Seasonal Effect of Heavy Rains on the Population Density of Australorbis Glabratus in a Puerto Rican Watershed

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A study was made of the seasonal effect of heavy rains and consequent flooding on the abundance of Australorbis glabratus in a 4,500-foot section of the Guaynabo River in Puerto Rico.

Twenty-two floods varying in degree were noted during a 17-month period. Of these, only five or possibly six were of sufficient magnitude (25 inches or more rise in water level) to decimate the stream snail population. Recovery after such severe storms was rapid in spite of repeated floods of a lesser degree (5–18 inches). It is suspected that upstream lateral seepage areas which serve as permanent breeding foci for the snail may play a role in repopulation of the main stream following severe floods.

Author Notes

Present address: Department of Biology, Middlebury College, Middlebury, Vermont.