Basin scale distribution of zooplankton in the Ligurian Sea (north-western Mediterranean) in late autumn |
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Authors: | P Licandro P Icardi |
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Institution: | (1) Sir Alister Hardy Foundation for Ocean Science (SAHFOS), Citadel Hill, Plymouth, PL1 2PB, UK;(2) Salita di San Barnaba 24, 16136 Genoa, Italy |
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Abstract: | Mesozooplankton biomass and abundance were evaluated in epipelagic waters at 59 stations covering the Italian sector of the
Ligurian Sea (north-western 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 north-western Mediterranean in late autumn-winter and shows that their distribution is
mainly related to the main mesoscale hydrographic features characterising this basin.
Guest editors: S. Souissi & G. A. Boxshall
Copepoda in the Mediterranean: Papers from the 9th International Conference on Copepoda, Hammamet, Tunisia |
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Keywords: | Mediterranean Zooplankton Biomass Deep-waters Diversity Mesoscale |
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