Growth and reproduction of Cyclograpsus pumilio(Brachyura: Varunidae) on a cobble shore in Suruga Bay, Japan

Abstract

The life history characteristics of the varunid crab Cyclograpsus pumilio were studied by monthly sampling at a cobble shore in Ooigawa Port (34°46′35.2″N, 138°17′59.3″E), located in the inner part of Suruga Bay, Japan, between March and December 2017. A total of 964 individuals were collected, including 410 males (2.91–5.90 mm carapace width, CW) and 554 females (3.81–10.30 mm CW). The number of individuals collected exceeded 100 each month until August and then abruptly decreased to<10 per month. The monthly frequency distribution of mode CW showed no temporal changes in males and a slight decrease in females, from 9.5 mm in March to 7.0 mm in October. Smaller females of CW<4.5 mm were obtained between April and August. The changes in the relative growth of propodus height in males and abdominal width in females versus CW were determined by model analysis. The sizes at morphological maturity were estimated to be 3.98- and 6.39-mm CW for males and females, respectively. Ovigerous females with CW 6.92–9.29 mm (n=18) were obtained between June and August and again in October. During the study period, the population of C. pumilio in Ooigawa almost went extinct due to habitat loss in September, when a layer of cobbles collapsed following a typhoon. This local population was characterized by very low proportions of ovigerous females (<11%) each month, lower and variable batch fecundity, and shorter recruitment period compared with the proportions found in other areas.