Rapp. Comm. int. Mer Médit., 36,2001
247
Introduction
Researches about Adriatic cladocerans (the Gulf of Trieste) date back to
1876 (1) and many studies have been carried out in this area (2, 3) and in
the open Adriatic Sea (4). On the contrary, seasonal variations of cladocer-
an populations densities in the eastern part of Adriatic are mostly unknown
(2). Particular investigations were performed in Rijeka Bay (5), in Mali
Ston Bay (6, 7) and in the coastal region of the south Adriatic (8).
Study area
Station P-100 (fig.1.) is posi-
tioned extend from the coast, above
isobaths of 100 m, directly ex
p
o
s
e
d
to the incoming open sea current.
This is the zone of the lowest pro-
duction in the Adriatic Sea on the
base of concentrations of nutrition
(<0.2
µ
mol l
-
1
P
O
4
and <3µmol l
-
1
N
O
3
), primary production, abu
n-
dance of populations and phy
t
o-
plankton volumes, and bacterio-
plankton population densities (9,
1
0
)
.
Material and methods
Material was collected at P-100 station during 44 cruises from 16 May
1995 till 9 December 1996. Samples were taken with 200 µm Nansen net,
255 cm in length, 54 cm in diameter, by hauling speed of 0.5 ms
-1
, in the
depth layer 0-75m. All samples were preserved in 2.5% formaldehyde,
neutralized with a calcium carbonate buffer.
Results and discussion
At P-100 station a regular seasons successions of cladoceran species
was noted. Penilia avirostrisDana 1849 was dominant species (fig. 2.)
with portion of 97% in whole number of cladocerans with the maximum
number of 827 ind.m
-3
, found on 26 September 1996. P. avirostrisalways
dominated during the summer (2, 4, 6). Evadne spiniferaP. E. Müller 1868
was the second quantity important cladocera at this station. It is the most
common open water species with optimal salinity values of 38.1 psu that
clearly indicates the in?uence of open sea waters and stability of environ-
ment (11, 4). Maximum 31 ind./m
3
was found on 4 July 1996. (fig. 4.).
Evadne tergestinaClaus 1862 was noted from the beginning of July till the
end of October with maximum 7.6 ind./m
3
on 26 September. It was not
found during the winter (fig. 3.). E. tergestinashows similar seasonal ?uc-
tuations in abundance as P. avirostris.Evadne nordmanniLoven 1836 is
rare species at the investigated station. It is found in only 16% samples
(fig.3.), particularly represented in the winter period from 26 February till
17 May 1996. Maximum number of Podon intermediusLilljeborg 1901
(fig. 4.) 37 ind./m
3
was found on 23 May 1995. On the contrary, one year
later, on 24 May 1996 only one specimen was found. Adriatic cladoceran
speciesP. polyphemoideswas not found because it preferes low salinity
coastal waters. It is numerous in pollution harbor areas (12) as it is in
Marseilles Bay (13, 14). The observed changes show progressive in?uence
of open sea waters at P-100 station, despite of small vicinity of the inves-
tigated station from the coast.
References
1. Claus C., 1877. Zur Kenntniss des Baues und der Organisation der Polyphemoiden.
Denksckr d K K Akad Wiss Mat Naturw Wien37: p 138
2. Fonda-Umani S., 1980. I cladoceri dell’Adriatico: un “review” critico. Nova Thalassia
4: 107-133.
1. Lipej L., Mozetic P., TurkV., MAlej A., 1997. The trophic role of the marine cladoceran
Penilia avirostrisin the Gulf of Trieste.Hydrobiologia360: 197-203
4. Bender A., Cladocera in the open waters of the Adriatic Sea 1984 M. Sc. Thesis
University of Zagreb p. 181 (in Croatian with English summary)
5. Benovic A., VuceticT. and Skaramuca B., 1981. Joint investigations of the Rijeka Bay -
net zooplankton. Thalassia Jugoslavica17: 257-274
6. Onofri V., 1986. Mezozooplankton in the Bay of Mali Ston and the Neretva Channel
during 1979-1980. Studia Marina17/18: 131-158 (in Croatian with English summary)
7. Lucic D., and Onofri V., 1990. Seasonal variations of neritic mesozooplankton in Mali
Ston Bay (Southern Adriatic). Acta Adriat 31: 117-137
8. Brautovic I., Lucic D. AND Njire J., 2000. Annual distribution of marine Cladocerans
in the coastal area of the Southern Adriatic (Croatia) Period biol, 102 Suppl 1: 545-551.
9. Buljan M., Stojanovski L. and Vukadin I., 1975. Distribution of nutrient salts in waters
of the middle and southern Adriatic Sea. Thalassia Jugosl11: 139-149
10.Vilicic D., 1989., Phytoplankton population density and volume as indicators of
eutrophication in the eastern part of the Adriatic Sea. Hydrobiologia174: 117-132
11. Della Ccroce N., and VengopaL P., 1972., Distribution of marine cladocerans in the
Indian Ocean. Marine Biology 15: 132-138.
12. Specchi M., and Zitter M., 1973/74. I cladoceri del genere Podon nel Golfo di Trieste
notizie sul ciclo biologico di Podon polyphemoidesePodon intermedius. Boll Soc
Adriatica Sc Trieste59:173-182
13. LetourneauM., 1961., Contribution et l’étude des cladocéres du Golfe de Marseille.
ReclTrav Stn mar Endoume22: 123-151
14. Patriti G., 1973., Les cladocéres des milieux portuaires de Marseille. Mar Biol20: 50-57
ANNUAL DISTRIBUTION OF CLADOCERANS IN THE OPEN SEA NEAR DUBROVNIK (SOUTH ADRIATIC)
Igor Brautovic
Institute of Oceanography and fisheries-Split, Laboratory of plankton ecology, Dubrovnik, Croatia - igor@labdu.izor.hr
Abstract
The quantitative and qualitative composition and annual changes of abundance of cladocerans have been investigated. A weekly samplings
were taken at the station one mile southwest from the island of Lokrum (sea depth 100 m) from 16 May 1995 till 9 December 1996. Five
cladoceran species were found. A maximum density of 845 ind/m
3
was recorded on 26 September 1996 with Penilia avirostrisaccounting
for 97.6% of the total number.P. avirostrisandEvadne tergestinadisplay similar seasonal ?uctuations in abundance.
Keywords : Adriatic Sea, plankton, open sea, population dynamics
Fig. 4. Number of individuals of species Podon intermedius and
Evadne spinifera
Fig.1.Location de P-100 station
Fig. 2. Number of individuals of species Penilia avirostris
Fig. 3. Number of individuals of species Evadne tergestina andEvadne
