Are the littoral zone conditions suitable for tropical planktonic microcrustaceans?

Abstract

The occupation of the littoral and limnetic zones by planktonic species has led to questions about whether littoral macrophytes would be a suitable habitat or refuge. These questions guided our field and laboratory studies on the spatial occupation and the food suitability for microcrustaceans of a shallow tropical lake. Replicated zooplankton samples were collected over 18 days, at intervals of 3 days, at three zones (the middle and edge of the stands of the emergent macrophyte, Ludwigia sp., and the limnetic zone). Some species, such as the cladocerans Diaphanosoma birgei and Daphnia ambigua , showed preference for the littoral zone and the limnetic zone, respectively. Copepodites, and adult copepods Thermocyclops decipiens and Tropocyclops prasinus meridionalis are mainly limnetic dwellers. The size of the cladocerans Ceriodaphnia richardi and Daphnia gessneri did not differ between the zones, nor did the clutch size of the former species; smaller individuals of D. ambigua were found within macrophyte stands. In laboratory experiments, the seston of the three zones did not negatively affect the development of the cladocerans C . richardi and D. birgei . On the contrary, the seston of the middle of the macrophyte stands promoted better growth rates of both cladocerans and some of the life table parameters of D. birgei than the seston of the other two zones. Food quantity and quality are not negative factors to microcrustaceans in the littoral and limnetic zones. The preference or indifference of microcrustaceans to habitats may be part of their adaptive strategies regarding other factors, including predation.