POPULATION-STRUCTURE AND REPRODUCTIVE PERIOD OF THE TROPICAL HERMIT-CRAB CALCINUS TIBICEN (DECAPODA, DIOGENIDAE) IN THE REGION OF UBATUBA, SAO-PAULO, BRAZIL

The population of the hermit crab Calcinus tibicen in the Ubatuba regi on was studied with emphasis on seasonal abundance, seasonal size-freq uency distribution, sex-ratio, and reproductive period based on the pe rcentage of ovigerous females. The animals were collected at 2-month i ntervals for 2 consecutive years (from January 1993 to November 1994). Total mean animal size in shield length was 5.14 +/- 1.23 mm for male s, 4.23 +/- 0.79 mm for females, and 4.53 +/- 0.60 for ovigerous femal es. A discontinuity in reproduction was observed, with an absence of o vigerous females in July (winter) and a high incidence from September to May (spring to autumn). Calcinus tibicen is sexually dimorphic in r elation to size, with a higher growth rare in males. The sex-ratio pat tern changes with season, indicating that it is more a function of sea son or habitat than of size.