The macro-invertrbrates of the rubble banks of the Abcoudermeer by P. Kramers J.E.T. Moen & P.J. Roos Zoological Laboratory, University ofAmsterdam, The Netherlands Abstract HYDROGRAPHY In the Abcoudermeer, a small lake S.E. of Amsterdam, the The lake (fig. 1) has on the western and south- rubble banks were investigated on macro-invertebrates. At eastern side connections with the rest of the least 46 species were encountered, insects and their larvae not system of canals and former rivers of which it included: 1 of 1 of 6 species sponge, species hydrozoan, forms part. This is species of free-livingflatworms, 17 species of snails, at least 3 drainage system separated by species of mussels, 8 species of leeches, 3 species of dikes from lower lying areas. Dependent on the and of Differences between crustaceans 7 species bryozoans. needs of water is into this agriculture pumped up two banks are discussed. system, or water may be let in the lower lying area. Circulation in the lake depends on the water control of the surrounding area. The salinity of the lake water varies with the amount INTRODUCTION of rainwater or brackish drainage water from surrounding ditches (table I). situated The Abcoudermeer, a small lake, is at about 10 km S.E. of Amsterdam. Its surface area is about 18 ha. In its present form it is already to 14th The lake forms be found on century maps. former part of the water circulation system of the river Amstel. The banks are periodically strengthened with rubble, this being a general feature in this part of the country. The resulting "artificial rocky coast" consists predominantly of bricks and parts of masonry. The lake has a scattered, but sometimes dense vegetation of mainly Phragmites, Typha and lacks Carex. The open water vegetation. Espe- cially along the exposed northern and western banks vegetation is scarce. Fig. 1. Map of the Abcoudermeer. Dots representing vegeta- tion. Downloaded from Brill.com10/01/2021 09:03:17PM via free access 216 P. KRAMERS ET AL. - MACRO-INVERTEBRATES OF THE ABCOUDERMEER BANKS Table I. Chlorinity of the Abcoudermeer water in mg/l from prefering overgrown stones. In the summer the January 1973 to January 1974. acoele Oligochoerus limnophilus is present. The leech the Jan. 1-555 July 17-369 most common during year Jan. 31-632 1-266 Aug. appears to be Glossiphonia complanata. During Feb. 14-606 Aug. 15-250 spring Herpobdella octoculata and Glossiphonia Feb. 28-404 Aug. 29-330 heteroclita in considerable gradually appear Mar. 14-291 Sept. 12-470 numbers too. Other species, viz. Mar. 28-376 Sept. 26-535 Hemiclepsis Apr. 11-553 Oct. 17-675 marginata, Piscicola geometra, Helobdella stagna- May 1-486 Oct. 31-196 lis, Theromyzon tessulatum and Herpobdella testa- May 16-369 Nov. 14-392 scattered and in smaller cea, occur only numbers. May 30-335 Nov. 28-360 lesser The isopods Asellus aquaticus, and to a June 13-275 Dec. 12-252 extent A. meridianus scut- June 27-637 Jan. 3-409 are seen everywhere, tling about. Under every stone the amphipod Gammarus tigrinus is present, often in great numbers. The most abundant insect larvae are those of the Chironomidae, but towards the summer the METHODS AND RESULTS number oflarvae of Trichoptera rises strikingly. Most bryozoan colonies found on stones near Bricks and of to a of the pieces masonry were, depth bank, belong to the moss animal Plumatella 50 cm, taken from the water by hand or tongs. This is mentioned in all observa- repens. species The stones were searched for inverte- this lake 1900 carefully tions on since (Lacourt, 1949). brates. Differences in numbers of animals were There at least two the first are generations a year, between that so great, even bricks, neighbouring in late spring (May-June), the second in autumn no has been made to the attempt compare (September). In summer the colonies degenerate, samples for the total num- quantitatively, except probably because the temperatures in the shallow ber of snails and the total number of leeches from water are too high. The colonies develop from different banks. statoblasts, present in the plankton in quantities in table A complete list of species is given II. to liter up 2,000 per (December 1974), or sesso- In terms the fauna is described as general blasts which remain attached to the substrate. follows: The latter the in which Fredericella are only way Within the snail population, Bithynia tentacu- sultana survives. Colonies of this species are the whole Other lata dominates during season. found along all banks, but much less abundant snails found regularly are Theodoxus fluviatilis, than Plumatella repens. Another bryozoan of Viviparus and Regular- viviparus Lymnaea peregra. which colonies were found is Paludicella articu- to be found but in much smaller numbers ly too, lata, also mentioned by Lacourt (1949). Of the are Valvata cristata, V. Bithynia leachii, piscinalis, moss animals Cristatella mucedo, Plumatella Physa fontinalis, Viviparus Lymnaea contectus, pa- emarginata. P. fruticosa and Lophopus crystallinus, lustris. L. auricularia, Acroloxus lacustris. Planor- The only statoblasts were seen. latter three are bis carinatus, P. crista, P. and planorbis Segmen- new records for the lake, as are the colonies of tina complanata. Potamopyrgus jenkinsi was found Fredericella sultana. only once. The hydrozoan Cordylophora caspia occurs on The mussels Pisidium and are sp. Sphaerium sp. the stones in small colonies. These are lower and found in clusters on the underside predominantly less ramified in comparison with colonies on of stones, in direct contact with the muddy water-lily stalks in neighbouring waters. Dreissena bottom. polymorpha is present as well, The lacustris sponge Spongilla grows irregularly in although scattered and mostly deeper water. scattered, often in large colonies. The dominant free-living flatworms are Den- drocoelum lacteum and Dugesia polychroa. They With the exception of Plumatella, which is absent occur amidst their egg cocoons, small dark-red during winter, and the larvae of Trichoptera, found which in to black spheres. Also to be are Polycelis appear the second half of April, the animals sp., Dugesia lugubris and D. tigrina, the latter are to be found all the year round. Downloaded from Brill.com10/01/2021 09:03:17PM via free access 217 46 - 1977 BIJDRAGEN TOT DE DIERKUNDE, (2) DISCUSSION Table II. Species composition of the banks of the Abcouder- meer (insects not included). No differences in species composition could be PORIFERA established between the different banks of the Spongilla lacustris (Linnaeus) lake. All species found are common and have a wide distribution. CNIDARIA the there is a remarkable During year however, Cordylophora caspia (Pallas) shift in appearance of the snail population. round. In TURBELLARIA Bithynia is present all the year early Dendrocoelum lacteum (Müller) of adult spring there are a great number large, Dugesia polychroa (O. Schmidt) Lymnaea present, together with a great number Dugesia lugubris (O. Schmidt) of their These adults, being annual, dis- Dugesia tigrina(Girard) eggs. appear during spring and in the same period the Polycelis sp. & Oligochoerus limnophilus Ax Dörjes number of Bithynia eggs grows steadily. In sum- mer the young Lymnaea appear first, followed by GASTROPODA the new generations of other snail species. Theodoxus fluviatilis (Linnaeus) It that the total number of snails is Viviparus contectus (Millet) appears bank Viviparus viviparus(Linnaeus) significantly higher at the northwestern as Valvata cristata Müller compared with the eastern bank. On the contra- Valvata piscinalis (Müller) leeches the northwest- ry, the total number of at Potamopyrgusjenkinsi (Smith) ern bank is lower than that of the eastern bank. Bithynia leachii (Sheppard) These differences Bithynia tentaculata (Linnaeus) significant are proved by using Physafontinalis (Linnaeus) Wilcoxon's two-sample test. No differences are Lymnaeaauricularia (Linnaeus) to be shown between other banks or populations Lymnaea (Müller) palustris of other animals. The significant differences Lymnaeaperegra (Müller) found between leeches and snails from different Planorbis carinatus Müller banks can be accounted for exposition to Planorbis planorbis (Linnaeus) by Planorbis crista (Linnaeus) prevailing wind directions, arrangement of stones Segmentina complanata (Linnaeus) and steepness of the bank. Acroloxus lacustris (Linnaeus) The northwestern bank consists of heteroge- rubble and is lack of PELECYPODA nous relatively exposed by Pisidium sp. reed growth over most of its length; the bottom Sphaerium sp. slopes down steeply. This results in a diversity of Dreissena polymorpha (Pallas) habitats in clean, clear water. Organic decay is therefore HIRUDINEA transported to deeper water, many Glossiphonia complanata (Linnaeus) algae grow on the upper sides of the stones and Glossiphonia heteroclita (Linnaeus) algae-eating molluscs find food and shelter. The Helobdella stagnalis (Linnaeus) eastern bank is protected by vegetation, has a Theromyzon tessulatum (Müller) more uniform and densely packed bottom, Hemiclepsis marginata(Müller) stony Piscicola which Silt rests between the geometra (Linnaeus) slopes very gently. octoculata Herpobdella (Linnaeus) stones, inhabited by chironomids and Herpobdellatestacea Savigny oligochaetes. This less exposed area is apparently leeches their CRUSTACEA preferred by and prey. Asellus aquaticus (Linnaeus) The community found on the rubble stones Asellus meridianus Racovitza along the banks of the Abcoudermeer is charac- Gammarus