NSW Department of Primary Industries, Lord Howe Island Marine Park News, The Lord Howe Island Signal

Warming waters

With global sea surface temperatures being warmest on record for the past nine months consecutively, there is potential for marine heat stress impacts this summer including in the Lord Howe Island Marine Park (LHIMP). In anticipation, monitoring is underway throughout the Lord Howe Island lagoon to detect signs of disturbance from elevated water temperatures.

Regionally, increased sea surface temperatures are being driven by global warming and the recent transition to El Nino climate conditions. Around Lord Howe Island they are also affected by the movement of warm water eddies from the Eastern Australian Current. Local weather conditions such as swell, cloud cover and tidal height further influence water temperatures and heat stress, particularly in the sheltered lagoon.

How corals respond to heat stress

One of the most obvious impacts from marine heat stress is coral bleaching, which has been documented in waters around LHI in 1998, 2010, 2011, and 2019. During these events shallow corals in the lagoon were most affected, with many deeper reefs and some reefs within the lagoon remaining largely unaffected. Coral mortality was documented from these bleaching events, however fast recovery and coral recruitment has also been observed since the most recent bleaching event in early 2019. This reinforces the importance of understanding both the extent of impacts as well as the process of recovery, to inform how we can best support reef resilience into the future.

Another recent sign of warmer water was a mass coral spawning which occurred in the LHIMP between 29 December, 2023 and 4 January, 2024. This was earlier than predicted, with slicks observed in the lagoon only 2 days after the full moon when it would normally occur 6-10 days after. A similar scenario was observed at Norfolk Island, and early spawning has previously occurred in the LHIMP when water temperatures have been higher than usual. It is likely a reflection that coral development happens faster in warmer conditions. It is also a sign of hope that corals in the LHIMP have adaptive strategies to help persist in the face of rising sea temperatures driven by climate change.

Understanding and adapting to change

Climate change presents a significant threat to the marine park’s social, cultural, economic and environmental values. In the next 20 years, it is likely to affect water temperatures, the supply of nutrients, ocean chemistry, food chains, wind systems, ocean currents and extreme events such as east coast lows. It is currently predicted that marine heat stress impacts will increase in frequency and severity.

Research and monitoring collaborations are key to understanding and addressing the impacts of marine heat stress in the LHIMP, both in identifying potential solutions to promote reef resilience, and in helping the community prepare and adapt for future changes. LHIMP staff are collaborating with researchers from DPI Fisheries, Southern Cross University, and University of New South Wales to implement a marine heat stress monitoring and response plan which includes:

• a bolstered array of water temperature loggers in the lagoon
• targeted drone aerial mapping to identify heat stress impacts
• systematic in-water visual surveys to assess heat stress impacts and recovery
• solution sharing to identify strategies to support reef resilience.

A team from the University of New South Wales is due to visit the LHIMP in late January to assist with monitoring efforts and will return to document impacts and recovery if bleaching is observed to occur.

The team is also working extensively to document impacts on reefs around Norfolk Island and can help implement a regionally coordinated response.

Additionally, Reef Life Survey, a non-profit citizen science program, will visit the LHIMP in March to continue their long-term monitoring on a range of species. Their work will include an assessment of the Community Temperature Index (CTI) for fish to help identify changes in the distribution and abundance of fish species over time. This long-term monitoring program is critical to help identify ecological changes in habitats and species since their first visit in 2006.

Reefs protected to maximise their resilience

Despite historic impacts from heat stress, marine tourism experiences (including snorkelling, diving and fishing) in the World Heritage-listed LHIMP still rank among the best in the world. The resilience and recovery of marine life is supported by the presence of the marine park, with management rules and programs implemented to conserve biological diversity and maintain ecosystem integrity and ecosystem function. These include sanctuary zones, shipping and vessel pollution controls, permit conditions to limit impacts from activities, planning and development controls, anchoring restrictions, maintenance of courtesy moorings for accessing lagoon reefs, monitoring and response to aquatic biosecurity risks, fishing gear and species restrictions, limits on collection, prohibition of aquaculture and exploratory industries, ongoing research and monitoring programs, and education.

Keeping an eye out

So far this summer there have been no reports or observations of coral bleaching in the LHIMP. However, residents and visitors to Lord Howe Island are encouraged to report any observed impacts to the marine park office. There are also online resources which provide information on sea surface temperatures and heat stress in the LHIMP.

The Bureau of Meteorology provides a sea surface temperature forecast illustrating the predicted movement of hot water eddies from the EAC, available via: http://www.bom.gov.au/oceanography/forecasts/idyoc300.shtml?region=LordHowe&forecast=SSTCur#

NOAA Coral Reef Watch (CRW) has developed a set of Regional Gauges to predict the risk of coral bleaching and heat stress impacts based on sea surface temperature forecasts. The Heat Stress Gauge for Lord Howe Island is available via: https://coralreefwatch.noaa.gov/product/vs/gauges/lord_howe_island.php

This article appeared in The Lord Howe Island Signal, 31 January 2024.