4 - Temporal and spatial dynamics of meiofaunal assemblages in the hyporheic interstitial of a gravel stream

Summary

ABSTRACT The meiofaunal assemblages within the interstitial hyporheic (0–40 cm) of a gravel stream were studied at fortnightly sampling intervals between October 1991 and October 1992. Four taxa constituted 79.7% of the community: Nematoda, Rotifera, Cyclopoida and Gastrotricha. Significant seasonal variation occurred in most meiofaunal groups, and were characterized by either one abundance peak (gastrotrichs and harpacticoids) or two abundance maxima (microturbellarians, nematodes, rotifers and cyclopoids). These taxa showed significant differences in their mean densities between sediment depths. Most meiofaunal groups exhibited highest densities at sediment depths between 20 and 40 cm, whereas the depth distribution of Rotifera was more variable among the sites without a distinct depth maxima.

The effect of variables such as sediment depth, water depth, temperature, variation of groundwater levels and discharge was tested upon the mean abundances of each taxa. Except for Rotifera, a combined effect of some of these variables was detected in most taxa. Sediment depth was positively related to meiofauna densities suggesting that densities increased with increasing depth.

INTRODUCTION

In freshwater pelagic ecosystems the role of micro-meiozooplankton (i.e. Protozoa and Rotifera) as important groups in the food chain is well known (Pace & Orcutt, 1981). In streams there is an increasing awareness that these micromeiofaunal groups may constitute a potential link between the heterotrophic production and the meio- and macro-invertebrate predators. Recently, Schmid (1994) demonstrated that rotifers are important prey items for early instars of predatory chironomids in a gravel stream.