Aquatic macroinvertebrates and environmental gradients inPhragmites reedswamps: implications for conservation

Abstract

1. Aquatic macroinvertebrates were sampled from 22 sites in three contrasting reedswamps in the Burry Inlet, south-west Wales, which were respectively estuarine and tidal (Llangennech), coastal and artificial (Ashpits), and inland freshwater (Ffrwd). Species assemblages were ordinated by DECORANA, classified by TWINSPAN and related to physico-chemical factors using correlation, ANOVA and principal components analysis. 2. Reedswamps were not physico-chemically uniform, but varied in dissolved oxygen, nitrogen species, conductivity, water depth and reed character. 3. Among these factors, invertebrate species characteristic of the TWINSPAN groups suggested that conductivity, due to salinity, was an important influence on community composition; different communities were dominated by stenohaline to facultative euryhaline species, or by those characteristic of freshwater. Also, conductivity varied highly significantly across TWINSPAN groups: saline sites supported a higher abundance of fewer taxa, while freshwater sites were characterized by speciose assemblages with more beetles. 4. While major changes due to salinity occurred between and within reedswamps, different reedswamps nevertheless held distinct communities. This suggestion of ‘island’ effects prompts further data on aquatic invertebrates in reedswamps as part of the ‘SLOSS’ debate on their conservation. 5. These data show how salinity in maritime reedswamps provides strong habitat diversity in what appear superficially to be uniform habitats, with importance for example to general site design or managed retreat. The data also reveal that risks to speciose freshwater communities in such sites might arise from tidal inundation or sea level change. © 1997 John Wiley & Sons, Ltd.