Alexandre M. Garcia

Effects of 1997-1998 El Nino on the dynamics of the shallow-water fish assemblage of the Patos Lagoon Estuary (Brazil)

Abstract High rainfall associated with El Nino events significantly increases runoff and stream discharge in southern Brazil. High freshwater discharge changes salinity, temperature, and water circulation patterns that can affect the fish estuarine assemblage. Using long-term data obtained from standardized surveys, we analyzed fish assemblage structure and dynamics in shallow waters of the Patos Lagoon estuary in southern Brazil before, during, and after the 1997–1998 El Nino event. Overall, the relative abundance of all the fish groups in the estuary was about five times lower during the El Nino than before and after. Freshwater vagrants were the only group with greater abundance during El Nino. Fish species richness was higher in the estuary during the El Nino event, when many freshwater species expanded their ranges into the Patos Lagoon estuary, than before or after the El Nino. El Nino-induced assemblage changes were not highly persistent, and the estuarine fish assemblage returned to its pre-El Nino state within 18 months after the El Nino period. Densities of many marine and estuarine fishes increased to pre-El Nino levels within 3–6 months of the end of the El Nino period. We suggested that the rapid recovery of fish estuarine populations after the 1997–1998 El Nino may have been caused by one or some combination of: (a) enhanced productivity stimulated by nutrients contained in newly deposited alluvial sediments, and (b) enhanced larvae transport in the large saltwater intrusion that followed the El Nino event. Clearly, fish population dynamics and assemblage structure of the Patos Lagoon estuary can neither be interpreted nor predicted on a long-term basis without explicit consideration of El Nino Southern Oscillation patterns.

Spatiotemporal Variation in Shallow-Water Freshwater Fish Distribution and Abundance in a Large Subtropical Coastal Lagoon

Patos Lagoon is located off the southern Brazilian coast and represents one of the largest coastal lagoons in the world. We estimated hydrological and physicochemical conditions associated with spatial variation in the abundance and diversity of freshwater fishes along the lagoon, and inter-annual variability in abundances of freshwater fishes occurring in its estuarine zone. During our study, the region experienced two periods of average rainfall and two periods with above-average rainfall. The characids Astyanax eigenmaniorum and Oligosarcus jenynsii and the siluriform Parapimelodus nigribarbis were the most abundant freshwater fishes in the estuary during wet periods when water levels were higher and salinity was lower. Increases in abundance of these species in the estuarine area, all of which members of primary-division freshwater families, apparently were associated with pulses of reproduction and passive transport from freshwater habitats located near middle and upper lagoon reaches. Abundance of species from secondary freshwater families, such as poeciliids and cichlids, were less correlated with hydrological conditions, and their patterns of occurrence in the estuary suggest active migration from nearby freshwater habitats draining into this area. Findings indicate that freshwater discharge in the basin and expansion/retraction of freshwaters in the middle-upper lagoon determined patterns of freshwater fish abundance and species richness in the estuarine zone.

Checklist comparison and dominance patterns of the fish fauna at Taim Wetland, South Brazil

Taim Hydrological System is a unique subtropical wetland in southern Brazil harboring an exceptional biological diversity. In 1978, an ecological reserve was established to protect part of this area from increasing anthropogenic impacts in its surroundings. Fishes have been poorly investigated in this system. Based on a multi-gear sampling study encompassing several years (2001-2005), and on comparisons with previous fish inventories, we provide an up-to-date species list of fishes occurring in the Taim Wetland. In addition, we made the first preliminary description of fish dominance patterns found in the main lakes of the system (Flores, Nicola, Jacare and Mangueira). Checklist comparison resulted in 62 fish species distributed in 24 families, with Characidae (19 species) and Cichlidae (7) showing the highest species richness. Six species are cited for the first time in the reserve: Trachelyopterus lucenai (Auchenipteridae), Hoplosternum littorale (Callichthyidae), Rineloricaria cadeae (Loricariidae), Eigenmannia trilineata (Sternopygidae), Odontesthes mirinensis and O. perugiae (Atherinopsidae). Apparently, the black catfish T. lucenai invaded the system in the last decade and became one of the dominant species in the pelagic waters. Although differences in gears hindered direct comparisons, differences in species composition and dominance patterns between shallow margins and pelagic waters of lakes seem to occur in the lakes. A more diverse assemblage dominated by small fishes ( 15 cm) seemed to dominate in pelagic waters. O Sistema Hidrologico do Taim e um banhando subtropical localizado no sul do Brasil que abriga uma diversidade biologica excepcional. Em 1978, uma reserva ecologica foi estabelecida para proteger parte dessa area do crescente impacto de acoes antropicas nos seus arredores. Os peixes tem sido muito pouco investigados nessa regiao. Baseado em coletas com varios amostradores durante varios anos (2001-2005), e em comparacoes com estudos previos, esse trabalho fornece uma lista de especies atualizada dos peixes ocorrendo no Taim. Tambem e apresentada a primeira descricao preliminar dos padroes de dominância nos principais lagos que compoem o sistema (Flores, Nicola, Jacare e Mangueira). A analise comparada indicou a presenca de 62 especies de peixes distribuidas em 24 familias, sendo Characidae (19 especies) e Cichlidae (7) as familias com o maior numero de especies. Seis especies sao registradas pela primeira vez na reserva: Trachelyopterus lucenai (Auchenipteridae), Hoplosternum littorale (Callichthyidae), Rineloricaria cadeae (Loricariidae), Eigenmannia trilineata (Sternopygidae), Odontesthes mirinensis e O. perugiae (Atherinopsidae). Aparentemente, o penharol T. lucenai invadiu o sistema na ultima decada e tornou-se uma das especies dominantes nas zonas pelagicas das lagoas. Embora diferencas nos amostradores nao permitam comparacoes diretas, parecem ocorrer diferencas na composicao de especies e padroes de dominância entre as margens rasas e as zonas pelagicas dos lagos. Uma assembleia de peixes mais diversa, dominada por peixes pequenos ( 15cm) parece dominar as zonas pelagicas.

Evidence of habitat fragmentation affecting fish movement between the Patos and Mirim coastal lagoons in southern Brazil

The communication between the Patos and Mirim lagoon systems occurs via a natural channel called Sao Goncalo. In 1977, a dam was built in this channel to prevent entrance of saline waters from Patos Lagoon estuary into the Mirim Lagoon. Our results showed an abrupt discontinuity in salinity and fish species distribution along the study sites. Sites below the dam showed salinity values higher than zero, whereas sites above had zero salinity values across all sampling periods. Marine and estuarine fishes (e.g., mullets Mugil platanus, M. curema, silversides Odontesthes argentinensis, Atherinella brasiliensis, sardine Brevoortia pectinata, and white croaker Micropogonias furnieri) were not captured above the dam. If these juvenile fishes could enter the Mirim lagoon in greater numbers, they probably would enhance catches in the artisanal fishery. We hypothesized that the Sao Goncalo dam acts as a barrier hindering the entrance of salinity water and fishes inside the Mirim Lagoon. A comunicacao entre o sistema lagunar Patos-Mirim ocorre atraves de um canal natural denominado Sao Goncalo. Em 1977, foi construida uma eclusa com o objetivo de evitar a entrada de agua salgada, proveniente do estuario da Lagoa dos Patos, para o interior da Lagoa Mirim. Os resultados mostraram uma descontinuidade abrupta na distribuicao da salinidade e dos peixes ao longo da area de estudo. Estacoes de coleta abaixo da barragem tiveram valores de salinidade acima de zero, enquanto os valores foram iguais a zero nas estacoes acima da barragem durante o periodo amostrado. Peixes marinhos e estuarinos (p.ex., tainhas Mugil platanus, M. curema, peixes-rei Odontesthes argentinensis, Atherinella brasiliensis, sardinha Brevoortia pectinata) nao foram capturados acima da barragem. Caso entrassem em abundância na Mirim tais especies poderiam contribuir positivamente para os desembarques da pesca artesanal nessa regiao. Dessa forma, e sugerida a hipotese de que a barragem do Sao Goncalo atua como uma barreira impedindo a entrada de aguas salobras e peixes marinhos e estuarinos para o interior da Lagoa Mirim.

Evidences of El Niño effects on the mullet fishery of the Patos Lagoon estuary

Episodios El Nino ocorrem na regiao tropical do Oceano Pacifico e estao associados com o aumento da descarga continental de agua na Lagoa dos Patos (10.360 km2) e sua regiao estuarina (971 km2). A partir de um banco de dados meteorologicos e biologicos de longo prazo (1979-1983 e 1996-2000), este trabalho investiga as variacoes no recrutamento de juvenis e no desembarque da pesca artesanal da tainha (Mugil platanus) no estuario da Lagoa dos Patos e suas relacoes com anomalias regionais de chuva e anomalias locais de salinidade durante dois fortes episodios El Nino (1982-1983 e 1997-1998). Tanto os juvenis quanto a captura dos adultos na pesca artesanal diminuiram em abundância durante as chuvas excessivas e salinidades proximas a zero que prevaleceram no estuario durante ambos eventos climaticos. Duas hipoteses sao sugeridas para explicar os efeitos ocasionados pelo El Nino sobre as fases juvenis e adultas da tainha no estuario da Lagoa dos Patos. Primeiro, a elevada descarga continental durante forte eventos El Nino poderia afetar negativamente o transporte passivo de juvenis de tainha para o interior do estuario, o que levaria ao declinio de juvenis na regiao nesse periodo. Segundo, as salinidades proximas a zero durante varios meses no estuario durante forte eventos El Nino poderia acarretar maior dispersao dos cardumes de tainhas adultas durante a sua migracao reprodutiva para o mar, resultando em menores capturas pelos pescadores artesanais da regiao.

Preliminary examination of food web structure of Nicola Lake (Taim Hydrological System, south Brazil) using dual C and N stable isotope analyses

Taim Ecological Reserve is located within the Taim Hydrological System and was created to protect a heterogeneous and productive landscape harboring exceptional biological diversity in southern Brazil. Using stable isotope ratio analyses of carbon (d13C) and nitrogen (d15N), we provide a preliminary description of the food web structure, including estimates of production sources supporting fish populations and vertical trophic structure, within a representative lake of this system. A total of 21 organisms (5 macrophytes, 3 mollusks and 13 adult fishes) representing 16 species were collected for isotope analysis. Fishes had d13C values ranging from -24.30o/oo to -28.31o/oo , showing concordance with the range of values observed for macrophytes (-25.49 to -27.10o/oo), and suggesting that these plants could be a major carbon source supporting these fishes. d13C signatures of Corbicula (-30.81o/oo) and Pomacea (-24.26o/oo) indirectly suggest that phytoplankton and benthic algae could be alternative carbon sources for some consumers. Nitrogen isotope ratios indicated approximately three consumer trophic levels. The pearl cichlid Geophagus brasiliensis was a primary consumer. Two catfishes (Trachelyopterus lucenai and Loricariichthys anus) were secondary consumers. Two congeneric pike cichclids (Crenicichla lepidota and C. punctata), a catfish (Pimelodus maculatus) and the characids Astyanax fasciatus and Oligosarcus robustus were tertiary consumers. Further studies including additional primary producers and consumers and greater sample numbers should be conducted to provide a more complete and detailed description of food web structure and dynamics within the reserve.

Diet composition and feeding strategy of the southern pipefish Syngnathus folletti in a Widgeon grass bed of the Patos Lagoon Estuary, RS, Brazil

Peixes-cachimbo sao especies pouco conhecidas da familia Syngnathidae, os quais tem sido amplamente ameacados por atividades antropicas. Este trabalho descreve a composicao da dieta e estrategia alimentar de uma populacao do peixe-cachimbo Syngnathus folletti habitando uma pradaria de fanerogama submersa no estuario da Lagoa dos Patos, RS, Brasil. Tambem e investigado como a amplitude bucal afeta o tamanho das presas consumidas e, baseado em evidencias indiretas, sao sugeridos padroes de deslocamento da especie no interior da pradaria. Entre Dezembro de 1994 e Marco de 1995, os individuos foram coletados de dia e de noite numa pradaria de Ruppia maritima L. localizada no estuario da Lagoa dos Patos. Os conteudos estomacais de 108 individuos (54 machos e 54 femeas) foram analisados. Ambos os sexos parecem ser carnivoros diurnos com uma dieta composta principalmente de copepodes e isopodes. Os resultados sugerem uma estrategia alimentar do tipo mista com varios graus de especializacao para determinadas presas. As femeas tiveram uma dieta mais diversa, consumindo maior variedade de presas, as quais mostraram maior variabilidade em tamanho, enquanto os machos parecem ter se concentrado em presas menores, como o isopode Uromunna peterseni e copepodes. Essas diferencas entre sexos sugerem que as femeas sao mais moveis e ativas dentro da pradaria do que os machos. Houve uma boa concordância entre o tamanho medio das presas dominantes e a amplitude bucal (0,4 e 1,4mm), contudo, algumas femeas foram capazes de consumir presas tres vezes maiores do que sua maxima amplitude bucal. Um diagrama mostrando a utilizacao de micro-habitats pelas presas sugere que machos e femeas do peixe-cachimbo capturam presas sob todo o substrato vegetal disponivel no interior da pradaria de R. maritima.

Estuary hydrogeomorphology affects carbon sources supporting aquatic consumers within and among ecological guilds

The relative importance of carbon sources supporting aquatic food webs within and among estuaries may be influenced by factors that affect relative availability of autotrophic carbon sources, as well as movement of individuals among marine, estuarine and freshwater zones. We used stable isotopes of carbon and nitrogen to examine (1) the relative importance of carbon sources supporting estuarine consumers among estuaries with different hydrogeomorphic characteristics, (2) stable isotope signatures of consumer ecological guilds defined by dependence on estuarine habitats and residence time, and (3) if patterns in stable isotope signatures of ecological guilds repeat across estuaries with distinct hydrogeomorphological features. At the assemblage level, consumer carbon isotope signatures reflected the consumption of locally abundant primary production sources and differed across estuary types (choked lagoon, coastal river). Consumer ecological guilds differed in δ13C within sites, and the same trend repeated across sites but with differing magnitudes. This variation is attributed to movement and residence patterns in addition to differences in the relative abundances of autotrophic sources across sites. Although within-estuary variation in consumer resource use is to be expected, estuarine food webs may be broadly classified according to landscape-scale hydrogeomorphic factors that allow an initial prediction of the relative importance of carbon sources to secondary production. Predictions may be refined at the species level using knowledge of habitat use and residence time. Such predictions are useful as a starting point for poorly studied regions such as ours in southern Brazil, as well as for global-scale analyses of patterns in estuarine food webs.

Distribuição, dominância e estrutura de tamanhos da assembleia de peixes da lagoa Mangueira, sul do Brasil

Este estudo apresenta a composicao de especies, os padroes de distribuicao e dominância, e a estrutura de tamanhos da assembleia de peixes em diferentes unidades de habitat (zonas litoral, profunda e limnetica costeira) da lagoa Mangueira, no extremo sul do Brasil. As amostras foram obtidas no norte, centro e sul da lagoa, entre os anos de 2001 e 2007 utilizando-se de diversos amostradores (rede de emalhe, tarrafa, rede de arrasto de praia, puca e rede de arrasto de fundo). Um total de 52 especies foi identificado, 46 na zona litoral, 33 na limnetica costeira e 26 na profunda, distribuidas em 17 familias, das quais, Characidae, Cichlidae, Loricariidae e Atherinopsidae foram as mais diversas. As especies dominantes somaram 91,1 %, 92,9 % e 82,7 % dos individuos capturados nas zonas litoral, profunda e limnetica costeira respectivamente. A zona litoral e constituida de pequenos peixes, quase 70 % entre 25 e 50 mm de comprimento. Os padroes de dominância mostraram que, nesta zona, 19,5 % das especies foram dominantes, embora quatro dessas tambem predominaram nas demais zonas. Na zona profunda, 7,6 % das especies capturadas foram dominantes, com tamanhos semelhantes aos da zona litoral. Para as demais especies, os tamanhos se assemelham aos da zona limnetica costeira. A zona limnetica costeira e constituida de peixes de maior porte, a maioria entre 150 e 200 mm de comprimento total, tais como os grandes caracideos, o biru e os peixes-rei. Observou-se uma maior diferenca na composicao de especies entre as zonas litoral e limnetica costeira, com as especies Jenynsia multidentata, Bryconamericus iheringii, Hyphessobrycon luetkenii e Gymnogeophagus gymnogenys dominando exclusivamente no litoral, e as especies Oligosarcus jenynsii, Cyphocharax voga, Odontesthes perugiae e Astyanax fasciatus dominando exclusivamente a zona limnetica costeira. A zona litoral apresentou diferencas na composicao e dominância das especies entre as porcoes norte e sul da lagoa. As 52 especies registradas neste estudo representam uma alta riqueza de peixes na lagoa Mangueira, sobretudo quando comparada a outras lagoas costeiras do RS. Padroes diferenciados de composicao e abundância de especies parecem refletir caracteristicas distintas dos habitats litorâneos amostrados.

Diet and feeding strategy of the dusky grouper Mycteroperca marginata (Actinopterygii: Epinephelidae) in a man-made rocky habitat in southern Brazil

The dusky grouper (Mycteroperca marginata) is a marine species usually associated with rocky bottoms and reefs. The present work investigated the diet and feeding strategy of a dusky grouper population inhabiting a 4.5 km long pair of rocky jetties located in the mouth of Patos Lagoon estuary. No prior research has been conducted in such man-made habitat and the current study provides a basis for comparative studies on the diet of the dusky grouper populations inhabiting natural vs. man-made rocky habitats. Similarly with previous studies on natural substrates, crabs and fishes were the main food categories consumed (%IRI = 85.1 and %IRI = 12.6, respectively), whereas shrimps and mollusks had lower importance in the diet (%IRI = 1.9 and 0.4, respectively). As previously reported for dusky grouper populations inhabiting reefs and rocky bottoms, the present work revealed conspicuous size related dietary shifts. Blue crabs and fishes become increasingly important food items in the diet of larger individuals (> 500 mm, TL). Finally, it was found that the studied dusky population has a generalist feeding strategy with a high between-individual variation in prey consumption. Such strategy remained similar across the size increment of the species. Our findings suggest that man-made rocky substrates provide suitable feeding grounds for the dusky grouper in southern Brazil and could be used as an additional tool in the conservation efforts of this endangered species.