Food web structure in a tropical stream ecosystem

This study investigated the structure and properties of a tropical stream food web in a small spatial scale, characterizing its planktonic, epiphytic and benthic compartments. The study was carried out in the Potreirinho Creek, a second-order stream located in the south-east of Brazil. Some attributes of the three subwebs and of the conglomerate food web, composed by the trophic links of the three compartments plus the fish species, were determined. Among compartments, the food webs showed considerable variation in structure. The epiphytic food web was consistently more complex than the planktonic and benthic webs. The values of number of species, number of links and maximum food chain length were significantly higher in the epiphytic compartment than in the other two. Otherwise, the connectance was significantly lower in epiphyton. The significant differences of most food web parameters were determined by the increase in the number of trophic species, represented mainly by basal and intermediate species. High species richness, detritus-based system and high degree of omnivory characterized the stream food web studied. The aquatic macrophytes probably provide a substratum more stable and structurally complex than the sediment. We suggest that the greater species richness and trophic complexity in the epiphytic subweb might be due to the higher degree of habitat complexity supported by macrophyte substrate. Despite differences observed in the structure of the three subwebs, they are highly connected by trophic interactions, mainly by fishes. The high degree of fish omnivory associated with their movements at different spatial scales suggests that these animals have a significant role in the food web dynamic of Potreirinho Creek. This interface between macrophytes and the interconnections resultant from fish foraging, diluted the compartmentalization of the Potreirinho food web.

Yeasts and others parameters of pollution of the Ribeirao Claro stream in Rio Claro, São Paulo

The main water source of the Rio Claro municipal district (DAAE) was analysed for determining the level of organic contamination. Temperature, pH, light penetration, conductivity, dissolved oxygen, total dissolved phosphate, ortophosphate, ammonia, heterotrofic bacteria, total coliforms, fecal coliforms, total yeasts and fermentative yeasts were analysed during one year with samples being collected on a monthly basis. Bathing quality of the water from sites 1, 2 and 3 were classified, respectively, as Satisfactory, Very Good and Improper based on fecal coliform counts. Total yeast counts were appropriate as a complement for the appraisal of fresh water contamination by coliform counts. Seventeen yeast species belonging to genera Candida, Cryptococcus, Kloeckera, Pichia and Rhodotorula were found but none of them could be correlated with a level of contamination. Candida famata, C. robusta-like and C. colliculosa were isolated at all of the sites and between the five species found only at the more polluted site, Rhodotorula mucilaginosa was prevalent.

Anthropogenic influences on annual flux of cations and anions at meio stream basin, São Paulo State, Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Phenology of a dioecious population of Batrachospermum delicatulum (Batrachospermales, Rhodophyta) in a stream from southeastern Brazil

The seasonal dynamics of a dioecious population of Batrachospermum delicatulum (Skuja) Necchi and Entwisle was evaluated biweekly during the growth period of the macroscopic gametophyte, from late autumn (May) to early spring (October) in a third-order stream from the northeast region of Sao Paulo State, southeastern Brazil (20°43'S, 49°13'W). The population fluctuated throughout the study period in terms of percentage cover, frequency and chlorophyll content. Percent cover and frequency showed a clear pattern with the lowest values at the initial and final stages of the growth period and the highest in July-August (winter). Gametophyte growth was associated with high illumination and low temperature, which agrees with most observations on Batrachospermales in stream environments. Relatively wide variations in reproductive characteristics were observed during the growth period, which were not correlated with percentage cover, frequency and chlorophyll content. The phenologic pattern observed in this population was characterized by a synchronic development of female/male plant ratio with the number of spermatangia per plant resulting in. (i) a higher proportion of fertilized (carposporophytic) plants associated with more male plants; (ii) higher fertilization rates during the periods with higher production of spermatangia per plant; and (iii) higher production of spermatangia per plant when the population had more male plants. These characteristics were largely associated with water temperature and ion content. In terms of reproductive success, the population studied can be regarded as highly efficient, considering the relatively low proportion of male to female plants and high fertilization rates. These data are consistent with a hypothesis to explain high fertilization rates in dioecious species in lotic habitats consisting of outcrossing among adjacent plants with intermingled male and female branches within an algal cluster. Efficient reproductive strategies have been reported in dioecious, monoecious and even mixed populations of B. delicatulum and can be interpreted as adaptations to successfully colonize streams with different characteristics.

Photosynthetic responses to temperature in tropical lotic macroalgae

A comparative analysis of the photosynthetic responses to temperature (10-30°C) was carried out under short-term laboratory conditions by chlorophyll fluorescence and oxygen (O2) evolution. Ten lotic macroalgal species from southeastern Brazil (20°11-20°48′S, 49°18-49°41′W) were tested, including Bacillariophyta, Chlorophyta, Cyanophyta, Rhodophyta and Xanthophyta. Temperature had significant effects on electron transport rate (ETR) only for three species (Terpsinoe musica, Bacillariophyta; Cladophora glomerata, Chlorophyta; and C. coeruleus, Rhodophyta), with highest values at 25-30°C, whereas the remaining species had no significant responses. It also had similar effects on non-photochemical quenching and ETR. Differences in net photosynthesis/dark respiration ratios at distinct temperatures were found, with an increasing trend of respiration with higher temperatures. This implies in a decreasing balance between net primary production and temperature, representing more critical conditions toward higher temperatures for most species. In contrast, high net photosynthesis and photosynthesis/dark respiration ratios at high and wide ranges of temperature were found in three species of green algae, suggesting that these algae can be important primary producers in lotic ecosystems, particularly in tropical regions. Optimal photosynthetic rates were observed under similar environmental temperatures for five species (two rhodophytes, two chlorophytes and one diatom) considering both techniques, suggesting acclimation to their respective ambient temperatures. C. coeruleus was the only species with peaks of ETR and O 2 evolution under similar field-measured temperatures. All species kept values of ETR and net photosynthesis close to the optimum under a broad range of temperatures. Increased non-photochemical quenching, as a measure of thermal dissipation of excess energy, toward higher temperatures was observed in some species, as well as positive correlation of non-photochemical quenching with ETR, and were interpreted as two mechanisms of adaptation of the photosynthetic apparatus to temperature changes. Different optimal temperatures were found for individual species by each technique, generally under lower temperatures by O2 evolution, indicating dependence on distinct factors: increases in temperature generally induced higher ETR due to increased enzymatic activity, whereas increments of enzymatic activity were compensated by increased respiration and photorespiration leading to decreases in net photosynthesis.

Ecology and morphological characterization of gametophyte and 'Chantransia' stages of Sirodotia huillensis (Batrachospermales, Rhodophyta) from a stream in central Mexico

The morphology and phenology of Sirodotia huillensis was evaluated seasonally in a central Mexican first-order calcareous stream. Water temperature was constant (24-25°C) and pH circumneutral to alkaline (6.7-7.9), and calcium and sulfates were the dominant ions. The gametophyte stages were characterized by the presence of a distinctive mucilaginous layer, a marked difference in phycocyanin to phycoerythrin ratio between female and male plants, and the presence of a carpogonia with a large trichogyne (>60 μm). Occasionally three capogonia were observed on a single basal cell. The 'Chantransia' stages were morphologically similar to those described for the other members of Batrachospermales. A remarkable observation was the formation of dome-shaped structures, consisting of prostrate filaments that are related with the development of new gametophytes. Chromosome numbers were n = 4 for fascicle cells, cortical filament cells and dome-shaped cells, and 2n = 8 for gonimoblast filament cells and 'Chantransia' stage filaments. Gametophytes and 'Chantransia' stages occurred in fast current velocities (60-170 cm/s) and shaded (33.1-121 μmol photons/m2/s) stream segments. The population fluctuated throughout the study period in terms of percentage cover and frequency: the 'Chantransia' stages were most abundant in the rainy season, whereas gametophytic plants had the highest frequency values during the dry season. These results were most likely a result of fluctuations in rainfall and related changes in current velocity. Some characteristics of this population can be viewed as probable adaptations to high current velocities: the mucilaginous layer around plants that reduces drag; potential increase in fertilization by the elongate and plentiful trichogynes and abundant dome-shaped structures producing several gametophytes.

Cytogenetic analysis of three sympatric Gymnotus species (Teleostei: Gymnotidae) from the Fundo Stream, MG, Brazil

Three sympatric species of Gymnotus from the Fundo stream, a small tributary of the Sapucai river, Minas Gerais State, Brazil, were studied in relation to their karyology. Gymnotus sylvius presented 2n=40 chromosomes (36 m/sm+4 st/a), Gymnotus sp. presented 2n=50 (26 m/sm+ 24 st/a) and Gymnotus paraguensis had 2n=54 (50 m/sm+4 st/a). C-banding demonstrated positively stained heterochromatic blocks in the centromeric position of few chromosomes on G. sylvius and in the centromeric region of all chromosomes on G. paraguensis samples. The nucleolus organizer region (NOR) was located on the short arm of one st chromosome pair in G. sylvius and Gymnotus sp., and in the interstitial position on the short arm of the pair number one and below the centromere on a third chromosome on G. paraguensis. The cytogenetic data obtained indicate that Gymnotus sp. represent a new Gymnotus specie with a karyotypic constitution never observed on others species from this genus. Some aspects related to the chromosome diversification of these Gymnotus are discussed. © 2007 The Japan Mendel Society.

Reproductive cycle and fecundity of Potimirim glabra (Kingsley, 1954) (Caridea, Atyidae) from a littoral stream

The reproductive cycle of Potimirim glabra, especially the female size at sexual maturity, reproductive period and fecundity, was studied at two sites of one of the northern littoral streams in the state of São Paulo, Brazil. Prawns were collected monthly for one year. The minmum size at sexual maturity was estimated from the smallest ovigerous female (cephalothorax length = CL), and the reproductive period was determined monthly by examining the relative frequency of ovigerous females. Size comparisons between sampling sites was carried out using the Mann-Whitney u test. The relationship between environmental factors and reproductive aspects was verified using the Spearman's rank correlation. At Site 1, the collected ovigerous females had a CL mean size of 4.24±0.36 mm (n=481); at Site 2, ovigerous females (n=391) had a CL mean size of 5.48±0.49 mm. The reproductive pattern in Camburi is seasonal, with the highest frequency of ovigerous females in February. The frequency of ovigerous females was positively correlated to organic matter content in the substratum, rainfall and temperature. Increased percentage organic matter may indicate greater food availability whereas higher rainfall increases the velocity of the current, thereby aiding the larvae, which depend on brackish water to complete their development, to reach the estuarine region. The temperature acts on the speed of larval development. At Site 1, the mean fecundity obtained was 202±72.31 eggs (90 females; CL from 2.7 to 4.7mm PL), whereas at Site 2, it was 433.3±120.7 eggs (46 females; CL from 4.0 to 5.5mm PL). © 2010 Balaban.

Distribuição ecológica das comunidades de macroalgas de ambientes lóticos em duas unidades de conservação abrangendo os biomas da Floresta Estacional Semidecidual e Campos no estado do Paraná

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Efeitos da textura e heterogeneidade de substratos artificiais em função da velocidade da correnteza e da escala temporal sobre as comunidades de macroalgas de ambientes lóticos

Pós-graduação em Ciências Biológicas (Biologia Vegetal) - IBRC

Características fotossintéticas de produtores primários de ambientes lóticos

Pós-graduação em Ciências Biológicas (Biologia Vegetal) - IBRC

Flora e distribuição ecológica de comunidades de macroalgas lóticas de fragmentos florestais da região noroeste do estado de São Paulo

Pós-graduação em Ciências Biológicas (Biologia Vegetal) - IBRC

Análise da variação espaço-temporal em diferentes escalas sobre a distribuição ecológica das comunidades de macroalgas de duas bacias de drenagem da região centro-sul do estado do Paraná

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Development of habitat suitability criteria for Neotropical stream fishes and an assessment of their transferability to streams with different conservation status

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)