Table 1. Details of sampling sites and the number Mytilus specimens used for marker discovery and marker validation.

* One of the M. trossulus from Penn Cove was re-assigned as M. edulis during the marker development/validation stage (see Results). † Additional samples used only for marker validation.

Site location	Site coordinates	Species reported	Me15/16 screening	SNP discovery	KASP validation
LR—Loch Ryan	54°56'06.8"N 5°03'38.7"W	M. edulis	50	10	50
RB—Rascarrel Bay	54°48'53.1"N 3°51'22.7"W	M. edulis	50	10	50
BP—Bay of Piran	-	M. galloprovincialis	50	15	50
PC—Penn Cove	-	M. trossulus	8	4+1*	8
MON—Montrose	56°42'16.3"N 2°28'13.7"W	M. edulis	50	-	50
LET—Loch Etive†	56°27'05.5"N 5°19'13.3"W	M. trossulus (juvenal)	20	-	20
BDL—Bras d’Or Lake†	45°59'55.4"N 60°43'31.0"W	M. trossulus	50	-	50