Ecology of Pinna bicolor gmelin (Mollusca : Bivalvia) in Gulf St Vincent, South Australia: density, reproductive cycle, recruitment, growth and mortality at three sites

Abstract

Random samples of P. bicolor were taken from one intertidal and two subtidal sites over 3 years and tagged individuals of P. bicolor were followed for up to 6 years at two other sites. P. bicolor is dioecious. Mature gonads were observed in early summer (November-January) with a peak in December each year. The pattern appeared to differ little between years or sites but the period of maximum gonad activity was shorter at the intertidal site. Growth was slower at the intertidal site and animals reached a smaller maximum size there than at the subtidal sites, which differed slightly. It is concluded that P. bicolor can reach reproductive size (15 cm shell length) in little more than a year but, at least subtidally, have a low mortality rate (less than 0.1 year-1) thereafter. Recruitment is variable and it is argued that at some sites superficially 'stable' densities of P. bicolor are maintained by occasional strong recruitments, which are 'stored' in the population because of low adult mortality. The implications of this for management and for the use of P. bicolor as a biological monitor are discussed.