Rapp. Comm. int. Mer Médit., 36,2001
242
BIODIVERSITY OF DEMERSAL FISH IN THE SOUTHERN TYRRHENIAN SEA
(WESTERN MEDITERRANEAN)
BottariT.*, Giordano D., Perdichizzi F., Greco S.
Istituto Sperimentale Talassografico CNR Messina, Italy - greco@talas.ist.me.cnr.it
Abstract
The biodiversity of demersal ichthyofauna was analysed using the ecological indices of Shannon-Weaver (H’) and Pielou’s (E). The data
comes from seven Medits trawl surveys carried out from 1994 to 2000 in the Southern Tyrrhenian Sea. A total of 88 demersal fish species
was collected. Demersal fish diversity is strictly correlated with the depth.
Keywords: Biodiversity, demersal fish, Tyrrhenian Sea
Introduction
Studies on diversity in biological communities has been carried out
over the last twenty years by ecologists and applied to different
ecosystems. In particular, demersal fish biodiversity studies have been
carried out in different Italian seas, the North Tyrrhenian (1), the South
Adriatic (2) and the Ionian seas (3). The demersal fish biodiversity in
an area of the South Tyrrhenian Sea was analysed using the Shannon-
Weaver diversity index (H’) and Pielou’s evenness index (E).
Materials and methods
The data reported here was gathered during seven trawl surveys car-
ried out, from 1994 to 2000, during the Medits project (International
bottom trawl survey in the Mediterranean Sea) funded by the
European Community.
They were conducted every year between the end of spring and the
middle of summer.The study area was situated between Suvero Cape
(the Calabrian coast) and S. Vito Cape (the Sicilian coast) (Fig. 1). The
gear used had a small codend (20 mm, stretched mesh) and 2-2.5 m of
vertical opening (4). A total of 194 hauls were carried out randomly
allocated into 5 depth strata (A: 10-50 m; B: 51-100 m; C: 101-200 m;
D: 201-500 m; E: 501-800 m). All fish were identified and counted
(N/h), the mean number (1994-2000) of each stratum was calculated.
Pelagic species, occasionally collected by gear, were excluded for this
study, as well as the individuals with N/h values less than 4. For each
stratum and year the Shannon-Weaver (H’) and Pielou (E) indices
were calculated. Because the annual variations of both indices E and
H’were not significant, the mean index, calculated over the seven
years, has used (Tab. 1).
Fig.1 - Study area
From Suvero Cape (Calabria) do S.Vito Cape (Sicily)
Results and discussion
A total of 88 demersal fish species with 265.720 specimens were
collected in the study area. The diversity and evenness indices mean
values in five strata are reported in table 1. Generally the diversity and
evenness values showed a similar trend in accordance to the depth.
The H’and E indices showed the highest values in the B stratum with
2,96 and 0,7 respectively. In this stratum a mean of 23 species was
recorded with 8507 specimens. For the A stratum the diversity value is
also high (2,83) and the evenness index shows a value of 0,64. 20
species (mean value) were in this stratum found with a number of
specimens totalling 4384. The most abundant species in the first two
strata are Trachurus trachurus(n° specimens totalling 11014), Mullus
barbatus(n° specimens totalling 10944), Pagellus acarne(n° speci-
mens totalling 10840), Spicara ?exuosa(n° specimens totalling 8898)
andLepidotrigla cavillone(n° specimens totalling 6050). On the con-
trary the D stratum showed the lowest H’(2,12) and E values (0,47).
The most abundant species is Clorophtalmus agassizi(n° specimens
totalling 44334).
Tab.1 - Shannon-Weaver diversity index (H) and Pielou's (E)
values
(mean. s.d., min., max).
For the C stratum the diversity value is 2.55 and the evenness index
shows a value of 0,54. Finally in stratum E both H’(2,46) and E (0,60)
values were quite high.
Analysing the data here reported, it is clear that demersal fish diver-
sity is strictly correlated with the depth. The lowest strata (10-50 m
and 51-100 m) showed the highest biodiversity, but the stocks have a
low homogenity structure dued to many dominant species. The D stra-
tum (201-500 m) showed the lowest diversity because of the heavier
dominance of some species (C. agassizi, A. sphyraena, G. argenteus)
which often reach a number of specimens higher than the other species
that characterize the other bathymetric strata. On the contrary, in the
deepest stratum (501-800 m), although both the ecological indices
showed low values, the diversity is quite high because the species are
represented by homogeneus individual numbers. In particular, during
2000 this stratum registered the highest H’values (3,82) compared to
all other strata and years.
References
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16pp.
stratan of haulsH'means.d.H'minH'maxEmeans.d.EminEmax
A272.830.61.943.340.640.120.450.76
B272.960.61.643.310.70.140.330.72
C422.550.51.883.270.540.100.390.7
D492.120.51.182.420.470.120.240.62
E492.460.81.513.820.60.170.390.88
