After my visit to Moorea in French Polynesia, I spent a spellbinding day and night at Tetiaroa. Tetiaroa (Tahitian for "far in the ocean") is a coral atoll sitting north of Tahiti and Moorea, a Tahitian "leh" (garland) of tree-wreathed coral sand islands (“motus”) wrapped round a turquoise lagoon. This is probably as close to an apparent archetypal tropical island paradise as it is possible to imagine. The archipelago was inhabited by Polynesians for many centuries, and was a retreat for Tahitian royalty. As elsewhere, its population went into decline following European contact, and it was sold by the Tahitian king to his American dentist a century ago. He converted the vegetation of many of the motus to dense coconut plantations for the production of copra from the fibres, but these were abandoned a few decades later as the copra market went into decline. The dentist’s daughter then lived almost alone on the atoll into her old age.
In the 1960s Marlon Brando, at the peak of his Holywood stardom, came upon the islands while looking for sets for the filming of Mutiny on the Bounty. He was bewitched by the place and bought the entire archipelago. He visited it often as a retreat from the world of Holywood, and also set up a basic hotel on one motu. But is his later decades the hotel struggled to survive and the island went into slow neglect, while also avoiding the expansive development of many other Polynesian atolls. Soon after Marlo Brando’s death, the atoll was bought up by a very high-end eco-resort, the Brando, which has established an aesthetically and environmentally discrete hotel on the south-western motu, Onetahi that has won a Platinum LEED (Leadership in Energy and Environmental Design) award.
Thus, by historical circumstances Teriatoa offers a chance to study a coral atoll with a modest contemporary human footprint, but one which faces many of the legacies issues and future challenges faced by many Pacific atolls (see below). I have been invited to look at the potential for terrestrial ecosystems science at Tetiaroa. My host is the Tetiaroa Society, a non-profit environmental organisation that manages conservation and scientific research in the atoll in collaboration with the hotel.
We journeyed at dawn by dinghy from Moorea to Tetiaroa, a bumpy journey of 2.5 hours. It’s a short journey, but halfway through in a small dinghy I gained a huge sense for the vastness of of the Pacific, and respect for the Polynesian navigators who made this vast ocean and its ever-shifting swells their home. Soon after we sighted the motus of Tetiaroa as thin slivers of trees on the horizon. As we approach we were greeted by a young humpback whale joyfully breaching clear of the water, followed soon after by an encounter with a mother and child humpbacks, and a host of spinner dolphins buzzing our boat. The waters of the lagoon are higher than the surrounding ocean, filled by waves crashing against the surrounding reef, so we had to navigate a precarious cascade to work our way into the light turquoise waters of the lagoon and dock on a sandy beach. Black tipped reef sharks, striking but only a metre in length, circled curiously as we waded on shore. We stayed at the Ecostation, a comfortable research facility with excellent labs within the hotel grounds.
There is a fair amount of marine research occurring on Tetiaroa, but almost nothing on the terrestrial ecosystems. One of the downsides of being an ecologist is that we know too well that there is often trouble in paradise (beware of taking an ecologist on honeymoon!). Most tropical islands hold a legacy of extinction and invasion - the extinction of over a thousand species of birds in the Pacific following human settlement was probably the biggest extinction event of the Holocene.
There are two main current terrestrial environmental issues on the atoll: the challenge of of rat invasion, and the legacy of the dense coconut plantation. To a holiday visitor the white sandy beach lined by dense groves of coconuts is archetypal paradise. Indeed, the Polynesians found a multitude of uses for the coconut and it is an indispensible part of the cultural heritage of the Pacific islands. But this is an ecosystem out of kilter. The coconut groves, especially if untended, form dense stands with fallen palm fronds suppressing regeneration by other plant species, and providing a poor habitat for nesting birds. It is debatable whether coconut was naturally found in Polynesia, or was brought by the Polynesians. But dense coconut stands are a legacy of copra plantation. There are two species of rat on the atoll, the smaller Polynesian rat or kiore (Rattus exulans), which arrived with the first Polynesian settlers (deliberately - it was regarded as a luxury food), and the black rat (Rattus rattus), which arrived after European contact. Both rats negatively affect the ecosystem but the larger black rat is particularly problematic, by eating up seeds and preventing new plant recruitment, and by raiding nests and eating young chicks. They also feed off the plentiful coconuts, which results in a large and active rat population. Hence there is an ecological meltdown, with dense coconut stands reducing bird habitat and support an large rat population, and the rat population suppressing plant diversity and consuming young birds. Land birds are long gone. And as sea birds now largely avoid the most rat-abundant islands, the inflow of nutrients from ocean to land through bird guano is greatly reduced.
I visited with James Russell of Auckland University (see his National Geographic blog here), who hopes to implement a rat eradication effort on some of the motus, and others are also thinking of reducing coconut abundance in some areas. A key ecological question here is: “can we restore plant and animal diversity and ecosystem nutrient cycling function here by removing rates and/or reducing coconut abundance?”. To do this we are contemplating arranging an array of small ecosystem monitoring plots across various motus, covering a range of invasion and disturbance histories. The spatial patterns across these motus now will be interesting in themselves, but they plots would also provide a baseline for future experiments with rat eradication or coconut thinning.
A different, longer-term question is climate change: how will these low-lying atolls cope with sea level rise? Will the rate of coral aggradation and motu deposition be sufficient to keep up with the rising seas, and how will vegetation and biodiversity respond to these shifts? Again, establishing a baseline plot network now could provide valuable insights into how these ecosystems cope, and what interventions might help.
Moorea, French Polynesia
Last week I visited the Pacific island of Moorea, which sits just next to Tahiti in the Society Islands, in French Polynesia, an array of islands widely scattered across the Central Pacific. The islands form a progression of volcanic seamounts, with youngest in the south-east peaking in the 2100 m peaks of Tahiti, and the oldest in the north-west subsiding into perfect coral atolls. My host was Neil Davies, Director of the Gump Research Station in Moorea, and I am here to discover a little more about the forests of Polynesia, to find ways of supporting and devleoping some of the forest research here, and to bring in some of the ecosystem process studies that we do elsewhere across the tropics, with the potential of bring some of these forests into our Global Ecosystems Monitoring Network. Moorea is the focus of the IDEA Digital Avatar project, and effort to digitise an entire island ecosystem from 'genes to satellites'. There is an article about this project in Nature. As a result the biodiversity of the land and marine ecosystems in Moorea is particularly well catalogued.
The landscapes of Tahiti and Moorea (and many other Pacific volcano islands) are truly breath-taking, with the basalt volcanoes eroding way into almost vertical-sided mountains and towers, some of the most astounding topography I have seen anywhere. As Darwin noted when stopping at Tahiti after his explorations of South America: “in the Cordillera, I have seen mountains on a far grander scale, but for abruptness, nothing at all comparable with this". The high mountains hold on to native cloud forest and rocky scrub, but the lower levels are a lush green mosaic of invasive species, farms and light green fernlands. The islands are surrounded by a skirt of coral reef holding in a lagoon of perfect turquoise waters.
In between meetings and visiting the forest and lagoon, I tried and absorb all I could about this mesmerising land I found myself in and knew so little about. My sources on the geology and vegetation history were “Vegetation of the Tropical Pacific Islands” by Dieter Mueller-Dombois and Raymond Fosberg. I also borrowed off Neil an excellent biography of James Cook by Frank McLynn, and read particularly closely the descriptions of Cook’s several contacts with Tahiti and the societies he found there, and how both reacted to the “other” in this collision of worlds. A highly recommended book that highlights how astonishing both Cook and the Polynesian societies were, and captures the astonishing nature of the first contacts.
We visit the Opunohu valley, a lush mosaics of forests, farmlands, archaeological remains. This area was densely populated and farmed at the time of European contact, and suffered a population crash and almost complete depopulation over the 18th and 19th centuries. Feral chickens, first brought over by the Polynesians, run wild over the landscape, itself almost entirely free of predators. The mapae are rectangular stone enclosures that were used for religious ceremonies, and are now groves of Tahitian chestnut trees (Inocarpus fagifer) with wonderful fluted buttress roots.
Some of the key trees that may have been brought by the Polynesians or that may be native include Hibiscus tiliaceus, Pandanus tectonis, Casuarina equisetifolia. As in many islands, the main environmental story is one of biological invasion, Big invasive species here include Tecoma stands, Psidium cattleianum (strawberry guava) and most recently, the all-smothering Miconia calvescens.
The view from Moorea is of an ocean planet. Polynesia sits in the middle of a hemisphere that is probably over 95% ocean, with what continental area there is is ringing its fringes, and scattered throughout this planet-sized ocean are small islands that are legacies of volcanic hotspots. Every wave of “discovery” of these is an astounding tale. First the various species of plant, bird and insect that manage to make it across thousands of miles, often by accident, to stumble on an island refuge. There they slowly specialise and diverge and take advantage of this new ecosystem that they build. Then the human discovery, an amazing tale of Polynesian adventures reading the stars, winds and swells to cross vast distances and create unique cultures. Then the Europeans, with adventurers such as Cook and his sailors expanding the known world with their exploration of a new ocean world and civilization. Each "discovery" has been accompanied by ecosystem disruption and loss, as well as the creation of something new.
Yadvinder Malhi is an ecosytem ecologist and Professor of Ecosystem Science at Oxford University