In Arctic and Subarctic Seas, and the Modifying Ejfects of Hydrographic Differences in the Environment'
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The Journal of Marine Research is an online peer-reviewed journal that publishes original research on a broad array of topics in physical, biological, and chemical oceanography. In publication since 1937, it is one of the oldest journals in American marine science and occupies a unique niche within the ocean sciences, with a rich tradition and distinguished history as part of the Sears Foundation for Marine Research at Yale University. Past and current issues are available at journalofmarineresearch.org. Yale University provides access to these materials for educational and research purposes only. Copyright or other proprietary rights to content contained in this document may be held by individuals or entities other than, or in addition to, Yale University. You are solely responsible for determining the ownership of the copyright, and for obtaining permission for your intended use. Yale University makes no warranty that your distribution, reproduction, or other use of these materials will not infringe the rights of third parties. This work is licensed under the Creative Commons Attribution- NonCommercial-ShareAlike 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/4.0/ or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA. Journal of Marine Research, Sears Foundation for Marine Research, Yale University PO Box 208118, New Haven, CT 06520-8118 USA (203) 432-3154 fax (203) 432-5872 [email protected] www.journalofmarineresearch.org The Life Cycle of Sagitta elegans in Arctic and Subarctic Seas, and the Modifying Ejfects of Hydrographic Differences in the Environment' M. J. Dunbar McGill University ABSTRACT Sagi/la elegans arctica of the Canadian eastern Arctic waters has a life sp:111 of two years. Its breeding cycle is two-phase, or a!tern?.ting, and the population consists of two distinct groups breeding in different years. The spawning period is long, ex tending from July into the winter, probably up to February. Winter spawning is taken to imply that the breeding behaviour is not timed to coincide with the maximum abundance of food, but that the cycle is determined by the growth limitations imposed by the low temperature. H ydrographic differences between Hudson Bay, Foxe Channel, Ungava Bay and Fro- bisher Bay, though not great, are reflected in the biology of Sagitta. Strong tidal turbulence in Ungaya Bay and Frobisher Bay appears to remove the young-of-the-year from these two areas quickl y, or to cause such vertica l mi xing that they are not properly sampled. The very special co nditions in Lake Og~c produce rapid growth, small size and a sin gle-phase or nonalternating breeding cycle. Introduction. Much effort is currently going into the study of primary production in the sea, the rate at which living stuff is produced by plant plank- ton, as a measure of the relative productivity of different marine regions. This primary production, however, gives a real measure of usable resources only so far as the phytoplankton is used by the zooplankton, which in turn has to be converted to fish and mammal before the seas can be harvested, at least until the direct use of plankton becomes economically feasible on a large scale. The rate at which the zooplankton populations grow, and their abundance, depend on many factors besides the phytoplankton production, and hence a com- plete understanding of marine productivity demands the study of the zooplankton populations themselves: their growth, metabolism, reproduction, distribution. 1 Ca/anus Series No. 1.4. M. J. Dunbar: The life cycle of Sagitta elegans 77 The chaetognaths of subarctic and arctic waters are represented almost exclusively by one .form, the highly successful and abundant Sagitta elegans arctica Aurivillius, a cold-water variant of Sagitta elegans Verrill. In an earlier publication (Dunbar, 1941 ), Sagitta material from the eastern and southern coasts of Baffin Island, and from Hebron in northern Labrador, was analyzed in terms of size-frequency and breeding cycles, with the conclusion that there was a spawning period in spring and summer, probably extending from June to October, and that the individual Sagitta took two years to reach maturity. Populations from the Disko Bay area in western Greenland have been treated in the same way (Dunbar, 1940). The present account is much more extensive, covering material collected in 1947 at Ungava Bay, in 1951 at Ungava Bay and Frobisher Bay, in 1953 at Hudson Bay, and in 1955-56 during an over- wintering expedition in Foxe Basin. Certain material from 1948, 1949, 1950 and 1951, from Ungava Bay, has also been used to corroborate the 1947 results, as mentioned in the text. Only those plankton hauls in which Sagitta was found appear in the tables; the full field data may be obtained in manu- script from the Arctic Unit, Fisheries Research Board of Canada. All of the collection comes from CALANUS Expeditions. The Frobisher Bay collection includes samples from Lake Ogac, a meromictic lake on the southwestern shore of the Bay, which offers special environmental conditions and specialized planktonic cycles. For the winter specimens from Foxe Basin the author is indebted to Dr. E. H. Grainger, Arctic Unit, Fisheries Research Board of Canada. Methods. The chaetognath populations were sampled with open stramin nets and open silk and nylon nets which were hauled horizontally and verti- cally; during the 1955-56 winter the sampling was done twice or three times per month by hauling half-metre nets vertically through the ice. Collection data are given in Table I; the station lists have already been published (Dun- bar and Grainger, 1952; Grainger, 1954; Grainger and Dunbar, 1956). The Foxe Basin collections were made near Igloolik (Grainger, 1959) in water of 50 m depth. The map (Fig. 1) shows the areas covered. The specimens, preserved in 5 °/o formalin in sea water, were measured in the laboratory under a low power microscope and analyzed for maturity stages. Subsamples were randomly taken from the larger catches; the smaller catches were examined completely. Measurements were made to the nearest quarter- millimetre and referred to integer millimetre pivotal lengths for presentation in the size-distribution histograms. The Environment. The physical oceanographic results of the CALANUS Expeditions of 1949-55 have been published (Dunbar, 1958), as have those of the 1947 season in Ungava Bay (Dunbar, 1951) and the Foxe Basin win- tering expedition (Grainger, 1959). The whole region is dominated by arctic Journal of Marine Research [20,1 v.Jl\p· '··· ·. I ·)J·. ·..: . ... - • :' I : .... /"I / Figure 1. Stations at which Sagi/la material was taken. For station lists, see Grainger (1952, 1954), Grainger and Dunba r (1 956). water, originating in the Arctic Sea, modified by coastal and other influences. The extent of intrusion of Atlantic water appears to be significant in the bio- logy of Sagitta, as wi ll appear below. There is evi dence of intrusion of Atlantic water, usually below 100 m, in Frobisher Bay and Ungava Bay, and recent biological evidence, from the distribution of Ca/anus finmarchicus and C. glacia- lis in the eastern Arctic, suggests that Atlantic water also penetrates into Foxe Basin to some extent (Grainger, in press), which may also be re fl ected in the Sagitta behaviour. Evidence of penetration into Hudson Bay is not convincing. In some parts of the area the tidal ranges are extremely high, res ulting in strong currents and turbulence which are clearly very important environ- mental factors. The maximum ranges involved (at sp rings) are as follows: head of Frobisher Bay (Frobisher's Farthest), 38 feet; Port Burwell, at the northern tip of the Labrador, 22.5 feet; K oksoak River entrance at the head of Ungava Bay., 45 feet; Leaf Basin (Ungava Bay), 54.5 feet; Lake Harbour (so uthern Baffin Island), 35 feet ; W akeham Bay, 30 feet; Nottingham Island, 15 .7 5 fe et. Tides in Hudso n Bay and Foxe Basin are less. 1962] M. '].Dunbar: The life cycle of Sagitta elegans 79 TABLE I. COLLECTION DATA FOR THE Sagitta elegans MATERIAL. ALL HAULS ARE HORIZONTAL UNLESS OTH ERWISE STATED . DEPTHS OF HAULIN G ACCURATE TO CA . ± 10 °/ 0 • ,- Depth (m) Haul St. Time Duration Date N o . No. St. Haul Net• EST (min.) 1947 June 29 .... P-6 3 28 1.5 Str. 1 1200 30 29 .... P-8 3 28 6 0 1204 25 July 3 . P-1 I 7 JO 5 0 1000 30 3 . P-12 7 JO 9 Str. I 1000 30 3 . ... P-13 7 JO 6 6 1004 25 JI . .... P-14 9 24 15-17 0 1320 30 I 1 ... P-15 9 24 13 Str. I 1320 30 11. .... P-17 9 24 7.5 6 1323 25 13 . ... P-18 13 46-55 31-50 0 0936 30 13 .. .. P-19 13 46- 55 39 Str. I 0936 30 13 . .... P-21 13 46-55 17 6 0938 25 13 . .. .. P-22 13 46-55 6 0 1100 30 13 . .. P-23 13 46-55 4-5 Str. I JIOO 30 17 .. ... P-24 18 84 21-16 0 1340 30 17 . .. .. P-26 18 84 50 Str. I 1340 30 18 .. .. P-28 22 II 10-0§ 6 2100 18 ... .. P-30 22 JI 3-0 Str. I 2125 30 20 ... P-31 31 6 Str. I 1220 30 20 ... .. P-32 31 12 0 1220 30 20 . P-33 31 10 6 1220 30 20 ... .. P-34 31 14 Str. I 1317 30 20 . .. P-36 I 31 20 0 1317 30 Aug. JO . P-41 33 15 JO 0 0910 30 I I. ... P-42 37 4 1-0 6 1140 30 II .