Basin-scale patterns of mtDNA differentiation and gene flow in the bay scallop Argopecten irradians concentricus

Abstract

The bay scallop Argopecten irradians concentricus Say is a commercially and recre- ationally important species along the East Coast of the US that consistently shows evidence of recruitment limitation. To determine if limited planktonic larval exchange between populations inhabiting lagoonal basins or sounds contributes to recruitment limitation in central North Carolina, a hypervariable portion of mtDNA (885 bp) was sequenced from 219 adults from 4 sounds (Topsail, Bogue, Back, and Pamlico), 3 of which (Bogue, Back, and Pamlico) are connected by inshore water- ways. Although the largest sound (Pamlico) harbored the greatest genetic diversity, diversity was high in all 4 sounds, with no evidence of recent bottlenecks. An analysis of molecular variance indi- cates significant genetic structure among sounds (φCT = 0.0069, p = 0.023); all pairwise comparisons among sounds were significant, with the exception of those involving Pamlico Sound. Despite being connected by a short (3 km) inshore waterway, adjacent Bogue and Back Sounds were highly signif- icantly differentiated (φCT = 0.0145, p = 0.000). Coalescent-based estimates of gene flow indicated that most sounds exchange ≤4 migrants each generation. Bogue and Back Sound populations, which were heavily impacted by a localized red tide outbreak in 1987 and which subsequently experienced a recruitment failure, each receive <4 migrants each generation from all other sounds combined. Dynamic physical processes in the vicinity of Beaufort Inlet can explain such limited larval exchange between Bogue and Back Sounds, but if dispersal is primarily controlled by tidally dominated surface flow, net dispersal distances may be limited throughout the region. Therefore, patterns of gene flow and genetic differentiation are consistent with the hypothesis that individual sounds are demograph- ically independent and are closed with respect to fishery management issues.