CATTON, Cynthia A.; Univ. of California, San Diego: Temperature effects on the larval duration of the Wavy Turban Snail, Megastraea undosa (Wood, 1828) (Gastropoda: Turbinidae)

Megastraea undosa is a large herbivorous gastropod, reaching basal diameters up to 150 mm, making it a prime target for commercial and recreational harvesting. Its range is limited to the region between Pt. Conception and southern Baja California, where it is common from the low intertidal zone to depths of approximately 35 m. In the San Diego area, the temperature within this depth range varies between 10°C and 24°C throughout the year. The coldest temperatures are realized during the spring upwelling season ending in June, before the reported start of the local spawning season in late June and July. In order to test the effects of this broad temperature range on the larval development and settlement, larvae were reared in four different temperature treatments: 10°C, 15°C, 20°C, and 25°C. Eggs in the 10°C treatment developed abnormally beyond the first cleavage, whereas normal development proceeded in all of the other treatments. Growth rate increased with increased temperature. By day 2, the majority of larvae in the two warmer-water treatments reached the �-whorl stage, potentially indicating competency for settlement. The larvae in the 15°C treatment reached that stage between day 3 and 4. On the fourth day, a small coralline-covered rock was added to each container of larvae to induce settlement. The response time to this settlement cue was faster in the warmer-water treatments. All larvae in the 25°C treatment settled within three days of induction. The maximum time to settlement in the 20°C treatment was 5 days, and 8 days in the 15°C treatment. These results suggest that the larval duration of the species may range between two and eleven days depending on the temperature of the water at the time of release.