A calibration method to generate seasonal hatching profiles for the fiddler crabs Uca pugnax (Smith, 1870) and Uca minax (LeConte, 1855) (Decapoda : Brachyura)

A statistical method for generating seasonal egg hatching profiles is applied to the brachyuran crabs Uca pugnax (Smith) and U. minax (LeConte) in New Jersey. Calibration experiments quantified the time course of egg development, using serial egg sampling at 1- to 2- day intervals from marked ovigerous females maintained in cages in the field. Egg stage was ranked from 1 to 10, based on morphological changes during development. Equations for predicting the number of days remaining until hatching from egg developmental stage were obtained from the calibration experiments, using stepwise polynomial regression. To cover the reproductive season, three consecutive calibration experiments using 15 or more females were run for U. pugnax; two for U. minax. Significant seasonal differences in the time course of egg development were detected. Weekly collections of females for each species were made; the date of larval release for each ovigerous female was predicted from the proximate calibration equation, yielding weekly hatching profiles. Weekly hatching profiles were summed to obtain seasonal hatching profiles. The average number of broods produced per female over the reproductive season was 1.9 for U. pugnax and 1.6 for U. minax. Hatching peaks for both species were associated with spring tides. The merits of this and other methods used to estimate daily variation in egg hatching of crabs are discussed.