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The Málaga Bay was sampled from 1992 to 2000 as part of the ECOMÁLAGA time-series operated by the Instituto Español de Oceanografiía (IEO). In 2010, sampling at Station MA2 of the Málaga transect was restarted. Station MA2 is located within the Bay of Málaga (36 41.76 N, 4 24.35 W), in the northwest Alboran Sea, with a bottom depth of 28 meters.
Zooplankton samples were collected on a quarterly basis from near bottom to the surface using a double bongo net (40 cm diameter, 200 µm mesh). Once on board, samples were preserved in 100 ml plastic jars with 4% buffered formalin seawater (pH 7.0) for abundance and taxonomic composition analyses. Abundance counts and taxonomical identification were done with a binocular macroscope (Zeiss, Stemi SV11). Prior to the analyses, samples were stained with Rose Bengal to facilitate identification of gelatinous plankton. A Seabird25 CTD was used to obtain in situ profiles of temperature and salinity.
Seasonal and Interannual Trends
The northwest region of the Alboran Sea presents high variability in hydrologic as well as physical and chemical conditions. This is due to the presence of an anticyclonic gyre originated by the jet of Atlantic water than enters the Mediterranean through the Gibraltar Strait. The Atlantic jet circulation affects the open waters. However, within the shelf, local currents are defined by winds. In the northwest section of the jet, divergence areas appear between Gibraltar and the Bay of Málaga, associated with westerly wind induced upwelling events. In this frontal area increases of nutrients and plankton have been detected.
The peculiar oceanographic conditions generate an annual zooplankton cycle differentiated from nearby areas, with communities typical from upwelling zones and warm waters, with predominant neritic species dominated by copepods. Maximum zooplankton abundances were observed in summer and autumn, while minimum zooplankton abundances were observed in winter. Copepods were the most abundant group in spring, autumn and winter, while in summer cladocerans were the dominant group. At the interannual scale an increasing trend was recorded from 1994 to 2000 in total copepod density although the mesozooplankton diversity showed a decreasing trend. However, this trend in total zooplankton seems to have changed in 2010. In spite of the interannual variations, the different phases of the annual cycle and the occurrence of several plankton species were remarkably regular.
In the Bay of Málaga, water temperatures in the top 20 meters have been increasing since 1992. However, no correlation has been found between copepods abundance and hydrological parameters (temperature and salinity).