Genetic and migratory evidence for sympatric spawning of tropical Pacific eels from Vanuatu

The spawning areas of tropical anguillid eels in the South Pacific are poorly known, and more information about their life histories is needed to facilitate conservation. We genetically characterized 83 out of 84 eels caught on Gaua Island (Vanuatu) and tagged 8 eels with pop-up satellite transmitters. Based on morphological evidence, 32 eels were identified as Anguilla marmorata, 45 as A. megastoma and 7 as A. obscura. Thirteen of these eels possessed a mitochondrial DNA sequence (control region, 527 bp) or nuclear haplotype (GTH2b, 268 bp) conflicting with their species designation. These individuals also had multi-locus genotypes (6 microsatellite loci) intermediate between the species, and 9 of these eels further possessed heterozygote genotypes at species-diagnostic nuclear single nucleotide polymorphisms (SNPs). We classified these individuals as possibly admixed between A. marmorata and A. megastoma. One A. marmorata and 1 A. megastoma migrated 634 and 874 km, respectively, towards the border between the South Equatorial Current and the South Equatorial Counter Current. Both species descended from around 200 m depth at night to 750 m during the day. Lunar cycle affected the upper limit of migration depths of both species. The tags remained attached for 3 and 5 mo and surfaced <300 km from the pop-up location of a previously tagged A. marmorata pop-up location. A salinity maximum at the pop-up locations corresponding to the upper nighttime eel migration depths may serve as a seamark of the spawning area. The similar pop-up locations of both species and the evidence for admixture suggest that these tropical eels share a sympatric spawning area.

Fisheries stocks from an ecological perspective: Disentangling ecological connectivity from genetic interchange

The concept of a stock of fish as a management unit has been around for well over a hundred years, and this has formed the basis for fisheries science. Methods for delimiting stocks have advanced considerably over recent years, including genetic, telemetric, tagging, geochemical and phenotypic information. In parallel with these developments, concepts in population ecology such as meta-population dynamics and connectivity have advanced. The pragmatic view of stocks has always accepted some mixing during spawning, feeding and/or larval drift. Here we consider the mismatch between ecological connectivity of a matrix of populations typically focussed on demographic measurements, and genetic connectivity of populations that focus on genetic exchange detected using modern molecular approaches. We suggest that from an ecological-connectivity perspective populations can be delimited as management units if there is limited exchange during recruitment or via migration in most years. From a genetic-connectivity perspective such limited exchange can maintain panmixia. We use case-studies of species endangered by overexploitation and/or habitat degradation to show how current methods of stock delimitation can help in managing populations and in conservation.

Fisheries stocks from an ecological perspective: Disentangling ecological connectivity from genetic interchange

The concept of a stock of fish as a management unit has been around for well over a hundred years, and this has formed the basis for fisheries science. Methods for delimiting stocks have advanced considerably over recent years, including genetic, telemetric, tagging, geochemical and phenotypic information. In parallel with these developments, concepts in population ecology such as meta-population dynamics and connectivity have advanced. The pragmatic view of stocks has always accepted some mixing during spawning, feeding and/or larval drift. Here we consider the mismatch between ecological connectivity of a matrix of populations typically focussed on demographic measurements, and genetic connectivity of populations that focus on genetic exchange detected using modern molecular approaches. We suggest that from an ecological-connectivity perspective populations can be delimited as management units if there is limited exchange during recruitment or via migration in most years. From a genetic-connectivity perspective such limited exchange can maintain panmixia. We use case-studies of species endangered by overexploitation and/or habitat degradation to show how current methods of stock delimitation can help in managing populations and in conservation.

Understanding the Mechanisms of Cell and Population Responses of Coccolithophores to Changing Ocean Chemistry

The calcifying coccolithophores have been proposed as a potentially vulnerable group in the face of increasing surface ocean CO2 levels. A full understanding of the likely responses of this group requires better mechanistic information on pH- and CO2-sensitive processes that underlie cell function at molecular, cellular and population levels. New findings on the mechanisms of pH homeostasis at a molecular and cellular level in both diatoms and coccolithophores are shaping our understanding of how these important groups may respond or acclimate to changing ocean pH. Critical parameters including intracellular pH homeostasis and cell surface pH will be considered. These studies are being carried out in parallel with genetic studies of natural oceanic populations to assess the natural genetic and physiological diversity that will underlie adaptation of populations in the long term.