Morphological and commercial quality variation of the stalked barnacle Pollicipes pollicipes: Patterns and drivers

Abstract

Fishers and consumers recognise that there is important variation in the morphology and quality of the stalked barnacle Pollicipes pollicipes. Two extreme phenotypes can be identified: thick/short barnacles associated with a high commercial quality; and thin/long barnacles associated with low commercial quality. This work describes morphological/biochemical differences between the two extreme phenotypes, and investigate the main drivers causing these differences. The perception of the variation in quality and morphology of P. pollicipes by scientists and fishers was similar. The ratio of the width of the capitulum base to its total length (CB/TH) was used and validated as a good proxy variable for evaluating quality. There were no significant differences in the individual biomass of high and low quality barnacles. The biochemical composition of the edible part of P. pollicipes of high commercial quality barnacles presented a higher protein, energetic value and fat, and low commercial quality barnacles presented a higher water content. Regional differences were also detected in the biochemical composition of P. pollicipes. On the SW coast of Portugal (SW), barnacles presented a higher ash, protein and water content, and a lower glucose and energetic value, than in two regions of the centre coast. The influence of potential drivers of variation in morphology/quality of P. pollicipes was tested through a manipulative experiment. The results suggest that the elongation of P. pollicipes is related to the greater density of the barnacles on a group scale. Furthermore, the shortening of P. pollicipes may be related to the lower density of the barnacles at the group scale and to specific microhabitat environmental conditions, such as hydrodynamics. The variation in the quality/morphology of P. pollicipes that was recognized by fishers and scientists, was associated with a different biochemical composition. Density and specific local conditions were identified as drivers of this variation.