Morphometrics, Growth and Condition of the Invasive Bivalve Rangia cuneata during Colonisation of the Oder Estuary (North-Western Poland)

The aim of this study was to determine the biological, morphometric, and shape characteristics of the bivalve Rangia cuneata in the initial phase of colonisation. A total of 504 specimens were caught for the study. Their average length was 31.06 mm (range 12.7–43.2 mm) and weight 6.0 g (0.5–15.3 g). The population was dominated by individuals of 25–30 mm and 30–35 mm in length and the age of 3+ and 4+. The standard major axis regression for measurable traits describing shell cross-section indicate the allometric nature of growth for most parameters. Elongation and convexity indices by age group indicate a change in the shell shape as it becomes more elongated and convex in individuals that have already reached sexual maturity. The collected specimens were of larger sizes compared to other Baltic populations of the species, and similar in size to populations found in the neighboring Pomeranian Bay. The increase in length of R. cuneata in the Oder estuary is smaller compared to the species native sites, probably due to the lower water temperature in the study area. Considering the invasive potential of R. cuneata, it seems necessary to monitor closely its population and distribution in the estuary of Western Baltic.