I. Siokou-Frangou et al.: Mediterranean plankton
1567
revealed a preference for the frontal area (Youssara and
Gaudy, 2001).
In the North-East Aegean frontal region,
two distinct copepod assemblages inhabit the areas occu-
pied by the modified Black Sea Water and by the Aegean
Sea Water, respectively, due to the strong salinity differ-
ences (up to 8) (Zervoudaki et al., 2006; Siokou-Frangou
et al., 2009). An interesting aspect regarding the influence of
mesoscale features is revealed when studying cyclonic and
anticyclonic eddies synoptically. In the Algerian basin, the
eastern edge of an anticyclonic eddy seems to be favorable
for Paracalanus/Clausocalanus, Calocalanus, and Calanus,
due to the downward entrainment of chl a down to a depth
of 200 m. Chaetognaths were more abundant in the center
of the above structure. In the neighboring cyclonic eddy,
the highest abundance of filter-feeders (ostracods, cladocer-
ans, doliolids and salps) was attributed to enhanced trophic
conditions (Riandey et al., 2005). Dissimilarities in copepod
assemblages between cyclonic and anticyclonic gyres in the
EMS in the autumn of 1991 were recorded only in the sub-
surface layer (50–100 m). The cyclonic gyres were charac-
terized by the copepods C. pergens and Ctenocalanus vanus,
while the anticyclonic ones were dominated by C. paulu-
lus, Mecynocera clausi and Lucicutia flavicornis; differences
were attributed to the higher chl a values of the cyclonic
gyres compared to the anticyclonic ones (Siokou-Frangou
et al., 1997).
In the hydrodynamically very active area of the Ligurian
Sea, zooplankton assemblages showed distinct patterns at
small spatial scale due to both physical environment and ani-
mal behavior (Pinca and Dallot, 1995). The copepods C. hel-
golandicus,
C. typicus,
Oithona spp., and
Oncaea spp. were
associated with the frontal zone; Acartia spp. and salps had a
scattered distribution while Clausocalanus/Paracalanus did
not show a clear pattern. The cross-shore zooplankton dis-
tribution appeared strongly influenced by both the North-
ern Ligurian current and the Ligurian front (Molinero et al.,
2008).
5.4
Production
Data of mesozooplankton production in the open epipelagic
MS are restricted in space and time. In the Gulf of Lion, the
Catalan Sea and the North-East Aegean Sea, copepod pro-
duction ranges from 19 to 58 mg C m
−
2
d
−
1
over the seasons
(Table 7). The values are much lower in the North and South
Aegean Sea, in accordance with the remarkable oligotrophy
of these areas.
Most studies on mesozooplankton production in the MS
are limited to coastal species and sites and based mainly on
the egg production method; their results are hardly applica-
ble to open waters, dominated by copepod species whose
reproductive biology is very poorly known (e.g., Clauso-
calanus, Calocalanus, Ctenocalanus, Oithona and Oncaei-
dae). A few studies were conducted in the open MS for the
egg-carrying Oithona and Oncaeidae, and the egg-carrying
Fig. 19. Distribution of mesozooplankton biomass (dry mass in
mg m
−
3
) in the 0–200 m layer of the Almeria-Oran area, as affected
by the hydrological features. Modified with permission from Yous-
sara and Gaudy, 2001).
species belonging to the genus Clausocalanus (Zervoudaki
et al., 2007; Peralba, 2008). As the egg-carrying strategy
implies lower egg production but also lower egg mortality
in comparison to egg broadcasting (Kiørboe and Sabatini,
1995), these species can maintain quantitatively limited but
persistent populations in a wide range of trophic conditions.
In fact, the cosmopolitan and abundant Oithona similis has
very low and similar egg production rates (∼2 eggs f
−
1
d
−
1
)
in the North Aegean Sea (Zervoudaki et al., 2007) and in
the more eutrophic North Atlantic Ocean (Castellani et al.,
2005), without significant seasonal differences in either sea.
By contrast, for the broadcast-spawners C. typicus, T. stylif-
era and
Clausocalanus lividus, egg production rates recorded
in the Catalan Sea are lower than the maximal rates reported
for the same species in the literature. This indicates that their
production is limited by the oligotrophic conditions of the re-
gion (reviewed by Saiz et al., 2007). Unfortunately, no infor-
mation is available so far on the reproduction of Calocalanus
species, and a few data have been provided only recently for
Ctenocalanus vanus in the Red Sea (Cornils et al., 2007).
5.5
Respiration and excretion
The metabolic rates of bulk mesozooplankton communities
of the epipelagic MS have been examined only in a very
limited number of studies conducted in the WMS (Alcaraz,
1988; Calbet et al., 1996; Gaudy and Youssara, 2003; Gaudy
et al., 2003), except for one trans-Mediterranean cruise in the
spring of 2007 (Minutoli and Guglielmo, 2009). Zooplank-
ton respiration rates in the MS appear to vary across space
and seasons, according to community composition and water
mass characteristics. In the Catalan Sea, the specific respira-
tory carbon demand of zooplankton is slightly but not signif-
icantly lower in winter-spring (0.180 d
−
1
) than in summer-
autumn (0.219 d
−
1
) (reviewed by Alcaraz et al., 2007). By
contrast, in the Gulf of Lion respiration increases during
spring, in correspondence with the increase of the general
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