Altair de Jesus Machado

A note on the occurrence of the encrusting foraminifera Homotrema rubrum in reef sediments from two distinctive hydrodynamic settings

Sediment samples from two different reef environments were analyzed for their foraminiferal content: the Sioba/Rio do Fogo reefs, located in a broad shallow shelf dominated by strong currents (Rio Grande do Norte State), and the Praia do Forte reefs, located in a narrow shelf under the influence of wind-induced waves (Bahia State). The recorded foraminiferal fauna, from forty-six samples, is represented by 113 species, being the encrusting species Homotrema rubrumpresent in nine samples from the Sioba/Rio do Fogo reefs and in 11 samples from Praia do Forte reefs. Homotremafragments recovered from Sioba/Rio do Fogo are mostly polished with rounded edges (51.59%) and some have a whitish color, whereas the specimens from Praia do Forte reefs are predominantly composed of reddish fragments (82.41%) with sharpened points (63.88%). The high wave energy on the reef environment of Praia do Forte is responsible for the fragmentation of living Homotrematests (red color), which are deposited near to their source area. The effects of the strong current system operating in the broad continental shelf of Sioba/Rio do Fogo is the major cause of sediment reworking, producing polished grains accumulated in its reef surroundings.

Caracterização do Estuário do Rio Caravelas (Bahia) a partir de Análises de Distribuição Temporal da Microfauna de Foraminíferos

The objective of this study was to evaluate the temporal distribution of the foraminifera microfauna of the Caravelas River estuary (Bahia) to determine the different stages of marine influence on this ecosystem. For this purpose, two core samples 60 cm in length were collected at different sites in the estuary. In the laboratory, subsamples were taken from the sediment columns every 2 cm. The samples were subjected to standard analysis for foraminifera. We collected, stored, and identified the first 100 samples to determine the fauna diversity. The data analysis involved calculation of relative abundances, occurrence frequencies, diversity indices, richness, dominance, and confinement. The integrated analysis of the richness and diversity indices for the TCV1A core indicated that the oscillations between the highest and lowest marine influences were not representative to the point of promoting marked events of enrichment and depletion of the fauna at this sampling site. In contrast, analysis of the TCV2A core showed a restricted marine influence during the deposition period of this sediment column, especially since the 1980s. This hypothesis can be confirmed by the richness and diversity values, which show signs of faunal impoverishment in different sections of this core.The objective of this study was to evaluate the temporal distribution of the foraminifera microfauna of the Caravelas River estuary (Bahia) to determine the different stages of marine influence on this ecosystem. For this purpose, two core samples 60 cm in length were collected at different sites in the estuary. In the laboratory, subsamples were taken from the sediment columns every 2 cm. The samples were subjected to standard analysis for foraminifera. We collected, stored, and identified the first 100 samples to determine the fauna diversity. The data analysis involved calculation of relative abundances, occurrence frequencies, diversity indices, richness, dominance, and confinement. The integrated analysis of the richness and diversity indices for the TCV1A core indicated that the oscillations between the highest and lowest marine influences were not representative to the point of promoting marked events of enrichment and depletion of the fauna at this sampling site. In contrast, analysis of the TCV2A core showed a restricted marine influence during the deposition period of this sediment column, especially since the 1980s. This hypothesis can be confirmed by the richness and diversity values, which show signs of faunal impoverishment in different sections of this core.

The occurrence of Carterina spiculotesta (Carter, 1877) on an artificial substrate

Carterina spiculotesta is an extant foraminifera species that makes a calcareous test with secreted spicules embedded into its wall. Modern populations are reported from few regions in Brazil, but this is the first report of living C. spiculotesta found on an artificial substrate, which is located near industrial outfalls.

Relação entre a microfauna de foraminíferos e a granulometria do sedimento do Complexo Recifal de Abrolhos, Bahia, a partir de análises multivariadas

Resumo O presente trabalho tem como objetivo identificar, por meio de analises multivariadas, assembleias de foraminiferos que apresentem distribuicao influenciada pela granulometria do sedimento. Para tanto, foram analisadas 38 amostras de sedimento superficial de fundo do Complexo Recifal de Abrolhos, na Bahia, com base em criterios sedimentologicos e faunisticos. A analise sedimentologica considerou o percentual das classes texturais cascalho, areia e lama. A analise faunistica foi realizada a partir da triagem e da identificacao dos 300 primeiros foraminiferos. A partir desses dados, foram realizadas analises multivariadas de classificacao e ordenacao. A analise de classificacao das amostras, com base nos teores de cascalho, areia e lama, revelou a formacao de dois grupos (I e II) e quatro subgrupos (IA, IB, IIC e IID), caracterizados pelo predominio das fracoes sedimentologicas especificas e confirmados atraves da analise de ordenacao. A analise de classificacao das especies constantes evidenciou a separacao de Archaias angulatus dos tres agrupamentos microfaunisticos formados (assembleias I, II e III). A correlacao entre os agrupamentos sedimentologicos e microfaunisticos permitiu identificar a formacao de diferentes assembleias, constituidas a partir de especies cuja distribuicao na area revelou influencia direta com o padrao textural do sedimento. Palavras-chave: foraminiferos; granulometria; analises multivariadas.