Plate coral in Emily Bay exhibiting signs of white syndrome on 9 May 2021 & 15 July 2021 respectively. Credit: norfolkislandreef.com.au

Friday 10 September 2021

Since early 2020, Parks Australia has worked with the Sydney Institute of Marine Science (SIMS) to monitor reef health in Emily and Slaughter Bay. SIMS’ first survey, in March 2020, was timed to provide a baseline of coral health before a predicted marine heatwave and coral bleaching event.

Monitoring has now captured a one-year snapshot of the reef, from March 2020 to April 2021. The results of this work are detailed in the SIMS, University of New South Wales, James Cook University, and the University of Newcastle report: ‘Norfolk Island Lagoonal Reef Ecosystem Health Assessment 2020–2021’.

To understand what was happening in the lagoon the SIMS researchers conducted surveys of the reef, noting the coral species, type and extent of any algal cover, and any evidence of disease. SIMS also undertook extensive monitoring of the direction and speed of water flows around the bays, the tides and water temperatures. Water sampling and testing for nutrient levels, organic matter loads, turbidity, temperature, and salinity were conducted at key locations in the bay at different times.

Midway through the research period, at the end of July 2020, a major rainfall event caused the plug of sand in the creek entering Emily Bay to open, inundating the bay with polluted wastewater. This highlighted the issue of contaminated water upstream of Emily Bay and gave the researchers an opportunity to record impacts on the health of the bays and reef.

At that time, and since, concentrations of nitrates, ammonium, and phosphates (which are concentrated in animal waste and human sewerage) have far exceeded Australian and New Zealand Environment and Conservation Council recommendations. Following this event there was a dramatic increase in algal cover within Emily and Slaughter Bays.

The research team found that algal blooms in the water column, increased algal growth and coral diseases are all problems caused directly by contaminated water entering the lagoon. The two surveys conducted since the pollution event have detected coral disease outbreaks of both black band disease and white syndrome. On some coral colonies disease was observed to progress very rapidly- resulting in tissue death of up to 20 years growth in an eight-week period.

The research found that Slaughter Bay, and to a lesser degree Emily Bay, continues to have high nutrient levels even during dry periods, suggesting that it isn’t just the overflowing creek causing the poor water quality, but also chronic long-term delivery of nutrients via seepage into the bays from polluted groundwater.

We will continue to work with the SIMS team to monitor reef health this coming summer. We know the Emily and Slaughter Bay coral reef ecosystems are of great significance to the local community. As part of this ongoing monitoring, some ‘larval settlement plates’ (roof tiles attached to Besser blocks) will soon be placed into Slaughter Bay to ‘cure’, so they are ready for the Summer coral spawning season. These plates will give us valuable information about the success of coral spawning. If you see them, please don’t disturb them.

To improve reef health, Parks Australia is working closely with our catchment management partners to understand and improve what’s happening upstream. The Norfolk Island Water Quality Working Group consists of representatives from the Norfolk Island Regional Council, the Department of Infrastructure, the Office of the Administrator, and Parks Australia. Together, we are committed to improving the quality of the water running into the marine park and to making sure we have safe swimming beaches and a healthy reef to protect our shores to enjoy for the future.

Reports we have commissioned to support this work are available on the web. Hard copies are also available for viewing - please contact Norfolkmarinepark@environment.gov.au to arrange a time with Jim Castles, our on-island project officer.