During the last 30 years the importance of riparian
areas and marginal wetlands along the course of rivers
and channels has been increasingly acknowledged, due
to their role as natural filters for diffuse nutrients
control and because they host peculiar niches and nur-
sery areas for a variety of organisms, from microbial,
meio and macrobenthic communities to fish and birds
(Wetzel 1990, Reddy & D’Angelo 1994, Mitsh & Gos-
selink 1993, Cronk & Fennessy 2001). The control of
nutrients is a result of the combined action of macro-
phytes and the associated epiphytic communities; but
important biogeochemical processes such as denitrifi-
cation and phosphorus sequestration occur within sur-
face sediments (Soderquist et al. 2000, Kadlec &
Knight 1996). Rooted wetland macrophytes connect
sediments to the atmosphere with their aerenchima:
gas transport mechanisms favour the loss or the reoxi-
dation of end products of the anaerobic metabolism
and create microoxic zones around root hair with im-
plications for microbial coupled processes (i.e. nitrifi-
cation and denitrification) and benthic meiofauna co-
lonisation (Armstrong 1964, Dacey 1981, Mevi-
Schutz & Grosse 1988). In Northern Italy, floodplains
of larger rivers host marginal wetlands which are seve-
rely threatened by water pollution, rapid burial, and in-
vasions by exotic species. Extreme and apparent
consequences of such pressures are the simplification
of plant communities due to low water transparency
and reduced anoxic sediments and general loss of the
above mentioned wetland functions.
Ann. Limnol. - Int. J. Lim. 2004, 40 (4), 329-341
Limnological characteristics and recent ostracods (Crustacea,
Ostracoda) of freshwater wetlands in the Parco Oglio Sud
G. Rossetti1*, M. Bartoli1, K. Martens2
We report the results of a study carried out in 2002 on the main limnological characteristics and on the ostracod communities
of 16 wetlands of the Parco Oglio Sud (Northern Italy). Physical and hydrochemical variables were measured and ostracod
samples were collected in different seasons (April, June, August, and October). Most of the considered sites were characterised
by high concentrations of nitrogenous compounds due to washing out from cultivated areas, intermittent river flooding and inter-
nal recycling. Observed differences in macrophyte communities were consistent with trophic status of waters, with pleustonic
forms dominating most degraded areas. Both morphology of valves (by scanning electron microscopy) and anatomy of soft parts
were analysed for ostracod species identification. Nineteen ostracod species in five families were found. Two species, Candona
weltneri and Pseudocandona compressa, are new records for Italy. Cypria ophthalmica was collected from all sampling sites;
other relatively common species were Cypridopsis vidua, Cyclocypris ovum, and Candona weltneri. No clear seasonality was
observed in community structure; highest species diversity occurred in June in most of the studied wetlands. The maximum
number of species per site was seven, and a maximum of six species was found in a single sample. Ostracod occurrence in rela-
tion to environmental factors was examined using Canonical correspondence analysis (CCA). Total alkalinity and pH were the
most important variables structuring the species assemblages. The ostracod fauna found in this area was compared to the known
distribution of recent non-marine ostracods in Italy, and the validity of published checklists is discussed.
Keywords : riverine wetlands, water quality, Oglio River, ostracods, biodiversity.
1Department of Environmental Sciences, University of Parma, Parco Area delle Scienze 33A, I-43100 Parma, Italy
2Royal Belgian Institute of Natural Sciences, Freshwater Biology, Vautierstraat 29, 1000 Brussels, Belgium.
* Corresponding author :
E-mail : email@example.com
Article available at http://www.limnology-journal.org or http://dx.doi.org/10.1051/limn/2004030
Ostracods are bivalved Crustacea commonly found
in most inland waters where they abound in the benthic
and periphytic animal communities, but also occur in
marine, interstitial and even (semi-) terrestrial environ-
ments (Horne et al. 2002). Although the autoecology
of ostracods is still largely unknown and often based
on speculative assumptions, these organisms are of
particular interest as environmental indicators in fresh-
water ecosystems. Recently, several papers have been
published on this subject, considering both fossil (Be-
lis 1997, Park et al. 2003) and recent (Curry 1999, Ro-
senfeld et al. 2000, Mezquita et al. 2001, Külköylüoglu
2003) ostracod faunas. Here, we describe the main
limnological features of lowland wetlands located
along the lower stretch of the Oglio River and we aim
to analyse the ostracod distribution in relation to phy-
sical and chemical habitat characteristics. This contri-
bution is part of a larger project to investigate the va-
lues and functions of wetlands of the Parco Oglio Sud,
aimed at the management and restoration of the aqua-
tic ecosystems (Delfini 2003). As pointed out by Ros-
si et al. (2003), data on recent freshwater ostracods in
Italy are relatively scarce, although the checklist com-
piled by Ghetti & McKenzie (1981) reported an extra-
ordinary high species diversity and a large number of
endemic taxa. Unfortunately, the prevalent inadequacy
of taxonomic descriptions and often also the absence
of collections and type repositories make it difficult to
confirm the reliability of many earlier Italian records.
In the present paper, special attention is paid to the
taxonomic analysis of the present faunas, and Scan-
ning Electron Microscope images of ostracod valves
are also offered to confirm identifications.
Material and methods
Four sampling campaigns were carried out in 2002
(April 8, June 4, August 5, and October 31). On each
date, 16 wetlands were visited, all included within the
Parco Oglio Sud, a regional park established in 1988
which encompasses the lower plains along the Oglio
River in the provinces of Cremona and Mantova (Nor-
thern Italy) (Table 1, Fig. 1). The area is characterised
by industrial crop productions, and poplar plantations
prevail in the embanked floodplain. Different kinds of
wetlands (ponds, channels, oxbows, peatlands) are still
a conspicuous element within this landscape; those
G. ROSSETTI, M. BARTOLI, K. MARTENS
Table 1. Location and selected habitat features of the study sites.
considered in this study are mainly lentic environ-
ments fed by surface aquifers associated with the river
or are occasionally flooded; OG06 and OG11 are chan-
nels with slowly flowing water. Two wetlands (OG01
and OG03) were found to be devoid of water in Au-
gust; other permanent wetlands are stocked with diffe-
rent fish species.
Water temperature, electric conductivity at 25°C,
pH, and dissolved oxygen concentration were measu-
red by a YSI 560 multiprobe. Water samples were col-
lected from a depth of 0.5 m (or from the surface water
layer in shallower sites) and kept refrigerated until
analysed in the laboratory, where additional hydroche-
mical and physical variables and parameters were de-
termined as follows: total alkalinity by potentiometric
end-point titration at pH 4.5 and 4.2 (TIM 90, Radio-
meter) and linearization according to Rodier (1984);
ammonium (Koroleff 1970), nitrous nitrogen (APHA,
AWWA, WPCF 1975), nitric nitrogen (Rodier 1984),
dissolved reactive silica (APHA, AWWA, WPCF
1975), soluble reactive phosphorus (Valderrama
1981), and chlorophyll-a (Golterman et al. 1978) by
spectrophotometry (Beckman DU 65).
Ostracods were collected with a 250 µm handnet
pulled close to the sediment and through the vegetation
along the wetland shore or within the water body from
shallower sites. Living samples were transferred to the
laboratory, where specimens were sorted under a bino-
cular microscopy and then fixed in 90% ethanol. Both
soft parts (dissected in glycerine and stored in sealed
slides) and valves (stored dry in micropal slides and
used for scanning microphotographs) were checked
for species identification, using Meisch (2000) and the
papers by Danielopol (1980), Meisch (1984) and
González-Mozo et al. (1996) as reference. All the
illustrated material is deposited in the Ostracod Col-
lection (OC) of the Royal Belgian Institute of Natural
Similarity between species assemblages was asses-
sed by Cluster Analysis (CA) (unweighted pair-group
average) performed by means of the software package
PAST ver. 1.06 (Hammer et al. 2001), using the Jac-
card coefficients derived from the matrix of presen-
ce/absence data. The same matrix and the full hydro-
chemical data set were used to examine the relation-
ships between ostracod distribution and environmental
data by Canonical Correspondence Analysis (CCA)
using the software package CANOCO version 4.5 (ter
Braak & Milauer 2002). Hydrochemical variables we-
re transformed using log(x+1), except for pH. The di-
rect gradient technique of CCA constrains ordination
axes as linear combination of environmental variables.
Monte Carlo permutation tests were used to assess the
significance of the canonical axes and of the environ-
mental variables that were selected in the forward se-
Seasonal temperatures displayed wide fluctuations
due to the general shallowness of the investigated en-
vironments. The highest water temperatures, between
20 and 35°C, were found during the survey of August.
The relative maximum was measured at OG10, a shal-
low open water body (~20 cm deep). Conductivity va-
lues were high and typical for shallow eutrophic envi-
ronments on the Oglio plain, ranging between ~300
and >900 µS cm-1. At OG05, OG09, OG13, OG14,
OG15 and OG16, conductivity values were strongly
correlated with temperatures and exhibited maximum
summer values (up to 951 µS cm-1measured in August
at OG09), whilst at OG01, OG02, OG03, OG04,
OG06, OG07 and OG08, on the contrary, conductivity
peaks occurred in autumn (up to 681 µS cm-1measu-
red in October at OG03).
In most of the investigated environments (11 out of
16 sites), dissolved oxygen concentrations were below
saturation for the entire investigated period; in particu-
lar, at OG01, OG03, OG04 and OG05 the imbalance
between primary production and system respiration
was extreme during summer, when the water column
WETLAND OSTRACODS IN NORTH ITALY
Fig. 1. Map of the Parco Oglio Sud showing location of sampling
sites (see also Table 1).
was strictly anoxic. Conversely, at OG07, OG08,
OG10, OG15 and OG16 dissolved oxygen saturation
was never below 50%. In August, at OG10 dissolved
oxygen concentration reached 17 mg l-1(~300% satu-
ration) and gas bubbles were evident on the sediment
surface. Saturation values above 100% were also occa-
sionally found at OG12, OG13, OG14, OG15 and
OG16. In all the sites, pH values were always ≥ 7, the
only exception being the measurement of June at
OG03 (6.96); values above 8 were found at sites with
photosynthetically active submerged vegetation or wi-
th dense microalgal assemblages (OG05, OG10,
OG12, OG13, OG14, OG15 and OG16). At OG10, du-
ring summer, a maximum of 9.67 was measured, pre-
sumably due to intense assimilation of inorganic car-
bon by microphytobenthos. Total alkalinity showed si-
gnificant fluctuations among sampling sites. The lo-
west values (ranging from 2.2 to 4.1 meq l-1) were
measured in OG16, the highest in OG06 and OG08
(peaks of 24.4 and 27.2 meq l-1, respectively).
Water column chlorophyll-a concentrations were ex-
tremely variable among sites and seasons, ranging bet-
ween ~3 and over 230 µg l-1; highest values were ge-
nerally found in spring and fall, when macrophytes
were absent or less abundant and thus when light and
nutrients were available to phytoplankton. Relatively
homogeneous chlorophyll-a values of less than 10 µg
l-1were found at OG01, OG07 and OG15; such low
concentrations were most likely the result of shading
and nutrient limitation (i.e. reactive phosphorus, see
below), amongst others. Chlorophyll-a values above
50 µg l-1, typical of eutrophic environments, were
found at OG02, OG04, OG05, OG06, OG08, OG09,
OG10, OG12, OG13, OG14 and OG16. Values above
100 µg l-1were found at OG5, OG8 and OG14. The
three southernmost environments (OG14, OG15, and
OG16) had a different chlorophyll-a content, despite
their proximity and the similar morphometric and
structural features. For example, OG15 was always
characterised by very transparent waters and chloro-
phyll-a values never exceeded 3 µg l-1.
Ammonium concentrations were extremely variable
between sites and sampling periods, showing values
between 1 and 92 µM. Annual average values above
20 µM were found in 8 out of 16 sites (OG01, OG02,
OG03, OG04, OG05, OG06, OG09 and OG10); values
below 10 µM were determined at OG07, OG08, OG11,
OG13, OG14 and OG15. Nitrous nitrogen was the
least abundant form of dissolved inorganic nitrogen,
with concentrations ranging between 1 and 13 µM; in
a few sites (OG02, OG06 and OG09), the annual ave-
rage was above 5 µM. Nitric nitrogen content was one
order of magnitude higher and reached values up to
800 µM. At OG01, OG10, OG12, OG13, OG14,
OG15 and OG16 this oxidised form of nitrogen was
relatively low (<40 µM), whilst at OG06, OG07,
OG08, OG09 and OG11 its concentration was on ave-
rage >400 µM. For most of the sites the NOx- to NH4+
ratio was always far above 1, with peaks of ~600 at
OG09. Reactive phosphorus concentrations were low
and generally ranged between 0 and 2.5 µM; values
above 5 µM were determined at OG01 and OG05 and
Altogether 19 ostracod species were collected (Table
2, Figs. 2-4). Ostracod diversity was highest in June
(with an average of c. 3 species per site and a maxi-
mum of 6 species in OG03) and lowest in August (wi-
th an average of less than 2 species per site and a maxi-
mum of 3 species in OG07, OG09, and OG11). A tem-
porary wetland, OG03, exhibited the highest number
of ostracod species (7). Cypria ophthalmica occurred
in all the study sites and Cypridopsis vidua in 13 habi-
tats; conversely, 10 species were found exclusively in
one site (Fig. 4). Co-occurrence of Cyclocypris ovum
and C. laevis was observed only in OG08, but the two
species were not found at the same time. The most fre-
quent species were generally detected throughout the
sampling period, without showing any clear seasonal
pattern. Amongst species collected from more than
one site, Fabaeformiscandona fragilis was found only
in April and June (Table 3).
CA separated four distinct groups of ostracod as-
semblages (Fig. 4). Grouping of habitats mostly re-
flects their geographic location, with the exception of
OG09 and OG11 (Fig. 1). Cluster I includes sites with
high species diversity, and it is mainly characterised by
the presence of Candona weltneri and Pseudocandona
compressa; it also incorporates the two lotic environ-
ments considered in this study (OG06 and OG11). The
second cluster (II) aggregates communities with low
diversity (except for OG10), in which Cypria ophthal-
mica and Cypridopsis vidua are each time associated
with species rarely encountered in the area (e.g., Dar-
winula stevensoni, Dolerocypris sinensis, Herpetocy-
pris chevreuxi, and Potamocypris smaragdina). Cyclo-
cypris ovum and other rare species (Ilyocypris deci-
piens, I. monstrifica, Prionocypris zenkeri, and Pseu-
docandona hartwigi) are found in cluster III, which
consists of only two sites (OG07 and OG08). Also
cluster IV groups two sites (OG01 e OG02), i.e. the
only habitats in which Notodromas persica is present.
The first two axes of CCA ordination account for
G. ROSSETTI, M. BARTOLI, K. MARTENS
WETLAND OSTRACODS IN NORTH ITALY
Table 2. Taxonomic status of the ostracods identified in this study.
G. ROSSETTI, M. BARTOLI, K. MARTENS
Fig. 2. Scanning electron micrographs of ostracods found in the studied wetlands: Candona weltneri (A-D), Fabaeformiscandona fragilis (E-K),
Pseudocandona hartwigi (L-N), Pseudocandona compressa (O-R), Candonopsis kingsleii (S-U). RV: right valve; LV: left valve; Cp: carapa-
ce; ev: external view; iv: internal view; lv: lateral view; dv: dorsal view. All adult specimens. Scale bar: 457 µm for A-D; 400 µm for E, F, H-
U; 13 µm for G. A: OC2845, female, RV, ev (OG06). B: idem, LV, ev. C: OC2852, male, RV, ev, (OG09). D: idem, LV, ev. E: OC2847, male,
RV, ev (OG10). F: idem, LV, ev. G: idem, RV, ev, detail of valve striature. H: idem, LV, iv. I: idem, RV, iv. J: OC2838, female, LV, iv, (OG03).
K: idem, RV, iv. L: OC2839, male, LV, iv (OG08). M: idem, RV, iv. N: OC2841, male, Cp, right lv (OG08). O: OC2843, female, LV, iv (OG09).
P: idem, RV, iv. Q: OC2846, female, LV, ev (OG09). R: idem, RV, ev. S: OC2849, male, RV, ev (OG09). T: idem, LV, ev. U: OC2853, female,
Cp, dv (OG15).
WETLAND OSTRACODS IN NORTH ITALY
Fig. 3. Scanning electron images of ostracods found in the study wetlands: Ilyocypris gibba (A-C), Ilyocypris monstrifica (D-J), Prionocypris
zenkeri (K, L), Potamocypris smaragdina (M, N), Herpetocypris brevicaudata (O, P), Herpetocypris chevreuxi (Q), Dolerocypris sinensis (R,
S). RV: right valve; LV: left valve; Cp: carapace; ev: external view; iv: internal view; dv: dorsal view. All adult specimens. Scale bar: 400 µm
for A-J; 667 µm for K, L; 250 µm for M, N; 800 µm for O-S. A: OC2851, female, LV, iv (OG06). B: idem, RV, iv. C: idem, RV, ev. D: OC2836,
female, LV, iv (OG07). E: idem, RV, iv. F: OC2837, female, LV, ev (OG07). G: idem, RV, ev. H: OC2842, female, Cp, dv (OG07). I: OC2835,
male, RV, ev (OG07). J: idem, LV, ev. K: OC2840, female, LV, iv (OG08). L: idem, RV, iv. M: OC2850, female, RV, ev (OG16). N: idem, LV,
ev. O: OC2848, female, LV, iv (OG06). P: idem, RV, iv. Q: OC2834, female, RV, iv (OG10). R: OC2844, female, LV, iv (OG12). S: idem, RV,
G. ROSSETTI, M. BARTOLI, K. MARTENS
Fig. 4. Dendrogram obtained from the CA showing the similarity level between ostracod communities. The occurrence of ostracod species in ea-
ch site is also indicated. S: number of total record per species. ∑: number of species per site.
Table 3. Temporal occurrence of ostracod species in the studied wetlands (Ap: April; J: June; Au: August; O: October).
29.0% and 22.9% of the total variance. The species-
environment correlations are 0.837 for axis 1 and
0.772 for axis 2. The Monte Carlo permutation test
shows that all the canonical axes are significant (P <
0.001). Total alkalinity (permutation test: F= 3.33, P =
0.006, A = 0.32) and pH (permutation test: F=3.07, P =
0.002, Lambda A = 0.29) have the strongest correla-
tions to the first and second canonical axes and are
most important in explaining the observed ostracod
distribution (Fig. 5). The most common species are
displaced in the lower part of the ordination diagram; a
first group of species (Ilyocypris decipiens, I. monstri-
fica and Notodromas persica) are placed along a gra-
dient of alkalinity, while a second group (Candona
weltneri, Fabaeformiscandona fragilis, Cyclocypris
ovum, Pseudocandona compressa and Candonopsis
kingsleii) is primarily associated with higher trophic
conditions and elevated ionic content. Rare species
form two distinct clusters in the upper part of the ordi-
nation diagram, denoting a preference for higher pH
values and dissolved oxygen content; their position
with respect to the temperature gradient indicates a
prevailing summer occurrence. The upper right part
displays species which prefer well-buffered waters; the
upper left quadrant comprises species which seem to
be related to a higher habitat productivity.
Most of the investigated sites are remnant of wider
wetland areas previously connected to or periodically
flooded by the Oglio River, and are characterized by
extreme shallowness, small surface area and expan-
ding belts of macrophytes. Dissolved nitrogen and
phosphorus concentrations were typical of eutrophic
aquatic environments; loads were probably a conse-
quence of washing out from surrounding cultivated
fields, occasional floodings by nutrient-rich Oglio wa-
ters, or internal recycling. During early spring and au-
tumn nitric nitrogen was the dominant inorganic nitro-
gen form with concentrations in the order of mM; am-
monium and reactive phosphorus peaked on the
contrary during summer months. Organic loads resul-
ted in anoxic sediments and fuelled intense microbial
activity, determining low summer oxygen concentra-
tions and nutrient regeneration (Delfini 2003). Light
and nutrient availability explained production rates by
planktonic and macrophytic primary producers resul-
ting in high sedimentation rates and enhancing the
shift of these water bodies towards terrestrial environ-
ments. In the summer of 2002, two sites characterised
by organically rich, chemically-reduced sediments
(OG01 and OG03) fell dry and the reed belts expanded
toward the centre of the ponds.
At OG11 and OG15 the presence of submerged ve-
getation (Myriophyllum demersum) was coupled with
well-oxygenated, transparent waters with minimum
concentrations of planktonic chlorophyll-a. In a few
sites, sediments were colonized by rooted plants such
as Nuphar luteum, Nymphaea alba, and Nymphoides
peltata. The ability of these plants to detoxify sedi-
ments through root radial oxygen loss is widely de-
monstrated (Dacey 1981, Smits et al. 1990) and this
has important implications for meio- and macroben-
thic communities, due to simultaneous occurence of
oxic-anoxic conditions whitin surficial sediment hori-
zons, causing higher environmental heterogeneity
(Begg et al. 1994, Carpenter et al. 1983). On the
contrary, at most sites, macrophytic vegetation was
WETLAND OSTRACODS IN NORTH ITALY
Fig. 5. CCA ordination of ostracod species and environmental para-
meters on the space defined by the first two canonical axes. Dste:
Darwinula stevensoni. Cwel: Candona weltneri. Ffra: Fabaefor-
miscandona fragilis. Phar: Pseudocandona hartwigi. Pcom:
Pseudocandona compressa. Ckin: Candonopsis kingsleii. Coph:
Cypria ophthalmica. Clae: Cyclocypris laevis. Covu: Cyclocy-
pris ovum. Igib: Ilyocypris gibba. Imon: I. monstrifica. Idec: I.
decipiens. Nper: Notodromas persica. Pzen: Prionocypris zenke-
ri. Hbre: Herpetocypris brevicaudata. Hche: H. chevreuxi. Dsin:
Dolerocypris sinensis. Cvid: Cypridopsis vidua. Psma: Potamo-
cypris smaragdina. EV: eigenvalues. Temp: water temperature.
EC: electric conductivity at 25°C. TA: total alkalinity. DO: dis-
solved oxygen. SRP: soluble reactive phosphorus. DIN: dissol-
ved inorganic nitrogen (sum of ammonium, nitrous nitrogen, and
nitric nitrogen). DRSi: dissolved reactive silica. Chl: chloro-
mainly composed by floating plants (Lemnaceae and
the aquatic fern Salvinia natans) which exploit nu-
trients directly from the water column (Koles et al.
1987). Dense floating beds of pleustonic communities
inhibited light penetration, microalgal photosynthesis
and the development of submerged vegetation. They
also turned out to be a physical barrier for the gas ex-
changes through the atmosphere-water interface. At
OG03, OG04 and OG05, in full summer, pleustonic
communities caused water column anoxia.
All the ostracods found in the study area are typical
members of the Western and Central Europe ostracod
fauna, apart from Dolerocypris sinensis which is fre-
quently encountered in the circum-Mediterranean re-
gion (Meisch 2000). Two species, Candona weltneri
and Pseudocandona compressa, are new for Italy.
Candona weltneri has a Palaearctic distribution. It has
frequently been recorded in Central and Northern Eu-
rope, although it is rare or absent from the South. Pseu-
docandona compressa has a broader distribution,
being widespread throughout Europe, Turkey, Iran, Si-
beria and probably North America (Meisch 2000). The
occurrence of Ilyocypris monstrifica is also of particu-
lar interest, since this species was known in Italy only
from two ricefields in the Po River Valley and one lo-
cality in Sicily (Rossi et al. 2003). It is nevertheless
possible that this species has previously been reported
as I. gibba, so its exact distribution remains at present
unknown. Congeneric species (Herpetocypris brevi-
caudata and H. chevreuxi, Pseudocandona hartwigi
and P. compressa and, to a lesser extent, also Cyclocy-
pris laevis and C. ovum) found in the study area are
displaced in opposite directions with respect to the pla-
ne defined by the first two canonical axes, most likely
revealing different ecological requirements. In the ca-
se of Ilyocypris, I. decipiens and I. monstrifica are
found in the same habitat, whilst I. gibba seems to pre-
fer more buffered waters and higher pH. Species cha-
racterising cluster I obtained from CA tend to also be
aggregated in the CCA distribution. They are preferen-
tially found in habitats with elevated ionic content and
higher concentrations of chlorophyll-a and inorganic
nutrients, and seem to be tolerant of lower oxygen
concentrations. Species that are mainly associated wi-
th higher pH values (Dolerocypris sinensis, Herpeto-
cypris chevreuxi, H. brevicaudata, Darwinula steven-
soni, and Potamocypris smaragdina) are found only in
spring and summer months and denote a preference for
well-oxygenated waters. Herpetocypris brevicaudata
seems to prefer waters with high alkalinity as well; this
is also true for the other species (in particular Priono-
cypris zenkeri and Pseudocandona hartwigi) located
on the right side of the first axis of CCA. Darwinula
stevensoni is an obligate parthenogen with a cosmopo-
litan and ubiquitous distribution (Rossetti & Martens
1996, 1998); for this species, a broad tolerance to dif-
ferent environmental conditions has been demonstra-
ted and the existence of a general purpose genotype
has been proposed (Rossi et al. 2002, Van Doninck et
al. 2002). Nevertheless, D. stevensoni is rare in the stu-
dy area, where it was collected from April to August
only in OG10, usually at low densities. Its disappea-
rance in October is puzzling, because this species is
thought to have no resting stages and long life cycles
(up to 3-4 years, Ranta 1979), although temporary di-
sappearance of D. stevensoni from typical sampling
stations was also reported by Gandolfi et al. (2001).
Herpetocypris brevicaudata and Ilyocypris gibba were
found in only one of the two lotic environments inclu-
ded in this study (OG06). In fact, these two species are
commonly (but not exclusively) found in slowly flo-
wing waters, brooks and springs (Meisch 2000, Mez-
quita et al. 1999). The other ostracods collected in the
two lotic biotopes (Candona weltneri, Pseudocandona
compressa, Cypria ophthalmica, and Cypridopsis vi-
dua) were also present in the neighboring lentic wa-
Although the results of this study seem to indicate a
fairly clear relationship between the occurrence of os-
tracod species and the physical and chemical characte-
ristics of habitats measured here, other environmental
factors may be invoked to explain the observed distri-
bution. Fish are likely to have a substantial effect by
predation on the ostracod assemblages (Torras et al.
2000, GarcÌa-Berthou 2001, Zimmer et al. 2002). It is
interesting to note that the highest ostracod diversity is
found in a temporary habitat (OG03), even though the
species occurring there are not necessarily typical of
astatic waters and all of them are also present in per-
manent waters within the study area.
As reported above, aquatic macrophyte cover stron-
gly influences water and sediment characteristics of
shallow wetlands and, as a consequence, the structure
of invertebrate communities. For instance, CCA re-
sults showed that dissolved oxygen and chlorophyll-a
arrows are perpendicular, indicating that the two va-
riables are uncorrelated and that oxygen content of the
waters is likely to be regulated by macrophytes and by
sediment respiration and re-oxidation processes, rather
than by planktonic algae production. Ostracods may
also use macrophytes as refugia from fish predators
(Roca et al. 1993).
This preliminary study lacks a detailed characterisa-
tion of surface sediment (i.e. organic matter content,
G. ROSSETTI, M. BARTOLI, K. MARTENS
oxygen, sulphide and redox potential microprofiles)
which could be related to the ostracod species rich-
ness. Recent studies have also demonstrated that pre-
sence/absence of at least some ostracod species can be
related to aspects of solute composition not measured
here (Forester 1983). Nevertheless, the ostracod distri-
bution in relation to some environmental factors seems
to confirm the relevance of these organisms as envi-
ronmental indicator species. The need for a solid taxo-
nomic approach as an indispensable basis for further
ecological research is stressed.
The investigated area can be regarded as a hotspot of
ostracod diversity, when compared with other freshwa-
ter ecosystems in Northern Italy. For example, the
taxon richness of the Oglio River wetlands is compa-
rable to that found in ricefields (Rossi et al. 2003), but
with a much greater proportion of autochthonous taxa.
Also, the number of identified species in the Oglio
wetlands was higher than that of a group of 31 lowland
springs (Rossetti et al. 2004). A full-scale comparison
with the Italian ostracod fauna, however, is hampered
by the fact that most records listed in the synopsis by
Ghetti & McKenzie (1981) originate from publications
with substandard descriptions and illustrations. Accor-
ding to these authors, c. 134 non-marine species are
present in Italy (not including taxa at subspecific
rank); c. 10% are «ospiti esteri», i.e. species introdu-
ced in Italy via the spread of useful plants (McKenzie
& Moroni 1986), while endemic species show a stri-
king prevalence in Sardinia and account for c. 16% of
the total Italian ostracod diversity.
It is interesting to note that a total of 157 freshwater
species have been retained by Meisch (2000) in his sy-
nopsis, which includes the ostracod faunas of British
Isles, Northern France, Belgium, the Netherlands,
Luxembourg, Germany, Switzerland, Austria, Hunga-
ry, Czech Republic and Slovakia. Germany has the hi-
ghest number of ostracod species (126): this is not too
surpring, considering the size of this country and, abo-
ve all, the high number of German ostracodologists
and the long tradition in ostracod studies.These data
reinforce the belief that Italy potentially may host an
extraordinary diversified ostracod fauna, mainly due to
its latitudinal extension which guarantees a wide range
of climatic conditions and broad environmental hete-
rogeneity. An interesting picture arises when analysing
the ostracod diversity of the Iberian Peninsula, which
shares more similar climatic and geographic characte-
ristics with Italy. Baltanás et al. (1996) reported a total
of 86 species, also including ostracods from Canary Is-
lands (belonging to the Macaronesian subregion) and
retaining those taxa whose presence or taxonomic sta-
tus must be confirmed.
According to what is shown above, it seems plau-
sible that the ostracod diversity depicted by the avai-
lable Italian checklist (Ghetti & McKenzie 1981) may
be overestimated. This is certainly true for some
groups included in recent taxonomic revisions, e.g. for
the genus Herpetocypris (González Mozo et al. 1996).
A preliminary appraisal of the extant diversity of non-
marine ostracods (from surface, crenal, and subterra-
nean waters) in Italy, following synonymisation of se-
veral taxa, elimination of doubtful records and inclu-
sion of new species (e.g., Martens 1992 on Eucypridi-
ni, Martens et al. 2002 on Heterocypris, Karanovic &
Pesce 2000 on Mixtacandona talianae) and new re-
cords for Italy (e.g., Stoch 1998, Bellavere et al. 2002,
Rossi et al. 2003, this paper), leads to a rough estima-
tion of about one hundred valid species, of which c.
15% are exotic and less than 5% endemic (Rossetti &
Martens in preparation).
In the Parco Oglio Sud wetlands, external and inter-
nal nutrient loads, combined with dominant primary
producer dynamics, trigger positive feedback mecha-
nisms that accelerate their burial and, in the more ex-
treme situations, their complete disappearance. This
evolution actually appears to be irreversible, unless ra-
pid interventions (such as sediment dredging, vegeta-
tion control, and water quality improvement) are car-
ried out by local authorities, aiming at the preserva-
tions of the most valuable sites, e.g. OG07, OG08,
OG12 and OG13. In fact, although these aquatic eco-
systems are small and highly fragmented, the results of
this study on the ostracod fauna indicate that they may
represent important biodiversity spots within a heavily
The authors are indebted to two referees whose comments helped
in improving the manuscript. Susanna Perlini (Parco Oglio Sud) is
thanked for making possible this research. Greta Delfini and Rossa-
no Bolpagni (D.E.S., Parma) are acknowledged for their participa-
tion in the fieldwork and for the chemical analysis of water samples.
Julien Cillis (R.B.I.N.Sc., Brussels) offered technical assistance wi-
th the scanning electron micrographs. Raul Primicerio (The Norwe-
gian College of Fishery Science, University of Troms¯) kindly read
an earlier version of the manuscript. The ostracods were mostly
identified and illustrated during several visits of GR to KM, founded
by the EU Project ABC granted to the R.B.I.N.Sc. This work was
partly financially supported by the Parco Oglio Sud.
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