INFLUENCE OF TEMPERATURE ON LARVAL SURVIVAL, DEVELOPMENT, AND RESPIRATION IN CHASMAGNATHUS-GRANULATA (CRUSTACEA, DECAPODA)

Larvae of an estuarine grapsid crab Chasmagnathus granulata Dana 1851, from temperate and subtropical regions of South America, were reared in seawater (32 parts per thousand) at five different constant tempera tures (12, 15, 18, 21, 24 degrees C). Complete larval development from hatching (Zoea I) to metamorphosis (Crab I) occurred in a range from 15 to 24 degrees C. Highest survival (60% to the first juvenile stage) was observed at 18 degrees C, while all larvae reared at 12 degrees C died before metamorphosis. The duration of development (D) decreased with increasing temperature (T). This relationship is described for al l larval stages as a power function (linear regressions after logarith mic transformation of both D and T). The temperature-dependence of the instantaneous developmental rate (D-1) is compared among larval stage s and temperatures using the Q(10) coefficient (van't Hoff's equation) . Through all four zoeal stages, this index tends to increase during d evelopment and to decrease with increasing T (comparing ranges 12-18, 15-21, 18-24 degrees C). In the Megalopa, low Q(10) values were found in the range from 15 to 24 degrees C. In another series of experiments , larvae were reared at constant 18 degrees C, and their dry weight (W ) and respiratory response to changes in T were measured in all succes sive stages during the intermoult period (stage C) of the moulting cyc le. Both individual and weight-specific respiration (R, QO(2)) increas ed exponentially with increasing T. At each temperature, R increased s ignificantly during growth and development through successive larval s tages. No significantly different QO(2) values were found in the first three zoeal stages, while a significant decrease with increasing W oc curred in the Zoea IV and Megalopa. As in the temperature-dependence o f D, the respiratory response to changes in temperature (Q(10)) depend s on both the temperature range and the developmental stage, however w ith different patterns. In the zoeal stages, the respiratory Q(10) was minimum (1.7-2.2) at low temperatures (12-18 degrees C), but maximum (2.2-3.0) at 18-24 degrees C. The Megalopa, in contrast, showed a stro nger metabolic response in the lower than in the upper temperature ran ge (Q(10) = 2.8 and 1.7, respectively). We interpret this pattern as a n adaptation to a sequence of temperature conditions that should typic ally be encountered by C. granulata larvae during their ontogenetic mi grations: hatching in and subsequent export from shallow estuarine lag oons, zoeal development in coastal marine waters, which are on average cooler, return in the Megalopa stage to warm lagoons. We thus propose that high metabolic sensitivity to changes in temperature may serve a s a signal stimulating larval migration, so that the zoeae should tend to leave warm estuaries and lagoons, whereas the Megalopa should avoi d remaining in the cooler marine waters and initiate its migration tow ards shallow coastal lagoons.