Distributions and impacts of microparasites on Daphnia in a rockpool metapopulation

We examined the spatial distributions of the microparasites on two species of Daphnia in rockpools in four areas along the coast of the Gulf of Bothnia, central Sweden. We found five taxa of parasites, of which the microsporidian Larssonia sp. occurred in all the four subareas studied, and in 44% of the pools. Other parasites, such as a microsporidian intestinal parasite of the Glugoides type and the nematode Echinura uncinata, were much less common. Larssonia had a large impact on reproduction in both Daphnia species, although D.␣longispina seemed to be somewhat less affected than D.␣pulex. We used a spatial autocorrelation method (correlogram using Moran's coefficient) to analyse the spatial distribution of the two Daphnia species and the most abundant parasite species Larssonia sp. All three species showed positive spatial autocorrelations over small distances, indicating an aggregated distribution. This suggests that colonization-extinction dynamics may be important in both host species as well as in the parasite. Larssonia showed no relation to environmental factors, while the distributions of the two Daphnia species were significantly related to the water volume of the pools. D. pulex was more often found in small pools, while D. longispina more often inhabited larger pools. Our study suggests that microparasites in rockpools have substantial effects on Daphnia demography and through this they may influence population dynamics and local extinctions.