Kj. Collier et al., Patch- and reach-scale dynamics of a macrophyte-invertebrate system in a New Zealand lowland stream, HYDROBIOL, 392(2), 1999, pp. 89-97
Abundant growths of macrophytes are a common feature of streams in open low
land areas of New Zealand during summer, but the values of these to aquatic
biota are poorly understood. We studied the temporal dynamics of, and asso
ciations amongst, elements of a macrophyte-invertebrate system to provide a
n improved information base for lowland stream management. The biomass of m
acrophytes increased significantly over the four quarterly sampling occasio
ns from 43.8 g m(-2) in June to 370.8 g m(-2) in March; biomass was dominat
ed by Egeria densa on all dates, except in December when Potamogeton crispu
s was dominant. We did not detect strong associations between epiphyton bio
mass and invertebrate abundance in our study, but this may reflect the fact
that we sampled loosely-adhering epiphyton on young, surface-reaching shoo
ts whereas invertebrates were collected from macrophytes growing through th
e water column. Density of some invertebrate species per gram dry weight of
plant material varied by macrophyte type, with the chironomids Tanytarsus
vespertinus and Naonella forsythi displaying positive correlations with Ege
ria and Potamogeton biomass, respectively. The shrimp Paratya curvirostris
accounted for 50% of phytophilous invertebrate biomass, with Chironomidae t
he only other group to comprise more than 9%. Abundance of total phytophilo
us invertebrates displayed a positive linear relationship with macrophyte b
iomass in a sample (0.1 m(2)), and a humped relationship with species richn
ess, such that highest numbers of taxa occurred at macrophyte biomass level
s around 400 g dw m(-)2. Our study suggests that intermediate macrophyte bi
omass levels are likely to enhance macroinvertebrate biodiversity in sandy-
bottomed lowland streams.