Náttúrufræðingurinn - 2010, Side 93

93
Tímarit Hins íslenska náttúrufræðifélags
9. mynd. Fæðuvefur Laxár. Helstu leikendur eru sýndir feitletraðir með sverari umgjörð.
Orkan kemur frá Mývatni með þörungum (phytoplankton), groti (detritus) og dýrasvifi (zoo-
plankton). Aðalleiðin er um bitmý (Simulium vittatum). Önnur leið er í gegnum botnþör-
unga (ásætuþörunga) árinnar, sem étnir eru af kísilþörungaætum (vorflugunni randaváru
(Apatania zonella) og Limnephilus-vorflugulirfum, vatnabobba (Radix peregra). Annars
stigs neytendur, aðallega bitmýslirfur og rykmýslirfur, eru étnir af risaváru (Potamophylax
cingulatus), laxfiskum (Salmonidae), öndum (diving ducks) og ýmsum rándýrum af ættbálki
tvívængna, t.d. ránmýi (Chironomidae-Tanypodinae), lækjarflugu (Limnophora riparia)
og strandflugu (Clinocera stagnalis). Efst trónir maður, fálki og fiskiendur. – Foodweb of the
River Laxá. The main players are shown in bold letters and bold boxes. The main pathway
is through phytoplankton (Þörungasvif), detritus (Grot) and zooplankton (Dýrasvif)
from Lake Mývatn. The pathway goes through Simulium vittatum, and further through
Potamophylax cingulatus, salmonids (Laxfiskar) and diving ducks (Kafendur). An-
other pathway is through the river’s periphyton (Botnþörungar), further through diatom
feeders (Apatania zonella, Limnephilus, Chironomidae and Radix peregra). Finally P.
cingulatus, Tanypodinae, Limnophora riparia, Clinocera stagnalis, salmonids and div-
ing ducks are eaten by top predators, including man (Maður), Falcon (Fálki) and Goosand-
er (Gulönd). Teikn./Drawing: Árni Einarssonar o.fl. 2004.36
9. mynd
Fálki Maður
Kafendur
Gulönd
Laxfiskar
Dýrasvif Þörungasvif Grot
Vatnsbolur Mývatns Botnþörungar Laxár
Simulium vittatum
Radix peregra
Hydra sp.
Tanypodinae
Limnophora riparia
Clinocera stagnalis
Potamophylax
cingulatus
Chironomidae
Limnephilus spp
Apatania
zonella
been carried out since 1977 and from
1977 to 1985 a comprehensive study on
the production of blackflies (Simulium
vittatum) and non-biting midges
(Chironomidae) was conducted. It sup-
ported a comprehensive study on the
population sizes of brown trout (Salmo
trutta) and diving ducks of the river.
Blackflies and chironomids were 95–98%
of the benthos in the river, dominated by
S. vittatum and a few species of
Orthocladiinae. The population size of S.
vittatum fluctuated with phytoplankton
and drifting from the Lake Mývatn (Fig.
7). The food of the chironomids was the
river periphyton (Fig. 8). The S. vittatum
production was 56–95% of the benthic
production (Fig. 3–5). Population size of
the brown trout, Harlequin duck
(Histrionicus histrionicus) was determined
by the S. vittatum population size, and
backfly larvae and pupae were 56% of
the trout gut content and 98% of the
Harlequin duck’s food. The population
changes of the midges are monitored by
window traps (Fig. 2 and 6) which reflect
changes in their benthic production. The
food web of the River Laxá is simple and
is based on drift of fPOM from Lake
Mývatn, fed upon by S. vittatum (Fig. 9).
A smaller pathway originates in the river
periphyton, upon which chironomids
and Trichoptera feed. The blackflies and
chironomids are mainly eaten by trout
and diving ducks, but on top of the food
web are three species: man, the gyrfal-
con and the American mink.
The River Laxá is a unique ecosystem,
with rather simple foodweb that is easily
understood. It is also one of the rivers
with the highest known secondary pro-
duction in the subarctic/arctic region,
with large stocks of brown trout, salmon
and duck species not found elsewhere in
Europe. It should be a priority for the
Environmental Agency and the Ministery
for the Environment to remove con-
structions from the river, such as dams
associated with hydroelectric produc-
tion, since Laxá’s contribution to the
electrical production is not significant.
High nature conservation value of the
Ramsar site of Lake Mývatn and the
River Laxá should be a constant re-
minder for us to look carefully into all
anthropogenic developments in their
catchment area.
ins 1978. Einnig er náttúrufegurð
Laxár einstök og ættu næstu skref
í verndun árinnar að felast í því
að fjarlægja virkjanamannvirki úr
henni og gera jafnframt allt til að
stuðla að áframhaldandi verndun
Mývatns og Laxár.
Summary
Midge production and food-
web in the River Laxá
River invertebrate production is a major
factor in understanding community
structure and function. Research on pop-
ulation sizes and fluctuations in the
River Laxá in NE-Iceland (Fig. 2) has
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