Macroinvertebrate size spectra of Mediterranean ponds with differing hydroperiod length

1. The size spectra of the macroinvertebrate community in ponds with different hydroperiod length were compared along the Tyrrhenian coast of central Italy. Invertebrate sampling was conducted in 21 ponds (8 permanent and 13 temporary) in three different mesohabitats (central sediments. littoral sediments and macrophytes) during spring 2002. Several pond characteristics were also recorded. 2. Density and biomass size spectra were calculated for 123 samples and covered six orders of magnitude in size ranging from 0.126 mu g to 0.5 g. The shape of the density size distribution was unimodal, the mode being around 0.05-0.1 mg, with Oligochaeta and Diptera (Chironomidae) numerically dominant in almost all size classes. 3. The periodic drying affected the total biomass per size class, shown by comparing spectra among mesohabitats and pond types. The higher biomass in all size classes showed by permanent pond and central sediments reflects the major stability of permanent biotopes and, within these, of central sediments. 4. The overall shape of the size spectrum was similar among pond types, mesohabitats and sampling dates. Biomass of larger size classes was linked to variables describing pond stability. 5. We suggest that the biomass size spectrum of benthic macroinvertebrates is a potentially useful tool for quantitative wetland biomonitoring. In small Mediterranean ponds, the regularity of biomass size spectra implies that size-structuring processes are independent of the hydrological stress. Copyright (c) 2005 John Wiley & Sons, Ltd.