Positive effects of large concentration in culture on the development of the lecithotrophic larvae of Babylonia formosae (Sowerby) (Prosobranchia: Buccinidae)

Abstract

The negative effects of large larval concentration on larval development have been reported for many marine planktotrophic invertebrates. Comparable data for the lecithotrophic species are, however, not available. The present study was therefore undertaken to determine the influence of varying larval concentrations on the developmental performance of Babylonia formosae (Sowerby). The larvae of B. formosae were cultured at four concentrations: 1, 2, 4 and 8 larvae ml−1. Over the 6-day experimental period, the cumulative percent settlement increased from 73, 83, 89 to 95%, and the mean settling time decreased from 3.88, 4.46, 3.62 to 3.21 days as the concentration increased from 1, 2, 4 to 8 larvae ml−1, respectively. What was found was a positive correlation between larval concentration and cumulative percent settlement (Y=74.35+2.80X; R2=0.61; p<0.01) as well as a negative correlation between larval concentration and mean settling time (Y=4.31−0.14X; R2=0.59; p<0.01). It was hypothesized that lecithotrophic larvae accelerate their developmental rate to shorten the suboptimal planktonic period and to minimize substrate competition with increased larval concentration. When juveniles were reared at 0.2 individuals ml−1 in one experiment, they all survived regardless of the concentration at which larvae were reared, and no significant difference was found in the cumulative increment of shell length on days 4, 8, 12 or 16. The mean growth rate was 39 μm d−1. In a second experiment, however, juvenile mortality was 37 to 47% when juveniles were reared at higher concentrations (1 to 8 juveniles ml−1). The juvenile growth rate also decreased from 29, 26, 23 to 18 μm d−1 as the concentration increased from 1, 2, 4 to 8 juveniles ml−1, respectively. The cumulative increment of shell length in different concentrations was significantly different on day 16 (P<0.05), and there was a negative correlation between juvenile concentration and cumulative increment of shell length (mm) (Y=0.469−0.024X; R2=0.12; P<0.01). Although juveniles clearly do better at low juvenile concentrations, the experiences of planktonic larval concentration may influence the rate of early juvenile growth was not indicated.