Seasonal variation of the main zooplanktonic groups of the protected natural area estuary El Salado, Jalisco, Mexico

Abstract

Estuarine systems are the most important aquatic natural resources of the nation from various perspectives; fisheries use them mainly through studies that allow the detection and evaluation of the areas of concentration of adults on reproduction phase and potentially exploitable species. This present paper analyzes the spatial and temporal variation of the abundance of zooplankton groups in the Estuary El Salado, Puerto Vallarta, Jalisco. Eight zooplanktonic trawls were conducted during diurnal periods from spring to winter 2001, trawls were superficial, lasting ten minutes, by using a standard “Zeppelin” net with a mesh size of 505 µm with a length of 1.50 m mouth width of 0.60 m which was equipped with a digital flow meter to calculate the volume of filtered water, abundance data were normalized to a volume of 1000 m3. The total catch was 101,968.4 organisms, represented in eleven groups, the brachyurans were the most important group in the order of abundance accounting for 44.5 %, followed by 24.1 % in chaetognaths, decapod with 6.78 %, euphausiids with 11.84 %, and less abundant copepods with 6.18 %, 3.37 % siphonophores small jellyfish, stomatopods 2.83 %, 0.22 % amphipods, cladocerans with 0.33 %, 0.08 % gastropods and finally rare organisms with 0.02 % (appendicular, polychaetes and cumaceans). Variations in both spatial and temporal abundance were influenced by tidal conditions as well as variations in temperature and salinity. All registered major zooplankton groups abundances were homogeneous in the four seasonal periods, however spring was characterized by low abundance, while for summer and winter, the highest values recorded were represented mainly by the Brachyura order, and those abundances were associated with two reproductive periods in both seasons.