The succession dynamics of a macroalgal community after a flood disturbance in a tropical stream from São Paulo State, southeastern Brazil

The succession dynamics of a macroalgal community in a tropical stream (20º58' S and 49º25' W) was investigated after disturbance by a sequence of intensive rains. High precipitation levels caused almost complete loss of the macroalgal community attached to the substratum and provided a strong pressure against its immediate re-establishment. After this disturbance, a weekly sampling program from May 1999 to January 2000 was established to investigate macroalgal recolonization. The community changed greatly throughout the succession process. The number of species varied from one to seven per sampling. Global abundance of macroalgal community did not reveal a consistent temporal pattern of variation. In early succession stages, the morphological form of tufts dominated, followed by unbranched filaments. Latter succession stages showed the almost exclusive occurrence of gelatinous forms, including filaments and colonies. The succession trajectory was mediated by phosphorus availability in which community composition followed a scheme of changes in growth forms. However, we believe that deterministic and stochastic processes occur in lotic ecosystems, but they are dependent on the length of time considered in the succession analyses.

The succession dynamics of a macroalgal community after a flood disturbance in a tropical stream from São Paulo State, southeastern Brazil

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

Diet and trophic groups of an aquatic insect community in a tropical stream

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

Independent and interactive effects of a top and an intermediate fish species on the food web structure of a tropical stream

Two fish species, one top predator (Imparfinis mirini) and one intermediate detritivorous species (Hisonotus depressicauda), were experimentally manipulated to evaluate their relative importance in structuring the periphytic community, as well as their effects on the other trophic levels. An enclosure experiment was conducted in the Potreirinho creek, a second order tributary of Paranapanema River, SE Brazil. Five treatments were used: enclosure of the predator species. enclosure of the detritivorous species, enclosure of both together, exclusion of all fish species (closed control cage), and cage open to all fish community, (open control). Through direct and indirect effects, I. mirini, when alone gave rise to a trophic cascade that resulted in a positive effect on algal resources. Through direct effects, H. depressicauda. when alone, reduced the amount of organic matter, resulting in a positive indirect effect on algae. In addition, when the two species were enclosed together, only the effects determined by the detritivorous species were present. The results indicate the important role of the intermediate detritivorous species in the maintenance of the composition and trophic structure of the analyzed community by reducing the effects caused by the top predator.

Feeding selectivity of ichthyofauna in a tropical stream: space-time variations in trophic plasticity

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Evaluation of seasonal dynamics and bioindication potential of macroalgal communities in a polluted tropical stream

Macroalgal communities and environmental variables were analyzed seasonally along a polluted tropical stream in São Paulo State, Brazil, We aimed to improve the knowledge of tropical macroalgal communities, to study the longitudinal and seasonal dynamics of these communities in influenced environments, to evaluate the relationship of algal frequency and abundance with selected environmental variables, and to look for potential macroalgal species indicators. The seasonal abundance pattern was similar to natural or low influenced systems and was mainly determined by rainfall regime. However, community composition was closely related to some chemical water pollution indicators, such as phosphorus and nitrogen compounds. Some species are suggested as potential indicators of organic pollution (e.g. Oscillatoria ornata, Stigeoclonium helveticum and Schizomeris leibleinii), but more detailed studies have to be developed to determine the tolerance limits of these species. on the basis of our results and literature data, the use of occurrence of Oscillatoriales in relation to other orders of Cyanoprokaryota is suggested to be a good indicator of organic pollution in tropical lotic ecosystems.

Effects of artificial substratum types and exposure time on macroalgal colonization in a tropical stream

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

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.

Diet of invertebrates sampled in leaf-bags incubated in a tropical headwater stream

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Retention of particulate organic matter in a tropical headstream

Retention of particulate organic matter was investigated over a range of water discharges in pool and riffle zones of a tropical stream (Itauna Stream, São Paulo, Brazil). A closed-system leaf release and capture method was used to quantify leaf retention in a 50-m reach of the stream. Instantaneous retention rates (k) were calculated by a negative exponentialmodel and specific retention rates (ke) computed for each 1m interval. The mean k was 0.0161 +/- 0.0101 (S.E.) and ranged from 0.005 to 0.036 during the study period. This suggests a low retention of particulate matter. The evidence provided by this study shows that there was a relationship between retention and discharge. At low discharges, greater percentages of leaves were retained in a 3-h period while high discharges resulted in low retention percentages within the studied reach. In the Itauna Stream, no significant difference (p < 0.05) was found between the ke values of pool and riffle zones.

Input of litter in deforested and forested areas of a tropical headstream

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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.

Preferência alimentar por insetos aquáticos em espécies de peixes de riacho tropical

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)