A massive aggregation of the mangrove snail Bakawan rotundata (A. Adams, 1850) (Cephalaspidea: Haminoeidae) in India

In this work we report on a mating aggregation of the marine mangrove dweller gastropod Bakawan rotundata (A. Adams, 1850), observed in the Sewri mud flats near Mumbai in western India. From October 2018 the area has been surveyed monthly for its biodiversity composition. In April 2019, large amounts of snails were observed and their abundance was quantified with quadrates of 0.25 m2 along three parallel transects and sampling in three ecologically distinct zones: high tidal zone (HTZ), mid-tidal zone (MTZ), and low-tidal zone (LTZ). An average of 2117 ± 989 individuals/m2 was estimated for the HTZ, 651 ± 284 individuals/m2 for the MTZ, and 202 ± 48 individuals/m2 for the LTZ. Abundances in May dropped drastically with snails only present at the HTZ (59 ± 55 individuals/m2). Previous to April and after May no unusual numbers of individuals were seen in the mudflats. This is the first time an aggregation of this scale is observed in the genus Bakawan and it is one of the largest aggregations documented among gastropod molluscs. •Mating aggregations of marine gastropods in India.•One of the largest aggregations of marine snails ever documented worldwide.•Preference for high-tidal areas for aggregation.