Proceedings ofthe United StatesNational MuseumSMITHSONIAN INSTITUTION ? WASHINGTON, D.C.
Volume 118 1966 Number 3534THE EURYHALINE COPEPOD GENUS EURYTEMORAIN FRESH AND BRACKISH WATERS OF THECAPE THOMPSON REGION, CHUKCHI SEA, ALASKA
By Mildred Stratton Wilson and Jerry C. Tash i
Collections made in the vicinity of Cape Thompson, AJaska, on thecoast of the Chukchi Sea during the course of biological investigationsby the Atomic Energy Commission (Project Chariot), have yieldedSLX species of the euryhaline copepod genus Eurytemora. These oc-curred in brackish waters (coastal lagoons, pools, and ponds) and infresh waters (inland lakes, pools, ponds, and pools and ponds nearthe coast). Collections were made in 1959 by Douglas HiUiard andin 1950-1961 by J, C. Tash. These data partly supplement those ofJohnson (1961) who collected from some of the lagoons in 1959.Additional data come from samples from other regions of Alaskaaccumulated by M. S. Wilson and referred to herein as the Wilsoncollection. Reports on other copepods and crustacean groups ofthe Cape Thompson collections are included in papers by Wilsonand Tash (MS.) and Hilliard and Tash (1966).Financial support of the Atomic Energy Commission for field workin 1959 by Douglas Hilliard and in 1960-1961 by J. C. Tash, and ofthe National Science Foundation for studies by M. S. Wilson (grant
' Wilson: Arctic Health Research Center, U.S. Public Health Service, An-chorage, Alaska; Tash: U.S. Public Health Service, Klamath Lake Project,Klamath Falls, Oregon. 553
554 PROCEEDINGS OF THE NATIONAL MUSEUM vol. us iG 21643 to the Smithsonian Institution) is acknowledged. We are i|indebted to Mr. Hilliard for collections, some physical data and critical ireading of the manuscript, and to Miss Gayle Heron for making ,available, prior to publication, a copy of her paper (Heron, 1964).Inland Lakes, Pools, and PondsOnly one species of Eurytemora, new to science, occurred in samplesfrom 4 of 10 small, shallow, permanent, unnamed bodies of freshwater (herein termed lakes) and 7 nearby smaller, less permanentpools and ponds situated in wet Carex marsh and meadow. Onelake (reference no. 9), located about 11 miles inland from CapeThompson, has an outlet to a small creek draining to the KukpukRiver. The other three lakes, located near one another about 7miles inland, have no defined inlets or outlets, the incoming wateroriginating from drainage of the surrounding marsh during snowmeltand rains. Emergent vegetation occurs at the edges of the lakes; inthe type locality (Lake 4), broad-fingered beds of Arctophila extendtoward the center. The lakes are ice-free for about 2^-3 months ofthe year (from early to mid-June to early September). In 1960, themaximum temperature range recorded weekly for Lake 4 from July 1to August 11 was 13.2-15.5? C; by September 4, this dropped to 4? C.Quantitative and qualitative samples were taken at regular intervalsand stations from the open, deep water of Lake 4 with no. 12-meshplankton nets on an open Clarke-Bumpus sampler. The other lakeswere sampled on one or two dates by casting nets from the shore.The existence of the new species, described below, has been knownfor many years from immature copepodid stages collected at Umiat(Wilson collection) but it was impossible to define until adults werecollected in the Cape Thompson samples. The Umiat collection andone made by Tash in the Noatak region extend the known distribu-tion of the species beyond the Cape Thompson region.Family TemoridaeEurytemora arctica, new speciesFigures 1-3Type locality.?Unnamed lake (reference no. "Lake 4"), about7 mUes inland from coast of Chukchi Sea, Cape Thompson region,Alaska, 68?11'09" N., 165?42'05" W.; surface area, 2.1 hectares;maximum depth, 2.4 meters.Types.?Holotype 9, USNM 106647; allotype c^, USNM 106648.Definition.?Female: Metasomal wings and genital segment notlaterally expanded ; caudal rami slightly longer than urosome segments2 -}- 3; antennules reaching to near end of metasome. Leg 5: Exopod
NO. 3534 EURYTEMORA?WILSON AND TASH 555segment 1 with 2 outer spines; inner process directed inwards andabout 4 X width of distal part of segment; inner apical spine ofexopod 2 much longer than outer apical spine. Male: Antennules alittle longer than metasome, mth stout, long aesthetes; spines ofsegments 8-12 of right antennule not more developed than those ofleft. Leg 5 of adult: Right exopod 2 constricted near middle withbasal part wider than distal; anterior proximal part of left basalsegment 2 produced into spinous point; left exopod 2 without apicaldigitiform protrusion. Leg 5 of copepodid stage V: Inner apical spineof exopod 2 much longer than outer spine, that of left side the longer,equaling half or more of the length of its segment.Description of female.?Total length: 1.85-2.02 mm.(metasome=total anterior division, 1.09-1.16; urosome, 0.765-0.855; measure-ments middorsal line, top of head to end of caudal rami, from specimensin which urosome was separated and mounted in shallow depressionslide to overcome effect of ventral curvatm'e). All segments ofmetasome well defined (figs, la, 6) ; greatest width in second segment(thoracic somite 1) equal to about one-half total length of metasome.Cephalic segment rounded anteriorly, slightly broadened at midpoint,without pronounced cephalic depression (viewed laterally in exactmidline); dorsal cuticular protuberance at distal midpoint of seg-ment, variable in size and prominence (fig. la). Last 2 segmentsof metasome reduced in both width and length (fig. 16); wings of lastsegment not expanded laterally, nearly symmetrical, produced posteri-orly to near midpoint of genital segment, apices rounded and eachbearing a fine, sensory setule (figs. Ic, d).Urosome (figs. Id, e) : Genital segment rounded laterally in proximalhalf but without prominent protrusions either laterally or ventrally;operciJum (external genital flap) broader than long, rounded distally,partially encircled by depressed cuticular ornamentation of nar-row, lobed sclerotizations armed with short setules (fig. \e).Segments 2 and 3 with lateral hau-s that extend over distal outerportion of dorsal surface of segment 3. Caudal rami a little longer thansegments 2 + 3 (about 1.13:1); widest just below base, length about6 X this greatest width; inner and outer margins with fine hairs anddorsal surfaces with closely placed, short, scalelike hairs. Terminalcaudal setae (except short, dorsally placed seta) slender, unjointed,longer than rami; lateral seta a little shorter, plumose only on innermargin; second apical seta (from outer margin) the longest.Antennule Cfig. \g) reaching to about middle of metasomal wings ora little beyond; 24-segmented (counting imperfectly separated seg-ments 8-9); beginning with 12, the segments regularly elongated;

EURYTEMORA?WILSON AND TASH 557
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558 PROCEEDINGS OF THE NATIONAL MUSEUM vol. us
3, that of legs 3-4 longer than exopod 3 (leg 3, from 1.02 to 1.10:1;leg 4, from 1.08 to 1.17:1); inner apical seta reaching almost to endof or a little beyond inner spine in leg 2, shorter than spine in legs 3-4.(Measiu'ements of exopod segments in midline, exopod 1 measuredfrom exact base which is inserted deeply into basal segment 2; inabove ratios, exopod 3 expressed as 1).Leg 5 (figs. 2a, 6): Exopod segment 1, outer spines variable inlength, first usually longer than width of segment, second as long asfirst spine or shorter; outer margin of segment constricted distad toinsertion of first spine; inner process slender throughout, du-ectedinwards, tip upcurved and finely serrate, about 4 X width of distalpart of segment (process measured from notch near base to its tip;segment from notch of process to insertion of distal spine). Exopodsegment 2 slender, length less than twice width (about 1.7:1);length of outer apical spine variable, ranging from about one-half toa little more than that of segment (figs. 2a and 26 show extremes)
;
inner apical spine elongate, shorter than or subequal to total exopodlength and ranging from 5.6 to 7 X length of segment 2 and from3.2 to 4.8 X that of outer spine; segment not produced to sharp pointbetween spines, with or without setule on inner margin.Copepodid stage V: Total length (1 specimen, Lake 4, July 28,1960): 1.72 mm. (metasome, 1.025; urosome, 0.695). Cephalic pro-tuberance present. Metasomal wings shorter than in adult but ofsimilar form. Proportional length of urosome segments similar toadult, but caudal rami shorter, their length less than segments 2 +3 (0.8:1), width about 4 X length; genital segment without lateralprotrusions. Antennules a little shorter than metasome. Leg 5(fig. 2b) : Inner process of exopod 1 a little longer than width ofsegment. Length of specimens from Umiat less than that of Lake 4specimen (1.32-1.43 mm.); length of theu' caudal rami subequal toor only a little less than urosome segments 2 + 3.Description of male.?Total length: 1.56-1.65 mm. Greatestwidth of metasome in segments 2-3; distal segments not so narrowedas in female. Distal cephalic protuberance present. Urosome (fig.3/) without ornamentation; segment 4 the shortest, segment 5 thelongest. Caudal rami: Length subequal to urosome segments 3 +4 + 5, about 7 X greatest width; with inner marginal and outerdistal hairs but no surface ornamentation; caudal setae similar tothose of female, lateral seta subequal to and others longer than rami.Antennules reaching a little beyond metasome. The left differmg
Figure 2.
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Eurylemora arctica, new species, female (appendages drawn to same scale):a and c, leg 5, adult, showing variation in outer spines and detail of bases of exopod 3spines; b, leg 5, copepodid stage V; d, leg 2; e, leg 1;/, leg 3, exopod 3; g, leg 4.
EURYTEMORA?WILSON AND TASH 559
For explanation, see opposite page
560 PROCEEDINGS OF THE NATIONAL MUSEUM vol. iiafrom female in more distinct separation of segments 8-9 and in havingonly 1 seta on segment 11 and sometimes 2 setae on segment 4 (thislatter possibly an anomaly) ; aesthetes on all of segments 1-19 excepton 4; setae not as long as those of female; many of the aesthetesmore developed than in female (fig. 36), those of segments 13, 15,and 17 unusually stout and elongate, each reaching almost to end of thesucceeding 3 segments. Right antennule: Spines of segments 8-12 allvery short (fig. 3c), not more developed than reduced spines of seg-ments 8, 10, and 12 of left antennule; aesthetes of segments 13 and 15stout and elongate (fig. 3a), reaching beyond succeeding 2 segments;apical portion beyond geniculation 2-segmented, subequal in lengthto combined segments 15-18; approximate ratio of lengths of last4 segments (segment 17 expressed as 1): 1:1.4:2:2.6.Mandible blade and legs 1-4 similar to female.Leg 5 (figs. Sd, e; drawn from legs mounted in shallow depression,slides so that structural features not distorted by cover glass pressure)
:
First basal segments fused, remnant of connecting plate present;left longer than right; right mth inner marginal lobes. Right leg:Basal segment 2 \^dth small inner proximal lobe, distal part of segmentibroadened inwardly; exopod 1 with prominent inner distal swelling;exopod 2 only a little longer than exopod 1, constricted near middlebut without segmental separation in any observed specimens, basalpart broader than distal and with marginal sclerotization and short!inner and outer spines, narrowed distal part a little longer than basal.Left leg: Inner proximal portion of anterior face of basal segment 2sclerotized (or cuticle thickened), forming narrow plate producedinto spinous point; outer spine of exopod 1 longer than width of seg-ment; exopod segment 2 a little longer than right exopod 2, distal por-'tion broadened beyond middle, apex irregular in shape but without iprominent protrusion and armed with very short spinules.Copepodid stage V: Total length range: 1.275-1.56 mm. (Lake 4,1.38-1.46 mm.; Lake 3, 1.56 mm.; Umiat, 1.275-1.40 mm.). Form!of metasome similar to adult; cephalic protuberance not prominent.Urosome 4-segmented, last segment (= segments 4 + 5 of adult)subequal in length to segments 2 + 3; caudal rami subequal to seg-ments 3-5, as in adult. Antennules reaching to end of metasome or alittle beyond. Leg 5 (fig. 3^) : Spines of exopod segments stout; innerapical spine longer than outer, that of left side longer, usually morethan one-half length of segment (a single specimen collected from
Figure 3.
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Eurytemora arctica, new species, male (appendages drawn to same scale):a, right antennule, from segment 7 to apex; h, left antennule, segments 11-20; c, rightantennule, spines of segments 8-12; d and e, leg S, adult, anterior view (from 2 specimensin slightly different positions and undistorted by cover glass pressure); f, urosome, dorsal;g, leg 5, copepodid stage V, posterior view.
EURYTEMORA?^WILSON AND TASH 561
For explanation, see opposite page219-932?66 2
562 PROCEEDINGS OF THE NATIONAL MUSEUM vol. lisLake 8 had this spine less developed than in all other specimens, itslength being less than half the segment).Taxonomy.?E. arctica is easily distinguished from other species ofthe genus by the combination of characters summarized in the def-inition. It does not appear to be closely related to any known speciesbut can be assigned on the basis of characters of the antennules andfemale leg 5 to a broadly defined group that includes E. composita andE. gracilicauda. Leg 5 is distinctive in both sexes?that of the femalein the unusually long extension of the inner process of exopod 1 andthat of the male in the lobes and processes of the basal segments andthe structm'e of exopod 2 of both legs.Leg 5 of the male is also distinctive in copepodid stage V. No otherspecies illustrated in literatm'e or observed from North Americanfresh and brackish waters has long apical spines (as shown in fig. 3^)
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The specimens from Umiat and Noatak can therefore be assigned tothis species, even though adidts were not observed. It is also possiblethat the inner process of leg 5 of stage V female is longer than in otherspecies of Alaskan Eurytemora, but more study is required to deter-mine this. OCCUERENCE IN CaPE THOMPSON REGIONLake 4 (type locality; see above, p. 554).?Only 33 individuals werecaptured in both quantitative and qualitative open-water and littoralsamples taken on 17 dates between June 24 and November 7, 1960;no specimens occurred after September 8 nor in mid- and late wintersamples in 1961. The species was present in open-v/ater samplestaken in the deepest part of the lake on 10 of the 17 dates in 1960and in 1 littoral sample (June 24). Of the total 11 dates, only 1specimen occiu-red on 4 dates, from 2 to 6 on 6 dates, and 9 adults,the largest number, were taken on the remaining date. From July 21,specimens were in copepodid stages V and VI. Stage VI (adults) firstappeared on July 14 and was the only one present in samples of lateAugust to mid-September. Of the 10 adult females, none carriedovisacs or spermatophores. Three of the 6 males taken on August 27and September 8 had spermatophores attached to the apex of left leg 5.Summary of number of specimens of copepodid stages (C) collectedon the 11 dates of 1960:June July August September4 19 27 8 14
22 4 15 1
NO. 3534 EURYTEMORA WILSON AND TASH 563In 1961, collections were made in Lake 4 from April to August 7.No specimens of E. arctica were taken in open water until July 6.On July 13 and two subsequent dates, both open water and the bedsof rooted vegetation (mostly Arctophila fulva) were sampled, thelatter by hand-dipping a net. The samples from the two areas arenot quantitatively comparable, but it is believed that due to thedifficulty of maneuvering both the boat and the net in the thickvegetation,only a small part of the popidationof thelatterwas sampled.Summary of number of specimens of copepodid stages (C) collectedon four dates of 1961: ope7i water vegetationCIV CV? C Vd^ CIV CV9 CVd^July 6 1 not collectedJuly 1.3 1 12 5August 2 1 29 22August 7 13 6 5Total specimens 7 70Ponds and pools near lake 4.?The poorl}^ drained Carex marshsurrounding Lake 4 has numerous ponds and pools of varying sizeand permanence. In 1960, E. arctica was collected from 3 of thosehaving a heavy growth of vegetation around the perimeter or partiallycovering the water. Collection records: (1) Pond (estimated area,500 square meters; maximum depth about 1 meter; permanent),July 7: 1 C III, 2 C V9; occurring with Heterocope septentrionalis andDiaptomus arcticus. (2) Pool (estimated area, 83 square meters;maximum depth about 1 meter), September 8: 1 C VI9 with ovisac,15 C VI cf, some with spermatophores attached to apex of leg 5.(3) Pool (estimated area, 10 square meters; maximum depth about 1meter), September 8: 2 C Vl9 (1 with mcomplete ovisac), 6 C VI cf".Lake 3 (68?11'09" N., 165?42'02'' W.; surface area, 1.8 hectares;maximum depth, about 1.52 meters).?In 1 of 2 samples collectedon different dates from open water, August 19, 1960: 2 C Vcf . OnJuly 17, 1959, 4 specimens presumed to be this species (C III, C IV)were collected by D. Hilliard from 2 separate pools in the vicinity ofLake 3.Lake 8 (68?11'06" N., 165?42'04'' W.; area 0.03 hectares; max-imum depth about 1.52 meters).?In 1 of 2 samples collected ondifferent dates from open water, August 19, 1960: 1 C VcT, 1 C Vl9.In 1961, no specimens occurred in collections made on one occasionfrom open water and weeds of Lakes 3 and 8.Lake 9 (68?14'08" N., 165?34'09" W.; about 4 miles northeast ofLake 4, in Saligvik Valley ; outlet to creek tributary to Kukpuk River;surface area about 12 hectares; maximimi depth unknown but prob-
564 PROCEEDINGS OF THE NATIONAL MUSEUM vol. iis
ably not over 3 meters) .?The single collection from this lake, August21, 1960, contained 7 adults: 6 9 (5 with ovisacs), 1 cT.Ponds and pools near lake 9.? (1) Pool (about 1 mile north-west; estimated area, 25 square meters; maximum depth about 1meter; vegetation largely Carex and Sphagnum), August 23, 1960:1 C VI 9, 1 C VI cf. (2) Pond (about 1 mile southwest; estimatedarea, 627 square meters; maximum depth about 1.5 meters; vegetationlargely Hipperus, Arctophila, Sphagnum) , August 21, 1960: 1 C V9.Coastal region south of cape Thompson.?One or two specimenswere collected from each of four more or less brackish pools nearSingoalik Lagoon in 1960 (table 1). Large numbers of E. gracili-cauda of similar size and habitus (see p. 567), occurred in two of thesesamples and early copepodid stages (C II-C III) that were presentmight be either of the two species. In 1961, recognizable stages ofE. arctica were not collected in any coastal pools that were sampled.Occurrence in Noatak River WatershedLocality about 58 miles inland from Chukchi Sea, near junction ofKelly and Noatak Rivers, about 67?58' N., 162?20' W. Tash collec-tion: 12 C V 9^; permanent freshwater pond, area about 0.2 hectares,depth about 1.8 meters, from weedy margin {Carex dominant), July29, 1961; occurring with Diap>tomus gracilis. This region is a partof the Brooks Range physiographic province southeast of CapeThompson; the Noatak River and its tributaries drain a considerablepart of the western portion of the northern mountains of Alaska.Eurytemora yukonensis, not yet known from the Arctic Slope province,also occurred in shallow bodies of water of the Noatak region withD. gracilis. Occurrence at UmiatLocality on Colville River in northern Alaska, in foothills of BrooksRange, about 65 miles inland from Beaufort Sea, about 69?24' N.,152?15' W. Wilson collection: 41 specimens (9 C TV9^; 32 C V9c?)taken by casting small net an unknown distance from shore in shallow,freshwater permanent pond, estimated area about 0.2 hectares,July 29, 1949, collector, C. S. WUson; occurring with a few specimensof Heterocope septentrionalis (C VI) and Diaptomus prihilojensis (CIV-VI). BionomicsRestriction to either brackish or fresh water cannot be assumed forspecies of Eurytemora, but some occur much more commonly in onethan in the other. E. arctica was rare in brackish coastal pools andwas not found in the lagoons at Cape Thompson, although all other
NO. 3534 EURYTEMORA?WILSON AND TASH 565Arctic Slope species that range from brackish into fresh water werecollected in them. As presently known the species occurs commonlyin small, shallow freshwater tundra lakes, pools, and ponds, andrarely in coastal brackish pools. Its distributional range is in theArctic Slope and Brooks Range physiographic provinces, from thecoastal region of Cape Thompson east to Umiat and south to theNoatak River watershed, between about 67?-70? N. latitude and152?-166? W. longitude.The species of Eurytemora found in fresh water occur in a varietyof bodies of water, ranging in size from shallow pools to large, deeplakes. Although some species appear environmentally restricted,others seem ubiqmtous, and it is difficult to judge from distributionaldata what habitats are marginal for such species. For instance, inAlaska E. yukonensis occurs in the largest and deepest lakes of theState (those of the Bristol Bay region) but is also found in shallow lakesand ponds along the lower Yukon and Noatak Rivers, where it hasbeen collected from both open waters and submerged vegetation.Other species of Eurytemora have been found abundantly in the rootedvegetation of small, shallow lakes and ponds; for example, E. gracili-cauda was collected in large numbers from grassy margins and frombeds of Arctophila of small, shallow lakes and ponds on eastern SaintMatthew Island in the Bering Sea, about 60?30' N., 173?30' W. (Wilsoncollection : August 1954, R. and R. Rausch, collectors; a iew Diaptomuspribilofensis occiured in some of the weed collections). There arerecords in the literatm'e of other species of Eurytemora associatedwith weeds. Willey (1923a, p. 331 ; 1923b, p. 6) records a reproducingpopulation of E. affinis "amongst dwarf weeds in the littoral zone ofa swampy shore" of Lake St. John, Quebec, and Lowndes (1935)reports E. velox as not only common among weeds but as being found
"attached to algae." From these observations it appears that studiesof freshwater calanoid copepods in geographic regions in whichEurytemora is expected to occur must include exploration of morethan the open waters of lakes and ponds, usually considered as thetypical habitat for calanoids.Eurytemora arctica in the Cape Thompson region represents anexample of this need for detailed examination of weed beds. Inthe open waters of Lake 4 (depth, 2.4 meters) large numbers of threeother calanoid copepods (Heterocope septentrionalis, Diaptomus arc-ticus and D. pribilofensis) were collected throughout the season in 1960in noticeable contrast to the small numbers of E. arctica. This erraticoccurrence of E. arctica in open-water samples suggested a popidationlocalized within the lake and from which occasional individualswandered into the selected areas being routinely sampled. Therefore,in 1961, other areas of the lake were investigated and larger numbers
566 PROCEEDESTGS OF THE NATIONAL MUSEUM vol. lis
of E. arctica were captured from the thick beds of Arctophila thatextend out into the lake (water depth, 1.0-1.5 meters) than in openwater (see above, p. 563)?in contrast to rehitively few individualsof the other calanoid copepods. Although the data are not as exhaus-tive as is desirable, we believe it reasonable to assume that the popula-tion of this lake is localized in the Arctophila beds. In the NoatakRiver pond, the species was likewise collected among weeds but notfrom open water. Other records of occurrence contribute little to thequestion of localization in weed beds. The vegetation of the pond atUmiat, from which fanly large numbers were taken, is unknown, butthe method of collecting precluded sampling of both the deepest openwater and thick weed beds, while not excluding thinly developedlittoral growths. Excepting Lake 4, none of the bodies of water in theCape Thompson region were sampled adequately or frequentlyenough to determine the absence or the preferences of a highly localizedor rare species.It is reasonable to suggest from the available data that the popula-tion of E. arctica in Lake 4 is monocyclic and overwinters as restingeggs, rather than as adults or late copepodid stages, as is probablytrue for many other calanoid copepods in shallow bodies of freshwater on the Ai'ctic Slope of Alaska (Wilson and Tash, MS.). Dataare not conclusive because the localized habitat was not adequatelysampled for a critical study of the life cycle, and the suggestionoriginates from these observations: (1) littoral and open-water samplesof late spring-early summer in 1960 and 1961, during and after thawing,had neither adults nor late copepodid stages; (2) copepodid stagesfound in 1960 showed seasonal progression from early to adult stage,and developmental stages were not collected after adults had becomeestablished; ^3) samples from the deep, open waters taken under icein January 1961 (ice depth, 1.22 meters) and in April when ice depthwas greatest (1.75 meters) contained no Eurytemora of any stage.The weedy portion of the lake in which the population is presumablyestablished is of such depth (1.0-1.5 meters) that it freezes to thebottom by the end of winter (April) so that copepodid stages wouldnot sm'vive dming the winter. It should be noted also that nospecimens were collected in open water after September 14, 1960,although other calanoids were present in samples taken until Novem-ber 7. Presumably, reproduction takes place in the Arctophila bed, andoverwintering resting eggs would be deposited there. The only indica-tions of dates of breeding and egg production were late in the season(August 21, 27, and September 8) when males with spermatophoreson leg 5 and females with ovisacs were taken in Lake 4 and nearbypools, and in Lake 9.Field studies on coastal pool populations were too few to supply
NO. 3534 EURYTEMORA?WILSON AND TASH 567
evidence for the bionomics of E. arctica, and only some speculativepoints that might have value in future studies can be offered. Pre-svmiably development in some pools is both earlier and more rapidthan in other pools and in Lake 4. The appearance of adults of E.arctica in one pool and of E. gmcilicauda in two pools as early as June29, 1960, cannot be accounted for by overwintering of live specimens,because the pools are so shallow they would freeze to the bottombefore thawing. It is more reasonable to assume that the populationsof these two species developed from overwintering resting eggs inbodies of water that not only melted early (as was observed in thecoastal area for some bodies of water in May) but had a high enoughtemperature to permit a comparatively rapid development of some ofthe population to the adult stage. If such bodies of water did notdry out daring the summer season there would be time for develop-ment of a second generation as Oloffson (1918) postulated for E. raboHin Spitzbergen and as may be true for some Alaskan Eurytemora. Onthe other hand, adults of a monocyclic population that developedrapidly might not persist long after egg production in a shallow^ poolwith fluctuating water level where it is associated with a related andmore dominant species. Successful collection of a short-lived, mono-cyclic species would be dependent upon an element of chance insampling the body of water at the particular short period of time whenidentifiable copepodid stages were present. Such factors might ac-count in part for failure to collect more specimens of E. arctica in thecoastal pools. An additional factor that might be very important butdifficult to assess until more of the numerous bodies of water along thecoast of Alaska are investigated, is that brackish water even of verylow salinity is a marginal habitat for E. arctica, it being dominantlya freshwater species. Coastal Pools and PondsThree species of Eurytemora were collected in pools and ponds onthe coast (table 1). Of these, precisely identifiable copepodid stagesof E. arctica occurred only as one or two specimens in four pools in1960, so that its importance as part of the coastal brackish fauna isnot known. The other two species, E. canadensis and E. gracilicauda,occurred in large numbers and frequently enough to be consideredcharacteristic elements of both fresh and brackish coastal bodies ofwater. They were associated with one another in brackish pools oroccasionally with Limnocalanus johanseni, a dominant associate ofEurytemora in nearby lagoons and the only other calanoid copepodfound in the brackish pools. In freshwater pools, E. gracilicaudaoccurred with the freshwater calanoid Heterocope septentrionalis.
568 PROCEEDINGS OF THE NATIONAL MUSEUM vol. iisSamples reported here represent only a small part of such habitatsin the entire Cape Thompson region. Most are from the marshy areanear Singoalik Lagoon and are characterized as pools because of theirintermittent nature and small size. Many are shallow, ranging fromonly 15 to 30 cm. in depth but some have a maximum depth of about1 meter. Those near Singoalik and Mapsorak Lagoons are consideredas more or less brackish; precise salinity records associated with thecollections are not available but other records indicate that they arenot continuously fresh. Salinity undoubtedly varies with the fluctu-ating water level which may be considerable both during a season andfrom one year to another.Records are summarized by year of collection in table L ExceptingPool 1, the pools from which collections were made in 1961 were notcorrelated with any of the previous year, and it is not known whichcorrespond to the pools listed for 1960. Copepodid stages are listedfor each date. In no instance do the collections furnish adequate datafor life cycle studies, but they do emphasize the value of the locale forsuch studies. Of particular interest is the question of whether suchpopulations of Eurytemora, unlike most other calanoids of continentalbodies of water on the Arctic Slope, produce more than one generationa year (Wilson and Tash, MS.) . The copepodid stages present in theseries of 1960 collections in Pool 1 (table 1) suggest two generations ofE. gracilicauda. Absence of any specimens in the middle of the seasonmay have been due to the presence of the species only as naupliarstages which collecting gear failed to sample. Production of twogenerations in a season would undoubtedly be dependent upon earlymelting of snow and ice in the region, as probably happened in 1960when adults bearing ovisacs were collected as early as June 29 (seediscussion under E. arctica, p. 567). As with E. gracilicauda, therecords of E. canadensis in shallow pools that freeze to the bottom,not only in the Cape Thompson region but in other parts of its dis-tributional range, suggest overwintering of the species as resting eggs.Coastal Lagoons |Including those studied by Johnson in 1959, a total of 11 lagoonshas been surveyed. As Johnson (1961) indicated, they group natural-ly into those lying north and south of Cape Thompson, and the}^ aresummarized here by these geographic subdivisions (table 2). Theyare dish shaped in profile, range in length from 3.2 to 8.0 km., areshallow (maximum depth, 3 meters), and are free of ice cover forabout 2)2-3 months. Most do not now have direct connections withthe sea. Maximmn temperatures recorded in 1960 were 13.7? C. onJuly 18 for Mapsorak Lagoon and 16.2? C. for Pusigrak Lagoon.
EURYTEMORA?WILSON AND TASH 569Table 1.
?
Calanoid copepod species composition {genera Eurytcmora and Lim-nocalanus) of Cape Thompson coastal pools and ponds, 1960-1961Body of
570 PROCEEDINGS OF THE NATIONAL MUSEUM vol. nsWith a few exceptions during the observed periods, salinity wasrelatively low (table 2). It seems logical to expect, however, thatthe salinity of all the lagoons may be subject to greater or lesservariation both throughout the season and from one year to anotherbecause of physical factors influenced by the weather and climateof this high latitude region. Strong winds are frequent even in thesummer months, resulting in practically no thermal or haline strati-fication and contributing also to an erratic sampling of planktonorganisms. Thus, data from one week or year to another are notnecessarily sufficient to estimate accurately the quantitative abun-dance of a species or to assume that its absence from a sample meansthat it was also absent from the lagoon. Records in table 2 shouldbe viewed on the basis of these considerations.Johnson found four species of Eurytemora in nine of the lagoonsin 1959. Two of these {E. herdmani, E. pacifica) were not foundin our collections, but three additional species (E. composita, E.raboti, E. gracilicauda) occurred. E. arctica was not present inthe lagoons but was collected in pools, so that eight species of Euryte-mora occur in the coastal area. In order to indicate what is knownof the continuity of species composition shown by three years ofcollecting, Johnson's records for August 1959 are combined herewith our records of July 1959 and of 1960-1961 (table 2).With two exceptions, collections from the eight lagoons south ofCape Thompson yielded only E. canadensis, usually in associationwith and in smaller numbers than Limnocalanus johanseni. Both ofthese species in Alaska occur along the coast in waters ranging fromlow salinity to fresh, but there are more known records of E. canaden-sis than of L. johanseni in fresh water with associated freshwatercalanoid genera such as Heterocope and Diaptomus (literature andWilson collection).Mapsorak Lagoon (Johnson no. 2S) presents a striking example ofthe temporal nature of the copepod communities that may at timesbe collected. In 1959, Johnson found nine marine species that he con-sidered as having been "probably only recently recruited from thesea." He describes the lagoon as having "a narrow above-sea-outletthat probably floods with sea water during high storms." That thislarge assemblage of species probably had been washed into the lagoonfrom the sea is suggested by the high saUnity and by the fact thatnone of the species was found in series of samples taken weekly in1960 and 1961. The difference in the species of Eurytemora found inthe three years is noteworthy. E. herdmani and E. pacifica, occurringonly diu-ing the period of high salinity in 1959, are typical of inshorewaters of the Alaskan coast but are not known from fresh waters norfrom waters of extremely low salinity. In 1960, relatively low salinity
NO. 3534 EURYTEMORA?WILSON AND TASH 571
was recorded and foiir other species of Eurytemora were found (table 2),all of which range from brackish to fresh waters. Of these, E. com-posita and E. raboti were not collected again in Cape Thompson sam-ples, but since they are known to be widely distributed in diverse bodiesof water along the northwestern Alaskan coast, they may well occur inunsampled ponds or pools of the area. Whether populations are estab-lished in inshore-offshore waters is unknowm but both have beenrecorded from coastal continental bodies of water of high salinity(Mohr et al, 1961; Holmquist, 1963; Heron, 1964). Since ovigerousfemales and developmental stages of both species were found in thelagoon in 1960 on several dates, it w^as sm'prising not to find them in1961 samples. The other tw^o species of 1960 samples, E. canadensisand E. gmcilicauda, are both highly characteristic of waters of verylow salinity and commonly range into fresh waters. E. gracilicaudaoccurred in very small niunbers on only two different dates in 1960,and its absence in 1961 suggests it may have been a straggler washedinto the lagoon from nearby pools.The sparsity of numbers of individuals of species such as E. cana-densis, and the lack of knowledge of occurrence of other speciesthroughout the season, did not make the collections of value for Hfecycle studies. However, observations of the populations of ?'./oi'6o/afrom the lagoons north of Cape Thompson indicated that they werereproducing. Collections in July contained ovigerous females withdeveloping ova, accompanied by all copepodid stages, suggesting thepossibility that this species could produce two generations dm-ingfavorable seasons. Aiautak Lagoon is very large (about 8 km. inlength), and the single collection, a littoral tow from the south end,may give an incomplete indication of its calanoid species composition.E. foveola has not yet been found in fresh water (Wilson collection),but its occiu-rence in lagoons of low, variable salinity and associationwith other species of Eurytemora that are known to range frombrackish to fresh waters, suggest a greater eiu-yhalinity than indicatedby the presently known occurrences.Crustaceans other than calanoid copepods were at times abundantin the lagoons, especially Cyclops spp. and Daphnia spp. (Johnson,1961; Hilliard and Tash, 1966). Both of these freshwater generaare recorded throughout literature from brackish waters along sea-coasts (examples can be found in Giu-ney, 1933; C. B. Wilson, 1932;Lagerspetz, 1958; Carpelan, 1964). Some species are tolerant of lowsalinities and of changing conditions throughout the season. Thealmost universal tendency to consider them as genera confined tofresh water may be misleading when attempting to characterizecoastal bodies of water by their faunal elements. In some regions,the absence of freshwater calanoid genera is probably more significant
572 PROCEEDINGS OF THE NATIONAL MUSEUM
? 4-c^ 4-
C3i =3
EURYTEMORA?WILSON AND TASH 573
VOL. 118574 PROCEEDINGS OF THE NATIONAL MUSEUMin determining brackishness in absence of other data. In the CapeThompson lagoons of very low salinity, the common freshwatercalanoid genera of the region, Heterocope and Diaptmnus, have notestablished populations. A few specimens of D. arcticus were foundin one lagoon in August 1960, but since none were collected at otherdates, we believe them to be stragglers washed into the lagoon froma freshwater soiu-ce. The few harpacticoid copepod genera that werecollected are, like the calanoid genera Eurytemora and Limnocalanus,those having species with varying degrees of euryhalinity?Z)ameZs-senia, Nitocra, Onychocamptus.Distribution of Cape Thompson EurytemoraThe group of eight species of Eurytemora in the relatively small areasurveyed on the coast of the Chukchi Sea, ranging 39 miles north andsouth of Cape Thompson (from latitude 68?15'-67?55' N. and longi-tude 165?02'-166?0S' W.) and about 11 miles inland (from latitude68?11'-68?14' N.) is the largest assemblage of species of the genusrecorded from any similar-sized area of the world. This group alsorepresents about one-half of the species known for the world andnearly all of those known for Alaska (8:10) or North America (8:11).Similar large numbers of species occur in coastal areas south of CapeThompson, where Heron (1964) found, in a single sample, five speciesin Kivalina Lagoon and four species in two samples from KrusensternLagoon. Including those of neritic waters and continental bodies ofwater, five species are currently known (Hteratm-e and Wilson col-lection) along the Beaufort seacoast from Point Barrow eastwardsas well as along the coast of the Bering Sea south to the AlaskaPeninsula. Similar numbers occm* in nearby Asian waters so thatthe geographic region of northern and western Alaska and north-eastern Asia is, in present-day distribution, richer in numbers of speciesthan any other of the world. This large representation probablyreflects the northern origin of both the genus and many of its species,and emphasizes how well the biological requirements of the speciesare met by the arctic-subarctic en\Tronment. The species of alltypes of habitat illustrate the strong zoogeographic affinity betweenthe copepod faunas of Alaska and northeastern Asia, previouslypointed out by M. S. Wilson (1953b).The eight species of Cape Thompson Eurytemora include all butone of the total number known for landlocked bodies of water ofthe Arctic Slope physiographic province of Alaska, of which theCape Thompson region is a part. In this province, comprising theArctic coastal plain and the foothills of the Brooks Mountain Range,
NO. 3534 EURYTEMORA?WILSON AND TASH 575including the Chukchi seacoast south to about Cape Krusenstern,Euryiemora is known from scattered locahties along the Beaufort andChukchi seacoasts to about 65 miles inland. The nine Arctic Slopespecies include those of inshore-offshore waters (E. americana, herd-mani, pacijica) which have been found at least once in a body ofwater on land. The species composition of the tAvo large lagoonssouth of Cape Thompson at Kivalina and Cape Krusenstern, studiedby Heron (1964), is similar to that of some lagoons at Cape Thompsonexcept that E. americana was present and E. canadensis was absentfrom Heron's samples. Further exploration of fresh waters may addto the Arctic Slope list the tenth species known from Alaska, E.yukonensis M. S. Wilson (1953a). The northernmost record of thisspecies is just southeast of Cape Thompson in the Noatak Riverwatershed (above, p. 564).Four Cape Thompson species are recent additions to NorthAmerican fauna. In addition to E. arctica described above, Efoveola was described from Cape Thompson lagoons by JohnsonC1961). E. raboti ranges from Spitzbergen and the Siberian coast tothe Barrow region, Alaska, where it has been found in collections ofJ. L. Molir and associates, made in 1953 in brackish ponds (Wilsoncollection) and in 1960 in Nuwuk Lake (Mohr et al, 1961). It wascollected in 1961 from Sinclair (or Minga) Lake, east of Barrow, byHolmquist (1963). It was first recognized in North American watersby Heron (1964) in 1959 samples from Krusenstern and KivalinaLagoons. E. gracilicauda, another Asian species new to NorthAmerica, was described by Akatova (1949) from freshwater Siberianlakes in the basin of the Kolyma River (about 69? N., 161? E.).The Wilson collection has several samples of E. gracilicauda fromAlaskan fresh and brackish waters, ranging from the Arctic Slopesouth to the Alaska Peninsula; figm-es and notes are in manuscript tobe published elsewhere. Literature CitedAkatova, N. A.1949. Zooplankton Reki Kolymy i ee basseina. Uchenye Zapiski Lgu.,no. 126, Ser. Biol. Nauk [Sci. Rep. Univ. Leningrad, no. 126, Biol.Sci. Ser.], vol. 21, pp. 341-367, 5 figs. [In Russian.]Carpelan, Lars H.1964. Effects of salinity on algal distribution. Ecology, vol. 45. no. 1.pp. 70-77, 3 figs.GuRNEY, Robert1933. British fresh-water Copepoda, vol. 3, 384 pp., figs. 1196-2061. Lon-don: Ray Society.Heron, Gayle A.1964. Seven species of Eurytemora (Copepoda) from northwestern NorthAmerica. Crustaceana, vol. 7, pt. 3, pp. 199-211, 26 figs.
576 PROCEEDINGS OF THE NATIONAL MUSEUM vol. iisHiLLiARD, Douglas K. and Tash, Jerry C.1966. Notes on the freshwater algae and zooplankton. In Environmentof the Cape Thompson region, Alaska, U.S. Atomic Energy Com-mission, pp. 36.3-413.HoLMQUiST, Charlotte1963. Some notes on Mysis relicta and its relatives in northern Alaska.Arctic, vol. 16, no. 2, pp. 109-128, 7 figs.Johnson, Martin W.1961. The zooplankton of some Arctic coastal lagoons of northwesternAlaska with description of a new species of Eurytemora. PacificSci., vol. 15, pp. 311-323, 19 figs.Lagerspetz, Kari1958. The brackish-water tolerance of some freshwater crustaceans.Verh. Internat. Ver. Limnol., vol. 13, pp. 718-721, 2 figs,Lowndes, A. G.1935. The swimming and feeding of certain calanoid copepods. Proc.Zool. Soc. London, 1935, pt. 3, pp. 687-715, pis, 1-2MoHR, John L.; Reish, Donald J.; Barnard, J. Laurens; Lewis, Roger W. ;and Geiger, Stephen R.1961. The marine nature of Nuwuk Lake and lesser ponds of the peninsulaof Point Barrow, Alaska. Arctic, vol. 14, no. 4, pp. 210-223, 7 figs.Olofsson, Ossian1918. Studien liber die Siisswasserfauna Spitzbergens, Beitrag zur Sys-tematik Biologie und Tiergeographie der Crustaceen und Rota-torien. Zool. Bidrag Uppsala, vol. 6, pp. 183-648, 69 figs.WiLLEY, Arthur1923a. Notes on the distribution of free-living Copepoda in Canadianwaters. Contr. Canadian Biol., new ser., vol. 1, pp. 303-334,23 figs.1923b. Ecology and the partition of biology. Trans. Royal Soc. Canada,ser. 3, vol. 17, pp. 1-9, 1 fig.Wilson, Charles Branch1932. The copepods of the Woods Hole Region, Massachusetts. U.S. Nat.Mus. Bull. 158, 635 pp., 316 figs., pis. 1-41.Wilson, Mildred Stratton1953a. New Alaskan records of Eurytemora (Crustacea, Copepoda), Pa-cific Sci., vol. 7, pp. 504-512, 7 figs.1953b. Some significant points in the distribution of Alaskan fresh-watercopepod Crustacea. Proc. Second Alaskan Sci. Conf. (1951),pp. 315-318.Wilson, Mildred Stratton, and Tash, Jerry C,MS. The life cycles of freshwater calanoid copepods of the Arctic Slopeof Alaska.
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