| Popis: |
Based on the earlier studies and the appearance of the growth lines, the indicative size-age relationship which evolved from counts of the lines, it is likely that the counted lines are annual in nature. Age at size matches to relationships found for a UK population (Essex-Black River). If this assumption is true, it means that the 14 year old shell (#006) which was collected in December 2015 must have settled in the period 2001-2002, depending on the exact timing of line formation. In this study 12 shells were analyzed. Assuming annual growth lines, any shell collected in 2015 older than 7 years (i.e., 2 shells), or collected in 2017 and older than 9 years (i.e., 3 shells) would have been present before 2008, that is, before designation of the Natura 2000 site Voordelta in 2008. The results show that this is the case for 5 out of 12 of the analyzed shells. This leads to the conclusion that at the moment of Natura 2000 site designation, the oyster bed probably was already present to some extent. |
