Recruitment, growth and population size structure of Pollicipes pollicipes in SW Portugal

Abstract

A general model for the life cycle of Pollicipes pollicipes in SW Portugal is proposed integrating results from a study on recruitment, growth and population size structure. A brief summary of literature concerning Pollicipes published since Margaret Barnes' review paper of 1996 is presented.

Recruitment of P. pollicipes on conspecifics (number of cyprids and juveniles with Rostro-Carinal length (RC) < 0.6 mm per adult) was intense during summer and autumn, but inter-annual variation in the timing and duration of recruitment season was observed. Different indices of recruitment used in Iberian studies were compared. Spatial correlation between shores (not, vert, similar 40 km apart) in SW Portugal suggests that cyprids of P. pollicipes are being affected by the same larval pool and physical transport processes operating at this scale. Recruitment of P. pollicipes in SW Portugal was higher on the low shore (not, vert, similar 2.5 times) than on the high shore. Most recruits were attached to the lower half of the adult peduncle. The period of maximum attachment of juveniles (RC < 12.5 mm) to conspecifics was summer and autumn (average of 15 juveniles per adult), while spring was the season with a lower number of juveniles growing on adults (average of 2 juveniles). Size of juveniles attached to conspecifics was rarely greater than 6 mm RC.

Individual annual growth rate of P. pollicipes that settled on a denuded surface was 15.7 mm RC (individuals ? 1 year old) which corresponds to a monthly increment of 1.3 mm RC in their first year of life.

Size structure analyses of P. pollicipes attached directly to primary substratum and/or to the base of conspecifics showed that barnacles at the low tide level reached a higher maximum size, indicating that growth at this level was faster than on the high shore. A higher temporal variability between these size-frequency distributions was detected in spring (March to May). In March, two cohorts (< 1 year old, > 1 year old) were identified. In May and August, it was difficult to identify individual different cohorts. From mid autumn to early spring, as a consequence of recruitment of barnacles to the primary substratum, it was again possible to identify two cohorts.

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