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1235

Biogeography of the albifrons superspecies (, ) on the Atlantic coast of

MICHEL VEUILLE Laboratoire de Biologic et Genetique Evoltttives dn C.N.R.S., 91190, Gifsur Yvette, Received January 20. 1976

VEUILLE. M. 1976. Biogeography of the superspecies (Isopoda. Asellota) on the Atlantic coast of Canada. Can. J.Zool. 54: 1235-1241. The biogeographical study of the four Canadian forms of the Jaera albifrons superspecies leads to a division into two groups. J. (a.)albifrons, J. (a.) ischiosetosa, and J. (a.) praehirsuta are spread along the whole Atlantic coast, from cold to temperate shores but. as in , salinity and exposure affect their relative abundance. J. (a.) posthirsnta occurs only in the warm shallow protected from currents. The presumably postglacial origin of its disjunct distribu­ tion is discussed.

VEUILLE. M. 1976. Biogeography of the Jaera albifrons superspecies (Isopoda. Asellota) on the Atlantic coast of Canada. Can. J. Zool. 54: 1235-1241. L'etude biogeographique des quatre formes canadiennes de la super-espece Jaera albifrons amene a y distinguer deux groupes. Les especes J. (a.) albifrons. J. (a.) ischiosetosa et J. (a.) praehirsuta colonisent tout le littoral atlantique. des cotes froides aux rivages temperes, mais comme en Europe, la salinite et ["exposition influencent leur abondance respective. L'espece J. (a.) posthirsnta ne setrouve que dans les eaux pluschaudeset peu profondesdes rivages proteges de l'infiuence des eaux arctiques. L'origine vraisemblablement post-glaciaire de son aire de repartition disjointe est discutee.

Introduction Main Features of the Although the superspecies Jaera albifrons is This survey deals with the and Gulf a common component of the shore fauna of of St. Lawrence, the southern coast of New­ , very little is known about the foundland, , and the of Fundy. distribution of its various forms in this large From a biogeographical point of view, it is a area. The identification from the Gaspe Penin­ part of the subarctic boreal region, which is sula of three samples belonging to the species cooled by the Labrador current and extends albifrons, ischiosetosa, and praehirsuta by Fors- south to the Gulf of . Cold deep layers man (Brunei 1970c/) and the study by Steele and of seawater enter the St. Lawrence through the Steele (1972) of a natural population of ischio­ Laurentian Channel as far as the Saguenay setosa from Newfoundland are the only reports Fjord and their effects are felt in the main part for this area. of the estuary. The stirring effect of the The Atlantic coast of Canada is a very hetero­ of the lowers the surface temper­ genous biogeographical region, and systematic atures of this other arm. investigations were required to establish the Some shallow waters remain protected from distribution of these species according to boreal waters: the southwestern Gulf of St. environmental conditions. A second problem Lawrence and the have warm was provided by the species posthirsnta, known waters in summer, with relatively low salinities, until now only in Massachussets, where it was contrasting with the boreal euhaline areas described by Forsman (1949) and Bocquet and (Lauzier et al. 1951; Bousfield 1962). Otherwise, Prunus (1963); the northern limit of the range of the outflow of the St. Lawrence River gives the this species remained unknown. estuary a decreasing salinity from seawater In addition to the collections made by the landwards to freshwater, mainly south from the author, data were supplied by loans from the Saguenay Fjord, and with an abrupt change Smithsonian Institution, the Marine Biology between baie St. Paul and Riviere du Loup Station of Grande Riviere, and by extensive (Lavoie and Beaulieu 1971). South of this last collections of the National Museum of Natural limit is a low-salinity brackish that is Sciences of Ottawa. also warmed in summer (Bousfield 1955). 1236 CAN. J. ZOOL. VOL. 54, 1976

12 3 4 5 6 7

FIG. 1. Key to males of Canadian species of Jacra. Top, male in ventral view; 1, 2, 3, 4: four anterior pairs of pereopods; 6, 7: two posterior pairs of pereopods; po, Jaera (alhifrons) posthirsuta; i, J. (a.) ischiosetosa; a, J. (a.) alhifrons; pi; J. (a.) praehirsuta.

Salinity and surface temperature are important Canadian Species of Jaera alhifrons factors in the biology of intertidal , Jaera alhifrons are minute isopods from 1 to and all these features divide the coast into sub- 5 mm in length; they live intertidally beneath with different physical conditions. Since stones or on Fucus. They show a conspicuous they are close to the boundaries of two bio- widening of their lateral margins, and their geographical provinces, the subarctic boreal minute biramous uropods seem to emerge and the temperate ones, they provide a shelter posteriorly out of a pleotelson notch (Fig. 1, top). to of various origins and they determine The T-shaped praeoperculum of males is another a mosaic of faunal elements superimposed on fairly distinctive feature of the superspecies. corresponding heterogenous environmental Jaera alhifrons (Leach) was split by Forsman factors. They may be useful in the study of the (1949) and Bocquet (1953) into five sibling main factors that act on the distribution of the forms, which the latter recognized to be true littoral species; their effect on the different species. Four of these forms occur on the forms of the Jaera alhifrons group is obvious. eastern coast of Canada and show no mor- VEUILLE 1237

Atlantic

Ocean

FIG. 2. Distribution of Jaera (albifrons) ischiosetosa. &i stations with one recorded species of Jaera albifrons; •• stations with two sympatric species; O* stations with three sympatric species; ••• stations of ischiosetosa.

phological difference from previously described Such variations were previously reported from populations. They may be identified by the European and American representatives of these secondary sexual characters of the pereopods species, and appear to be expressions of a (Fig. 1) in the males. natural intraspecific variability within each In species lacking anterior differentiations, form (see Bocquet 1953; Bocquet and Veuille the sixth and seventh pairs of pereopods bear 1973; Prunus 1966, 1968; Solignac 1967). long setae from ischiopodite to carpopodite Only one Fj hybrid, albifrons x ischiosetosa, {Jaera (a.) posthirsuta), or a brush of long curved was found at the Pilot Station (Quebec North setae on a distally broadened ischiopodite Shore). (Jaera (a.) ischiosetosa), or a distal lobe with a Jaera albifrons is widespread throughout the comb of short setae on the carpopodites eastern coast of Canada, and 157 different (Jaera (a.) albifrons). The only species with stations were recorded, but it is misleading to anterior differentiations (Jaera (a.) praehirsuta) look at a mixing of species as a whole, and the possesses long curved setae on pereopods 1 124 stations that are known to the species level through 4 (except in young males) and a stout (ischiosetosa (36), albifrons (34), praehirsuta distal spine on the two last pairs of carpopodites. (41), and posthirsuta (13)) are a good illustration Variations occur among Canadian popula­ of this. tions in the expression of these characters, with­ out affecting the certainty of their determina­ Jaera (albifrons) ischiosetosa (Fig. 2) tion (e.g. graduations in the length of the lobe in This form is found all over the coast with albifrons, and in the number of setae in praehir­ abundance varying according to the subregion. suta, and extension, in large specimens, of the Most of the samples come from the St. Law­ secondary sexual characters to other legs). rence Estuary (19 out of 36). Numerous popula- 1238 CAN. J. ZOOI.. VOL. 54. 1976

FIG. 3. Distribution of Jaera (albifrons) albifrons. A A stations with one recorded species of Jaera albifrons; QB stations with two sympatric species; O* stations with three sympatric species; ••• stations of albifrons. tions have also settled in the Bay of Fundy and Jaera (albifrons) albifrons (Fig. 3) la baie des Chaleurs. These are sheltered areas The distribution of this form is very similar with variable temperatures and salinities (down to that of ischiosetosa, since there appears to be to 10%0 in the southern Estuary of St. Lawrence, no exclusion regarding salinity or temperature. at He aux Coudres). J. (a.) albifrons is well represented in the St. In contrast, very few ischiosetosa were col­ Lawrence Estuary (19 out of 34 populations) lected on exposed shores, such as the southern and sparse on the Atlantic coast of Nova Scotia. coast of Nova Scotia. The two populations Nevertheless, it has been recorded in several known from this subregion were found in the stations of the eastern coast of the Gaspe estuary of Halifax harbour and in an isolated Peninsula, and is significantly less common in rock pool. Both stations are presumably refuges the Bay of Fundy. This scarcity cannot be for this organism, and since such places occur in explained from the factors analyzed at the a scattered way along the shore, they may lead very macroscopic level of this survey. The to an underestimation of its true abundance in ecological preferences of Canadian populations exposed areas. of albifrons with regard to main physical factors We conclude that ischiosetosa is a eurythermal are very close to those of European ones. and euryhaline species, occurring from euhaline to mesohaline waters (according to the "Venice Jaera (albifrons) praehirsuta (Fig. 4) system') and living in sheltered places. Similar The prominent characteristic of this species ecological characters are reported from Euro­ is its dominance along the exposed shores of pean populations of this species. and the coasts of New- VEUII.LE 1239

FIG. 4. Distribution of Jaera (albifrons) prachirsuta. AA stations with one recorded species of Jaera albifrons; •• stations with two sympatric species; O* stations with three sympatric species; • •• stations of praehirsuta.

foundland. It is well represented in the Bay of sula, Newfoundland, Nova Scotia, and the Bay Fundy, but, in contrast to albifrons and ischio- of Fundy and occurs only in the Virginian setosa, it is poorly established in the St. Law­ refuges of la baie des Chaleurs. the south­ rence Estuary, where it is confined to the western Gulf of St. Lawrence. Prince Edward northern part. This limit corresponds to the Island, Magdalen Islands, and the Minas Basin. end of the Laurentian Channel, off the mouth Its presence at He aux Coudres, in the southern of the Saguenay Fjord, where oceanic waters no St. Lawrence Estuary, is in agreement with its longer maintain high-salinity brackish condi­ limitation to warm shallow waters. There is only tions through blending with upper layers. Only one atypical population north of Digby, in the one population was recorded in the southern Bay of Fundy. This is the typical disjunct estuary (20°^„ salinity). Although this might have distribution of the relict populations of a been achieved through competition with other temperate thermophilic species. forms, praehirsuta is obviously limited to We may add that it is a euryhaline organism euhalinc and polyhaline waters. All these (down to mesohaline waters), yet the brackish features unite the North American and Euro­ and sheltered nature of the Virginian shallow pean representatives of this species. waters of Canada does not tell us whether or not it can live in pure seawater and on an exposed Jaera (albifrons) posthirsuta (Fig. 5) shore. There is an obvious difference between the distribution of this form and those of its sister Discussion species. It is absent in all the cold boreal waters On the basis of the preceding observations, of the St. Lawrence Estuary, the Gaspe Penin­ the Canadian species of Jaera may be divided 1240 CAN. J. ZOOL. VOL. 54. 1976

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FIG. 5. Distribution ofJaeva(a.) posthirsuta. A A stations with one recorded species oUaera albifrons; DM stations with two sympatric species; O* stations with three sympatric species; TB# stations of posthirsuta; • • • limit of warm surface temperature in summer (arbitrarily set at 15 rC in August). into two groups: (1) ischiosetosa, albifrons, and resentatives of these species. Furthermore, praeliirsuta; and {2) posthirsuta. Canadian forms show even more similarity to J. (a.) ischiosetosa, albifrons, and praeliirsuta oceanic European populations than do those are amphi-Atlantic species, well acclimatized to inhabiting the , where, for instance, boreal and temperate waters of both sides of the praeliirsuta withstands the very dilute seawater ocean, and of Greenland, Iceland, and the of the (Haahtda 1965) or of the British Isles. The ecological preferences they Bay of Puck (Jazdzewski 1969). show on the oceanic coasts of France and In contrast, posthirsuta is a temperate Amer­ Great Britain are consistent with their dis­ ican endemic species. It lives more or less tribution along the shore of Canada. The de­ sympatrically with each of its sibling species creasing euryhalinity from ischiosetosa and all along its range, and does not extend further albifrons to praeliirsuta is noted by Bocquet south (according to observations made by (1953) and Naylor (1972) and emphasized by Hoestlandt in the United States), but it is physiological experiments carried out by Jones strikingly limited northward. Its situation ap­ (1972a, 19726). Their distribution regarding ex­ pears to parallel that of Jaera (a.) forsmani, posure agrees with observations made by Bocquet which is known only from Brittany (Bocquet in Brittany and, on the whole, it is noteworthy 1953) and from the British Isles (Jones and that the rough inventory on a large scale is in Naylor 1971). agreement with the careful study of their The main feature of this organism is a clear- microhabitat. cut division of its range into two groups of On the basis of these few characteristics and populations of nearly similar extent. The former from morphological data, we can conclude that inhabits the coast of New England northward no striking differentiation or speciation occurred to the southern (the National between European and North American rep­ Museum of Natural Sciences owns samples VEU1LLE 1241 from Cape Neddick and Magnolia Beach, 1962. Studies on littoral marine from the and Bocquet and Prunus (1963) report it from Bay of Fundy region. Bull. Natl. Mus. Can. 183: 42-62. 1973. Shallow- gammaridean Amphipoda of south of Boston). The other group lives in the New England. Cornell University Press. Ithaca and warm pockets of , and gives rise to an London. interesting problem, since it cannot have BOUSFIELD. E. L.. and D. R. LAUBITZ. 1972. Station lists settled there before the melting of the North and new distributional records of littoral marine inver­ American ice cap of the 'classical Wisconsin,' tebrates of the Canadian Atlantic coast and New Eng­ land regions. Natl. Mus. Nat. Sci. (Ottawa) Publ. Biol. about 15 000 years ago. Oceanogr. 5: 1-51. A consideration of the flora (Fassett 1928) BOUSFIELD. E. L., and M. L. H. THOMAS. 1975. Post­ and of the fauna (Ganong 1890; glacial dispersal of littoral marine invertebrates of the Bousfield and Laubitz 1972), of the Gulf of Canadian Atlantic region. J. . Res. Board Can. BRUNEI.. P. 197ft/. Catalogue d'invertebres benthiquesdu St. Lawrence also poses this problem, to which golfe St. Laurent recueillis de 1951 a 1966 par la station Fassett (1928) and Bousfield (1962) have con­ de Biologic Marine de Grande Riviere. Trav. Pech. Que. tributed to give an attractive solution. Ac­ 32: 1-55. cording to them, a postglacial transgression sub­ 1970/). Essai: les grandes divisions du St. Laurent: merged the , separating commentaires. Rev. Geogr. Phip. Geol. Dyn. 24: 291-294. the Bay of Fundy from the Northumberland FASSETT. N. C. 1928. The vegetation of the of Strait, during the warm thermal optimum, northeastern . Proc. Boston Soc. Nat. 10 000-6000 years ago. The diversion of the Hist. 39: 75-130. Labrador current by the presumably raised FORSMAN. B. 1949. Weitere Studien iiber die Rassen von banks of the continental shelf offered temperate Jaera albifrons. Leach. Zool. Bidr. Uppsala. 27: 451- 463. species a sheltered way northward (Bousfield 1973) GANONG. W. F. 1890. Southern invertebrates on the and the spreading of posthirsuta populations out shores of Acadia. Trans. R. Soc. Can. Sect. 4. 8: of their previous range is likely to have happened 167-185. at that time; the subsequent isostatic rise of the HAAHTEI A. 1. 1965. Morphology, habitats and distribution Isthmus of Chignecto cut off this way, while the of species of the Jaera albifrons group (Isopoda. Janiridae) in Finland. Ann. Zool. Fenn. 2: 309-314. uplift of the sea level submerged the banks, open­ JAZDZEWSKI. K. 1969. Ecology and biology of species of ing the way to cold currents into the Gulf of Maine. the Jaera albifrons group (Isopoda Asellota) in the Bay This sequence of events leads to the cohabitation of Puck. Polish Baltic Sea. Crustaceana (Leiden), 17: of two faunas, a situation that occurs within the 265-281. superspecies Jaera albifrons. JONES. M. B. 1972C; . Osmoregulation in the Jaera albifrons Leach group of species (Isopoda: Asellota). J. Mar. Biol. Assoc. U.K. 52: 419-427. Acknowledgments 1972/). F.ffects of salinity on the survival of the Jaera albifrons Leach group of species (Crustacea: I am much indebted to Dr. E. L. Bousfield. Isopoda). J. Exp. Mar. Biol. Ecol. 9: 231-237. National Museums of Canada, for making JONES. M. B.. and E. NAYLOR. 1971. Breeding and available the examination of his collections at bionomics of the British members of the Jaera albifrons Ottawa, and for reviewing the manuscript, to group of species. J. Zool. 165: 183-199. LAUZIER. L.. R. W. TRUES, and H. B. HACHEY. 1951. Dr. T. E. Bowman, Smithsonian Institution, Some features of the surface layer of the Gulf of St. and Dr. P. Brunei, Universite de Montreal, for Lawrence. Publ. Publ. Joint Comm. Oceanogr., Atl. loans of further valuable material, and to Dr. C. Group.. St. Andrews. N.B. Bocquet, Universite Pierre et Marie Curie. LAVOIE. R.. and G. BEAULIEU. 1971. Salinite des eaux de Paris, for helpful discussions. surface dans I'estuaire du St. Laurent. Nat. Can. (Ot­ tawa). 98: 191-193. BOCQUET. C. 1953. Recheiches sur le polymorphisme NAYLOR. E. 1972. British marine isopods. Academic nature! des Jaera marina (Fabr.) (Isopodes Asellotes). Press. Inc.. London. Arch. Zool. Exp. Gen. 90: 187-450. PRUNUS. G. 1966. Le caractere "supermale" de Jaera BOCQUET. C. and G. PRUNUS. 1963. Recheiches (albifrons) albifrons Forsman. Arch. Zool. Exp. Gen. complementaires sur le polytypisme de la super-espece 109:643-702. Jaera albifrons Leach: Jaera marina Fabr. Bull. Biol. 1968. Etude de systematique des populations chez Fr. Belg. CVII(2): 343-353. ITsopode Jaera (albifrons) albifrons Forsman. Arch. BOCQUET, C. and M. VEUILLE. 1973. Le polymorphisme Zool. Exp. Gen. 109: 643-702. des variants sexuels des males chez Jaera (albifrons) SOLIGNAC, M. 1967. Etude d'une nouvelle forme. ischiosetosa Forsman. Arch. Zool. Exp. Gen. 114(1): paiuahisnta. de I'espece Jaera (albifrons) praehirsuta 111-128. (Isopodes Asellotes) Arch. Zool. Exp. Gen. 108: 139. BOUSFIELD. E. L. 1955. Stud ies on the shore fauna ot the STEELE. D. H., and V. J. STEELE. 1972. The biology of St. Lawrence Estuary and Gaspe Coast. Bull. Natl. Jaera spp. in the northwestern Atlantic. 1. Jaera Mus.Can. 136:95-101. ischiosetosa. Can. J. Zool. 50(2): 205-211.