Odonata - Entomological Society of Latvia - Latvijas Daba

3.3. THE OCCURENCE AND POPULATION DENSITY OF GOMPHIDAE LARVAE IN RIVER GAUJA
Distribution. Three species of gomphid larvae were found in the River Gauja – Gomphus
vulgatissimus, Onychogomphus forcipatus and Ophiogomphus cecilia. Gomphidae were present in
21 squares. G. vulgatissimus was recorded in 20 squares, O. forcipatus – in eight squares and
O. cecilia larvaes in 5 squares. Gomphus flavipes was not found in this study.
Occurrence. Overall, gomphid larvae were found in 37 quantitative samples from 18 sites of
river Gauja. Larvaes of G. vulgatissimus mostly were found in samples, less – O. forcipatus
(Table 5).
Table 5. Number and occurrence of gomphid larvae in quantitative samples of macrozoobenthos
collected in the River Gauja from Taurene upstream to Carnikava downstream in 1998.
Species
Total number of
samples with
Gomphidae
Total number of
specimens
% from all
(n=280) samples
% from samples
with Gomphidae
(n=37)
Gomphus vulgatissimus 28 34 10.0 75.6
Onychogomphus forcipatus 14 19 5.0 37.8
Ophiogomphus cecilia 2 2 0.7 5.4
Seven substrate components from samples were selected: sand, gravel, pebbles, cobbles,
mud, detritus and macrophytes. In 11 % of the samples the substrate was uniform, in 49 % there
were two components, in 32 % – three components, and in 8 % – four components. Sand, gravel
and mud occurred most frequently and was found in all samples. In Gomphidae samples the best
represented component was cobbles also (Figure 9). In the analysis of the distribution of the sample
substrate components for G. vulgatissimus and O. forcipatus it was found that for G. vulgatissimus
the larvae mainly inhabit sandy and muddy micro habitats, while O. forcipatus prefers micro
habitats with gravel and pebbles (Figure 10).
Pe
4%
Gr
24%
Co
10%
Ma
5%
all samples (n=280)
Mu
19%
Sa
36%
De
2%
Pe
7%
Co
17%
Gr
20%
Ma
4%
Mu
20%
De
1%
Sa
31%
samples with Gomphidae (n=37)
Figure 9. Division of substratum by components represented in the samples (Sa – sand; Gr – gravel;
Pe – pebbles; Co – cobbles; Mu – mud; De – detritus; Ma – macrophytes) in the River Gauja from
Taurene upstream to Carnikava downstream in 1998.
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