When the Great Barrier Reef was a land of hills and trees

There is a great deal of academic research being conducted into how and when Aboriginal people arrived in Australia. The one be assumption is that people arrived when sea levels were at their lowest, to as much as 130 m below present levels during glacial periods. Lower sea levels reduced the gaps between land masses and are thought to have made island hopping much easier. At these times, all of the coral reefs we know today would have been on land. The Great Barrier Reef was a chain of limestone hills. All of this was only 10000 years ago. This transformation between terrestrial ecosystem into marine fires the imagination. What would it have been like to wander in a landscape where coral reefs were hills? There places on earth where it is possible to do so today. One of those places is the coast of Papua New Guinea. 

Diagram from Sceptical Sciences

On the southern coast of PNG, at a place called Bluff, which is in Gulf Province near Kerema there are a few uplifted coral reefs which are morphologically similar to the reefs of the present day Great Barrier Reef.  The headland of Bluff is one such old coral reef. It is formed of dense coral rock where the detail of the polyps has been lost. Caverns run through the headland.

This headland has a legend about a battle between a hunter and boar.

One of the caverns which face the sea and are partially filled at high tide

Not much detail in the rock, mainly live embedded sea anemones

To the north of Bluff is a low linear plateau with coral reef and rubble slopes on its southern end. Gulf Province is a land of large rivers that pump out stupendous quantities of sand and mud and looking now, I think the plateau is formed mainly from mud stone or argillite with a veneer of coral.

Waterfall from top of plateau, which is only about 20 m high.

Gulf Province has about 9 m of rain each year and the land is sparsely settled area of swamps and heavy jungle. The plateau is the only raised land for several kilometres. No-one lived there although springs on the side of the hill did provide drinking water for local villagers. 

Waterfront at Kerema 2012, plateau visible in background

The southern end of the plateau has sides covered with coral rubble which often has well preserved polyps. 

Coral colonies are clear visible

Coral rubble from beside drinking water spring

Ancient coral colonies become boulders on the beach.

On the western face of the plateau are some small caves and grottos. After squeezing into one grotto, I found that I was less than a metre from a rather deadly looking snake. I later identified it as a viper boa and not a viper. Viper boas are a type of boa, like a python but as they have live young are a boa and not a python. 

Entrance to a grotto which opens up inside

A viper boa was inside (Candoia aspera)

Also in caves were enormous cave crickets. They were lined up on the ledges and scurried around when I got close.

The limestone nature of the hills was clear from the cave features such as shawls that were developing in larger caverns.

Wildlife of Clairview and St Lawrence

Clairview and St Lawrence are important habitats for larger creatures such as koalas, greater gliders, possums, goannas, emus and a wide variety of wallabies but these creatures are not easy to find. The area is on the threshold for many wildlife species and they occur only in the better pockets of land or at low densities. It is easier to find smaller creatures that can live in smaller patches habitat. Wetlands and watercourses are where the action is.

Roadside tree with koala and possum scratches (click to zoom in)

A brushtail possum in BarraCrab Caravan Park

At Clairview, at the southern end of the beach past the caravan park is a tidal creek with large colonies of fiddler crabs on the adjacent flats about 100 m out from the beach. There are two main species, a large species with hot pink nippers and green backs and a small species with a grey-white nipper. The smaller species makes up for lack of colour by waving so frantically that the crabs sometimes bounce across the ground. It is a great place for kids to discover a few wild creatures and perhaps even catch some. 

Fiddler crab colonies are on side opposite this large mangrove

Uca seismella - little white bouncing fiddler crabs are on the lower bank

Two-tone fiddler crabs (U. vomeris) and smaller pink fiddler crabs

Pink fiddler crab - Uca polita

Near the mangroves are red climber crabs (Metapograpsus frontalis)

Male fiddler crabs have one large nipper for demonstrating their power and a tiny nipper for feeding. Very rarely a crab will have two large nippers. Finding one of these is the Queensland equivalent of finding a four leaf clover and I found one at Clairview. In forty years, I have only seen four such crabs.

The fiddler crabs that dominates the banks of St Lawrence Creek are a different species, one which prefers salt pans to the intertidal mud flats. 

Uca signata (click to enlarge)

If you are lucky to be present when the tide is rising and filling the creek out from the beach, you may see popeye mullet. These strange fish swim with the eyes above water so that they can see predatory birds. The lower part of their eye has differently shaped optics so that they can see underwater. If the tide is out, the bottom of the creek is filled with fine soft silt that perfectly records the prints of a multitude of mostly unseen creatures including sea turtles, gropers, giant mud skippers, mud crabs and much more. Working out which creatures made which prints can be a challenge.

Pop-eye mullet in St Lawrence Creek

Unfortunately, the popeye mullet are not reliably present and chances of seeing these strange fish are better in St Lawrence Creek, which flows past the town of St Lawrence and is about 20 km from Clairview. Clairview is an old volcanic area and has low hills of volcanic origin, whereas St Lawrence is located in an ancient coal basin, filled with deep sediments. Despite their spatial proximity Clairview and St Lawrence are in different bioregions, which are the ecological equivalent of countries. The climate, landforms and geology differ enough that different groups of species dominate. At Clairview the eucalypts have green foliage and close to St Lawrence the foliage is usually grey. The boundary is diffuse being about 10 km wide and there is no sudden change. 

Colour of ironbark leaves near St Lawrence

Coal basins are full of fine mobile sediments. St Lawrence Creek is more like liquid mud that water and it is no wonder that popeye mullet with there ability to look above the water to see where they are are so abundant. Another fish that revels in liquid mud is the blue mud hopper, which is a relative of the mud skipper. This muddy world is alien and worthy of a visit. 

Small mudskipper (left) and a blue mudhopper (right)

In only 8 km, St Lawrence Creek which becomes tidal at the highway, increases from a few metres wide to approximately 500 m wide and with 8 m tides, has swirling waters and standing waves caused by racing tides. The Styx River, which is only 20 km away has tidal bore, a wave up to 1 m high caused by the rush of the incoming tide. Unfortunately this river is inaccessible and it is quite possible St Lawrence Creek also has dramatic incoming tides. Only some tides have strong bores but these are predictable. Perhaps the combination of soft ground and violent tides creates these strange creeks which are a metre wider for every ten metres downstream. 

St Lawrence Creek just beside Bruce Highway is about 10 m wide

St Lawrence Creek is 500 m wide, only 8 km downstream

St Lawrence is famous for wetlands and waterbirds. The small seasonal creeks also have their own fauna which is adapted to floods and droughts. However, it is the marine environment that interests me. I want to see and understand the biodiversity of the muddy waters, a largely ignored scientific frontier.

Where pipes run under the highway, there are often moulted crab shells

A freshwater crab caught in a drain beside the highway

See also: Postcard from Clairview