Seasonal Variation in Diet and Feeding Strategy of Three Mayfly Species

Abstract

Understanding the feeding habits of aquatic invertebrates under reference conditions can contribute to our understanding of community assemblages in fresh waters. Here, seasonal changes in the diet of three species of Ephemeroptera from Irish high status rivers were investigated. A fluorescent dye, 4'6 diamidino-2-phenylindole, was used to differentiate the various types of gut contents and to allow bacteria and biofilm matrix to be visualised. Through interpretation of gut contents and feeding strategy plots, Baetis rhodani was found to have a generalist diet with detritus, algae and biofilm the main food types. Two congeneric species, Ecdyonurus venosus and E. insignis, were found to be detritus specialists. Seasonal sampling indicated that biofilm can provide a valuable food source to E. venosus at times of high flow when detritus is not readily available. There was evidence of niche separation in summer when E. insignis and E. venosus co-existed. E. insignis fed on coccoid algae while E. venosus consumed no coccoid algae. B. rhodani consistently ingested a similar broad diet throughout the year. A detritus-based diet is likely nutrient poor leading to lower growth rates. These findings are discussed in the context of the behaviour of these species and sensitivity to nutrient enrichment.