Comparison of the zooplankton from two different temperate tidal systems in Western Portugal: the Mondego Estuary and Ria de Aveiro Lagoon

This study examines the zooplankton assemblages in the Mondego estuary and Ria de Aveiro lagoon (Western Portugal) and discusses how different conditions between the two tidal systems may influence the abundance and diversity of the zooplankton. Both tidal systems are located in a warm temperate region with a basic continental temperate climate. The two systems differ in geomorphology, freshwater inputs and tidal dynamics. The statistical tested values of salinity and temperature were significantly different according to tidal, monthly and estuarine situations. The chlorophyll-a values were highest at low tide, in the Mondego estuary in summer months. The significant differences found are mainly explained by the different freshwater inputs in the systems. As far as zooplankton densities are concerned, the Mondego estuary presented high abundance in May in high tide and the Canal de Mira in August in low tide. Higher diversity values were found in the Mondego estuary in May, June and July in high tide and in June, July and August in low tide. Higher diversity values were found in Canal de Mira for the rest of the year. Diversity values were also significantly different in the tidal, monthly and estuarine situations. The physical and chemical (temperature and salinity) and biological (chlorophyll-a) differences between the two systems should explain the significant differences in the zooplanktonic densities and the diversity between them.