Modulation of gregarious settlement of the stalked barnacle, Pollicipes pollicipes: a laboratory study

Although recruitment patterns of Pollicipes pollicipes (Crustacea: Scalpelliformes) in the wild have been inves- tigated, no studies have yet focused on the factors that affect settlement. In the present paper, settlement of P. pollicipes on conspecifics (gregarious settlement) was investigated in the laboratory as a function of environmental conditions (hydrody- namics, temperature, light and salinity), larval age and batch. This study aimed to understand how these factors modulate set- tlement in the laboratory and elucidate how they might impact recruitment patterns in nature. Maximum attachment on adults was 30-35%, with a one-week metamorphosis rate of 70-80%. Batch differences affected both attachment and metamorpho- sis. Attachment rate was higher at natural salinity (30-40 psu), with lower salinity (20 psu) decreasing metamorphosis rate. Cyprid attachment was stimulated by light conditions and circulating water. This might relate to a preference for positioning high in the water column in nature, but also to increased cyprid-surface contact in conditions of circulating water. Older cyprids (3 or 6 days) showed higher attachment than un-aged larvae, though fewer 6-day-old larvae metamorphosed. Tem- perature did not affect attachment rate, but the metamorphosis rate decreased at 14°C (compared with 17 or 20°C), implying that differences in temperature during the breeding season can affect how quickly cyprids metamorphose to the juvenile. Cyprids survived for prolonged periods ( 20 days; 40% survival), likely due to efficient energy saving by intercalating long periods of inactivity with fast bursts of activity upon stimulation.