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. Seminara
M. B a z z a n t i '
C. T a m o r r i
1
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'tcrenatum 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 Composantes Principales permet de différencier un groupement des stations profondes à - 2 0 , - 3 0 e t - 4 0 m d'un groupement
des stations de la zone sublittorale à - 10 m. Le premier groupement est caractérisé par les genres Microspsectra, Procladius, Microtendipes, Tanytarsus et Paratendipes et le deuxième par les genres Cryptochironomus, Polypedilum bicrenatum gr., Cladopelma lateralis gr. et C. laccophila gr. Corrélativement aux données chimiques, la communauté chironomidienne 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
T h e family C h i r o n o m i d a e constitutes a widesp r e a d , diverse a n d a b u n d a n t g r o u p of invertebrates inhabiting all freshwater ecosystems. Their c o m m u n i t y structure has traditionally been investigated,
a n d m a n y workers underlined their relevant role
b o t h in lake m e t a b o l i s m a n d water quality assessm e n t (Warwick 1975, G a l l e p p et al. 1978, Granéli
1979, Saether 1979, W i e d e r h o l m 1980, G a r d n e r 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 R o m a , Italia.
In E u r o p e a n countries some topics involving chir o n o m i d s , e.g. c o m m u n i t y s t r u c t u r e , c o m p o s i t i o n ,
p h e n o l o g y a n d seasonal v a r i a t i o n s , have b e e n long
a n d extensively studied, while o t h e r aspects, e.g.
depth distribution, are r e p o r t e d less frequently in
literature (Laville 1971, A a g a a r d 1978, L i n d e g a a r d
1980, Kansanen et al. 1984, Gerstmeier 1989 a, Heinis 1989, Heinis et al. in press).
This paper deals with t h e sublittoral and p r o f u n dal chironomid c o m m u n i t i e s of L a k e Vico ( C e n t r a l
Italy) in order to examine their structure, their depth
distribution, a n d their relationships with the trophic
status of the lake. T h e results of this paper also contribute t o 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
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M. S E M I N A R A , M. B A Z Z A N T I , C. T A M O R R I
Central Italian lakes (Nocentini 1973, Bazzanti 1981,
Bazzanti & L o r e t 1982, M a s t r a n t u o n o 1986, Bazz a n t i & S e m i n a r a 1987 a & b , M a s t r a n t u o n o 1987,
M a s t r a n t u o n o & L a Rocca 1988, S e m i n a r a & Bazz a n t i 1988). T h i s study f o r m s part of a wider
research ( P . I . M . ; P i a n o I n t e g r a t o M é d i t e r r a n é e )
a i m e d at assessing t h e lake water quality a n d at an
a d e q u a t e strategy t o improve local fish m a n a g e m e n t .
D a t a a b o u t the whole profundal benthic c o m m u n i t y
of t h e lake will b e published elsewhere.
2. S t u d y area and m e t h o d s
L a k e Vico (Fig. 1) is a volcanic water b o d y surr o u n d e d b y b o t h agricultural a n d n o n - a n t h r o p i z e d
l a n d s . It is situated a b o u t 50 k m N o r t h of R o m e in
t h e volcanic a r e a of the Cimini M o u n t a i n s , w h e r e
a R e g i o n a l N a t u r e Reserve including t h e lake a n d
t h e n e i g h b o u r i n g a r e a was instituted in 1982. T h e
l a k e h a s a c a t c h m e n t area of 28.05 k m a n d a t h e o retical water renewal time of a b o u t 17 years (Barb a n t i 1969). Specific m o r p h o m e t r i c d a t a are reported in figure 1. C o m m e r c i a l fish stock (mainly coreg o n i d s ) is m a n a g e d by means of artificial r e p r o d u c t i o n of the a u t o c h t h o n o u s breeding individuals.
M o r e o v e r , the lake waters are utilized for sportfish i n g a n d r e c r e a t i o n a l p u r p o s e s . In the s u r r o u n d i n g
g r o u n d s a massive use of fertilizers a n d pesticides
for agricultural practices was recorded over the last
t w o d e c a d e s . L a k e Vico was first studied b y the
H y d r o b i o l o g i c a l I n s t i t u t e of P a l l a n z a d u r i n g
1969-1970 ( B a r b a n t i et al. 1971). T h e results, based
o n b o t h physico-chemical a n d biological d a t a , indicated a m e s o t r o p h i c condition of the w a t e r s . In
1985-1986, a similar content of nutrients but a higher o r t h o p h o s p h a t e concentration and a more pron o u n c e d s u m m e r - a u t u m n deoxygenation in the deepest layers of t h e h y p o l i m n i o n were observed
( T a b l e I). D u r i n g t h e study, p H ranged from 7.1 t o
8.7, t e m p e r a t u r e f r o m 6.2 t o 25° C a n d t r a n s p a rency f r o m 3.5 to 12.6 m.
Table I. Selected chemical parameters monthly registered from
May 1985 t o March 1986 in the waters of Lake Vico (Nicotra,
1987).
0
10
20
30
min.
Oxygen (mg/1) m e a n
max.
8.2
9.4
11.0
9.0
10.3
12.2
4.2
8.4
11.2
1.0
6.2
11.1
0.2
5.3
11.0
Total P (pg/l)
min.
mean
max.
9
13.7
10
15.8
22
11
19.1
28
12
18.9
25
11
35.2
125
P - P 0 4 (^g/1)
min.
mean
max.
4.0
6.4
11.0
4.1
7.1
4.0
19.4
10.0
2.0
5.6
9.0
13.1
66.0
N - N 0 3 (^g/1)
min.
mean
max.
2.0
6.9
14.0
2.0
7.6
12.0
4.0
8.6
17.0
4.0
13.7
38.0
6.0
28.4
77.0
N - N 0 2 (^g/1)
min.
mean
max.
0.1
0.4
0.8
0.1
0.3
0.8
0.0
0.4
1.0
0.1
0.7
1.8
0.0
2.1
14.0
N - N H 3 (^g/1)
min.
mean
max.
1.0
3.4
6.0
2.0
3.5
6.0
2.0
4.8
14.0
3.0
13.5
36.0
1.0
61.6
243.0
D e p t h (m)
2
B e n t h i c samples w e r e collected b i m o n t h l y from
M a y 1985 t o M a r c h 1986 in t h r e e sites of the lake
(Fig. 1). Sampling depths were established at 10, 20,
30 a n d 40 m at site A , and at 10 a n d 20 m at sites
B a n d C . At each d e p t h and d a t e triplicate samples
w e r e o b t a i n e d by a n E k m a n g r a b (area : 225 c m ) ,
for a total of 144 samples d u r i n g the s t u d y . M a t e rial was filtered t h r o u g h a 0.28 m m mesh screen and
preserved in 10 °Io formalin. C h i r o n o m i d larvae a n d
p u p a e were h a n d - s o r t e d , counted, weighed a n d then
2
20
3.0
6.7
40
identified at the genus or species g r o u p level. A d d i tional samples were collected for l a b o r a t o r y larval
rearing in order t o o b t a i n specific adult identification of the most diffused taxa. T h e oligochaete/chironomid ratio ( O / O + C°fo Wiederholm 1980) was
adopted t o point out the trophic status of Lake Vico.
T h e S h a n n o n diversity index (Pielou 1969) was calculated as a synthetic expression of chironomid comm u n i t y structure. Principal C o m p o n e n t Analysis
( P C A ) , largely utilized in benthic studies o n freshwater ecosystems t o evidence e n v i r o n m e n t a l gradients (Rae 1985, Bradt & Berg 1987, Glazier &
G o o c h 1987, Allison & Harvey 1988, Diaz 1989,
Reynoldson 1990), was carried out o n the log ( +
1) t r a n s f o r m e d densities t o detect relationships between depths a n d c h i r o n o m i d assemblages. Linear
correlations were m a d e on log ( + 1) (Elliott 1977)
or arcsin \f¥ (Sokal & Rohlf 1973) t r a n s f o r m e d
absolute and relative data, respectively. Statistical treatments were performed using SPSS/PC software.
r
x
H
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C H I R O N O M I D S C O M M U N I T I E S O F LAKE VICO
185
Fig. 1 : Morphometric d a t a a n d sketch m a p of Lake Vico with sampling sites (A, B a n d C) and depths (from Barbanti, 1969).
186
M. S E M I N A R A , M. B A Z Z A N T I , C. T A M O R R I
3 . Results
A b o u t 7000 c h i r o n o m i d larvae a n d p u p a e belon­
ging t o 15 t a x a w e r e collected and identified during
t h e s t u d y {Table II). Sublittoral a n d p r o f u n d a l chir o n o m i d s of L a k e Vico a c c o u n t e d , o n a v e r a g e , for
36.04 °7o of density of the total benthic f a u n a , with
a m i n i m u m of 0.3 % a n d a m a x i m u m of 7 6 . 0 % .
T h e m i n i m u m , m e a n a n d m a x i m u m percentage
values o n total f a u n a biomass were 0.2 % , 36.25 %
a n d 80.6 % , respectively. Seasonal values of chiro­
n o m i d densities a n d biomasses at sampling sites and
d e p t h s are r e p o r t e d in figure 2. T h e e x t r e m e values
registered were 15 a n d 12 976 i n d / m for densities,
0.01 a n d 11.63 g/m for biomasses. In all t h r e e sites,
t h e highest densities a n d biomasses generally occur­
red at 20 m depth a n d the lowest ones at 40 m depth,
whereas intermediate values were recorded at 10 and
30 m d e p t h s . B o t h density a n d b i o m a s s decreased
with increasing d e p t h (r = - 0 . 5 3 , p < 0.001 and
r = — 0 . 4 3 , p < 0 . 0 1 , respectively). T h e n u m b e r
of t a x a s h o w e d t h e highest values at 10 m a n d the
lowest at 40 m , significantly decreasing with depth
(r = - 0 . 7 4 , p < 0.001). Diversity ranged from 0,
s o m e t i m e s r e c o r d e d at 30 a n d 40 m, t o 2.54 occur­
ring at 10 m ( T a b l e I I ) , a n d was inversely correla­
ted t o the d e p t h (r = - 0 . 7 0 , p < 0.001). T h e most
frequent a n d a b u n d a n t g e n e r a (Table II a n d Fig. 3)
were Proctadius,
Tanytarsus a n d Micropsectra,
fol­
lowed by Paratendipes
a n d Microtendipes.
The
r e m a i n i n g taxa were less frequent a n d / o r present in
low n u m b e r s a n d p e r c e n t a g e s . Polypedilum
nubeeulosum g r . , P. bicrenatum
gr.,
Parachiranomus,
Chironomus
s p . a n d Pentaneurini were present only
in 10 m samples (Table I I ) .
2
2
T h e o l i g o c h a e t e / c h i r o n o m i d ratio (Table II) gene­
rally s h o w e d a n n u a l m e a n values from 4 4 . 3 °7o to
8 2 . 4 °/o at 10 a n d 20 m d e p t h s , a n d increased at 30
a n d 40 m , w h e r e the theoretical m a x i m u m was rea­
ched at t h e e n d o f t h e t h e r m a l stratification. The
values of this index significantly increased with
increasing d e p t h (r = 0.46, p < 0.001). A n inverse
c o r r e l a t i o n (r = - 0.57, p < 0.001) was f o u n d bet­
ween c h i r o n o m i d diversity a n d o l i g o c h a e t e / c h i r o ­
nomid ratio.
T h e statistical c o m p a r i s o n s p e r f o r m e d o n several
p a r a m e t e r s of t h e c o m m u n i t y structure (i.e. density
of taxa, percentages, diversity, total density a n d bio­
m a s s , etc.) by m e a n s of the n o n - p a r a m e t r i c Wilc o x o n test ( E a s o n et al. 1980) did n o t suggest any
(4)
clear pattern in the c h i r o n o m i d spatial distribution
and seasonal variation a m o n g the three sites, so that
such aspects are not considered.
T h e P C A analysis (Fig. 4, T a b l e III) was perfor­
m e d o n a set of 48 d a t a (8 d e p t h stations per 6 s a m ­
pling visits). T a x a occurring with percentages lower
t h a n 1 % of the total c h i r o n o m i d fauna were not
considered (taxa 1, 2, 12, 15 in T a b l e II). T h e first
two principal c o m p o n e n t s a c c o u n t e d for 53.5 % of
the total variance. T h e second factor separates most
of the 10 m stations from t h o s e situated in the dee­
pest area of t h e lake. T h e latter stations a r e o r d e ­
red a l o n g factor 1 according to a gradient of d e p t h .
In fact, excluding 10 m stations f r o m the previous
pool of d a t a , there is a highly significant correla­
tion (r = 0.89, p < 0.001) between depth a n d 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
Eigenvalue
Variance accounted for (%)
Principal
1
Components
2
3.98
36.2
1.90
17.3
Variables
Micropsectra
Procladius
Microtendipes
Tanytarsus
Paratendipes
Cryptochironomus
Polypedilum
bicrenatum gr.
Cladopelma lateralis gr.
C. laccophila gr.
0.85
0.81
0.73
0.72
6.51
0.85
0.76.
0.57
0.55
4. Discussion
C h i r o n o m i d s of L a k e Vico were essentially cha­
racterized by densities a n d biomasses strongly
infuenced by increasing depth. Diversity values indi­
cated a m o r e diversified c o m m u n i t y at 10 a n d 20 m ,
whereas a m o r e simplified a n d m o n o t o n o u s struc­
ture was generally present at 30 and 40 m , especially
during the stratification period when the oxygen
deficit c o m e s into effect.
A clear picture of t h e d e p t h distribution of chi­
r o n o m i d s is provided by t h e plot of the sampling
stations derived from t h e P C A analysis. It describes
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187
C H I R O N O M I D S C O M M U N I T I E S O F LAKE VICO
Table II : Mean a n d range of density, number of taxa, diversity and oligochaete/chironomid ratio of sublittoral a n d profundal chironomids at the sampling sites and depths in Lake Vico. Proctadius choreus (Meigen), Cladopelma virescens (Meigen),
Microtendipes
cf. pedellus ( D e G e e r ) and Paratendipes aibimanus (Meigen) resulted from the adult identification.
Sites
Depth (*)
l.PsKtrgçUdjM
Nueber al ts»i
lin.
nan
2.5*
2.22
l.îî
55.7
il.B
13.9
**.J
50.0
82.i
3M
57.1
92.B
"M
65.4
95.7
188
M. S E M I N A R A , M. BAZZANTI, C. T A M O R R I
J
Fig. 2 : Densities ( i n d / n r ) and biomasses (g/m ) of the total chironomids at sites A, B and C and depths.
Interrupted lines indicate annual mean values.
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CHIRONOMIDS COMMUNITIES
O F L A K E
SITE A
SITE B
10m
10m
13
2.10
1,8,12.15
20
I"
189
VICO
1
40
0
20
20 m
40
601
20m
10
1,6 7 . 1 3 , 1 4
6,13
20
40
60%
40
ISITE C|
30 m
20
60%
60%
10m
[i
M.8,12
40 m
110
D
}
20
40
20
40
60%
60%
111
110
16 7 14
20 m
40
60%
F i g . 3 : A n n u a l m e a n p e r c e n t a g e s o f t a x a o n t h e t o t a l c h i r o n o m i d s a t t h e s a m p l i n g sites a n d d e p t h s . T a x a n u m b e r e d a s in T a b l e I I .
190
M . S E M I N A R A , M . BAZZANTI, C. T A M O R R I
2
y-'
2
2
2
®a
/2
*
/'
1
X
/
V
2 2 %
2
,'3 3
!3
2
(8)
"~3?
1 /
/ ,
•
:1
1
1
1
v :
\ 4 \
3
1/
M
\ 3
©
1
;
'"•4 4 ;
Fig. 4 : Plot of factors I and 2 of the P C A analysis. Numbers 1, 2, 3 and 4 indicate the 10, 20, 30 and 40 m depth stations, respectively.
Circled n u m b e r s represent centroids.
the s e p a r a t i o n of t h e sublittoral stations at 10 m
f r o m t h o s e at d e p t h s of 20, 30 and 40 m , which
represent the true profundal zone with homogeneous
e n v i r o n m e n t a l features. T h e a r r a n g e m e n t of 20, 30
a n d 40 m d e p t h s along F l indicates that t h e chiro­
n o m i d structure in Lake Vico (i.e. p r o p o r t i o n of the
m o s t relevant taxa) substantially remained the same
a l o n g the depth gradient, changing mainly as a result
of a g r a d u a l loss of taxa a n d lowering of absolute
densities. Typically profundal c h i r o n o m i d s resulted
t o be Micropsectra,
Procladius,
Microtendipes,
Tanytarsus a n d Paratendipes. A m o n g t h e m , Microp­
sectra appeared m o r e closely linked to the deeper
part of the lake {Fig. 3 and Table III). T h e other
genera were well represented at all d e p t h s , but they
were almost the only taxa present in the profundal
of the lake. O n the c o n t r a r y , the higher variability
in both occurrence and densities of chironomid taxa
a m o n g 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
g r o u p of 10 m stations should be ascribed t o a dis­
tinct sublittoral zone with characterizing elements
such as Cryptochironomus,
Polypedilum
bicre-
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C H I R O N O M I D S C O M M U N I T I E S O F LAKE VICO
natum gr., Cladopelma
lateralis gr. a n d C. laccophila gr., well represented also in the littoral of the
same lake ( M a s t r a n t u o n o & La Rocca 1988). T h e
distinction between t h e sublittoral and the profundal zone is also s u p p o r t e d by the occurrence of taxa
exclusively present at 10 m s t a t i o n s , a n d of vegeta­
tion debris (mainly C h a r a c e a e ) only in t h e samples
from these d e p t h s . O t h e r a u t h o r s (i.e. Laville 1971,
L i n d e g a a r d 1980, Heinis 1989) already found t h a t
c h i r o n o m i d c o m m u n i t y structure shifts from a lit­
toral to a p r o f u n d a l p a t t e r n showing t h a t t h e inter­
mediate e n v i r o n m e n t a l character of the sublittoral
zone is often related t o changes in s u b s t r a t e type,
food availability, oxygen content, water quality, etc.
A similar picture has been observed also for lacus­
trine m a l a c o c o e n o s e s ( M o u t h o n 1989), m a k i n g it
a p p a r e n t that m a n y benthic animals are distributed
along a d e p t h - d e p e n d e n t e n v i r o n m e n t a l gradient.
Chironomids can also provide useful trophic indi­
cations for L a k e Vico. U n f o r t u n a t e l y , t h e absence
of the required indicator t a x a a n d the lack of speci­
fic identifications m a d e it impossible t o evaluate the
lake t r o p h y level by m e a n s of Saether's t r o p h i c key
(Saether 1979), b u t the occurrence of good q u a n t i ­
ties of Tanytarsini s h o u l d traditionally lead to the
assessment of a m e s o t r o p h i c condition of the p r o ­
fundal sediments (cf. T h i e n e m a n n 1925 & 1954,
Brundin 1949 & 1956). Indeed, especially in recent
decades, the specific identification of taxa belonging
t o this g r o u p has been strongly r e c o m m e n d e d for
a better c o m p r e h e n s i o n of the relationship a m o n g
these taxa a n d the t r o p h i c level of lakes. In fact, i.e.
the genus Tanytarsus holds species with very diffe­
rent ecological sensitivity, varying from oligotrophy
t o slight e u t r o p h y (Reiss & Fittkau 1971, Saether
1979, Kansanen et al. 1984, Gerstmeier, 1989b).
Conversely, a reliable m e s o t r o p h y indication is p r o ­
vided by the presence in large a b u n d a n c e s of
Micropsectra,
considered as an oligo-mesotrophic
taxon with a n a r r o w t r o p h i c range even at the level
of genus ( W i e d e r h o l m 1973 & 1976, Saether 1979,
W i e d e r h o l m & E r i k s s o n 1979, Gerstmeier 1989b).
T h u s , this taxon can be considered as a key indica­
tor in detecting future trophic changes in Lake Vico.
T h e other c o m m o n genera were all eurytopic forms
living in a wide t r o p h i c r a n g e , with t h e exception
of the traditionally e u t r o p h i c Chirortomus
plumosus gr.
T h e o l i g o c h a e t e / c h i r o n o m i d ratio seems t o con­
firm the diagnosis of m e s o t r o p h y indicated by the
191
previous considerations. In fact, t h e values registe­
red in Lake Vico are lower t h a n those r e c o r d e d at
the s a m e depths in slightly t o strongly e u t r o p h i c
waters of Central Italy (Bazzanti & Seminara 1987a
& 1987b, Bazzanti & S e m i n a r a 1988, S e m i n a r a &
Bazzanti 1988). M o r e o v e r , the inverse trend of this
environmental index and of the chironomid diver­
sity with respect to depth is indicative of t h e suita­
bility of this latter in m o n i t o r i n g ecological chan­
ges a l o n g a depth gradient, as already observed for
entire benthic communities (Bazzanti & S e m i n a r a
1987c, Bazzanti & Seminara 1988).
In synthesis, according t o chemical data, t h e s u b littoral a n d profundal c h i r o n o m i d s of L a k e Vico
indicated a mesotrophic condition of the w a t e r s .
However, emphasis should be laid o n the t e n d e n c y
t o w a r d s increasing t r o p h y in the deepest layers of
the hypolimnion, as revealed by high values of total
P , the occurrence of s u m m e r - a u t u m n oxygen deple­
tion, reduction of diversity a n d a b u n d a n c e s of chi­
r o n o m i d c o m m u n i t i e s , a n d c o n s t a n t l y high values
of o l i g o c h a e t e / c h i r o n o m i d r a t i o .
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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