Reproductive ecology of the estuarine burrowing mud crab Helice crassa (Grapsidae)

Abstract

The reproductive cycle and population biology of the endemic, burrowing mud crab Helice crassa Dana, 1851 (Brachyura, Grapsidae) in the Avon-Heathcote Estuary (44°33′S, 172°44′E), Christchurch, New Zealand, was studied from April 1975 to December 1976. Juvenile crabs (≤4 mm carapace width) were present throughout the year, but were most numerous from February to April. Males of all sizes (4.1–18.0 mm carapace width) were significantly (tested by χ 2 ) more abundant than females and the overall sex ratio was 1.48♂♂: 1♀. Maximum carapace widths were 17.7 mm for male crabs, 15.8 mm for non-ovigerous females and 15.1 mm for ovigerous females. Ovigerous females occurred from August/September to March with maximum numbers present in November. Peaks of egg production were found in October and January. Egg volume at oviposition was constant throughout a breeding period; however, eggs from August–November 1975 ( volume=0.0099 μl±0.0032) had a significantly larger volume ( t =3.68, P <0.01 for 45 D.F.) than those from September–December 1976 ( volume=0.0074 μl±0.0021). Eggs did not increase in volume during development and had no measurable mortality. Egg numbers were not affected by season and were related to female carapace width according to the equation y =−13931.8+1890.8 x ( r 2 =0.886). These findings are compared with studies on the reproduction of this species from marine habitats elsewhere in New Zealand, and are considered with respect to the influence of latitude and environment on the breeding biology of H. crassa .