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ISRA FACTSHEETS

AUSTRALIA AND SOUTHEAST INDIAN OCEAN

ISRA FACTSHEETS

AUSTRALIA AND SOUTHEAST INDIAN OCEAN

Nightcliff-Casuarina Beach ISRA

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Nightcliff-Casuarina Beach ISRA

Nightcliff-Casuarina Beach

Summary

Nightcliff-Casuarina Beach is located in northern Darwin Harbour, Northern Territory, Australia. The area is characterised by shallow rocky reefs, a rocky headland, a tidal creek (Rapid Creek), sandy beaches, and soft substrates. It is influenced by large tidal amplifications. Within this area there are: threatened species and feeding areas (Reef Manta Ray Mobula alfredi).

Nightcliff-Casuarina Beach

Nightcliff-Casuarina Beach

DESCRIPTION OF HABITAT

Nightcliff-Casuarina Beach is located in northern Darwin Harbour, Northern Territory, Australia. The area extends from Nightcliff Headland in the south to Lee Point in the north. It is characterised by varied habitat types including shallow hard coral communities, rocky reefs, seagrass, macroalgae, sponges, octocorals, filter feeder communities, and sand or other soft substrates (Lucieer et al. 2025). The area includes the lower estuarine portion of a small tidal creek with fringing mangroves (Rapid Creek) and a sandy beach (Casuarina Beach). Nightcliff-Casuarina Beach is subject to a monsoonal wet-dry season climate, with ~90% of rainfall occurring in the wet season (roughly November–April; Nicholls et al. 1982). The wet season is also characterised by tropical storm activity and periodic cyclones.

Darwin Harbour is a large embayment opening to Beagle Gulf in the Timor Sea, Eastern Indian Ocean. Large freshwater input from the Elizabeth River and Blackmore River occur during the wet season. The harbour is subject to large semidiurnal tidal amplifications, with a tidal range of 0.1–7.8 m and tidal currents ranging from 0.25–1.4 ms-1 (Semeniuk 1985). Water temperatures may reach 36°C at high tide, with tide pools exceeding 43°C at low tide (Ferns 2016). As such, reef flats in Darwin Harbour are subject to a wide variety of daily and seasonal fluctuations in temperature, light availability, and sedimentation (Ferns 2016).

The area overlaps with Casuarina Coastal Reserve (PWCNT 2016).

This important Shark and Ray Area is benthic and pelagic and is delineated from inshore and surface waters (0 m) to 11 m based on the bathymetry of the area.

CRITERION A

VULNERABILITY

One Qualifying Species considered threatened with extinction according to the IUCN Red List of Threatened Species regularly occurs in the area. This is the Vulnerable Reef Manta Ray (Marshall et al. 2022).

CRITERION C

SUB-CRITERION C2 – FEEDING AREAS

Nightcliff-Casuarina Beach is an important area for feeding of one ray species.

Between 2021–2025, Reef Manta Rays were recorded feeding in this area every year during the months of January, March, April, May, and October. Citizen science records (n = 13) mined from Facebook (Facebook 2025) and an additional unpublished observation (n = 1; PM Kyne unpubl. data 2024) of Reef Manta Rays highlight that this species comes nearshore to feed. Within Nightcliff-Casuarina Beach, the species has been observed adjacent to Nightcliff Headland, at the mouth of Rapid Creek, and along Casuarina Beach in shallow waters. An additional two records of ‘manta rays’ were not directly identifiable, however, it was inferred that these too were records of Reef Manta Ray owing to the shallow depth, consistent seasonal occurrence, and the lack of any Oceanic Manta Ray Mobula birostris records in Darwin Harbour or adjacent areas (in a meta-analysis of Australian manta ray records, there were only two Oceanic Manta Rays from the Northern Territory, one in the western Gulf of Carpentaria and one offshore in the Timor Sea; Armstrong et al. 2020). Feeding behaviour was inferred for 13 of 16 records (81%), with seven records (44%) being of somersault feeding behaviour and five records (31%) being straight feeding and/or surface feeding (as per feeding behaviours outlined in Stevens 2016). This is the only location in the Northern Territory where feeding behaviour has been regularly observed and documented.

Nightcliff-Casuarina Beach

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