Comparison of multiple techniques to evaluate reproductive variability in a marine bivalve: application to the scallop Pecten novaezelandiae

Abstract

Reproduction and spawning of the scallop Pecten novaezelandiae were monitored at four sites in the Hauraki Gulf, New Zealand, from July 2000 to July 2001. A visual grading system based on the macroscopic appearance of the gonad was developed and tested, and changes in visual grade, quantitative histology, and standardised gonad mass were used to describe seasonal and spatial patterns in gametogenesis and spawning. Visual grade was significantly correlated with histological and gonad mass data (r 2 = 0.74–0.87) and validated as an accurate method for measuring reproduction in P. novaezelandiae. Visual grading facilitates rapid assessment of reproductive condition and can be conducted non-destructively, thus providing a tool allowing long-term studies of individual spawning behavior in relation to environmental signals. Scallops exhibited episodic spawning, with spawning events detected in spring, summer, autumn, and even early winter. Gonad recovery and subsequent gamete development and maturation were apparent between spawnings. Within-season variability in gonad size and condition could be the result of multiple (serial) spawnings during a season. The timing of spawning varied among populations, probably reflecting differences in environmental conditions that influenced reproduction. However, the largest spawning events occurred at all sites in early summer (December/January), coincident with wind-driven upwelling conditions.