The importance of aquatic margins to invertebrates in English chalk streams
Harrison, Simon S. C.
Archiv für Hydrobiologie Volume 149 Number 2 (2000), p. 213 - 240
published: Sep 29, 2000
ArtNo. ESP141014902003, Price: 29.00 €
Standardized kick-sweep samples of invertebrates were taken from three habitats - mid-channel gravel, Ranunculus and marginal vegetation - in six lowland chalk streams, on four sampling occasions between May 1996 and January 1997. Several types of marginal vegetation were sampled, including the stems and leaves of trailing terrestrial vegetation and semi-emergent marginal macrophytes. There was little difference in invertebrate community composition between the different marginal vegetation types, despite fine-scale differences in habitat architecture. The invertebrate communities in mid-channel gravel, Ranunculus and marginal vegetation were very different from each other over most of the year, particularly in spring and winter. Each habitat was characterised by a suite of invertebrates, reflecting the physical and biological differences between the habitats. Community diversity and equitability were greatest in the physically complex margins and least in the more simply structured Ranunculus. Invertebrate abundance per sample was greatest in Ranunculus. Approximately one half of all taxa in the chalk streams showed no significant preference for any single habitat. Of those taxa that significantly preferred one habitat, many more preferred marginal vegetation compared to either gravel or Ranunculus. Many taxa found throughout the investigation avoided gravel and Ranunculus, but very few taxa avoided marginal vegetation. Rare taxa also occurred more frequently in the margins. Marginal vegetation was used by invertebrates both as a favoured site of oviposition and as a conduit between the aquatic and terrestrial environments. Margins thus acted as a focus for reproduction and recruitment for chalk streams. The relative importance of marginal vegetation for stream invertebrate biodiversity and reproduction is high relative to other mid-channel habitats. More attention should be given to this habitat than has been in the past, particularly in the fields of stream conservation and restoration.