NTU Undergraduates' research April 2014 - Biosciences | Page 117

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Use of Subsurface Sediment as a Refuge by Gammarus pulex: An Experimental Approach
Abstract: The role of the hyporheic zone as a refuge by benthic macroinvertebrates is a key part of the hyporheic
refuge hypothesis. Where stream invertebrates seek refuge in a more stable environment during disturbance events.
The effects of fine sediment on the aquatic environment have also been studied in depth, however the effects of fine
sediment on the hyporheic zone is little understood. With the effects of fine sediment (particles <2mm in size) on the
migration of aquatic macroinvertebrates remaining sparsely studied. Gammarus pulex was used as a test species, as it
is known to undertake migration from the benthic zone into the hyporheic zone when subjected to water removal. The
effects of fine sediment present were studied by altering the percentage sediment present in the substrate and
removing water as to prompt migration into the hyporheic zone. The migration of G. pulex was then measured using
proportion migration. A decline in the migratory activity was observed, with migration ceasing when fine sediment
reached 17.5% saturation levels. With coarse sediment also studied in the same way, providing evidence that no
migration occurs when sediment 2-3mm in size is present in the substrate. These results clearly demonstrate the
importance of considering the relationships between fine sediment, migration and the aquatic fauna present in a
stream.
Key words: Hyporheic zone, fine sediment, hyporheic refuge hypothesis, Gammarus pulex, macroinvertebrates,
benthos, refuge, migration.