Vertical distribution and secondary production of invertebrates in three streams of the Cass Basin
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
The vertical distribution of benthic invertebrates was assessed seasonally in three contrasting streams at Cass, inland Canterbury using freeze core and substrate colonisation techniques. Biomass and production of selected invertebrate taxa were also measured at the three sites that differed in water chemistry, bed stability, and riparian setting. Densities of aquatic invertebrates differed seasonally, with greatest numbers of most common taxa being present in summer and autumn. Overall, greatest abundances of invertebrates were found in the top 10 cm of the stream beds with densities being lowest at 20-30 cm, the deepest stratum sampled. Biomass and secondary production were calculated for Deleatidium spp., two species of Olinga (O.feredayi and O.jeanae) , and Chironomidae, to determine whether conventional Surber sampling led to underestimations compared with freeze cores to a depth of 30 cm in the hyporheic zone. Results for the two streams for which full data sets were collected indicated that Surber sampling underestimated production of the different taxa to varying degrees although. Deleatidium production estimates for both streams were similar when calculated with freeze core data. However, estimates obtained for Olinga and Chironomidae were between 6.8 to 9.5 times greater. My findings have important implications for the accurate sampling of stream benthos, and indicate that conventional collection methods that consider only the top 10 cm or so of stream beds may severely underestimate the density and biomass of invertebrates.