Tracks, trails - and bubbler crabs!

 
Little did I expect, when I wrote the post about bubbler crabs a week or so ago (purely on a whim because I’d been intending to for a while), that I would shortly encounter these little sand artists up close and personal – and in profusion.

I have just returned from a restorative sojourn away from the urban chaos of Jakarta on the fascinating island of Bangka, off the east coast of Sumatra. There will be further reports (because, of course, sand figured strongly as a destination criterion), but for starters, my astonishment on walking down to the beach last Friday afternoon makes for an introduction. From a distance, I could not make out why the texture of the beach seemed so roughened – I thought that perhaps it was the result of birds marching about, but few birds were apparent. It was only on closer examination that I realised (while exclaiming loudly and enthusiastically) that the culprits were bubbler crabs – essentially the entire beach was a teeming metropolis of the critters, and smooth sand was the exception rather than the rule.

Herewith, the evidence:

 


This was an ongoing enterprise, but difficult to detect – fleeting scurryings sensed out of the corner of the eye, brief glimpses of moving sand grains as a burrow’s inhabitant disappeared down the hole. But, a little patience, a mime-like immobile stance, a finger on the camera shutter, and, lo and behold, a portrait of a bubbler crab:

On the few areas of the beach not covered in the output of the bubbler crabs, all kinds of other tracks and trails were apparent:

I have no idea what critters made this calligraphy in the sand, but this was simply that day’s version of runes that have been etched in sediments and preserved in the rocks that they would become for billions of years. The study of trace fossils, these indirect testimonies to the business of life (think dinosaur footprints) has long made a key contribution to our understanding of our ancestors. I wrote a little about this a couple of years ago – see “Giant sand worms of Torbay.”

So, but one excitement of rambling on the beaches of Bangka. And here, a sample of those beaches, and of things to come:

[For a good description and more photos of sand bubbler crabs - family Ocypodidae, Scopimera sp. - see http://wildfilms.blogspot.com/2008/05/fiddler-crabs.html and scroll down to the bubblers.]

Comments

[Mark Dalrymple]

Although I did not make it to Bangka, this blog is a delightful escape from Jakarta! Any thoughts on preservation potential of the bubbler crabs' sand 'bubbles'? Perhaps not all geologically identified adhesion ripples / welts are such, and some ancestral crab is responsible? - Thanks Mike!

[Sandglass]

Given the constant revelations of the subtle roles of life on our planet, the boundary between organic (in the original sense) and inorganic seems to be becoming more blurred. And, given the mysterious runes and sculptures that we encounter in ancient sediments, who knows what some of these features might really be? So many features can be preserved when logic would say that they shouldn't be, my money's on the crabs.