Population dynamics of Dynoides (Crustacea: Isopoda) in the Cape d'Aguilar Marine Reserve, Hong Kong

An undescribed species of Dynoides occurs on exposed rocky shores, inhabiting beds of the mussel Septifer virgatus, empty barnacle, Tetraclita squamosa squamosa, shells, as well as clumps of the algae Dermonema frappierii, Pterocladia tenuis, Chaetomorpha antennina and Ulva fasciata in the Cape d'Aguilar Marine Reserve, Hong Kong. The population dynamics of this species had been studied in this reserve. The maximum body length of Dynoides sp. was 7.9 mm for males and 5.5 mm for females. At hatching, juveniles were 0.9 mm long and 0.5 mm wide and sexually indistinguishable. Sexual characters appeared in males with the emergence of a pair of short penises or a median process projecting from the postero-dorsal margin of the pleon, and in females with the appearance of three pairs of triangular oostegite buds at the bases of pereiopods 2-4. Recruitment occurred at three times in May, September and December. Ovigerous females were present throughout the year with peaks reaching 91% of the total complement of females in warm months and lows of 25% in cold months. Isopods grew and matured faster from spring to late autumn and attained overall smaller body lengths. They grew slower in winter though attained larger sizes. The fecundity of Dynoides sp. ranged from 26 to 56 eggs per brood, correlated with body length of the ovigerous females. The first juvenile molt occurred 25 days after hatching and newly released juveniles were photopositive in the laboratory and capable of swimming.