Late maturity and evidence for female biennial spawning in the sea pen Pennatula aculeata (Anthozoa, Pennatulacea) in eastern Canada

Abstract

Little is known about reproduction of the sea pen Pennatula aculeata, which is found at high densities and constitutes vulnerable habitat in the Gulf of St. Lawrence, Canada. Sex ratio, size at maturity, and reproductive status were investigated for colonies collected in May, August, and October 2015 along the Gaspé Peninsula. Reproductive status was assessed by histological determination of gamete sex and maturity and by stereomicroscope measurement of the diameters of the leading cohort of oocytes (LCO) or sperm cysts of histologically mature colonies. Colonies were gonochoric, with a sex ratio of 1:1. Based on the distribution of gamete diameters in May, three groups of female and a single group of male colonies were identified. Female colonies classified in the group of LCO with the smallest diameter (0.10–0.39 mm) were shorter in total length (TL < 130 mm) than females in the other two groups of LCOs with larger diameters, and very few spawned from May to October. A major reduction in the proportion of large female colonies (TL ≥ 130 mm) belonging to the group with the largest diameter (≥0.55 mm) and of mature male colonies between May and August indicated one annual spawning event. Persistence of histologically mature (vitellogenic) female colonies classified in the two smaller oocyte diameter groups after spawning is indicative of prolonged oogenesis (at least 24 months). The fact that only approximately half of the large female colonies had ripe oocytes (diameter ≥0.55 mm) in May prior to spawning, while the other half had vitellogenic oocytes of much smaller diameter which persisted after the spawning period, suggests that they reproduce only every other year. Estimated size and age at which 50% of colonies spawned were greater in females (148 mm TL, 11–14 years) than in males (101 mm TL, 8–11 years). These reproductive characteristics may reduce resilience of P. aculeata to various anthropic stressors.