Abstract Fish otoliths store geochemical and isotopic signatures that can be used as proxies for environmental conditions in ecological investigations. We investigated the δ13C and δ18O of otoliths of four freshwater fish species (Astronotus ocellatus, Serrasalmus brandtii, Plagioscion squamosissimus, and Cichla ocellaris) from the Moxotó Reservoir in the São Francisco River, Brazil. The enriched δ13C signatures that distinguish A. ocellatus from other species could be caused by dissolved inorganic carbon (δ13CDIC) in reservoir waters. Macrophytes growing along the reservoir margins would favor photosynthetic uptake of 12C, leading to enriched δ13CDIC incorporated into the otoliths of those fish. Otolith δ18O signatures appear to reflect water column preferences, in which species preferentially inhabiting surface waters (such as S. Brandtii) show more enriched values (due to high surface evaporation ratios), while bottom water species show depleted δ18O values. Our results represent the first investigation of the isotopic compositions of fish otoliths in freshwater environments in the São Francisco River, and shed light on the interpretation of isotopic information stored in otoliths and how they can be used to infer the ecological strategies of freshwater fish.

ABSTRACT Coral reefs are one of the most vulnerable ecosystems to ocean warming and acidification, and it is important to determine the role of reef building species in this environment in order to obtain insight into their susceptibility to expected impacts of global changes. Aspects of the life history of a coral population, such as reproduction, growth and size-frequency can contribute to the production of models that are used to estimate impacts and potential recovery of the population, acting as a powerful tool for the conservation and management of those ecosystems. Here, we present the first evidence of Siderastrea stellata planulation, its early growth, population size-frequency distribution and growth rate of adult colonies in Rocas Atoll. Our results, together with the environmental protection policies and the absence of anthropogenic pressures, suggest that S. stellata population may have a good potential in the maintenance and recovery in the atoll. However, our results also indicate an impact on corals' recruitment, probably as a consequence of the positive temperature anomaly that occurred in 2010. Thus, despite the pristine status of Rocas Atoll, the preservation of its coral community seems to be threatened by current global changes, such as more frequent thermal stress events.

RESUMO Esqueletos de corais contêm excelentes registros de condições ambientais passada, devido à sua longevidade e assinaturas geoquímicas bem calibradas. Registros de isótopos estáveis de C e O de isótopos em corais são especialmente interessantes, porque eles podem destacar a variabilidade multidecadal das condições climáticas locais além do registro instrumental com alta fidelidade e resolução sub-anual. Aqui nós relatamos um dos primeiros registros climáticos com base em coral do Atlântico Sul Equatorial, através de perfis isotópicos de duas colônias de Porites sp. do Atol das Rocas, um localchave para reconstruções climáticas e anteriormente não estudada. Aqui são apresentados dados de perfis ao longo do vale entre coralitos de uma colónia e na parte central do leque de coralitos de outra colónia. Embora exista diferenças significativas nos valores isotópicos entre as duas colônias, ainda são observados em ambas o registro do evento do ENSO 2009/2010 - um episódio de branqueamento do coral mundial - através de valores anômalos de δ18O negativos (até 1 permil mais negativo do que os valores de base). Valores de isótopos estáveis de C também aparentam ser afetada pelo evento do ENSO. Nossos resultados indicam que os corais do Atol das Rocas são substratos ideais para monitorar grandes oscilações climáticas no Oceano Atlântico tropical Sul.

ABSTRACT Coral skeletons contain records of past environmental conditions due to their long life span and well calibrated geochemical signatures. C and O isotope records of corals are especially interesting, because they can highlight multidecadal variability of local climate conditions beyond the instrumental record, with high fidelity and sub-annual resolution. Although, in order to get an optimal geochemical signal in coral skeleton, sampling strategies must be followed. Here we report one of the first coral-based isotopic record from the Equatorial South Atlantic from two colonies of Porites astreoides from the Rocas Atoll (offshore Brazil), a new location for climate reconstruction. We present time series of isotopic variation from profiles along the corallite valley of one colony and the apex of the corallite fan of the other colony. Significant differences in the isotopic values between the two colonies are observed, yet both record the 2009/2010 El Niño event - a period of widespread coral bleaching - as anomalously negative δ18O values (up to −1 permil). δ13C is found to be measurably affected by the El Niño event in one colony, by more positive values (+0.39 ‰), and together with a bloom of endolithic algae, may indicate physiological alteration of this colony. Our findings indicate that corals from the Rocas Atoll can be used for monitoring climate oscillations in the tropical South Atlantic Ocean.

Localizada 266 km da costa brasileira, o complexo recifal de Rocas representa o único atol do Atlântico Sul. Duas expedições científicas foram realizadas para um detalhado estudo sedimentológico do ambiente. No ambiente sedimentar predominou a textura areia, embora outras texturas, como cascalho, cascalho arenoso, areia cascalhosa também foram observadas. O tamanho médio do grão variou de areia fina a areia grossa para (2.34 - 1,23 ø), com um valor médio de 0.69ø (fração areia), que em uma perspectiva geológica representa um ambiente de alta energia. Os valores de tamanho médio variou nos diferentes compartimentos geomorfológicos, uma resposta à hidrodinâmica variáveis sobre o recife. O grau de selecionamento variou de muito bem selecionado a pobremente selecionado, com um valor médio de 0.97ø (moderadamente selecionado). Os valores de diâmetro médio e de selecionamento são diretamente proporcionais (ou seja, quanto maior o tamanho do grão, melhor será a separação), um fato que pode ser controlada pela diminuição da diversidade de organismo que contribuem para o ambiente de sedimentação com o aumento do tamanho médio das partículas. Parâmetro de assimetria foi utilizado para correlacionar valores positivos para ambientes deposicionais. O parâmetro Curtose mostrou pouca relevância neste estudo. As partículas sedimentares analisadas são exclusivamente compostas de grãos biogênicos. No total, 11 grupos principais foram descritos, sendo as algas coralinas o mais incomum.

Located 266 km offshore Brazilian coast, Rocas Reef complex is the only atoll in the South Atlantic. Two scientific expeditions carried out detailed sedimentological studies of the complex. Sand texture was dominant in the sedimentary environment, although other textures such as gravel, sandy gravel and gravelly sand, were also observed. Mean size ranged from fine sand to coarse sand (-1.23 to 2.34ø), with an average value of 0.69ø (sand fraction), which from a geological perspective represents a high-energy environment. The values of mean size varied in the different geomorphologic compartments, a response to variable hydrodynamics on the reef. Sorting ranged from very well sorted to poorly sorted, with a mean value of 0.97ø (moderately sorted). The values of mean size and sorting are directly proportional (i.e. the larger the grain size, the better the sorting), a fact that might be controlled by the decreasing of organism diversity that contributes to the sedimentary environment as the mean size of the particles increase. Skewness parameter was used to correlate positive values to depositional environments. The Kurtosis parameter showed little relevance in this study. The sedimentary particles analyzed are exclusively composed of biogenic grains. In total eleven major groups were described, coralline algae being the most unusual.