Estrutura da comunidade de macroinvertebrados aquáticos associados a mauritia flexuosa linnaeus (arecaceae), fitotelmata, na Amazônia central, Brasil

Abstract

Adult Mauritia flexuosa L. (Arecaceae) palms, known locally as buriti, have large individual axilae that can store substantial volumes of water (phytotelmata). The objectives of the present study were to compare the aquatic macroinvertebrate fauna associated with the axilae of palms occurring in groups and as isolated trees in order to verify the relationship between abiotic factors (volume of water, pH, electrical conductivity, dissolved oxygen and height above the ground) and the macroinvertebrates, in addition to inferring a trophic web for these organisms. A total of 60 axilae were sampled in May and June 2006, distributed over 17 rural and semiurban locations in Manaus and President Figueiredo counties, Amazonas state, Brazil. A total of 31,135 individuals distributed over 19 macroinvertebrate taxa were collected. The families Chironomidae and Ceratopogonidae were the most abundant (32.2% and 29.6%, respectively), followed by Oligochaeta (17.5%), Acarina (9.6%) and Culicidae (Culex (Microculex) stonei Lane & Whitman, 1943 (3.4%), Culex (Mcx.) pleuristriatus Lutz, 1903 (2%), Culex (Mcx.) sp.1 (1.8%), Culex (Culex) mollis Dyar & Knab, 1906 (0.6%), Wyeomyia sp. (16 individuals) and Toxorhynchites (Haemorrhoidalis) haemorrhoidalis (Fabricius, 1794) (1 individual)). For each axila, the following averages (±SD) were calculated: individuals per axila: 519 (±348); volume of water: 1075 mL (±972); temperature: 27.3 ºC (±1.4); pH: 5.6 (±0.7); electrical conductivity: 25.2 μS/cm (±18.4) and dissolved oxygen: 7.3 mg/L (±1.3). The most frequent taxa were Culicoides spp. and Endotribelos sp., both with 100% occurrence, followed by Oligochaeta (93.3%), Acarina (85%) and Culex (Mcx.) stonei (75%). The final multiple regression model relating macroinvertebrate abundance to the abiotic variables explained 25.3% of the variance (F4.55=4.66; p=0.0026), volume being the only variable that was related to abundance (p=0.007). Multiple regression for species richness was not significant (F4.55=2.31; p=0.069). The numbers of Culicidae and Odonata individuals showed significant positive relationships with water volume (p=0.0009 and p=0.045, respectively). The distribution of macroinvertebrates not differed between grouped and isolated palm trees (ANOSIM, R=0.037; p=0.029), the abundance of Odonata being influenced by the grouping of the trees (t-test, p=0.048). The presence of Odonata larvae (top predators in the ecosystem) appears not to influence the abundance of Culicidae larvae in the axilae of M. flexuosa (t-test, p=0.382). Analysis of the stomach content of Odonata representatives found in the buriti (Coenagrionidae sp. and Erythrodiplax sp.) revealed Chironomidae, Ceratopogonidae and Culicidae as the most frequent prey. Diptera was the most frequent and abundant group, confirming the importance of this insect in communities associated with phytotelmatas. In comparison with other phytotelmata studies, the trophic web found in the M. flexuosa axilae is relatively complex, involving 20 taxa; the top predador of this web is represented by Coenagrionidae sp. and Erythrodiplax sp.