Pea crabs (Pinnotheres pisum) colonisation of five commercial bivalve species from southern Portugal

Abstract This study reports the spatial and depth distributions, occurrence and prevalence, infestation rate and intensity of the pea crab Pinnotheres pisum colonising five commercial bivalve species (Chamelea gallina, Donax semistriatus, Donax trunculus, Donax vittatus, and Spisula solida) along the south and southwest coasts of Portugal. In addition, the study also analysed the colonisation pattern, morphometric measurements and relative growth of P. pisum inhabiting those bivalve species. Overall, 33,370 bivalves were analysed, collected in 371 sampling stations at depths ranging from 3 to 25 m. A total of 102 bivalves hosted 106 P. pisum, corresponding to an infestation rate of 0.31%. Besides 13 juveniles, were recorded 60 males and 33 females of P. pisum, corresponding to a male-biased sex ratio (1M: 0.6F). Pea crabs carapace width ranged from 1.3 to 13.5 mm and males were smaller than females (hard females were also smaller than ovigerous soft females). In general, larger and heavier bivalves hosted larger and heavier P. pisum. Pea crabs morphometric relationships presented negative allometries, reflecting slower growth rates in carapace length and total weight compared to carapace width throughout the species ontogeny. Overall, this study provides valuable insights into diverse descriptors of bivalves' colonisation by P. pisum, comparing the main results and trends with analogous information available throughout the species distributional range. Although the current fairly low infestation by P. pisum does not constitute a health concern for these bivalve species, its evolution under a climate change scenario should be periodically monitored in the mid- and long-term.