On the natural diet of Daphnia laevis in the eutrophic Pampulha reservoir (Belo Horizonte, Minas Gerais)

Abstract

The aim of this study was to assess the major food items ingested by adult specimens of Daphnia laevis within the eutrophic Pampulha reservoir in Belo Horizonte, Minas Gerais, Brazil. The gut content was analyzed after addition of sodium hypochlorite and also through the examination of dissected guts under scanning electron microscopy. The results showed that Chlorophyceae was the main food item ingested, representing c. 80.5% of the total ingested food. Moreover, Eutetramorus fottii, Coelastrum pseudomicroporum and Oocystis lacustris, the dominant phytoplankton species within the reservoir, were the most frequent cells found in the gut contents. Euglenophyta also represented an important food item accounting for 15% of the ingested material, including mainly Trachelomonas volvocina and Euglena oxyuris, although less abundant in the reservoir (< 10% of total phytoplankton). Blue-green algae occurred at much lower percentages in the guts than in the phytoplankton. A small amount of undigested Microcystis aeruginosa colonies were also found in the gut content of D. laevis. Scanning electron microscopy results showed that, besides phytoplankton cells, a great amount of abiogenic material was also ingested. The amount of this inorganic material increased considerably in the tract (from 15% to 75% of the gut content), when a peak of D. laevis was observed in the reservoir. Our assumption is that the ingestion of this inorganic material can be a strategy used by D. laevis to obtain additional food supply.

Fluctuations of the population of Daphnia laevis Birge 1878: a six-year study in a tropical lake

“…Pinto-Coelho (1998) observed a significant and positive relationship between total phosphorus and D. laevis in Lake Pampulha (Belo Horizonte, Minas Gerais, Brazil), where the increase of carbon particles, total phosphorus and total nitrogen were identified as species-density regulating factors. According to Eskinazi-Sant'Anna et al (2002), during the population peaks of D. laevis in Lake Pampulha, the proportion of amorphous material in the digestive tract of individuals of this species increased considerably, reaching 75% of the total ingested, whereas in other periods, this material contributed less than 15%. Subsequently, Pinto-Coelho et al (2003) observed that the eutrophication of Lake Pampulha decreased the food quality (algae) and was a key factor in the collapse of the D. laevis population.…”

The resting eggs of zooplankton from a tropical, eutrophic reservoir (Pampulha Reservoir, south‐east Brazil)

“…Significant alterations in the structure of the lake's zooplanktonic community have been reported by Pinto‐Coelho (1998) and Eskinazi‐Sant'Anna et al . (2002), including the disappearance of zooplanktonic species which were previously abundant in the reservoir, including Bosmina sp., Daphnia laevis and Scolodiaptomus corderoi .…”