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The geographic structure of marine fish populations is an important element used in defining stock units, and genetic data have historically been used for this purpose. Here, genetic data were used to elicit population genomic patterns for Atlantic Croakers Micropogonias undulatus collected at five locations in the Gulf of Mexico (hereafter, "Gulf") and a single location in the southern U.S. Atlantic. Mitochondrial DNA (mtDNA) haplotypes were used as a baseline for historical lineage delineation and in a comparison with a previous Atlantic Croaker study that was centered on the Atlantic coast. A genomic data set consisting of 3,682 single-nucleotide polymorphism (SNP)-containing loci was used to assess contemporary gene flow throughout the sampled area. Both the mtDNA and SNP data sets showed significant between-basin estimates of genetic divergence (Φst = 0.049 and FST = 0.002, respectively), while pairwise FST implied a low magnitude of divergence (FST ≤ 0.002) at all geographic scales. Comparison of patterns obtained from putatively "neutral" versus "outlier" SNP loci suggested contrasting genetic patterns at the extremes of the sampling distribution in the Gulf. Putatively neutral SNPs implied a single stock in the Gulf, whereas a handful of outliers suggested distinct populations in the eastern and western Gulf. The pattern observed at outlier loci could imply either the presence of natural selection impacting a small number of loci or otherwise could be explained as a remnant pattern reflective of historical geographic isolation. In either case, the weak population structure observed at a small number of SNP loci may be indicative of a more significant demographic structure; for this reason, caution is urged when treating Atlantic Croakers as a single stock in the Gulf. [ABSTRACT FROM AUTHOR]

Genomic and physiological responses in Gulf killifish (Fundulus grandis) in the northern Gulf of Mexico have confirmed oil exposure of resident marsh fish following the Macondo blowout in 2010. Using these same fish, we evaluated otolith microchemistry as a method for assessing oil exposure history. Laser-ablation inductively-coupled-plasma mass spectrometry was used to analyze the chemical composition of sagittal otoliths to assess whether a trace metal signature could be detected in the otoliths of F. grandis collected from a Macondo-oil impacted site in 2010, post-spill relative to pre-spill, as well as versus fish from areas not impacted by the spill. We found no evidence of increased concentrations of two elements associated with oil contamination (nickel and vanadium) in F. grandis otoliths regardless of Macondo oil exposure history. One potential explanation for this is that Macondo oil is relatively depleted of those metals compared to other crude oils globally. During and after the spill, however, elevated levels of barium, lead, and to a lesser degree, copper were detected in killifish otoliths at the oil-impacted collection site in coastal Louisiana. This may reflect oil contact or other environmental perturbations that occurred concomitant with oiling. For example, increases in barium in otoliths from oil-exposed fish followed (temporally) freshwater diversions in Louisiana in 2010. This implicates (but does not conclusively demonstrate) freshwater diversions from the Mississippi River (with previously recorded higher concentrations of lead and copper), designed to halt the ingress of oil, as a mechanism for elevated elemental uptake in otoliths of Louisiana marsh fishes. These results highlight the potentially complex and indirect effects of the Macondo oil spill and human responses to it on Gulf of Mexico ecosystems, and emphasize the need to consider the multiple stressors acting simultaneously on inshore fish communities. [ABSTRACT FROM AUTHOR]

Population structure of adult red snapper ( Lutjanus campechanus ) from the southeastern coast of the United States (Atlantic) and the northeastern Gulf of Mexico (Gulf) was assessed using genotypes at 16 nuclear-encoded microsatellites and mitochondrial (mt)DNA haplotypes of the NADH dehydrogenase 4 (ND4) gene. Initial tests ( F ST -based, hierarchical AMOVA) of spatial genetic homogeneity within and between regions were non-significant, consistent with a single population or stock of red snapper in the Atlantic and Gulf. Inferences derived from other statistical approaches were consistent with genetic and/or demographic differences within and between the two regions. The estimated, average, long-term migration rate between the two regions (0.27%) was well less than the 10% rate below which populations can respond independently to environmental perturbation. Comparisons of global estimates of average, long-term effective size ( N eLT ) with estimates from individual sample localities indicated genetic heterogeneity within both the Atlantic and Gulf. These results paralleled those of prior genetic studies of red snapper from the Gulf. Future genetics studies and other work on red snapper in both the Atlantic and Gulf should include approaches to identify demographically independent units within each region and assess their size, patterns of connectivity, and contribution to the fishery. Monitoring global and/or local effective size also should be considered. [ABSTRACT FROM AUTHOR]