Australian Geographic
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and witness the tiny and complex
communities living within.
leopard anemone shrimps, which live
only on their namesake anemone.
These solitary creatures are only the
size of a grape. Here you can see both
the larger female shrimp and smaller
male (to the le ) on an anemone.
and the shrimps that live on them mimic their
colours and patterns accordingly.
MANY THOUSANDS OF species are supported by coral reefs – Earth’s most biodiverse marine ecosystems. Some are conspicuous and easily recognisable, including well-known turtles, lobsters, corals, sharks, sponges and stingrays. But look more closely, scrutinise every detail and a new layer of life appears. Tiny eyes peer from within sea squirts and unexpected flashes move deep inside giant clams. Many of these creatures are very precise about where they live, and rather small. Most would comfortably perch on a 5c coin.
The calcium carbonate skeletal structures that form the basis of coral reefs are built by many millions of tiny individual coral animals called polyps, via a close relationship they have with algae living within them (see AG 142). This symbiosis has built colossal reefs in nutrient-poor, clear tropical waters where you would hardly expect such a profusion of life. It isn’t the only intimate connection between different species on coral reefs. Other kinds of symbiosis are also widespread. Many species survive with another in an association biologists call commensalism, during which neither is harmed nor helped.
Then there are organisms that coexist in a long-lasting, close relationship known as mutualism, from which each gains benefit. Clownfish are perhaps the best known of these particular specialists. In the Disney animation Finding Nemo, several artistic liberties were taken, notably ignoring the transition Nemo’s
There are many other examples of symbiosis on coral reefs, including Coleman’s shrimp living on fire urchins and the stunningly camouflaged leopard anemone shrimp. My research focuses on tiny, well-camouflaged species of pygmy seahorse. This group was only discovered relatively recently. In 1969 a researcher in New Caledonia was collecting a sea fan for a museum in Nouméa. Upon close inspection, he noticed two tiny fish clinging to the sea fan’s surface. The species was later named in his honour as Bargibant’s pygmy seahorse. No bigger than a $1 coin, it’s not surprising it eluded discovery for so long. ►
first generations to have had the freedom to explore the world’s shallow seas using modern scuba.
_____________
renowned Australian
naturalist Neville Coleman,
Coleman’s shrimp live in
pairs between the venomous
spines of fire urchins.
My research on the population biology of South-East Asia’s pygmy seahorses was the first of its kind. I studied Bargibant’s and another species that lives on the surface of sea fans and found them to be much rarer than their larger relatives, which are more relaxed regarding habitat choice. This is a typical trend and, in fact, highlights the precarious nature of habitat specialists on reefs. Bargibant’s is found only on the surface of sea fans in the genus Muricella. So far, I have recorded the other species I studied, Denise’s pygmy seahorse, living on 10 different kinds of sea fan. In terms of conservation, the risk of extinction is greater for the extreme habitat specialist Bargibant’s, compared with the more cosmopolitan Denise’s. If the Muricella sea fan homes of Bargibant’s were to die out from a disease, for example, the seahorse would likely follow suit. Denise’s pygmies, on the other hand, could seek refuge on one of their other potential hosts. Worryingly, certain sea fans in the Mediterranean have suffered mass die-offs due to warming waters resulting in increased susceptibility to disease.
IT’S EASY TO FORGET we’re among the first generations to have had the freedom to explore the world’s shallow seas using modern scuba. Due to the sad decline already in larger reef organisms, particularly in Asia, divers have begun focusing at the smaller scale. One positive result is that recreational diving enthusiasts and citizen scientists have been responsible for the discovery of many new habitat specialists during recent decades.
Among the most amazing examples I’ve seen is a tiny species of porcelain crab. This yet-to-be-named pea-sized crustacean lives only among the tentacles of just one species of anemone that sticks only to the dead shell of a snail inhabited by a nocturnal hermit crab! It wasn’t until friends of mine, naturalists and conservationists Ned and Anna DeLoach, discovered this gem that it was realised it actually isn’t uncommon – often hiding in plain sight. Looking back over old photos I realised I’d photographed the crab years earlier but hadn’t noticed it in my pictures.
Coral reefs face an increasing threat from climatic warming, which causes bleaching. As well as corals and other conspicuous reef species that may disappear after a mass bleaching event, there are also many organisms whose disappearance goes almost unnoticed. Consider, for example, diminutive coral hermit crabs and Christmas tree worms sheltering in holes on coral heads, filtering passing water for food with specially adapted feather-like appendages. Inch-long pink-eyed gobies, which need healthy
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Much like hard corals, anemones suffer bleaching, because they too have symbiotic algae in their tissues. When anemones bleach, the fish inhabiting them also suffer. Many die and what survivors there are produce considerably fewer offspring. While some clownfish can inhabit a variety of anemones, others are restricted to just a single species, which can put them in a precarious position.
McCulloch’s anemonefish, an Australian endemic, is an example. Found only off Lord Howe Island and a couple of remote Tasman Sea reefs, it lives with one species of anemone and has a very small geographic range, which means it also has a naturally small population size. Together, these factors put the species at an even higher extinction risk compared with less picky and more widespread species.
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THE LAST GREAT WILDERNESS
Indigenous rangers, scientists, conservationists and pastoralists are working together to ensure the Kimberley remains one of the world’s great wildlife havens.
Ultimate survivor
The short-beaked echidna is found from deserts to mountain peaks; from Tasmania, across the Australian mainland to southern New Guinea. Its unique backwards-pointing feet give it an advantage when digging. Echidnas also use extended claws on the second toes of the hind feet to scratch and groom between the spines.
WALKING WITH FIRE
Linton Burgess performs a traditional dance during patrula, a return of important cultural fire practices to farmland on the midland plains of Tasmania for the first time in 200 years.
Running Man Rock
IT WAS ABOUT SIX YEARS ago that I first discovered him, purely by chance. At an hour and a half out of Sydney, my commercial flight turned north-west towards Darwin. And there he was in all his rampant majesty. Running Man Rock, I call him.
Travel with us
It’s one of Earth’s most complex natural systems, home to countless animals. And to the rest of the world it’s one of the most identifiably Australian places. We all know what it is – the Great Barrier Reef (GBR)– and that it’s under pressure. But how can we frame its intricate natural architecture in a new way that inspires people to love it enough to care about its future?