Michaelmas and Upolu Cays

Michaelmas and Upolu Cays National Park protects two small coral sand cays on the outer Great Barrier Reef, north of Cairns in far north Queensland. Michaelmas Cay is one of the most significant seabird nesting colonies on the Great Barrier Reef, supporting tens of thousands of nesting seabirds annually. Upolu Cay is a smaller but similarly important reef cay. The park protects these vulnerable sandy islands and the surrounding reef ecosystems, which form part of the Great Barrier Reef Marine Park World Heritage Area.

Michaelmas Cay hosts one of Australia's largest seabird colonies, with thousands of sooty terns, crested terns, black noddies, and brown boobies nesting on the cay during the breeding season. Sea turtles — primarily green turtles — nest on the cays' beaches, and the surrounding reef supports spectacular coral reef fish diversity. Reef sharks, rays, and sea turtles are commonly observed while snorkelling. The marine environment around the cays is one of the most accessible sections of outer reef near Cairns.

The vegetation on the cays is sparse, consisting of low-growing salt-tolerant pioneer plants typical of coral cays, including beach morning glory (Ipomoea pes-caprae) and low shrubs. Pisonia trees provide some structure on larger sections. The sparse vegetation reflects the harsh conditions on the sand cays — intense sun, salt spray, and periodic storm wash-over. The reef ecosystem surrounding the cays is the dominant ecological feature, with diverse coral communities including staghorn corals, brain corals, and soft corals.

The cays are unconsolidated coral sand deposits accumulated on the reef flat over thousands of years from broken coral, shell, and other calcium carbonate material. They are low-lying, rarely more than 2–3 metres above sea level, and inherently dynamic, shifting in shape and position with storm events and changing sediment transport patterns. The underlying reef structure is composed of coral limestone built up over thousands of years. The cays are vulnerable to sea level rise associated with climate change.

The cays experience a tropical climate with a distinct wet season from November to April, when strong north-westerly winds and occasional tropical cyclones can affect the reef. The dry season from May to October brings the trade winds, calmer conditions, and good visibility for reef activities. Water temperatures are warm year-round at 24–29°C. Marine stingers are present in inshore waters from October to May, though the outer reef areas around the cays have lower stinger density. Cyclones pose an intermittent threat.

The outer reef cays have been known to the Traditional Owners of the adjacent coastal areas — the Yirrganydji and Gunggandji peoples — whose sea country extends to the reef. European explorers, whalers, and bêche-de-mer (sea cucumber) fishermen used the reef cays from the early 19th century. The Great Barrier Reef's significance led to its designation as a Marine Park in 1975 and World Heritage listing in 1981, providing the framework for protecting the cays and reef ecosystems.

Michaelmas and Upolu Cays National Park was established to protect the cays and their nesting seabird colonies within the broader context of Great Barrier Reef conservation. The park is jointly managed by Queensland Parks and Wildlife Service and the Great Barrier Reef Marine Park Authority. Visitor numbers to Michaelmas Cay are strictly managed to avoid disturbing the nesting seabirds, and specific areas are closed during the nesting season. The reef has faced significant challenges from coral bleaching events.

The primary experience at Michaelmas Cay is snorkelling the surrounding reef and observing the extraordinary seabird colony. The cay is accessible by day trip from Cairns, with numerous tour operators offering half-day and full-day reef trips. Visitors can swim, snorkel, and use glass-bottom boats. Turtle spotting is reliable, and experienced snorkellers can see impressive coral diversity and reef fish on the surrounding reef. A small portion of the cay is accessible, with the nesting colony areas fenced off.

Michaelmas Cay is reached by commercial day-trip boats from Cairns and Port Douglas (approximately 1.5–2 hours). Most operators provide snorkel gear, lunch, and guided commentary. There are no public facilities on the cay itself — all visitor services are provided by the tour boats. The park is closed to overnight stays. Upolu Cay is primarily a snorkelling destination with fewer visitor facilities.

The cays face significant conservation challenges including seabird disturbance, plastic marine pollution, coral bleaching from warming ocean temperatures, and sea level rise. Major coral bleaching events — particularly in 2016, 2017, 2020, and 2022 — have damaged sections of the surrounding reef. Visitor management is critical to protect the nesting seabirds, with strict limits and zoning. Climate change is the greatest long-term threat, as both the cays (through sea level rise) and the reef (through bleaching) are fundamentally vulnerable.