Last autumn, a lecture engagement for my wife, Nancy, an orchid expert, allowed us to spend a few weeks in Western Australia, one of that nation's six states. When we left the United States, Bay Journal Editor Karl Blankenship quipped: "Well, I can't imagine you getting a 'Prologue' article out of this trip." Surprise!

Australia is an unusual continent. It was separated from Earth's primordial landmasses, Gondwana and Pangaea, by continental drift in the dimmest reaches of time. Its native terrestrial species evolved with virtually no outside contacts from other land masses until aboriginal humans arrived about 40,000 years ago. They brought hunting weapons such as atlatl-thrown javelins and the boomerang. Most likely, they also brought Australia's wild dog, the dingo, which has subsequently helped to extirpate some of the continent's indigenous animals.

Among Australia's thousands of native plants are about 700 extraordinarily diverse species of the woody plant genus Eucalyptus, which range from flowering shrubs in Australia's desert to towering karri, tingle and jarrah trees in its temperate, hilly southwest. This one genus occupies, in Australia, the ecological niches inhabited by many genera of diverse hard and softwood species in our Chesapeake forests. Many other genera also fill out the plant ecosystem, including the large marri tree, one of 113 species in the genus Corymbia.

Where we have only a single marsupial-the opossum-Australia has amazingly diverse marsupials, from the koala to the foot-long, mouselike bilby. There are a variety of kangaroo species, ranging from the cat-size quokka to the larger red and gray kangaroos. The red kangaroo is the largest, and some males stand 6-and-a-half feet tall. The non-marsupial species include outlandish reptiles like the blue-tongued goanna and arguably the world's widest assortment of toxic-often deadly-organisms from venomous vipers to box jellyfish and the Portuguese man-of-war. In the northwest (remember, in the Southern Hemisphere, this is near the equator) huge, aggressive saltwater crocodiles are found, including one that caught and completely devoured a tourist while we were in country.

We saw tall, old growth karri forests, fostered by the southwest's moist climate, the remnant of a brutal harvest in the 19th and early 20th centuries. The ancient trees-once claimed to have been the largest on earth-are gone, save for small, preserved virgin stands. Their history was not unlike the earliest virgin timber cut in Chesapeake forests, when a single tree's logs could fill an entire narrow gauge railroad train.

The quality of karri and jarrah wood is extraordinary. River bridges are still framed and made with pilings of karri, and jarrah bar tops in the villages are seamless, wide planks, knot-free with a rich grain. It is disturbing to know that wood with this furniture quality was once sent by the shipload to serve as tunnel props during the construction of London's subway.

When compared with our equally improvident use of the Chesapeake's once virgin forests, it would appear that people certainly did not realize how long it takes a wood resource like this to be replaced. (Even today, tours of many upscale homes in the United States reveal tropical hardwoods still being exploited for someone's vanity, with the resultant incremental loss of rainforest ecosystems worldwide.)

Indenting Western Australia's west coast is Shark Bay-an embayment system that, including an offshore barrier island-is about 138 miles from north to south and about 69 miles wide. Like the Chesapeake, it grew as a result of inundation from a rising sea level, which began 17,000-18,000 years ago at the end of the last ice age.

Shark Bay's Peron Peninsula, a significant central landmass, divides the bay into two arms, similar in orientation to the chain of smaller, discontinuous islands separating the Chesapeake from Tangier Sound.

One can almost consider Shark Bay a southern hemisphere mirror image of the Chesapeake. Both open to the equator, and while Shark Bay's 'arms' stretch down toward the South Pole, the Chesapeake's reach upward, toward the North Pole. The Chesapeake is on the U.S. East Coast; Shark Bay is on Australia's West Coast. Shark Bay is closer to the equator, its mouth near 24 degrees south latitude, while the Chesapeake opens to the sea at 37 degrees north. Both are strongly affected by a vast coastal current flowing near shore. In the Chesapeake, it is the Gulf Stream, in Western Australia, it is the Leeuwin Current. Both of these current systems channel or guide weather systems along the coast. In the Chesapeake, storms circulate counter clockwise around the system's center, while below the equator, in Australia, they circulate clockwise, because of Coriolis' force. Because both major "ocean river" currents and storm tracks are directed away from the equator, they are a factor in moving more tropical species into the bays.

We consider the Chesapeake Bay a national treasure; Shark Bay was, in 1991, designated a World Heritage site. Fulfilling all of the necessary criteria, it represents major stages in the Earth's geological and biological processes, natural beauty and is the home of threatened species. Sounds like the Chesapeake to me.

Shark Bay was discovered by Dutch mariner Dirk van Hartog in 1616, but was named by English explorer William Dampier in 1699. I suspect he chose this name because of the great whale sharks, largest of all fishes-they can reach 50 feet-which breed along this coast.

The native Malanga people, whose ancestors have lived here for more than 40,000 years, called this estuary "Gatthaaguda," which means "two bays."

Chesapeake Bay's names is from the 16th century Algonquian Chesapioc, which has been interpreted as "mother of waters" or "great shellfish bay," although no one is certain what it really meant. It's a testimony to John Smith, whose map recorded so many Native American names that the vast number of Algonquian appellations survive on our maps. English settlers in North America were eager to apply familiar names from home wherever possible, and when native names were retained, perhaps thousands of years old, no one wasted time learning their meanings.

The Malanga waded out to shallow islands in Shark Bay to harvest eggs from densely packed cormorant rookeries. English settlers looked beyond the eggs and mined the huge, ancient deposits of phosphate-rich bird guano, shipping it to England as fertilizer. Baltimore, in the 19th century, also received shipments of bird guano from other ocean islands (See "Past is Prologue," October 2002); the start of our society's disastrous overuse of nitrogen on soils.

Shark Bay, like the Chesapeake, had an oyster fishery nurtured by superb water quality. It developed in the 19th century-not for the oysters' meat, but the shell of Pinctada maxima, which can reach 12 inches over its 20-year life. These were the source of "mother-of-pearl," which was cut into clothes buttons, made into handles for table knives, letter openers and the legendary pearl-handled revolver. For a while, Australia supplied 75 percent of the world's market.

In the early 1800s, it was discovered that occasionally, under the right conditions, a natural gem-quality pearl develops within these shells as the oyster covers some grain of natural irritant trapped its mantle or "lung" tissue with sequential layers of nacre.

During the 20th century, oysters were dredged with small sailing vessels, often carrying the two-masted ketch rig, but also with skipjack-like sloops. These workboats hauled eight or 10 small dredges (less than 2 feet wide) at once. Oysters were shucked for their shells and meat, as well as to look for pearls. The largest shells-the prime harvest-were also ecologically the best potential breeders for future generations. Like high quality "select" oysters in the Chesapeake, all were killed in the process.

Pearls promised a higher return than mother-of-pearl, so a new strategy was sought. By the 1950s, Japanese oyster farmers had developed the process for "cultured" or farmed pearls, in which suspended or tray-grown oysters had small irritant items inserted manually and were cared for until pearls formed.

Eventually, the proprietary secrets of how to reliably insert a nucleus to make pearls in living oysters leaked out, and oyster farming was tried in 1958 in Shark Bay by Nicholas Paspaley, with the help of Japanese technicians. Today, the pearl industry is very lucrative; even locally sold pearls command high prices. An oyster in good condition can tolerate up to four pearls at a time -a period which can stretch to eight years. Sometimes an oyster survives the tissue damage from the removal of the pearls and a new nuclei can be inserted.

Healthy oyster populations depend on clear water and unpolluted environments. These conditions still abound in Shark Bay, while our wild Chesapeake oyster fishery has been irretrievably compromised. There are a few reasons why Shark Bay is virtually pristine, not the least of which is clear, nutrient-poor water from the Indian Ocean introduced at the mouth by tides. The watershed of Shark Bay, except during "the wet season," is extremely arid, so there is no constant influx of nutrient-laden river waters. Most notably the drainage basin has a very small human population and tilled agriculture is not practiced on a broad scale, resulting in little conventional pollution.

We saw two significant extractive industries. The first and most forward-looking was a series of windpower farms, some with 50 or more generator towers, slowly turning in constant trade winds. Australia's Alinta Wind Farm produces a pretty constant 90 million watts of electricity. We should be more open to these pollutant-free harvesting machines around the Chesapeake.

On Shark Bay's western (seaward) shore, there is a large sea-salt extraction facility, with huge mounds of glistening salt that can be seen for miles across the bay. Natural lagoons, in the absence of much rain, become hypersaline, and the resulting salt-rich brines can be impounded and further concentrated by hot sunshine until the salt precipitates out as crystals and is scooped up by the ton.

In Shark Bay's southeast arm, a natural sandbar restricts tidal circulation, and the entire head of the bay is hypersaline. Because many predator species-like algae-grazing snails-cannot tolerate it, this backwater, called Hamelin Pool, is home to stromatolites, one of the oldest life forms on earth. These populations of Cyanobacteria form mushroom- or pillow-shape colonies which have grown undisturbed for 4,000-6,000 years. Fossil remains of now-dead colonies elsewhere on Earth date back an estimated 3.5 billion years to the dawn of the Palaeozoic Era. This is a very different "head of bay" habitat from the Chesapeake with its constantly running, salinity-reducing rivers, even during the most severe droughts!

This arid landscape could support only relatively small groups of aboriginal peoples and low-intensity uses then-and today.

In fact, the entire Australian continent is lightly populated: 19,169,083 people in the 2002 census. The state of Western Australia contained just 2,054,000, with more than a million living in the Perth metropolitan area, including the port of Fremantle and surrounding residential areas.

Don Stone, owner of the remote Billabong Roadhouse south of Shark Bay, says his place is surrounded by a "station" or parcel of 750,000 acres, on which 30,000 sheep (and maybe 3,000 unwelcome feral goats) can subsist. That's 25 acres for each sheep, but raise those numbers and the system could collapse and be unable to support them, or the native species. "That's exactly what the whole world is doing [to itself]," Stone said. I could not but agree; human development in the Chesapeake watershed has gone far beyond what sheep and goats could ever do, leaving an unsustainable ecosystem.

We visited the old Peron family sheep station, now a protected Australian National Park on the Peron Peninsula, between Shark Bay's two principal arms.

The Peron Station depends on water, and sparse seasonal rains recharge near-surface groundwater aquifers These are most often accessed by windmills, which are found all over Western Australia. Many harvest the region's abundant wind, providing water simply by flipping a clutch and letting the whirling blades do their work.

At Peron, wild emus come most days to drink at the station's old water tanks. Because the female expends so much energy producing her grapefruit-size eggs, the male emu raises their chicks. I followed one papa down a dusty side road. He looked like a fuzzy brown "Big Bird" with his two turkey-size chicks tagging along.

Emus and kangaroos, like our white-tailed deer, do not fare well on Australia's straight highways. Trucks exceed anything we're used to, with "road trains" containing three or four large trailers roaring along behind a single tractor cab. These, especially after dusk and before dawn, take a constant toll on wildlife and even half-ton stray cattle. In one long day's drive, we counted 49 kangaroos in various stages of decomposition along the highway. Trucks' front ends are heavily armored with welded steel screens and "Roo-bars," resulting in less vehicle-and human-damage than what is caused by frequent deer collisions on Eastern North American roads.

Seasonal rains roaring down dry riverbeds in Western Australia carry large amounts of sediment into parts of Shark Bay and the coastal Indian Ocean. Where the geography is right, the resulting shallow ebb tide sediment deltas provide a base for developing mangrove forests. These act somewhat like Bay tidal marshes, trapping sediments, taking up nutrients and providing habitat for a host of marine species.

At New Beach, one of these sites, we met a large, extended Aboriginal family out for a day of fishing. Most of the women and seven children were ranged along the mangrove-lined creek with fishing poles.

As Nancy and I started off to prospect the flats for interesting species, I asked if the tide was rising or falling. A man started to reply but an older woman interjected, "When the foam is blowin' in from the sea it's comin' with the (rising) tide." She spoke local lore born of 40,000 years of experience and 29 million tides come and gone.

The waves were breaking miles out across the flats, making foam on a slowly building membrane of rising water, which sailed before the wind and onto the shore where we stood.

As we left New Beach and entered high dune country farther south, land appeared on the horizon: Beagle Island, home to Australia's largest sea lion colony. I marvelled at how, aboard the voyage of the British expeditionary ship HMS Beagle (1831-36), a young Charles Darwin, described this coast as "dull and uninteresting."

The combination of low-and low-nutrient-runoff, small population and minimal episodic flows of freshwater and sediments make Shark Bay a poster child for pristine water quality. Shark Bay has 988,400 acres of submerged aquatic vegetation, the largest beds on Earth. Beds of the seagrass Posidonia come right up to the road abutment of main street in the town of Denham. One can walk the tiny strip of beach at the water's edge and pick up scores of indigenous mollusk species-from delicate augur-shaped snails to big meaty squids-all within spitting distance of one's parked car. You can't do that in the Chesapeake with a drainage basin overwhelmed by more than 16 million people, their waste and discards.

The Chesapeake Bay Program invested a great deal of effort looking at the scientific defensibility of what conditions and what SAV resources might have existed in the early 17th century, and came up with was 185,000 acres. In the past quarter century, the peak acreage attained was about 90,000 in 2002. In 2007, there were 64,912 acres. Contrast this with the acreage in Shark Bay and one can see the potential of an ecosystem with truly minimal adverse human impacts.

As we've found in the Chesapeake, SAV beds have remarkable abilities for trapping sediment and clarifying natural waters. From the cliffs at Eagle Bluff on the west side of the Peron Peninsula one can look down 150 feet or more on a dark, seemingly endless carpet of underwater meadows stretching as far as the eye can see.

This is comparable to the view from Calvert Cliffs on the Chesapeake's Western Shore. Scientist Joe Mihursky, who has lived atop those cliffs for decades, once figured that on a clear day he could survey 600 square miles of the Bay and the Choptank River. Despite his commanding position, Mihursky sees no SAV.

As in the Chesapeake, there are about a dozen significant SAV species in Shark Bay. The dominant plant is the fernlike Amphibolis antarctica. Second is Posidonia, which has broad, grasslike blades similar to North America's turtle grass. We also saw patches of Syringodium sp., a genus which is also present in tropical American habitats.

Collectively, these plants efficiently manage the quantities of sediment that seasonally arrive in Shark Bay, quieting the water, growing up and through depositing materials until the plants are eventually overwhelmed. What the plants have "created" are very shallow inshore flats, which eventually emerge above water and can be colonized by terrestrial species. These SAV plants actually "build" land, rather than prevent its loss, which is often perceived as a valuable role in the Chesapeake.

Seeing these vast beds adjacent a land largely empty of man's works, and a bay rich with aquatic life, swirling seabird colonies and fascinating seasonal populations of large marine fishes, simply stunned me to silence.

Sea turtles, chiefly the same green turtle species which spends time in the Chesapeake, depend almost entirely on seagrasses for their diet in Western Australia. Along some parts of this Indian Ocean coast, an algal epiphyte coats the seagrass beds, making the plants unpalatable for sea turtles. Shark Bay's pristine conditions favor seagrasses, and create habitat which encourages many other vertebrate and invertebrate species in this ecosystem.

At Monkey Mia on Peron Peninsula's East Coast, (There are no monkeys and the origin of the name is obscure.) schools of inshore dolphins usually come, twice a day, to be hand-fed as hundreds of tourists stand in awe, sometimes personally approached by these wonderful mammals. The tourists go away forever changed by the experience, the local economy is enriched and the dolphins' role is voluntary.

Such things are possible when the ecosystem is strong and marching to its own lights.

Humans have introduced many European species atop the broad, and unique natural spectrum of Australian plants and animals. Many of these, the rabbit, fox and feral cat in particular, were placed in habitats where they had no natural predators. Each of these and many others, have become plagues on the face of the continent.

The Chesapeake is the site of a continuing roulette game with exotic species arriving by land and sea: most recently the Japanese mitten crab, the rapa whelk, the Asian nut clam and emerald ash borer; our list is in the hundreds. Each threatens another once secure component of the Chesapeake's natural fabric.

Australia has walled off parts of its ecosystems, like the Peron Peninsula, for the protection of indigenous species. Scorched earth barrier zones are bisected with solar-powered electric fences and barbed wire.

At the seaward margins, these fences carry out hundreds of feet into the water, far beyond the tide line. The government's intent within these zones is to exterminate invasive species. Australia's goal is to reintroduce into these exclusion zones some extirpated species, like the bilby, other marsupials and several of the goanna lizards, in an effort to rebuild a more natural ecosystem based on native species.

Are the Chesapeake's stakeholders this wise? Are we courageous and willing to make sacrifices to reverse the terrible mistakes made in our ecosystem over the last four centuries?

This is not just a job for government. Stopping population growth, indeed reversing the population trend to a decline is necessary; strict pollution controls for agriculture, industry and people; the removal of impervious surface; reforestation; and an end to sprawl must take place if this estuary is to have the faintest chance of restoration.

Capt. Reginald Townsend, who has sailed most of the way around this planet, just the day before I finished this draft, said, "When I go out on this Bay, even when I take out my kayak...I just don't know how long it can go on. I believe that in 20 years, the Chesapeake, as we know it will be gone...and lost forever." I believe him.