Rocks at Cape Tribulation

The striped and layered rocks that underlie the promontory at Cape Tribulation look like sedimentary strata. They were just that at one time in the past but they have been  altered and partly metamorphosed into metasedimentary rocks. They belong to a group known as the Hodkingson Formation and are the result of transformations brought about as two tectonic plates of the earth’s crust collided, with one plate then sliding under the other (subduction), generating tremendous heat and pressure that altered existing sedimentary rocks, promoted magma movements below the crust (leading to intrusive igneous rocks), and stimulated surface volcanic activity (making extrusive igneous rocks).

More Sand Pellets from Crab Feeding Activities

The topography of the shore near Cape Tribulation varies. At one point it is semi-vegetated with salt-tolerant shrubs. Here the substrate holds water for longer at low tide and the root systems of the plants trap finer sediments and nutrients that are washed down the beach from the nearby forest.

The different composition and consistency of the beach sediments in this place has given rise to a variation on the theme of sand ball patterns made by feeding crabs. The crabs may be the same species or a related species to Scopimera inflata which created the scatters and radiating patterns of drying-out pellets further along the beach (see the previous post). In this location, however, the enriched sand was relatively wet, which meant that the pellets coalesced into discrete linear masses that made very interesting designs on the surface of the beach.

Sand Bubbler Crab Pellets at Cape Tribulation

Small ball-shaped sand pellets produced by the feeding activities of the "Sand Bubbler" Crab

On many sandy beaches along the Queensland coast of eastern Australia there are millions of small sandy balls. Each one is just a few millimetres across. They can form extensive mats or patterns as they cover the shore at low tide. There were many decorating the sand at Cape Tribulation when I visited in 2011. Closer inspection reveals small holes in the sand, usually at the centre of radiating lines of balls. These balls are the result of the feeding activities of small sandy coloured crabs that are themselves rarely seen. The holes are their burrows. They are the “Sand Bubbler” crabs belonging to the genus Scopimera, often S. inflata. The balls are created as the crab feeds on the organic matter attached to the sand grains on the surface around its burrow, and rolls up the cleaned grains into balls before moving on to the next spot.

The patterns vary according to the moisture level of the sand and its organic content, as well as the species concerned, I would imagine. I’ll post some more pictures later showing an interesting variation on the sand ball patterns from the other end of Cape Tribulation beach.

Crabs at Port Douglas

 

Fiddler crab by its burrow on a muddy seashore in AustraliaOne of many fiddler type crabs (Uca spp.) found on the low-tide mud at Port Douglas in Queensland, Australia. These small colourful crustaceans with their tall stalked eyes emerge from their burrows as the tide goes out to feast on the surface biofilm of the sediments. The one in the video clip is shielding itself, and protecting its territory, with its large right claw while it daintily scoops up mud and food with its tiny left claw and pops it into its mouth. This specimen has a blue patterned carapace about an inch across (2 cm).

Fiddler crab on a muddy seashore

Spoonbill and Friend

I love to take short video clips. I have many of them and they can be viewed with perfect clarity on my desktop computer screen. They even look good when they are first uploaded to posts on my blog and viewed from the admin side in the Media folder. However, once they are actually inserted into the post, they become too pixelated to view. This is very disappointing. I have contacted WordPress on a couple of occasions and it does not seem to be anything to do with their software. I have even tried posting them on You Tube and the same thing happens. I have concluded that it is something to do with my latest camera. I have experimented with conversions to other file formats without success. I think it is something to do with the specific way this particular camera captures videos – I mostly use the zoom to get fine detail. This is confirmed by the fact that the short clip shown here of a spoonbill and accompanying egret, taken with an earlier camera in Cairns 2011 seems OK.

Natural Patterns at Cairns Botanic Gardens

It is cold today. I wanted to think of a time and place where it was much warmer. I thought back to the holiday I spent in Queensland, Australia, several years ago. It is a wet tropical region and the vegetation is luxurious in the Daintree Rainforest. We did explore the wild as best we could but there was nothing to beat visits to Cairns Botanic Gardens where we could enjoy the wonderful plants without so many of the attendant dangers. Here is a gallery of some of the amazing and beautiful natural plant patterns, colours and textures that I photographed among the vegetation in these fabulous gardens.

A Bunch of Coconuts

Coconuts on the tree at Port Douglas, Four Mile Beach.

To most of us who are unfamiliar with the natural world of the tropics, coconuts are the small brown hard hairy things that you very rarely buy in the supermarket, or maybe have tried once in a blue moon to hit on a coconut shy at the fair. A song springs to mind:

I’ve got a lovely bunch of coconuts
There they are, all standing in a row
Big ones, small ones, some as big as your head
Give them a twist a flick of the wrist
That’s what the showman said.
I’ve got a lovely bunch of coconuts
Every ball you throw will make me rich
There stands my wife, the idol of me life
Singing roll a bowl a ball a penny a pitch …..
etc.

Fred Heatherton

The reality, of course, is that the fruits of the Coconut Palm (Cocos nucifera) look very different at the point of origin, as I found out on a visit to the north Queensland palm-fringed tropical coast some years back. They do come in all sizes in their own wrapper – including a smooth outer shell, which varies from yellow, to green, to brown, according to age.

The thick fibrous layer between the outer cover and the nut itself helps the coconuts to disperse by allowing them to float and travel long distances at sea. I found coconuts on the beach with stalked or goose barnacles attached – indicating that they had been in the water for some time before washing ashore again.

Other coconuts lying on the sand have strange characteristic holes in them, gnawed by the nocturnal White-tailed Rat (Uromys caudimaculatus) that chews right through all the hard layers to get to the white flesh inside. And coconuts are still in great demand as the basis for exotic beach-side cocktails even in far-away and isolated places, as evidenced by a barrow-load of them in the shade near a bistro hidden among the trees at Cape Tribulation.