Spatial and size distributions of early recruits of Cucumaria frondosa in a coastal nursery (Nunavut, Canadian Arctic)

The discovery of nursery sites of the sea cucumber Cucumaria frondosa in the Canadian Arctic offers opportunities to gather knowledge on the ecology of juveniles. Here, their size and spatial distributions were examined and inter-individual and inter-specific relations were assessed. Out of 893 juveniles collected between 1 and 3 m depths in the fall, 95% were early recruits (<1-year-old). They chiefly occurred on rubbles (~80%) representing the main substratum (~49%) in the nursery. The length of early recruits across all depths was ~1,520 μm, with the smallest found at 3 m (~1,407 μm). Fewer recruits were identified in the following spring (51.5%), allowing the calculation of a growth rate (~114 µm mo −1 ). Their density was consistently ~7,400 ind m² across depths. Juveniles were mostly found aggregated on flat surfaces (62.7%) or in shallow depressions (18.4%) on the underside of the stones, but also occurred on seaweed holdfasts (2.7%). The nearest neighbour distance was ~0.37 cm, with some juveniles touching each other. More individuals were observed with their body oriented in the same direction (45%) than in opposite directions (25%). Four sympatric species were identified on the same substratum; the polychaete Spirorbis spirorbis (49.7%), encrusting bryozoans in order Cheilostomatida (40.5%), the limpet Testudinalia testudinalis (6.9%), and calcareous encrusting algae (2.9%). Data on newly settled sea cucumbers in the wild are rare. The present findings provide essential information on the population dynamics and carrying capacity of C. frondosa in support of local subsistence harvests and emerging small-scale commercial fisheries led by the Inuit community. • Juveniles in the nursery were mostly found aggregated under rubbles at 1–3 m depths. • A first ever growth rate of new recruits in the wild was determined (~114 µm mo −1 ). • Analysis of fall and spring cohorts showed that juveniles exit the nursery at ~6 mm. • Four species co-occurred with the juveniles on the underside of the stones.