Annls
Limnol.
21 ( 3 ) 1 9 9 1 ; 2 8 7 - 2 9 8
Sandy bottom macroinvertebrates in two moderately polluted
stations of the River Treia (Central Italy) : structural and
functional organization
M.
Bazzantii
K e y w o r d s : S a n d y b o t t o m , m a c r o i n v e r t e b r a t e s , c o m m u n i t y s t r u c t u r e , functional feeding g r o u p s , m o d e r a t e pollution, river.
A s t u d y o n s a n d y b o t t o m m a c r o i n v e r t e b r a t e s in t w o m o d e r a t e l y p o l l u t e d s t a t i o n s o f t h e R i v e r T r e i a ( C e n t r a l I t a l y )
w a s c a r r i e d o u t in o r d e r t o a n a l y z e t h e i r s t r u c t u r a l a n d f u n c t i o n a l feeding o r g a n i z a t i o n . A lotal o f 6 0 t a x a were collected
d u r i n g the s t u d y . O l i g o c h a e t a , G a m m a r i d a e , D i p t e r a - C h i r o n o m i d a e a n d E p h e m e r o p t e r a c o n s t i t u t e d the bulk o f t h e l o t a l
f a u n a . M o s t o f t h e t a x a w e r e typical o f s a n d y b o t t o m h a b i t a t s a n d m o d e r a t e c u r r e n t flow. C o l l e c t o r s and s h r e d d e r s
w e r e t h e d o m i n a n t feeding g r o u p s in b o t h s t a t i o n s . P r e d a t o r s w e r e s t r o n g l y a n d p o s i t i v e l y c o r r e l a t e d w i t h the a b u n d a n ces of c o l l e c t o r s a n d s h r e d d e r s ( p o t e n t i a l p r e y ) . M o r e o v e r , t h e direct r e l a t i o n s h i p s f o u n d b e t w e e n t a x o n o m i c a n d t r o p h i c
diversities o r b e t w e e n t a x o n o m i c a n d t r o p h i c e v e n n e s s suggest a relatively g o o d p a r t i t i o n i n g o f f o o d r e s o u r c e s a m o n g
t h e t a x a . T h e m o s t c o m m o n o r g a n i s m s f o u n d in b o t h s t a t i o n s were typical o f m e s o s a p r o b i c e n v i r o n m e n t s , i n d i c a t i n g
t h a t t h e m a c r o f a u n a o f fine s e d i m e n t s s e e m s t o be s u i t a b l e for d e t e c t i n g m o d e r a t e o r g a n i c p o l l u t i o n in r i v e r s .
M a c r o i n v e r l é b r é s des s u b s t r a t s s a b l e u x d e d e u x s t a t i o n s m o d é r é m e n l p o l l u é e s d e l a rivière T r e i a ( I t a l i e c e n t r a l e ) : o r g a n i s a t i o n s t r u c t u r a l e et f o n c t i o n n e l l e
M o t s clés : S é d i m e n t s s a b l e u x , m a c r o i n v e r t é b r é s , structure d e c o m m u n a u t é , g r o u p e s f o n c t i o n n e l s , pollution modérée, rivière.
La s t r u c t u r e d e la c o m m u n a u t é et l ' o r g a n i s a t i o n f o n c t i o n n e l l e a l i m e n t a i r e d e s m a c r o i n v e r t é b r é s d e s s u b s t r a t s s a b l e u x
o n t é t é é t u d i é s d a n s d e u x s t a t i o n s m o d é r é m e n t p o l l u é e s d e la rivière T r e i a (Italie c e n t r a l e ) . 6 0 t a x o n s ont été r é c o l l é s .
O l i g o c h a e t a , G a m m a r i d a e , D i p t e r a - C h i r o n o m i d a e et E p h e m e r o p t e r a c o n s t i t u e n t la p l u s g r a n d e p a r t i e d e la f a u n e . P r e s q u e t o u s les t a x o n s s o n t t y p i q u e s des m i l i e u x s a b l e u x à vitesse d e c o u r a n t m o d é r é e . C o l l e c t e u r s et b r o y e u r s sont les g r o u pes f o n c t i o n n e l s a l i m e n t a i r e s d o m i n a n t s . L ' a b o n d a n c e d e s p r é d a t e u r s est bien c o r r é l é e a v e c celle des c o l l e c t e u r s et des
b r o y e u r s ( p r o i e s p o t e n t i e l l e s ) . E n o u t r e , les r e l a t i o n s d i r e c t e s e n t r e la d i v e r s i t é t a x o n o m i q u e et la diversité t r o p h i q u e
o u l ' é q u i t a b i l i t é t a x o n o m i q u e et l ' é q u i t a b i l i t é t r o p h i q u e m o n t r e n t u n e b o n n e r é p a r t i t i o n d e s r e s s o u r c e s a l i m e n t a i r e s e n t r e
les d i f f é r e n t s t a x o n s . L e s o r g a n i s m e s d e s d e u x s t a t i o n s d e l a rivière s o n t p o u r la p l u p a r t t y p i q u e s des milieux m é s o s a p r o bes et i n d i q u e n t q u e la m a c r o f a u n e d e s s u b s t r a t s fins s e m b l e bien refléter l ' é t a t des r i v i è r e s , l o r s q u e la p o l l u t i o n o r g a n i q u e est m o d é r é e .
1.
Introduction
( D o l é d e c 1 9 8 7 ) t h a t is o f t e n u n d e r e s t i m a t e d
of the greater recovery efficiency
T h e ecological effects o f o r g a n i c p o l l u t i o n o n lotie
macroinvertebrates
have
been
long
recognized
( H y n e s 1960, Klein 1962, H a w k e s 1979, Hellawell
1978,
1986, a n d o t h e r s ) . W h e r e a s heavy o r g a n i c pol-
lution generally p r o d u c e s drastic effects o n t h e bent h i c f a u n a , m i l d o r m o d e r a t e o r g a n i c e n r i c h m e n t is
less r e c o g n i z a b l e ( H y n e s 1960, 1970, C o o k
and can constitute an insidious form of
1976),
pollution
of lotie
because
waters
w h e n c o m p a r e d with lentic ecosystems.
It is g e n e r a l l y a c c e p t e d t h a t r i f f l e c o m m u n i t i e s a r e
m o r e sensitive to o r g a n i c p o l l u t i o n than c o m m u n i ties i n h a b i t i n g s l o w e r
flowing riverine z o n e s
(cf.
H a w k e s 1979, G o l d m a n & H o m e 1983, W h a t t o n &
H a w k e s 1 9 8 4 ) , a n d in f u n d a m e n t a l a n d a p p l i e d s t u d i e s , b i o l o g i c a l c o m m u n i t i e s in soft s u b s t r a t e
and
low current velocity have often been neglected, even
if g o o d r e s u l t s h a v e b e e n r e c e n t l y o b t a i n e d
I. Dipartimemo di Biologia Animale e dell'Uomo, Unîversità
• La Sapienza », vtale deU'Università 32. 00185 Roma, Italia.
(Cook
1976,
W h i t m a n & C l a r k 1984, R a e 1985, M c C u l l o c h
1986,
Roeding & Smock
Article available at http://www.limnology-journal.org
or http://dx.doi.org/10.1051/limn/1991021
1989).
M. BAZZANTI
288
O n t h e o t h e r h a n d , d e o x y g e n a t i o n , w h i c h is t h e
m a j o r f a c t o r i n v o l v e d in o r g a n i c p o l l u t i o n ,
affects
(2)
t w o s t a t i o n s (fig.
2) a n d i n d i c a t e d a m o d e r a t e o r g a ­
nic p o l l u t i o n revealed by values of N a n d P
com­
t h e o r g a n i s m s living b o t h in h a r d a n d soft s u b s t r a t a ,
p o u n d s , exceeding those of unpolluted waters
according to the different oxygen d e m a n d and pol­
T u m p l i n g 1969, Nisbet & V e r n e a u x 1970, S c h m i t z
(cf.
lution t o l e r a n c e of t h e various species
inhabiting
et al. 1979, L e c l e r c q & M a q u e t 1987). T h e o x y g e n
macroinvertebra­
content was high a n d B O D values were low d u r i n g
tes of soft b o t t o m habitats with a low current velo­
the year, indicating a good self-purification of the
city m a y b e efficient t o detect c o m p l e m e n t a r y infor­
river. Benthic f a u n a was s a m p l e d b y m e a n s of a d r a g
m a t i o n t o assess a m o d e r a t e state of organic pollu­
n e t ( C u m m i n s 1 9 6 2 , H e l l a w e l l 1978) p u s h e d t h r o u g h
tion of
t h e s t r e a m b o t t o m a t a f i x e d d e p t h o f a b o u t 10 c m
t h e m (Klein 1%2). Consequently,
In
rivers.
1978, a research program promoted
ACEA
(« A z i e n d a
Comunale
by
the
Energia
e
A m b i e n t e ») w a s c a r r i e d o u t in o r d e r t o a s s e s s t h e
w a t e r q u a l h y in t w o s i t e s o f t h e R i v e r T r e i a ,
Cen­
tral Italy (Ferrero, unpublished report). In the pre­
sent paper, data on the macroinvertebrate c o m m u ­
nities o f t h e s e t w o s a m p l i n g sites with c o m p a r a b l e
characteristics (sandy substrate a n d low current flow
prevailing) are reported with the following aims :
a) t o c o n t r i b u t e to the knowledge of the structu­
ral a n d functional p a r a m e t e r s of the macroinverte­
b r a t e c o m m u n i t y o f soft s u b s t r a t e s in
moderately
p o l l u t e d w a t e r s , c o n s i d e r i n g t h a t r e l a t i v e l y little d a t a
h a v e b e e n published a b o u t this type of habitat ;
b) to confirm the value as a bioindicator of the
s a n d y b o t t o m f a u n a in relation to the c h e m i c a l dia­
gnosis of the surface
water.
2. Site description and
a n d d r a g g e d u p s t r e a m f o r a l e n g t h o f 0 . 5 m in o r d e r
t o c o m p l e t e l y r e m o v e 0 . 1 5 m^ o f s e d i m e n t . T h e n e t
h a d a f r a m e of 30 x 20 c m a n d a 0.28 m m
mesh
opening. At each station, two samples were collec­
ted a c r o s s t h e river b e d at a b o u t 0 . 3 m d e p t h . M a t e ­
r i a l w a s p r e s e r v e d in t h e l a b o r a t o r y a t l o w t e m p e ­
rature and sorted out within two days. Macroinver­
t e b r a t e s w e r e p i c k e d live b y h a n d , s t o r e d in 7 0 ° a l c o ­
h o l a n d identified at t h e lowest p o s s i b l e t a x o n o m i c
level. T h e n u m b e r s of o r g a n i s m s f r o m t h e t w o s a m ­
ples p e r station w e r e a v e r a g e d a n d t h e results e x p r e s ­
sed a s n u m b e r / m ' . O r g a n i s m s were assigned t o t h e
functional feeding categories according to Merritt
&
Cummins
(1984)
and
Cummins
&
Wilzbach
(1985). Diversity a n d evenness indices (Pielou 1969)
were performed
on both taxonomic and
feeding
g r o u p n u m b e r s . Similarity was calculated by m e a n s
o f P S c i n d e x ( W h i t t a k e r & F a i r b a n k s 1958) a n d t h e
results reported in d e n d r o g r a m s following
methods
UMPGA
(unweighted pair g r o u p using mathematical avera­
T h e River Treia (drainage basin area : 497 km^)
ges)
clustering
method
(Sneath
&
Sokal
1973).
is l o c a t e d N o r t h o f R o m e in t h e v o l c a n i c district o f
A c c o r d i n g t o W i l l i a m s et a l . ( 1 9 6 9 ) , a m a t r i x o f c o r ­
t h e S a b a t i n i M o u n t a i n s . It o r i g i n a t e s f r o m
r e l a t i o n c o e f f i c i e n t s (r) u s i n g all s a m p l e s f r o m
several
the
s p r i n g s a n d a f t e r a b o u t 35 k m f l o w s i n t o t h e R i v e r
t w o sites (considering seasonal s a m p l e s as replica­
T i b e r (fig.
sewage
tes) w a s c a l c u l a t e d t o e x a m i n e r e l a t i o n s h i p s a m o n g
f r o m a n u m b e r o f t o w n s l o c a t e d i n its d r a i n a g e b a s i n
structural a n d functional p a r a m e t e r s of the c o m m u ­
1). T h e T r e i a r e c e i v e s d o m e s t i c
a n d n u t r i e n t s from agricultural a n d p a s t u r e activi­
n i t y . S i g n i f i c a n c e in s o m e c o m m u n i t y c h a r a c t e r i s ­
ties in s u r r o u n d i n g a r e a s . D e t a i l e d d e s c r i p t i o n s o f
tics b e t w e e n t h e t w o stations w a s calculated b y t h e
geological and botanical characteristics of the zone
non-parametric
can
r a n k s t e s t ( E a s o n et a i . 1 9 8 0 ) . F i n a l l y ,
be found
in A l v a r e z
( 1 9 7 2 ) a n d B l a s i et
al.
Wilcoxon
matched-pair
signedPrincipal
(1981), respectively. Since 1988, m o s t of the drai­
C o m p o n e n t A n a l y s i s ( P C A ) , w i d e l y u s e d in a q u a ­
n a g e basin area of t h e River Treia has been part of
t i c e c o l o g y , w a s a p p l i e d t o l o g (x -i- 1) t r a n s f o r m e d
a
densities of taxa and functional
suburban
Viterbo and
park
located
the
from the stations A and
180 m a.s.I. a n d 4 0 m a.s.l.,
of
B
respectively)
w e r e c o l l e c t e d six t i m e s f r o m J a n u a r y t o
1978.
cities
feeding
groups.
Rome.
Macroinvertebrates
(about
between
October
S a m p l e s were restricted to a sandy b o t t o m area
with a relatively low current speed (generally <
30
c m / s ) . T h e w a t e r q u a l i t y w a s r a t h e r s i m i l a r in t h e
3.
Results
3 . 1 . C o m p o s i t i o n , c o m m u n i t y structure and func­
tional
organization
A t o t a l o f 60 t a x a , m o s t l y b e l o n g i n g t o
Diptera-
C h i r o n o m i d a e (24), O l i g o c h a e t a (15) a n d E p h e m e r o p t e r a
(3)
289
SANDY BOTTOM MACROINVERTEBRATES IN THE RIVER TREIA
CampagnanosX
Fig. 1. M a p of the River Treia showing the two sampling stations.
(10), were collected during the s t u d y (Tables I a n d
B. A positive correlation between taxonomic
II). T h e most a b u n d a n t g r o u p s were O l i g o c h a e t a ,
feeding g r o u p diversities (r = 0 . 9 2 , p < 0 , 0 0 1 ) a n d
Gammaridae, Diptera Chironomidae and Epheme­
between t a x o n o m i c a n d feeding g r o u p evenness was
r o p t e r a {fig.
found. Since the t w o indices displayed a very simi­
3).
and
lar p i c t u r e , o n l y t h e e v e n n e s s v a l u e s are g r a p h i c a l l y
In
both
stations,
total
collectors
(almost
all
r e p o r t e d h e r e ifig.
4). Figures 5 and 6 illustrate a
collector-gatherers) and shredders were the domi­
significant
nant groups (Table III), together reaching an annual
densities
average percentage of 87.7 % in A a n d 89.2 %
collector-gatherers) and shredder
in
positive correlation
and
both
total
between
collector
predator
(particularly
densities.
M . BAZZANTI
290
(4)
mg/1
A
1 0 ^
DO
•
B O D 5
0
NH4*
m
•
/
NO2
i
NO3
•
10°-
/ m
0
10-'-
y/A
X
10^-
^
A
'-2 °
'
'-1
1 0
10
10°
10'
mg/l
Station
A
Fig. 2. Chemical comparison of the two stations (data from December 1977 t o October 1978). Median line indicates equal concentra­
tions of chemical parameters. Points above the line indicate higher concentrations at Station B and points below the line indicate
higher concentrations at Station A .
3 . 2 . Differences between the two
The
stations
absolute
numbers
of
total
collectors,
collector-gatherers a n d p r e d a t o r s were higher in A
A s i m i l a r n u m b e r o f t a x a ( 4 6 in A a n d 4 0 in B)
w a s collected d u r i n g the s t u d y , 27 of w h i c h
t h a n in B ( T a b l e IV), but n o significant
differences
being
w e r e r e c o r d e d i n t h e p r o p o r t i o n s o f all t h e f e e d i n g
p r e s e n t in b o t h s t a t i o n s ( T a b l e s I a n d II). O n l y Oli­
categories. C o m p a r e d with the P S c results using taxa
gochaeta,
a b u n d a n c e , PSc d e n d r o g r a m based on the relative
Hirudinea
and
Chironomidae
resulted
significantly m o r e a b u n d a n t in station A t h a n in B
a b u n d a n c e of the feeding groups shows a
(Table IV). C o n s i d e r i n g the most a b u n d a n t species
s i m i l a r i t y b e t w e e n t h e s t a t i o n s (fig.
i n b o t h s t a t i o n s , Psammoryclides
t a x o n o m i c a n d feeding g r o u p diversities a n d even­
dritus
hoffmeisten,
Polypedilum
Dina
scalaenutn
Uneata,
(syn.
barbatus,
Caenis
Limnosp.
and
breviantennatum)
o c c u r r e d in h i g h e r d e n s i t i e s i n A t h a n in B .
PSc
8).
higher
Although
n e s s s h o w e d a g r e a t e r n u m e r i c a l v a r i a t i o n in s t a t i o n
B t h a n in A , n o significant d i f f e r e n c e s w e r e n o t e d
in the values of these indices (Table IV). T h e hig­
a r r a n g e m e n t of t a x o n o m i c d a t a during the sampling
her variability in m o s t of the c o m m u n i t y
p e r i o d ifig.
of
ters at station B can be partly ascribed to t w o fac­
50 % )
t o r s : a) t h e higher n u m e r i c a l presence of o p p o r t u ­
7) r e v e a l e d a q u i t e clear s e p a r a t i o n
the t w o stations a n d a strong similarity ( >
only within station A
samples.
parame­
nistic t a x a , such as N a i d i d a e , w h i c h rapidly increase
(5)
SANDY B O T T O M M A C R O I N V E R T E B R A T E S IN T H E RIVER T R E I A
291
Table I. Macroinvertebraie taxa collected at Station A. Densities are r e p o n e d as follows : 0 = absent ; 1 = l - l O i n d / m ' ;
2 = I MOO ind/m^ ; 3 = 101-iOOO ind/m= ; 4 = 1001-5000
i n d / m ^ Letters in parentheses indicate feeding categories ;
Jtfi.
F,b. Apr. Jun. Aug.
Oct,
CG = Collector-gatherers. C F = Collector-filterers, P
OLieOCNAETD
e n s t i ! ' umtU h u r w ICB)
PriïtlOÉ >P. 'CBI
COHU!!!! Piîuït (CSI
N, Umi I""ll.r) (CGI
«UOWi! ItolKr (CB)
DfTO d i l i t i t i llttllKl (CBI
l l K l H t l CPiïuitl ICG)
i l l M e r i ç U m fcirt*t«! 'Srub.l (CG)
^ î i M t h r i ï t i ï g U ï ! IDichunn) ICG)
i M i t w i tnklflcidi lith mir c h u t » (C6i
UBWfrUtI l l i î a i i t ç r i Cltptrldi ICEI
U a U K r i l i » ! ! «*titl 'CG)
I, mMm\
CUpiTMi (CG)
Lmbriculidit ICSI
Table II. Macroinvertebrates taxa collected at Station B. Den-
O-ii*
sities a n d feeding categories are reported as in Table I.
MMiiii
mmm
Çl!» U!!»*ti (Hun^l (PI
Mmm
mmi
a.i if)
=
P r e d a t o r s , SH = Shredders, SC = Scrapers.
till
Uti. Fib. M'- Jun. hiq.
2 21 \
1
1
7
2
2
Oct.
tixa
XISOCHKIA
Oghidoniig w { M t t M (HùlUrl (CG)
!!ir?ii5S!!ir«îîi^''CBI
bfrbitM (Grub.) (CGI
iiMture tubificiil; «ith hiir cKietit (CGI
U«9«j:il!l! hûHHiitçri Clip.r.ds ICG)
( (C6)
Encliytr«id« (CGI
ci!* lioï?!? '""iKri (PI
ANPHIPDDA
ISOPOM
EîbinogiiMruï mm^
?t9n?Uw t c . j l i i Mli. (SHI
<SH)
I5DP0DA
PLECDPTERA (SH, t)
P ; S ! H l l ï ! E ! ï i U ! » « l l * ' ISHl
mimmm
Çmi* l>içtu«i lBur«ut»r) (Cfi, SCI
ÇmqI» IP. (C6, sci
1851!»
ICG, SCI
Ç'ntrWtilM lulMlM INull*r) (CB, SC)
HibroBMib.i fuiH ICuftill (CB, SC)
PLECDPIERA (SH, PI
mtVJJMi
£«e«BOPIER«
ISbUS?!!!» wtl!!!!!:!! ""L-U»') (CG, SCI
Ecdïonurui ip. ICG, SCI
Bjêtîrriefnui Curtis ICG, SCI
B. riiodani (Pictït) (CG. SC)
gUlûneBr.eUi rhjniM U.hoffl (CFI
Ç«ai!
IBui-Mistfr) ICS, SC)
Çiwiï ip. (CB, SCI
EBbSKt!!!* mM 'P="l" ICS. SCI
OSONATA
-MHiKI'. itTfllCHDPtER*
HydroptycliiilJt (CF, P)
COLEOPtEH»
Eliidu <ce. 50
DIPIERA Chireneiid4i
I
ÇtttÇtOBM i.ïV.VMî '"^tiitn) (Cfi, S*»
8!!«ç[içoig!«it fiimvAiw: 'cs, s«, pi
PlIOdlJieH QiUKU "«19" I " )
Pntineurini IPI
fflCtW?!??!! tp./spp. (P)
^!«t[9t!îï!!!!
f»brlciui IP)
ImUmi w.'m- (C6, CF)
Çli<9t«it,rMi»p./w (CG, Cn
?t!Mt!!!«IÎW! ip.'spp- ICF)
PoLIEHUm briviMtMnitM Chrfi. ICB, SH, PI
P'ritMdieti «./!pp. (CB)
P!!«!!M»«trf ip./spp. ICB, SC)
ÇtntKbtt»!!"!!» «».'*|IP- IP)
^^Amm thuwi gr. ICS, SH)
!
2
t
0
2
0
1
!
2
1
2
0
Z
DIPTERA ChirmMidM
OrthgcUdius sp./ipp. ICG)
ÇclÇotom iiciQctw ("«ig»»! <CG, 5H)
Ça!:t?!!!!lilitï! Il^cg-' ICB. SHI
«fc'KtimSÎÏÎ r*<«S!:<!»t»[ ICS. SH, P)
P»C»tnçhgçUSLS» *P.'»PP. (CSI
Ç h « M i w : l ! l - r p b « P y ! ICS, SCI
P*r»«tnoç!!««5 'P^/^PD. ICS, SCI
Çorïaoneurj ip./ipp. fCSl
tjtimtfinnitlU sp./spp, <C6)
P»ntifiHirini (P)
!!iÇ[9E1«trJ ip./spp. (CBI
DIPTEBll CirttopajNidit ICB, P)
ImU'.m v-'m- icg, cfi
Çl»^9ÎMïti:»y! s p - ' W . (CG, CFI
••îwtîMt'rws sp./tpp. ICFI
PolïEBililut brdriatitNnitui Chtrn. (Cfi, SH, PI
Pi L « t l ! ! V- ICS, SH. P)
PKltwdiH} (p./fpp. ICSI
BAStdOPQDA
tîmothirooMu» 4»./(pp, (PI
Pisidiui ipp. ICFI
eiVALVIA
PlsUiul spp. (CF)
DIPTERA Ctritopoqanidif (CB, PI
(6)
M . BAZZANTI
292
January
February
April
June
August
October
60
<
c
o
o
20-
A
^
O
r
AI
0
œ
c
o
S 40
55
60
80
lOQJ
%
Fig. 3. Seasonal relative abundances of the macroinvertebrate groups at the two stations during 1978.
O = Oligochaeta. A = A m p h i p o d a , E = Ephemeroptera, C = Chironomidae, Al = Alia.
2
2.5
3
3.5
Total Collectors (log number/m^l
Fig. 4. Linear relationship (two-tailed test) between taxonomic
(Jl) and feeding g r o u p (Jf) evenness. Circles and dots indicate
Station A and Station B values, respectively.
Fig. 5. Linear relationship (two-tailed test) between Toi.;
Collector and Predator densities. Circles and dots as Jr
Fig, 4 .
(7)
293
SANDY BOTTOM MACROINVERTEBRATES IN THE RIVER TREIA
Table IV. Significanee of Wilcoxon-tesI comparisons for absolute numbers of the most abundant taxa and of t h e functional feeding groups, a n d for community parameters between
the two stations (in all comparisons Station A > Station B).
n.s. = not significant. Only taxa present in both stations are
considered.
Totil
2
25
3
3,5
itmi
n,s.
Oligochaeta
p<0.l>5
Hirudinea
p<0,OS
Epheieroptera
r.s.
Chirotioaidae
p<0.<»5
Ceratopogonidae
S h r e d d e r s i l o g number/m^)
Fig. 6. Linear relationship (two-tailed test) between Shredder and
Predator densities. Circles and dots as in Fig. 4.
^1 §li!191ji§
K barbatus
L, i i o i f i e i s t e r i
D, î i Q e a t i
I: EÏOaÇO!
ÇafQis s p .
Itiçtyosa
ignita
Orthocladius sp./spp.
ÇrygtgçhirorjOfys sp./spp.
Paratendiges s p . / s p p ,
Çi
Fig. 7. Similarity (PSc) among stations (A and B) and dates, based
on macroinveriebrate taxa abundances.
Table III. Seasonal and annual mean (a.m.) values of functional feeding group percentages at the two stations. Feeding
categories as in Tables I a n d II ; T C = Total Collectors.
Jin.
FM.
TC
C6
CF
P
5N
SC
iO.O
58.2
1.!
3.5
31,1
0.1
71.7
TC
CG
Cf
P
91.1
i9.5
57.3
12.2
7t.5
3.2
5.5
18.5
1.3
«pr.
Jun.
lé.t 39.0
38.7
t5.5
1.1
0.3
Dug.
4.1.
J8.9
34.4
2.5
11.2
42.4
7,3
52.0
50.4
1.5
2.8
O.i
0.7
49.0
57.9
11.1
4.8
53.2
44.3
7,0
3.7
71,3
1.7
95.2
0.8
12.8
11.4
34.0
7.0
1.9
45.2
6.3
12.0
48.i
0.4
42.1
47.9
24.2
21.3
2.9
52.7
Oct.
52.2
0.5
21.4
23.0
1.1
n.s.
1'^'
p<0.05
p<0.05
P<O.OS
n-s,
p<0.D5
n.s,
n.s.
n.s.
n.s,
n,5.
^C?ïUDt?QQâty!
Pisidiyi spp.
p<0.05
Total C o l l e c t o r
p<0.O5
Collector-gatherer
p<0.05
Collector-filterers
Shredders
Scrapers
Predators
n.s.
n.s.
n.s.
n.s.
p<0.05
Kuiber of t a x a
n.s,
laionoiic diversity
n,s,
Taionoiic evenness
n,s.
F u n c t i o n a l f e e d i n g group d i v e r s i t y
n,s.
Functional feeding group evenness
n,s.
9.3
33.
7
3.1
in a b u n d a n c e o v e r a relatively short period o f t i m e
SH
SC
90.5
0.9
2.t
3.8
2.2
i.i
19.2
5.7
14.2
3.8
13.9
20.2
5,3
2.7
(Hughes
1 9 7 5 , R o d r i g u e z 1 9 8 4 ) , a n d b) t h e p o s t -
reproductive high percentages of
Echinogammanis
pungens.
P G A analysis using taxa abundances showed n o
consistent pattern in t h e spatial distribution a n d
294
M. BAZZANTI
(8)
Table V. Factor loadings of the first two principal components
from ordination of functional feeding groups, r = coeffi­
cient of correlation between principal component scores and
environmental parameters. Level of significance : - not signi­
ficant, • p < 0.05.
p < 0.01.
Principal
Factors
) Oct
B
Apr
B
Jan Feb Aug
A
•
1
Eigenvalue
Fig. 8. Similarity (PSc) among stations (A and B) and dates, based
on functional feeding group abundances.
Variance account (or
Coiponents
(II
2
2,78
1.14
55.70
22.90
Variables
s e a s o n a l v a r i a t i o n s a m o n g tlie s a m p l e s , s o t h a t the
g r a p h i c is n o t r e p o r t e d i n t h i s p a p e r .
P G A based o n functional
(fig.9
Conversely,
feeding g r o u p
densities
a n d Table V) illustrates a clear s e p a r a t i o n of
station
A
from
station
B.
Predators,
collector-
gatherers and shredders resulted the m a j o r variables
of
PCI,
while
collector-filterers
and
Predators
0,94
Collector-gatherers
0,92
Shredders
0.71
Collector-filterers
0.B7
Scrapers
0.78
scrapers
influenced the definition of P C 2 . M o r e o v e r ,
PCI
scores were negatively correlated with D O values a n d
Coefficient
of c o r r e l a t i o n
(r)
positively with N 0 3 a n d N 0 2 c o n t e n t s (Table V).
T h e s e r e s u l t s s u g g e s t t h a t t h e a x i s is i n t e r p r é t a b l e
DO
as a g r a d i e n t of w a t e r quality a n d the
BOO
abundance
of predators, collector-gatherers a n d shredders were
N-N03
f a v o u r e d b y little increases o f o r g a n i c
N-N02
pollution.
-O.tO*
0,74«
0.5B»
N-NH4
4. Discussion and
The
two stations
P-P04
conclusion
supported
communities
with
partly different c o m p o s i t i o n a n d absolute densities
of s o m e taxa a n d of functional feeding g r o u p s . H o w e ­
ver, they also s h o w e d similar a n n u a l a v e r a g e diversity
a n d e v e n n e s s v a l u e s , a n d p r o p o r t i o n s o f f u n a i o n a l fee­
ding g r o u p s . This partial similarity was probably due
absent
from
the samples.
between
sediment composition have been already observed
in r i v e r s b y s e v e r a l a u t h o r s . T o l k a m p ( 1 9 8 2 ) r e p o r ­
to their similar substrate and water quality.
t e d Polypedilum
A s expected, the c o m m u n i t y in b o t h stations was
mainly composed
Relationships
s o m e m a c r o i n v e r t e b r a t e species a n d / o r g e n e r a a n d
of typical m a i n g r o u p s
(Oligo­
breviamennalum
and
Gammarus
preferring s a n d y s u b s t r a t e . R a e (1985) also
Paratendipes
as
a
characteristic
found
chironomid
of
chaeta, A m p h i p o d a , some E p h e m e r o p t e r a a n d Dip­
coarse sand, a n d M c C u l l o c h (1986) noted that
t e r a C h i r o n o m i d a e ) generally i n h a b i t i n g soft b o t t o m
nodrilus,
with a m o d e r a t e current flow ( H y n e s 1970,
Lear­
were mainly restricted to sandy substrates. Finally,
n e r et a l . 1 9 7 1 , W a r d
1979,
E d m u n d s (1984) considered Caen/s typical of d e p o -
Corkum
sitional h a b i t a t . All these observations are in agree­
Wielgosz
1989).
1975, B a r t o n & C o c k
1979, W h i t m a n & Glark
Conversely,
Plecoptera,
1984,
Trichoptera,
Polypedilum,
Paralendipes
and
LimCaenis
and
ment with the present data a b o u t some of the most
rheophilous Ephemeroptera were almost completely
a b u n d a n t a n d diffuse t a x a f o u n d in t h e R i v e r T r e i a .
295
SANDY BOTTOM M A C R O I N V E R T E B R A T E S IN T H E RIVER T R E I A
(9)
PC 2
Fig. 9. Plot of factors 1 and 2 of the P C A analysis. Circles and dots indicate Station A and Station B samples, respectively. R o m a n
numbers indicate sampling m o n t h s .
The dominance of collectors and shredders
in
dered i m p o r t a n t for processing C P O M into F P O M ,
b o t h s t a t i o n s is i n d i c a t i v e o f a r i c h q u a n t i t y o f f i n e
favouring
particulate organic matter ( F P O M ) a n d coarse par­
(Short & M a s l i n 1977). M o r e o v e r , t h e direct
the availability
of
ticulate organic matter ( C P O M ) . T h e s e results agree
tionships between t a x o n o m i c a n d trophic diversities
nvith t h e o b s e r v a t i o n s o f R a b e n i & M i n s h a l l ( 1 9 7 7 ) ,
and between t a x o n o m i c and trophic evenness indi­
fcvho e x p l a i n e d t h e p r e f e r e n c e o f d e t r i t i v o r e m a c r o i n ­
cate t h a t a n increase in t h e t w o structural p a r a m e ­
v e r t e b r a t e s f o r s a n d y s u b s t r a t e b e c a u s e it s e r v e d a s
ters o f t h e c o m m u n i t y i n d u c e s a l s o a n i n c r e a s e in
n better detritus food-collecting device than did the
specific feeding types a n d a m o r e equitable distri­
toarser bottom. Functionally, shredders are consi­
bution of
individuals a m o n g
food
them,
for
collectors
rela­
suggesting
a
M. BAZZANTI
296
(10)
q u i t e g o o d p a r t i t i o n i n g of f o o d resources a m o n g the
o r d e r t o test t h e g e n e r a l v a l i d i t y o f t h e s e o b s e r v a ­
taxa. Finally, the trophic relationship between pre­
tions, further studies o n rivers with different degrees
d a t o r s a n d their potential preys (i.e. collectors a n d
of organic enrichment are
s h r e d d e r s ) f o u n d in t h e River T r e i a w a s a l s o r e c o r ­
In
conclusion
our
required.
results
suggest
that
more
d e d in o t h e r lotie e n v i r o n m e n t s w i t h a different (or
emphasis should be placed on
m i x e d ) substrate c o m p o s i t i o n , and different chemi­
living in this t y p e o f s u b s t r a t e in f u t u r e
cal features of the water ( F a h y 1975, H a w k i n s &
r e s e a r c h e s , a l s o c o n s i d e r i n g t h a t , d e s p i t e its p h y s i ­
S e d e l l 1 9 8 1 , H i l d r e w et al. 1984, B u n n 1986. B a r -
cal instability d u e t o f l o o d s , this h a b i t a t can be v e r y
muta
c o m m o n a n d s o m e t i m e s d o m i n a n t in several lotic
1988).
W i t h respect to water quality, the macroinverte­
brate
fauna
comprised a
relevant
proportion
of
macroinvertebrates
stream
e n v i r o n m e n t s (i.e. l o w l a n d rivers, regulated rivers,
channels). According to Logan & Brooker
(1983)
G a m m a r i d a e a n d , t o a lesser e x t e n t , o f E p h e m e r o p ­
and Lenat (1988), studies of biological surveillance
tera, i.e. g r o u p s t h a t are notoriously sensitive
to
could be carried o u t o n the f a u n a of m o r e diverse
d e o x y g e n a t i o n (cf. H y n e s I 9 6 0 , H a w k e s 1 9 7 9 ) , in
type of h a b i t a t s , i n c l u d i n g soft b o t t o m s , to o b t a i n
o u r c a s e i n d i c a t i n g t h e a b s e n c e o f h e a v y o r g a n i c pwl-
c o m p a r a b l e d a t a o f use in p r o v i d i n g a m o r e relia­
l u t i o n in b o t h s t a t i o n s . I n p a r t i c u l a r ,
marus
pungens
is
usually
oligosaprobic-Bmesosaprobic
Echinogam-
considered
element
an
(Zelinka
ble a n d c o m p r e h e n s i v e diagnosis of the biological
w a t e r q u a l i t y in r i v e r s .
&
M a r v a n 1 9 6 1 , S l â d e c e k 1973) w h i c h c a n t o l e r a t e a
Acknowledgements
mild organic pollution (Watton & Hawkes
We wish lo thank Dr L. Ferrero for organizing the general
research on the River Treia and the following people for identi­
fication of some macroinvertebrate groups : Dr F. Baldari (P.
coxalis), Dr C. Belfiore (Ephemeroptera), Prof A. Minelli (Hiru­
dinea). Prof B. Rossaro (Chironomidae : Orthocladiinae), and
Prof S. Ruffo (E. pungens). Thanks are also due to Dr A. Borgioli for providing chemical data and the A C E A for permission
to publish them, Dr C. Tamorri for his valuable help with com­
puting, Dr N. Falchi for drawing the figures and Dr M. Seminara for typing the manuscript. Finally, two anonymous refe­
rees kindly provided comments on the manuscript.
1984).
A c c o r d i n g to G o o d n i g h t & W i t h n e y (1961), also the
percentages of Oligochaeta on the total macroinver­
t e b r a t e s , not e x c e e d i n g 80 % , c a n e x c l u d e f o r m s of
gross organic pollution and suggest a m o d e r a t e state
of o r g a n i c e n r i c h m e n t . At the s a m e time, the large
p r o p o r t i o n o f O l i g o c h a e t a r e c o r d e d in s o m e s a m ­
pling dates indicates an a b u n d a n t presence of orga­
n i c m a t t e r in b o t h s t a t i o n s . A c c o r d i n g t o c h e m i c a l
d a t a (cf. v a l u e s o f N c o m p o u n d s ) a n d P C A r e s u l t s ,
this fact seems to b e m o r e a c c e n t u a t e d at station A,
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