The mysterious multitude of holes

The sand flats of Deeban Spit resembles a lunar landscape pockmarked with craters. All agree that they are a sign of life, but there is some mystery as to which form of life is active here.  There are the obvious human makers of holes who descend on a fine fishing day to pump bait from the sand. They carry a stainless steel cylinder to jab into the wet sand and extract a core of sand which is then dumped on the surface for inspection. The fisher person is only interested in finding nippers, the ghost shrimp Trypaea australiensis. The nipper is a bountiful little crustacean that is a natural food source for estuarine fish and makes good live bait. Research done here in 2004 estimated that 4500 nippers are extracted from the sand in Maianbar on a typical weekend day in summer. That is a lot of nippers and a lot of holes made in the sand. The good news is that despite the pumping less than 2% of the total stock of nippers are removed by bait pumping. (Rotherham 2004) And yet this does not explain the vast bulk of holes in the sand. The sand is like a whiteboard, each incoming tide goes some way to erasing the marks made before. Holes made last summer may be hard to find. Depending on the strength of the current and the action of the water all holes will be filled and levelled in time. Yet new holes appear, thousands of holes, even when there is no fishing and pumping for bait. Fresh holes appear in the winter when a fisher person is not seen for weeks. Other life is obviously at work.

If I was to begin my life again as a student in search of serious study I could do worse than measure all the holes on Deeban Spit.  Each imprint in the sand is a sign of life that communicates some activity. The sand reveals an interactive pattern of movement, of feeding, of hunting and hiding. The traces in the sand can be deciphered and the holes would be the basis of this study.

At the outset I would probably try to save myself some effort by finding a system to sample the holes, then I could avoid measuring every single hole and extrapolate answers from a limited study. This need to form an answer by sampling is central to scientific research of all kinds and is in itself a science, call it statistics. If the entire sandflat is one uniform canvas evenly covered in holes it would be easy to sample, a study of one small area could be scaled by multiplication to arrive at an answer for the whole area. This would be too simple and no fun at all. The real world is rarely uniform and patterns of all types are recognisable. Perhaps the most useful pattern in statistical studies is the idea of the random pattern, where there is no particular order in things. In physics this might be compared to entropy and the famous second law of thermodynamics in which the universe winds down to a bland nothing-much-happening-here lifeless energy-free state. Life itself is a system of order and living things are not often following random paths. And so we can use the random concept as a tool to measure living systems. By comparing measurements taken from the real world to random patterns we can assess whether there is some order that needs investigation. This is the basis of fundamental statistical models, is there a variation in the real numbers that differs from a hypothetical random set of numbers? If you can believe this then you can believe in science as it is practiced today.

Back to the holes.

Some guesswork

1/  I think the holes would fall into size categories – there would not be a random pattern of holes from pinprick sized to the size of Fishermans bay itself. There would be clusters of holes that conform to different types of animals. The burrows of nippers would cluster around one range of sizes and the holes of soldier crabs would cluster around another range of sizes. All the animals that make an imprint in the sand would leave a set of holes that would form groups of numbers that are not random. There may be overlap between different animals, but there would be distinct size classes.

2/ The distribution of the holes across the landscape would not be random. Different animals have different ranges and so we would not expect to find evidence of all animals in all places. We would expect to find clusters of holes in different zones of the environment.

These two simple expectations form the basis of ecological study; the abundance and distribution of life. But a theoretical framework is complimented by the simple act of observation. I have seen animals make similar marks to these and so I believe that these marks are made in a similar way. A little faith is always necessary.