Christina Wyss Castelo Branco

Restoration of shallow lakes by nutrient control and biomanipulation—the successful strategy varies with lake size and climate

Major efforts have been made world-wide to improve the ecological quality of shallow lakes by reducing external nutrient loading. These have often resulted in lower in-lake total phosphorus (TP) and decreased chlorophyll a levels in surface water, reduced phytoplankton biomass and higher Secchi depth. Internal loading delays recovery, but in north temperate lakes a new equilibrium with respect to TP often is reached after <10–15 years. In comparison, the response time to reduced nitrogen (N) loading is typically <5 years. Also increased top-down control may be important. Fish biomass often declines, and the percentage of piscivores, the zooplankton:phytoplankton biomass ratio, the contribution of Daphnia to zooplankton biomass and the cladoceran size all tend to increase. This holds for both small and relatively large lakes, for example, the largest lake in Denmark (40 km2), shallow Lake Arreso, has responded relatively rapidly to a ca. 76% loading reduction arising from nutrient reduction and top-down control. Some lakes, however, have proven resistant to loading reductions. To accelerate recovery several physico-chemical and biological restoration methods have been developed for north temperate lakes and used with varying degrees of success. Biological measures, such as selective removal of planktivorous fish, stocking of piscivorous fish and implantation or protection of submerged plants, often are cheap versus traditional physico-chemical methods and are therefore attractive. However, their long-term effectiveness is uncertain. It is argued that additional measures beyond loading reduction are less cost-efficient and often not needed in very large lakes. Although fewer data are available on tropical lakes these seem to respond to external loading reductions, an example being Lake Paranoa, Brazil (38 km2). However, differences in biological interactions between cold temperate versus warm temperate-subtropical-tropical lakes make transfer of existing biological restoration methods to warm lakes difficult. Warm lakes often have prolonged growth seasons with a higher risk of long-lasting algal blooms and dense floating plant communities, smaller fish, higher aggregation of fish in vegetation (leading to loss of zooplankton refuge), more annual fish cohorts, more omnivorous feeding by fish and less specialist piscivory. The trophic structures of warm lakes vary markedly, depending on precipitation, continental or coastal regions locations, lake age and temperature. Unfortunately, little is known about trophic dynamics and the role of fish in warm lakes. Since many warm lakes suffer from eutrophication, new insights are needed into trophic interactions and potential lake restoration methods, especially since eutrophication is expected to increase in the future owing to economic development and global warming.

Relations among heterotrophic bacteria, chlorophyll-a, total phytoplankton, total zooplankton and physical and chemical features in the Paranoá reservoir, Brasília, Brazil

The plankton community, chlorophyll-a, heterotrophic bacteria and physical and chemical features of the Paranoá Reservoir were studied at monthly intervals at seven stations from March 1988 to March 1989. Thermal structure had a circulation period from May to July and stratification during the other months. The phytoplankton consisted of 76 taxa, was dominated by the cyanophyte Cylindrospermopsis raciborskii and attained concentrations ranging from 7,759,000 up to 98,160,000 org. l−1. The zooplankton consisted of 36 taxa and was present in densities between 8 and 8,056 org. l−1. In stations, or seasons with highly eutrophic conditions, there was a decrease in total phytoplankton and an increase in bacteria and total zooplankton. The results had spatial and temporal variations. Spatial variation demonstrated the existence of water quality deterioration at two or three sampling points. Temporal variation showed the influences of water column stability and the dry versus rainy seasons on nutrient concentrations and the planktonic community.

Mercury distribution in different tissues and trophic levels of fish from a tropical reservoir, Brazil

Concentrations of organic (OrgHg) and inorganic mercury (InorgHg) were assessed in different fish tissues (liver, muscle, kidney, gut and gonads) and trophic levels collected in an impacted tropical reservoir in southeastern Brazil. Organic mercury concentrations in muscle were remarkably higher in the carnivorous species Hoplias malabaricus and Oligosarcus hepsetus. The ratios of OrgHg in relation to total mercury (%OrgHg) in muscle also varied according to the species trophic level: 93% for carnivores, 84% for omnivores, 73% for algivores/planktivores and 58% for detritivores. The %OrgHg in the gut tissue of carnivores (78%) was much higher than that found in omnivores (30%), possibly reflecting a process of trophic biomagnification in the reservoir. On the other hand, the InorgHg concentrations in muscle decreased with the trophic level increase, suggesting that this form of mercury did not biomagnify through the food web. Gonads contained the least total mercury, and approximately all of this mercury was represented by the organic form (83 to 98%). The kidney and the liver of all fish species contained less than 50% OrgHg. We suggest that the low %OrgHg in the liver is related to different capacities or strategies of OrgHg detoxification by the fish.

Environmental changes and zooplankton temporal and spatial variation in a disturbed brazilian coastal lagoon

The Imboassica lagoon, located in the Municipality of Macaé (RJ), is separated from the sea by a sand bar, and its surroundings are partially occupied by residential areas. This coastal lagoon has undergone environmental degradation due to sewage input and artificial sand bar openings. The temporal and spatial variation of environmental variables and zooplankton were studied monthly for four years. There were five artificial openings of the sand bar during the period of study, mostly in the rainy season. Besides osmotic changes, these events caused the drainage of the water of the lagoon into the sea, loss of total organic nitrogen, and an increase of total phosphorus. The zooplankton community of Imboassica lagoon included freshwater and marine taxa, holoplanktonic, meroplanktonic and nectobenthonic forms. Polychaeta, Bivalvia and Gastropoda larvae, and the taxa of Rotifera Hexarthra spp., Lecane bulla, Synchaeta bicornis, nauplii of Cyclopoida and Calanoida copepods were considered constant taxa. Distinct zooplankton assemblages were found during zooplankton spatial surveys in oligohaline and mesohaline conditions. The successful zooplankton populations were either favored by the disturbance of the sand bar opening, such as the veligers of the gastropod Heleobia australis, or capable of fast recovery after the closing of the sand bar, during the succession from a marine into an oligohaline environment, such as Hexarthra spp.. Such populations seemed well adapted to the stress conditions usually found in the lagoon due to osmotic changes, column mixing, nutrient input, and high fish predation pressure. Rare species in the community, such as Moina minuta, presented population increases all over the lagoon under oligohaline conditions.

News records of phoresy and hyperphoresy among treefrogs, ostracods, and ciliates in bromeliad of Atlantic forest

The bromeliad habitat contributes to a high biodiversity and we recorded three treefrog species as new phoretic agents of ostracods, and a first case of hyperphoresy among treefrogs, ostracods and ciliates, in these habitats of Atlantic Forest. Densities of ciliates and ostracods showed significant relationships suggesting the importance of hyperphoresy for ciliate dispersion.

Diet of the clupeid fish Platanichthys platana (Regan, 1917) in two different Brazilian coastal lagoons

Platanichthys platana is considered a constant species in both Cabiunas and Imboassica lagoons that are characterised by different marine and freshwater inputs, and anthropogenic influences. The stomach content analysis of P. platana captured between July 1991 and July 1993 revealed filamentous algae, detritus, eggs of benthic invertebrates, larvae of chironomids and bivalves as the main food sources in Imboassica lagoon. Small-sized cladocerans, copepods and shrimp larvae were the prevailing items in Cabiunas lagoon. Seasonal food variations were noted for the fishes of Imboassica lagoon. Diet differences were highlighted within specimens lesser than 40 mm standard length in Imboassica lagoon, and were related to the increase of marine influence due to artificial sand barrier openings. Dissimilarities among size classes in relation to invertebrate larvae consumption were observed in fishes from Cabiunas lagoon.

Current knowledge of environmental exposure in children during the sensitive developmental periods

OBJECTIVE This study aims to identify the scientific evidence on the risks and effects of exposure to environmental contaminants in children during sensitive developmental periods. DATA SOURCE The search was performed in the Bireme database, using the terms: childrens health, environmental exposure, health vulnerability, toxicity pathways and developmental disabilities in the LILACS, MEDLINE and SciELO systems. DATA SYNTHESIS Children differ from adults in their unique physiological and behavioral characteristics and the potential exposure to risks caused by several threats in the environment. Exposure to toxic agents is analyzed through toxicokinetic processes in the several systems and organs during the sensitive phases of child development. The caused effects are reflected in the increased prevalence of congenital malformations, diarrhea, asthma, cancer, endocrine and neurological disorders, among others, with negative impacts throughout adult life. CONCLUSION To identify the causes and understand the mechanisms involved in the genesis of these diseases is a challenge for science, as there is still a lack of knowledge on childrens susceptibility to many environmental contaminants. Prevention policies and more research on child environmental health, improving the recording and surveillance of environmental risks to childrens health, should be an ongoing priority in the public health field.

Zooplankton of an urban coastal lagoon: composition and association with environmental factors and summer fish kill

Zooplankton may be regarded as a sensitive tool for monitoring environmental variations in coastal lagoons due to their ability to immediately react to changes in the water column trophic features and salinity levels. As a coastal lagoon with a broad history of anthropic influence, Rodrigo de Freitas Lagoon (Rio de Janeiro, Brazil) is widely used for water sports and artisanal fishing. The present study aimed to expand the knowledge base about zooplankton in the Rodrigo de Freitas Lagoon by assessing the composition and time-spatial distribution of the major zooplankton groups. Samples were collected fortnightly from at four distinct sampling points August 2001 to July 2002. At each point, salinity, temperature, dissolved oxygen and water transparency were measured. During the study period, the lagoon behaved as an spatially homogeneous environment in what regards the abiotic variables. However, all these variables showed significant differences along the time, mainly related to seasonality (air temperature and rainy and dry periods). The zooplankton community showed low taxonomic richness, with the predominance of species commonly found in coastal lagoons, especially with mesohaline conditions, as well as those found in estuaries. An interesting fact was the rise in zooplankton abundance at all sampling points right after a fish kill event. Such increase was caused mainly by the Brachionus plicatilis O.F. Muller 1786 species. Thus, the zooplankton community was affected by physical and chemical factors, mainly by the dissolved oxygen decline event and variations in the influx of seawater into the lagoon. In addition, phytoplankton availability and fish predation pressure were suggested as important regulating factors of the zooplankton community.

The diet of Scinax angrensis (Lutz) tadpoles in an area of the Atlantic Forest (Mangaratiba, Rio de Janeiro) (Amphibia, Anura, Hylidae)

Scinax angrensis (Lutz, 1973) e uma especie endemica ocorrendo em florestas de encosta de baixa altitude, no sul do Estado do Rio de Janeiro, Brasil. O objetivo do presente estudo foi o de comparar a morfologia e verificar o espectro alimentar de girinos de S. angrensis de dois estagios diferenciados de desenvolvimento. A morfologia bucal dos dois estagios (27 e 37) apresentou-se similar, havendo diferenca de tamanho da abertura oral, bem como aumento das dimensoes do corpo e da cauda. A especie examinada apresentou um espectro trofico integrado por algas, protozoarios, rotiferos, microcrustaceos, nematodeos, restos de vegetais e de invertebrados, hifas de fungo e graos de areia. Foram verificadas diferencas significativas entre as dimensoes dos dois estagios, embora nao se tenha encontrado uma diferenca significativa entre as dietas, apesar de se ter observado uma preferencia diferenciada por itens planctonicos. Os resultados sugerem que a partilha de recursos alimentares esta relacionada nao so com a morfologia e ocupacao de diferentes microhabitats, mas tambem ao comportamento alimentar dos girinos. A relevância de itens importantes para a dieta natural dos girinos de S. angrensis, especialmente as algas diatomaceas e filamentosas, revela a importância da comunidade perifitica para a conservacao desta especie de anuro na Mata Atlântica.

Larval Diet in Bromeliad Pools: A Case Study of Tadpoles of Two Species in the Genus Scinax (Hylidae)

Many species of frogs that breed in bromeliads exhibit parental care as females deposit unfertilized eggs to feed the tadpoles. Treefrogs of the genus Scinax are not known to exhibit this behavior, even though they have exotrophic tadpoles. The purpose of this study was to describe qualitatively and quantitatively the diets of tadpoles of hylids S. littoreus and S. perpusillus developing in the phytothelm of Alcantarea glaziouana (Bromeliaceae). We evaluate if there are seasonal and spatial differences (between tadpoles living in the central tank and the lateral tanks) in the diet, and to test for food selectivity of the species. The most abundant items in the diet of tadpoles of both species were, respectively, algae, fungi, and protozoa. Detritus and plant debris were present in the diet of more than 90% of the tadpoles of the two species. The trophic niche breadth for S. littoreus was 1.26, whereas that for S. perpusillus was 1.54. The tadpole diets were seasonally conservative for both tadpole species and spatially similar only for S. perpusillus. Tadpoles of Scinax littoreus showed differences in diet, depending on the microhabitat in which they developed in the bromeliad, and showed electivity favorable for fungi but negative for copepods. Our data suggest that tadpoles of S. perpusillus are, in general, non-selective omnivores feeding on items in a similar proportion to their occurrence in the environment, while tadpoles of S. littoreus are more selective-feeders, avoiding animal items. Muitas espécies de anuros que se reproduzem em bromélias apresentam cuidado parental com fêmeas depositando ovos não fertilizados para alimentar os girinos no fitotelma. Os hilídeos do gênero Scinax não apresentam este comportamento, mesmo apresentando girinos exotróficos. O objetivo do presente estudo foi descrever quali-quantitativamente a dieta dos girinos das espécies S. littoreus e S. perpusillus que se desenvolvem no fitotelma da Alcantarea glaziouana (Bromeliaceae). Avaliamos se há diferenças sazonais e espaciais (entre girinos que residem no vaso central e nos vasos laterais da bromélia) na dieta, além de testar a existência de seleção de itens alimentares pelas espécies de anuros. Os itens mais abundantes na dieta de ambos os girinos foram respectivamente: algas, fungos e protozoários. Detrito e restos vegetais estavam presentes em mais de 90% dos estômagos de ambas as espécies. A amplitude de nicho trófico para S. littoreus foi 1,26 enquanto para S. perpusillus foi 1,54. As dietas foram sazonalmente conservativas para ambas as espécies e espacialmente similar apenas para S. perpusillus. Os girinos de Scinax littoreus apresentaram diferenças na dieta de acordo com o microhabitat em que se desenvolviam na bromélia além de apresentar eletividade positiva para fungos e negativa para copépodos. Nossos dados sugerem que S. perpusillus é, em geral, um onívoro não seletivo, alimentando-se de itens em proporção similar da que estes ocorrem no fitotelma, enquanto os girinos de S. littoreus são mais seletivos evitando itens animais.