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Previous issue date: 2013-02-22 === FAPERJ === Coastal lagoons can have different salinity gradient depending on the geographical position, hydrological balance, type of sea connection and other environmental conditions, which influence structure of fish assemblages that uses these systems. The aim of this study was to assess the use of ichthyofauna and eventual changes in structure of fish assemblages in relation to environmental variables, mainly the salinity, in three choked lagoon systems of the coastal lowlandsof Rio de Janeiro State (Maric?, Saquarema and Araruama). The raised hypothesis wasthat different fish assemblages use lagoons with different salinity gradient and that the species richness is directly associated to salinity with optimum at normal marine water (36), and that changes above or below this value can limit occurrence of species. Beach seines and environmental variables measurements were performed during the winter 2011 and the summer 2012. Three zones determined according to distance from the connection with the sea (Inner zone ? the farthest area from the channel that connect the lagoon to the sea with lesser marine influence; Middle zone ? the central part of the lagoon; and Outer zone - next to the channel thatconnect the lagoon to the sea, with more marine influence) and ten sites evenly distributed in each lagoon were sampled in three replicates, totaling 168 samples. Environmental variables of salinity, temperature, depth, transparency and turbidity were measured in each sampling occasion. Considering all pooled samples, the environmental variables that most contributed to lagoon separation was the salinity (higher in Araruama and lower in Maric?) and temperature between the two sampled periods (winter and summer). A total of 57,083 fishes were collected in 44 species. The more representative families were Gerreidae with six species, Clupeidae and Gobiidae with cinco species and Sciaenidae with four species. Twenty species were common to the three lagoons with more represented species being Atherinella brasiliensis and Anchoa januaria with frequency of occurrence higher than 65%. Despite of differences in environmental gradient, mainly the salinity, only the fish assemblage of Araruama lagoon differed from the other two lagoons, although with high fish sobreposition. The highest richness found in the hyperhaline Araruama lagoon (32 esp?cies) was very close of fish richness in the Saquarema lagoon (30 species), although the latter had a much smaller area, which confirm the hypothesis that the highest richness occur in salinity near to the marine water salinity. Differences in environmental conditions among the three lagoon zones were significantly only in Maric? lagoon, which may be related to its estuarine conditions. Salinity, transparency and turbidity were the most important factors influences fish assemblages depending on the lagoon, with Maric? having a higher influence of transparency on fish assemblages, while the turbidity had higher influence during the Summer in Saquarema and Araruama fish assemblages. Such information are a baseline to future evaluation of the environmental condition of these systems aiming the resources conservation, but other studies need to be incorporate to these analyses, mainly the influences of physical habitat on fish assemblages structure. === Lagunas podem assumir diferentes gradientes de salinidade dependendo de sua localiza??o geogr?fica, balan?o h?drico, conex?o com mar e outras condi??es ambientais, as quais influenciam a estrutura das assembleias de peixes que utilizam esses ambientes. O objetivo deste trabalho foi avaliar o uso da ictiofauna e eventuais varia??es na estrutura das assembleias de peixes em rela??o ?s vari?veis ambientais, principalmente o gradiente de salinidade em tr?s sistemas lagunares sufocados da Baixada Litor?nea do Estado do Rio de Janeiro (Maric?, Saquarema e Araruama). A hip?tese testada foi a de que diferentes assembleias de peixes usam lagunas com diferentes gradientes salinos, e que a riqueza de esp?cies ? diretamente associada a salinidade at? o valor da salinidade normal da ?gua do mar (36), e que varia??es acima ou abaixo destes n?veis poderiam restringir a ocorr?ncia das esp?cies. Arrastos de praia e medi??es de vari?veis ambientais foram realizados durante o Inverno de 2011 e Ver?o de 2012. Tr?s zonas foram determinadas a partir da dist?ncia da conex?o com o mar (Zona Interna ? mais distante do canal de conex?o com o mar e com menor influ?ncia marinha; Zona Central ? parte mais central da laguna, e Zona Externa ? mais pr?xima do canal de conex?o com o mar e com maior influ?ncia marinha) e dez locais de coleta foram amostrados, com tr?s r?plicas cada, distribu?dos entre estas zonas em cada laguna, totalizando 168 amostras. Vari?veis ambientais de salinidade, temperatura, profundidade, transpar?ncia e turbidez foram medidas em cada arrasto realizado. Considerando todo o conjunto de amostras, as vari?veis ambientais que mais contribu?ram para a separa??o das lagunas foram salinidade (maior em Araruama e menor em Maric?) e a temperatura entre os dois per?odos de coleta (Inverno e Ver?o). Foram coletados 57.083 indiv?duos em 44 esp?cies de peixes. As fam?lias de maior representatividade foram Gerreidae com seis esp?cies, Clupeidae e Gobiidae com cinco esp?cies e Sciaenidae com quatro esp?cies. Vinte esp?cies foram comuns ?s tr?s lagunas e as esp?cies de maior representatividade entre elas foram Atherinella brasiliensis e Anchoa januaria com frequ?ncia de ocorr?ncia superiores a 65%. Apesar das diferen?as no gradiente ambiental, principalmente na salinidade, somente a assembleia de peixes de Araruama diferiu das demais, embora com grande sobreposi??o de esp?cies. A maior riqueza foi encontrada na laguna hipersalina de Araruama (32 esp?cies), por?m muito pr?xima da riqueza na laguna de Saquarema (30 esp?cies), embora com esta ?ltima tendo uma ?rea bem menor, o que confirma a hip?tese de maior riqueza em salinidade pr?xima da ?gua do mar. As diferen?as nas condi??es ambientais existentes entre as zonas das lagunas somente foram significativas na laguna de Maric?, o que pode estar relacionado ao seu car?ter estuarino. A salinidade, transpar?ncia e turbidez foram os fatores que mais influenciaram as assembleias de peixes, com diferentes graus de influ?ncia dependendo da laguna, com Maric? tendo maior influ?ncia da transpar?ncia na assembleia de peixes, enquanto a turbidez teve maior influ?ncia no ver?o nas assembleias de peixes em Saquarema e Araruama. Estas informa??es servem de base para futuras avalia??es da condi??o ambiental deste sistema visando a conserva??o destes recursos, por?m outros estudos devem ser incorporados nas an?lises, principalmente as influ?ncias do habitat f?sico na estrutura das assembleias de peixes.
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