story by Dennis Hollier

photos by Sergio Goes

Yellow crazy ants have invaded Mokoli‘i. They swarm over every inch of the tiny islet off the Windward coast of O‘ahu that, because of its distinctive conic profile, is better known as “Chinaman’s Hat.” The small, long-legged ants have profoundly modified what’s left of the native habitat: They dominate the insect population, subvert native plant-life, and wreak havoc on the seabirds that nest there. This is not a problem unique to Hawai‘i: Yellow crazy ants have plagued island environments around the world. Their depredations endanger sooty terns on the Seychelles islands in the Indian Ocean. And, on Christmas Island in the South Pacific, they have decimated the population of land crabs. Now, the alien ants are on several of O‘ahu’s offshore islets and biologists are rushing to undo the damage.

Although these islets are prominent features of the coastline, much of their biology, geology and even their cultural history remain obscure. Most of O‘ahu’s offshore islets are part of the Hawai‘i State Seabird Sanctuary, with restricted public access administered by the state Department of Land and Natural Resources. There are seventeen of them in all, with many located along the island’s windward coast. In addition to Mokoli‘i, the larger O‘ahu islets include Manana—or “Rabbit Island”—and Kaohikaipu, both off Makapu‘u Point; Popoi‘a (a.k.a. “Flat Island”) and the two sets of twins, the Mokulua and Mokumanu islets, all in Kailua Bay; Kekepa, Kapapa and Mokuolo‘e, or “Coconut Island” in Kane‘ohe Bay; and Moku‘auia, or “Goat Island” near La‘ie.

Until recently, scientists more or less ignored Hawai‘i’s offshore islets. Because of their proximity, though, Hawaiians have for centuries made substantial use of them. It’s not surprising to find the islets figure prominently in history and legends. For instance, Royalists loyal to Lili‘uokalani buried guns on Rabbit Island in anticipation of a counter-revolution after the overthrow of the queen. On Popoi‘a, there are still traces of an ancient ko‘a—a fishing shrine. In fact, the name of the island can be interpreted to mean “rotten fish,” an allusion, perhaps, to the effects of nature on once-fresh offerings left at the shrine. Today, the ko‘a is all but invisible in the restricted bird preserve on the islet’s interior. Even so, local kupuna recall it being used “with appropriate pule” or prayers, at least into the 1920s. Archaeologists point out that there are ko‘a and more substantial heiau on many of the islets.

Kapapa, an unrestricted islet just outside the reef in Kane‘ohe Bay, bears the most obvious signs of past usage. Careful observation still reveals the outlines of a small heiau there. According to archaeologists, these are the ruins of a fishing shrine. As recently as the 1950s, scholars from Bishop Museum conducted modest digs on Kapapa. In addition to the ko‘a, their work revealed a canoe house and also unearthed tools, jewelry and human remains. Fishermen still visit Kapapa; at night, you can sometimes see their lanterns winking across Kane‘ohe Bay. Some years ago, when the DLNR tried to close access to the islet, there was such an outcry from the public that the idea was quietly shelved.

Hi‘ilei Kawelo, one of the managers at Pae Pae o He‘eia Fish Pond in Kane‘ohe Bay, knows Kapapa well. For generations, her family has gone out to the islet to fish and camp. “Kapapa was always an important stopover for fishermen,” Kawelo says. “It was difficult to navigate in the bay of Kane‘ohe, because of the patch reefs. But Kapapa is outside the reefs, and fishermen would always go there to camp and to dry their catch.” She laughs easily and adds, “If you’ve been out there, you know it’s hot; you can dry a lot of fish there.

“Because of its importance to our family, my Grandpa was a big part of the opposition when they were designating Kapapa,” Kawelo says. Even now, the family still visits the islet several times a year. “We surf and dive and throw net and catch crabs and gather limu kohu,” she says. But times have changed: In recent years, the islet has figured in guidebooks and television fishing shows, which has brought crowds. “When we used to go twenty years ago, there was nobody out there. Now it’s hard to find a day like that.”

For many years, Kawelo’s family has served as the unofficial caretakers of Kapapa. Her uncle, Richard Paglinawan, one of the founders of the influential group Pa Kui-A-Lua, has helped supervise the care of the cultural artifacts on Kapapa. “Five years ago or so, Pa Kui-A-Lua reburied eight skeletal remains that had been exposed there by waves,” Paglinawan says. They also care for the heiau on the islet. “We put up signs,” he says. “But the main thing we did was clear out the tree growth inside the fishing ko‘a.” Before that, uncaring visitors were using the shelter of the trees as a latrine. In fact, much of the work on Kapapa is just trying to deal with the effect of more visitors. “A few years ago,” Paglinawan says, “Kawelo’s family and mine organized a clean-up. We took out almost fifty bags of rubbish.”

The tension between preserving Kapapa and maintaining public access presents an irony not lost on Paglinawan. He points out that the islet is also a refuge for shearwaters, which are stressed by all the visitors. “We’re caught between this place of wanting to use Kapapa, but still protect the birds and the ko‘a,” he says.

The conflict between use and protection has been a recurring theme for biologists, too. Several years ago, the Department of Land and Natural Resources, Bishop Museum and a few other concerned agencies created the Offshore Islets Restoration Committee, an organization designed to address problems like the yellow crazy ant. Jaap Eijzenga—who has the charming title of Offshore Islet Biologist—spearheads most of the state’s work on these islands. His wife, Heather Eijzenga, works as the coordinator for Bishop Museum’s Hawai‘i Offshore Islet Project, a program funded in part by the National Fish and Wildlife Foundation to produce a complete inventory of the plants and arthropods on the offshore islets. Jaap and Heather form the bulkhead against waves of invasive species like the yellow crazy ant.

It would be hard to overstate the effect of the ants on Mokoli‘i. “In effect, it looks like one big anthill,” Jaap said during a recent visit to the island. He had tagged along with Heather and her volunteers, Kim Morishige and Maria Paresa, students from Kamehameha Schools who were there to help inventory the insect population. In fact, there were hardly any insects at all besides ants. “There are even ants on the beach,” Jaap said. “They’ll run right out to the edge of the water.” The superabundance of ants highlights one of their most pernicious characteristics. “They form what’s called ‘super-colonies,’” Jaap said. “They recognize one another, so they don’t compete. This whole island might be one super-colony.” That spells trouble for the island’s seabirds.

Protecting the seabirds has become one of the primary challenges for Jaap and Heather. Like many of O‘ahu’s offshore islets, the surface of Mokoli‘i is riddled with shearwater burrows. But the island’s birds have long been harassed by alien invasives. Before the ants, it was rats, which have now been eradicated from many of the islets. Heather points out that there were no seabirds on Mokoli‘i before the rats were eradicated. Once they were gone, the birds returned.

“In 2002, we counted 126 chicks on Mokoli‘i,” she says. “In ’03 there were 185.” But once the rats were gone, the ant population exploded. The ants disturb the adult birds with an irritating spray of formic acid. Worse still, they prey on hatchlings. “In ’04, it was down to 120,” Heather says. “But in ’05, there was only one chick. Now, nothing.”

Despite the problems with alien invasives, there’s a wild, primordial beauty to the offshore islets. They also offer extraordinary opportunities to see what Hawai‘i looked like before humans arrived in the Islands. “These islets are little jewels,” says Sheldon Plentovich, another UH biologist and the first to note the presence of yellow crazy ants. “They give us a kind of glimpse of what our coastal lowlands used to look like.” On the more remote islets, biologists have discovered plants that were thought to have gone extinct. But even busy Kapapa has yielded a beetle previously unknown to science. In her UH office, Sheldon proudly pulls up its picture on her computer. “I would love for people to see that weevil,” she says.

Kapapa, like many of the islets, also figures in the misty realm between Hawaiian oral history and legend. The islet belongs to the ahupua‘a, or district, of He‘eia, where the public wharf is today. One interpretation for the word he‘eia is “swept away.” This may be in reference to a great tidal wave that Hawaiians believe once inundated this coast, sweeping the villagers out to sea. According to the legend, the people adrift out in the bay couldn’t make their way back to shore, so they prayed to the god Kane for rescue, and he in turn raised Kapapa beneath them.

Perhaps the most famous legend associated with the islets deals with tiny Mokoli‘i. Here, a huge dragon—a mo‘o known as Mokoli‘i—is said to have battled with the goddess Hi‘iaka. As she tried to pass around the point at Kualoa, Mokoli‘i rose up to block her way. According to a version of the story recounted to noted archaeologist Nathaniel B. Emerson, Hi‘iaka slew the dragon and afterward installed its flukes as a landmark “which now forms the rock known to this day as Mokoli‘i.”

The scientific explanations of the islets’ origins are no less fantastic. “Goat Island is really a mini-geology museum,” says Chip Fletcher, who is chairman of the University of Hawai‘i’s geology department and an expert on coastal geology. For Chip, the story of Hawai‘i is written clearly on the tortured features of its islets—and in some cases, this story is startling.

One of the typical aspects of Hawai‘i’s coastline—especially the offshore islets—is a set of characteristic shelves that stair-step out to sea. Often, these shelves are just below low tide and are washed by waves. Many, though, are high and dry. “We call them ‘wave-cut benches,’” says Fletcher, “but I think they’re really biological.” He attributes the process to a familiar resident of Hawai‘i’s rocky shorelines: urchins. With the ceaseless scraping of their spines, millions of small helmet urchins and spiny urchins that live in the inter-tidal zone slowly bore their way into the rock, riddling it with holes. In some places, thousands of these holes are visible, many of them with urchins still scouring away. Over time, wave action erodes the weakened rock and undercuts the shoreline. This leaves a visor—a rocky overhang—to be further pummeled and scoured by waves. When this visor eventually collapses and the waves wash away the debris, the result is a slowly expanding shelf just below the low water mark.

Sometimes, though, falling sea level exposes these shelves—as it has along the flanks of Hanauma Bay, a relic of a period 3,000 years ago when the sea level stood about 6 feet higher than today. Broad, wave-cut benches like the ones at Hanauma Bay also dominate the seaward side of Manana. Narrower versions gird all, or parts of the other islets. Kekepa, in Kane‘ohe Bay, is sometimes called “Mushroom Island” because none of its visor has yet collapsed. Instead, the whole islet is ringed with an overhang that makes access almost impossible.

Although laymen often view the geology of Hawai‘i as purely volcanic, an eternal pattern of eruption and erosion, the history of Hawai‘i’s offshore islets belies this simple scenario. Even the purely volcanic islets have surprisingly diverse geologies. Manana, for example, is a tuff cone, much like the familiar landmarks of Punchbowl and Diamond Head. Tuff cones are composed mostly of volcanic ash, the result of submarine eruptions where the contact of seawater with superheated lava produced cataclysmic steam explosions. These explosions were powerful enough to blast solid basalt into the ash and cinders that gradually harden into tuff cones like Manana. Molokini, a barren crescent off Moloka‘i, and Lehua, a precipitous wedge of ash 2 miles off the coast of Ni‘ihau, are also the remains of tuff cones that have largely eroded into the sea.

But changes in sea level can result in an entirely different story. Kaohikaipu, the flat island lying between Manana and Makapu‘u, is a good example. Like Manana, Kaohikaipu has a volcanic origin, but its surface is mostly lava rather than tuff. This points to a later birth, at a time when the sea level was lower. The vent that created the islet produced a relatively peaceful eruption rather than the explosive one that gave birth to the neighboring Manana. Then again, islets like the Mokulua and Mokumanu twins of Kailua Bay tell a different volcanic story. These islets, and their inshore equivalents like Mount Olomana and Keolu Hills, are the vestiges of the enormous Ko‘olau volcano—most of which vanished into the sea as many as 2 million years ago in a cataclysm known as the Nu‘uanu Landslide. Only its bare bones remain.

Chip describes the Mokulua islets as “dike swarms.” Magma within a volcano flows through a system of rifts and tubes. Sometimes it erupts to the surface as lava. Most of it, though, percolates through these fissures in the earth’s crust. This kind of lava cools quickly, forming layers of hard, glassy rock called dikes, which erode more slowly than the layers of lava around them. As softer stone wears away, the dikes stand out as vertical or diagonal walls. Obdurate dike swarms like Mokulua and Mokumanu are the remains of the great shield cone of the Ko‘olau volcano.

Dikes account for many of Hawai‘i’s most prominent features. Along the Pali—the pleated cliffs of the Ko‘olau ridge—erosion-resistant dikes create hanging valleys, which sometimes spout towering waterfalls when it rains. But the dikes of O‘ahu’s islets are much more intimate. On the windward side of North Mokulua, dikes form freestanding walls and arches that you can touch. Although the interior of the islet is kapu because of the seabirds, one can walk most of the way around the base. Sometimes you’re walking on old wave-cut benches. Sometimes you’re walking on the obsidian edge of an exposed dike. Looking back at the islet from the wild, seaward side, you can watch ranks of jagged, leaning dikes climb its flank. Small caverns sometimes form in the intersections of two dikes. Down near the rugged shoreline, where ferocious waves sometimes wash over them, these caverns form narrow inlets and picturesque tidal pools.

One of the more astonishing tales told in the geology of Hawai‘i’s offshore islets is about the changing level of the sea. “Let me show you the other kind of islet we have,” Chip says. “Kapapa, in Kane‘ohe, is composed of carbonates—sands put down by the wind as a dune.” This had to occur when the sea level was much lower than today, “around the time of the last Ice Age.” As calcium-rich pore-water seeped through the sand, it eventually hardened into stone. This sandstone—known to geologists as eolianite for the Greek god of the wind—is 80,000 years old. As the sea level rose, these “lithified” dunes gradually eroded away. Kapapa—and perhaps Kekepa—are nubs of what was once an extensive dune field. But there are other traces of these sands: A road cut in La‘ie Point exposes the inter-cut layers typical of lithified dunes. And the northern arm of Goat Island, just offshore, reveals traces of rhisoliths—“old ghost forests, buried by the dunes,” Chip says.

Chip and his graduate students have also taken core samples of Kapapa to help explain the history of changing sea level. “These represent thousands of years of stratiographic information,” he says. By carbon dating the layers, they’re able to chart the slow advance and retreat of the shoreline. Their work on the islet has given science a more nuanced understanding of changing sea level and its effect on coastal geology.

But Kapapa’s greatest legacy for geology lies right on the surface. Today we speak of the threat of rising sea levels caused of global warming. But a strip of sand on the seaward side of Kapapa, 6 to 8 feet above the current shoreline, suggests a time when sea level was much higher, the result perhaps of changes in the Earth’s shape and gravitational field caused by the end of the Ice Age. Geologists now believe this strip of sand represents a “fossil” beach laid down by waves three to five thousand years ago. The island has given its name to this geological period, called the Kapapa Stand of the Sea by Harold Stearnes, Hawai‘i’s first geologist, in the 1930s.

But that’s still not the highest sea level foreshadowed in the landscape of Hawai‘i’s islets. “The last time the climate was as warm as it is today,” Chip says, “was 125,000 years ago. Sea level then was thought to be even higher than the Kapapa Stand.” Popoi‘a, the flat islet in Kailua Bay, is made of reef rock formed during that time. “The same layers of rock are visible at Alala Point,” Chip says, referring to the high point between Kailua and Lanikai. Much of the sediments that form O‘ahu’s ‘Ewa Plain are also of that age. And similar reef rock was found years ago in the foothills of Waimanalo. Indeed, this mind-boggling up-swelling of sea level is known as the Waimanalo Stand of the Sea.

On Mokoli‘i, while Heather and her volunteers wade through the scratching under-story of lantana looking for insects, Jaap searches the broad hips of the island for traces of a native grass he saw on an earlier visit. He finds some sedges, and some orange-flowered ‘ilima, and a single scraggly specimen of ‘aweoweo. But not a trace of the grass. “Perhaps it’s the wrong season,” he says, pausing on a bluff to consider Kane‘ohe Bay.

The fragile ecosystems of Hawai‘i’s offshore islets are a testament to a world forever in flux, a world where something as modest as an ant wreaks comprehensive change. Gaze out over the islets of the bay, over the picturesque developments of the coastal plain and the marshy shore. See the ancient fishponds and the modern piers. The heiau and the shoreline mansions. See the naupaka and ‘ilima on salt-wracked headlands, and the alien mangroves in the mouths of the streams that empty into the bay. The history of Hawai‘i’s offshore islets tells us that all of it is temporary, even the islets themselves. All of it will one day be buried again beneath the unrelenting sea.