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Notes on some euryhaline gammarids (Crustacea, Amphipoda) from the west-coast of Norway by Henk G. Dennert Institute of Taxonomie Zoology, University of Amsterdam, The Netherlands Abstract 1852, Gammarus oceanicus Segerstrâle, 1947, Gammarus zaddachi Sexton, 1912, Gammarus fin- and Some data on the distribution in Norway on the marchicus Dahl, 1938, and Chaetogammarus ma- ecology of the euryhaline amphipods Gammarus duebe- rinus will be used in ni duebeni, G. oceanicus, G. zaddachi, G. finmarchicus (Leach, 1815) were found, and Chaetogammarus marinus are presented in this comparing the four biotopes. In the investigated paper. biotopes these five species were most abundant. Morphological differences between populations of G. Other as Gammarus salinus discussed. euryhaline gammarids, oceanicus are briefly Spooner, 1947, Gammarus setosus Dementieva, 1931, Chaetogammarus stoerensis (Reid, 1938) and obtusatus (Dahl, together I. INTRODUCTION Eulimnogammarus 1938), with number the a of other species belonging to Gammaridae and Talitridae, were found at several Relatively little is known about distribution and of the visited localities. ecology of members of the family Gammaridae in An extensive study of the limnicwaterbodiesand Norway. Records concerning the biology and distri- rivers in Norway was not made, since 0kland (1969 bution of the genera Gammarus, Chaetogammarus, & in detail about this In all of a b) reported subject. and Eulimnogammarus are found in the papers inland waters, Gammarus lacustris Sars, 1863, is Oldevig (1933 & 1959), Stephensen (1935-1942, the main Dahl representative. with a synopsis of the then known literature), At some inland localities Gammarus duebeni is (1938, 1946 & 1952), Sexton & Spooner (1940), found, but in a following it will be shown Sexton (1942), Schellenberg (1942), Segerstrâle paper that these localities have a mixohaline na- (1947, 1948 & 1959), Spooner (1951), Steen (1951), always and the found there is the brack - J. ture, subspecies Okland (1959), K.A. 0kland (1965, 1969 a & b, ishwater form, G. duebeni duebeni. For further in- 1970), Brattegard (1966), Ofstad & Solem (1966), formation regarding G. duebeni I refer to Pinkster Stock & Kant (1966), Stock (1967), Solem (1969) et al. (1970) and Sutcliffe (1972). and Vader (1969, 1971, 1972 a & b). In studying the samples it became that During a sampling trip in July 1971 along the apparent, some taxonomie characters used in distinguishing Atlantic coast of Norway an attempt was made to from varied further G. oceanicus other Gammarus species, obtain information about some euryhaline in the examined. In of the above. populations a separate chapter species genera mentioned A survey (III) these differences will be discussed. was made in four biotopes: supralittoral rock- pools, small springs in seacliffs with irregular sa- linity changes, small estuaries, and the intertidal II. METHODS zone of the fjords. For practical reasons, and be- the At all 177 localities visited and cause biotopes have some common character- temperature spe- certain in cific of determined. istics (such as a similarity gammarid conductivity the water was ++ fauna and periodical changes in salt-content of the From a water-sample both CI" and Ca contents determined in water) the small springs in seacliffs and small estu- were Amsterdam. aries Collected were considered together and the samples specimens have been deposited in the of Uni- from these biotopes were pooled. Especially locali- collection the Zoologisch Museum of the ties where Gammarus duebeni duebeni Lilljeborg, versity of Amsterdam. Downloaded from Brill.com10/06/2021 11:23:13AM via free access BIJDRAGEN TOT DE DIERKUNDE, 43 (2) - 1973 161 III. DIFFERENCES IN MORPHOLOGY BE- ment of Al are often somewhat shorter than the setae of the corresponding tufts in typical G. oceanicus males. TWEEN G. OCEANICUS POPULATIONS Typical G. oceanicus males show the following several As pointed out in the introduction, pop- features: ulations of G. oceanicus show characteristics de- — An A2 flagellum with calceoli. viating from the typical distinguishing characters — The third segment of the mandible palp is ventrally and used as introduced by Segerstrâle (1947) by armed with a row of spinules which are mutually of a Spooner (1951) and Kinne (1954). In these popula- size. — Segment 1 of Al carries on its ventral surface two tions, which include ovigerous females, the males (rarely a small third) tufts of setae and an apical tuft; differ from the G. oceanicus in the follow- typical has four setae the segment 2 or five tufts of (including ing characters: apical tuft). — The A2 flagellum is devoid of calceoli Confusion thus might be caused between the atypi- — The third segment of the mandible palp is ventrally cal G. oceanicus and of armed with a row of spinules, which diminish regularly some representatives the in size in direction. proximal G. locusta-group (e.g., G. inaequicauda Stock, — Segment 1 of Al bears on its ventral surface one thin 1966) but can be prevented by observing certain tuft bears of setae and an apical tuft of setae; segment 2 other typical G. oceanicus characters: three or four tufts of setae (including the apical tuft). The median palmar spine of the propodus of the The setae of the tufts on both the first and second seg- Fig.1. G. oceanicus: of the typical form, from fjord at Mandal (body length 16.5 mm) and of the atypical form, from Straumfjorden at Straumfjordnes (body length 16.3 mm). a, first antenna typical form (scale 1); b, mandible palp typical form (scale 2); c, first antenna atypical form (scale 1); d, mandible palp atypical form (scale 2). Downloaded from Brill.com10/06/2021 11:23:13AM via free access 162 H. G. DENNERT - EURYHALINE GAMMARIDS FROM NORWAY Table I Percentage of joint occurrence of Gammarus, Chaetogammarus, and Eulimnogammarus species in 3 investigated biotopes. G. duebeni G. oceanicus G. oceanicus G. zaddachi G. finmarchicus Ch. marinus ail samples atypical form REFT REFT REFT RE FT R EFTRE FT alone 82 54 37 62 — 40 38 33 45 36 — 31 — 24 —100 33 33 31 28 — — — G. duebeni 100 40 38 47 100 100 27 43 61 75 65 100 33 — 100 46 50 G. oceanicus 13 9 26 16 — 15 100 35 50 — 67 50 — 100 31 36 — G. zaddachi 37 11 13 — 40 17 18 — 100 — 7 — — — — G. finmarchicus 5 2 20 8 9 — 1814 G. setosus — 9 —-2 — 8 — 6 — — G. salinus 4 1 — — 25 6 Ch. marinus — 5 26 9 — 20 17 15 — — 9 7 —8—6 Ch. stoerensis — — 72 1514 Eu. obtusatus — 4 — 1 — — 4 3 total number 37 22 27 86 5 5 24 34 2 1 11 14 — 13 4 17 2 1 3 6 — 1 13 14 of the samples of 43 26 31 15 15 70 percentage 14 8 78 — 76 24 33 17 50 — 8 92 the samples in each biotope for each species R = F rockpools = fjords estuaries E = and small streams in sea-cliffs T total percentage of joint occurrence second leg is pointed and tapering (not "flask- IV. DISTRIBUTION OF THE INVESTIGATED shaped"), the propodus of the second leg is round- SPECIES ALONG THE ATLANTIC COAST the of the third has OF NORWAY. ish, exopod uropod many plumose setae, and the lateral lobes of the head are of the stations Lagunogammarus- type (see Sket, 1971) The maps (figs. 2 and 3) indicate the at which is for found in which the have been collected in Nor- instance G. zaddachhi, G. gammarids oceanicus and G. salinus. In 1 the differences Stations at which were found fig. way. no gammarids between the typical and atypical form are illus- are not indicated to avoid confusion. The appen- The localities trated. where the atypical form was dix contains a list of all the localities with gamma- found are indicated the in rids and data of each This on map fig. 3. some ecological locality. of includes number of records of the In the southern part Norway only specimens list a great new of the typical form were found, more to the north species concerned. mixed populations and populations with the atyp- In table I the joint occurence of the species as form ical only. Neither in the biotopes inhab- well as the frequency in each of the three biotopes ited the two nor in the live summarized. by forms, way they asso- investigated are ciated with other Gammarus species any difference It shows, that G. duebeni duebeni inhabits main- was found between the two forms (cf. table I, ly the supralittoral rockpools. Only in pseudo-su- chapter IV). However, it seems plausible to sup- pralittoral rockpools, situated in the lowest part of that the mentioned above the black the of the eulittoral pose variability may be zone, at boundary influenced by temperature and possibly by other and supralittoral, the species coexists with factors. factors These may have a considerable ef- G. oceanicus and G. finmarchicus. In small estu- fect on the of the animals development in a way we aries and at places where springs in seacliffs reach do not understand and lives yet quite may cause the the sea, the species associated with G. zad- morphological variability described. dachi. The substratum is mostly sand or mud with Downloaded from Brill.com10/06/2021 11:23:13AM via free access BIJDRAGEN TOT DE DIERKUNDE, 43 (2) - 1973 163 Norway. in duebeni duebeni G. with stations Positive 2. Fig. Downloaded from Brill.com10/06/2021 11:23:13AM via free access 164 H. G. DENNERT - EURYHALINE GAMMARIDS FROM NORWAY Norway. in duebeni, duebeni G. except gammarids, with stations Positive 3. Fig. Downloaded from Brill.com10/06/2021 11:23:13AM via free access BIJDRAGEN TOT DE DIERKUNDE, 43 (2) - 1973 165 scattered boulders. In fjords, G. duebeni is practi- tum is sand or gravel. cally limited to the upper algae zones with Pelvetia Ch.

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