Behavioural traits of competent Concholepas concholepas (loco) larvae

Swimming activity of competent Concholepas concholepas (Bruguiere, 1789) larvae, under different photoperiod, water turbulence and settlement cues were investigated in laboratory experiments. At night, larvae mainly swam to the water surface and then sank passively to the bottom. During the day, regardless of the photoperiod, larvae mainly stayed on the bottom, occasionally exhibiting upward movements. During the swimming period, larvae displayed the capacity to adhere to floating substrata through several mechanisms, including the secretion of a long and sticky mucous thread, air bubble capture or taking advantage of the water tension. The presence of C. concholepas prey, such as the mussel Semimytilus algosus and the chthamaloid barnacle Notochthamalus scabrosus, significantly influenced the swimming activity of competent C. concholepas larvae, inducing them to stay close to the bottom where prey were present. C. concholepas prey also triggered the initiation of larvae crawling, a characteristic of the early benthic life of C. concholepas. Although our laboratory experiments are proxies of nature, they are in good agreement with field observations in shallow nearshore areas (< ca. 0.5 km from shore) that recorded higher abundances of competent C. concholepas larvae (which are often associated with floating substrata) captured by surface planktonic tows during the night rather than day. Similarly, competent C. concholepas larvae abundances were higher in tows through inner nearshore foam slicks than in non-slick areas. The results suggest that the presence of endogenous swimming behaviour in these larvae may be a key factor enhancing adherence to floating substrata. The laboratory discovery of vertical buoyancy provides new information leading to a better understanding of the distribution and abundance patterns of these larvae in inner nearshore waters.