Reproduction and Growth of the Terebratulid Brachiopod Liothyrella neozelanica Thomson, 1918 From Doubtful Sound, New Zealand

The reproductive cycle and growth of the temperate New Zealand rhynchonelliform brachiopod Liothyrella neozelanica was examined over 12 months (December 2010 and December 2011). The research aimed to clarify the spawning cycle, life history, population size, and age structure of L. neozelanica and to enable more direct comparisons with the Antarctic brachiopod Liothyrella uva. Reproduction over the course of a year was quantified by monthly examination of gonad size and gametogenesis. Histological examination indicated a seasonal cycle with prolonged, potentially asynchronous spawning. Increased numbers of large oocytes in July followed by a significant decrease in September suggest that female spawning takes place in early austral spring. A decrease in the proportion of the gonad area occupied by sperm during September suggests a level of spawning synchrony between sexes. Somatic growth was modeled from 60 tagged individuals. A maximum size of approximate to 50-mm shell length is achieved at 17 years of age, and instantaneous growth is highest in juveniles (9.7 mm yr(-1)). Mortality rate was estimated from the age distribution at an instantaneous rate of 0.14 yr(-1). A left-skewed size-frequency distribution implies high mortality in juveniles.