Temporal patterns of arctic and subarctic Zooplankton community composition in Jones sound, Canadian arctic archipelago (1961-62, 1963).
ABSTRACT. An analysis of overwinter (1961-62) and early summer (1963) collections of zooplankton in Jones Sound, Canadian Arctic Archipelago, found 31 life forms and species, of which 11 species of copepods were dominant. The collections are the earliest on record from the archipelago. These 50-year-old data form a historical base that may assist in analyzing impacts of changing patterns of sea ice distributions. Water-mass-diagnostic copepod species in this study varied with the seasons; those with boreal Atlantic-Subarctic water affinities were present in the winter, but absent or few in number in the summer. Those with Arctic Basin water affinities were few or absent in winter but present or found in greater numbers in the summer. These variations in copepod species may be related to varying presence or proportions of boreal Atlantic water or Arctic Basin water in Jones Sound as also suggested by concurrent physical and chemical oceanographic data. The copepod species found in Jones Sound are also present or dominant in comparable Arctic waters from East Greenland to the Beaufort Sea and in the Arctic Basin, as reported elsewhere, and all reports differ significantly in the relative numbers of the species present from season to season or year to year. Such differences within Jones Sound are documented between the data reported here and those from the summer of 1980 reported elsewhere. It is suggested that these variations also reflect the differing presence or proportions of boreal Atlantic and Arctic Basin water. The conclusion is that Jones Sound and other High Arctic waters are subject to the presence or absence of Arctic Basin waters and boreal Atlantic waters and that the composition of the copepod communities is indicative of those changes.
Key words: Arctic zooplankton, Arctic and Subarctic waters, copepods, water masses
RESUME. L'analyse d'ensembles de zooplancton preleves au cours d'un hiver (1961-1962) et au debut d'un ete (1963) dans le detroit de Jones, archipel arctique canadien, a permis de reperer 31 especes et formes de vie, dominees par 11 especes de copepodes. Ces ensembles sont les plus anciens ensembles a avoir ete repertories au sein de l'archipel. Ces donnees prelevees ii y a 50 ans forment un fondement historique susceptible d'aider a analyser les incidences des tendances changeantes de la repartition des glaces de mer. Les especes de copepodes relevees en fonction du diagnostic de la masse d'eau dans le cadre de cette etude variaient d'une saison a l'autre. Les copepodes ayant des affinites avec l'eau boreale subarctique atlantique etaient presents en 'liver, mais absents ou en quantite restreinte en ete, tandis que ceux ayant des affinites avec l'eau du bassin arctique etaient absents ou en quantite restreinte l'hiver, mais presents ou en plus grand nombre Pete. Ces variations sur le plan des especes de copepodes pourraient etre attribuables A la presence ou aux proportions variees d'eau atlantique boreale ou d'eau du bassin arctique dans le detroit de Jones, telles que le suggerent egalement les donnees physiques et chimiques oceanographiques concurrentes. Les especes de copepodes reperees dans le detroit de Jones sont egalement presentes ou dominantes dans des eaux arctiques comparables, de rest du Groenland jusqu'a la mer de Beaufort et dans le bassin arctique, tel que signale ailleurs, et tous les rapports different considerablement quant au nombre relatif d'especes presentes de saison en saison ou d'annee en armee. Les differences relevees au detroit de Jones sont repertoriees entre les donnees communiquees ici et celles de Pete 1980 communiquees ailleurs. On suggere que ces variations sont aussi le reflet de la presence ou de proportions differentes d'eau boreale atlantique et d'eau du bassin arctique. On en conclut que les eaux du detrait de Jones et celles d'autres endroits de l'Extreme-Arctique sont assujetties A la presence ou A l'absence d'eau du bassin arctique et d'eau boreale atlantique, et que la composition des communautes de copepodes est indicative de ces changements.
Mots cies : zooplancton de l'Arctique, eaux arctiques et subarctiques, copepodes, masses d'eau
Traduit pour la revue Arctic par Nicole Giguere.
Temporal and spatial variations in the numbers and species compositions of Arctic marine copepods have previously been noted in a number of reports. This paper, together with oceanographic data reported elsewhere, supports the hypotheses that those variations reflect variations of Arctic and Subarctic water masses and that Jones Sound is a sensitive region for monitoring such changes. Previous to this work in Jones Sound in 1961-62 and 1963, the only comparable year-round zooplankton work in northern Canada was that of Grainger (1959) in Foxe Basin. None had been undertaken within the Canadian Arctic Archipelago. This work was part of a larger project concerned with physical and chemical oceanography through much of the year (Apol-lonio and Townsend, 2011), the first such study in the archipelago. That project also examined the effects of glaciers on Arctic waters (Apollonio, 1973) and nutrient chemistry, chlorophyll, and primary production in summer months (Apollonio and Matrai, 2011). The intent was to estimate primary production and to characterize zooplankton ecology within the context of physical and chemical oceanographic parameters. The zooplankton community of the archipelago, as was then anticipated, is dominated by pelagic copepods, which are the major link in the energy transfer between the primary producers and higher trophic levels in the pelagic food. chain (Michel et al., 2006). Prior to 1961, year-round zooplankton research had been undertaken in East Greenland (Ussing, 1938; Digby, 1954), and since 1963, a number of reports have documented summer zooplankton studies in the Canadian Arctic Archipelago and in adjacent waters. In all cases, copepods were the most numerous of all zooplank-ton species. Among other results, those studies documented a community of dominant copepod species in the zooplank-ton communities over a broad range of Arctic waters, and they noted substantial seasonal and interannual variation in the proportions of those species.
Zooplankton collections from a single location on the south side of Jones Sound off Devon Island in the Arctic Archipelago of Canada (Fig. 1) were made periodically from November 1961 into May 1962, and in June and July 1963, as part of a research program of the Arctic Institute of North America (AINA). This paper records the species and numbers of the collections on each sampling date. These data could contribute to the documentation of spatial-temporal distributions of zooplankton assemblages that can be used in modeling the impacts of a shift in sea ice regime on the trophodynamics and biogeochemical cycles of Arctic shelves (Wassman, 1998; Darnis et al., 2008).
Jones Sound lies between Ellesmere Island and Devon Island and is about 210 km in length and 29-72 km in width. The sound has a maximum depth of about 800 m, but the zooplankton sampling site lay over a shelf extending from the north shore of Devon Island. The depths do not exceed about 100 m for about 8 km from shore or 200 m at 11 km from shore. Water from the Arctic Basin enters the sound from the west through Cardigan Strait and Hell Gate, two narrow channels with strong south-flowing currents. Water from northern Baffin Bay and the North Water enters Jones Sound from the northeast through Glacier Strait. The main exit of water is Lady Ann Strait at the southeastern corner of Jones Sound. The sun is continuously below the horizon from 23 October to 8 February and continuously above the horizon from 30 April until early September. Sea ice forms along the coasts of Jones Sound in October, and most of the sound is ice-covered by December or early January. During the 1961--62 winter, the sea ice attained a thickness of about 2 m, with a maximum snow cover of 10-12 cm. The ice was snow-free by 12 June and broke up on 5 July 1962. In the spring of 1963, snow depth was 15-16 cm over 2 m of sea ice, and the ice broke up on 10 August. Collections were not feasible after breakup.
The collections began in mid November 1961, when the strength of sea ice was sufficient to sample more than 80 m of water about 3.6 km off the north shore of Devon Island. All the collections in 1961-62 were made from a heated hut over a hole in the ice at 75[degrees]44' N, 84[degrees]40' W. Samples were collected at approximately two-week intervals except in April 1962, when no collections were made. In 1961-62, the plankton net was 30 cm in diameter, with 76 Am mesh and 158 p.m mesh in the collecting cup. In 1963, the net was 38 cm in diameter, with 239 gm mesh in the net and collecting cup. In 1961-62, a first slow tow from 50 m was followed by a slow tow from 80 m. In 1963, a slow tow from 50 m was made on each sampling date at approximately two-week intervals. Only one slow tow from 80 m was made in 1963, on 5 July. The volume of water filtered in theory was calculated from the area of the mouth of the net multiplied by the length of the tow. A tow in 1961-62 from 50 m filtered 3.5 [m.sup.3]; a tow from 80 m filtered 5.6 m3. In 1963, a tow with the larger net filtered 5.6 m3 from 50 m and 9 m3 from 80 m, but 100% filtering efficiency cannot be assumed. Dawson (1978) estimated filtering efficiency at about 50%. Grainger (1959) was similarly cautious in his estimate of filtering efficiency. Collections were preserved in 5% formalin. The entire contents of all but one tow were identified when possible and counted. Because of the high numbers of cirriped nauplii, only one-third of the contents of the tow from 50 m on 23 July 1963 was counted. Those counts were multiplied by three to estimate the total numbers. Counts were made with a binocular microscope (25x) at the AINA research station on Devon Island.
TABLE 1. Numbers of zooplankton. Jones Sound, November 1961-May 1962. collected from 50-0 m, with the number collected from 80-0 m in parentheses. Date Zooplankton Nov 14 Nov 28 Dec 24 Jan 17 Feb 1 Feb 19 Silicoflagcllates Foraminifera 3 (1) 1 (2) 3 (5) 1 (1) 1 (4) Medusa 4 (4) 1 (6) 2 (0) 0 (1) 4 (3) 0 (1) Polychaetc larvae 0 (2) 1 (0) 0 (1) Calanus finmarchicus 37 (44) 20 4 (22) 6 (11) 18 4 (13) (24) (55) Pseudocalanus spp. 510 434 274 110 224 72 (1006) (416) (441) (83) (368) (232) Microcalanus 67 89 pygmaeus (98) (1521 Metridia longa 3 (7) 8 (9) 5 (8) 6 (5) 26 2 (24) (30) Acartia longiremis 5 (5) Oithona similis 370 407 436 172 463 133 (420) (528) (462) (183) (487) (297) Ovigerous O. similis 6 (9) 2 (6) 6 (14) 23 17 (17) (41) Oncaea borealis 3 (15 2 (0) 28 (6) 11 23 4 (28) (1)) (20) (17) Harpacticoids 0 (1) Unidentified 4 (4) 3 (0) 3 (0) 3 (1) 0 (3) 82 copepods (154) Copepod nauplii 7S (78) 192 553 329 273 138 (285) (457) (373) (391) (309) Zoea larvae Ostracods 1 (0) Decapod 0 (1) Euphausiid 1 (0) Veliger larvae 1 (2) 3 (4) 0 (4) Sagitta elegans 3 (2) 0 (1) 1 (0) 4 (4) 1 (0) Pluteus larvae 0 (2) Blastula larvae Echinoderm juvenile 0 (1) Larvacea 0 (4) 3 (5) 1 (0) 3 (1) 15 (6) 3 (1) Oikopleura 1 (0) Fish larvae Zooplankton Mar 7 Mar 18 May 25 Silicoflagcllates 0 (1) Foraminifera Medusa 0 (2) 0 (2) Polychaetc larvae 3 (5) Calanus finmarchicus 2 (3) 1 (4) Pseudocalanus spp. 34 560 37 (34 (58) (545) (1)) Microcalanus 71 36 171 pygmaeus (117) (35) (192) Metridia longa 1 (22) 6 (11) 10 (0) Acartia longiremis 1 (1) 9 (4) Oithona similis 203 169 120 (337) (115) (114) Ovigerous O. similis 16 12 (6) 11 (6) (19) Oncaea borealis 11 0 (9) 5 (5) (37) Harpacticoids 1 (1) Unidentified 70 93 66 copepods (167) (29) (53) Copepod nauplii 158 735 511 (436) (395) (322) Zoea larvae 0 (8) Ostracods 0 (1) Decapod Euphausiid Veliger larvae Sagitta elegans 0 (1) 1 (1) Pluteus larvae 1 (0) 0 (1) 2 (14) Blastula larvae 0 (163) Echinoderm juvenile Larvacea 4 (7) 4 (0) 3 (5) Oikopleura Fish larvae 1 (1) (1.) One ovigerous female found in tow from 80--0 m.
All the data are shown in Tables 1 (for overwinter 1961-62) and 2 (for June--July 1963). The overwinter and summer tows found 31 species and life forms, of which 11 copepod species, including unidentified species, were predominant. Frost (1989) reported that throughout the range of Pseudocalanus, P. minutus, and P. acuspes may co-occur extensively in the Arctic regions and may overlap extensively in size, so that these species were often confused. This information was not known at the time the samples from 1961-63 were analyzed, and this report does not attempt to distinguish between the two species. Those copepods considered here are referred to only as Pseudocalanus spp.
Acartia longiremis, not shown in Figure 2, was absent prior to mid February but then appeared in very small numbers (< 10) in all samples through July. Unidentified copepods were found in all samples except the 23 July sample. The highest numbers (154 and 167) were found in late February and early March.
Ovigerous Pseudocalanus spp. were found only in June and July. Ovigerous 0. simi/is were found in all samples except in December. There does not appear to be a preponderance of egg-bearing 0. simi/is in any one season. Copepod nauplii were found in large numbers (200-700) in all samples except the mid November sample (< 80). Cirriped nauplii were found only in June and July, increasing from approximately 80 in mid June to 1964 in early July.
The other life forms all occurred at irregular times and always in small numbers (< 10) except for polychaete larvae, which numbered 154 in late July; harpacticoids (49 in July): and Fritillaria (597 on 23 July). These high numbers may reflect reproduction or attraction into the euphotic zone of maximum primary production in July (Apollonio and Matrai, 2011). The relative numbers of ostracods and larvacea reflect the observations of Longhurst et al. (1984) that the former remain deep but the latter are found in near-surface waters. The small numbers of silicoflagellates and foraminifera were perhaps the result of undersampling of those single-cell organisms.
TABLE 2. Numbers of zooplankton. Jones Sound, June--July 1963. Tows From 80 m occurred only on July 5. Parentheses show number of ovigerous females. Date July 5 Zooplankton June 6 June 50-0 m 80-0 m July 19 23 Silicoflagellates 1 Medusa Aglanntha 4 1 0 9 9 digitale Siphonophore 0 9 Polychaete larvae 1 0 143 154 Calanus glacialis 15 35 290 341 18 Calanus hyperbureus 25 29 7 Pseudocalanus spp. 75 (1) 164 351 59 (1) Microcalanus 349 131 132 530 1038 pygmaeus Metridia longa 3 1 3 7 Acarlia longiremis 5 1 7 4 3 Oithona similis 123 85 (8) 182 372 128 (12) (1) (48) (14) Oncaea borealis 31 20 20 70 48 Harpacticoids 7 (1) 0 1 49 Unidentified 66 41 83 copepods Copepod nauplii 458 353 328 530 337 Cirriped nauplii 78 81 1235 1964 1043 Amphipods 1 2 1 Decapods 1 Sagitta elegans 3 1 I 5 2 Pluteus larvae 38 3 5 Oikopleura 228 Fritillaria 0 546 597
Figure 2 shows the copepod species from this collection that exhibit characteristic changes in numbers over time. Ca/anus finmarchicus was found in moderate and declining numbers in all but one of the winter-spring samples, but was not found in any of the June--July samples. Pseudoca-lanus spp. and Oithona similis were the most numerous of all taxa, the two comprising about 50% of the total number of individuals found. Both species occurred in all winter-spring and summer samples, but in summer, the numbers of both species collected from the 50 m tows averaged about one-half the numbers collected from 50 m in winter-spring. The apparently anomalous high number of Pseudo-calanus spp. on 18 March could reflect the opportunistic, tidally dependent feeding on ice algae concentrated at the ice-water interface documented by Conover et al. (1986). Metridia longa occurred in all samples, in small numbers in the winter-spring and in very small numbers in June--July. Oncaea borealis was found in all samples and in rather small but nearly constant numbers from 50 m (average 9.7) in winter-spring 1961-62; it was three times more numerous (average 29.7) in June--July 1963. Microcalanus pyg-maeus was not found prior to February but then was found in moderate numbers (up to 192) into May and increased to 1038 by 23 July, exceeding numbers of all species except cirriped nauplii. Ca/anus glacialis was found only in the June and July samples, and C. hyperboreus, only in July. C. glacialis was the more numerous of the two in any sample, reaching 341 individuals in the 80 m tow on 5 July. Figure 2 shows a progression of species from those most numerous in winter-spring to those most numerous in summer.
The variations of species and numbers in this collection suggest that the results were influenced by differing proportions of Arctic Basin water and boreal Atlantic (or Subarctic) water, or by the presence or absence of those water masses at the zooplankton sampling site on the south side of Jones Sound. This hypothesis is reinforced by physical and chemical oceanographic data collected from the south and north sides of the sound in May 1962 and by comparable oceanographic data from the north side collected in May 1969 (Apollonio and Townsend, 2011). Those oceanographic data suggest both regional and annual variations in the presence or absence of the two water masses.
The dominant species in this collection include C. finmarchicus, which is indicative of boreal Atlantic water (Grainger, 1962); Oithona similis, of no specific affinity; and C. glacialis, C. hyperboreus, M pygmaeus, and 0. borealis, which are indicative of Arctic Basin water (Smith and Schnack-Schiel, 1990) and are found from East Greenland (Digby, 1954) to the Chukchi and Beaufort Seas (Darnis et al., 2008).
A number of reports show commonality among the dominant copepod species over broad Arctic regions, but there is considerable variation in the relative proportions or presence or absence of those species, even among those considered to be characteristic of Arctic Basin water (e.g., Ussing, 1938; Grainger, 1959; Cairns, 1967). It is possible that the differences reflect differences among species in their vertical migrations. C. hyperboreus carries on seasonal migrations (Dawson, 1978), but it is unlikely that four species with Arctic Basin water affinities would carry out synchronized seasonal vertical migrations, as might be inferred from the present data. Longhurst et al. (1984) noted that diurnal migrations in Arctic Species have rarely been demonstrated unequivocally, and that in their work, diurnal migration was nowhere a major factor. in the distribution of biota. It is more likely that the differences reported within and among the several reports are functions of water masses originating from the Arctic Basin or from boreal Atlantic regions (Tidmarsh, 1973). The present data (Tables 1 and 2, Fig. 2) show that species showing affinities with Arctic water either appeared only in summer (e.g., C. glacialis, C. hyperboreus) or increased their numbers (averaged over each sampling date over the winter-spring season and from the summer season) from winter-spring to summer (87 v. 412 for M pygmaeus; 9.7 v. 29.7 for 0. borealis). M pygmaeus is the dominant copepod in the Arctic Basin for much of the year (Hughes, 1968). The large number found in late July 1963 in this work is consistent with the presence of other copepods with Arctic Basin water . affinities, and its increase in summer is consistent with the decline and disappearance from winter to summer of C. fin-marchicus, a species indicative of boreal Atlantic water.
Canadian Arctic Archipelago waters originate mainly from the Arctic Ocean (Jones and Coote, 1980; Michel et al., 2006), as shown by the widespread occurrence of C. glacialis, C. hyperboreus, M pygmaeus, and 0. borealis (Smith and Schnack-Schiel, 1990). Arctic Basin water and its characteristic species enter Jones Sound through Hell Gate and Cardigan Strait in the northwestern corner of the sound. The present data also include species (C. finmarchicus, A. longiremis, Tidmarsh, 1973) associated with boreal Atlantic or Subarctic water, which enters Jones Sound from the east through Glacier Strait. Glacier Strait receives water from northern Baffin Bay and the North Water, both of which contain portions of boreal Atlantic water. After passing through Glacier Strait, the Subarctic water flows westward along the northern part of Jones Sound (Fig. 1). Barber and Huyer (1977) suggest a cyclonic circulation across Jones Sound west of Cape Sparbo, Devon Island, which brings some boreal Atlantic water from the north side of Jones Sound to the vicinity of this zooplankton sampling site on the south side. The present data indicate that the inflow through Glacier Strait and this gyre may have seasonal or interannual variability. Water with species of boreal Atlantic affinity was present in the winter-spring of 1961-62 but much reduced (or absent) in the summer of 1963, when Arctic Basin water was in greater proportion. Unfortunately, the timing of the present data do not permit identification or direct comparison of specific seasonal versus interannual differences; winter-spring data were from 1961-62, but summer data were from 1963.
Pseudocalanus spp. and 0. similis are widespread, common species in both Arctic and Subarctic waters, but are not diagnostic of either water mass (Tidmarsh, 1973). Their occurrence in these collections is consistent with other reports, but the marked reduction of both species in summer further suggests a change in the character of water masses at the sampling site.
Comparisons among several reports suggest year-to-year variations in water mass composition in both Lancaster Sound (Longhurst et al., 1984 vs. Pomerleau et al., 2011) and Jones Sound (this paper and Longhurst et al., 1984). Further, the comparisons suggest variation in the relative proportions of species and mixing of Arctic Basin and boreal Atlantic waters in Jones Sound from year to year and within the year (this paper). For example, the Jones Sound collections in the summer of 1963 showed C. glacialis and C. hyperboreus, as did the observations in the summer 1980 (Longhurst et al., 1984). But the 1963 collections included M pygmaeus and 0. borealis, both indicative of Arctic Basin water, while the 1980 data did not. Thus the 1963 composition from the south side of the sound is more indicative, or shows a higher proportion of Arctic Basin water, than the 1980 composition from the north side. One can imagine Arctic Basin water entering Jones Sound from the west and flowing with little mixing along the south side of the sound, whereas boreal Atlantic water enters the sound from the east and mixes in varying proportions on the north side of the sound with Arctic Basin water coming from the west. The difference may also be indicated by oceanographic data from Jones Sound (Apollonio and Townsend, 2011). Those data indicate water at the zooplankton sampling site on the south side of Jones Sound that was less saline and somewhat colder, indicative of Arctic Basin water, than comparable oceanographic data (Apollonio and Townsend, 2011) from the north side of the sound and 65 km from the zooplankton sampling site, also collected in May 1962. That water was more saline and warmer, indicative of boreal Atlantic water. Interannual variation in the presence of different waters on the north side of the sound is suggested by comparison of 1962 and 1969 data (Apollonio and Townsend, 2011), which indicate a greater proportion of Arctic water in 1969 than in 1962. These differences in water masses could be caused by several factors (e.g., wind, ice cover). Bailey (1957) attributed such differences to changes of atmospheric pressure patterns. In the springs of 1961 and 1962, high pressure prevailed over the Arctic Basin northwest of the Canadian Arctic Archipelago, with low pressure east of Greenland. The pressure pattern was reversed in spring 1963, and the change of patterns may be the cause of the variations in copepod communities from 1961-62 to 1963 reported here.
Overwinter and summer collections of copepods from Jones Sound in the Canadian Arctic Archipelago, when compared with copepod data from other High Arctic areas, show a high degree of commonality of species but indicate considerable seasonal and interannual variation in the proportions of species. The reports from each area suggest that the changes in species composition result from the presence or absence of boreal Atlantic water in the several areas and the degree of mixing of that water with Arctic Basin water, which generally dominates the entire region. This conclusion is supported by previously published oceanographic data. Copepod data, together with oceanographic data from Jones Sound, provide support for the hypothesis that copepod community compositions reflect areal, seasonal, and interannual variations in the presence or mixing of Arctic Basin and Subarctic, or boreal Atlantic, water masses. These variations, observed 50 years ago, must be taken into account when considering the impacts of climate change on Arctic waters.
I thank David Townsend, School of Marine Sciences, University of Maine, for Figure I; David Libby, Maine Department of Marine Resources, for Figure 2; and Patricia Matrai, Bigelow Laboratory for Ocean Sciences, for technical assistance. I thank anonymous reviewers who made important suggestions for improvement of the paper. The expedition of which this work was a part was supported by funds and equipment from the Arctic Institute of North America, the Defence Research Board of Canada, the National Research Council of Canada, the Office of Naval Research (USA), the National Science Foundation (USA), the United States Weather Bureau, and the Meteorological Branch of the Department of Transport (Canada). Funds also came from the Royal Society, the United States Steel Foundation, and many private donors. Equipment was donated by Massey-Ferguson Ltd., British Petroleum, the Hudson's Bay Company, and other companies. All funds were administered by the Arctic Institute of North America.
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(1.) Arctic Institute of North America; present address: 43 Eastern Avenue, Boothbay Harbor, Maine 04538, USA; email@example.com
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