Unexpected Biodiversity Encountered in Southern Ocean

For many, the words “Antarctica” and “Southern Ocean” conjure up images of vast icy wastelands and chilly waters where few creatures but penguins would be expected to survive.  Even many scientists have long assumed the Antarctic, because of its very cold temperatures, was much less rich in species than the world’s temperate and tropical regions.  However a new survey of marine life around South Georgia Island, which is part of one of the southernmost large island chains in the world, has revealed waters that are actually full of life.  The continental shelf around South Georgia may harbor even more species than that surrounding tropical islands long recognized for their plentiful biodiversity.

In a study recently published in the online peer-reviewed journal PLoS ONE, scientists working for the British Antarctic Survey catalogued marine organisms found on South Georgia Island’s continental shelf.  By systematically sampling the waters around the island, the researchers made records of over 17,700 individual organisms belonging to 1,445 species.  Together these species represented twenty-two phyla, or major groups, of animals.  The authors of the study say their findings show the marine biodiversity of South Georgia rivals or surpasses that of tropical islands like the Galapagos.

Though north of the Antarctic Circle, South Georgia Island and the surrounding South Sandwich Islands are located in the Southern Ocean where marine life was once thought to be much less diverse than in warmer waters farther north.  The island is roughly parallel to the southernmost tip of South America, and slightly further south than the Falkland Islands.  The only human inhabitants of South Georgia, which remains a British territory, are scientists, researchers, and government overseers.  The island serves largely as a base for marine research the importance of which has increased with the realization that the Southern Ocean is feeling the effects of climate change more quickly than most other parts of the world.

The fish and invertebrates that comprise most of the newly-encountered species around South Georgia Island are as a rule neither cute nor cuddly—but what they lack in traditional wildlife charisma they more than make up for with their intriguing strangeness.  Creatures found on the continental shelf include giant spider crabs, elegant cold-water corals, pearly-shelled sea snails, and bottom-dwelling fish with enormous mouths.  Many of these species are probably endemic to South Georgia Island and the surrounding area, meaning they are found nowhere else and are particularly vulnerable to environmental change.  

Over the last fifty years water temperatures in the Southern Ocean have increased an average of one degree Celsius, or 1.8 degrees Fahrenheit.  This may not sound like much, but the warmer temperatures are already wrought changes on the environment, causing sea ice to melt and species distributions to shift.  Tiny crustaceans that serve as an important food source for many larger animal species have declined, while warmer waters have allowed invasive species to move into new areas and displace marine animals adapted to very cold temperatures.  Like the much more famous polar bear in the Arctic, many Southern Ocean species now stand to go extinct unless climate change can be quickly halted.

The extraordinary biodiversity around South Georgia Island can be attributed to a variety of factors that gave rise to a unique assemblage of species through evolution.  The island is far from any large land mass, and scientists believe it has been so for a very long time.  This has given many groups of marine animals a chance to evolve endemic species in the continental shelf area round the island.  South Georgia is also located at the intersection of major ocean currents flowing away from Antarctica and the tip of South America.  Both currents carry nutrients that have created a rich feeding ground for marine life.

As further exploration of life in the Southern Ocean proceeds, South Georgia Island is likely to continue to stand out as an area particularly rich in marine animals.  However today it is also something more: South Georgia’s newly discovered biological riches are a reminder of how much remains to be learned about Southern Ocean habitats, and how little we know about an area that’s rapidly changing because of human activities.

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