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By Kate Cranney 17 September 2021 5 min read

On land, each year thousands of birds cram on the four tiny islands to nest and rest: it’s no wonder it’s internationally recognised for its birdlife. Underwater, the coral reefs, seagrass meadows, sandflats and lagoons are home to a colourful array of life, like this bale of turtles.

A large bale of more than 50 sea turtles at Ashmore Reef. Image: Tommaso Jucker.

Sadly, weeds and introduced species like mice, tropical fire ants, and Asian house geckos could be putting Ashmore's island ecosystems at risk. To understand more, Parks Australia brought together a team of scientists to undertake the biggest ‘health checks’ of Ashmore Reef[Link will open in a new window]. The team took a 120-hour round trip from Broome to Ashmore Reef to do surveys on two voyages: in April and July of 2019.

Dr Bruce Webber, Principal Research Scientist at CSIRO, led the terrestrial survey.

“The good news is that, on the islands, we found the seabird colonies are still in good health. But weeds and pests pose key threats to Ashmore Reef Marine Park. Future management will need to take a holistic approach to managing species interactions if we are to successfully preserve this Marine Park's unique values."

Dr John Keesing, Senior Principal Research Scientist at CSIRO, led the marine science team.

“The 200 coral reef and seagrass habitats sites we surveyed are in good condition. We're happy to report the giant clam was found at Ashmore Reef for the first time since 2006. But some sea cucumber numbers are very low, indicating they have not recovered from historical illegal fishing; at least one species is locally extinct."

Bruce and John were supported by a multi-disciplinary team of scientists from CSIRO, University of Western Australia and independent consultants, Dr Daniela Ceccarelli and Dr Chris Surman.

“This integrated terrestrial-marine project is the first of its kind for the Park, consolidating our baseline understanding, adding to historical data sets, and providing insights into how species, communities and habitats have changed over time,” said Michelle Glover from Parks Australia.

Scientists have now analysed the vast volumes of data from the two voyages. Today, we released the final report on the findings[Link will open in a new window], including management recommendations, for Ashmore Reef Marine Park. Here are our top 10 findings from both the marine and terrestrial surveys.

Our top ten findings from the surveys

1. The coral cover was highly variable across habitat surveyed, but was very high on some sections. At the time of the survey there was no coral bleaching, disease, or signs of stress or major recent disturbances observed. Giant clams and another smaller species of clam were observed in low densities, and this indicates a slow recovery from previous overfishing.

The coral reefs of Ashmore Reef Marine Park. Image: Daniella Ceccarelli.

2. We recorded 15 seabird, two egret and one heron species on the islands and cays. Relative to previous years, numbers had increased for most species with expansion of breeding territory for five species. Of the 30 migratory shorebird species known from the islands, 17 species were observed overwintering.

Frigatebirds nesting on Ashmore Reef Marine Park's islands. Image: Ben Hoffman

3. We recorded 18 species of sea cucumbers (Holothurians). With the exception of three asexually reproducing species, these were low in densities. Many of these have not recovered from being exploited in the mid-1980s.

An elephant trunkfish sea cucumber (Holothuria fuscopunctata) from Ashmore Reef. Image: John Keesing.

4. Seagrass beds at Ashmore Reef are very widespread but the cover is generally low. The surveys indicated that the seagrass beds are heavily grazed (most likely by green turtles) and are a critical habitat despite being sparse. The dominant species was Pacific turtlegrass (Thalassia hemprichii).

Surveying the sea grass around Ashmore Reef Marine Park. Image: Lauren Hardiman.

5. The islands of Ashmore Reef Marine Park are home to grasses, herbs, shrubs and the occasional small tree. We found a total of 35 distinct plant communities across the four vegetated islands. This includes 20 native species, five native 'hogweeds' (Boerhavia), and eight non-native species.

Birds circle above different plant communities on Ashmore Reef. Image: Bruce Webber ©  Bruce Webber / CSIRO

6. The non-native Asian house gecko (Hemidactylus frenatus) was abundant on the West Island but it wasn't found on other islands. The potential ecological impact of geckos on the island ecosystems needs further investigation.

Asian House Gecko on Ashmore Reef Marine Park. Image: Ruchira Somaweera ©  Bruce Webber CSIRO

7. There has been a significant decline in sea snakes in the shallow waters at Ashmore Reef with only one olive sea snake (Aipysurus laevis) observed on the survey. The cause of this decline remains unknown.

The only sea snake seen during the survey was an olive sea snake. Image: John Turnbull. ©  John Turnbull

8. Non-native tropical fire ants (Solenopsis geminata) are present on the three largest islands with variable distribution and abundance. We didn't observe any evidence of interactions between these invasive ants and nesting birds or turtles.

The head of a tropical fire ant. Image: CSIRO

9. We observed a total of 365 species of fish, with the highest densities counted on the reef slope and in the western lagoon. Sharks were uncommon, but this finding is consistent with previous studies. (As part of the surveys, we used environmental DNA[Link will open in a new window] (eDNA) to detect fish species around Ashmore Reef Marine Park.)

Fish survey on Ashmore Reef Marine Park. Image: Lauren Hardiman.

10. Non-native buffel (Cenchrus) grasses cover large areas (1,200 m2), and beach caltrop (Tribulus cistoides) is increasing in abundance. Tree and large shrubs are dying and their health has decreased markedly.

Buffel grass smothering a part of Ashmore Reef Marine Park island. Image: Bruce Webber ©  Bruce Webber / CSIRO

For more on the Ashmore Reef Marine Park findings, you can read the final report, released today here[Link will open in a new window] and the data[Link will open in a new window] we collected here.

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