Die Tropenstation La Gamba

Die „Tropenstation La Gamba“ in Costa Rica – Wissenschaftlicher Bericht
TSCHELAUT, J.: Leaf litter decomposition and macroinvertebrates in a neotropical lowland
stream, Quebrada negra, costa Rica. – Diplomarbeit, Univ. Wien, Fakultät für
Lebenswissenschaften. Dep. für Limnologie und Hydrobotanik.
One of the primary objectives of the study was to investigate the rivernetwork within the
Rio Esquinas catchment. Rivers were analyzed with regard to abiotic parameters such as
morphology, hydrology, hydrochemistry, sedimentology and canopy cover by the riparian
vegetation. The work discusses differences between sites according to geological factors
and the seasonal hydrologic characteristics from streams within the catchment.
Furthermore, the morphometric-hydrological conditions of the Quebrada Negra, a 1 st
order stream, were investigated in more detail.
The decomposition and macroinvertebrate colonisation of leaf litter was investigated
using litter bags placed over a 28 day period in the Quebrada Negra. Leaf decay rates and
macroinvertebrate densities on leaf packs of Acalypha diversifolia (Euphorbiaceae),
Cecropia obtusifolia (Cecropiaceae), Tetrathylacium macrophyllum (Flacourtiaceae) and
Sloanea medusula (Elaeocarpaceae) were compared. The plants were chosen after their
frequency and life history strategy (r- and K- strategists).
Colonizer densities (total individuals and abundance of major taxa) were highest on
Cecropia and Tetrathylacium leaves and lowest on Sloanea. Densities first increased with
time on all 4 plant species but abundance on Acalypha, Cecropia and Tetrathylacium
declined at the end of the study (day 28) when little of the leaves remained in the bags.
Most of the variation in colonizer densities and species composition was explained by leaf
type and time.
The invertebrate community which colonised litter bags was dominated by taxa of
mayflies (mainly Leptohyphidae), caddiesflies and Chironomidae.
The plants differ in their content of tannins and anatomical cuts of the leaf material show
the varying nature of the leaf structure which supports the result of the differences in
decay.
Throughout this study we analysed the relationship between taxonomical composition and
functional organization of stream benthic communities and some environmental variables
in riffle and pool sites of the Quebrada Negra. Local variations of abiotic factors, such as
current velocity, substratum composition and water depth, shape the distribution of
invertebrates. This investigation represents the first survey of the benthic invertebrate
community from four different choriotops (habitat types) within the Q. Negra. Betweensite
differences are discussed in relation to physical factors.
Anschrift der Autorin:
Mag. Julia Tschelaut
tschuliebuhlie@hotmail.com
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