Schelpreparatie bij de Amerikaanse zwaardschede Ensis directus (Conrad, 1843)

Over 200 shells, 9-15 cm long, of the invasive American razor clam Ensis directus (Conrad, 1843) were collected in September 2015 on the North Sea beach of Texel. Ten percent of the shells showed deformations visible as a hollow blister at the posterior end of the shells. Similar shell deformations were almost absent in approximately 200 shells of the same size collected along the Wadden Sea beach of Texel. Differences in repaired shell damages are presumed to be related to the higher energy environment of the North Sea coast compared with that of the Wadden Sea. There is no reason to suspect a difference in predator activity between the two nearby sites. Moreover, all deformations were associated with the formation of the annual growth ring in wintertime. This is the time of the year with most gales and derived sediment movement along the bottom. I would relate the high frequency of small chips broken from the shells, described as ‘scalloped’ in the literature, mainly to the high energy environment in which this razor clam lives.