Annual and seasonal variation and the effects of hydroperiod on benthic macroinvertebrates of seasonal forest ("vernal") ponds in central Massachusetts, USA

Seasonal forest ponds (SFPs) are isolated, ephemeral lentic habitats in upl and forest ecosystems. These ponds occur commonly throughout temperate fore sts. Faunal communities of these ponds are dominated by invertebrates. Comp osition of these communities varies temporally both between years and also seasonally within a single hydrologic year, composition is most affected by pond permanence or hydroperiod. Benthic macroinvertebrates (BMIs) were sam pled up to three times a year in five SFPs between 1994 and 1996. The ponds were of short, intermediate, and long hydroperiod. Hydroperiod also varied among years, based on precipitation patterns. During the study, 64,000 spe cimens of 57 taxa were collected. No pattern was identified in the variatio n of BMI abundance among years and pond hydroperiod; abundance increased wi th successive surveys within years. Taxon richness and diversity varied sig nificantly with pond hydroperiod, increasing with increasing hydroperiod. D iversity measures increased over the three years of the study but without o bvious pattern across the successive surveys within years. Insects dominate d the samples, but large numbers of other Arthropoda and Oligochaeta were a lso collected. Chironomidae were dominant in most ponds, years, and surveys ; chironomid dominance was significantly greater in shorter hydroperiod pon ds. Seasonal forest ponds function as aquatic islands in a "sea" of terrest rial forest. The effect of hydroperiod on the composition of the benthic ma croinvertebrate community is analogous to that of size on marine island fau na, longer hydroperiod ponds generally have richer invertebrate communities just as larger marine islands typically have richer faunas. However, the e ffect is confounded by the close relationship between pond hydroperiod and pond size/volume.