The Larval Stages of Some Australian Species of Halicarcinus (Crustacea, Brachyura, Hymenosomatidae). II. Physiology

Five species of Halicarcinus were reared through complete larval development in the laboratory; of these, two species were tested in all combinations of four salinities and four temperatures. Upper temperature tolerance and tolerance of abrupt changes in salinity were also investigated.

Larvae of estuarine species, H. australis and H. paralacustris, complete their development over salinity ranges of 11.5‰-34.0‰ and 2.0‰-34.2‰, respectively, and temperature ranges of 13.1°-25.0°C and 13.0°-30.2°C, respectively. For each species there is a distinct region of optimum salinity-temperature conditions with 90-100 per cent survival. Salinity, temperature, and a salinity-temperature interaction strongly affect survival and duration of larval development and Q₁₀ values for rate of development are generally 2-3 in the range of highest survival. Temperature effects on larvae are influenced by the embryonic temperature regime.

Larvae of H. australis and H. paralacustris are more euryhaline and eurythermal than larvae of the marine H. ovatus, and they have shorter periods of development than those of H. ovatus and another marine species, H. rostratus, at similar temperatures. These differences are an adaptive advantage for estuarine habitation. Decreased surface-to-volume ratio and prolongation of the period of probable protection from osmosis, within the egg membrane, are physiological advantages of the absence of free larval stages in the freshwater species, H. lacustris.