Ricardo Motta Pinto-Coelho

The contribution of water hyacinth (Eichhornia crassipes) and zooplankton to the internal cycling of phosphorus in the eutrophic Pampulha Reservoir, Brazil

The contribution of zooplankton and the waterhyacinth, Eichhornia crassipes, to the internal cycling of phosphorus was investigated in Pampulha Reservoir, in the shallow and eutrophic Pampulha Reservoir. In the last 20 years, algal blooms, as well as outbreaks of the macrophyte, have been observed with increasing frequency. Previous investigations have suggested that phosphorus is the limiting nutrient controlling the plant production in this ecosystem. A restoration program is currently underway aiming at the complete removal of external nutrient input. Therefore, the knowledge of the magnitude of some internal metabolic processes would be desirable in order to estimate the time lag that would be necessary for the recovery of water quality. The production and loss of macrophyte biomass was monitored in limnocurrals between May 1994 and April 1995. The zooplankton was also monitored during this period at a central sampling point. The biomass losses of macrophytes were followed in marked plants during their growing season. The P-content of macrophyte biomass was also measured monthly. Excretion rates of zooplankton collected in the reservoir were determined using short time experiments at the laboratory. This study demonstrated that zooplankton was more important for the P-cycling during the dry season when it was able to recycle a maximum of 26% d-1 of total phosphorus in lake water. The macrophyte contribution was more important during the rainy season (especially at the end of the rainy season). In April 1995, the macrophytes were able to recycle as much as 26% d-1 of the total phosphorus present in the water. At this time of the year, both communities recycled more than 40% d-1 of the total phosphorus available in water. Therefore, it was demonstrated that zooplankton and macrophytes play a key role in the internal cycling of a limiting nutrient in this reservoir.

Produção e consumo de carbono orgânico na comunidade planctônica da represa da Pampulha, Minas Gerais, Brasil

The basic aim of the present investigation was related to the question: How important is the phytoplankton as a food resource for zooplankton in a tropical hypereutrophic reservoir? For answering this question, two different approaches were adopted. The first one included a regular monitoring program aimed to follow the composition and biomass of zooplankton as well as the major food resources, expressed in terms of C-biomass of sestonic particles. A second approach included the experimental determination of the balance between production and consumption of organic carbon in the planktonic community of Pampulha Reservoir. This was done through simultaneous determination of maximum potential primary production and assimilation rates of mesozooplankton estimated from respiration rates. The algal production was evaluated considering two different size fractions: a) nanno- (< 50 µm) and b) net phytoplankton (50-160 µm). The respiration of zooplankton community was restricted to larger organisms (mesozooplankton). These rates were determined at the laboratory under optimal conditions of illumination and temperature. Field data from the monitoring program showed that the limnetic zone of the reservoir supported a relatively low algal biomass for most parts of the seasonal cycle (< 30 µg.L-1). Except the short term algal (Microcystis spp.) blooming periods, chlorophyll-a concentrations in the water column remained at relatively low levels. The annual range of chlorophyll-a was 0-126 µg.L-1. Furthermore, field data also indicated that the bulk of the sestonic carbon was concentrated on non-pigmented particles. Evidences from laboratory suggested that the carbon demand of zooplankton could not be supplied by primary producers from the limnetic zone alone. The potential primary production ranged from low to moderate values (2.0-37.3 mgC. m-3h-1) and, as a consequence, assimilation rates of zooplankton remained higher than algal production (< 50 µm) for most parts of the year. Considering these evidences from field and laboratory, this study concludes that the energetic demand of (meso)zooplankton was, to a large extent, supplied by the detrital food chain.

The nutritional status of zooplankton in a tropical reservoir: effects of food quality and community structure

The temporal variability of energetic reserves of zooplankton in the eutrophic Pampulha reservoir was investigated during two successive annual cycles. The effects of dominance of large filter-feeding cladocerans (Daphnia) and the occurrence of massive blooms of the cyanobacteria Microcystis on the energetic reserves of zooplankton were tested. This study showed that phytoplankton composition has a greater effect on energetic reserves of zooplankton. Some associations between lipid levels and the specific composition of zooplankton were also found. This study also demonstrated that the elementary composition of phosphorus in zooplankton can be used as an estimator of the nutritional status of zooplankton.

Hydroacoustic assessment of fish and Chaoborus (Diptera-Chaoboridae) distribution in three Neotropical lakes

AIM: This study aims to demonstrate the potential of hydroacoustics in the study of behavior of the invertebrate Chaoborus and fish in neotropical water environments; METHODS: Synoptic campaigns were conducted in May and June-2008 in Dom Helvecio and Carioca lakes, at the Parque Estadual do Rio Doce (MG), and Nado reservoir, Belo Horizonte (MG). The acoustic scattering of targets was studied using a downward-oriented split-beam 200 kHz echosounder; RESULTS: We detected clear echo signals from fish and Chaoborus larvae, which can be viewed in high density in all environments studied. The normal migratory behavior of the larvae of Chaoborus could be easily monitored in the Dom Helvecio Lake and the Nado reservoir. However, this behavior was not seen in Carioca Lake; CONCLUSIONS: This study revealed the potential application of acoustic approaches to study the behavior of fish and zooplankton organisms in freshwater aquatic systems.

Diurnal variation of zooplankton biochemical composition and biomass in plankton production tanks

The nutritional value of zooplankton (lipid and phosphorus contents) was analyzed in outdoor, plankton-culture tanks, to monitor the effects of diurnal variation and fertilization. Total lipid contents were significantly higher (average values of about 14% DW) for the treatment fertilized during the sampling week. A significantly highher total lipid concentrations generally coincided with high biomass of Moina sp. (Cladocera) and Thermocyclops sp. nauplii (Copepoda), which is probably related to zooplankton filtration rates. The values tended to be higher during the afternoon and the night. Phosphorus contents in the zooplanktonic population varied from 0.15 to 0.91% DW, with significant differences among the tanks. The zooplankton nutritional quality was greatly influenced by fertilization, which also determined the species composition in the tanks.

Length-weight relationships and biomass of the main microcrustacean species of two large tropical reservoirs in Brazil

Length-weight equations were determined for the main microcrustacean species of Três Marias and Furnas reservoirs (state of Minas Gerais, Brazil), and evaluated the fluctuations of their biomass. We examined the following species: Thermocyclops minutus, Bosminopsis deitersi, Bosmina hagmanni, Ceriodaphnia cornuta, and Moina minuta (Três Marias Reservoir), and Notodiaptomus henseni, Daphnia ambigua, Ceriodaphnia silvestrii, Diaphanosoma spinulosum, D. fluviatile, and Bosmina freyi (Furnas Reservoir). Dry weight was obtained in a microbalance for each size class (Cladocera) or developmental stage (Copepoda). Microcrustacean mean biomass varied from 5.76 mg DW.m(-3) and 20.36 mg DW.m(-3) (Furnas Reservoir) and from 3.75 mg DW.m(-3) and 18.14 mg DW.m(-3) (Três Marias Reservoir). Significant differences (p < 0.000) between seasons were registered with higher biomass during the rainy seasons. Thermocyclops minutus was the most important species in Três Marias, whereas in Furnas, N. henseni contributed in equal proportion. In Furnas, the higher cladoceran biomass was explained by the contribution of larger-sized species, such as D. ambigua, C. silvestrii, D. spinulosum, and D. fluviatile. Even though both reservoirs are considered oligotrophic, there were significant differences in the estimated microcrustacean biomass, which reinforces the importance of this parameter for the description of the real contribution of each species in the community.

Implementation of hydroacoustic for a rapid assessment of fish spatial distribution at a Brazilian Lake - Lagoa Santa, MG

AIM: To study the distribution, structure, size and density of fish in the karst lake: Lagoa Central (Lagoa Santa, MG - surface area: 1.7 km2; mean depth: 4.0 m; and maximum depth: 7.3 m). METHODS: The hydroacoustic method with vertical beaming was applied, using the echosounder Biosonics DT-X with a split-beam transducer of 200 kHz. The analysis of the acoustic data was performed with the software Visual Analyzer (Biosonics Inc.). Thematic maps of density echoes associated with fish, estimated by the technique of echo-integration, were made using the kriging interpolation. The density and vertical distribution of insonified fish were estimated using the technique of echo-counting. RESULTS: The lake had a mean density of 0.89 echoes associated with fish per m2, showing large spatial variations in the density of fish. The size estimated for the echoes associated with fish range from 2.7 to 15.9 cm (mean = 5.3 cm). CONCLUSIONS: The use of hydroacoustic to obtain rapid and realistic estimates of fish abundance and vertical distribution of the fish stock was successful

Diel variations in respiration, excretion rates, and nutritional status of zooplankton from the Pampulha Reservoir, Belo Horizonte, MG.

This investigation is focused on the experimental determination of diel cycles of metabolic activity of zooplankton in a tropical reservoir. Water and zooplankton used in laboratory experiments were collected from the Pampulha reservoir. The experimental units were incubated in the light (1500 Lux) and in the dark at 25.0 +/- 1.0 degrees C during different periods of the diel cycle. At the end of each experiment, the following variables were measured: temperature, dissolved oxygen, ammonia, and orthophosphate as well as the composition, abundance and dry weight of the zooplankton. The specific respiration and excretion rates were determined considering the differences in concentration between experimental and control units. The effect of diurnal cycle on respiration rates was clearly more intense than the effect of light. The average values of respiration rates obtained in the morning hours oscillated between 0. 015 and 0.016 mgO(2)mgDW. hr(-1) (light and dark incubations). At night, these rates were higher and ranged from 0.020 to 0.035 mgO(2)mgDW. hr(-1). Increased biomass of zooplankton and longer incubation times produced lower respiration rates. The excretion rates of ammonia were higher at night, reaching a mean value of 4.2 microgN-NH(4)/mg DW. hr(-1) in illuminated units. The phosphate excretion rates were more elevated in the morning, reaching 0.58 microgP-PO(4)/mg/DW. hr(-1) illuminated vessels. The nanoplankton was able to actively absorb ammonia as well as phosphate. The highest ammonia absorption rates were measured at night, whereas the nanoplankton absorbed phosphorus only in the morning hours. The nutritional status of zooplankton also showed short-term variations. The mean phosphorus content of zooplankton biomass also varied between day and night as well as with incubation time. It ranged from 0.58-2.17%, whereas organic matter variation was more conservative, oscillating around 70-92% in all occasions.

Variação nictemeral da composição bioquímica e biomassa do zooplâncton em tanques de cultivo de plâncton

The nutritional value of zooplankton (lipid and phosphorus contents) was analyzed in outdoor, plankton-culture tanks, to monitor the effects of diurnal variation and fertilization. Total lipid contents were significantly higher (average values of about 14% DW) for the treatment fertilized during the sampling week. A significantly highher total lipid concentrations generally coincided with high biomass of Moina sp. (Cladocera) and Thermocyclops sp. nauplii (Copepoda), which is probably related to zooplankton filtration rates. The values tended to be higher during the afternoon and the night. Phosphorus contents in the zooplanktonic population varied from 0.15 to 0.91% DW, with significant differences among the tanks. The zooplankton nutritional quality was greatly influenced by fertilization, which also determined the species composition in the tanks.

ESTÃO AS BIBLIOTECAS UNIVERSITÁRIAS BRASILEIRAS ADEQUADAS AO ENSINO E À PESQUISA EM ECOLOGIA

Este trabalho procura tracar um painel da situacao do acervo bibliografico, em termos de periodicos especializados em ecologia, de algumas das principais universidades brasileiras. A pesquisa baseou-se na escolha de um topico basico o qual, vem recebendo grande enfase na literatura internacional ao longo dos ultimos anos: a producao secundaria. Todos os meios de procura disponiveis, sejam eles convencionais ¾ arquivos, ficharios, microfilmes ¾, ou aqueles recentemente implantados, tais como os bancos de dados em CD ROM, foram empregados. Das dez bibliotecas universitarias selecionadas, apenas a Universidade de Sao Paulo (USP) pode oferecer um acervo que cobre satisfatoriamente a maioria das referencias selecionadas. Um segundo grupo de universidades, composto pela Universidade de Campinas (UNICAMP), Universidade Estadual Paulista (UNESP) e Universidade Federal do Rio de Janeiro (UFRJ) apresentou percentuais de cobertura variando entre 40 e 60%. A maioria das outras bibliotecas universitarias, no entanto, manteve-se em um patamar comparavel ao da Universidade Federal de Minas Gerais (UFMG) ou Universidade de Brasilia (UNB), ou seja, com percentuais de cobertura inferiores a 40%. Destaca-se ainda, que muitas das universidades selecionadas, mesmo possuindo cursos de pos-graduacao em ecologia, exibiram, em seu conjunto, dados que demonstram inequivocamente a pobreza de seu, acervos na area de ecologia.