Ann Bucklin

The population genetics of Calanus finmarchicus in the North Atlantic

Abstract DNA sequence variation for a 350 base-pair portion of mitochondrial 16S rRNA gene was determined for the copepod, Calanus finmarchicus, collected from eight sites in the western N. Atlantic Ocean and seven sites in the Norwegian Sea. Among 104 individuals for which sequence data were obtained there were 30 mitochondrial haplotypes. One haplotype occurred in 59 individuals and was found in all but two of the samples, while 21 haplotypes were unique. Both nucleotide diversity (π = 0.0061) and haplotype diversity (h= 0.67) were moderate. There were significant differences in the frequencies of the haplotypes among the samples (P < 0.001 by chi-square test by Monte Carlo simulation). One sample collected from the Norwegian Sea and one sample from the northern Gulf of St. Lawrence were distinct from all other samples, perhaps as a result of advection from different oceartographic regions. Chi-square tests resolved four groups: one consisting of the three Georges Bank, two Gulf of Maine, and two (of th...

Voracious planktonic hydroids: unexpected predatory impact on a coastal marine ecosystem

Abstract-Hydroids are typically attached, benthic cnidarians that feed on a variety of small prey. During sampling on Georges Bank in spring 1994, we found huge numbers of hydroids suspended in the plankton. They fed on young stages of copepods that are an important prey for fish, as well as on young fish themselves. Two independent methods were used to estimate feeding rates of the hydroids; both indicate that the hydroids are capable of consuming from 50% to over 100% of the daily production of young copepods. These results suggest that hydroids can have a profound effect on the population dynamics of zooplankton and young fish on Georges Bank. Copyright 0 1996 Elsevier Science Ltd INTRODUCTION The life history of marine hydrozoans (Phylum Cnidaria) is typically an alternation between a sessile hydroid phase and a motile medusa. The hydroids form colonies attached to seaweed, rocks or other organisms, and their feeding polyps (hydranths) prey on small organisms, eggs and detrital matter. The medusae are usually released to feed and disperse in the plankton (Hyman, 1940). We report observations from Georges Bank on the occurrence of suspended colony fragments of the hydroid

Source regions for recruitment of Calanus finmarchicus to Georges Bank: evidence from molecular population genetic analysis of mtDNA

Abstract Molecular population genetic analysis has provided evidence that the copepod, Calanus finmarchicus , of the Labrador Current, Gulf of St Lawrence, Scotian Shelf, Gulf of Maine, and Georges Bank constitute a single, interbreeding population. The DNA sequence of a 350 base pair portion of the mitochondrial large subunit (16S) ribosomal RNA (rRNA) gene was determined for a total of 72 individuals collected in 1992, and 110 individuals collected in 1993 from these regions. There was significant heterogeneity in haplotype frequencies among the samples collected in 1992, but this heterogeneity did not resolve into regional patterns. The only regional differences seen were between pooled samples of the western N. Atlantic and those of the Norwegian Sea. There were no significant differences in haplotype frequencies among the samples collected in 1993, and fewer haplotypes were observed in these samples. Intraspecific molecular variation was typical of other marine species: there were 29 haplotypes among the 182 individuals sequenced. The frequency distribution of the haplotypes was highly skewed: 128 individuals shared one haplotype and 19 individuals were unique. There were 24 variable sites among the 350 bases sequenced; estimated nucleotide diversity was 0.0042. The genetic character of C. finmarchicus populations in the western N. Atlantic was stable over time in that three of the haplotypes (including the most abundant) occurred in both 1992 and 1993. However, haplotype frequencies differed significantly between the two years. The lack of regional structure in the 1992 samples and the genetic homogeneity of samples collected in 1993 across the domain from the Labrador Current to the Gulf of St Lawrence to Georges Bank and the Gulf of Maine indicated that there is significant gene flow across this region. The persistent genetic pattern suggests that the Gulf of St Lawrence may be an important source region for recruitment of C. finmarchicus to Georges Bank. Determination of zooplankton dispersal patterns within high gene flow species will provide information that may not be determined by conventional oceanographic analyses.

Acartia (Odontacartia) ohtsukai, a new brackish-water calanoid copepod from Ariake Bay, Japan, with a redescription of the closely related A. pacifica from the Seto Inland Sea

Acartia ohtsukai sp. nov. (Calanoida, Acartiidae), which has so far been identified as A. pacifica, is described from an estuary of Ariake Bay, Japan, with a redescription of A. pacifica s. str. from the Seto Inland Sea. The new species is distinguishable from A. pacifica by characters of the caudal rami and the antennule in female and those of the urosomal somites and the fifth leg in male. The most closely affinity of A. ohtsukai is seen with A. mertoni new rank, which was formerly a variety of A. pacifica and differs from A. ohtsukai by having dorsal spinule ornamentation on male urosome. DNA sequences of two mitochondrial genes differed between individuals of the new species from Ariake Bay and A. pacifica from the Seto Inland Sea and supported their designation as distinct species: 23–24% for cytochrome oxidase I (mtCOI) and 28% for 16S rRNA. The population in Ariake Bay is regarded as a continental relict, of which the main population is distributed in brackish waters along the coast of the East Asian continent.

Integrated biochemical, molecular genetic, and bioacoustical analysis of mesoscale variability of the euphausiid Nematoscelis difficilis in the California Current

Integrated assessment of the euphausiid Nematoscelis difficilis (Crustacea; Euphausiacea) and the zooplankton assemblage of the California Current was designed to investigate individual,population,and community responses to mesoscale variability in biological and physical characters of the ocean. Zooplankton samples and observational data were collected along a cross-shelf transect of the California Current in association with the California Cooperative Fisheries Investigations (CalCOFI) Survey during October 1996. The transect crossed three domains defined by temperature and salinity: nearshore,mid-Current,and offshore. Individual N. difficilis differed in physiological condition along the transect,with higher size-corrected concentrations of four central metabolic enzymes (citrate synthetase,hexokinase,lactate dehydrogenase (LDH),and phosphoglucose isomerase (PGI)) for euphausiids collected in nearshore waters than in mid-Current and offshore waters. There was little variation in the DNA sequences of the genes encoding PGI and LDH (all DNA changes were either silent or heterozygous base substitutions),suggesting that differences in enzyme concentration did not result from underlying molecular genetic variation. The population genetic makeup of N. difficilis varied from sample to sample based on haplotype frequencies of mitochondrial cytochrome oxidase I (mtCOI; P ¼ 0:029). There were significant differences between pooled nearshore and offshore samples,based on allele frequencies at two sites of common substitutions in the mtCOI sequence (P ¼ 0:020 and 0:026). Silhouette and bioacoustical backscattering measurements of the zooplankton assemblage of the top 100 m showed marked diel vertical migration of the scattering layer,of which euphausiids were a small but significant fraction. The biochemical and molecular assays are used as indices of complex physiological (i.e.,growth and condition) and genetic (i.e., mortality) processes; the bioacoustical observations provide insight into the ecosystem context for the single-species measurements. All data are intended for integration into predictive models of secondary production and biomass concentration in the ocean. r 2002 Elsevier Science Ltd. All rights reserved.

Population Genetics and Phylogeny of Planktonic Copepods

Patterns of dispersal of Zooplankton in the ocean are determined by biological processes (including life history and individual behavior) and by physical events and processes (ocean storms, circulation patterns and physical structure). Dispersal is difficult or impossible to observe directly in the ocean, especially for tiny, numerous and ubiquitous organisms such as zooplankton. In complex environments such as the ocean, inferences from geographic patterns of population genetic structure (i.e. division of a species into genetically distinct subpopulations) and estimation of gene flow (i.e. exchange of genes among subpopulations) may be the most reliable means of estimating dispersal. Individual genetic characteristics that have appropriate levels of variability may be assayed to describe population genetic diversity and structure; with some assumptions, gene flow may be estimated from these measurements. The resolving power of analyses of population genetic structure may be markedly increased by direct analysis of the variation of the DNA — especially through DNA sequencing of selected gene portions.