Creepy Crawlies and Mud
A global biodiversity “Hot Spot”
Mud-dwelling anemones are just one of a great many of the invertebrate wonders of Roebuck Bay. © 2009 Fiona Bishop. Press to enlarge.
The mud and sandlfats of Roebuck Bay are a haven for birds because it is teeming with a diversity of small invertebrate animals, like crabs, snails, shells and worms. Some crawling animals are not eaten by birds but add to the biodiversity and the ecological functioning of the bay. Brittle stars are an example. Some invertebrates are active when the flats are lying dry, and hide in burrows to escape predatory fish that come with the tide. Others become active when water full of food particles is coming in, but dig deeper in the mud when the water retreats to avoid drying out or heating up, and to escape the greedy bills of the birds.
Research undertaken by the Netherlands Institute has revealed that it contains some of the richest mudflats in the world in terms of biodiversity. International expeditions in 1997, 2000 and 2002 covered all of the intertidal flats with a fine grid of 1500 sampling stations. Many volunteers helped to sample and sort out all the material and pick out the tiny living animals. In total, about 30,000 animals were measured and indentified to about 265 species, a figure that will expand when specialists have sorted out the more difficult groups like the bristle worms.
A centre for research
Roebuck Bay is literally crawling with crabs. This one, Uca flammula, is a female Fiddler Crab. © 2009 Chris Hassell. Press to enlarge.
Through this major scientific effort, Roebuck Bay is now one of the most extensively sampled tropical mudflats in the world. Yet every year new animals are found in the bay, proving that its total richness of animal life is not uncovered completely. For example, the many samples taken during the research expeditions only covered the total surface of 40 square kilometres, a minuscule fraction of the whole intertidal area of the bay. Even in the samples taken, millions of tiny animals were flushed through the course (one millimeter) mesh of the sieves and escaped discovery.
One of many Brittle Star species on the bay. © 2009 Fiona Bishop. Press to enlarge.
The bewildering diversity of the Roebuck Bay mudflats is in stark contrast to that of equivalent habitats within temperate regions In the Wadden Sea in Western Europe for example, the diversity of bivalves is only a tenth of that of Roebuck Bay. There, the stress for animals due to the large changes in temperature, salinity and food over the course of a year must be even greater that at Roebuck Bay. In this context Roebuck Bay, with a world record number of species for a mudflat, is the more stable environment, although you would not say so while slowly sinking into the mud while sampling.