Evaluating growth and age of netted whelk Nassarius reticulatus (Gastropoda: Nassariidae) using statolith growth rings

摘要

The periodicity of growth rings in the statoliths of Nassarius reticulatus (Linnaeus, 1758) was validated using laboratory-reared larvae and juveniles of known age. Formation of the first ring occurred at larval settlement and subsequent rings were deposited annually. Wider light increments formed between March and June when seawater temperatures increased from 10.9 to 19.4℃, whereas darker narrow rings formed between the late summer and winter. Counts of the annual statolith rings were used to determine the age of N. reticulatus collected from six locations around the Anglesey coast, North Wales. The oldest whelks, 7 and 6 yr respectively, occurred in a sheltered lagoon at Rhosneigr and from a sheltered area between Cemlyn Bay and Carmel Head. Lack of geographical variations in settlement ring size suggests that the larvae spend a similar period of time in the plankton before settlement. Significant differences in the diameters of the annual rings indicate that wave exposure and food availability may affect growth at different locations. The relationship between statolith diameter (SDi) and shell length (ShL) for larvae, juvenile and adult N. reticulatus (0.3 to 31 mm) was SDi (μm) = 36.31 × ShL (mm)~(0.464). No statistically significant differences in this relationship were found amongst the 6 Anglesey locations or between whelks of different gender. Using the equation, ShL at formation of each annual ring was estimated, and von Bertalanffy growth (VBG) curves fitted to the length-age data. Whelks from the sheltered Rhosneigr lagoon had the highest asymptotic maximum ShL (L_∞ and the lowest growth constant (K), suggesting a slow growth over a period of time. Growth rates of males, females and imposex-affected females were similar.