Major Factors that Structure the Benthic Fauna of a Shallow, Tropical Lake, Lake Kuriftu, Ethiopia

Abstract

The aim of this study was to determine the community
structure of the benthos in Lake Kuriftu in relation to some environmental
variables. Benthic samples were collected with an Ekman grab (0.0225 m2)
from three sites (littoral, sub-littoral and profundal zones) on a monthly basis
from September 2009 to February 2010. Dissolved oxygen and temperature
were measured with a probe at different depths of each site. Sediment texture
was determined by the Bouyoucos hydrometer and organic matter content by
loss on ignition method. Chironomids, EPT (Ephemeroptera, Plecoptera,
Trichoptera), oligochaetes and coleopterans were abundant in littoral and
sub-littoral zones, with EPT much higher in the vegetated littoral area. The
mean density of benthic macro-invertebrates in littoral, sub-littoral and
profundal zones was 20,443, 18,251, and 4,388 ind/m2, and that of
Chironomids was 12,545, 14,003 and 3,215 ind/m2, respectively. The
profundal zone had the lowest diversity with abundant oligochaetes but no
EPT samples, despite the high oxygen content of the profundal zone (6.33
mg/l). Chironomids and oligochaetes were present in all zones which had
negligible difference in dissolved oxygen and organic matter content. The
littoral zone had highest diversity (H’=1.26) and richness (d=2.72). Our
results indicate that abundance of benthic macro-invertebrates of Lake
Kuriftu was best correlated with the presence of vegetation in the littoral zone
and sediment texture (high clay) in the littoral and profundal zones. We
conclude that benthic macro-invertebrate community structure in Lake
Kuriftu is mainly influenced by spatial variation in vegetation, sediment
texture and temperature, but not dissolved oxygen and organic matter
content