to moderate flooding of rivers.

The recent rainfall and cloud cover has cooled sea surface temperatures back down to average or slightly below average throughout most of the Marine Park. The exception is the far northern Marine Park where above average temperatures and thermal stress accumulation have persisted. In water surveys in the far north and north in late December 2018 showed some minor bleaching of individual coral colonies on reefs.

Tropical Cyclone Penny (Category 2) is currently in the Coral Sea well offshore of mainland Australia, however it is forecast to change direction back towards the Queensland coast over the weekend. While there is still uncertainty about the track it will take, the system is expected to weaken as it draws closer to Queensland in the early part of next week.

We will continue to monitor this system closely.

Update 2: 20 December 2018

Since our last update on 6 December 2018, ex-tropical cyclone Owen (in the form of a tropical low) crossed into the Marine Park from the Coral Sea before crossing into the Gulf of Carpentaria and reforming as a cyclone on 11 December 2018. This update relates mostly to cyclone impact and rainfall.

Cyclones

After reforming, tropical cyclone Owen tracked west across the Gulf of Carpentaria, intensifying to a category three system before changing direction and tracking eastwards.

Cyclone Owen crossed the southeast Gulf of Carpentaria coast between Kowanyama and the Gilbert River mouth as a low end category three system early on 15 December 2018.

The system weakened to a tropical low soon afterwards as it tracked east southeast across the northern interior of Queensland.

Upon reaching Queensland's east coast, the system adopted a southerly track, roughly parallel to the coast.

As of 19 December 2018, the tropical low was located off of the central Queensland coast.

Rainfall

Wind speeds significantly decreased as the system moved over land, however ex-tropical cyclone Owen still brought heavy rainfall to some areas.

The highest rainfall totals were recorded between the Cairns and Mackay regions.

Notably, the Halifax area (near Ingham) received 681mm in 24 hours, the highest 24 hour rainfall total ever recorded in Australia during the month of December.

River levels in the areas affected by heavy rainfall briefly increased, however the majority remained below flood level and there was no major flooding in the catchment.

Salinity

As a result of the increased freshwater runoff and heavy rainfall, salinity levels declined in the inshore waters between approximately Tully and Townsville.

As the cyclone only affected the Reef as a tropical low, no major wave damage impacts to coral are anticipated.

Sea surface temperature

The cloud cover and rainfall associated with ex-tropical cyclone Owen cooled sea surface temperatures back down from above average to average levels in the central region of the Marine Park.

However, in other areas such as the far northern Marine Park, above average temperatures and thermal stress accumulation have persisted.

Update 1: 6 December 2018

Environmental conditions

The El-Niño Southern Oscillation is currently neutral, bordering on an El Niño event. The Bureau of Meteorology's (the Bureau) December 2018 to February 2019 seasonal outlook for Queensland indicates that the state will experience above average temperatures, with average rainfall in the Great Barrier Reef catchment. While it is yet to fully develop, El Niño conditions may result in marine heatwaves and below average rainfall this summer these are the conditions that can lead to bleaching.

Sea surface temperatures

The Bureau's predictive modelling for the Great Barrier Reef indicates that sea surface temperatures are likely to be above average over the next three months, with thermal stress accumulating throughout the majority of the Marine Park. As of the start of summer, sea surface temperatures are above average throughout the Marine Park. Thermal stress has likely already been accumulating in the system this year, with Queensland experiencing its second hottest summer (2017/2018), fourth hottest April, fifth warmest winter and third warmest October on record in terms of mean air temperatures.

Cyclones

The tropical cyclone outlook from the Bureau indicates that this cyclone season (November to April) is likely to be slightly below average for the Great Barrier Reef. An average cyclone season is up to four cyclones developing in the Coral Sea, and at least one making landfall along the Queensland coast.

Flooding

Widespread flooding is unlikely, however localised flooding can still occur as part of any normal Northern region wet season.

Coral reef health reports

Recent reports from the Eye on the Reef network indicate that there are currently minor levels of coral bleaching, disease and damage in the Marine Park.

The impacts of Tropical Cyclone Iris (April 2018) in the Mackay/Whitsundays region remain to be verified with in-water surveys.

Established and severe outbreaks of the coral-eating crown-of-thorns starfish continue on some reefs in the northern, central and southern management areas.

The Great Barrier Reef Marine Park Authority's Crown-of-thorns Starfish Control Program has been expanded with four new vessels joining the fleet in 2018.

These new vessels join the two existing vessels already operating to protect coral in the Marine Park.

Trained divers on board these vessels will be culling crown-of-thorns starfish to ecologically sustainable levels on an expanded range of high value reefs in the Marine Park, including in the Swain Reefs where a severe outbreak was identified by the Field Management Program in 2017.