I. Siokou-Frangou et al.: Mediterranean plankton
1565
Fig. 17. Distribution of total mesozooplankton abundance (10
4
×
ind m
−
2
) in the 0–100 m layer during June
1999 (black circles) (Source: Siokou-Frangou et al., 2004) and of total copepod abundance (10
4
×
ind m
−
2
) in
the 0–200 m layer during September 1999 (white circles) (reproduced with permission from Dolan et al., 2002).
90
Fig. 17.
Distribution of total mesozooplankton abundance
(10
4
×
ind. m
−
2
) in the 0–100 m layer during June 1999 (black cir-
cles) (Source: Siokou-Frangou, 2004) and of total copepod abun-
dance (10
4
×
ind. m
−
2
) in the 0–200 m layer during September
1999 (white circles) (reproduced with permission from Dolan et al.,
2002).
their populations largely overlap, the peaks of
Clausocalanus
paululus,
C. pergens,
C. arcuicornis and
C. furcatus suc-
ceed each other from winter to autumn in the open Tyrrhe-
nian Sea (Peralba and Mazzocchi, 2004) as well as in the
Ionian Sea and in the Straits of Sicily (Mazzocchi, unpub-
lished data). Similar peak succession was observed in coastal
waters (Mazzocchi and Ribera d’Alcal´a, 1995). In the Io-
nian and South Aegean Seas, the dominant C. furcatus and
Oithona plumifera in the autumn are replaced by C. paulu-
lus and O. similis in the spring (Siokou-Frangou et al., 1997;
Mazzocchi et al., 2003; Siokou-Frangou et al., 2004). In the
EMS and in autumn, O. plumifera is abundant in the 0–50 m
layer whereas O. setigera dominates in the 50–100 m layer
(Siokou-Frangou et al., 1997).
West-to-east differences in the percentage contribution of
some important species to the whole copepod assemblage
might reflect differences in species biogeography, but might
also be indicative of different structural and functional fea-
tures of these systems.
For example, Centropages typi-
cus and Temora stylifera, also very common in neritic and
coastal waters, are mentioned among the dominant species
only in the WMS (Vives, 1967; Boucher and Thiriot, 1972;
Pinca and Dallot, 1995; Saiz et al., 1999; Fern´andez de
Puelles et al., 2003; Gaudy et al., 2003), in the Adriatic Sea
(Hure et al., 1980), and in the North Aegean Sea (Siokou-
Frangou et al., 2004)(Fig. 18). By contrast, Calocalanus spp.
(e.g., C. pavo, C. pavoninus), Haloptilus longicornis, on-
caeids (e.g., Oncaea “media” group, O. mediterranea), and
corycaeids (e.g., Farranula rostrata) contribute more to total
copepod abundance in the EMS than in the WMS (Weikert
and Trinkaus, 1990; Siokou-Frangou et al., 1997; Mazzocchi
et al., 2003; Ramfos et al., 2006).
The occurrence of large calanoids such as Calanus hel-
golandicus is much less important in the open MS than
in the North Atlantic (reviewed by Bonnet et al., 2005).
This species mainly inhabits intermediate and deep layers of
the NW MS, Adriatic Sea, and North Aegean Sea, and as-
cends to epipelagic waters in late winter-spring (e.g., Bonnet
et al., 2005, Siokou-Frangou, unpublished data). Its pres-
Fig. 18. Rank order of dominant copepod species or genera in the
0–200 m layer of several areas of the MS in spring. The rank order
of each species or genus is given in the y axis and the height of the
relevant column decreases with the rank order of the species. ALB:
Almeria-Oran area (Seguin et al., 1994); MCH: Mallorca Channel
(Fern´andez de Puelles et al., 2004, 0–100 m layer); NBA: North
Balearic Sea (Mazzocchi, unpublished); GLI: Gulf of Lion (Gaudy
et al., 2003); LIG: Ligurian Sea (Pinca and Dallot, 1995); ADR:
Adriatic Sea (Hure et al., 1980); ION: Ionian Sea (Mazzocchi et al.,
2003); NAG: North Aegean Sea, SAG: South Aegean Sea (Siokou-
Frangou et al., 2004, and unpublished); RHO: Rhodos cyclonic gyre
(Pancucci-Papadopoulou et al., 1992); LEV: Central Levantine Sea
(Pasternak et al., 2005, 0–150 m layer)
ence was considered extremely rare in the Levantine Sea
until an outstanding abundance was recorded in June 1993
(15.6×10
3
ind. m
−
2
in 4000 m water column), probably as a
consequence of changes in the deep circulation induced by
the EMT (Weikert et al., 2001). Seasonal and vertical pat-
terns similar to those of C. helgolandicus are reported for
the large Subeucalanus monachus in the Alboran, Ionian and
Levantine Seas (Andersen et al., 2004; Siokou-Frangou et al.,
1999; Weikert and Trinkaus, 1990). C. helgolandicus was
found in high density patches at the frontal zone in the open
Ligurian Sea, in association with high phytoplankton con-
centration (Boucher, 1984). S. monachus was very abundant
in the Rhodos Gyre during the spring of 1992 when the up-
welling of waters rich in nutrients led to high phytoplank-
ton biomass dominated by large diatoms (Siokou-Frangou
et al., 1999). The distribution of these two large calanoids
suggest that they are vicariant species that can co-occur but
peak in different areas of the MS. The copepods reported as
the strongest vertical migrants in the MS, i.e., Pleuromamma
gracilis,
P. abdominalis,
Euchaeta acuta, enter the epipelagic
layer only during their nocturnal ascent from deeper waters
(Scotto di Carlo et al., 1984; Weikert and Trinkaus, 1990;
Andersen et al., 2001b; Raybaud et al., 2008).
5.2.2
Other groups
The other mesozooplankton groups that contribute to com-
munity diversity in the open MS are much less abundant
than copepods (Gaudy, 1985). Among crustaceans, clado-
cerans are very abundant in coastal waters and expand their
distribution beyond the continental slope only in narrow ner-
itic areas, generally in summer (Saiz et al., 1999; Riandey
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