Shell morphometric relationships of the most common bivalve species (Mollusca: Bivalvia) of the Algarve coast (southern Portugal)

This study reports shell morphometric relationships (height/length and width/length) for the most common and abundant bivalve species of the Algarve coast (southern Portugal). The individuals were caught during periodic exploratory fishing surveys carried out during 2000 using artisanal fishing gears (clam dredge and razor clam dredge), on soft bottoms in the subtidal zone down to 25 m depth. For this particular study, a total of 7497 bivalves were sampled, belonging to 25 species distributed in 9 Families. Almost all regressions were significant (P <0.05 = 52%) or highly significant (P <0.01 = 44%), the only exceptions being the W/L relationships for two bivalve species (n.s. = 4%). The results revealed that both for height/length and width/length morphometric relationships most species presented positive allometric growth (H/L = 11 species; W/L = 15 species), followed by isometric growth (H/L = 7 species; W/L = 6 species) and by negative allometric growth (H/L = 7 species; W/L = 4 species). Data were compared with some morphometric relationships available for the same species in other geographical areas and several ecological hypotheses or explanations were formulated for the distinct types of growth exhibited by different bivalve species.