Rapp. Comm. int. Mer Médit., 36,2001
419
Introduction
European anchovy (Engraulis encrasicolis) is a highly important
fish resource of the western Mediterranean coasts. Several studies con-
cerning the ecology of this species in the gulf of Lions [1] and the
Catalan Sea [2] already exist. These works show that the diet of adult
anchovies constituted primarily of copepods over the spawning peri-
od. The copepod Centropages typicusis one of the most abundant
species of the northwestern Mediterranean coasts [3]. It also can dom-
inate other copepods in the diet of anchovy [2]. Consequently, this
copepod-anchovy interaction may play a determinant role in the
Mediterranean pelagic ecosystem [4]. However, due to the lack of
feeding ecology information in the present study area, the former con-
clusions are difficult to assume. Recently Daly Yahia [5] studied the
dynamics of zooplankton communities in the bay of Tunis over two
years. With this information the presence of anchovy eggs and larvae
is used to identify the spawning period and the temporal evolution of
the copepod Centropages kroyeri, the dominant species in summer, is
described.
The main aim of this paper results in discussing the biogeographic
importance of this copepod and its possible interaction with anchovy.
Sampling area
The bay of Tunis is located between 10°17’to 11°37’longitude East
and 36°42’to 36°53’latitude North); its surface area and average
depth are about 361 km
2
and 15m respectively.A monitoring program
of hydrology, phytoplankton, zooplankton and ichthyoplankton was
d
eveloped between December 1993 and November 1995 [6].
Zooplankton groups including copepods were identified and counted
down to species level.
Results and discussion
The species Centropages kroyericonsidered rare for the northwest-
ern Mediterranean coasts [7,8] can dominate the copepod communi-
ties in the Bay of Tunis, especially during summer (Figure 1B).
Abundant also off the southern Tunisian coasts it can tolerate high
salinity ranges [9]. Its reproductive activity has been correlated to
increasing temperature during spring and summer [5]. So, this species
can be considered as a biogeographic indicator for the warm waters in
the Mediterranean coasts.
A peak in abundance of anchovy eggs and larvae was observed in
July (Figure 1C). Both copepods and anchovy showed high spatial het-
erogeneity during July (Figure 1). Comparing the maps of E. encrasi-
coluseggs and C. kroyeriadults, Daly Yahia [5] concluded that
anchovy adults fed and spawned in the patches of C. kroyeri. During
the summer stratification period, C. typicusshowed a daily patchy ver-
tical distribution in the Catalan Sea [10]. In the same area, several
schools of anchovy were observed in day time at the same depths of
copepod patches [2].
On the basis of these first results, it is suggested that research pro-
grammes should be enlarged to be able to study and compare copepod-
anchovy interactions for both sides of western Mediterranean coasts.
References
1.Plounevez S. and Champalbert G., 2000. Diet, feeding behaviour and
trophic activity of the anchovy (Engraulis encrasicolus L.) in the Gulf of
Lions (Mediterranean Sea). Oceanol. Acta, 23: 175-192.
2.Tudela S. and Palomera I., 1997. Trophic ecology of the European anchovy
Engraulis encrasicolusin the Catalan Sea (northwest Mediterranean). Mar.
Ecol. Prog. Ser., 160: 121-134.
3. Mazzocchi M.G. and Rivera d'Alcalà M., 1995. Recurrent patterns in
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1972). (Bilan quantitatif, qualitatif et écologique). Bull. Ecol., 12: 29-60.
8. Vives F., 1978. Distribucion de la poblacion de copépodos en el
Mediterraneo occidental. Res. Exp. Clent. B/O Cornide. 7: 263-302.
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connaissance des cycles saisonniers du zooplancton de la mer de Bou Grara
(Ensemble de communauté zooplanctonique). Revue de l'INAT, 11: 7-27.
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phytoplankton maximum in the Western Mediterranean. J. Plankton Res., 12:
665-672.
PREDOMINANCE OF THE COPEPOD CENTROPAGES KROYERI(GIESBRECHT, 1892) IN
THE BAY OF TUNIS DURING THE SPAWNING PERIOD OF THE ANCHOVY ENGRAULIS ENCRASICOLIS.
Sami Souissi
1
*, Mohamed Néjib Daly Yahia
2
et Ons Daly Yahia-Kefi
3
1
Univ. Sciences et Technologies de Lille 1, C
NRS
- U
PRES
A 8013 E
LICO
, Station Marine, Wimereux, France -
sami.souissi@univ-lille1.fr
2
Laboratoire d’Ecobiologie Animale, Unité de Planctonologie, Faculté des Sciences, Zarzouna, Bizerte Tunisie - Nejib.Daly@rnu.fsb.tn
3
Laboratoire de Planctonologie, Institut National Agronomique, Tunis, Tunisie - dalyyahya.ons@inat.agrinet.tn
Abstract
A spatio-temporal survey of zooplankton and ichthyoplankton realised in the Bay of Tunis (south-western Mediterranean) between
December 1993 and November 1995 resulted in the identification of a spawning area during the summer of the anchovy Engraulis
encrasicolus. It is suggested that E. encrasicolusadults fed on the patches of the copepod Centropages kroyeri dominating the zooplankton
community over this period. This species, very abundant in the Tunisian coasts, showed high preferences for warmer waters, whereas the
species Centropages typicusis more abundant in the northern Mediterranean coasts.
Keywords: Centropages, anchovy, Bay of Tunis.
