Evidence of a mutualistic relationship between an algal epibiont and its host, Daphnia pulicaria

We examined seasonality, intensity, and level of epibiont infection by the green alga Korshikoviella gracilipes on the zooplankton community over 2 yr in. the high mountain Rio Seco lake. Daphnia pulicaria was the preferred substrate for the epibiont, whose life cycle was exclusively completed on this taxon. The density of epibiont dispersal stage and the epibiont prevalence and burden on crustacean zooplankton were directly related to D. pulicaria density in both years. Laboratory experiments showed that attached epibionts had a negative effect on Daphnia by increasing the weight and sinking rates of infected animals and a positive: effect by increasing its reproductive rates, with a neutral effect on survivorship. On the other hand, the epibiont dispersal stage was actively and intensively grazed by Daphnia, which implies a benefit for Daphnia and a cost for K. gracilipes. Thus, both species derived benefits and costs from this relationship. Our results indicate a positive cost-benefit balance for both epibiont and host in such a way that a mutualistic relationship can be suggested. This epibiont-host interaction may play an important role in population and community regulation in Rio Seco lake.