Basin scale distribution of zooplankton in the Ligurian Sea (north-western Mediterranean) in late autumn

Abstract

Mesozooplankton biomass and abundance were evaluated in epipelagic waters at 59 stations covering the Italian sector of the Ligurian Sea (northwestern Mediterranean) in December 1990. This region is characterised by a cyclonic circulation which encloses a central divergence zone and is associated with a main thermohaline front offshore the western Ligurian coast. At the end of autumn, mesozooplankton biomass (range: 0.80-4.24 mg DW m -3 ) and the abundance (range: 83.8-932 ind. m -3 ) were lower in the divergence zone. On the contrary, in the Ligurian frontal zone at the periphery of the divergence and on the eastern continental shelf the greatest values of biomass and abundance were recorded. Copepods and appendicularians dominated the mesozooplankton community, the main taxa being the copepods Clausocalanus spp. (46% of total zooplankton) and Oithona spp. (15%) and the appendicularian Fritillaria spp.(12%). Three hydrological sub-regions, i.e. the divergence, the eastern continental shelf and the periphery of the divergence, were characterised by different zooplankton communities and characteristic species. Environmental differences between the three zones were mainly related to changes in bottom topography, sea surface temperatures and quantity of particulate organic matter. Vertical mesozooplankton abundance and taxa distribution from the surface to 1,900 m depth were also examined in one station. The results showed that the bulk of the community was concentrated in the upper 200 m, small copepods being dominant particularly in the upper 50 m. The copepod community was more diversified in sub-superficial waters, with a maximum observed in the 200-400 m layer. The distributions of main zooplankton taxa described in epipelagic waters in the eastern Ligurian Sea in autumn were compared with their distribution at surface in the north-western Mediterranean obtained by sampling performed with the Continuous Plankton Recorder in 1997-1999. The analysis of the zooplankton community in CPR samples confirms the dominance of small copepods (Paracalanus spp., Clausocalanus spp., Oithona spp.) and appendicularians in the northwestern Mediterranean in late autumn-winter and shows that their distribution is mainly related to the main mesoscale hydrographic features characterising this basin.

Distribution of epipelagic metazooplankton across the Mediterranean Sea during the summer BOUM cruise

“…Brugnano et al, 2010) and mainly within the upper 50 m in both the eastern basin and the Ligurian Sea (Licandro and Icardi, 2009). Here, the bulk of both nauplii and small copepods presented a patchy vertical distribution (down to 120 m) throughout the Mediterranean Sea, mainly driven by the deep chlorophyll maximum (DCM) depth.…”

“…Indeed, many field studies have been realised at regional scales and have highlighted the impact of mesoscale features on the distribution and diversity of metazooplankton in both Mediterranean basins (Ibanez and Bouchez, 1987;Pinca and A. Nowaczyk et al: Distribution of epipelagic metazooplankton Dallot, 1995;Youssara and Gaudy, 2001;Mazzocchi et al, 2003;Siokou-Frangou, 2004;Pasternak et al, 2005;Riandey et al, 2005;Fernandez de Puelles et al, 2004Zervoudaki et al, 2006;Molinero et al, 2008;Licandro and Icardi, 2009;Siokou-Frangou et al, 2009). Mesoscale hydrodynamic structures are known also to enhance nutrient concentrations, and therefore, plankton patchiness stimulating trophic transfers towards large predators.…”

Plankton in the open Mediterranean Sea: a review

“…The range of their relative abundance was very wide among several regions of the EMS in the autumn of 1991, from 1% in the West Levantine Sea up to 23% at a station in the Rhodos Gyre area . The contribution of appendicularians to zooplankton abundance was very high (38%) in the Ligurian Sea in winter, when the group was dominated by Fritillaria (Licandro and Icardi, 2009).…”

“…A few small-sized and species-rich genera of calanoids (Clausocalanus and Calocalanus, together with Ctenocalanus vanus) and cyclopoids (Oithona, oncaeids, corycaeids) account for the bulk of copepod abundance and biomass in epipelagic layers of the MS (Seguin et al, 1994;Siokou-Frangou et al, 1997;Saiz et al, 1999;Andersen et al, 2001a;Youssara and Gaudy, 2001;Gaudy et al, 2003;Fernández de Puelles et al, 2003;Mazzocchi et al, 2003;Riandey et al, 2005;Licandro and Icardi, 2009) (Fig. 18).…”

“…19). Increased mesozooplankton standing stock values are associated with the fronts in the Balearic, Catalan, and Ligurian Seas (Razouls and Thiriot, 1973;Sabatés et al, 1989;Alcaraz et al, 1994;Pinca and Dallot, 1995;Mc Gehee et al, 2004;Licandro and Icardi, 2009). The hydrographic features of the frontal system in the Catalan Sea also affect the metabolic activities (e.g., respiration, excretion) of zooplankton in the area, as well as their variability in different seasons .…”