Microzooplankton herbivory on the Grand Bank (Newfoundland,Canada): A seasonal study

Grazing impact of microzooplankton on phytoplankton was investigated on the Grand Bank, Newfoundland, Canada, in April, July and October 1984, using a seawater dilution method. In April a large proportion of chlorophylla was in the microplankton size fraction (> 20µm) while in mid-summer and fall most was in the nanoplankton size fraction (< 20µm). Diatoms were the dominant phytoplankters in April, while undetermined flagellates and coccolithophores were abundant in other seasons. Major grazers were oligotrichous ciliates in all seasons. Instantaneous grazing rates on nanophytoplankton, as measured by changes in chlorophylla, varied from 0.12 to 0.43 d^–1 and those on microphytoplankton from 0.19 to 0.68 d^–1. Grazing rates did not change over 24 and 48 h intervals. This level of grazing corresponded to a daily loss of about 20 and 30% of standing stock of chlorophylla and about 50 and 70% loss of potential production in the two size fractions respectively. Taxon-specific grazing rates, calculated from microscopic enumeration, showed that small diatoms were grazed heavily, and their growth was controlled by grazing in late spring. In late summer and fall, undetermined flagellates and coccolithophores were also grazed at high rates but their growth rates were higher than the grazing rates, and therefore, were not controlled by microzooplankton. In general, microzooplankton grazed on whatever appropriate sized food was dominant in the experimental water. Their potential ability to control the growth of certain food species may be one of the causes determining the species composition of phytoplankton communities.     

Abundance and biomass of macrobenthos in the vicinity of Carson Submarine Canyon,northwest Atlantic Ocean

The abundance, biomass and mean weight of macrofauna in the Carson Canyon region (Lat. 45°30N, Long. 48°40W) of the Grand Banks were estimated from 40 quantitative infaunal samples taken at 15 stations in June 1980. In contrast to other areas, there were no significant differences in these values between samples taken in and outside of the canyon. Abundance ( = 716 individuals m^-2), biomass ( = 10.9 gm^-2), and mean weight ( = 0.03 g individual^-1) displayed no consistent relationship with depth, but stations grouped according to sediment type had differing dominant taxa. Biomass and abundance at the edge of the Grand Banks are unexpectedly low. Larger animals, including fishes, that forage there must depend more on pelagic than on benthic food sources.     

Biological and environmental influences on the trophic ecology of leatherback turtles in the northwest Atlantic Ocean

Understanding the causes and consequences of variability in trophic status is important for interpreting population dynamics and for identifying important habitats for protected species like marine turtles. In the northwest Atlantic Ocean, many leatherback turtles (Dermochelys coriacea) from distinct breeding stocks throughout the Wider Caribbean region migrate to Canadian waters seasonally to feed, but their trophic status during the migratory and breeding cycle and its implications have not yet been described. In this study, we used stable carbon and nitrogen isotope analyses of bulk skin to characterize the trophic status of leatherbacks in Atlantic Canadian waters by identifying trophic patterns among turtles and the factors influencing those patterns. δ¹⁵N values of adult males and females were significantly higher than those of turtles of unknown gender (i.e., presumed to be subadults), and δ¹⁵N increased significantly with body size. We found no significant differences among average stable isotope values of turtles according to breeding stock origin. Significant inter-annual variation in δ¹⁵N among cohorts probably reflects broad-scale oceanographic variability that drives fluctuations in stable isotope values of nutrient sources transferred through several trophic positions to leatherbacks, variation in baseline isotope values among different overwintering habitats used by leatherbacks, or a combination of both. Our results demonstrate that understanding effects of demographic and physiological factors, as well as oceanographic conditions, on trophic status is key to explaining observed patterns in population dynamics and for identifying important habitats for widely distributed, long-lived species like leatherbacks.     

Movements,environmental associations,and presumed spawning locations of Atlantic halibut (Hippoglossus hippoglossus) in the northwest Atlantic determined using archival satellite pop-up tags

Large Atlantic halibut (Hippoglossus hippoglossus) off the eastern coast of Canada were tagged with pop-up satellite archival transmission tags (N = 17) to track movements, determine ambient depth and temperature, and infer spawning activity. Many halibut showed seasonal movements from deepwater slope areas in fall and winter to shallower feeding grounds on the Scotian Shelf and Grand Banks in summer. Halibut depths ranged between 0 and 1,640 m. Mean temperature of occupation was 4.7 °C. Multiple short-term vertical ascents from a consistent baseline depth, characterized as spawning rises, were identified in seven of the tagged halibut south of the Grand Banks. All presumed spawning rises occurred in multiples of 2–6 events at 2- to 9-day intervals between October and January, spanning an average vertical extent of 50–100 m at depths of about 800–1,000 m. Given the direction and velocity of the slope water currents and the duration of the pelagic stage, the calculated 300–500 km drift of the eggs and larvae would take them onto the Scotian Shelf, as well as into the Gulf of St. Lawrence. Therefore, the location of the presumed spawning grounds is consistent with expectations based on migration compensation theory, the northeasterly migratory patterns of the juveniles, the relatively static distribution of the adults off southern Newfoundland, and the prevailing currents at depth.     

Growth of the Atlantic surfclam,Spisula solidissima,from Georges Bank to the Delmarva Peninsula,USA

Age/shell length data for offshore surfclam, Spisula solidissima (Dillwyn, 1817), populations were used to estimate the parameters of the von Bertalanffy growth model by time period and region, from Georges Bank in the north to the Delmarva Peninsula in the south. Randomization tests were used to compare curves. We tested the a priori hypothesis that growth curves would change over time in the south (i.e., New Jersey and Delmarva) but remain constant in the north (i.e., Long Island and South New England). This hypothesis was proposed because surfclam population structure in the south had been altered by the hypoxic event of 1976, and possibly by intense, long-term commercial harvesting. Northern regions, unaffected by these factors, served as natural controls. Based on a comparison of data collected in 1980 with pooled data from 1989 and 1992, the hypothesis was supported. Both the growth coefficient (k) and maximum shell length (L ) declined between two time periods in the two southern regions, while during the same time interval, no change occurred in the two northern regions. Differences in growth between regions were often statistically significant. For example, compared with the southern regions, the growth coefficient on Georges Bank was larger, and those clams attained a smaller maximum length. In a comparison of adjacent regions from Delmarva to S. New England, k increased from south to north. This could imply faster growth in cooler water, as well as no relationship between growth and primary productivity. Alternatively, size-selective mortality, imposed by the commercial fishery, was discussed as a mechanism that might account for this unexpected pattern.     

Organic and calorific content of the body tissues of deep-sea elasipodid holothurians in the northeast Atlantic Ocean

Data are presented on the biochemical analysis of protein, lipid, carbohydrate and ash for the ovary, testis, gut and body wall of six species of elasipodid holothurians at a variety of stations in the Porcupine Seabight and Abyssal Plain (northeast Atlantic Ocean). Samples were collected between 1980 and 1982. The species investigated were Benthogone rosea, Laetmogone violacea, Oneirophanta mutabilis, Deima validum, Benthodytes sordida and Psychropotes longicauda. Lipid was the dominant soluble constituent of the ovary and protein was dominant in the testis. Tissue calorific content was determined from the biochemical data and by microbomb calorimetry. The ovaries had higher calorific values than the other body tissues when determined by both methods. Comparison of the two methods suggests that the calorific values for testis, gut and body wall are significantly different, and this may be a function of the calcium-carbonate content of these tissues. Total-body calorific value varied from 24.26 J mg^-1 ash-free dry weight (AFDW) (5 799 cal g^-1 AFDW) to 25.43 J mg^-1 AFDW (6 078 cal g^-1 AFDW). Total holothurian-body calorific biomass at depths of 1 010, 2 000 and 4 000 m is 0.49, 3.69, and 0.25 kJ m^-2 (118, 882, 59.4 cal m^-2), respectively. Holothurians form a significant store of energy in the deep sea.     

Mitochondrial DNA sequence variation in deep-sea bamboo coral (Keratoisidinae) species in the southwest and northwest Pacific Ocean

The Keratoisidinae are a poorly known, but phenotypically diverse group of deepwater corals. Recent developments in deepwater trawling in the southwest Pacific have provided many more specimens of bamboo corals. Two sub-regions of the mitochondrial genome were sequenced to test genetic relationships among specimens collected over a wide geographical range (27–50° S): a sub-region of the large-subunit rRNA (16S rRNA), characterized by a highly variable insertion/deletion (INDEL#2) region; and a non-coding region between COII and COI. Based on DNA haplotypes, 14 species of Keratoisidinae were recognized among 88 specimens from deep water in the southwest Pacific Ocean. The common haplotypes also appeared in specimens collected in the northwest Pacific Ocean and may indicate that some bamboo coral species are widespread in the Pacific, or that the mitochondrial markers are insensitive to recent speciation events. Many specimens were taken from flat bottom areas and, contrary to assumptions, the bamboo corals are not endemic to seamounts. The closure of some seamounts to trawling will protect bamboo corals from extinction, but not from local depletion.Communicated by M.S. Johnson, Crawley     

Hydrology influences population genetic structure and connectivity of the intertidal amphipod Corophium volutator in the northwest Atlantic

The mechanisms driving genetic structure in marine systems are elusive due to the difficulty of identifying temporal and spatial barriers to dispersal. By studying marine invertebrate species with limited dispersal potential, genetic structure can be directly related to physical and biological factors restricting connectivity. In the northwest Atlantic, the benthic brood-rearing amphipod Corophium volutator is distributed across basins with distinct circulation patterns and has the potential to disperse passively during its adult stage. We analyzed spatial genetic variation and migration rates across C. volutator’s North American range with sequence data for mitochondrial DNA and three novel nuclear markers using frequency and coalescent-based methods. We found low genetic differentiation within basins, but strong subdivision within the Bay of Fundy and a striking biogeographic break between the Bay of Fundy and Gulf of Maine, suggesting that genetic drift may act on populations in which connectivity is restricted due to the limitation of passive dispersal by hydrological patterns.     

Food habits and intestinal parasites of deep demersal fishes from the upper continental slope east of Newfoundland,northwest Atlantic Ocean

Stomach contents and intestinal parasite faunas of 471 individuals of demersal fishes in 14 species were examined from the Carson Canyon region (Lat. 45°30N; Long. 48°40W) of the upper continental slope of the Grand Banks off Newfoundland, Canada. Individual species tended to feed either on benthic or on pelagic/benthopelagic organisms, but pelagic prey assumed the greatest importance overall. Data from stomach contents were supported by the parasite information. Prevalence of parasites was higher in benthic feeders (53.1%) than in pelagic feeders (28.9%), and relative abundance by major group was: Digenetic Trematoda 5.8% benthic vs 27.8% pelagic, Nematoda 53.1% vs 72.2%, and Acanthocephala 40.9% vs 0%. Of the dominant fishes, there were more species of benthic feeders (5) than pelagic feeders (3), but pelagic feeders were numerically more abundant (pelagic 70.9%, benthic 20.5%). Benthic feeders were on average larger (=270.6g) than pelagic ones (=130.6g), but pelagic feeders represented a larger proportion of the biomass (pelagic 43.3%, benthic 25.9%). The results of this study combined with those from other areas suggest that feeding from the pelagial by demersal fishes at upper continental slope depths is probably the general rule.     

Anthropogenic disturbance of deep-sea megabenthic assemblages: a study with remotely operated vehicles in the Faroe-Shetland Channel,NE Atlantic

The effects of local-scale anthropogenic disturbance from active drilling platforms on epibenthic megafaunal abundance, diversity and assemblage pattern were examined in two west of Shetland hydrocarbon fields at 420 and 508 m water depth. These areas were selected to include a range of disturbance regimes and contrasting faunal assemblages associated with different temperature regimes. Remotely operated vehicle (ROV) video provided high-resolution megafaunal abundance and diversity data, which were related to the extent of visible disturbance from drilling spoil. These data, in conjunction with a study deeper in the Faroe-Shetland Channel, have allowed comparison of the effects of disturbance on megabenthos across a range of sites. Disturbance to megafaunal assemblages was found to be high within 50 m of the source of drill spoil and in areas where spoil was clearly visible on the seabed, with depressed abundances (Foinaven 1,900 individuals ha⁻¹; Schiehallion 2,178 individuals ha⁻¹) and diversity (H′ = 1.75 Foinaven; 1.12 Schiehallion) as a result of smothering effects. These effects extended to around 100 m from the source of disturbance, although this was variable, particularly with current regime and nature of drilling activity. Further from the source of disturbance, megafaunal assemblages became more typical of the background area with increased diversity (H′ = 2.02 Foinaven; 1.77 Schiehallion) and abundance (Foinaven 16,484 individuals ha⁻¹; Schiehallion 5,477 individuals ha⁻¹). Visible effects on megafaunal assemblages as a result of seabed drilling were limited in extent although assemblage responses were complex, being controlled by differing effects to individual species often based on their motility.     

Horizontal movement of ocean sunfish, <Emphasis Type="Italic">Mola mola</Emphasis>, in the northwest Atlantic

Data were retrieved from 25 ocean sunfish (Mola mola) that were tagged with pop-up satellite archival tags in the southern Gulf of Maine (n = 6), off Nantucket Island (n = 17), and off the coast of Georgia (n = 2) between September 2005 and March 2008. Tags remained attached from 7 to 242 days, with a mean attachment period of (X ± SD) 107.2 ± 80.6 days. Ocean sunfish tagged in the Gulf of Maine and southern New England left those areas in the late summer and early autumn and moved south along the continental shelf break. Fish traveled as far south as the Bahamas and the Gulf of Mexico. By moving south, sunfish experienced similar mean sea surface temperatures throughout the tagging period. The maximum straight-line distance traveled by a tagged Mola mola was 2,520 km in 130 days. Two tagged ocean sunfish entered the Gulf of Mexico, one in the December and one in July. Movements were associated with frontal features created by the Gulf Stream and fish moved farther offshore in 2007 when the Gulf Stream was deflected from the shelf break.     

Diet of four species of deep-sea isopods (Crustacea: Malacostraca: Peracarida) in the South Atlantic and the Southern Ocean

The food of four species of asellote isopods (Crustacea, Malacostraca), Haploniscus rostratus, Haploniscus unicornis, Acanthocope galatheae and Betamorpha fusiformis, was evaluated by analysis of their gut contents. The isopods were sampled at several stations on the abyssal plains of Guinea Basin, Angola Basin and Cape Basin (southeast Atlantic), the Weddell Sea abyssal plain and the Antarctic continental slope during the DIVA and ANDEEP expeditions in 2000, 2001 and 2005. While all species had mineral particles in their guts and mucus material was the most frequent food item, the remaining gut contents differed among species. Betamorpha fusiformis fed mostly on phytodetritus, especially in the Southern Ocean basins and ingested along with it whole calcareous foraminifers. Acanthocope galatheae showed some differences in gut contents between basins, but in the Guinea Basin, the contents were to a large extent stercomata, i.e., waste pellets of soft-walled foraminifers, i.e., the Komokiaceae. Indications were that the haploniscids were feeding on detritus and agglutinating foraminifers (stercomata). This indicates spatial differences in food availability for this diverse group of deep-sea isopods and the importance of poorly known foraminiferal groups, like the Komokiaceae, as a food source in the deep sea.     

Oceanographic preferences of Atlantic bluefin tuna, <Emphasis Type="Italic">Thunnus thynnus</Emphasis>, on their Gulf of Mexico breeding grounds

Electronic tagging and remotely sensed oceanographic data were used to determine the oceanographic habitat use and preferences of Atlantic bluefin tuna (Thunnus thynnus L.) exhibiting behaviors associated with breeding in the Gulf of Mexico (GOM). Oceanographic habitats used by 28 Atlantic bluefin tuna exhibiting breeding behavior (259 days) were compared with available habitats in the GOM, using Monte Carlo tests and discrete choice models. Habitat utilization and preference patterns for ten environmental parameters were quantified: bathymetry, bathymetric gradient, SST, SST gradient, surface chlorophyll concentration, surface chlorophyll gradient, sea surface height anomaly, eddy kinetic energy, surface wind speed, and surface current speed. Atlantic bluefin tuna exhibited breeding behavior in the western GOM and the frontal zone of the Loop Current. Breeding areas used by the bluefin tuna were significantly associated with bathymetry, SST, eddy kinetic energy, surface chlorophyll concentration, and surface wind speed, with SST being the most important parameter. The bluefin tuna exhibited significant preference for areas with continental slope waters (2,800–3,400 m), moderate SSTs (24–25 and 26–27°C), moderate eddy kinetic energy (251–355 cm² s⁻²), low surface chlorophyll concentrations (0.10–0.16 mg m⁻³), and moderate wind speeds (6–7 and 9–9.5 m s⁻¹). A resource selection function of the bluefin tuna in the GOM was estimated using a discrete choice model and was found to be highly sensitive to SST. These habitat utilization and preference patterns exhibited by breeding bluefin tuna can be used to develop habitat models and estimate the probable breeding areas of bluefin tuna in a dynamic environment.     

Growth of the deep-sea irregular sea urchins Echinosigra phiale and Hemiaster expergitus in the Rockall Trough (N.E. Atlantic Ocean)

Growth in the deep-sea irregular sea urchins Echinosigra phiale (family Pourtalesiidae) and Hemiaster expergitus (family Hemiasteridae) was studied from deep-sea samples taken during the years 1973 to 1985 from two stations at 2900 and 2200 m depth in the Rockall Trough (N.E. Atlantic Ocean). Growth zones, similar to those described from sea urchins in shallow water, are present as a series of wide white bands separated by narrow, dark rings in the calcite stereom of the test plates after heating to 350°C. In shallow water, such growth zones seem to result from seasonally varying growth rates. In the supposedly constant conditions in the deep sea, a seasonal growth pattern is unexpected but may occur in response to recently discovered annual pulses in downward flux of detritus from the euphotic zone, providing a seasonally varying food supply for such deposit-feeding species living in the bottom sediment. On this assumption, growth curves were fitted to counts of growth zones (as representing age in years), in the larger lateral and ventral test plates of E. phiale and H. expergitus. The opportunity was also taken to fit growth curves derived from counts of growth zones in samples of the inshore spatangoids Spatangus purpureus and Echinocardium pennatifidum. Plots of counts against test length of Echinosigra phiale and H. expergitus, although scattered and not clearly asymptotic, indicate, growth to be slower than in the two inshore spatangoids, and than in the coastal species Echinocardium cordatum, for which there are good recent growth data, available.     

Annual migrations,diving behavior,and thermal biology of Atlantic bluefin tuna, <Emphasis Type="Italic">Thunnus thynnus</Emphasis>, on their Gulf of Mexico breeding grounds

Electronic tags were used to examine the biology of Atlantic bluefin tuna (Thunnus thynnus L.) on their breeding grounds in the Gulf of Mexico (GOM). The hypothesis that movement patterns, diving behavior, and thermal biology change during different stages of the breeding migration was tested. Mature Atlantic bluefin tuna tagged in the western Atlantic and the GOM, were on their breeding grounds from February to June for an average of 39 ± 11 days. The bluefin tuna experienced significantly warmer mean sea surface temperatures (SSTs) within the GOM (26.4 ± 1.6°C) than outside the GOM (20.2 ± 1.9°C). As the bluefin tuna entered and exited the GOM, the fish dove to daily maximum depths of 568 ± 50 and 580 ± 144 m, respectively, and exhibited directed movement paths to and from the localized breeding areas. During the putative breeding phase, the bluefin tuna had significantly shallower daily maximum depths (203 ± 76 m), and exhibited shallow oscillatory dives during the night. The movement paths of the bluefin tuna during the breeding phase were significantly more residential and sinuous. The heat transfer coefficients (K) were calculated for a bluefin tuna in the GOM using the recorded ambient and body temperatures. The K for this fish increased rapidly at the high ambient temperatures encountered in the GOM, and was significantly higher at night in the breeding phase when the fish was exhibiting shallow oscillatory dives. This suggests that the fish were behaviorally and physiologically thermoregulating in the Gulf of Mexico. This study demonstrates that the movement patterns, diving behavior, and thermal biology of Atlantic bluefin tuna change significantly at different stages of the breeding migration and can be used to define spawning location and timing. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

The ecology of cirratulid mudballs on the Oman margin, northwest Arabian Sea

Mudball-building cirratulid polychaetes have been described previously only from the southern California margin. During a study of oxygen minimum-zone benthos in fall 1994, we observed dense aggregations of agglutinated mudballs at 840 to 875 m on the Oman margin in the northwest Arabian Sea. These were inhabited, and probably constructed, by a cirratulid polychaete species in the genus Monticellina. The mudballs were cigar-shaped, 4.5 to 25 mm long, and positioned vertically so as to protrude several millimeters above the sediment–water interface. Total mudball densities were ∼16 000 m⁻². Occupied mudballs occurred at densities of 2 112 m⁻²; 89% were in the uppermost 2 cm of sediment, and no occupied mudballs were found below 10 cm. Organisms other than the cirratulid were present on 1.7% of the mudballs examined, and included epizoic polychaetes, agglutinated and calcareous Foraminifera. Various polychaetes, a nemertean and nematodes were found inside tests. Mudball abundance exhibited positive associations with densities of several paraonid polychaete species, and with densities of burrowing and subsurface-deposit-feeding polychaetes. Negative associations were observed between mudballs and three tube-building taxa (two polychaetes and an amphipod). Mudball-inhabiting cirratulids are abundant in at least two low-oxygen, margin settings. We expect further sampling of bathyal environments to yield additional systems in which cirratulid mudballs are common. Such observations are valuable because mudballs appear to represent a significant source of heterogeneity that can influence macrofaunal community structure in deep-sea sediments. Received: 15 January 1997 / Accepted: 30 January 1997     

Colonization of the northwest Atlantic by the blue mussel, <Emphasis Type="Italic">Mytilus trossulus</Emphasis> 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 divergence 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 species 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.