The Waiting Stage, Prolonged Residency in Nursery Habitats by Juveniles of the Predatory Sea Star Marthasterias glacialis

Abstract

Growth and recruitment of the sea star Martha- sterias glacialis was followed over six years in Lough Hyne, southwest Ireland. Juveniles from a 2-mm radius were found on algae at <1–2-m depth following what appeared to be gre- garious larval settlement. Data from Lough Hyne and Mulroy Bay (northwest Ireland) indicated that algal habitat serves as a nursery area for juveniles of M. glacialis. Successive size fre- quency modes of the juveniles at Lough Hyne indicated slow growth over 6 years, to a mean radius of 20 mm. The absence of additional recruitment allowed monitoring of a discrete population. Recruits in the nursery habitat over the six years q2 remained as waiting stage juveniles, a Peter Pan group with delayed maturity subsisting on a diet of epibionts. An initial sharp decline in numbers indicated post-settlement mortality, with subsequent decline likely due to migration to the adjacent shelly habitat, where subadult M. glacialis (30–70-mm radius) lives. In this habitat, M. glacialis preys on small bivalves and eventually joins the adult (maximum radius 5 280 mm) popu- lation on open sediment, where it feeds on large bivalves. Size frequency distributions of the juveniles and adults showed growth over the six years, with the waiting stage sea stars slowly merging in size with the adult population. It appears that the supply of new individuals into the adult population may take place six or more years following settlement. Strong connectivity between life stage habitats and prolonged recruit- ment into the adult population may contribute to balanced ex- ploitation of infaunal prey.