I want to visit a South Pacific Island

 

Venture inland on a high volcanic South Pacific island, and you enter a world that appears to be built around absence, but the biodiversity can be vast: Almost no native land mammals, which means that birds, reptiles, and insects have expanded to fill the niches
that foxes, badgers, and deer occupy elsewhere. Flying foxes, the size of dogs, and fruit bats the size of small cats, hang from the canopy by day and reign over pollination and seed dispersal at night. Kingfishers and lorikeets work the branches below. Geckos and skinks patrol the detrital undergrowth.

A large flying fox bat.

The most astonishing resident to me is the coconut crab, the largest land invertebrate on Earth. It climbs trees, cracks open coconuts with its claws, and can live for sixty years. If you see one moving through the forest at night, you might wonder what planet you are on. This is planet Earth.

Coconut crab hanging out on a garbage can.

On an atoll, the interior shrinks to almost nothing, a narrow ribbon of coral rubble and sand between the lagoon and the open sea. What it lacks in size it compensates for in noise: Frigatebirds, boobies, shearwaters, and terns nest in extraordinarily dense colonies, and they can be loud.

Birds finding protection on an offshore rock.

The trees of a South Pacific island are specialists. Coconut palms and pandanus tolerate salt spray and thin, calcium-rich soil. The ironwood stands in groves along the shore, its needled branches sighing in the trade wind. And then there is the Pisonia, a bird-catching tree. The seeds are coated in a gluey resin that sticks to feathers. Birds disperse the seeds; sometimes the seeds ground and dispatch the birds. Move through the canopy slowly, and you start to see it differently: orb-weaver spiders, geckos materializing at dusk, hermit crabs climbing the heights in search of fruit.

Pisonia tree seed, showing its sticky nature.

Birds nesting in a Pisonia tree.

On most South Pacific beaches, the sand is alive, or once was. It is not quartz ground by rivers, but biology: crushed coral, foraminifera shells, echinoderm fragments, mollusk remains. Much of it passed through the gut of a parrotfish. Parrotfish bite algae from coral rock, grind the coral as they eat, and excrete fine white sand. A single large parrotfish can produce hundreds of pounds of it per year. The beach you lie on is, in a real sense, digested reef.

White sand beach.

Beach sand close-up showing forams (1, 13), sponge and octocoral spicules
(6, 7, 12), mollusk parts (3,5), and a sea urchin spine (11). Source Sandatlas.org 

The debris ribbon at the high-tide mark, the wrack line, is not litter. It is a functioning community. From ghost crabs hunting in the moonlight, hermit crabs testing abandoned shells, isopods and amphipods quietly dismantling whatever washes ashore.

Ghost crab.

 

Sea turtles drag themselves up these beaches to nest. The sand temperature during incubation determines the sex of the hatchlings. Cooler sand = more males; warmer = more females. A warming climate will influence sex ratios, at least in the near term. When the eggs hatch, the young dig free in a coordinated burst, emerging at night and following the moonlight reflected on the water out to sea.

Step off the beach into the lagoon and the warm water closes around you. On an atoll, this enclosed body of water is usually calm, shallow, bathed in light, a nursery for juvenile fish and invertebrates; they shelter here until they grow big and strong, and many will then head out to the reef. The lagoon floor may be busy. Sea turtles grazing, stingrays half-buried in the sand with eyes protruding. Juvenile blacktip reef sharks cruise around. The unassuming sea cucumbers are keeping things in check by processing organics from the sand. When absence where they've been over-harvested, sea cucumber absence causes damaging ecosystem cascades that take years to appear.

Coral, a colonial animal living in a precise and fragile partnership with photosynthetic algae, makes up the core of the reef ecosystem; well, they are the reef. The algae live inside the coral's tissue and provide energy through photosynthesis. When the ocean warms past a threshold, the coral expels them. It turns white- coral bleaching- because the algae provided the pigment, and the coral’s white skeleton now shows through. If the stress continues, the coral dies, and the whole city that is the reef ecosystem goes with it.

Colorful coral outcrop.

Reef architecture: A back-reef on the lagoon side, calm and sandy. A reef flat that emerges at low tide, baking in the sun. A reef crest where waves break, and coralline algae cement the rubble. And the fore-reef slope, the wall, dropping away into blue shadow. The richest (in species) zone on Earth per square meter.

Coral Atoll from the air.

Some corals grow a centimeter a year and live for centuries, eventually forming massive structures. Each one is a climate archive, its growth rings encoding the temperature of every decade it has survived.

The herbivores are the reef's maintenance crew. Without them, algae may overgrow the coral,  smothering it. Surgeonfish graze in schools. Sea urchins rasp the reef clean at night. And parrotfish, those same fish building your beach, bite, crunch, and extrude their way through life with a reckless efficiency that is somehow both destruction and creation. They are feeding on algae but take coral, live and dead, in their bites.

When the sun sets, everything changes. The day shift retreats into coral heads. Octopus, lobster, and basket stars emerge. The same coral you hovered over at noon is a different world at midnight.

Past the reef crest, the bottom drops away. Schools of jacks hang in the blue, turning in unison. Dolphins spiral and leap. Tuna pass through on routes that span thousands of miles.

But the ocean's most astonishing events happen every night, invisibly, everywhere. Billions of small fish and countless invertebrates spend the day at depth, beyond the reach of sunlight. As darkness falls, they rise to feed at the surface. Before dawn, they descend again. It is the largest animal migration on Earth, measured by biomass, and almost no one has seen it.

Humpback whales move through these waters seasonally, using the South Pacific as a breeding ground. Tonga is one of the few places on Earth where you can enter the water alongside them, a 40-ton animal hanging motionless a few meters away, watching you back, apparently curious. It is an encounter I would do in a heartbeat, and I expect it would change my world.

Humpback and human floating in deep water.

The journey from interior jungle to open ocean is a tour of separate habitats but also a tightly connected system. Nutrients wash from the land and feed the lagoon. Seagrass filters the water that keeps the coral alive. Pelagic fish bring offshore nutrients onto the reef when they spawn and die there. Seabirds carry the ocean's richness back to the island in the form of guano that fertilizes the trees.

A dead reef produces less sand. A depleted lagoon loses its nursery function. A forest stripped of seabirds loses its fertility. The island ecosystem is connected.

Which is precisely why, if you have the chance, you should go. Take me!

Sources and Further Readings:

Kench PS. 2025. Effects of environmental and climatic changes on coral reef islands. Annual Review of Marine Science 17, 301–324. 

Kumar L, & Tehrany MS. 2017. Climate change impacts on the threatened terrestrial vertebrates of the Pacific Islands. Scientific Reports 7, 5030. 

Plaisance L, Caley MJ, Brainard RE, & Knowlton N. 2011. The diversity of coral reefs: What are we missing? PLOS ONE, 6(10), e25026. 

Sandatlas, sandatlas.org: is created and maintained by Siim Sepp.

Sengupta M, Ford MR, Kench PS, & Perry GLW. 2023. Drivers of shoreline change on Pacific coral reef islands: Linking island change to processes. Regional Environmental Change 23(3), 110. 

Taylor S, & Kumar L. 2016. Global climate change impacts on Pacific Islands terrestrial biodiversity: A review. Tropical Conservation Science 9(1).