Where
Ashmore Reef Marine Park, Timor Sea, approximately 630km north of Broome and 110km from the Indonesian Island of Roti.
Who
Dr John Keesing (Marine, CSIRO) and Dr Bruce Webber (Terrestrial, CSIRO) were supported by a multi-disciplinary team of scientists from organisations including the CSIRO and University of Western Australia.
When
May - June 2019
Why
Despite their diminutive size, Ashmore Reef Marine Park’s islands are a beacon for birds: seabirds flock here in their thousands to breed in the shrubs and sand, while migrating shorebirds stop to rest and forage on the vast sandflats exposed at low tide.
Historically, these islands and their surrounding waters have also been used by seafarers and traditional Indonesian fishers. Like a tropical iceberg, the islands are just the tip of what is happening at Ashmore. Extensive coral reefs (approximately 174 km2), sheltered lagoons, and seagrass beds fringe the islands, providing a home to more than 570 species of fish. Farther offshore, seasonal currents drive nutrient hotspots that attract species from all trophic levels. At depth, unexplored seafloor communities cling to the continental shelf as it slopes away to the abyssal plain.
Managing this diverse range of habitats and species, many of which are connected in ways we are just starting to understand, requires robust and reliable environmental data and careful interpretation. We also need a clear understanding of the pressures impacting on this complex system, as Ashmore Reef’s isolation is not enough to protect it from all threats.
How
A team of scientists and marine park managers made the 60-hour round trip to Ashmore Reef from Broome, twice! The first voyage carried a team of terrestrial experts who completed extensive surveys of island topography and their inhabitants, including seabirds, vegetation and a selection of terrestrial animals.
Of particular interest were the non-native pest and weed species that have been brought here accidentally by island visitors over the years. They identified species, estimated abundance and coverage, and mapped spatial distributions. This data was collected using a combination of transect and quadrat surveys, drones and baited traps, as well as novel approaches using drones to map habitats and count nesting birds.
Several weeks later, the marine team arrived to undertake similar surveys – but this time underwater. Transect and quadrat surveys were used to identify and count the sea life, including corals, seagrass, benthic and mobile invertebrates and fish. With more than 255 coral species present at Ashmore, team members certainly had their work cut out for them. Scientists also recorded signs of disease, the presence of predators and the percentage cover of different species. To capture data on harder-to-spot species, water samples were collected: back in the lab, these will be analysed to detect DNA signatures and then cross referenced to databases to identify which taxa were present. Trialling new and emerging survey methods like this eDNA technique is critical: it drives continuous improvement and insights and allows us to assess and monitor our marine parks using methods which are non-invasive and complement traditional quantitative surveys.
What did we learn?
As a result of the two voyages, the multi-agency team completed one of the most comprehensive ‘health checks’ of the ecosystems at Ashmore Reef. In addition to assessing the current status of habitats, species and pressures, this research built on the knowledge acquired from previous smaller projects completed in recent decades.
Early observations suggest that Ashmore is in pretty good shape. Corals showed positive signs of recovery from historical bleaching events, no signs of recent bleaching or damage from the coral eating crown-of-thorns starfish and the sea grass beds appeared healthy. The diversity of marine species remains high, although the absence of sea snakes continues to puzzle experts and species such as sea cucumbers, clams and trochus have been slow to recover from over-fishing in the 1980s. However, the islands are facing pressure from multiple invasive species, including the tropical fire ant and buffel grass. The extent to which these species are impacting Ashmore’s ecosystems is unclear and one of the many important questions this project set out to answer.
This project has contributed to our understanding of the complexity of Ashmore Reef’s marine and terrestrial biodiversity. This insight will help Parks Australia shape future management efforts to improve conservation outcomes. The work has also established a targeted, repeatable monitoring framework that means we will be collecting comparable data on future visits.
What next?
Regular monitoring will be very important to understand how Ashmore’s habitats and species are changing over time. Targeted work around key issues such as the impact of invasive species will ensure we can take appropriate, prioritised management actions. While this project was comprehensive, it couldn’t consider every aspect of Ashmore’s environment. Future efforts might include detailed surveys of dugong and deepwater sea cucumber populations, an assessment of plastic pollution, seagrass habitat mapping and investigations of why sea snake numbers have declined. On the islands, extending surveys to include more of the animal species and improving our understanding of their interactions with each other and the landscape would be beneficial.
Publications
Read more about the adventure or take a virtual trip and watch this 6-part video series