Rheotaxis and hygropetry governs the behaviour of Pirenella cingulata populations on a tropical mesotidal mudflat

Foraging epibenthic gastropods (Cerithiid horn snails) on the intertidal mudflats have a significant ecological function in terms of organic matter remineralisation. Vast coastal mudflats get inundated and exposed daily with varying degree of tidal cycles temporally influencing the distribution of cerithiid population. We identify the microhabitats of cerithiid's active feeding movement on the mudflats for a period of one and half year and discuss the noteworthy reasons for avoidance of mudflat regions by these populations. Empirical field data on population densities was plotted for two tropical coastal mudflats using GIS tools depicting their monthly distribution pattern. Cerithiid had active foraging movement on the 'hygropetric' sediments (surface with a film of water) in contrast to sluggish or no movement on dry sediment. The flow velocity on mudflat as a function of tidal egress resulted in behavioural response of negative 'rheotaxis' by P. cingulata - predominantly a movement for avoiding flow velocities. Dry sediment surface imposes physiological stress and areas with high flow velocities expend energy of individuals for resisting drift due to tidal flow; these together mark the functional limits for cerithiid population beyond which they showed impaired foraging. With each tidal regime over seasons profoundly compress and expand the foraging landscape of cerithiid populations and ultimately modulate their behaviour on such mesotidal mudflats.