Ecological adaptations of a freshwater sponge association in the River Rhine, Germany (Porifera: Spongillidae)

10 Pages·1999·2.2 MB·

by  J Gugel

ECOLOGICAL ADAPTIONS OF A FRESHWATER SPONGE ASSOCIATION IN THE
RIVER RHINE, GERMANY (POR1FERA: SPONGILLIDAE)
JOCHEN GUGEL
Gugel, J. 199906 30: Ecological adaptions ofafreshwatersponge association intheRiver
Rhine,Germany (Porifera:Spongillidae).MemoirsoftheQueenslandMuseum44:215-224.
Brisbane. ISSN 0079-8835.
The species composition and autecology of freshwater sponges (Porifera, Spongillidae)
were investigated inthe Rhine between Karlsruheand Bonn (Germany) between 1993 and
1995. Ephydatia fluviatilis, E. muelleri, Trochospongilla horrida, Spongilla lacustris,
Eimapiusfragilis and E. carteri were found. Ephydatiafluviatilis was classified as an
r-strategist due to its high ability to colonise new habitats, whereas other species placed
emphasis on successful establishment in more stable habitats and should therefore be
classified as K-strategists (among freshwatersponges). Similarly, the production oflarvae
wasanintegralpartofthelifecycleonlyinE.fluviatilis,whereasotherspeciesputtheirmain
efforts in producing gemmules as distribution-units. Asexual vs. sexual reproductive
strategies in freshwater sponges in running-water habitats is discussed in terms oftheir
G
prevalence, periodicityandinfluenceoflimnological factors. Porifera, Spongillidae, life
cycle, adaptions, centralEurope, runningwater, riverRhine.
Jochen Gugel (email: [email protected]) Darmstadt University of Technology,
,
Institute of Zoology, Schnittspahnstrasse 3, D-64287 Darmstadt, Germany. Present
address: Tel Aviv University, George S. Wise Faculty ofLife Sciences, Department of
Zoology, RamatAviv, TelAviv69978, Israel: 15March 1999.
A considerable number ofpublications on life Kinzelbach, 1995) have been taking place, and
cycles offreshwater sponges are now available have influencedthe biocoenosis considerably.
(e.g. Gilbert et al., 1975, Frost et al., 1982,
Courreges & Fell, 1989, Bisbee, 1992). Mostly Results ofFranz(1992) indicatethattheRhine
these focus on single life cycle events, such as isahighlysuitablehabitatforsessilefilterfeeders.
formation of larvae or gemmulation, and often Not only is the nutritional situation excellent for
include only a single species. Only a fewpapers these animals due to its eutrophic waters, butthe
deal with associations of several species, their banks are entirely covered by rocks which
colonisation strategies and spatial competition provide a suitable substrate. Filter feeding is not
(e.g. Williamson & Williamson, 1979; Mukai, restricted to sessile animals - in particular many
1989; Pronzato & Manconi, 1991). The present insectsalsogaintheirnutritionfromfilterfeeding
ioncvceusrtiinggatiionntrheepoRrhtisneonbefitvweeesnympKaatrrliscrushpeecaineds i-vaintydoMfanfinlteertfale.ed(e1r9s72i)s setxattreedmtehlayt thhieghprowdiutchti-n
Bonn (Germany), their reproductive strategies
waters disturbed by anthropogenic influences.
and colonisation.
Nevertheless, ourknowledge aboutfreshwater
At the beginning ofthe 20th century Lauter-
born distinguished 83 macrobenthic animals in sponges in theRhine is still fragmentary, despite
regular, general studies on the macrobenthic
the Rhine (Tittizer et al, 1990). In the 1970's
thesenumbersdecreasedto 12species(Conradet fauna. Such studies usually include sponges,
al., 1977), due to an extremely high level of althoughtheyareoftengivenonlycursoryconsid-
pollution. Since thattimegreateffortshave been erations.
undertakentopurifythewater,andthenumberof
This seems surprising since repeatedly high
macrobenthic animals has again risen steadily
(Scholl et al., 1995). This species diversity now abundances ofsingle species have attracted the
exceeds that ofLauterborn, whereas the species attention ofresearchersin thepast(Schon, 1957;
compositionisnotthesameasinthebeginningof Bartl, 1984). Large rivers are characterised by
thecentury(Tittizeretal., 1990), duetothehuge unpredictable changing water levels. This offers
changes in the Rhine. In recent years ongoing and destroys new habitats - a situation which
invasions of foreign species (Neozoa: seemsdifficulttodealwithforsessileorganisms.
216 MEMOIRS OF THE QUEENSLAND MUSEUM
TABLE 1.Collectingsitesanddatesofcollections Key: 1,NearthefacilitiesoftheBASFAG.2, Outflowofthe
coolingwatercircuitofthepowerplant,thetemperatureishereupto 10°Chigherthanthesurroundingriver.3,
Slightly polluted stagnant water. *, Collection undertaken with a grap dredger on board ofthe research ship
Argus'.
Locality eOr<n)nN mOnoSsaa- *mO'4s> #a0Xs0 rn mO"5N! c-i *a>* *'0o>>o »aom>s *a>•rssND o -a4Hr\ 1a/s1 ».cn—i aCIHTsOS a>s<
Iffezheim X
Neuburg X X X X
Leimersheim X X X X
Sondernheim X X X X
Altrip X X X X
Ludwigshafen1 X X X X
Lampertheim-Rosen-Garten X X X X X X X X
Worms X X
Biblis,nuclearpowerplant2 X X X X X X
Biblis,downstreamn.p.pl. X X
Worms-Rheinduerk-Heim X X X X
Gross-Rohrheim X X X
Gross-Rohrheim,2kmdownstream X X X X X X X
Gernsheim X X X X X X X X X
Kornsand X X X X X X X X X X
Nierstein X X X X
OxbowofGinsheim X X X X X X
Mainz-Laubenheim X X X X X X X
Mainz X X X X X
Heidenfahrt X X
Bingen X X X X X X
Bacharach X X X X
Boppard X X X X
Urmitz/Kaltenenger X X X X
BadBreisig X X X X
Remagen X
Bonn-BadGodesberg X
METHODS ethanol. From each individual sponge, one
microscope slide was prepared.
COLLECTION. Samples were collected from Individual sponges growing on approximately
many sites intheRhine (Germany) (Fig. 1), with 1.3m2 available substrate at each collecting site
were counted.
dates ofcollection foreach site listedin Table 1.
Collections weremostlymade from thebanks of The averagenumberofindividual spongesper
the river, by wading in the water and removing m ofavailable substrate were calculated (Figs
substrate by hand. Some collections were made 4-9). Onlyactivecolonieswerecounted,nodead
with a grab dredger aboard the research ship colonies or gemmules without their living
'Argus' ofthe federalstateHesse(indicatedwith mother-sponge.
an asterisk in Table 1). Methods of preparation for microscopy
Spongeswereremovedfromthesubstratewith followed Arndt (1928), with slight
a knife and preserved immediately in 70% modifications. Sponge identification was based
RIVERRHINE SPONGE ECOLOGY 217
As a rule, the larger rocks
(immovable by average
:JXj Hamburg Bonn-BadGodesbery currents) were more likely to
Jc •Amsterdam BadBreistg be colonised with sponges.
Urmitz/Kallenenge'
Boppard Smaller rocks (often moved
Bacharach
Bingen by average currents) were
Heidenfahrl rarely settled by sponges or
other sessile organisms.
These preliminary data agree
OxbowofGinsheim with those ofRutzler (1965),
Komsand who studied colonisation by
Gemsheim
GroR-Rohrhelm marine sponges in the
GroB-RohrtiBim
Biblis Mediterranean Sea.
Biblisnuclearpowerplan!
Lampertheim-Rosongarten DISTRIBUTION IN RELA-
TION TO DIFFERENT
FLOODING REGIMES. The
species-assemblages varied
considerably between sites
dependentonfloodingevents,
FIG. 1. Rhine collecting sites. comparingsitesfloodedmore
than six months before collecting, and those
on Arndt (1926, 1928) and Penney & Racek flooded only nineweeks priorto collection (Fig.
3). Ephydatia fluviatilis was the only species
(1968). occurring regularly at the more recently flooded
Slidespreparedduringthis studyaredeposited sites, whereas at sites flooded more than six
intheSenckenbergMuseumofFrankfurt(SMF). months before collecting this species had the
same absolute abundance in colony-counts, but
EVALUATION OF THE PERIOD OF
colonies grew much larger. The other species, T.
FLOODINGBEFORE COLLECTION. At each horrida, S. lacustris, E.fragilis and E. muelleru
collection site the actual water depth was alsoappearedatboththesecategoriesofsites,but
recorded for all sponge samples. Daily inform- only in very small numbers and small size at
ationonwaterlevelsatthestationsofWormsand recently flooded sites (with most having a
Mainz were recorded (Fig. 2), thus for each site diameter ofless than 1cm).
theperiod offloodingbefore collectioncould be Itwasalsoapparentthatdifferencesinflooding
calculated. events between the sites is a major factor
responsible for different depth preferences of
RESULTS sponge species. Places recently flooded were
very shallow, often dry, whereas places flooded
FAUNISTICS. Six species were found in the over6 months agowere deeper, belowthe levels
presentstudy,listedaccordingtotheirprevalence affected duringriver-level fluctuations.
from abundant to rare: Trochospongilla horrida Other factors show no depth dependent
Weltner, 1893; Ephydatiafluviatilis (L., 1758); variations in the river environment. Nutrient
Spongilla lacustris (L., 1758); Ephydatia levels should be evenly distributed within the
muelleri (Lieberkiihn, 1855); Eunapiusfragilis waterbody, due to turbulent currents, and light
(Leidy, 1851); Eunapius carteri (Bowerbank, canonlypenetrateabout0.75mthroughthewater
1863) column due to high turbitidy.
In Figure 3 and subsequent figures only
SUBSTRATE. Sponges were found settling on colony-countsaregiven,wherenodistinctionhas
all kind ofsolidsubstrates. WithintheRhinethis been made according to the size or local
mainly consists of rocks placed to support the abundance ofcolonies.
river banks; wood is rarely found. Aquatic
macrophytes are almost non existent in the SEASONAL DEVELOPMENT. The general
investigated area, only once was a small E. outline of the development of sponge species
A
fluviatilis found epizootic on Fontinalis sp, associations is given in Figure 4. generalised
(Bryophyta, Fontinalaceae). modelofalife-cycleofafreshwaterspongeinthe
218 MEMOIRS OF THE QUEENSLAND MUSEUM
clearly visible, not the
preceding states of larval
development, but it was not the
goalofthisstudytodescribethe
life history of these sponges,
onlytoreportonthepresenceor
absence of mature larvae, as
important indicators on the
ecology ofspecies.
Spongilia lacustris. This
species formed thick crusts
(l-3cm thick); the outline was
irregular with rounded edges.
Colonies could reach a
^&<P*xp^x^p xP^#^xp<Pxf^&^x^?.of^- a<*?.of^* ,o<f"P.of^" a^*.of^" ,t^> j|f^* x.p^xPVxP^x^pxp^x^pxp^x&pxp<Fd^p *pijrxp considerable size (up to lnr).
Only very few colonies showed
tendencies towards branching
FIG. 2. The niveau of daily water levels at Worms from July 1993- growth forms. Colonies of S.
December 1995;thevertical lines indicatetheturnoftheyears(thescale lacustrisalwaysdisintegratedin
isrelative, withoutadefined zero point). late autumn (October-
November). In winter
Rhine is as follows (Fig. 4). In March-April (December-February) only gemmules survived.
youngspongeshatched from theiroverwintering Thefirstyoungspongeshatchedfromgemmules
gemmules. Sponges grew until midsummer in spring (beginning of April), the number of
(July-August), sexually produced larvae may
occurfromMaytoJuly. Asexualgemmuleswere TcohleonhiiegshtnhuemnbreorsseostfecaodliolnyiuenstirlepOocrttoebdedru(rFiingg.t5h)e.
producedyear-round,butmoreregularlytowards
periodfromOctober-Decemberweremainlydue
the autumn. In September-October the colonies
tothesecoloniesbeingpresentatthebeginningof
declined and desintegrated, thus producing
October, whereas by the end of October their
overwintering units (gemmules).
numbers had declined rapidly. Furthermore, the
SPECIESAUTECOLOGY. Statementsaboutthe larger colonies observed in October fragmented
presence or absence of sexual reproduction intoseveralsmallercoloniesbeforedying,sothat
usuallyrequirehistologicalanalysisofspecimens, counts of number of colonies rose before they
whichwasnotconducted inthisstudy. Underlow dropped, andeventually disappearedcompletely
magnification only fully developed larvae were in December-March.
more than 6 months flooded less than 9 weeks flooded
T.honida
E.muelleri S.lacustris
16.9 colonies/ m2 5.7 colonies/ m2
FIG.3.Species-assemblagesatplaceswithdifferenttimesoffloodingbeforecollection(numbersarecalculated
for lnr): 26 collections were made at sites more than 6 months prior to flooding ofcollection sites; 28
collections took placeatsites less than 9 weeks priorto flooding.
RIVERRHINE SPONGE ECOLOGY 219
TABLE2. Life cycle dataandecological strategiesofthe five sympatric sponge species.
Event E.fluviatilis S. lacustris E. muelleri E. fragilis T. horrida
dTainmceeofgreatestabun- October(autumn) October(autumn) June(earlysummer) May-sJuumnmeer{e)arly Aug(luastte-sSuempmteerm)ber
Overwinteringunits Wholecolony Weakgleymmfuilxeedsfree Fixedfreegemmules Attachcerdusgtesmmule Attachcerdusgtesmmule
Distributionunits Larvae Driftinggemmules Driftinggemmules Larvae 7
Cesotlaobnliissahteidonhaobfitnaetswly sTwhirmomuignhgacltairvvaee Notobserved Notobserved Notobserved Notobserved
Ecologicalstrategy r-strategy K-strategy K-strategy K-strategy K-strateg;
Gemmules generally appeared from August, gemmules, due to an infestation with unicellular
buttheirappearanceseemedtobelessdependent symbiotic algae and a gemmule-polymorphism,
on seasonality and more dependent on colony as described by Gilbert & Simpson (1976) and
size. This was also true for other species (see Brondsted & Brondsted (1953), were not
Rasmont, 1962, 1963; Simpson, 1980). Colonies observed inthis study. Larvaewerenotobserved
ofS. lacustrislargerthan3cmindiameteralways in this species from the Rhine. This was very
contained at least some gemmules; smaller intriguinggiventhatin otherhabitats colonies of
coloniesweremostly free ofgemmules, atwhat- S. lacustris containing larvae were regularly
ever time of the year they were encountered. found (e.g. within the outflow of the
Gemmules were built singlywithin the tissue of 'Steinbriicker Teich\ a eutrophic pond near
themother-sponge, always withinthebasalparts Darmstadt,Germany,nearly 50% ofthecolonies
of the colonies. The gemmulation process was in July 1994 contained larvae).
more regular towards the end ofthe life span of In early autumn about 30% of colonies were
intact colonies. There were often dense, bright green due to the presence of symbiotic
single-layeredcarpetsofgemmules,restingwhere algae (Fig. 5). Only during this part ofthe year
they formed. The whole sponges disintegrated were water levels low enough to provide the
afterdeath,butshelteredpartsoftheskeletonstill preferred habitats forS. lacustris (i.e. in slightly
remainedintactsothatgemmulesrestinginthese deeper, permanently flooded water, Fig. 3), with
patches ofskeletal refugia were bound together sufficient light forthe successful photosynthesis
and weakly fixed to the substrate. Green ofsymbionts.
Eunapius fragilis. This species formed low
crusts (l-2cm thick), with an irregular outline
and rounded edges. Rarely it exceeded a
diameterof5cm.ColoniesofE.fragilisusually
disintegrated in summer (July-September). In
winter (December-February) intact colonies
were rarely found (Fig. 6). The first sponges
hatched from gemmules in spring (April).
Immediatelyafterhatchingthehighestnumbers
of colonies appeared (Fig. 6). The species
completed its gemmulation process up until
summer (July), after which colonies began to
JaMnauracrhy- April-June SepJtuelym-ber DOeccleobmebre-r disintegrate. Gemmules were formed in situ
producing a pavement-like gemmule crust,
Gemmules ;j£ Larvae Gemmulation 9 tairgehtvliyrtfuiaxleldytiomtmhoevsaubblsteraaten.dTihteissedgifefmicmuulltetso
perceice how they could contribute to the
dispersal within the habitat, whereas in
FIG.4.SeasonalappearanceofSpongillidaeingeneral in May-June 1994freemovablelarvaewerefound
theRhinestudysites.Thewhitebarindicateswhenonly in about 10% ofcolonies. Colonies containing
gemmulesarepresent; theblackbarrepresentstimesof symbiotic algae were not found within the
theyearwhenactivecoloniesarepresent;thetime-scale Rhine, probably because their preferred
ofthechartcorresponds with thatofthe bar. distribution was in permanently flooded,
. ;
MEMOIRSOI ENSLANDMUSEUM
ill! i,'i
c 2.5 «""Evmiicn o i place(June).InJulythe -i urvaehadsettled
10 andbuiltnewcolonics.Thegcmmulation process
c1 « i ..v.i r- i?vnn:I: 1 wcoanssiidrerreagbullaerntuhmrobuegrhooutf tchoelownhieoslewayesaralawnadysa
g t6 devoid of gcmmules. When gemmules were
present their numbers were reduced: in colonies
JiQ5 ' H: of 5cm diameter not more than 10 gemmules
were round. During fragmentation Of sponges
few gemmules were freed from the
januarv-Marcn April-June July*Septembsf Odotoer- mother-spongeandthese 'hatched' inspring.The
DeGember highest number of colonies was encountered
during October-December. As in the case n\ S
FIG.5, Seasonalappearanceand numberofsymbiotic lacustrisn the large colonies present in autumn
colonics in Spongillalacusfris. fragmented into several smaller colonies, nianv
of which died towards winter (December-
deeper habitats, where light regimes may be February), the overwintering colonics were also
insufficient forphotosynthesis (Fig. J). small.
L'j/iapius carteri. This species record from the In May-June about 25% ofcolonies produced
Rhine is the first time it has been encountered in larvae. This seemed to be the most important
central Europe lsee Gugel, 1995). ft was found event in the life cycle ofE.jlttvialilts, as in July
November 1993 within the cooling-water many very small colonies were seen in close
outflow ofthe nuclear power plant in Biblis A proximity to each other, a phenomen quoted as
detailed description and discussion about its- 'Spruhinfektion' (spray infection) by SleuslolY
dispersal are given in Gugel (1995). [1938). As already indicated, E. fiuviatilh was
Ephydaiin fluvialUis. This species forms theonlyspecieswInchoccurredinhighernumbers
lure-or-less thin encrustations (I-2cm thick). at sites flooded only a few weeks pnoi to
Smallercolonics (lessthan 5cm diameter), had a collection (Fig. 3). This was probably due to die
circular outline, whereas larger ones (mote than more active dispersal of larvae. Symbiotic
"on diameter), were more irregularly shaped. colonies were never found.
Colonics of this species grew up to 20cm Ephydaiiamuelleri. Coloniesofthisspecieswere
diameter Ephydatiaflitvlat'diswasregularlySeen mostly thickly encrusting (2-4cm thick), with
alive in winter(December-February), in contrast irregular outline and rounded edges. The
lotheotherspecies. Overwinteringcolonieswere diameter was rarely more than 10cm. The first
small crusts, only i.5em diameter, in which no colonics ofE. muelicn appeared in spring (atthe
canal systems were visible. These probably beginning of April), and soon after hatching
survive inareduced state, as suggested by Arndl colonies were found in large numbers, peaking
( i 928) and Weissenfels (1989) In early spring during summer (July/August). Alter completing
(April) their abundance was only slightly gcmmulation colonies died, usually from ihc
increased in comparison with winter (Fig. 7), beginning ofAugust to October (Fig. S). Active
probably due to hatching of gcmmules (see- colonies were not observed during winter
k-low), whereas the number of colonies (November-March), only dead colonies with
dramatically increased duringJune-July (Fig. 7), gemmules. Ephydaiia muelkri often used its
al which lime a large-scale production oflarvae entire tissue for gemmule-production, whereas
its skeleton remained intact for considerable
period of time after ihc death of the maternal
sponge. Large numbers ofgcmmules were fixed
bythe skeletonto theplaceofproduction. In this
way a successful recolomsation at the same site
was ensured in the following year. In addition,
when single gemmules became free and weic i
longer fixed to ihc substrate, they could be
Jamiwy-Mercn
distributed by the current within the habitat,
providing an effective mechanism for dispersal
PIG.6 Hal appearance ofEunapiusfragiiis. arid recolonisation ofadjacent habitats. Sexually
produced latvac were not observed in this
.
RIVER RHINE SPONGE ECOLOGY 221
mainly distributed in permanently flooded
habitats (Fig. 3).
Ecological strategies for each species are
summarised in Table 2.
DISCUSSION
Freshwater sponges often display a
considerable plasticity in their ecological
January-March April-June July-September October-December strategies (Pronzato & Manconi, 1994a), and
their life cycles are often adapted to the special
FIG. 7. Seasonal appearance ofEphydatiafluviatllis requirementsoftheirhabitats(e.g.E.fluviatilisin
temperate regions is usually active during
summer and inactive during winter). In hot, arid
species, and only a single symbiotic colony was regions the pattern of activity/inactivity is
found(fromSondernheim, inAugust 1994),close reversed (Harsha et al., 1983; Corriero et al.,
to symbiotic colonies ofS. lacustris. Ephydatia 1994). This shows that the life cycle is very
muelleri is mainly distributed in deeper waters, adaptabletospecificclimaticconditions(Pronzato
below the levels affected during river-level & Manconi, 1994b). According to Pronzato etal.
fluctuations (Fig. 3). (1993) the life cycle ofE.fluviatilis seems to be
Trochospongilla horrida. Colonies of this controlled by exogenous factors in regions with
species formedthin encrustations (less than 1cm strongly oscillatingenvironmentalconditions. In
thick), with a very irregular outline. Large morestablehabitatsendogenouscontrolseemsto
colonies may cover an area of 0.5m . dominate.
Trochospongilla horrida began hatching from
For several species the data presented in the
gemmules in spring (early April). The highest literature differ from those presented here. For
wabausndraenacceh,edinbinothsunmummbeerrs(Aaungdussitz;eoFfigc.ol9o)n.iesI,n eacxtaimvpelec,olBoinsibeesey(e1a9r9-2r)ournedpoirnteSd.tlhaecupsrtersiesncferoomf
autumn (September-October) colonies always NorthCarolina.Heobservedgemmulationinlate
disintegrated and leftthe gemmule crusts tightly spring-early summer, sexual reproduction in
adhered to the substrate. As in E. fragilis, April, and some sponges disappeared during
gemmules remain fixed to their place of summer. AccordingtoCheathum &Harris(1953)
production and itis difficultto imaginethatthey both E. fragilis and T. horrida were active year-
mightbe dispersedwithintheriver. Gemmulation round in Texas. Pronzato & Manconi (1995)
commenced in early summer (June-July), and at counted up to 324 gemmules cm" oftissue inE,
this time especially T. horrida was a successful fluviatilis from Sardinia.
space-competitor against the otherwise
dominating neozoan crustacean Corophium Ecological strategiesofthese speciesaregiven
curvispinum (Amphipoda). Whengrowing, small in Table 2. Ephydatia fluviatilis is considered to
coloniestendedtofusewithothercoloniesofthe beanr-strategist,mainlyforitsabilitytocolonise
same species, thus forming larger 'super- new habitats. In contrast, the remaining species
are characterised as k-strategists because they
colonies'.Neitherlarvaenorcoloniescontaining
symbiotic algae were observed. The species was lack this ability.
Thisgeneraltendency iscongruentwithresults
ofPronzato&Manconi(1991),whocomparedE.
fluviatilis and S. lacustris showing the formerto
be more successful in colonising new habitats,
whereas the latter was more successful as a
competitor.
Detailsinthe life cycle ofE.fluviatilis seemto
contradictthisclassificationasanr-strategist:the
dominance of sexual vs. asexual reproduction
January-March April-June July-September October- and its year-round presence; these are usually
December
quotedastypicalfork-strategists(Pianka, 1970).
The successful colonisation ofnew habitats is
FIG. 8. Seasonal appearance ofEphydatiamuelleri. here considered to be due mainly to active
MEMOIRS OK THE QUEENSLAND MUSEUM
or advantage in having a capacity for active
dispersal.
VandeVyver& WiIlenz( 1975)reportedthai in
E. fhtviarih's from Belgium sexual reproduction
anfined to overwintering colonies. In thai
species the developmentofoocytes commenced
in autumn ofthe year prior to larval production,
which occurred the fallowing June. Jn Belgium,
parts ofcolonies of£ fhtviotilis survived winter
as living, but reduced colonies, similar to the
asona! appearance of TrochaspongitUi Rhine populations. These results arc also
fda. continued by Wcissenfels (1989). Williamson&
Williamson (1979) discussed whether or not
distribution of iree larvae. Hie production of sexual reproduction was triggered by a phero-
larvae in Spongillidac is mostly controlled by moneinSpongillidac. Accordingtotheseauthors
endogenous faetors (Gilbert et aL IV7S) The sexual reproduction occurs rarely in running
seasonal appearanceoflarvaeisconfined toafew water because the postulated pheromone would
weeks in theyear, and thistimingissynchronous be diluted and ineffective (in contrast to
breeptowreteendvtahartiopursodluoccatliiotineso.fLIeavneaaeuixn(E1.9f4ht1v,i1a0ti4l2i)s swiotuulatdioenxsplmainsttahgenaonctcuwraetnecre),ofThmiasnyhylpaortvhaeesiisn
-Utral Europe is confinedto May-June, which colonies SfJS. lacustris within the outflow ofthe
corresponds to the results presented here. Since \Steinbriicker Teich' (see above), where the
timing in the production of larvae is severely water flows quickly but is only 5-10cm deep.
'ricted to certain weeks in the year and Here, the population ofS. lacustris is so dense
c;nnot be altered in the short term, producing that apheromonewould not be dilutedtoomuch.
larvae does notappearto be an effectivestrategy In all colonies of this species at least some
act tounpredictableenvironmentalchanges. gemmulesoccurredinaddition to larvae.Thefew
reportsoflarvae inE. niuelienand T. hoi) Ufaalso
The so-called k-strategists (T, horrida, S, originate from populations in stagnant water.
ur/r&j E muelteriwA E fragliiz) have the
potential to produce a large number ofoffspring The reportoflarvae in E.fragilis occurring in
f'.eiaatutrheei.r Tgheemsmeulsepse.citersadidtoionparlloyduacne ra-stlroattecg>yf •rienplryodoucnteioyneoacicur[sISm^MsJomseuygegaerss,tsevethnatinsspeexcuiaels
vmmules, but these usually stay at the pla without regular sexual reproductive strategic
their production (see Table 2). Many ofthe differentstrategies and life-cycles
According to Manconi & Proruato 1)901) £ omrenteinohnaendcaebovtehehenlpcsopmecpieetsiatviovidecoambpieltiittiieso.n
(dcustris follows the r-strategy in ihe short-term. Competitive interactions among sponges, or
mPuatniysesSsepnotnigalillylaidk-asei both stntrtahteelgoinegsteoncn.cuIrn between sponges and other organisms, are
simultaneously (Pronzato&Manconl 1995) regularly observed m the field. As shown abi
as diihsitrtihbeutsiaonm-eunsittrsucutnudreesr:atnher-gsetrmamtueglye.sansiedrvaes stpiemceiseosfhtahveeyetaheri(rFhiiggsh5e-s9t,aTbaubnleda2n1c.eMaatndyifdfeetraeinlst
Oflife historiescan be interpreted as median;
todies under a k-strategy
I to enhance competitive ahilj-
Jt wduacstiosnurwparsisclienagrly!•.dominant oVe u I ianbculnuddainngcetheoffac&t lhal duri;nvgtpheeripordospoorfthiiognhesotf
oduction. Larvae were only observed in E. colonies with symbiotic algai also
I \atili& and io a lesser degree in ceonnhsaindceerabtlhee(Fgirgowth fohfestehesiyrmbhioosntts[FsrtOrSoSngl&y
n the special limnological environment of liamsou, 1980).In EAdmtfcTsmallercoUi
running water it must be questioned whorl,, arly fuse to form larger ones. Neuberl &
ii'i gemmules are more suitable distribute, Eppler (1901 ) discussed wether the competitive
units than larvae, aside from their role as resting ability was reduced, and therefore T. honicht was
bodies lie more robust than larvae relatively rare compared to other freshwater
dispersal is passive via currents. Thereis noneed species, However my data show that it was the
RIVER RHINE SPONGE ECOLOGY 223
most abundant sponge in the Rhine, and is also J.-C.(eds) Sponges in time and space, (Balkema:
very competitive among sponges and in Rotterdam).
competitionwithotherorganisms.Itisconcluded COURREGES, V.C. & FELL, P.E. 1989. Sexual and
that competition for space is the species' main asexual reproduction by the freshwater sponge
Anheteromeyenia ryden\ with emphasis on
challenge.
spermatogenic activity. Transactions of the
ACKNOWLEDGEMENTS American Microscopical Society 108(2):
127-138.
I thank the Hessische Landesanstalt fur FRANZ, H.W. 1992. DerRhein und seine Besiedlung
Umwellformakingitpossibletousetheresearch im Wandel: Schwebstoffzehrende Organismen
ship 'Argus', the crew of the ship is (Hydrozoa, Kamptozoa und Bryozoa) als
acknowledged for their good humour and Indikatoren fur den okologischen Zustand eines
Gewassers. Pollichia-Buch 25: 1-167.
helpfulness. MrJ. Wittmannkindly provided me FROST, H.W. & WILLIAMSON, C. 1980. In situ
with Spongillidae of his collections from
determination ofthe effect ofsymbiotic algae on
11.05.1994, 08.06.1994 and 30.06.1994. Dr H. the growth of the freshwater sponge Spongilla
Pohl helped me a lot with some figures. J am lacustris. Ecology 61(6): 1361-1370.
grateful to an anonymeous reviewer, who FROST,T.M.,DENAGY,G.S.&GILBERT,JJ. 1982.
substantiallyimprovedthemanuscript.Thispaper Populationdynamicsandstandingbiomassofthe
waswrittenduringastayasapostdoctoral fellow fresh-water sponge Spongilla lacustris. Ecology
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