Seeing further into the early steps of the endangered atlantic goliath grouper (Epinephelus itajara): Eye lenses high resolution isotopic profiles reveal ontogenetic trophic and habitat shifts.

Estuarine mangroves are often considered nurseries for the Atlantic Goliath grouper juveniles. Yet, the contributions of different estuarine primary producers and habitats as sources of organic matter during early ontogenetic development remain unclear. Given the species' critically endangered status and protection in Brazil, obtaining biological samples from recently settled recruits in estuaries is challenging. In this study, we leveraged a local partnership with fishers and used stable isotope (C and N) profiles from the eye lenses of stranded individuals or incidentally caught by fishery to reconstruct the trophic and habitat changes of small juveniles. The eye lens grows by the apposition of protein-rich layers. Once these layers are formed, they become inert, allowing to make inferences on the trophic ecology and habitat use along the development of the individual until its capture. We used correlations between fish size and the entire eye lens size, along with estuarine baselines, to reconstruct the fish size and trophic positions for each of the lens layers obtained. We then used dominant primary producers and basal sources from mangrove sheltered, exposed estuarine and marine habitats to construct an ontogenetic model of trophic and habitat support changes since maternal origins. Our model revealed marine support before the juveniles reached 25 mm (standard length), followed by a rapid increase in reliance on mangrove sheltered sources, coinciding with the expected size at settlement. After reaching 60 mm, individuals began to show variability. Some remained primarily supported by the mangrove sheltered area, while others shifted to rely more on the exposed estuarine area around 150 mm. Our findings indicate that while mangroves are critical for settlement, as Goliath grouper juveniles grow, they can utilize organic matter produced throughout the estuary. This underscores the need for conservation strategies that focus on seascape connectivity, as protecting just one discrete habitat may not be sufficient to preserve this endangered species and safeguard its ecosystem functions.

Long-term trends in juvenile Mugil liza abundance in relation to selected environmental and fisheries influences in southern Brazil.

Overfishing constitutes a major threat affecting marine fish population worldwide, including mullet species that have been exploited by fisheries during the reproductive migration in temperate and tropical latitudes for millennia. In the present study, we investigated the relationship of fishing intensity of mullet Mugil liza during its reproductive migration and the abundance of their juveniles in an essential nursery ground for the species in the southwest Atlantic Ocean. To carry out this analysis, we used a 23-year standardized long-term time series (1997-2019) of monthly abundance of M. liza juveniles, local/regional (water temperature, salinity, water transparency and river discharge) and global (ENSO) environmental factors, along with compilations of fishing landing data for the species. Generalized Additive Models (GAM) revealed the negative effect of fishing adult populations on the abundance of juveniles when they reach the marine surf-zone and after recruiting into the estuary. Our results reinforce the importance of adequate conservation and fishery regulation policies to prevent the species' stock from collapsing.

Coastal upwelling influences population structure of dusky grouper Epinephelus marginatus: An integrative approach based on otolith chemistry and muscle stable isotopes.

The dusky grouper (Epinephelus marginatus) is an overfished and threatened fish species with coastal distribution. In the Southwestern Atlantic, it occurs across a broad region influenced by two major oceanographic features: the Cabo Frio (23°S) and the Cabo Santa Marta (28°S) upwelling systems. Along the Brazilian coast, the species may present continuous or discrete populations, depending on the methodological approach used. In this study we combined otolith chemistry and muscle stable isotope analyses to examine the population structure of dusky groupers and its association with the two upwelling systems. Fish were collected in shallow coastal waters of the Southwest Atlantic Ocean, covering the southeastern and southern Brazilian coasts, among Macaé (22°S), Santos (24°S), Florianópolis (27°S), and in Rio Grande (32°S). The results show three statistically well-separated population groups along the region. We named these population groups as North (north of Cabo Frio); Center (between upwelling regions); and South (south of the Cabo Santa Marta system). Our findings allow to suggest that the upwelling systems may influence the distribution of E. marginatus stocks along the Brazilian south-western coast, even though a causal effect may not be attributed at this point. Overall, this combined approach, leveraging information from distinct natural tags, and reflecting variability of water chemistry and food webs with latitude, allowed us to enhance our understanding on how major upwelling systems influence the structuring of fish populations along the southwestern Atlantic Ocean.

Hydroclimatic influence on the trophic ecology of Atlantic goliath grouper juveniles (Epinephelus itajara) in a tropical estuary using non-lethal methodologies.

The Atlantic goliath grouper Epinephelus itajara is the largest species of groupers in the Atlantic Ocean, reaching over 2 m total length and 400 kg. It has an ontogenetic migration, with adults using nearshore and offshore marine areas and juveniles inhabiting estuarine/mangrove areas. Despite of its high ecological relevance and classification as a threatened species for several decades in the IUCN red lists, critical phases of its life cycle, like juveniles inhabiting estuaries, are still poorly investigated. In this study, we evaluated if hydroclimatic changes may affect the trophic ecology of juveniles in a tropical estuary. We described their diet composition, isotopic niche area, food assimilation, and trophic position of juveniles across seasons using two non-lethal techniques: stomach content analysis using a stomach flushing procedure and stable isotope analysis using a dermal biopsy. A total of 87 individuals with TL ranging from 38 to 331 mm had their stomachs analyzed, of which 31 had food content. We identified 11 prey items, shrimp being the most abundant prey group (IRI% = 88.4), followed by fish (6.6), blue crab (2.8), and crab (2.2). A total of 93 specimens had their muscle's carbon (δ13C) and nitrogen (δ15N) stable isotope ratios analyzed (38-332 mm TL). Average δ13C values showed statistically significant changes across seasons, but no significant changes were observed for δ15N. As initially predicted, isotopic niche size of juveniles changed consistently along the entire hydroclimatic cycle, reaching its peak at the end of the wet season. We also observed changes in the proportion of prey assimilation by juveniles between seasons. Shrimp (92.1%) was the most assimilated prey group during the late dry season, whereas tidal crabs (36.7%), blue crab (27.8%), and shrimp (25.1%) were the most important in the late wet season. Average trophic position of juveniles remained similar across wet (3.32 ± 0.10) and dry (3.23 ± 0.11) seasons. These findings provide important information to help decision makers to promote more efficient management and conservation legislations to protect early life stages of the Atlantic goliath grouper in tropical estuaries.

Spatial analysis of mercury and stable isotopes in the vulnerable Dusky Grouper Epinephelus marginatus along the Brazilian coast.

Mercury (Hg) is a contaminant of global concern due to its damaging toxicological effects on organisms. For the vulnerable Dusky Grouper (Epinephelus marginatus) off the coast of Brazil, we investigated: i) spatial patterns in muscle tissue total mercury (THg) contamination; ii) the relationship between muscle THg concentrations and total length iii) the relationship between muscle THg and stable isotopes; and iv) THg concentrations among muscle, liver, and ovary tissues. Out of 134 fish sampled, 21.8 % were higher than 0.5 mg/kg wet weight (above the safe limit for human consumption). THg concentrations increased toward lower latitudes, but an opposite pattern was observed for δ13C and δ15N with decreased values toward lower latitudes. There were significant differences in THg concentration among the three tissues. Results of Hg concentrations are useful for understanding the potential adverse effects on the health of this vulnerable species and to serve as a guide to human consumers.

Mercury concentrations in dusky grouper Epinephelus marginatus in littoral and neritic habitats along the Southern Brazilian coast.

Our study incorporated a comprehensive suite of parameters (i.e., body size, age, diet and trophic position) to investigate mercury concentration in dusky groupers Epinephelus marginatus. This study was carried out in rocky bottoms in littoral and neritic habitats along the Southern Brazilian coast. We also determined spatial variation in mercury concentrations in individuals inhabiting both zones, which may provide insights into how dietary differences or potential pollution sources affect bioaccumulation. A total of 244 dusky groupers was analyzed to determine total mercury concentrations. Our study revealed that when considering similar body sizes, individuals inhabiting littoral rocky habitats had higher concentrations of mercury probably due to proximity to pollution sources associated with human activities in the estuary and its drainage basin. Furthermore, large individuals (>650mm and >8years old) showed mercury contamination levels that are potentially harmful for this endangered fish species and above the acceptable limits for human consumption.

What the largest tadpole feeds on? A detailed analysis of the diet composition of Pseudis minuta tadpoles (Hylidae, Dendropsophini).

We analyzed the diet of 25 individuals of Pseudis minuta tadpoles which consisted in debris with more than 30%, follow by diatoms, euglenids, green algae, and desmids. With regard to the feeding strategy, P. minuta tadpoles are generalist consumer. The negative correlation between the abundance of items in the digestive tract and the mouth width indicate an effect of metamorphosis on the diet.

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

A garoupa-verdadeira (Mycteroperca marginata) é uma espécie marinha geralmente associada a fundos rochosos e recifes. O presente trabalho investiga a dieta e estratégia alimentar de uma população da garoupa-verdadeira que habita um longo (4,5 km) par de molhes de pedra na desembocadura do estuário da laguna dos Patos, sul do Brasil. Não há trabalhos anteriores realizados nesse tipo de habitat construído pelo homem e este trabalho fornece uma base de comparação com estudos de dieta de outras populações da garoupa-verdadeira ocorrendo em habitats naturais. De modo similar ao encontrado em estudos prévios realizados em substratos naturais, caranguejos e peixes foram as principais categorias de alimento consumidas (%IRI = 85,1 e %IRI = 12,6, respectivamente), enquanto camarões e moluscos tiveram menor importância na dieta (%IRI = 1,9 e %IRI = 0,4, respectivamente). Como reportado anteriormente para populações de garoupa-verdadeira que habitam recifes e fundos rochosos, o presente trabalho revelou marcadas mudanças na dieta em função do tamanho da espécie. Siri-azul e peixes tornam-se gradativamente mais importantes na dieta de indivíduos maiores (> 500 mm de comprimento total, CT). Finalmente, foi observado que a população de garoupa-verdadeira teve uma estratégia alimentar generalista com uma elevada variação entre indivíduos no consumo de presas. Essa estratégia permaneceu similar ao longo do aumento em tamanho da espécie. Os resultados do presente trabalho sugerem que substratos rochosos estabelecidos pelo homem propiciam locais de alimentação adequados para a garoupa-verdadeira no sul do Brasil e que poderiam ser usados como ferramentas adicionais nos esforços de conservação dessa espécie ameaçada.

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. manmade 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 itemsin 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.

Age, growth, and reproductive aspects of the dusky grouper Mycteroperca marginata (Actinopterygii: Epinephelidae) in a man-made rocky habitat in southern Brazil

The dusky grouper, Mycteroperca marginata, is an important commercial marine fish that is currently considered an endangered species worldwide and listed as overexploited in Brazil. Although its reproductive biology has been studied elsewhere, no information is available for populations in its southernmost distribution limit on the Brazilian coast. The present work investigates age structure, growth and reproduction of individuals inhabiting a pair of rocky jetties, about 4.5 km long each, located in the mouth of Patos Lagoon in the municipality of Rio Grande, in the southwestern Atlantic Ocean. A total of 130 individuals obtained between February 2007 and May 2009 were analyzed, with total length ranging from 260 to 800 mm. The growth coefficient found in the present study (K: 0.069) was lower than values reported for dusky grouper populations from the Mediterranean Sea (0.087) and southeast Africa (0.09). This difference could be related to higher average water temperatures in these regions compared to the current study site or due to poorer habitat quality in terms of the shelters available for dusky grouper individuals to establish their territories. Microscopic ovarian analyses of individuals during three years of sampling revealed only the occurrence of immature and resting females. The absence of ripe or post-spawning individuals, associated with low GSI values (<0.2) over the studied months, indicates that the dusky grouper did not use this man-made rocky substrate as a spawning site. The current L50 estimate of 451.3 mm indicates that most individuals captured in this area are immature. Such fishing pressure on immature specimens, associated with its slow growth rates and complex reproductive characteristics, threatens sustainability of the current dusky grouper fishery at the study site.

A garoupa-verdadeira, Mycteroperca marginata, é uma espécie de importância comercial que atualmente é considerada como ameaçada mundialmente e sobre-explotada no Brasil. Embora sua biologia reprodutiva tenha sido estudada em outras regiões, nenhuma informação está disponível sobre populações que habitam o extremo sul da sua distribuição na costa brasileira. O presente trabalho investiga a estrutura de idade, crescimento e reprodução de indivíduos que habitam dois molhes de pedra, com cerca de 4,5 km de extensão cada, localizados na desembocadura da laguna dos Patos no município de Rio Grande, no Atlântico Sudoeste. Foram analisados 130 indivíduos obtidos entre fevereiro de 2007 e maio de 2009, com comprimento total entre 260 e 800 mm. O coeficiente de crescimento no presente estudo (K: 0,069) foi inferior aos valores reportados para oMediterrâneo (0,087) e sudeste da África (0,09). Essa diferença pode estar relacionada a temperaturas médias maiores nessas regiões comparadas ao presente local de estudo ou devido a menor qualidade de habitat em termo de abrigos para os indivíduos de garoupa-verdadeira estabelecerem seus territórios. Análises microscópicas dos ovários dos indivíduos durante esses três anos de amostragens revelaram somente a ocorrência de indivíduos imaturos e fêmeas em repouso. A ausência de indivíduos ovados ou em pós-desova, associada com baixos valores do IGS (<0,2), ao longo de todos os meses de coleta, indica que a garoupa-verdadeira não utiliza esse substrato rochoso construído pelo homem como um local de desova. A estimativa de um L50 de 451,3 mm indica que a maioria dos indivíduos capturados nessa região é imatura. Pressão de pesca sobre indivíduos imaturos, associada com a sua lenta taxa de crescimento e complexo modo reprodutivo, ameaça a sustentabilidade da atual pesca da garoupa-verdadeira na área de estudo.

Diet and food consumption of the pearl cichlid Geophagus brasiliensis (Teleostei: Cichlidae): relationships with gender and sexual maturity

Despite the importance of the pearl cichlid Geophagus brasiliensis for the aquarium fish trade worldwide and its wide distribution, many aspects of its biology, such as the relationships between its feeding ecology and reproductive behavior, are not fully understood in natural conditions on its native habitat. In this paper, we investigated its diet focusing on how differences in diet and food consumption are related to differences in gender and sexual maturity. The digestive tract of each individual was dissected and had its content analyzed, whereas each gonad was microscopically analyzed to determine gender (male/female) and sexual maturity (immature/mature). A total of 28 females and 31 males were analyzed. Mature individuals were more common than immature specimens both for males (64.50 percent) and females (64.30 percent). The analysis of 52 individuals with non-empty digestive tracts revealed a diet comprised of 27 items. According to the Index of Alimentary importance ( percentIAi), the most important food items in the diet were Gastropoda (37.30 percent), fragments of vascular plants (15.16 percent), detritus (10.14 percent), Amphipoda (9.24 percent), and fish scales (6.29 percent). Mature males had more empty stomachs (65.00 percent) when compared to immature males (27.27 percent) and immature (55.56 percent) and mature females (40.00 percent). Also, mature females seemed to have more food consumption (greater mean values of total volume) in their digestive tracts than mature males. Some hypotheses are proposed in order to distinguish if this gender-based difference in food consumption in mature individuals of the pearl cichlid could be associated with the development of primary and secondary sexual characteristics or with asymmetrical time invested in parental care activities.

Apesar da sua ampla distribuição e importância para o comércio aquariofilista, muitos aspectos da biologia do cará Geophagus brasiliensis no seu habitat natural, como a relação entre sua ecologia alimentar e comportamento reprodutivo, ainda não são bem conhecidos. Nesse trabalho foi investigada sua dieta, enfocando como as diferenças na dieta e no consumo alimentar estão relacionadas ao sexo (macho/fêmea) e a maturidade (imaturo/maturo). O trato digestório de cada indivíduo foi dissecado e teve seu conteúdo analisado, enquanto cada gônada foi analisada microscopicamente para determinar o sexo e a maturidade. Um total de 28 fêmeas e 31 machos foram analisados. Indivíduos maturos foram mais comuns do que espécimes imaturos, tanto para machos (64,50 por cento) quanto para fêmeas (64,30 por cento). A análise de 52 indivíduos com alimento no trato revelou uma dieta composta por 27 itens. De acordo com o Índice de Importância Alimentar ( por centoIAi), os itens alimentares mais importante na dieta foram Gastropoda (37,30 por cento), fragmentos de plantas vasculares (15,16 por cento), detrito (10,14 por cento), Amphipoda (9,24 por cento) e escamas de peixe (6,29 por cento). Machos maturos tiveram mais estômagos vazios (65,00 por cento) quando comparados com machos imaturos (27,27 por cento) e fêmeas imaturas (55,56 por cento) e maturas (40,00 por cento). Além disso, fêmeas maturas apresentaram maior consumo de alimentos (valor médio do volume total de alimentos) do que machos maturos. Algumas hipóteses são propostas na tentativa de explicar se essa diferença no consumo de alimento entre machos e fêmeas maturos está relacionada ao desenvolvimento de caracteres sexuais primários e secundários, ou com a assimetria na quantidade de tempo empregado em atividades relacionadas ao cuidado parental.

Aquatic food webs in mangrove and seagrass habitats of Centla Wetland, a Biosphere Reserve in Southeastern Mexico

Mangrove and seagrass habitats are important components of tropical coastal zones worldwide, and are conspicuous habitats of Centla Wetland Biosphere Reserve (CWBR) in Tabasco, Mexico. In this study, we examine food webs in mangrove- and seagrass-dominated habitats of CWBR using stable isotope ratios of carbon and nitrogen. Our objective was to identify the importance of carbon derived from mangroves and seagrasses to secondary production of aquatic consumers in this poorly studied conservation area. Carbon and nitrogen isotope ratios of basal sources and aquatic consumers indicated that the species-rich food webs of both habitats are dependent on riparian production sources. The abundant Red mangrove Rhizophora mangle appears to be a primary source of carbon for the mangrove creek food web. Even though dense seagrass beds were ubiquitous, most consumers in the lagoon food web appeared to rely on carbon derived from riparian vegetation (e.g. Phragmites australis). The introduced Amazon sailfin catfish Pterygoplichthys pardalis had isotope signatures overlapping with native species (including high-value fisheries species), suggesting potential competition for resources. Future research should examine the role played by terrestrial insects in linking riparian and aquatic food webs, and impacts of the expanding P. pardalis population on ecosystem function and fisheries in CWBR. Our findings can be used as a baseline to reinforce the conservation and management of this important reserve in the face of diverse external and internal human impacts.

Manguezais e pradarias de gramíneas são importantes componentes das zonas costeiras tropicais em todo o mundo, sendo habitats comuns nos ''Pântanos de Centla'', uma Reserva da Biosfera localizada em Tabasco, México. Nesse trabalho, são investigadas as teias alimentares de habitats dominados por manguezais e pradarias de gramíneas, através de isótopos estáveis de carbono e nitrogênio, tendo como objetivo identificar a importância do carbono derivado desses produtores para a produção aquática secundária nessa unidade de conservação tão pouco estudada. As razões isotópicas de carbono e nitrogênio das fontes basais e dos consumidores aquáticos indicam que as teias alimentares, ricas em espécies, de ambos os habitats, são dependentes da produção ripária. O abundante mangue-vermelho Rhizophora mangle parece ser a fonte primária de carbono no habitat dominado por manguezais. Em contraste, muito embora as pradarias de gramíneas sejam conspícuas no ambiente lagunar estudado, muitos dos consumidores da teia alimentar nessa região parecem depender do carbono oriundo da vegetação ripária (e.g. Phragmites australis).A espécie de bagre exótica Pterygoplichthys pardalis possui assinaturas isotópicas que se sobrepõem a das espécies nativas (incluindo algumas de elevado valor comercial na pesca), sugerindo competição potencial por recursos. Novas investigações deveriam avaliar o papel dos insetos terrestres como elo de conexão entre as teias alimentares da mata ripária e do ambiente aquático, bem como os impactos da expansão da população de P. pardalis sobre o funcionamento do ecossistema e das pescarias no ''Pântano de Centla''. Considerando os múltiplos impactos antrópicos na região, os resultados obtidos no presente trabalho podem ser utilizados como uma base de referência em programas de gerenciamento e conservação da diversidade nessa importante Reserva da Biosfera.