Drastic changes in the amphipod fauna (Crustacea) of Dutch inland waters during the last 25 years

12 Pages·1992·1.2 MB·English

by  Pinkster, Sjouk

Bijdragentot deDierkunde, 61 (4) 193-204 (1992)
SPBAcademie Publishingbv, The Hague
Drastic changes in the amphipod fauna (Crustacea) of Dutch inland waters
during the last 25 years
Sjouk Pinkster MaartenScheepmaker Dirk Platvoet& Nico Broodbakker
Institute of TaxonomieZoology (Zoölogisch Museum), University ofAmsterdam, P.O. Box 4766,
1009ATAmsterdam, TheNetherlands
Keywords: Netherlands, amphipods, changing distributions, allozyme electrophoresis, introduced species,
environmentalchanges
Abstract (Nijssen, 1963). G. roeseli Gervais, 1835 was re-
strictedto somesmallbrooks neartheGermanbor-
Aftertheintroduction ofGammarustigrinusinTheNetherlands der(collections Zoologisch MuseumAmsterdam =
some25 years ago and of otherrecently invadingamphipods ZMA). Echinogammarus berilloni (Catta, 1878)
(Crangonyxpseudogracilis and Corophiumcurvispinum) the
was found in some rivers in the south of the
native species decreased,the invaders increased. The successof
province ofBrabant and in the river Meuseand in
these invaders anditsimpactonthe localamphipodfaunaisdis-
cussed. Electrophoretictests giveevidence thata second inva- some ofits tributariesin theprovince of Limburg
sion ofGammarustigrinus, this time from Germany, is taking as farnorthas Neer, ca. 5 km south ofVenlo(col-
place. Somepredictions about future developmentsaremade. lections ZMA).
The more brackish waters, especially theIJssel-
meeraftertheclosing oftheformerZuiderZeeand
Résumé
theFrisianlakes, were populated by G. d. duebeni
Liljeborg, 1851 (Schijfsma, 1954; De Vos, 1941,
Aprèsl’introduction deGammarus tigrinusauxPays-Bas il ya 1954), while G. zaddachi (Sexton, 1912), often ac-
environ 25 ans, ainsi quecelle d’autres espèces d’Amphipodes
ayant envahi le pays récemment (Crangonyxpseudograciliset companied byG. d. duebeni,wasthedominantspe-
Corophium curvispinum) les espèces indigènesont diminués ciesin waterswithtidalinfluences likerivermouths
considérablement etles espèces envahisseurs ont gagné du ter- and isolatedwater bodiesnot farfrom thesea. All
rain. Le succès de ces invasions et leur conséquences pour les thesegammarid species are freeliving, benthic, and
Amphipodesindigènessontdiscutés. Des tests d’électrophorèse omnivorous.
montrent qu’uneseconde invasion de G. tigrinus, ayant son
origineenAllemagne,seproduitactuellement.Quelquesprédic- The most common tube-dwelling amphipods in
tions surles développementsfuturs sontfaites. inlandwaters atthattimewere Corophium insidio-
sum (Crawford, 1937), C. multisetosum Stock,
1952,C. lacustreVanhöffen,1911,and C. voluta-
Introduction tor (Pallas, 1766). Two other species, C. acherusi-
cum (Costa, 1851) and C. arenarium Crawford,
Untilthemidsixties the gammarid faunaof Dutch 1937werereported (collections ZMA) frommarine
inland waters was supposed to be rather stable. habitatsor sometimes from floating objects inin-
Mostofthe freshwaters were dominatedby Gam- landmixohalinewaters. All Corophium species are
marus p. pulex (Linnaeus, 1758), while G. fossa- filterfeeders andconstruct tubesofmud, ofwhich
rumKoch, 1836occurred insomeheadwatersinthe two differenttypes can be distinguished: (1) tubes
extreme south of the province ofLimburg and in burrowed in the substrate, which may vary from
some isolatedlocalities inthecentre ofthe country sandto soft mud, and(2) tubesthat havebeenbuilt
194 5. Pinkster et al. - Changes in the amphipod fauna ofDutch inlandwaters
upon a sessible substratum of any type. C. mul- Dutch amphipod fauna appeared on the scene:
tisetosum,C. insidiosum, and C. acherusicum can Crangonyx pseudogracilis Bousfield, 1958 (cf.
maketubes ofboth types; theother species are ex- Pinkster etal., 1980)and Corophium curvispinum
clusively burrowing. Sars, 1895(cf. Vanden Brink etal., 1989).A sum-
The first intrusionuponthis ratherstable situa- maryof the developments andthe actual situation
tion was noticedby Nijssen &Stock (1966) report- is given belowandinMaps 1and2(for comparison
ing Gammarus tigrinus (Sexton, 1939) in The see Fig. 1 inPlatvoetet al., 1989, withmaps ofthe
Netherlandsandits rapid spreading over theIJssel- situationin 1966, 1973, and 1986, and themap in
meer andcanalsinthenorthernpartoftheprovince Hautus & Pinkster, 1987). It must be stressed that
of Noord-Holland.This finding was not very sur- the whole country is carefully sampled (over 800
prising, since this originally North American spe- samples) but, for the ease of survey, the many
cies was already known from a large area in En- hundreds of negative sampling stations have not
gland, Ireland (Hynes et al., 1960), and Germany been indicatedin thepresent Maps 1 and2.
(Schmitz, 1960).
From 1966on,surveys (everytwo orthreeyears) Gammarus tigrinus. As canbe seen from themaps
throughout The Netherlandshave beencarriedout in this and preceding papers, G. tigrinus rapidly
to determineeventualchanges inthedistributionof spread over most meso- and oligohaline waters in
G. tigrinus andtheir impact onthe localgammarid TheNetherlands, reaching a moreor less stablesit-
fauna; thelast survey was carriedoutin1991.More uationat theend of 1979(Pinkster etal., 1980). In
than 800 stations have been sampled. thenortheasternparts ofthe country ittemporarily
lostlarge to G. d. duebeniand G. zaddachi. Like-
wise, considerablevariability in population densi-
Materialand methods ties could beobserved.
Pinkster etal.(1977) demonstratedin laboratory
Allsampling was donewith astandard dip-net,by experiments that the success of G. tigrinus was
turning stones, and by inspecting the vegetation. mainly dueto itsenormous reproductive capacity in
The population density was estimated by counting oligohaline waters as compared to G. zaddachi, G.
thenumberofassays necessary to collect asample d. duebeni, and G. p. pulex. Pinkster & Platvoet
of atleast 100 specimens. When population densi- (1983) mentionedthesevere and prolonged winters
ties were very low, this numberwas not achieved. of 1978/1979and 1979/1980and subsequent low
Animals were preserved in a4% formalinsolution watertemperaturesatthebeginning ofthebreeding
andinthe laboratory transferredto a70%aethanol season as themaincause forthetemporarydecline
solution.Forpartofourresearch weusedallozyme of G. tigrinus population densities in the north-
electrophoresis toestablish theorigin of somenew- eastern provinces. Because of these long lasting
ly found populations. The animals used for these winters, ovigerous females die before the new
electrophoretic experiments have beentransported generation can be released. G. tigrinus cannot
live tothe laboratoryand directlydeep frozenatmi- reproduce in waters below 5°C. Thiscauses adra-
nus 70°C. Fora furtherexplanation of theproce- maticdeclineinthepopulation (seealso Chambers,
dure see under Electrophoretic experiments (Ap- 1987).
pendix). This more or less stable situation drastically
changed in 1984andfollowingyears, whenG. tigri-
nusnot only appeared inthe river Rhineand its af-
Developments since 1965 fluents(Platvoet & Pinkster, 1985),but also on the
Frisian Isles of Texel, Terschelling, and Ameland
The developments that tookplace are summarized (Hautus & Pinkster, 1987).
inPinkster etal. (1977) and Platvoet et al. (1989). During the 1991 survey, G. tigrinus was first
During thesesurveys someothernewcomers to the recordedfrom theeasternpartofthecountry(Map
Bijdragen tot deDierkunde, 61 (4) - 1992 195
Map 1. Distribution ofGammarus tigrinus,G. zaddachi,G. d. duebeni,and G. p.pulexin TheNetherlands atthe end of 1991.
196 5. Pinkster et al. - Changes in theamphipodfauna ofDutch inlandwaters
1), in canals that are directly connectedwith the reported fromsomestationsintheNoordzeekanaal
German Ems River system in which also rich G. (Van Couwelaar&Van Dijk, 1989),fromsomeiso-
tigrinus populations occur (Herhaus, 1978). Starch lated water bodies resulting from ancient dike
gel allozyme electrophoresis experiments gave evi- bursts intheprovince of Noord-Holland, andfrom
dencethat thesepopulations indeedoriginate from theislesintheDeltaicregion ofRhine, Meuse, and
theseGerman populations andnot fromthe origi- Scheldt.
nalDutchstock. Fora detaileddescription of these
experiments wereferto theAppendix at the end of Gammarus p. pulex. Although this species lost
thispaper. ground to G. tigrinusand recently also to C.pseu-
In a few areas (e.g. in part of the Noord-Oost dogracilis, itis stillpresentthroughout thecountry.
polder) G. tigrinus was not foundagain in 1991, It is the most common freshwater gammarid in
while in other areas the population densitieswere natural and man-made waters, usually on sandy
very low. Weassume thatthisis likewise causedby substrates, intheeastern andsouthernparts ofThe
the severe and late winters of 1989/1990 and Netherlands. However, many of these waters are
1990/1991. On the other hand some progress in now devoid ofany gammarid faunadue to severe
western direction was made in the province of pollution ofthese water systems, especially inthe
Noord-Brabant. province ofBrabant and theriver Meusebetween
the Belgian town Liège and Venlo.
Gammarus zaddachi. As could be expected (see Intheprovince ofZuid-Hollandand inthe areas
Pinkster et al., 1977) G. zaddachi is completely between the large rivers Meuse, Rhine, and Waal
replaced by G. tigrinus inmost ofthe formerly in- thereis aspatial separationbetweenG.p. pulexand
habited oligohaline waters in the northern G. tigrinus: G. p. pulex inhabits the relatively un-
provinces of Groningen and Friesland and in the polluted ditches, brooks, and lakes with a well-
Deltaic region. Itis stilldominantininlandwaters developed anddiverseflora,whileG. tigrinus is the
oftheDeltaicregion ofRhine, Meuse, andScheldt, dominant (often only) species in the surrounding
in waters with chlorinitiesranging from 3,000 to morepolluted canalsandsmallerrivers.Thisagrees
10,000 mg l"1, and in the Noordzeekanaal that completely withtheobservationsofVan denBrink
connects Amsterdamwith the North Sea andin its (1990). He observed a spatial segregation between
side-canals(Van Couwelaar& Van Dijk, 1989). It G. tigrinusand G.p. pulexinthestream system of
is also presentinsomeisolatedbrackish water bod- the rivers Rhine andWaal. G. tigrinus inhabitsthe
iesbehindtheseadikes.It couldnottakeadvantage major, more polluted waters, while G. p. pulex
ofthetemporarydeclineofG. tigrinus inthenorth- thrivesbest inallsurrounding smaller, andless pol-
ern provinces to enlarge its range. lutedwaters.
A new phenomenon is that G. zaddachi is now In thenorthern provinces G.p. pulex can hardly
regularly found (although not reproducing; Van maintainitsposition infreshandoligohaline waters
den Brink, pers. comm.) in the cooling water- on sandy bottoms; some habitatshave beenlost to
intakesoftheGelderlandpowerstation intheriver C. pseudogracilis or G. tigrinus, especially in the
Waal(the mainbranchof theriver Rhine). Accord- province of Groningen. Itis still foundinnearly all
ing to Den Hartog etal. (1989) and Van der Velde Frisian lakes, except in those in the westernmost
et al. (1990) this is due to the increased salinity in partof the province.
the last few decades.
Gammarusfossarum. This species is a real fresh-
Gammarusd.duebeni.For this species thedistribu- water gammarid, inhabiting the upper reaches of
tion has changed even moredramatically. It disap- relatively unpolluted streams. In the middle and
peared from all Frisian lakes, the IJsselmeer, and lower reaches it is gradually replaced by otherspe-
canals in the provinces of Noord- and Zuid- cies (forreferences seeKaraman&Pinkster, 1977a:
Holland. During the last few years, it was only 53-54). It is very susceptible to both organic and
Bijdragen tot deDierkunde, 61 (4) - 1992 197
inorganicpollution andhigher water temperatures. shire, with records from some other more or less
This is perfectly illustrated by the gradual disap- isolated populations more northward(Gledhill et
pearance of the species in the province of Noord al., 1976). In1975itwas also recordedfromapond
Brabant.Thepopulations inthe centralpartofthe in Dublin, Ireland(Holmes, 1975). This species in-
country, recorded by Nijssen (1963) and still habits all kinds of habitats like rivers, canals,
present in 1970 (own observations), are now ponds, lakes, andreservoirs, tolerating both fresh
reduced to a single habitat (the Beekhuizense Beek and brackish, cleanand polluted waters.
in the national park "The Veluwezoom"). The Nevertheless, its appearance in 1979near Boer-
populations inthe rivers Meuse and lower Rhine, akker in theprovince of Groningen camemore or
stillpresent in1986(Hautus &Pinkster, 1987),have less as a surprise. Thearea was well studied during
now completely disappeared. manyyears and hadrich populations ofboth G.p.
pulex and G. tigrinus. From its first discovery, a
Gammarus roeseli. This is so far the only in- monthly sampling programmewas carriedout with
digenous species that takes some advantage ofthe additional laboratory experiments in order to col-
changing conditions. (According to Jazdzewski, lectinformationonthebiology ofthis so newly in-
1980and Karaman& Pinkster, 1977b, this species troducedspecies (Pinkster & Platvoet, 1983). The
invadedwestern Europe only in the last few centu- species proved to have a high reproductive out-
ries and thus also should be seen as an invader.) putand especially a high fecundity as compared to
However, it is common in The Netherlandssince local species. Rapid range extension in southern
the endofthelast century(collections ZMA). Itin- and southeastern direction into the provinces of
habitsrelatively slowly flowingrivers andcan stand Drentheand Friesland was to be expected. In this
a high degree of organic pollution (Karaman & partof The Netherlands, stagnant or slowly flow-
Pinkster, 1977b). ing waters onsandy bottomprevail and G.p. pulex
Until thebeginning oftheninety seventies it was used to be the only gammarid species.
only found in the extreme eastern part of the Inthe firstfew years after C. pseudogracilis was
province of Gelderland, near the German border discovered however, hardly any range extension
andinsomewatersintheprovince ofLimburg (col- was observed. During the 1988 survey it appeared
lections ZMA). The progressing pollution and the thatsomeminorextensionintosouthernandnorth-
continuing canalization of previously natural ern directionshad taken place. In 1991 this exten-
brooks intheeastern parts ofthe countrycreate an sion continued in a more rapid way, in southern
idealenvironment for this species. It has now ad- directionintotheG.p.pulex areabutalso in north-
vancedinwestern directionintothe Veluwe, a san- ern andeastern directionintothe G. tigrinus terri-
dyand wooded areawest of the river IJssel. tory, replacing both species in many localities.
Moreover, itwas found farfrom its maindistribu-
Echinogammarus berilloni. During our last four tion area, in western Friesland, inthe river Eem in
surveysE. berillonicouldnotbe foundagain inthe the province ofUtrecht, andneartheoutletofthis
localitieswhereitusedtoliveinthepast(collections river in the IJsselmeer.
ZMA; MollerPillot, 1971), sowemustassume that
it is the only species which has completely disap- Corophium species. Almost alldataon the inland
peared from Dutch inlandwaters. species ofCorophium datefrombeforetheclosing
ofthe ZuiderZee andmost branches ofthedeltaic
Crangonyx pseudogracilis. Like G. tigrinus this region oftheriversRhine, Meuse, andScheldt (col-
species is a newcomer to the Dutch fauna. This lections ZMA and reports of local and provincial
originally North American species was recently in- water authorities). C. insidiosum, C. lacustre, c.
troducedinto England and has becomea common multisetosum, andC. volutatorusedtobe common
inhabitant of central and southern England and in meso- and oligohaline waters in the provinces
Wales since 1975.Itis extending north upto York- bordering the North Sea, ZuiderZee, andWadden
198 S. Pinkster et al. - Changes in the amphipod fauna ofDutch inlandwaters
Zee. Of these four, C. lacustreand sometimes C. lished by Van denBrink (in prep.). Inthe present
multisetosum penetrated far inland, into almost review we only indicate not yet known localities
fresh waters. Inour surveys before 1991 no Coro- (Map 2).
phium species have been collected in the major According to Van den Brink et al. (1991a) this
rivers in TheNetherlands, eventhough these rivers species builds tubes on hard substrates like stones
have been intensively sampled. of breakwaters and river dikes. During our survey
Although nospecific research on Corophium has wealso foundC.curvispinum digging into thesub-
beendonesincetheearlysixties, itcanbe concluded strate, butnot on hardsubstrates, like pebbles and
fromthemany reportsoflocalandprovincialwater deadshells, in between thegroynes, inwaters that
authorities that all four species gradually disap- are not exposed to the continuous supply of silt.
peared frompartofthe previously inhabitedareas Moreresearch onthistopic is presently carriedout
becauseof the continuing decrease insalinity after atthe Catholic University of Nijmegen.
theclosureoftheZuiderZeeandmanybranchesin
the Deltaic Region ofRhine, Meuse, and Scheldt.
C. insidiosum, common in the Noordzee kanaal Conclusions
andconnecting canalsinthefirsthalfofthiscentu-
ry(Stock, 1952)was not foundagaininanextensive Fromthe data discussed in theprevious sections it
study in 1988(Van Couwelaar& Van Dijk, 1989). will be clear that enormous changes have taken
Klink & Moller Pillot (1982) did not find any placeinthedistributionofAmphipoda overthelast
Corophium species during anextensive study onthe 25 years, and are still continuing. Looking at the
macro-invertebrates of the major rivers in The numberofspecies onemayhavetheimpressionthat
Netherlands. theamphipod faunahasbecome richerwiththe ap-
pearanceofthree species new to the Dutch fauna.
Corophium curvispinum. After the first report of However,a closer study reveals the contrary to be
C.curvispinum Sars, 1895intheriver Rhine, close true;those species that are characteristicof certain
to theGermanborder(Van denBrink etal., 1989), types ofhabitatlike G. fossarum, G. p. pulex, G.
dramatic changes in the macrofauna of the river d. duebeni, E. berilloni, and to a lesser extent G.
Rhine took place. Within a few years the small zaddachihave disappeared froma greatpartofthe
population recorded from stones of groynes grew previously inhabitedwaters. They are now limited
out to dense populations with a maximum of to morescatteredareas, inwhich somekindofpro-
100,000 specimens per square metre (for compari- tectedconditionsoccur (as is thecasewithG. fossa-
son: thehighest density ever found for G. tigrinus rum in some spring regions in the south). Even
is 13,628 per square meter found in the Frisian more serious is the complete disappearance in a
Tjeukemeer by Chambers (1971)). This explosion very shortperiod (some 5 years)ofamphipods from
first occurredin the middleRhine in Germany and large areas (compare Maps 1 and 2 with Fig. 1 in
a year later in the lower Rhineover a distance of Hautus&Pinkster, 1987). Thiscertainly is not due
200-500km, indicating anenormous rangeexten- to insufficientsampling but morelikely topooren-
sion (Van den Brink et al., 1991a). According to vironmentalconditionsor complete destructionof
theseauthors, itnow livesinall major rivers ofThe thenaturalhabitats.Thisis especially trueforlarge
Netherlands, as well as in the Amsterdam-Rijn areas in the southernand middlepart ofthe coun-
kanaal. They expected it to reach the IJsselmeer try, where most waters have sandy bottoms and
andothergreaterwater bodies withahigh silt con- where intensive factory farming ("bioindustry")
tent within short time. Indeed (although we used (combined withan extreme acidificationofsurface
different gear) we found it in the IJsselmeer and and groundwaters) has led to deteriorationof the
somelarge canalsin thewestern andeasternpartof water quality.
TheNetherlands(see Map 2). Acomplete mapwith Thus, themostimportant factorsinfluencingand
the present distributionof this species will be pub- limiting the range ofthe Dutch amphipod species,
Bijdragen tot deDierkunde, 61 (4) - 1992 199
Map2. Distribution ofCrangonyxpseudogracilis, Gammarusfossarum,Gammarus roeseli,andnewlocalities ofCorophiumcurvispi-
numatthe end of 1991.
200 S. Pinkster et al. - Changes in theamphipodfauna ofDutchinlandwaters
apart from competition with local and newly in- major rivers and most other larger waters in The
troduced species, are: progressing eutrophication, Netherlands. It can be limited by a high degree of
increasing water temperatures,changes in salinity, inorganic pollution (Jazdzewski, 1980).
acidification of both surface and groundwaters,
and man-made changes in hydromorphology like
canalization and constructionof dams. These fac- Future developments
tors together lead to a loss in diversity and/or a
complete destructionofspecial habitats.Itis often It is always a hazardous venture to predict future
not exactly known which is the directcause ofthe developments but nevertheless we will try.
disappearance of certainspecies, sincemany ofthe
above-named factors are interacting. Gammarus tigrinus. The situation has become
Intheriver Meuse downstreamofthe highly in- somewhat complicated for G. tigrinus withtheap-
dustrializedareafromLiège (Belgium) up to Venlo pearanceofpopulations originating from theGer-
(Netherlands) all the factors listed above are man river Ems system. TheseGerman populations
present and a general, sharp declineof the entire are descendantsof anEnglish population that has
macrofauna community is found. This not only been purposely introduced into the river Werra in
causes the extinction of the formerly common G. 1957(Schmitz, 1960). Fromthere itrapidly spread
fossarum andE.berilloni,butlikewiseprevents the over mostGermanriver systems, aidedby thecon-
newcomers Gammarus tigrinus and Corophium struction of canals between the various systems,
curvispinum from colonization (d'Udekem & reaching the river Ems system in 1977 (Herhaus,
Stroot, 1988). 1978).
Thenewcomers G. tigrinusandC.pseudogracilis TheDutch G. tigrinus most probably originates
are bothwell equipped forthechanging conditions from a population in Lough Neagh, Northern
ina greatpart ofTheNetherlands, viz. progressing Ireland, releasedinthe IJsselmeeron 29 July 1960.
eutrophication, increasing water temperatures, and Fromthere itrapidly spread over TheNetherlands,
changes in salinityandhydromorphology. They do virtually reaching the limit ofits range some years
not have high demandsupon theirhabitat and can ago. The German populations not only differge-
live inbothrunningandstagnantwaters ofallsizes. netically fromtheirDutch congeners, asis shownin
They have a greater reproductive outputthan the the Appendix, but they are also better adapted to
indigenous Gammarus species and consequently life in (almost) fresh waters as can be concluded
outnumberthem.Factors limiting the distribution from theiroccurrence infreshstreamsjust over the
ofG. tigrinus arelowsalinitiesandlowwintertem- Germanborder(ownobservations), ahabitatupto
peratures; factors limiting thedistribution (chemi- nownot colonizedbyDutchG. tigrinus. Thisopens
cal factors; temperature) of C. pseudogracilis are perspectives for this population to invade un-
not yet fullyknown(for a more detaileddiscussion colonized waters in the eastern provinces of
ofthese factors see Pinkster etal., 1977and Pink- DrentheandOverijssel. Itwill beinteresting to fol-
ster & Platvoet, 1983). lowwhatwillhappen whendescendantsofthetwo
Fortheoriginally Pontocaspian species Corophi- stocks meet, both from the genetical and zoo-
um curvispinum thesituationisalmostideal; it can geographical point of view.
invadeabiotope inwhich sofarno otherCorophi- In the waters up to now populated by "Dutch"
um species occurred, or from which the local G. tigrinus the perspective is different, since the
Corophium species have disappeared since the otherrecent invaderC.pseudogracilis is now enter-
damming of the Zuider Zeeand most branches of ing the G. tigrinus territory. Ithasalready replaced
the Rhine, Meuse, and Scheldt estuaries. It de- G. tigrinus in some localities in the provinces of
mands rather high water temperatures, a high ion Groningen andFriesland(1991 survey). Sowemust
content, andaconstant supplyoffoodandsiltpar- assume thatinthenear futureG. tigrinus willloose
ticles. These conditionsare readily available in all some ground not just in this part of The Nether-
Bijdragen tot deDierkunde, 61 (4) - 1992 201
lands but also in the IJsselmeer. provementofthewater quality mightpossibly give
it a chance to repopulate theDutch streams in the
Gammaruszaddachi. Wedonotexpect achange in southernpartofthecountryfromtheupperregions
thepresentsituation.Thewaters inwhich itstilloc- which originate in a rather unpolluted area in
curs havea relativelyhigh salinity and underthese Belgium.
conditionsitsreproductive capacity is high enough
to withstand the pressure of G. tigrinus. Possibly, Crangonyx pseudogracilis. After acertainperiodin
in the long run, it will disappear again from the which it has consolidated its position C. pseu-
Rhine, when salinity drops to aconsiderably lower dogracilis has good prospects ofenlarging its area
level(as willhappen, according to policy makersin since it has successfully penetrated into waters
thecountries bordering the Rhine). previously inhabitedby G.p.pulexand G. tigrinus.
It mightalso colonize waters so far devoidof any
Gammarus d. duebeni. This species has already gammarid species. Weexpect to finditin duetime
beenpushed backto theutmost limitsofitsrange. inmost canalsand lakes oftheprovinces of Fries-
Although it can thrivein waters varying from fresh land, Groningen, and Drenthe, and also intheIJs-
to hypersaline and from unpolluted to very pollut- selmeer, starting fromitspresentadvancedposition
ed, its reproductive capacity is too low to compete inthemouthofthe river Eem.It is hard to predict
successfully withtheotherspecies nowpresent(see if it will be able to penetrate into the oligo- and
Pinkster etal., 1977). It willsurvive only in waters mesohalinewaters in the western part of thecoun-
with extreme conditions. try, sincewehavenodataonits reproductive capac-
ity under these conditions.
Gammarusp. pulex. Up to now, this species has
withstoodG. tigrinusinmost oligohalineand fresh Corophium curvispinum. As mentionedbefore, C.
waters, but the introduction of C. pseudogracilis curvispinum entered into a habitat, which at the
again hasputanewpressureonits distribution.The moment ofits firstappearancewas not inhabitedby
first results can already be seen in the province of any other tube-dwelling amphipod species. So we
Friesland. In our opinion itwillin theendbe forced may expect a rapid furtherrange expansion over a
back intoits "original" habitat, themiddlereaches greatpartofTheNetherlandsintheyearstocome.
offresh, running waters. This is already becoming obvious from the results
of our last survey. Although no special attention
Gammarusfossarum. The situationhas reached a was given to this species, it was found farbeyond
finalstageforthisspecies. Itstilloccurs insomeup- theareaknown atthe beginning of 1991 (Van den
per reachesofsmall streams in protected areas but Brink et al., 1991a; pers. comm.). During our last
its disappearance fromthe lower reaches ofthese survey, weobserved that C. curvispinum not only
streams and theriver Meusemake repopulation of settled on the stones of groynes and dikes but was
otherstreams almostimpossible, unless drastic im- also digging into the substrate.
provement of the water quality takesplace. Although C. curvispinum is no directcompetitor
oftheotheramphipod species, its high abundance,
Gammarus roeselishall be ableto enlarge its terri- especially on hard substrates, could havean enor-
tory, since (in spite of protests fromenvironmen- mous influenceonthemacrofaunacommunity as a
talists) canalizationis still going on, creating suit- whole. It uses the same substrate and food as the
ablehabitats forthe species. Thereare not enough mussel Dreissena polymorpha (Pallas, 1771) and
data yet to ascertain its capacity to compete with Trichoptera of the genus Hydropsyche. Van den
C. pseudogracilis. Brink etal.(1991b) already reporta declineofthese
organisms inareas with a high densityofthis new
Echinogammarus berilloniis already expelled from invader and they predict major changes in the
the formerly inhabited waters. Only a drastic im- ecosystem as awhole. Moreresearch on this topic
202 S. Pinkster etal. - Changes in the amphipod fauna ofDutchinlandwaters
is presently done at the Laboratory of Aquatic Chambers,M.R., 1987.Thestatusofthe alien amphipodGam-
Ecology, CatholicUniversity Nijmegen. marus tigrinus(Sexton, 1939)in Friesland twenty yearsafter
itsintroduction into the Netherlands. Bull. zoöl. Mus. Univ.
Amsterdam, 11 (7):65-67.
Echinogammarusischnus. A possibility that sofar
Couwelaar,M.van&J. vanDijk, 1989. Onderzoekoeverfauna
has notbeendiscussedistheeventualappearanceof Noordzeekanaal,zijkanalenen havens: 1-50, 1-XI (Rijks
Echinogammarus ischnus (Stebbing, 1906) in the Waterstaat Noord-Holland,notaANW89.17).
eastern part of The Netherlands. This originally Gledhill,T.,D.W.Sutcliffe&W.D.Williams,1976.Key tothe
British freshwater Crustacea: Malacostraca., Scient. Publ.
Pontocaspian species has rapidly spread over Eu-
Freshwat. biol. Ass., 31: 1-72.
rope inthe last few decades and reached the Ger- Hartog, C. den,F. van den Brink &G. van der Velde, 1989.
man river Ems system in 1978(Herhaus, 1978). In Brackish-water invaders in theriver Rhine. A bioindication
spite ofour intensivesampling, we didnot yetfind for increased salinity level over the years. Naturwissen-
it in TheNetherlands, butit seems most likely that schaften, 76: 80-81.
induetimethis species willalso entertheDutchin- Hautus,T.& S. Pinkster, 1987.Rangeextension in the period
1985-1986 ofthe alien amphipods,Gammarus tigrinusSex-
landwaters.
ton, 1939,and CrangonyxpseudogracilisBousfield, 1958,in
the Netherlands (Crustacea, Amphipoda).Bull. zoöl. Mus.
Univ. Amsterdam, 11 (6): 57-64.
Acknowledgements Herhaus, K.F., 1978. Die ersten Nachweisen von Gammarus
tigrinus Sexton, 1939 und Chaetogammarus ischnus (Steb-
bing, 1906)(Crustacea, Amphipoda,Gammaridae)im Ein-
Theauthorsareindebtedtothe Beyerinck-PoppingFondsofthe zugsgebiet der Ems und ihre Verbreitungsgeschichtliche
RoyalDutchAcademyofSciencesfortheir supportinfinancing
Einordnung.Natur und Heimat, 38 (3):71-77.
the fieldwork, tothe manyemployeesoflocal waterauthority Holmes,J.M.C., 1975. Crangonyxpseudogracilis Bousfield,a
boards forprovidinginformation,and toDrs.F.W.B,van den freshwater amphipod new to Ireland. Ir. Nat. J., 18:
Brink oftheLaboratoryofAquaticEcology,Catholic Universi-
225-226.
ty Nijmegen,for givinginformation and critical remarks. Hynes,H.B.N.,T.T.Macan& W.D.Williams,1960.Keytothe
British species ofCrustacea: Malacostraca occurringin fresh
water. Scient. Pubis. Freshwat. biol. Ass., 19: 1-36.
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