Dispersal sets the fundamental scales for the ecological and evolutionary dynamics of populations, and understanding dispersal patterns has important implications for population dynamics and persistence. Our current understanding of dispersal in marine species remains poor, in part because dispersal varies widely between individuals and over time, but natural tags harbored within biological collections can help retroactively track individuals across space. Here, we used otolith microchemistry and double-digest restriction-site associated DNA (ddRAD) sequencing data from archived collections of larval summer flounder (Paralichthys dentatus; n = 428) captured from 1989 – 2012 at six locations along the U.S. East coast to understand dispersal and population connectivity through time. Specifically, we ask: (1) How do microchemical signatures of the natal site differ across space and time? (2) Do larval summer flounder exhibit regional population structure and has it remained stable over time? and (3) Can otolith microchemistry and genetic markers be combined to accurately assign larval summer flounder back to spawning adult populations along the U.S. East coast over a 24 year time period?
Results/Conclusions
Otolith (ear bone) microchemistry at the natal core exhibited differences across collection locations and time periods, suggesting that elemental differences along the coast could be used to assign larvae back to putative spawning grounds. Linear discriminant function analysis (LDA) revealed that the majority of individuals had an elemental signature characteristic of other larvae collected at the same location. Using 1904 single nucleotide polymorphisms (SNPs), we found no indication of population structure across ingress sites or time. Combining the otolith and a subset of the genetic datasets allowed us to perform population assignments and revealed that the most likely source for many larvae was from adults in the vicinity of Cape Hatteras. Together, these complementary datasets reveal that summer flounder dispersal is widespread along the U.S. East coast, both on intra- and inter-generational timescales, resulting in high exchange rates along the coast. These congruent patterns suggest that dispersal is likely an important process both synchronizing population dynamics and maintaining genetic diversity across strong environmental gradients in summer flounder.