Effects of salinity on larval survival and development of the decorator crab Camposcia retusa and food consumption patterns of megalopae

The effects of salinity on the survival and development of zoeae and megalopae of the decorator crab, Camposcia retusa, were investigated by two separate experiments. When newly hatched zoeae were reared at salinities of 26, 29, 32, 35, 38, 41, and 44, all larvae died within 3 days when the salinity was ≤32. However, survival to megalopae was achieved for salinities of 35–44. Zoeal survival was significantly higher at salinities of 35 and 38 (81.7 ± 3.3 and 78.3 ± 1.7%, respectively) when compared to a salinity of 44 (61.7 ± 3.3%; p < 0.05). No significant differences in zoeal development duration were detected among all salinity treatments. In the subsequent experiment, newly molted megalopae were subjected to six salinity conditions (26, 29, 32, 35, 38, and 41). Megalopal survival to the first crab stage was highest when reared at a salinity of 32 (84.0 ± 11.7%), which was significantly higher than at salinities of 26, 38, and 41 (p < 0.05). Meanwhile, megalopal development was significantly shorter when reared at lower salinities (26–32) than when reared at higher salinities (35–41; p < 0.05). To better understand the underlying mechanisms of salinity effects on megalopae, the daily Artemia ingestion rate was measured throughout megalopal development for 30 megalopae cultured individually at one of three salinity conditions: low (27), optimal (32), and high salinity (37). The mixed-effects model analysis suggested that salinity significantly affected the feed intake of megalopae, especially during the first half of their intermolt duration (p < 0.01). The two-segmented regression of days of megalopal development and the cumulative Artemia consumption by individual megalopa showed that at the optimal salinity, the breakpoint in daily Artemia ingestion was 58.1 ± 3.8% of megalopal duration, which was significantly earlier than that recorded for megalopae reared under unfavorable salinities (73.6 ± 3.7% and 71.3 ± 5.4% for salinities of 27 and 37, respectively; p = 0.018). The results of this study reveal that salinity is a crucial factor that affects the larval survival and development of C. retusa, while a substantial difference in salinity preference exists between zoeae and megalopae.