Australia is a land of vast proportions. However, divers generally make a beeline for the Great Barrier Reef, scarcely sparing a thought for the rest of the continent. For coral reefs and colourful tropical fish, this is obviously a fantastic place to start, but for something out of the ordinary I believe the real gems of Australia’s rich waters are to be found further south.
“Muck diving” is a term more commonly associated with tropical Southeast Asia and the sheltered waters of Lembeh Strait, Milne Bay and Anilao, than cooler climes. It refers to a specialist form of diving where sandy or soft sediment areas, ostensibly devoid of life, are slowly scoured for the amazingly well-camouflaged critters that lurk amongst the scant debris. Since the 1990s, when muck diving was first pioneered, divers have begun to explore similar such habitats in other parts of the world. As it happens, the extensive coastline of Australia offers many opportunities for amazing world-class muck diving with the chance to encounter creatures found nowhere else.
GO WITH THE FLOW
Australia experiences interesting oceanographic conditions, which in turn help to shape the ecosystems and organisms that inhabit its waters. Both the east and west coasts experience significant currents that flow in a southerly direction parallel to their shores. The East Australian Current (EAC) flows all the way from the Great Barrier Reef to the east coast of Tasmania. The EAC famously carried poor little Nemo all the way from his home on the Barrier Reef, down to Sydney. The west coast experiences a similar current flow, the Leeuwin. The Leeuwin begins in northwest Australia, travels past Perth and across the Great Australian Bight before reaching the west coast of Tasmania, albeit with a relatively weak and disrupted flow.
Over millions of years, these currents have influenced the evolution of Australia’s marine life. Many marine species exploit currents to disperse throughout the ocean, particularly in the period straight after hatching. If a tiny planktonic fish fry, on the reefs of Indonesia for example, is caught in the right current it can be swept across huge swathes of the ocean between reefs. In southern Australia, the situation is rather different. The southerly flows of the EAC and Leeuwin current act as barriers to the northerly movement of many creatures during their ocean wandering stage, effectively isolating them in southern waters. Much like the isolation of Darwin’s finches and iguanas in the Galápagos Islands, when prevented from mixing with other populations, organisms tend to evolve to suit their local conditions. Over millions of years the result is a unique suite of species found nowhere else.
AUSSIE MUCK CRITTERS
Living in Brisbane for several years afforded me the opportunity to explore many of the muck dives Australia has to offer. Being a muck-diving aficionado, I have been lucky enough to observe a number of Southeast Asia’s wish-list critters such as mimic octopus, Ambon scorpionfish, blue-ringed octopus and hairy frogfish. Because of this, I really wanted to find some of the rare and endemic creatures (those found in a restricted geographical area) on Australia’s muck dives. Whilst some of these organisms are found throughout the country’s southern region, others have a distribution of only a few hundred kilometres – and some significantly less than that!
Australia has one of the world’s greatest diversities of seahorses, pipefish and their relatives, collectively known as syngnathids. Many of these are found only in Australian waters and, given their preference for inshore sheltered waters, are often encountered by eagle-eyed muck divers.
One of the first very restricted-range Australian fishes to register on my radar was the Sydney pygmy pipehorse (Idiotropiscis lumnitzeri). These small, five to six centimetre-long fish were only scientifically described in 2004 and, as their name suggests, are only known from a short stretch of coast around Sydney and south to Jervis Bay. They became somewhat of a nemesis of mine and after a couple of failed attempts searching for these highly camouflaged fish off Bare Island in Sydney’s Botany Bay, I gladly accepted the offer of being guided by a local naturalist to search for them. Despite their being several times bigger than pygmy seahorses (the focus of my PhD research), I was unprepared for how difficult the pygmy pipehorses would be to find. When the naturalist found and (finally!) showed me an adult animal, the disruptive filaments covering the body superbly broke up its outline, rendering it invisible until I finally managed to distinguish the eye.
Another syngnathid, and a true Australian icon, that has been high on my Aussie endemic wish list is the weedy seadragon (Phyllopteryx taeniolatus). These large pipefish- like animals can be found all the way from Newcastle in the east, around the southern coastline to Geraldton in Western Australia. They inhabit areas of kelp and algae, but one of the most reliable places I have been able to find them is beneath Flinders Jetty, off Victoria’s Mornington Peninsula. This jetty, along with several others on the inside of Port Phillip Bay, is a fantastic dive with many special and endemic creatures to search for. Whilst waiting for my buddy to giant-stride into the sea, in only two metres of water, I spotted my first three juvenile weedy seadragons. Over the course of the dive we found a further seven! Once my brain had developed a search image, it was relatively easy to spot the dragons passively floating amongst the weeds, despite their best efforts to remain undiscovered.
There are around a dozen species of seahorses known from Australian waters, several of which are endemic. The largest of all seahorses, the pot-bellied (Hippocampus abdominalis), is commonly found in southern areas as well as in Tasmania and New Zealand. On one of the inner bay dives off Mornington Peninsula near Melbourne, I found 15 individuals, in addition to several of the much smaller short-head seahorse (H. breviceps). Beneath the jetties the seahorses can be found clinging motionlessly to algal fronds or sponges, so like all muck dives, a slow and deliberate search of every piece of weed or debris will help find these camouflaged critters. Another species, White’s seahorse (H. whitei), prefers slightly warmer water and is found in similar habitats around New South Wales.
Another group of organisms that are well represented amongst the endemic marine life of Australia are the cephalopods. This lineage of highly adapted molluscs
are better known as squid, octopus and cuttlefish. Being a die-hard Southeast Asian muck diver, one of the most highly desired of all critters is the blue-ringed octopus. These gem-like, thumb-sized octopuses are well known for packing a deadly punch. The first one I ever saw was after a week of dawn dives in Indonesia searching Wakatobi Dive Resort’s bountiful House Reef. The dazzling blue rings caught my eye but within a fraction of a second, the whole animal had been swallowed by a flounder – which seemed none the worse for its hazardous diet!
Thankfully, my first encounter with the Australian blue-lined octopus (Hapalochlaena fasciata) was less dramatic. Predictably, the rings in this species are replaced by vivid blue lines, which cover the animal’s body. They serve the same function in advertising the tetrodotoxin, which can fell an adult human in one bite. Indeed, the blue-lined octopus is known to have caused at least one human fatality. These small octopuses are only found along the coastlines of New South Wales, but I have most reliably seen them at a dive site called The Pipeline in Nelson Bay, Port Stephens.
Nelson Bay is probably one of the most fruitful areas in terms of muck diving for Australian endemics. In addition to the blue-lined octopuses, there are many interesting nudibranchs, Sydney octopus (Octopus tetricus), White’s seahorses and endemic blind sharks (Brachaelurus waddi). If the tides work in your favour, this is also a great place to night dive in search of the adorable striped pyjama squid (Sepioloidea lineolata). Searching a shallow sand flat revealed half a dozen of these small squid one evening.
Interestingly, I recently discovered that one of the most distinct nudibranchs in this area, Polycera capensis, is actually a South African native. It is believed that they hitched a ride to Australia on the hull of ocean tankers whilst feeding on Bryozoans. Hitching a ride in ships’ ballast waters has been implicated in the translocation of various marine species, some of which have gone on to wreak havoc in areas where their presence is unintended. In the absence of their natural predators controlling their populations, they have the potential to exploit their new home without any control on their numbers.
THE ULTIMATE ENDEMIC
The spotted handfish (Brachionichthys hirsutus) is a member of an unusual group of a dozen or so southern Australian handfishes, which are distantly related to the frogfishes. They have a rudimentary lure, like their relatives, and a superficially similar body shape. This, however, is where the similarities end. The spotted handfish is found only in the Lower Derwent Estuary and during three dives one morning, I dived almost the whole area in which this fish is naturally found.