Hidden Giants: The Story of Bolbometopon muricatum at Ningaloo Reef

Bolbometopon muricatum (bumphead parrotfish, Valenciennes, 1839) is a conspicuous, iconic and ecologically important coral reef fish species. B. muricatum plays an important role in the bioerosion of the reef framework and as a result has been described as both an ecosystem engineer and keystone species. Despite the complete absence of B. muricatum from 32 years of scientific surveys across the Ningaloo Reef World Heritage Area, we recorded a total of 155 individuals of B. muricatum across 63.2 ha of reef crest surveys, equating to mean density of 2.38 ind/ha. Our observations represent the first record of this iconic species in scientific surveys at Ningaloo and in combination with qualitative observations of B. muricatum by expert witnesses, indicate B. muricatum is likely to have been present in ecologically relevant densities since 2006. The densities of B. muricatum observed at northern Ningaloo in 2021 suggest this species is removing an estimated 13.42 tonnes/ha or 1.34 kg/m2 of calcium carbonate per year, which is broadly comparable with estimates of total parrotfish bioerosion across many reefs in the central Indian and Pacific Oceans. Although not currently afforded elevated conservation status within management plans, B. muricatum possess many life-history characteristics that make them vulnerable to overfishing and may justify consideration for increased protection within the world heritage listed Ningaloo Reef Marine Park.

Acoustic Telemetry Around Western Australia’s Oil and Gas Infrastructure Helps Detect the Presence of an Elusive and Endangered Migratory Giant

Subsea infrastructure of the oil and gas industry attracts commercial fish species as well as megafauna including sea lions, turtles, sharks and whales. Potential impacts of this attraction, whether positive or negative, are unknown. As part of a pilot study, we deployed acoustic telemetry equipment around offshore infrastructure to assess its effectiveness in detecting tagged marine animals and to gain insights into patterns of megafauna occurrence around these structures. Acoustic receivers were placed around four oil and gas platforms and on two remotely operated vehicles (ROVs) on Australia’s North West Shelf. Two whale sharks (Rhincodon typus) tagged in the World Heritage Ningaloo Reef Marine Park were detected at two platforms, North Rankin A and Pluto, located up to 340 km to the northeast. The shark at North Rankin A was detected infrequently and only 15 times over ∼6 weeks. The shark at Pluto was detected each day of the 24-day deployment, in total 4,894 times. Detections at Pluto platform were highest during the day, with peaks at dusk and dawn. Our study indicates that acoustic telemetry around platforms may be an effective method for understanding how marine megafauna utilise these structures. We recommend collaborating with industry to undertake receiver detection range testing to understand the effectiveness of the method. Furthermore, future studies should co-occur with tagging programs at sites like Ningaloo Reef and around the structures themselves to maximise the probability of detecting animals at these sites, thereby improving our understanding of how marine megafauna interact with these structures.

Preliminary observations of corallivorous Drupella cornus feeding aggregations at Rottnest Island, Western Australia

Predation by the corallivorous gastropod Drupella cornus is well studied in the tropical and subtropical waters of the Indo-Pacific, including Ningaloo Reef and the Houtman Abrolhos Islands, Western Australia. In 1983, Drupella was not found in the Pocillopora colonies of Rottnest Island (Black and Prince 1983), and there has only been one record of D. cornus on Rottnest Island until today. We show the first feeding aggregations of D. cornus on these higher-latitude reefs of Rottnest Island, and highlight the importance of these findings.

Multiple climate impacts on seagrass dynamics: Amphibolis antarctica patches at Ningaloo Reef, Western Australia

The impacts of tropical cyclones combined with a marine heatwave are reported for a seagrass community at Ningaloo Reef, Western Australia. A community of 9.5ha of Amphibolis antarctica was lost following a combination of cyclone-induced burial and a marine heatwave. No new seedlings have been observed since the loss; recruitment of seedlings may be impeded by local ocean circulation.