Climate Change and the Hydrology and Morphology of Freshwater Ecosystems - Climate Change Impacts on Freshwater Ecosystems - page 75

2.0

1.5

Spring

1.0

0.5

HAB107

0.0

S_POOL
M_POOL

CH_RUN
CH_RIF
CH_POOL

-0.5

Autumn

-1.0

-1.5

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5

MDS1

Figure 4.4 Comparison of macroinvertebrate communities (using multidimensional
scaling) among habitat types in stretches of the river Becva. (S_POOL, side arm;
M_POOL, main-channel margin; CH_RUN, CH_RIF and CH_POOL, main-channel run, riffle
and pool, respectively.)

habitat type. Furthermore, organisms need places for hiding, resting, mating,
copulation and egg deposition, increasing the importance of in-stream habitat
variability. The survey included an unsilted reference and a degraded, silted
site. The glossosomatid Agapetus ochripes scrapes algae and other micro-organisms
from stable substrates and is found in large numbers at the reference site but
is scarce at the degraded site. Pupae are only found at the reference site,
suggesting that conditions at the degraded site prevent larvae of this species
from becoming adults. Lype phaeopa is a scraper that only occurs on woody
debris and is found at eight times higher densities at the reference site in
comparison with the degraded site. The carnivorous species Brachycentrus
montanus needs stable substrates on which to fix its case, to be able to stretch
its spiny legs as a filtering apparatus into the current. Three different instars
could be found at the silted site in quite high densities, but again there were
no pupae, whereas at the reference site, all instars and a high number of pupae
were recorded. Another example is Lasiocephala basalis ( Lepidostoma basale ),
which mainly lives on woody debris, feeding on bacteria and fungi. Density is
comparable between sites, but again pupation takes place exclusively at the
reference site (Fig. 4.5).