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Annls LimnoL 26 (2-3) 1990 : 183-193
Sublittoral and profundal chironomid (Diptera) communities of Lake
Vico (Central Italy) : relationship to the trophic level
M. Seminara1
M. Bazzanti'
C. Tamorri
Keywords : Chironomidae, community structure, depth distribution, trophic level, lake, Italy.
Sublittoral and profundal chironomid community structure, depth distribution and relationship to the trophic level
of the waters were investigated in Lake Vico (Central Italy) during 1985-1986. PCA analysis indicated a depth-dependent
group of true profunda! stations at 20, 30 and 40 m depths, characterized by Micropsectra, Procladius, Microtendipes,
Tanytarsus and Paratendipes, and a group of 10 m stations, characterized by Cryptochironomus, Polypedilum b'tcrena-
tum gr., Cladopelma lateralis
gr.
and C. laccophila gr., representing the sublittoral features of this depth. In agreement
with the chemical data, the chironomid community indicated a mesotrophic condition of Lake Vico, with a tendency
towards an increasing trophic level in the deepest zone. A significant role in revealing future trophic changes in the lake
may be attributed to the key-indicator Micropsectra.
Communautés de Chironomidés (Diptera) des zones sublittorale et profonde du Lac Vico (Italie Centrale) : relation avec
le niveau trophique.
Mots clés : Chironomidés, structure des communautés, distribution selon la profondeur, niveau trophique, lac, Italie.
La structure des communautés sublittorale et profonde des Chironomidés, leur distribution selon la profondeur et
leur relation avec le niveau de trophie du Lac Vico ont été étudiées au cours des années 1985-1986. L'Analyse en Compo-
santes Principales permet de différencier un groupement des stations profondes à -20, -30et -40 m d'un groupement
des stations de la zone sublittorale à - 10 m. Le premier groupement est caractérisé par les genres Microspsectra, Procla-
dius, Microtendipes, Tanytarsus et Paratendipes et le deuxième par les genres Cryptochironomus, Polypedilum bicrena-
tum gr., Cladopelma lateralis
gr.
et C. laccophila gr. Corrélativement aux données chimiques, la communauté chirono-
midienne correspond bien à l'état mésotrophique du lac avec une tendance à l'augmentation de la trophie dans la zone
profonde. Le rôle significatif du genre Micropsectra dans la détection de futurs changements trophiques du lac est souligné.
1.
Introduction
The family Chironomidae constitutes a wides-
pread, diverse and abundant group of invertebra-
tes inhabiting all freshwater ecosystems. Their com-
munity structure has traditionally been investigated,
and many workers underlined their relevant role
both in lake metabolism and water quality assess-
ment (Warwick 1975, Gallepp et al. 1978, Granéli
1979,
Saether 1979, Wiederholm 1980, Gardner et
al.
1983, Wasson 1984, Seminara & Bazzanti 1988).
I. Dipartimento di Biologia Animale e deH'Uomo, Université
« La Sapienza », v. te del l'Uni versità 32, 00185 Roma, Italia.
In European countries some topics involving chi-
ronomids, e.g. community structure, composition,
phenology and seasonal variations, have been long
and extensively studied, while other aspects, e.g.
depth distribution, are reported less frequently in
literature (Laville 1971, Aagaard 1978, Lindegaard
1980,
Kansanen et al. 1984, Gerstmeier 1989 a, Hei-
nis 1989, Heinis et al. in press).
This paper deals with the sublittoral and profun-
dal chironomid communities of Lake Vico (Central
Italy) in order to examine their structure, their depth
distribution, and their relationships with the trophic
status of the lake. The results of this paper also con-
tribute to the knowledge of this dipteran family in
Article available at http://www.limnology-journal.org
or http://dx.doi.org/10.1051/limn/1990016
184 M. SEMINARA, M. BAZZANTI, C. TAMORRI
Central Italian lakes (Nocentini 1973, Bazzanti 1981,
Bazzanti & Loret 1982, Mastrantuono 1986, Baz-
zanti & Seminara 1987 a& b, Mastrantuono 1987,
Mastrantuono & La Rocca 1988, Seminara & Baz-
zanti 1988). This study forms part of a wider
research (P.I.M. ; Piano Integrato Méditerranée)
aimed at assessing the lake water quality and at an
adequate strategy to improve local fish management.
Data about the whole profundal benthic community
of the lake will be published elsewhere.
2.
Study area and methods
Lake Vico (Fig. 1) is a volcanic water body sur-
rounded by both agricultural and non-anthropized
lands.
It is situated about 50 km North of Rome in
the volcanic area of the Cimini Mountains, where
a Regional Nature Reserve including the lake and
the neighbouring area was instituted in 1982. The
lake has a catchment area of 28.05 km2 and a theo-
retical water renewal time of about 17 years (Bar-
banti 1969). Specific morphometric data are repor-
ted in figure 1. Commercial fish stock (mainly core-
gonids) is managed by means of artificial reproduc-
tion of the autochthonous breeding individuals.
Moreover, the lake waters are utilized for sportfis-
hing and recreational purposes. In the surrounding
grounds a massive use of fertilizers and pesticides
for agricultural practices was recorded over the last
two decades. Lake Vico was first studied by the
Hydrobiological Institute of Pallanza during
1969-1970 (Barbanti et al. 1971). The results, based
on both physico-chemical and biological data, indi-
cated a mesotrophic condition of the waters. In
1985-1986, a similar content of nutrients but a hig-
her orthophosphate concentration and a more pro-
nounced summer-autumn deoxygenation in the dee-
pest layers of the hypolimnion were observed
(Table I). During the study, pH ranged from 7.1 to
8.7, temperature from 6.2 to 25° C and transpa-
rency from 3.5 to 12.6 m.
Benthic samples were collected bimonthly from
May 1985 to March 1986 in three sites of the lake
(Fig. 1). Sampling depths were established at 10, 20,
30 and 40 m at site A, and at 10 and 20 m at sites
B and C. At each depth and date triplicate samples
were obtained by an Ekman grab (area : 225 cm2),
for a total of 144 samples during the study. Mate-
rial was filtered through a 0.28 mm mesh screen and
preserved in 10 °Io formalin. Chironomid larvae and
pupae were hand-sorted, counted, weighed and then
(2)
Table I. Selected chemical parameters monthly registered from
May 1985 to March 1986 in the waters of Lake Vico (Nicotra,
1987).
Depth (m) 0 10 20 30 40
min. 8.2 9.0 4.2 1.0 0.2
Oxygen (mg/1) mean 9.4 10.3 8.4 6.2 5.3
max. 11.0 12.2 11.2 11.1 11.0
min. 9 10 11 12 11
Total P (pg/l) mean 13.7 15.8 19.1 18.9 35.2 Total P (pg/l)
max. 20 22 28 25 125
min. 3.0 2.0 4.0 4.1 4.0
P-P04
(^g/1)
mean 6.7 5.6 6.4 7.1 19.4
P-P04
(^g/1)
max. 10.0 9.0 11.0 13.1 66.0
min. 2.0 2.0 4.0 4.0 6.0
N-N03
(^g/1)
mean 6.9 7.6 8.6 13.7 28.4
N-N03
(^g/1)
max. 14.0 12.0 17.0 38.0 77.0
min. 0.1 0.1 0.0 0.1 0.0
N-N02
(^g/1)
mean 0.4 0.3 0.4 0.7 2.1 N-N02
(^g/1)
max. 0.8 0.8 1.0 1.8 14.0
min. 1.0 2.0 2.0 3.0 1.0
N-NH3
(^g/1)
mean 3.4 3.5 4.8 13.5 61.6 N-NH3
(^g/1)
max. 6.0 6.0 14.0 36.0 243.0
identified at the genus or species group level. Addi-
tional samples were collected for laboratory larval
rearing in order to obtain specific adult identifica-
tion of the most diffused taxa. The oligochaete/chi-
ronomid ratio (O/O + C°for Wiederholm 1980) was
adopted to point out the trophic status of Lake Vico.
The Shannon diversity index (Pielou 1969) was cal-
culated as a synthetic expression of chironomid com-
munity structure. Principal Component Analysis
(PCA),
largely utilized in benthic studies on fresh-
water ecosystems to evidence environmental gra-
dients (Rae 1985, Bradt & Berg 1987, Glazier &
Gooch 1987, Allison & Harvey 1988, Diaz 1989,
Reynoldson 1990), was carried out on the log (x +
1) transformed densities to detect relationships bet-
ween depths and chironomid assemblages. Linear
correlations were made on log (H + 1) (Elliott 1977)
or arcsin \f¥ (Sokal & Rohlf 1973) transformed
absolute and relative data, respectively. Statistical treat-
ments were performed using SPSS/PC software.
(3) CHIRONOMIDS COMMUNITIES OF LAKE VICO 185
Fig. 1 : Morphometric data and sketch map of Lake Vico with sampling sites (A, B and C) and depths (from Barbanti, 1969).
186 M. SEMINARA, M. BAZZANTI, C. TAMORRI (4)
3.
Results
About 7000 chironomid larvae and pupae belon-
ging to 15 taxa were collected and identified during
the study {Table II). Sublittoral and profundal chi-
ronomids of Lake Vico accounted, on average, for
36.04 °7o of density of the total benthic fauna, with
a minimum of 0.3 % and a maximum of 76.0 %.
The minimum, mean and maximum percentage
values on total fauna biomass were 0.2 %, 36.25 %
and 80.6 %, respectively. Seasonal values of chiro-
nomid densities and biomasses at sampling sites and
depths are reported in figure 2. The extreme values
registered were 15 and 12 976 ind/m2 for densities,
0.01 and 11.63 g/m2 for biomasses. In all three sites,
the highest densities and biomasses generally occur-
red at 20 m depth and the lowest ones at 40 m depth,
whereas intermediate values were recorded at 10 and
30 m depths. Both density and biomass decreased
with increasing depth (r =
-0.53,
p < 0.001 and
r =
—0.43,
p < 0.01, respectively). The number
of taxa showed the highest values at 10 m and the
lowest at 40 m, significantly decreasing with depth
(r = -0.74, p < 0.001). Diversity ranged from 0,
sometimes recorded at 30 and 40 m, to 2.54 occur-
ring at 10 m (Table II), and was inversely correla-
ted to the depth (r = -0.70, p < 0.001). The most
frequent and abundant genera (Table II and Fig. 3)
were Proctadius, Tanytarsus and Micropsectra, fol-
lowed by Paratendipes and Microtendipes. The
remaining taxa were less frequent and/or present in
low numbers and percentages. Polypedilum nube-
eulosum gr., P. bicrenatum gr., Parachiranomus,
Chironomus sp. and Pentaneurini were present only
in 10 m samples (Table II).
The oligochaete/chironomid ratio (Table II) gene-
rally showed annual mean values from 44.3
°7o
to
82.4 °/o at 10 and 20 m depths, and increased at 30
and 40 m, where the theoretical maximum was rea-
ched at the end of the thermal stratification. The
values of this index significantly increased with
increasing depth (r = 0.46, p < 0.001). An inverse
correlation (r = - 0.57, p < 0.001) was found bet-
ween chironomid diversity and oligochaete/chiro-
nomid ratio.
The statistical comparisons performed on several
parameters of the community structure (i.e. density
of taxa, percentages, diversity, total density and bio-
mass,
etc.) by means of the non-parametric Wil-
coxon test (Eason et al. 1980) did not suggest any
clear pattern in the chironomid spatial distribution
and seasonal variation among the three sites, so that
such aspects are not considered.
The PCA analysis (Fig. 4, Table III) was perfor-
med on a set of 48 data (8 depth stations per 6 sam-
pling visits). Taxa occurring with percentages lower
than 1 % of the total chironomid fauna were not
considered (taxa 1, 2, 12, 15 in Table II). The first
two principal components accounted for 53.5 % of
the total variance. The second factor separates most
of the 10 m stations from those situated in the dee-
pest area of the lake. The latter stations are orde-
red along factor 1 according to a gradient of depth.
In fact, excluding 10 m stations from the previous
pool of data, there is a highly significant correla-
tion (r = 0.89, p < 0.001) between depth and dis-
tances of the remaining sampling stations from fac-
tor 2.
Table III : Factor loadings of chironomid taxa from Lake Vico.
Values lower than | 0.50 | were arbitrarily neglected.
Factors
Principal
1
Components
2
Eigenvalue 3.98 1.90
Variance accounted for (%) 36.2 17.3
Variables
Micropsectra 0.85
Procladius 0.81
Microtendipes 0.73
Tanytarsus 0.72
Paratendipes 6.51
Cryptochironomus 0.85
Polypedilum bicrenatum gr. 0.76.
Cladopelma lateralis gr. 0.57
C. laccophila gr. 0.55
4.
Discussion
Chironomids of Lake Vico were essentially cha-
racterized by densities and biomasses strongly
infuenced by increasing depth. Diversity values indi-
cated a more diversified community at 10 and 20 m,
whereas a more simplified and monotonous struc-
ture was generally present at 30 and 40 m, especially
during the stratification period when the oxygen
deficit comes into effect.
A clear picture of the depth distribution of chi-
ronomids is provided by the plot of the sampling
stations derived from the PCA analysis. It describes
(5)
CHIRONOMIDS COMMUNITIES
OF
LAKE VICO
187
Table
II :
Mean
and
range
of
density, number
of
taxa, diversity
and
oligochaete/chironomid ratio
of
sublittoral
and
profundal chiro-
nomids
at
the sampling sites and depths
in
Lake Vico. Proctadius choreus (Meigen), Cladopelma virescens (Meigen), Microtendipes
cf. pedellus
(DeGeer)
and
Paratendipes aibimanus (Meigen) resulted from
the
adult identification.
Sites
Depth
(*)
l.PsKtrgçUdjM
Nueber
al
ts»i
2.5*
2.22 l.îî
lin. 55.7 13.9 50.0
nan
il.B **.J 82.i
3M
"M
57.1
65.4
92.B
95.7
188 M. SEMINARA, M. BAZZANTI, C. TAMORRI (6)
Fig. 2 : Densities (ind/nr) and biomasses (g/mJ) of the total chironomids at sites A, B and C and depths.
Interrupted lines indicate annual mean values.
CHIRONOMIDS COMMUNITIES
OF
LAKE
VICO
189
SITE
A
10m
1,8,12.15
20 40
SITE
B
10m
13
2.10
0 20 40 601
I"1
20
m
1,6
7.13,14
20 40
60%
10
6,13
20m
40 60%
30
m
20
60%
110
40
m
} 20 40
60%
ISITE
C|
[i
10m
M.8,12
D 20 40
60%
111
110
16
7 14
20
m
40 60%
Fig.
3 :
Annual mean percentages
of
taxa
on
the
total
chironomids
at the
sampling
sites
and depths.
Taxa
numbered
as in
Table
II.
190 M. SEMINARA, M. BAZZANTI, C. TAMORRI (8)
2 *
y-'
2 2 2 /'
/2 ®a 21/ X
22%
V
2
,'3 3 "~3? /,
!3 • :1 1
v: 3
\ 4 \
1
M 1
\ 3 ;
'"•4 4;
1
©
1 /
1/
Fig. 4 : Plot of factors I and 2 of the PCA analysis. Numbers 1, 2, 3 and 4 indicate the 10, 20, 30 and 40 m depth stations, respectively.
Circled numbers represent centroids.
the separation of the sublittoral stations at 10 m
from those at depths of 20, 30 and 40 m, which
represent the true profundal zone with homogeneous
environmental features. The arrangement of 20, 30
and 40 m depths along Fl indicates that the chiro-
nomid structure in Lake Vico (i.e. proportion of the
most relevant taxa) substantially remained the same
along the depth gradient, changing mainly as a result
of a gradual loss of taxa and lowering of absolute
densities. Typically profundal chironomids resulted
to be Micropsectra, Procladius, Microtendipes,
Tanytarsus and Paratendipes. Among them, Microp-
sectra appeared more closely linked to the deeper
part of the lake {Fig. 3 and Table III). The other
genera were well represented at all depths, but they
were almost the only taxa present in the profundal
of the lake. On the contrary, the higher variability
in both occurrence and densities of chironomid taxa
among sites and seasons at 10 m makes these sta-
tions more highly dispersed and not comparable with
a real profundal biocoenosis. Thus, on this basis the
group of 10 m stations should be ascribed to a dis-
tinct sublittoral zone with characterizing elements
such as Cryptochironomus, Polypedilum bicre-
(9) CHIRONOMIDS COMMUNITIES OF LAKE VICO
191
natum gr., Cladopelma lateralis gr. and C. lacco-
phila gr., well represented also in the littoral of the
same lake (Mastrantuono & La Rocca 1988). The
distinction between the sublittoral and the profun-
dal zone is also supported by the occurrence of taxa
exclusively present at 10 m stations, and of vegeta-
tion debris (mainly Characeae) only in the samples
from these depths. Other authors (i.e. Laville 1971,
Lindegaard 1980, Heinis 1989) already found that
chironomid community structure shifts from a lit-
toral to a profundal pattern showing that the inter-
mediate environmental character of the sublittoral
zone is often related to changes in substrate type,
food availability, oxygen content, water quality, etc.
A similar picture has been observed also for lacus-
trine malacocoenoses (Mouthon 1989), making it
apparent that many benthic animals are distributed
along a depth-dependent environmental gradient.
Chironomids can also provide useful trophic indi-
cations for Lake Vico. Unfortunately, the absence
of the required indicator taxa and the lack of speci-
fic identifications made it impossible to evaluate the
lake trophy level by means of Saether's trophic key
(Saether 1979), but the occurrence of good quanti-
ties of Tanytarsini should traditionally lead to the
assessment of a mesotrophic condition of the pro-
fundal sediments (cf. Thienemann 1925 & 1954,
Brundin 1949 & 1956). Indeed, especially in recent
decades, the specific identification of taxa belonging
to this group has been strongly recommended for
a better comprehension of the relationship among
these taxa and the trophic level of lakes. In fact, i.e.
the genus Tanytarsus holds species with very diffe-
rent ecological sensitivity, varying from oligotrophy
to slight eutrophy (Reiss & Fittkau 1971, Saether
1979,
Kansanen et al. 1984, Gerstmeier, 1989b).
Conversely, a reliable mesotrophy indication is pro-
vided by the presence in large abundances of
Micropsectra, considered as an oligo-mesotrophic
taxon with a narrow trophic range even at the level
of genus (Wiederholm 1973 & 1976, Saether 1979,
Wiederholm & Eriksson 1979, Gerstmeier 1989b).
Thus,
this taxon can be considered as a key indica-
tor in detecting future trophic changes in Lake Vico.
The other common genera were all eurytopic forms
living in a wide trophic range, with the exception
of the traditionally eutrophic Chirortomus plumo-
sus gr.
The oligochaete/chironomid ratio seems to con-
firm the diagnosis of mesotrophy indicated by the
previous considerations. In fact, the values registe-
red in Lake Vico are lower than those recorded at
the same depths in slightly to strongly eutrophic
waters of Central Italy (Bazzanti & Seminara 1987a
& 1987b, Bazzanti & Seminara 1988, Seminara &
Bazzanti 1988). Moreover, the inverse trend of this
environmental index and of the chironomid diver-
sity with respect to depth is indicative of the suita-
bility of this latter in monitoring ecological chan-
ges along a depth gradient, as already observed for
entire benthic communities (Bazzanti & Seminara
1987c, Bazzanti & Seminara 1988).
In synthesis, according to chemical data, the sub-
littoral and profundal chironomids of Lake Vico
indicated a mesotrophic condition of the waters.
However, emphasis should be laid on the tendency
towards increasing trophy in the deepest layers of
the hypolimnion, as revealed by high values of total
P,
the occurrence of summer-autumn oxygen deple-
tion, reduction of diversity and abundances of chi-
ronomid communities, and constantly high values
of oligochaete/chironomid ratio.
Acknowledgements
This research was partly supported by an M.P.I, grant. We
wish to thank D' E. Gelosi for the general organization of the
main research on the lake and for permission to publish the che-
mical data.
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