MEPS 325:165-180 (2006)  -  doi:10.3354/meps325165

ABSTRACT: The influence of constant temperature on the survival and development rate of Upogebia africana and U. capensis larvae was evaluated in the laboratory. U. africana larvae were reared at 7 constant temperatures between 12 and 29°C, and U. capensis larvae at 6 temperatures between 11 and 26°C. U. africana larvae were also exposed to fluctuating-temperature regimes, some of which simulated fluctuations in nearshore marine waters off the ovigerous female collection locality, to determine whether regression models describing the influence of constant temperature on the cumulative larval period can be extrapolated to predict the larval period under temperature conditions typical of those in the natural environment. Larval development in both species comprised 3 zoeal stages prior to a metamorphic moult to the Decapodid. A stage intermediate between the Zoea 3 and Decapodid was occasionally detected at high temperatures (26 and 29°C) for U. africana, and at 26°C for U. capensis. U. africana larvae completed development to the Decapodid at all temperatures, with highest survival at 23°C. U. capensis larvae were unable to complete development to the Decapodid at 11°C, showing highest survival at 17°C. Stage-specific and cumulative duration of development in both species decreased sharply with increasing temperature until a threshold was reached, further increases in temperature having little additional effect on development rate. The temperature dependence of duration of development at temperatures below the threshold could be described by power functions for all zoeal stages as well as the cumulative larval period in both species. The thermal tolerance patterns for U. africana and U. capensis larvae agree well with geographical ranges of adults of both species along the southern African coastline, while differences in the optimal temperature for survival also agree with differences in their ranges. The effect of temperature fluctuations of the type simulated on U. africana larval development was expressed principally through variation in the rate of development, survival generally little affected, suggesting that U. africana larvae are physiologically well adapted to survive wide, rapid fluctuations in water temperature in the natural environment. Regression models describing the influence of constant temperature on the cumulative larval period appear to reliably predict the larval period under temperature conditions typical of those in the natural environment, with most reared larvae completing development at or shortly after the predicted period and with few exceptions within the predicted development period range.

KEY WORDS: Larval development · Temperature · Upogebia africana · Upogebia capensis