In situ growth rate of Solen cylindraceus (Mollusca: Euheterodonta: Solenidae) in the St Lucia estuarine lake, South Africa

Soien cylindraceus, an infaunal bivalve, can reach a maximum length of 95 mm. However, in the St Lucia estuarine system specimens are seldom larger than 55 mm. Thus, the primary aim of this study was to investigate the growth rate and morphometrics of S. cylindraceus in St Lucia. Growth lines of this species are too indistinct and irregular to be of any use. This study, therefore, adopted a more direct method of monitoring the shell length of individuals, by caging them in situ. Shell measurements were taken from the individuals in cages and the surrounding environment at monthly intervals for one year. Thereafter, salinities decreased below their tolerance range and the experiment was terminated. Caged and uncaged animals had a shell length of 31.0 +/- 4.5 and 31.7 +/- 2.3 mm after a year of growth, respectively. An overall growth rate of 0.049 +/- 0.059 mm/d was derived for the caged animals. In conclusion, first year growth rates appeared lower than previously recorded for S. cylindraceus. Additionally, it appears that animals are unable to survive in the prevailing harsh environment of St Lucia to reach maximum size.