The study of zooplankton in two coastal lagoons, Estany of Cullera and Albufera of Valencia (E, Spain), were carried out between October 1980 to August 1982 and between July 1982 to July 1983, respectively.

The Estany of Cullera is a meromictic coastal lagoon with an anoxic monimolimnion of sea water and a mixolimnion of continental oligohaline water. During the time of study a fluctuating halocline between 1 to 3 m of depth and an oxycline between 3 to 5 m was recognized. Seventy-eight zooplankton taxa (8 marine taxa) were identified, with a mean biomass and zooplankton density of 3.6 g m^-2 and 1368 x 10^3 indiv. m^-2 (63.9% rotifers, 18.6% copepods, 12.2% protozoans, 3.9% polichaetes and 1.3% cladocerans), respectively. The most abundant species were: (1) Brachionus calyciflorus, Brachionus angularis, Asplanchna brightwelli, Polyarthra vulgaris-dolichoptera, and Notholca salina in the oligohaline surface waters; (2) Acanthocyclops robustus, Metacyclops minutus, Moina micrura and Synchaeta tremula between the halocline and the surface; (3) Calanipeda aquae-dulcis, Brachionus plicatilis, Synchaeta oblonga and Hexarthra oxyuris-fennica in the halocline; (4) the marine species Synchaeta grimpei, Mercierella enigmatica and ciliates Euplotidae in the halocline or below it. Despite these differences in the vertical profile, seasonal succession is the most important cause of variation of the species density and composition. The Albufera of Valencia is a hypertrophic lagoon with mean conductivity and chlorophyll a concentration of 2335 =B5S cm^-1 and 400 =B5g l^-1, respectively. Thirty-two zooplankton taxa were identified, with a mean biomass and zooplankton density of 3.24 mg l^-1 and 2076 indiv. l^-1 (77% rotifers, 22.8% copepods, 0.2% cladocerans), respectively. The most abundant species was the permanent copepod A. robustus and the rotifer B. angularis (with maximums of up to 12,000 indiv. l^-1 in summer). Other abundant species were M. micrura, B. plicatilis, B. calyciflorus, Asplanchna girodi and Polyarthra spp. in summer; (2) S. oblonga and B. urceolaris in autumn; and (3) Daphnia magna and Brachionus leydigi in spring. The species B. calyciflorus, B. urceolaris and M. micrura were more abundant at the northern stations with less density of cyanobacteria.