This high productivity is primarily linked to the enrichment of the euphotic layer
with inorganic nutrients (mainly nitrate), which supports communities of phytoplankton usually dominated by diatoms (Rodríguez et al. 1998; Arin et al. 2002;
Reul et al. 2005; Mercado et al. 2005, 2007, 2011). However, the analysis of the
interannual variability in the taxonomic composition reveals complex patterns (Balle
1963; Margalef 1969; Delgado 1990; Rubín et al. 1999; Mercado et al. 2005). Thus,
the early works of Rodríguez et al. (1982) and Delgado (1990) reported a community
dominated by small flagellates and diatoms which can be considered typical of
upwelling areas. However, Mercado et al. (2005) described two well-differenced
communities: one was dominated by small flagellates and diatoms (diatomdominated community), while the other community was characterized by the dominance of coccolithophorids and dinoflagellates (non-siliceous algal-dominated communities). The analysis of time series for the period 1992–2002 revealed that both
communities were temporally segregated, with diatom-dominated community
prevailing from 1994 to 1997 and non-siliceous algal-dominated communities
doing it from 2000 to 2002. The diatom-dominated community was mainly composed of chain-forming pennate diatoms belonging to the genus Pseudo-nitzschia
and the centric diatoms Thalassiosira, Rhizosolénia, Leptocylindrus, and
Skeletonema. The dinoflagellates belonging to the species Scrippsiella trochoidea,
Protoperidinium depressum, and Prorocentrum minimum also appeared frequently.
The second community was characterized by the coccolithophorids Calcidiscus and
Gephyrocapsa and the dinoflagellates Prorocentrum compressum, Ceratium
extensum, and Ceratium furca which were dominant during 2000–2002 (in special
Gephyrocapsa sp.).
Irrespective of these interannual patterns, the abundance of diatoms is usually
greater in spring, coinciding with greater nutrient availability. In contrast, the
abundance of dinoflagellates does not follow a clear seasonal pattern. The analysis
of the zooplankton abundance data also reveals a seasonal cycle characterized by
maxima in summer (1964 ind m
À3 ) and minima in spring (467 ind m
À3 , Sampaio
et al. 2005). Copepods are the predominant group throughout the year, doubling
their abundance in summer. However, at this time, cladocerans represent up to 40%
of the relative abundance. Gelatinous plankton in general represents less than 5% of
the community (Rodríguez et al. 1982; Sampaio et al. 2005). Interestingly, this
seasonal cycle in zooplankton contrasts with the seasonal variations obtained for
other locations in the western Mediterranean Sea, where lower biomasses of zooplankton are usually found in summer whereas higher values are obtained from April
to June (Sabates et al. 1989; Fernandez de Puelles 1990; Champalbert 1996).
The joint analysis of the phytoplankton and zooplankton data series for the
Alboran Sea carried out by Mercado et al. (2008) revealed that zooplankton exerts
a strong top-down control on phytoplankton at the seasonal scale. However, the
aforementioned interannual changes in phytoplankton composition reflected in
changes in the zooplankton composition as the abundance of copepods and brachiopods decreased in 1992–1999 (possibly due to the interannual shifts in the phytoplankton communities). Furthermore, strong spring blooms of phytoplankton are
normally followed by noticeable peaks of zooplankton in summer. In fact,
500
A. García et al.
with inorganic nutrients (mainly nitrate), which supports communities of phytoplankton usually dominated by diatoms (Rodríguez et al. 1998; Arin et al. 2002;
Reul et al. 2005; Mercado et al. 2005, 2007, 2011). However, the analysis of the
interannual variability in the taxonomic composition reveals complex patterns (Balle
1963; Margalef 1969; Delgado 1990; Rubín et al. 1999; Mercado et al. 2005). Thus,
the early works of Rodríguez et al. (1982) and Delgado (1990) reported a community
dominated by small flagellates and diatoms which can be considered typical of
upwelling areas. However, Mercado et al. (2005) described two well-differenced
communities: one was dominated by small flagellates and diatoms (diatomdominated community), while the other community was characterized by the dominance of coccolithophorids and dinoflagellates (non-siliceous algal-dominated communities). The analysis of time series for the period 1992–2002 revealed that both
communities were temporally segregated, with diatom-dominated community
prevailing from 1994 to 1997 and non-siliceous algal-dominated communities
doing it from 2000 to 2002. The diatom-dominated community was mainly composed of chain-forming pennate diatoms belonging to the genus Pseudo-nitzschia
and the centric diatoms Thalassiosira, Rhizosolénia, Leptocylindrus, and
Skeletonema. The dinoflagellates belonging to the species Scrippsiella trochoidea,
Protoperidinium depressum, and Prorocentrum minimum also appeared frequently.
The second community was characterized by the coccolithophorids Calcidiscus and
Gephyrocapsa and the dinoflagellates Prorocentrum compressum, Ceratium
extensum, and Ceratium furca which were dominant during 2000–2002 (in special
Gephyrocapsa sp.).
Irrespective of these interannual patterns, the abundance of diatoms is usually
greater in spring, coinciding with greater nutrient availability. In contrast, the
abundance of dinoflagellates does not follow a clear seasonal pattern. The analysis
of the zooplankton abundance data also reveals a seasonal cycle characterized by
maxima in summer (1964 ind m
À3 ) and minima in spring (467 ind m
À3 , Sampaio
et al. 2005). Copepods are the predominant group throughout the year, doubling
their abundance in summer. However, at this time, cladocerans represent up to 40%
of the relative abundance. Gelatinous plankton in general represents less than 5% of
the community (Rodríguez et al. 1982; Sampaio et al. 2005). Interestingly, this
seasonal cycle in zooplankton contrasts with the seasonal variations obtained for
other locations in the western Mediterranean Sea, where lower biomasses of zooplankton are usually found in summer whereas higher values are obtained from April
to June (Sabates et al. 1989; Fernandez de Puelles 1990; Champalbert 1996).
The joint analysis of the phytoplankton and zooplankton data series for the
Alboran Sea carried out by Mercado et al. (2008) revealed that zooplankton exerts
a strong top-down control on phytoplankton at the seasonal scale. However, the
aforementioned interannual changes in phytoplankton composition reflected in
changes in the zooplankton composition as the abundance of copepods and brachiopods decreased in 1992–1999 (possibly due to the interannual shifts in the phytoplankton communities). Furthermore, strong spring blooms of phytoplankton are
normally followed by noticeable peaks of zooplankton in summer. In fact,
500
A. García et al.