Lady Elliot Island, 1863–2026

On 10 November 1863 the Queensland government leased Lady Elliot Island, the southernmost cay of the Great Barrier Reef, to a Hobart guano syndicate for ten years. The rent was £300 a year, and the lease required 200 tons a year to be kept back for sale in Queensland ports (Crowther 1938, The Development of the Guano Trade from Hobart Town). Captain J. W. Robinson came ashore as manager on 30 September 1865, bringing twelve labourers and 30,000 feet of sawn timber. Crowther describes an island “occupied by countless sea birds.” By the time the lease ran out in 1873, the surface had been stripped bare of vegetation, and the figure usually given is about 20,000 tonnes taken off. What came after is normally told as a redemption story, and that is how ABC told it this week (via MetaFilter). Goats kept the island bare for a century. In 1969 an aviator got a lease in return for building an airstrip, and he started planting. Since 2005 more than 20,000 trees have gone in. The island is now 70% revegetated, and about 100,000 black noddies come back each year. All of that is true. My argument is narrower: nobody knows what “restored” means here, because the baseline was shipped off with the guano.

The most careful bird record is T. A. Walker’s “Seabird Islands No. 201” (Corella 13(4), 1989), which is based on twelve visits between 1986 and 1989. It says outright that “there are no records of the bird fauna present before mining and the depositors of the guano are unknown.” Walker’s own counts suggest the birds that returned are not obviously the ones that left. Before 1985, he writes, few black noddies visited. The first colony had 30 nests in 1985–86, and the counts after that were 327, 455 and 570. Most of those nests were in introduced Casuarina, not in the Pisonia forest that noddies use on the neighbouring cays. The first red-tailed tropicbird pair ever recorded on the island nested in 1983. The mining figures don’t settle the question either. Accounts say about a metre was taken off the island, and a metre over Walker’s 35 ha would be hundreds of thousands of tonnes. Spread over the same area, 20,000 t is about 6 cm. So either the deep stripping covered only a small part of the cay, or the tonnage counts what was shipped and not what was dug up. Either way, you can’t work out the size of the original colony from the ledger.

There is another copy of the record. Seabird nitrogen does not stay on land. On Surprise Island in New Caledonia, Choisnard, Sigman, Lorrain and colleagues (Limnology & Oceanography 69:309–324, 2024) followed guano into the brackish groundwater lens, where it is nitrified almost completely. It then seeps out onto the reef flat as nitrate at a δ¹⁵N of 13.7‰, against 6–7‰ for open-ocean nitrate. The signal shows up in coral skeletons: 10.5‰ at 25 m from shore, 7.0‰ at 200 m, 4.3‰ at the reef rim. Work on five Indian Ocean islands points to the same pathway, and the CACAO project is already coring massive Porites to read it. This is more than bookkeeping. In the Chagos, Graham et al. (Nature 559:250, 2018) found that islands without rats had 760× the seabird density and 251× the nitrogen deposition of islands with rats, and the reefs next to them carried 48% more fish biomass. On a coral cay, the guano is part of how the reef works.

Massive Porites lay down annual bands and can live for centuries. A colony on Lady Elliot’s reef flat that was alive in 1850 would hold a dated, year-by-year record of the nitrogen subsidy: the period before mining, the collapse of 1863–73, the century of goats, and the noddy surge after 1985. That would give the restoration a quantitative target for the first time, and one that can be falsified. My bet is that a reef-flat core would show skeletal δ¹⁵N falling by several per mil across the mining decade and staying low through the goat years. I also expect today’s values, even with 100,000 noddies, to be below the pre-1863 level, because a colony that left guano a metre deep was either bigger than the modern one or had been there far longer than forty years of birds roosting in Casuarina. If the core shows the modern signal at or above the 1850s baseline, then the redemption story is completely true, and the island has done something a 1960s herpetologist said it would probably never do. Whichever way it comes out, the coral can answer a question the island’s own records can’t.

A note on sources: ABC names a different first lessee for 1863 than Crowther, who worked from the original indenture. That person may have been the applicant or the agent on the ground. I follow Crowther on the lease terms. Further reading: Wikipedia: Lady Elliot Island.