Ecosystem
At this point, no marine system in the world is completely untouched. That being said, the Ross Sea has sustained the least damage of any open ocean ecosystem. There has been no widespread pollution, no mineral extraction, no native fisheries, and no introduction of alien species. Perhaps most importantly, all the natural predators that existed in the Ross Sea before our arrival are still there, and are close to their original densities. This is not the case in any other open ocean ecosystem on earth. To say it another way, in the Ross Sea, and nowhere else, the dynamic balance is still intact. The ecosystem is still healthy, and it is breathtaking.
Throngs of Adélie and Emperor penguins rocket past the edges of the ice just under the surface, trailing long bridal-veils of white bubbles in the cerulean blue. They explode from the water like corks, speeding past the dangerous edge where Leopard seals may lay waiting. The penguins crash onto the floating ice, leaving parts of their stories written in the snow. Adélies breed on Antarctica’s few patches of bare ground – pinprick islands and rock outcrops. They return, for the most part, to the same colonies where they were born, making their nests from the same pebbles that their ancestors have used for thousands of years. The pebbles are worn smooth.
Over the nutrient-rich waters of the continental shelf break, perhaps half of the world population of Antarctic petrels swirls about in search of food – Antarctic krill and small fish – and pure white snow petrels glow against over-cast skies. They bank hard left and right on delicately pointed origami wings, like flecks of paper suspended in swirling winds. They look impossibly small and fragile against the ice and clouds, but in fact they are the southern-most breeding animals in the world. They make their nests in exposed rock cliffs, a hundred kilometers into the Antarctic continent itself, many sites as yet unseen by human visitors.
Deep into the pack ice, the floating puzzle-pieces are huge – 600 square kilometers – and act like tectonic plates. They collide to form jumbled piles of ice at the margins, and when they spread apart, the seascape looks strangely like aerial views of lakes and connecting rivers; but of course this is an illusion. These lakes and rivers continually open and close as the pack ice shifts. Still, the open water teams with phytoplankton, tiny shrimp-like krill and Antarctic silverfish. Minke whales and killer whales follow the seams between the plates, finding these most inaccessible pockets of water to eat the bounty.
To the north in the Southern Ocean, industrial whaling of the last century removed an estimated 90% of the great whales. By evolving to thrive in the pack ice, Minkes have succeeded where all other baleen whales have failed: they are the only species to have survived the tragic destruction. A misty cloud drifts across the ice when one of the animals breaks the surface, exhaling a salty spray, and then filling its huge lungs with another breath.
Pods of killer whales, sometimes 100 strong, patrol the ice edges. The males are easy to pick out – 2-meter-tall dorsal fins cut through the water, black knifes against the ice. Three separate ecotypes live in the Ross Sea, each specializing in different diet. Type A’s occur over the continental slope and northward, and prefer to hunt minke whales. Type B’s hunt seals and perhaps emperor penguins; and Type C’s eat mostly fish. While A’s and B’s are spread around the continent, the “Dwarf” or Type C killer whale, possibly a distinct species, is centered in the Ross Sea.
As a killer whale rises from a dive, the water bends and stretches around its head in the instant before it breaks through. In that split second, the whale is nothing more than a ghostly shape beneath the water – an errant wave – and the ocean has eyes.
Around the borders of the Ross Sea, sections of sea ice remains locked in place almost all year long by capes and grounded icebergs. On this fast ice, facing pairs of emperor penguins croon their ancient song. Unlike Adélies, the Emperors breed on the sea-ice itself, laying a single egg in the dead of winter. They have no nest, and the males stand upright for the months of Antarctic night, holding the eggs on their feet, protecting the precious packages from the deadly cold. They are the best avian divers in the world, reaching depths of 600 m, and dive times of up to 20 minutes. On the longest of these dives, an emperor can slow its heart rate to 6 beats a minute.
Deep in McMurdo Sound, a small black volcanic island juts out of the fast ice, dwarfed by Mount Erebus. Around the island the fast-ice buckles, forming a complex of ridges and cracks as currents slowly shove the entire mass of floating fast-ice into the rocky shore. The ridges and pressure cracks provide precious portals to the water beneath the ice. Weddell seals rest on the surface next to the cracks. Weddells are the southern-most mammals in the world. Adélie penguins, whales and petrels all migrate north in the winter, but the Weddells stay. They maintain the portals all winter long, raking their teeth along the edges to keep them from freezing shut.
And this is all just the view from above water. To see the rest of the system, you have to don a dry suit and a tank of air, and squeeze through one of the holes yourself.
Dropping through the tunnel of ice at Turtle Rock, shades of blue and cyan replace the veils of white, and the ice above becomes the low-hanging blanket of expectant clouds in a slow-moving front. It connects with the black water at the margin in a seamless hinge. There is no current, and visibility is nearly half a mile – 10 times that of the clearest water anywhere else in the world.
And then there are the sirens… Above water Weddell seals are barely mobile as they lie on the ice, but below water they are dancers. Their voices are more than sound. The call seems to start as semi-conscious thought, a memory of wind whistling through a drafty window, sharp and sweet. It has no direction, no source, and it cuts cleanly through the dark shadows of the mind even before the tone starts to accelerate and deepen, crossing fully into consciousness as the long descending note breaks abruptly into thumping vibration, almost too deep to hear.
If the seal is very close, as when, say, a big male has decided that you, yes you, should really steer clear of his ice cave, the buzz from the final deep-throated thumping notes can be enough to blur vision, immobilize muscles, and will even knock sea stars off of rocks.
Beneath the seal colony, the ocean floor is a mosaic. Writhing piles of the lurid sea stars, urchins and meter-long nemertean worms eat anything a seal drops – a scrap of fish or other detritus. Attached to the rocks, anemones wave their many arms in search of food. Giant sea spiders walk the substrate with their bizarre walk, sometimes taking amphipods or other freeloading passengers along for the ride on their vivid red legs. Deeper still, giant sponges filter the water, some larger than 50-gallon drums
Trematomus bernacchii, like other fishes in this icy water, is equipped with natural antifreeze, but this fish will die of heatstroke at only 6°C, the lowest heat threshold of any animal. It hunts small prey just above the benthic communities, while Pagothenia borchgrevinki (the “borck”) hides in the labyrinth of delicate platelet ice on the underside of the fast ice.
Luminous ctenophores float in mid-water, covered in lines of cilia, like finely-toothed combs. The teeth of the combs flex in coordinated waves, allowing them to move slowly forward. As each wave passes through the lines of cilia, they emit bursts of deeply saturated color. One species unfurls a net of fine filaments behind it, like a drop of milk spreading out in a cup of water. It is hunting for those that go almost unseen without a microscope. A forest of floating microbes like Phaeocystis antarctica, an algal “plant,” is on the way.
In the winter, unobstructed by obstacles, 200 kph winds shoot off the Ross Ice Shelf and out across the Ross Sea. These winds push the blanket of seasonal ice away from the edge of the shelf, creating a large pool of open water – a polynya – even when the rest of the sea is covered in ice. When the sun finally rises after the long night, phytoplankton bloom prolifically with the light and open water. The bloom is so large and so dense that it can be seen from space. Later in the season, a clockwise current pulls the bloom under the fast ice and into McMurdo Sound. The crystal clear water turns to a greenish soup on the order of weeks. This is the big feed.
But for the ctenophore, getting bumped will spoil even this meal: it quickly winds its milky net into long trailing arms and retracts them into its body, moving on to a better place to hunt.
The Ross Sea ecosystem is unique. It is composed of species found nowhere else in the World, all still co-evolving in an ancient process uninterrupted by humans. One highly-adapted species of fish living many millions of years ago radiated into a community of 30 separate species – a ‘species flock’ – that swim the mid-waters, hide in the underside of the ice, or cruise the ocean floor amongst lush communities of sponges, sea fans and other invertebrates, some also endemic to the Ross Sea. Nearly 38% of the world’s population of Adélie penguins and 26% of all emperor penguins breed here. Add to that the four species of ice seals, the three types of killer whales, the Antarctic minke whale, and countless others. It’s an amazing, intact community of creatures. It is, in a word, a triumph.
But this is where the Ross Sea story gets complicated, because deep, deep in the icy water, there is another inhabitant – a giant fish, and the only likely encounter with this member of the ecosystem is when a Weddell seal brings one to the surface, or when a diner orders it in a fancy restaurant 12,000 km away in New York.