NW Atlantic Research Articles

Domoic acid production and elemental composition of two Pseudo-nitzschia multiseries strains, from the NW and SW Atlantic Ocean, growing in phosphorus- or nitrogen-limited chemostat cultures

Here we compare cell physiology and domoic acid (DA) production for two strains of the diatom Pseudo-nitzschia multiseries originating from two opposite latitudes: Canada (CA) and Brazil (BR). The algae were grown as chemostat cultures at 0.2, 0.3 and 0.4 day ―1 under nitrogen (N)- and phosphorus (P)-deficient conditions. The level of deficiency significantly affected the atomic C:N, C:P, C:Si and N:P ratios in both strains. In both strains, P per cell was 2―4 × higher in the N- than in the P-deficient cultures. The opposite was not found for N in the P-deficient cultures, as shown by the N:P ratios and C:N ratios. The C:N and C:P ratios were significantly lower in the CA strain, and this did not change due to the level of deficiency. The concentration and production of DA per cell per day were significantly higher for both strains under P deficiency as expected since the toxin is rich in N. However, DA was also produced by both strains during continuous cell division under N deficiency. High or low bacterial densities associated with P. multiseries did not increase or decrease DA production. Our data imply that more attention needs to be given to the N:P ratios and concentrations in the waters where these algae occur, as both N and P deficiencies affect DA production and cellular DA concentrations.

Role of ciliates and other microzooplankton in the Irminger Sea (NW Atlantic Ocean)

This study focuses on a large region of the open ocean where we predict microzooplankton significantly influence foodweb structure over much of the year. The Irminger Sea exhibits low primary production that is generally poor for copepod production; in such waters ciliates and other microzooplankton can contribute significantly to the diets of holo- and mero- mesozooplankton and are major grazers of primary production. Surface plankton samples were collected during an extensive survey, across the basin and along one transect at several depths, over three seasons (winter, spring, summer), but not including the spring bloom. Microzooplankton and phytoplankton samples were fixed with Lugol’s solution and microscopically enumerated for species abundance; biomass was determined from cell volumes. Basin-scale distributions of abundance, biomass, and production were examined by geostatistical and multidimensional scaling methods. The dominance of the < 10 µm phytoplankton suggests that this should be a microzooplankton-dominated food web. Ciliates and heterotrophic dinoflagellates are abundant, in terms of numbers and biomass; heterotrophic dinoflagellates are more abundant than ciliates, but are less dominant in terms of biomass. Using ciliates as a proxy for all microzooplankton we suggest that there are seasonal patterns in occurrence, and there is no basin-scale patchiness related to hydrographic features. Through some simple, albeit “rough” calculations, we suggest that ciliate production may be sufficient to account for the removal of 15-30% of the < 10 µm primary production. If heterotrophic dinoflagellates were included in these estimates, they may be doubled (i.e. 30-60%). We, thus, contend that microzooplankton are major phytoplankton consumers in the system and should be carefully parameterised in models of this region.

Spatial and inter-decadal variability in plankton abundance and composition in the Northwest Atlantic (1958–2006)

The results of Continuous Plankton Recorder sampling in the NW Atlantic between 1958 and 2006 are presented for 11 plankton taxa in eight shelf and deep ocean regions. For shelf regions, phytoplankton abundances increased in the early 1990s, mainly in winter, as the contribution of Arctic-derived freshwater to the Newfoundland (NLS) and Scotian shelves (SS) increased. Farther east, in the sub-polar gyre, phytoplankton levels increased with rising temperatures during the 1990s and 2000s. In both areas, the changes can be explained by increased stratification. The increased influx of arctic water to the NLS in the 1990s was also probably directly responsible for the increased abundances of two arctic Calanus species (C. glacialis and C. hyperboreus) and indirectly responsible for the decreased abundance of Calanus I–IV (mainly C. finmarchicus), perhaps via changes in food composition. On the SS the arctic Calanus species increased in abundance in the 2000s, likely as the result of increased transport from the Arctic via the Gulf of St Lawrence. In the deep ocean, plankton seasonal cycles changed little over the decades and increasing phytoplankton levels in the 2000s were accompanied by increases in zooplankton abundance, suggesting bottom-up control. In shelf regions, phytoplankton increases in the 1990s were in winter and Calanus I–IV appeared earlier in spring than in previous decades. Zooplankton levels generally did not change overall however, perhaps because the species examined were mainly inactive during winter.

Regional decoupling between NW Atlantic barnacle recruit and adult density is related to changes in pelagic food supply and benthic disturbance

We investigated the regional variation in barnacle ( Semibalanus balanoides) recruit and adult abundance on the NW Atlantic coast. At the end of the recruitment season (June–July), we sampled wave-exposed rocky intertidal sites in two regions on the open Atlantic coast (Maine, AM, and Nova Scotia, AN) and in two regions on the Gulf of St. Lawrence coast (Northumberland Strait, GN, and Cape Breton Island, GC). Recruit density was highest in the southernmost region (AM), followed by GN and, then, by AN and GC. Regional values of nearshore primary productivity (satellite data of chlorophyll- a concentration, a surrogate for phytoplankton abundance) were highest for AM and GN, suggesting that food supply (barnacles are filter feeders) is an important factor determining regional recruitment patterns. Adult barnacle density was regionally decoupled from recruit density. Adults occurred in very low abundances on the Gulf of St. Lawrence coast (GN and GC) and were relatively abundant on the Atlantic coast (AM and AN), although always in much lower abundances than recruits. The low adult densities on the Gulf of St. Lawrence coast seem to result mainly from intense ice scour, as this coast freezes extensively every winter, as opposed to the ice-free Atlantic coast. Ice scour thus appears to override regional recruitment differences in determining adult density. Therefore, our data suggest that both pelagic food supply and benthic disturbance contribute to setting regional patterns in barnacle population structure on the NW Atlantic coast.

Morphological and phylogenetic comparisons of Neodenticula seminae (Bacillariophyta) populations between the subarctic Pacific and the Gulf of St. Lawrence

Neodenticula seminae is a very important member of modern diatom assemblages in the Bering Sea and at middle to high latitudes of the North Pacific. In the North Atlantic, this species was considered extinct until it was recorded in high abundance in the 2001 spring phytoplankton bloom of the Gulf of St. Lawrence, Eastern Canada. Here, we discuss some of the most distinctive features of its morphology, including variation in some characters between the subarctic Pacific and the Gulf of St. Lawrence specimens. Most importantly, we observed that the deck and basal ridges, and the solid-walled costae (formerly known as primary pseudosepta) characteristic of N. seminae were present in the subarctic Pacific material, but were absent or vestigial in the Gulf of St. Lawrence material and in cultures from both regions. This morphological variation was most likely due to differences in physico–chemical water properties between the subarctic Pacific and the Gulf of St. Lawrence. Phylogenetic analyses of the internal transcribed spacer regions of the nuclear ribosomal DNA showed that the strains of N. seminae collected in the Gulf of St. Lawrence and the subarctic Pacific clustered in two sister clades, but differed from each other only slightly more than the variation among the subarctic Pacific strains. These results confirmed the reappearance of N. seminae in the NW Atlantic after an absence of ∼0.8 Ma. In addition, the phylogenetic analyses based on the large subunit of the nuclear ribosomal DNA positioned N. seminae firmly within the Bacillariaceae (i.e. diatoms with a fibulate raphe system) and proved a close relationship to species of Fragilariopsis.

Observations on the Kalliapseudid Tanaidacea (Crustacea: Malacostraca: Peracarida) from the Northwestern Atlantic, with an Illustrated Key to the Species

New information for the kalliapseudid Tanaidacea occurring in the northwestern Atlantic is presented and discussed, including data on range extensions and new depth ranges for 4 species. The taxa studied came from the shelf and coastal waters of the southeastern United States, Puerto Rico and Trinidad. The occurrence of Mesokalliapseudes baha- mensis Sieg is extended from the Bahamas and Belize to the coastal waters of East and Gulf coasts (South Carolina to West Florida). The range of Psammokalliapseudes granulosus Brum is expanded northward into the eastern Gulf of Mexico and new locality records for this species are established for Tobago and Puerto Rico. Mesokalliapseudes brasiliensis (Bacescu), previously known from the southwestern Atlantic off Brazil, is reported from the coastal waters off Trinidad. The range of Tanapseudes gutui Hansknecht, Heard, and Bamber is expanded northward into the eastern Gulf of Mexico. New depth ranges are established for Alokalliapseudes macsweenyi (Drumm) (82 m), M. bahamensis (52 m), P. granulosus (53 m), and T. gutui (82 m). An offshore form of A. macsweenyi occurs at depths ranging from 10-82 m on the inner and mid con- tinental shelf off the west coast of Florida (Gulf of Mexico); it differs from the coastal form by the shape and dentition of the male and female chelipeds. Synonymies, diagnoses, life history remarks, and an illustrated key to the seven kalliapseudid species known from the NW Atlantic are presented.

Habitat use in Atlantic bluefin tuna Thunnus thynnus inferred from diving behavior

To examine habitat use in Atlantic bluefin tuna Thunnus thynnus, we used time series records from 20 archival tags and 7 pop-up satellite archival tags. Daily vertical profiles were classified into 3 dive types: (1) profiles restricted to surface waters by either bathymetry or thermal constraints; (2) profiles with frequent V-shaped dives that may be associated with transiting or searching behaviors; and (3) U-shaped profiles associated with putative foraging behavior. Fixed kernel probability contours were calculated for each of the dive profile classes. Key potential North Atlantic foraging habitats were identified in the NW Atlantic (Gulf of Maine/Scotian Shelf, Grand Banks and Flemish Cap), off Florida and the Bahamas and in the NE Atlantic. These ‘hotspot’ regions encompass areas of high seas that may be important to future conservation and management of the species. U-shaped dive profiles were shallower and surface returns were more frequent in areas where subsurface temperatures were coldest. The presence of Atlantic bluefin tuna coincided with peak productivity and sea surface temperatures in 3 of the 5 hotspot areas. Further analyses examined spatial and temporal patterns of transatlantic migrations and deep diving behavior in the Strait of Gibraltar.

Deep-sea octocorals and antipatharians show no evidence of seamount-scale endemism in the NW Atlantic

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 397:25-35 (2009) - DOI: https://doi.org/10.3354/meps08318 Deep-sea octocorals and antipatharians show no evidence of seamount-scale endemism in the NW Atlantic Jana N. Thoma*, Eric Pante*, Mercer R. Brugler, Scott C. France** University of Louisiana at Lafayette, Department of Biology, PO Box 42451, Lafayette, Louisiana 70504, USA *Jana N. Thoma and Eric Pante have contributed equally to this project**Corresponding author. Email: france@louisiana.edu ABSTRACT: Seamounts are undersea mountains commonly characterized by accelerated currents, exposed hard-substrates, and relatively high biomass and biodiversity. Hydrographic features associated with seamounts have led authors to hypothesize that benthic invertebrate populations from geographically separated seamounts (and the continental slope) may experience varying degrees of genetic isolation, resulting in high levels of endemism. While this hypothesis has been tested for multiple taxonomic groups in the Pacific, it has rarely been addressed in the Atlantic. We tested the null hypothesis that the geographic ranges of corals from NW Atlantic seamounts are restricted to individual seamounts. We examined 188 octocoral and 50 antipatharian colonies (representing 6 and 2 genera, respectively) from 14 seamounts, spanning 1700 km, and the adjacent continental margin and estimated their genetic variation using mitochondrial loci (msh1 for all octocorals, as well as an intergenic region for isidids, and 3 multi-gene spanning segments for antipatharians). Well-sampled haplotypes were not geographically isolated on individual seamounts, thus refuting the hypothesis of local endemism of coral fauna on the New England and Corner Seamounts. The narrow geographic distribution of rare haplotypes is most likely due to undersampling rather than endemism. Our results do not preclude that cryptic variation and endemism not revealed by mitochondrial DNA may become evident should more variable markers be developed. KEY WORDS: Endemism · Biogeography · Marine connectivity · Dispersal · Chrysogorgiidae · Paramuricea · Black coral · Anthozoa Full text in pdf format Supplementary material PreviousNextCite this article as: Thoma JN, Pante E, Brugler MR, France SC (2009) Deep-sea octocorals and antipatharians show no evidence of seamount-scale endemism in the NW Atlantic. Mar Ecol Prog Ser 397:25-35. https://doi.org/10.3354/meps08318Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 397. Online publication date: December 17, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Checklists of the Parasites of Dolphin, Coryphaena hippurus, and Pompano Dolphin, C. equiselis with New Records, Corrections, and Comments on the Literature

We report 125 parasites and associates of Dolphin, Coryphaena hippurus, and 28 of Pompano Dolphin, Coryphaena equiselis, including 8 new host records. We correct and explain problems in the literature in updating these checklists, including 64 confusions, 63 synonyms used, 51 omissions, 14 errors, 13 stomach contents called parasites, 9 incorrect species, 7 nomen nudums used, 7 incorrect higher classifications, 6 false hosts, and resolve the old controversy of Bathycotyle branchialis/B. coryphaenae preferred location in the gills, but not of its identity, the identity of Benedenia hendorffii, nor the mysterious rarity of Echinophallus lonchinobothrium and Plicocestus janickii. Most of the known parasites of dolphins actually rarely occur on these hosts. Dinurus hippurus, D. ivanosi, Floriceps saccatus, Metabronema magna, and Pennella sp. occur in limited geographic areas. However, 14 species of parasites occur commonly in the Dolphin and 5 in the Pompano Dolphin around the world. Charopinopsis quaternia is almost host specific and a characteristic parasite; Hysterothylacium pelagicum is genus specific and characteristic; Dinurus barbatus, D. breviductus, D. hippurus, D. longisinus, and D. tornatus are characteristic; Caligus quadratus, Hirudinella ventricosa, and Tetrochetus coryphaenae are primary parasites; Bathycotyle branchialis (or B. coryphaenae), Benedenia hendorffii, and Stephanostomum coryphaenae are host specific to the Dolphin; Pennella sp. is genus specific to dolphins. The Dolphin is the preferred host of Euryphorus nordmanni, a preferred host of Lernaeenicus longiventris, and dolphins are preferred hosts of Caligus coryphaenae. Rhadinorhynchus pristis is a secondary parasite. Caligus quadratus and Kudoa thyrsites may, and Neobenedenia melleni and M. pargueraensis will cause problems in Dolphin aquaculture. Only nine species of parasites have been shown to harm the Dolphin in nature, but this area is largely unknown. More dolphin parasites are known from the NW Atlantic, but this is study bias, not reality. Dolphins appear to be parasitologically isolated from other families of fishes. The distributions of some Dolphin parasites suggest this worldwide host may be separated into populations that have little communication.

Prey selection by larval haddock and cod on copepods with species-specific behavior: an individual-based model analysis

Coupled biological-physical models of larval fish have become a widely used tool for studying recruitment variability. Within these models, foraging components include prey selection as a determinant of food availability but have not yet considered species-specific escape behaviors of prey, which can be important in determining capture success. Furthermore, there has been extensive work on some species (e.g. cod Gadus morhua), but less on others (e.g. haddock Melanogrammus aeglefinus). We collected information from the literature on the escape behaviors of the copepods Calanus finmarchicus, Pseudocalanus spp., Oithona similis, and Centropages typicus, the dominant prey of larval haddock and cod on Georges Bank (NW Atlantic), for use in a mechanistic foraging model. The foraging model was coupled to a bioenergetics model to simulate larval haddock and cod feeding and growth. Larval haddock and cod demonstrated positive selection of Pseudocalanus spp. and negative selection of C. finmarchicus based on modeled Chesson's preference index. Species- specific differences in escape abilities affected selection more than encounter rate. Prey escape behavior explained why larval cod rarely feed on C. typicus, although these prey items are numerous in the water column. Disparities between larval haddock and cod in their simulated prey selection and growth rates were the result of different mouth sizes and metabolisms. Simulated haddock foraging agreed with gut content observations of the size and species composition of ingested prey. These models are the first to describe haddock foraging and to include species-specific prey behaviors.

Methyl iodide in the NW Atlantic: Spatial and seasonal variation

While the global ocean is an important source of atmospheric methyl iodide (CH3I), the major producers of CH3I within the ocean remain unclear. During a seasonal study in the NW Atlantic, the relationship between CH3I and some characteristic phytoplankton pigments was examined in order to identify possible phytoplankton producers of CH3I. Although no characteristic pigments exhibited a strong positive correlation with CH3I, in the surface mixed layer, there was a weak correlation (R = 0.35, n = 70, p = 0.003) between the concentrations of CH3I and zeaxanthin, a pigment characteristic of cyanobacteria in the open ocean. In this study, a moderate correlation was observed between the surface mixed layer CH3I concentration and depth‐averaged daily radiant exposure (R = 0.61, n = 15, p = 0.02), which indicates a positive influence of solar radiation on CH3I production. However, the results from this study do not conclusively show whether the influence was exerted through photochemistry or other pathways. A positive correlation between the CH3I concentration and sea surface temperature was also observed (R = 0.61, n = 79, p ≪ 0.001).

Colonization of the northwest Atlantic by the blue mussel, Mytilus trossulus postdates the last glacial maximum

Blue mussels in the genus Mytilus first arrived in the Atlantic Ocean from the Pacific during the Pliocene, following the opening of the Bering Strait. Repeated periods of glaciation throughout the Pleistocene led to re- isolation of the two ocean basins and the allopatric diver- gence of Mytilus edulis in the Atlantic and M. trossulus in the Pacific. Mytilus trossulus has subsequently colonized the northwest Atlantic (NW Atlantic) so that the two spe- cies are presently sympatric and hybridize throughout much of the Canadian Maritimes and the Gulf of Maine. To estimate when M. trossulus arrived in the NW Atlantic, we have examined sequence variation within a portion of the female mtDNA lineage large untranslated region (F-LUR) for 156 mussels sampled from three Pacific and eleven Atlantic populations of M. trossulus. Although we found no evidence of reciprocal monophyly for Pacific and NW Atlantic M. trossulus, limited gene flow between ocean basins has led to the divergence of unique sequence clades within each ocean basin. In contrast, relative genetic homogeneity indicates high levels of gene flow within each basin. Coalescence-based analysis of the F-LUR sequences suggests that M. trossulus recolonized the NW Atlantic from the northeast Pacific subsequent to a demographic expansion in the Pacific that occurred *96,000 years before present (ybp). Estimates of timing of divergence for Pacific and NW Atlantic populations and the time since expansion among NW Atlantic sequence clades indicate that M. trossulus arrived in the NW Atlantic more recently, between 20,000 and 46,000 ybp. Given that these estimates overlap with the dates of peak ice in the NW Atlantic during the last glacial maximum (LGM, *18,000- 21,000 ybp), we suggest that colonization of the NW Atlantic by M. trossulus occurred during, but more likely just subsequent to, the LGM and was followed by rapid temporal and spatial expansion in the region.

Historical invasions of the intertidal zone of Atlantic North America associated with distinctive patterns of trade and emigration.

Early invasions of the North American shore occurred mainly via deposition of ballast rock, which effectively transported pieces of the intertidal zone across the Atlantic. From 1773-1861, >880 European ships entered Pictou Harbor, Nova Scotia, as a result of emigration and trade from Europe. The rockweed Fucus serratus (1868) and the snail Littorina littorea ( approximately 1840) were found in Pictou during this same period. With shipping records (a proxy for propagule pressure) to guide sampling, we used F. serratus as a model to examine the introductions because of its relatively low genetic diversity and dispersal capability. Microsatellite markers and assignment tests revealed 2 introductions of the rockweed into Nova Scotia: 1 from Galway (Ireland) to Pictou and the other from Greenock (Scotland) to western Cape Breton Island. To examine whether a high-diversity, high-dispersing species might have similar pathways of introduction, we analyzed L. littorea, using cytochrome b haplotypes. Eight of the 9 Pictou haplotypes were found in snails collected from Ireland and Scotland. Our results contribute to a broader understanding of marine communities, because these 2 conspicuous species are likely to be the tip of an "invasion iceberg" to the NW Atlantic from Great Britain and Ireland in the 19th Century.

Carbon-to-chlorophyll ratio and growth rate of phytoplankton in the sea

Observations from offshore regions (NW Atlantic and Arabian Sea) and from a semi- enclosed bay (Tokyo Bay) were used to study the relationships between chlorophyll and particulate carbon in the sea. A simple conceptual model was then developed to infer in situ phytoplankton car- bon as a function of chlorophyll a. This allowed indirect estimates of the carbon-to-chlorophyll ratio of phytoplankton in the sea. Using data from high-performance liquid chromatography, field samples dominated by diatoms, dinoflagellates, green algae, prymnesiophytes and cyanobacteria were iden- tified, and their carbon-to-chlorophyll ratios were established. The computations yielded conserva- tive estimates for the ratio (15 to 176 weight:weight). The results were applied to satellite data to map the carbon-to-chlorophyll ratios in the NW Atlantic. Since methods were already in place to estimate photosynthesis-irradiance parameters for the region by remote sensing (Platt et al. 2008), we showed that it was possible, using remote sensing, to compute carbon-based phytoplankton growth rates by making use of the existing information on photosynthesis-irradiance parameters and carbon- to-chlorophyll ratios. The method makes it possible to compute primary production by using either carbon-based growth models or photosynthesis-irradiance models in ways that are fully comparable with each other.

Planulation of deep-sea octocorals in the NW Atlantic

Planulation of deep-sea octocorals in the NW Atlantic

Molecular and isotopic constraints on the sources of suspended particulate organic carbon on the northwestern Atlantic margin

The abundance, carbon isotopic composition (Δ 14C and δ 13C), and lipid biomarker (alkenones and saturated fatty acids) distributions of suspended particulate organic matter were investigated at three stations centered on the 2000, 3000, and 3500 m isobaths over the New England slope in order to assess particulate carbon sources and dynamics in this highly productive and energetic region. Transmissometry profiles reveal that particle abundances exhibit considerable fine structure, with several distinct layers of elevated suspended particulate matter concentration at intermediate water depths in addition to the presence of a thick bottom nepheloid layer at each station. Excluding surface water samples, the Δ 14C values of particulate organic carbon (POC) indicated the presence of a pre-aged component in the suspended POC pool (Δ 14C<+38‰). The Δ 14C values at the 3000 m station exhibited greater variability and generally were lower than those at the other two stations where the values decreased in a more systematic matter with increasing sampling depth. These lower Δ 14C values were consistent with higher relative abundances of terrigenous long-chain fatty acids at this station than at the other two stations. Two scenarios were considered regarding the potential provenances of laterally transported POC: cross-shelf transport of shelf sediment (Δ 14C=−140‰) and along-slope transport of the slope sediment proximal to the sampling locations (Δ 14C=−260‰). Depending on the scenario, isotopic mass balance calculations indicate allochthonous POC contributions ranging between 15% and 54% in the meso- and bathy-pelagic zone, with the highest proportions at the 3000 m station. Alkenone-derived temperatures recorded on suspended particles from surface waters closely matched in-situ temperatures at each station. However, alkenone-derived temperatures recorded on particles from the subsurface layer down to 250 m were lower than those of overlying surface waters, especially at the 3000 m station, implying supply of phytoplankton organic matter originally produced in cooler surface waters. AVHRR images and temperature profiles indicate that the stations were under the influence of a warm-core ring during the sampling period. The low alkenone-derived temperatures in the subsurface layer coupled with the lower Δ 14C values for the corresponding POC suggests supply of OC on resuspended sediments underlying cooler surface waters distal to the study area, possibly further north or west. Taken together, variations in Δ 14C values, terrigenous fatty acid abundances, and alkenone-derived temperatures among the stations suggest that input of laterally advected OC is a prominent feature of POC dynamics on the NW Atlantic margin, and is spatially heterogeneous on a scale smaller than the distance between the stations (<150 km).

Possible countergradient variation in growth of juvenile cod Gadus morhua from the northwest Atlantic

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 375:229-238 (2009) - DOI: https://doi.org/10.3354/meps07760 Possible countergradient variation in growth of juvenile cod Gadus morhua from the northwest Atlantic Manjusri P. Wijekoon1, Velmurugu Puvanendran2,*, Danny W. Ings1, Joseph A. Brown1,† 1Ocean Sciences Centre, Memorial University of Newfoundland, St. John’s, Newfoundland A1C 5S7, Canada 2Nofima, Muninbakken 9-13, 9291 Tromsø, Norway *Corresponding author. Email: velpuvy@nofima.no †Deceased ABSTRACT: To test the countergradient variation (CnGV) hypothesis and determine any genetic differences among populations, we conducted an experiment with juvenile cod originating from 3 regions in the NW Atlantic, 3Ps (Placentia Bay, Newfoundland, Canada; 48°N, 54°W), 4T (southern Gulf of St. Lawrence; 46°N, 61°W), and 4X (44°N, 67°W), at 2 temperatures (7 and 11°C) for 15 wk. Results indicated that temperature influenced the growth rates of individuals in all 3 populations, and juveniles reared at 11°C were significantly bigger (length and weight) than those reared at 7°C. No significant differences in growth and food conversion efficiency were found among the 3 populations. Although 3Ps juveniles were significantly smaller in length and lighter in weight than 4T and 4X juveniles at the start of the experiment, length and weight did not differ among populations at the end of the experiment. Survival of both 3Ps and 4T juveniles was significantly higher than that of 4X cod in both high and low water temperature treatments. Although statistical analyses showed no significant differences in growth and food conversion efficiency among juveniles from the 3 populations, reaction norm analysis showed a strong genotypic influence on growth and survival (no genotype × environment interactions) but a genotypic × environment interaction in food conversion efficiency. Our results suggest that Atlantic cod juveniles from these 3 regions do not show CnGV in growth and food conversion efficiency. However, performance differences among populations may be stage specific, and this may have masked CnGV in traits among Atlantic cod populations in our study. KEY WORDS: Growth · Geographic variation · Survival · Adaptation · Atlantic cod Full text in pdf format PreviousNextCite this article as: Wijekoon MP, Puvanendran V, Ings DW, Brown JA, † (2009) Possible countergradient variation in growth of juvenile cod Gadus morhua from the northwest Atlantic. Mar Ecol Prog Ser 375:229-238. https://doi.org/10.3354/meps07760 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 375. Online publication date: January 26, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Genetic conspecificity of the worldwide populations of Didemnum vexillum Kott, 2002

A colonial tunicate belonging to the genus Didemnum has recently been found in many temperate coastal regions throughout the world, as well as large areas of Georges Bank in the NW Atlantic. It continues to spread rapidly and compete aggressively with native, hard substrate species (e.g., mussels, barnacles, bryozoans, other ascidians). In addition, it can form dense mats on deepwater cobble-gravel substrates and influence the abundance and species composition of benthic epifauna and infauna. Thus, its ever-increasing presence is creating potentially severe detrimental economic and ecological impacts. This invasive species, referred to in recent publications as Didemnum sp. A, has been misidentified as five previously described species native to the regions where Didemnum sp. A has been discovered and has been described as two new species based solely on morphological characteristics. There are relatively few diagnostic characters and a great deal of variability in the relevant characters, making the task of identification very difficult. Adding to the confusion has been the widespread and apparently disjunct distribution of the species. Here, we present molecular data on both mitochondrial and nuclear genes from colonies sampled from Europe, east and west coasts of North America, Japan, and New Zealand. These data strongly indicate that Didemnum sp. A is a single species, possibly native to the northwestern Pacific Ocean, that has become established globally. Considering genetic and morphological evidence, the most appropriate name for this species is Didemnum vexillum Kott, 2002.

Assessing the effects of the Prestige oil spill on the European shag ( Phalacrocorax aristotelis): Trace elements and stable isotopes

The Prestige oil spill resulted in the mortality of several seabird species on the Atlantic NW coast of Spain. Shag casualties were particularly relevant, since populations are resident in the area the whole year round and because of several features which make them highly vulnerable to environmental hazards. Ecological catastrophes give us the opportunity of collecting samples which, otherwise, would be difficult to obtain. We examine the potential of shag corpses as bioindicators of inorganic pollution and the possible factors of variability, such as biological traits (sex, age) or nutrition status. We determined trace elements (Hg, Se, Cr, Pb, Zn and Cu) and isotopic signatures ( 15N, 13C) in soft tissues (muscle, liver) and in primary feathers formed at different times (before and after the Prestige) in individuals of known sex and age, collected at the time of the Prestige disaster. These were compared with data from another group of shags trapped accidentally in fishing gear in 2005. Our results did not seem to be affected by sex or age on any of the analysed variables. The higher nitrogen isotopic signatures in the soft tissues of the Prestige shags may be related to the nutrition stress caused by a poorer body condition, which is also reflected in increasing levels of some metals in the liver. This isotopic enrichment was also observed in newly forming feathers when compared to the old ones. On the other hand, the lower δ 15N and Hg values in shag feathers from 2005 point to a shift in feeding resources to prey of lower trophic levels. We found that feather features (being an inert tissue and having a conservative composition), if combined with careful dating and chemical analysis, offer a very useful tool to evaluate temporal and spatial changes in seabird ecology in relation to pollution events.

Two cryptic species of the Hediste diversicolor group (Polychaeta, Nereididae) in the Baltic Sea, with mitochondrial signatures of different population histories

A presence of two cryptic biological species of Hediste diversicolor complex polychaetes was corroborated in a geographical survey of some 30 populations from the eastern and southern coasts of the Baltic Sea, with data from four completely diagnostic allozyme characters. Species A was dominant in the northernmost part of the Baltic Hediste range (Bothnian Sea), whereas Species B alone was found in the south (Poland, Germany, Denmark). In the intervening region, comprising the majority of the sites studied in southern Finland and Estonia, the two species were usually found together, with no evidence of recent hybridisation (i.e., no heterozygote genotypes). While mitochondrial DNA also distinguished the two taxa, it was not similarly completely diagnostic, but there were rare cases (ca 5%) of lineage mismatch indicating that some introgression has occurred in the past. Comparison with published data suggests that species A also inhabits the North Sea–NE Atlantic–Mediterranean coasts, and species B is also present in the North Sea and the NW Atlantic (Canada). Within the Baltic, the two species show distinctly different patterns of mtDNA diversity, plausibly related to different colonisation histories. Species A shows a generally high haplotype and nucleotide diversity, whereas in species B we found only four deeply diverged groups of closely related haplotypes. Hypothetically this could indicate a recent expansion of species B from a small number of colonising individuals. Moreover, species B showed marked intraspecific geographical structuring, with co-incident genetic changes along the N Estonian–S Finnish coasts both in mtDNA and an allozyme marker; this pattern suggests a contact between two genetically distinct invasion waves of different origins. In all, species A and B represent good, reproductively isolated and partly sympatric species which require to be recognised in ecological work. A formal taxonomical description is needed, but awaits better, range-wide distributional and ecological characterisation and working out of morphological differences that enable a practical identification.