LAUSR

Thirty-one tidepools were sampled a total of 69 times and 4,104 fishes were collected from three separate Pacific coastal areas of Costa Rica. Sixty-five species were determined, weighed and measured according to tidepool. Biomass and species diversity for each area were plotted against depth, surface area, volume and a tidepool diversity factor which was determined from the informat­ ion theory formula. Only the relationship between species diversity and tidepool diversity for Playas del Coco showed significant correlation. At Playas del Coco and Rincon de Osa, rotenone poisoning of the same tidepools during successive low tides resulted in an increase in average fish length. At Tamarindo this was not evident. Biomass changes induced by successive rotenone poisonings varied among the three sites.