EFFECTS OF TEMPERATURE ON THE EMBRYONIC AND EARLY LARVAL DEVELOPMENT OF HIGH-VALUED TROPICAL SEA URCHIN, Tripneustes gratilla (LINNAEUS, 1758)
Global warming has and will to be continued to warm the world's ocean, which may have unfavorable significances for oceanic bio-resources. Temperature is one of the most important factors affecting the normal functioning of marine invertebrates, especially for sea urchin, i.e. living in shallow tidal water. Studies weighing the impact of climate-change stressors on early life stages of marine invertebrates have focused on immediate fertilization success or larval development, but have so far not been considered gamete longevity. The study was evaluated the effects of different levels (16, 19, 22, 25, 28, 31, and 34oC) of temperature on the embryonic and early larval development of high-valued tropical sea urchin, Tripneustes gratilla. The growth performances of the larva were investigated in a wide range of water temperature between 16oC and 34oC under an organized laboratory condition. The critical lower and higher temperature for embryonic development was found at 16oC and 34oC, respectively. Embryos reared in both of these two temperatures exhibited 100% abnormality within 48 h post-insemination. The time required to reach these embryonic and larval stages was increased with temperature treatments from 28oC followed by 31oC, 25oC, 22oC, and 19oC each and individually. The developmental times of 2-cell stage until 4-arm pluteus larvae showed significant differences (P < 0.05) among the temperature levels evaluated. The larvae in the stage of prism and 2-arm pluteus were survived at temperature ranges from 19oC to 31oC, while 4-arm pluteus larvae survived at temperature from 22oC to 31oC. In regards of survivality, the survival rate of different stages of the larvae was observed in dissimilar at different temperatures (220C to 430C), and the highest values of survival at prism, 2-arm and 4-arm stages were always found at 25oC and 28oC temperatures. However, the development of larvae within the temperature range from 22oC to 31oC revealed that they were able to tolerate a wide range of temperature without getting any abnormality. The morphometric characteristics from prism to 4-arm pluteus larvae in all temperature treatments were differed significantly (P > 0.05). Among the temperatures evaluated, 28oC was found to be the best temperature in respect of highest growth and development of larvae in all stages. The findings appeared from our study will not only be helpful to understand the critical limits of temperature but also to find out the appropriate suitable temperature levels for the optimum growth and development of embryos and larvae as well as to facilitate us to develop captive breeding and mass seed production of economically important sea urchin (T. gratilla) and other important marine invertebrates for aquaculture in commercial scale.
Key words: Tripneustes gratilla, Temperature, Effect, Breeding, Embryo, Larvae, Development.