Natural wonders #3

I was hoping to take a photo of the little blue crabs which covered this beach the last time we went in February 2011. 
Today there wasn't a crab in sight; instead the beach was covered in these tiny whelks (?) which were crawling creepily
in all directions. Will try for the crabs again either at a different time of day (not 1.45pm) or during a different season (Chinese New Year again).