Renato Rodrigues Neto

Organic matter assimilation and selective feeding by holothurians in the deep sea: some observations and comments

The selective feeding behaviour and assimilation efficiencies of deep-sea holothurians were investigated in order to assess their impact on carbon and nitrogen remineralisation on the Porcupine Abyssal Plain (PAP; ∼ 49°N 16°W, ∼ 4850 m water depth). Unfortunately, reliable determination of organic matter in the gut contents of the organisms proved to be difficult, because of the lysis of cells associated with the death of the animals on recovery. This was expressed in high levels of free fatty acids in the gut contents of Oneirophanta mutabilis, which we ascribe to unregulated lipolysis of phospholipids and triacylglycerides. It was not possible to estimate accurately the contribution that such material made to the gut contents, but based on the distributions of sterols in the gut sediments, it is likely to have been substantial. Therefore, all assimilation efficiencies calculated for holothurians in the deep sea should be treated with caution. Fortuitously, a bloom of holothurians that feed on the sediment surface (namely Amperima rosea and Ellipinion molle) during the period of study provided an opportunity indirectly to assess the impact of megafauna on organic matter cycling at the PAP. Observations suggest that the depletion of phytosterols from the surficial sediments between July and October 1997 resulted from the selective uptake of fresh phytodetritus by the blooming species. Deep-sea holothurians do not biosynthesise sterols de novo and an estimate of the sterol required by the increased population of A. rosea and E. molle is equivalent to the sterol flux to the seafloor during the spring/summer of 1997. The implications are dramatic. Firstly, these and other megafauna apparently turned over and selectively removed phytosterols from the freshly arrived phytodetritus and the surficial sediment (0–5 mm) at the PAP in less than four months. Secondly, their action impacted the food resource available to other organisms. Finally, as phytosterols are expensive to biosynthesise and are apparently an important resource for holothurians, we speculate that the supply of these compounds to the sedimentary community may be one important control on their population in the abyssal ocean.

The impacts of the Samarco mine tailing spill on the Rio Doce estuary, Eastern Brazil

Over 50 million cubic meters of mining tailings were released in the Rio Doce basin after the collapse of the Fundão dam (Samarco) in November 2015. Predicting significant impacts on the Rio Doce estuary, we sampled sediments to investigate short-term impacts on the benthic assemblages and trace metal accumulation on estuarine sediments. With the arrival of the tailing plumes in the estuary, we detected a predominance of clay particles and increased trace metal concentrations of up to 5 times in some areas. The rapid sedimentation after the impact also impacted estuarine macrofaunal assemblages through loss surface-dwelling taxa. As expected, the impacts on benthic assemblages observed up to 3days after the arrival of tailings were not clearly associated with trace metal concentrations, but long-term effects need to be studied. We recommend that the high spatial variability within the estuary be considered in future impact assessment studies.

Evaluation of metals and hydrocarbons in sediments from a tropical tidal flat estuary of Southern Brazil

Although the Passagem Channel estuary, Espírito Santo State, Brazil, is located in an urbanized and industrialized region, it has a large mangrove system. Here we examined natural and anthropogenic inputs that may influence trace metal (Cd, Cr, Cu, Ni, Sc, Pb and Zn) and hydrocarbon (n-alkane and terpane) deposition in three sediment cores collected in the tidal flat zone of the estuary. The cores were also analyzed for carbonate, grain size and stable isotopic composition (δ(13)Corg. and δ(15)Ntotal). Metal enrichment and its association to petroleum hydrocarbons in the surficial sediments of one of the cores, indicate crude oil and derivative inputs, possibly from small vessels and road run-off from local heavy automobile traffic. At the landward sites, the major contributions for metals and hydrocarbons are from natural sources, but in one case, Cu may have been enriched by domestic effluent inputs.

Spatial and temporal distribution of thermotolerant coliform in Canal de Passagem (Vitória - ES) - related to physico-chemical parameters and tide

O Canal de Passagem, Vitoria, ES, e um sistema estuarino em processo de degradacao ambiental devido a descarga de esgoto in natura e semitratado. Os usos da comunidade do entorno dos recursos locais estuarinos sao conflitantes com a qualidade ambiental, o que pode oferecer riscos para a saude publica. Os objetivos do presente trabalho foram: 1. avaliar a distribuicao de coliformes termotolerantes dentro do HCP (metodo dos tubos multiplos), relacionando-a com a distribuicao das fontes de poluicao fecal, a dinâmica de mares e parâmetros fisico-quimicos, e 2. avaliar os resultados dentro das leis brasileiras de limites sanitarios para os variados usos da agua e balneabilidade. Amostras foram feitas espacialmente e temporalmente, visando cobrir o ciclo de mares de sizigia no inverno, outono e primavera, e tambem cobrindo uma quadratura e uma sizigia na amostragem no verao. Foram considerados os parâmetros sanitarios - coliformes termotolerantes, fisicos e quimicos e a acao das mares. Correlacoes significativas foram encontradas com o regime das mares e distribuicao de coliformes. A conclusao retirada do trabalho foi que a distribuicao de coliformes termotolerantes esteve relacionada com as fontes pontuais de poluicao, e as concentracoes foram diferentes entre as mares de quadratura e sizigia. Variacao entre tais mares nao e observada ate o momento pela Legislacao Brasileira para as aguas balneaveis.