Abstract
Global climate change is transforming life on earth, causing widespread effects on all ecosystems. Among marine ecosystems, estuaries are considered as nursery grounds for marine and fresh water species. M. rosenbergii, a euryhaline species, migrate to the estuaries for breeding and spawning. The subsequent larval rearing takes place by experiencing variations in temperature and salinity conditions. The present study examines the effect of different temperature and salinity on the larval development and survival by observations on stored yolk utilization, cardiac performance, as well as changes in the rate of growth in body appendages and larval activity. The larvae showed 100% mortality at higher temperature (33.5 ± 0.5 °C) in all the salinity conditions (12 PPT, 15 PPT, and 20 PPT). The survival rate varied between 76-96 % on exposure to lesser temperature conditions. Likewise, the post-embryonic yolk lasted for 4 days at ambient temperature (29 °C); whereas, at 33.5 ± 0.5 °C, it lasted only for 2-3 days. There was an increase in total length of larvae, when exposed to higher temperature and salinity, independently or in combination, but at 33.5 ± 0.5 °C under all salinity conditions the larvae died on the 5th day. For the cardiac performance, larval heart beat (fH) significantly increased for higher temperature and salinity conditions (20 PPT; 33.5 °C) and lowered at ambient condition 12 PPT; 29°C. Larval stroke volume Vs, and Cardiac output Q□ were higher in ambient conditions and lowest in higher temperature and salinity conditions. However, temperature and salinity together did not show any significant effect on cardiac performance. On the other hand, the larval activity decreased significantly at higher temperature and salinity conditions, compared to ambient conditions but the interactive effect did not show any change. Thus, the physiological responses to temperature and salinity by the early life stages of M. rosenbergii could restrain the tolerance capability of the organism, thereby interfering in the successful completion of the larval development under the altered climatic conditions.
