Molluscs of the outlet stretch of the Krutynia river (Masurian Lakeland)

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1 .278/v annales universitatis mariae curie-skłdwska lublin plnia VOL. LXIII, 2 SECTIO C 28 Beata Jakubik, Krzysztf Lewandwski Institute f Bilgy, University f Pdlasie B. Prusa 2, 8- Siedlce, Pland bjakubik@ap.siedlce.pl Mlluscs f the utlet stretch f the Krutynia river (Masurian Lakeland) Mięczaki ujściweg dcinka Krutyni (Pjezierze Mazurskie) Summary Studies carried ut twenty years ag n mlluscs f the Krutynia river fcussed mainly n bivalves f the family Uninidae and n Dreissena plymrpha. These studies shwed the richness f Uninidae in the utlet part f the river. The same site was analysed in details in the years The Krutynia at its utlet is 2 2 m wide and m deep. Malacfauna was cmpsed f cmmn species f bivalves and snails dminated in numbers and bimasses by bivalves f the family Uninidae and the snail Viviparus viviparus. Five species f Uninidae: Uni tumidus, U. pictrum, Andnta anatina, A. cygnea and Pseudandnta cmplanata were always present during the whle study perid. Mst numerus was U. tumidus, whse density reached 6 ind. per m 2 f the bttm. The species cntributed in 75 85% t the ttal density f all Uninidae. V. vivparus achieved similar densities. Malacfauna in the utlet part f the Krutynia was characterised by a high stability. Streszczenie Badania nad mięczakami Krutyni prwadzne przed dwudziestma laty dtyczyły głównie małży z rdziny Uninidae raz Dreissena plymrpha. Wykazały ne duże bgactw Uninidae w części ujściwej rzeki. Stanwisk t bjęt szczegółwymi badaniami w latach Krutynia w tym miejscu ma szerkść 2 2 m i głębkść maksymalną m. Malakfauna składała się z psplitych gatunków ślimaków i małży, wśród których dminwały w liczebnści i bimasie małże z rdziny Uninidae raz ślimak Viviparus viviparus. W ciągu całeg kresu badań stwierdzn becnść pięciu gatunków Uninidae: Uni tumidus, U. pictrum, Andnta anatina, A. cygnea i Pseudandnta cmplanata. Najliczniejszym gatunkiem był U. tumidus, któreg za-

2 5 Beata Jakubik, Krzysztf Lewandwski gęszczenie dchdził d 6 sbników na m 2 dna. Stanwił n d 75% d 85% wszystkich Uninidae. Pdbne zagęszczenia siągał V. vivparus. Malakfauna w ujściwym dcinku Krutyni charakteryzwała się dużą stabilnścią. K e y w r d s: river, mlluscs, Uninidae, Viviparus viviparus Intrductin The Krutynia is ne f the mst imprtant rivers f Masurian Lakeland. It is km lng and flws thrugh several lakes frming a unique river-lake system typical f pstglacial landscapes f nrthern Pland. The river was an bject f detailed physical, chemical and bilgical studies at the end f the 98 s (). Mlluscs were ne f the then studied cmmunities but the study invlved nly mlluscs f the family Uninidae and Dreissena plymrpha (5). The entire malacfauna f the river was earlier studied by Hilbert (3) and Berger (, 2). These studies demnstrated that the utlet stretch was ne f the richest sites in the river. The site was analysed in details in the years Species cmpsitin, density and ther indices f mlluscan cmmunity structure were studied. The aim f the study was als t cmpare present malacfauna f the Krutynia river with data frm befre several dzen years. Material and methds Selected sampling site was lcated in Iznta, in the utlet part f the Krutynia 5 m upstream its utflw and was identical with that frm earlier studies (5). The river is 2 2 m wide and m deep there. The bttm is sandy and silty, scarcely vergrwn by the yellw water lily (Nuphar lutea) and the cmmn reed (Phragmites australis). Mlluscs were sampled every year at the break f July and August (25 28) frm a depth f.2 t. m with a drag f a frame area f.25 m 2. The frame was randmly thrwn n the river bttm. Cllected material was washed n a sieve with a mesh size f mm. In the field mlluscs f the family Uninidae were determined t species; their age and size were estimated and then live individuals were released back t water. Other mlluscs were preserved in 5% alchl. T btain fresh bimass (with shells), preserved mlluscs were washed, dried n absrbent paper and weighed. The bimass f Uninidae was estimated cnsidering species cmpsitin and size structure based n abundant data gathered frm the Krutynia in the year 989 (5). Results Twenty-three species f mlluscs (5 species f snails and 8 species f bivalves) were fund in the utlet stretch f the Krutynia (Tab. ). Species cmpsitin practically did nt change with years. Changes cnsisted nly in the presence f live individuals f particular species r nly their empty shells. Average density f mlluscs ranged frm 5 t 8 ind./m 2. Dminating taxa were bivalves f the family Uninidae and the snail Viviparus viviparus.

3 Mlluscs f the utlet stretch f the Krutynia River (Masurian Lakeland) 55 Table. Mlluscs in the lwer part f the Krutynia river: numerus (density abve ind./m 2 ), scarce (density up t ind./m 2 ), empty shells N Taxn Frequency f ccurrence Gastrpda Thedxus fluviatilis (L.) Viviparus viviparus (L.) Viviparus cntectus (Mill.) Valvata piscinalis (Müll.) Bithynia tentaculata (L.) Lymnaea stagnalis (L.) Radix peregra (O. F. Müll.) Radix auricularia (L.) Stagnicla crvus (Gmel.) Planrbis planrbis (L.) Anisus leucstmus (Mill.) Anisus vrtex (L.) Bathymphalus cntrtus (L.) Gyraulus albus (O. F. Müll.) Planrbarius crneus (L.) Bivalvia Andnta anatina (L.) Andnta cygnea (L.) Pseudandnta cmplanata (Rssm.) Uni pictrum (L.) Uni tumidus (Philips.) Sphaerium crneum (L.) Pisidium subtruncatum (Malm.) Dreissena plymrpha (Pall.) During the whle study perid (and in the year 989) five species f Uninidae: Uni tumidus, U. pictrum, Andnta anatina, A. cygnea and Pseudandnta cmplanata were present in the utlet part f the Krutynia. Every year sme differences were, hwever, nted in species cmpsitin f live individuals. Only 3 species were fund in 25, in ther years fur species were nted. Uni tumidus dminated in every year cnstituting frm 75 t 85% f all cllected mlluscs. Always present was als A. anatina ranging frm 6 5%. U. pictrum was less frequent (maximum 9%) but its absence in the year 25 was rather casual since the species was nted befre and after this year. Pseudandnta cmplanata was nted in the years (in 2%) but it had nt been fund in earlier studies. A. cygnea was recrded in 989 and in 28. The density f Uninidae in the utlet stretch f the river was usually f the rder f several dzen individuals per m 2. The lwest densities (belw 3 ind./m 2 ) were fund in 27; in ther years they ranged frm 6 t 7 ind./m 2 (Tab. 2). The highest lcal density (6 ind./m 2 ) was nted in 989. Dminating spe-

4 56 Beata Jakubik, Krzysztf Lewandwski Table 2. Changes in the density (mean and range in ind./m 2 ) f bivalves f the family Uninidae (data frm 989 after Lewandwski 996a) Taxn Years Uni tumidus Uni pictrum Andnta anatina Andnta cygnea Pseudandnta cmplanata 56 (6-96) (-8) (-8) 2 (-) 5 (52-56) 6 (-8) 8 (-2) 52 (36-68) 6 (-8) 8 (-6) (-8) 2 (6-28) (-) (-2) (-) 36 (28-6) 2 (-) 5 (-2) (-2) (-8) Uninidae 66 (6-6) 68 (6-72) 7 (8-92) 27 (2-32) 58 (8-66) cies U. tumidus was usually present in average densities f c. 5 ind./m 2 and nly in the year 27 in a lwer density f ca. 2 ind./m 2. Other species reached the density f several individuals per m 2 and nly lcally they were mre dense: A. anatina 6 ind./m 2 in 26 and P. cmplanata 2 ind./m 2 in 25. Large and lder individuals were mst numerus amng cllected bivalves. Fr example in the dminating species U. tumidus mst (75 9%) individuals were 7 years ld and 5 7 mm lng. The ldest U. tumidus achieved 8 9 years and the length f 75 mm, the yungest were scarce and in sme years they were absent. The snail Viviparus viviparus was als present in high densities in the utlet stretch f the Krutynia. Its mean density in the years varied frm 3 t ver 5 ind./m 2. Maximum lcal density was up t ind./m 2. Individuals f medium and large shell size predminated. In all study years females f V. viviparus were mre numerus (6 7% f the ppulatin) than males. Mean fresh weights f mlluscs were c. several hundred g/m 2 (frm 99 g in 27 t g in 26). The highest lcal bimasses were 68 g/m 2 in 989 and 33 g/m 2 in 26. Frm 59 t 98% (mean ca. 8%) f the bimass f all mlluscs was cmpsed f bivalves f the family Uninidae. Discussin Accrding t the earliest studies by Hilbert (3) 3 species f mlluscs including 3 species f snails and 2 species f bivalves lived in the Krutynia river. The same number f species but with different prprtin f snails t bivalves (2 t 9 species, respectively) was fund by Berger ().

5 Mlluscs f the utlet stretch f the Krutynia River (Masurian Lakeland) 57 Similar numbers f species were nted in ther medium-size rivers f Pland. Fr example, Piechcki (8) fund 3 species f mlluscs in the Pasłęka river (Masurian Lakeland) and 5 species in the Grabia river (7). Ntewrthy is the large number f bivalves f the genus Pisidium ( species) nted in the Krutynia by Berger (, 2). Hilbert (3) fund nly 3 species f the genus. In ur studies we fund nly cmmn species P. subtruncatum in the utlet part f the Krutynia. Other mlluscs fund there als belnged t cmmn and widespread species in Plish waters (9). Frm amng native species f Uninidae, Uni crassus was absent in the river utlet but it ccurred upstream where water velcity was much higher (5). Tw mst cmmn Plish species: Uni tumidus and Andnta anatina were present in high densities. Tw ther species A. cygnea and Pseudandnta cmplanata are prtected in Pland. Mderate water current which carries large amunts f fine sestn creates particularly favurable cnditins fr filter feeders in the river utlet; hence the richness f bivalves f the family Uninidae and f snails f the family Viviparidae. The stretch can be dealt with as a river-lake ectne. High density and bimass f macrbenths and especially f filter feeders were frequently nted in such znes (6,, ). Acknwledgements We are grateful t Lech Kufel fr his valuable remarks and translatin f this paper. References. Berger L. 96. Badania nad mięczakami (Mllusca) Pjezierza Mazurskieg. Bad. Fizjgr. Pl. Zach. 6: Berger L Uwagi rzmieszczeniu małżów Sphaeriidae w Krutyni na Pjezierzu Mazurskim. Fragm. Faun. : Hilbert R. 93. Die Mlluskenfauna des Kruttinflusses, Kr. Sensburg, Ostpr. Archiv fűr Naturgeschichte 2: Hillbricht-Ilkwska A., Wiśniewski R. J. (eds) 996. Funkcjnwanie systemów rzeczn-jezirnych w krajbrazie pjeziernym: rzeka Krutynia (Pjezierze Mazurskie). Zeszyty Naukwe Kmitetu Człwiek i Śrdwisk 3: Lewandwski K. 996a. Występwanie Dreissena plymrpha (Pall.) raz małży z rdziny Uninidae w systemie rzeczn-jezirnym Krutyni (Pjezierze Mazurskie). Zeszyty Naukwe Kmitetu Człwiek i Śrdwisk 3: Lewandwski K. 996b. Bents rzeczn-jezirnych stref przejściwych systemu rzeki Krutyni (Pjezierze Mazurskie). Zeszyty Naukwe Kmitetu Człwiek i Śrdwisk 3:

6 58 Beata Jakubik, Krzysztf Lewandwski 7. Piechcki A Mięczaki (Mllusca) rzeki Grabi i jej terenu zalewweg. Fragm. Faun. 5: Piechcki A Materiały d pznania mięczaków (Mllusca) rzeki Pasłęki. Fragm. Faun. 8: Piechcki A., Dyduch-Falniwska A Mięczaki (Mllusca). Małże (Bivalvia). Fauna Słdkwdna Plski. 7A. PWN, Warszawa Pznań.. Richardsn J. S., Mackay R. J. 99. Lake utlets and the distributin f filter feeders: an assessment f hyptheses. Oiks 62: Wttn R. S Very high secndary prductin at a lake utlet. Freshw. Bil. 2: 3 36.