Valéria Gomes Veloso

Effect of morphodynamics on the spatial and temporal variation of macrofauna on three sandy beaches, Rio de Janeiro State, Brazil

Three exposed sandy beaches were selected to compare fluctuations in density of the most abundant species, and to verify the influence of spatial and temporal variations on the community structure. Sampling was carried out every three months, from June 1993 to May 1995, on Fora, Prainha, and Boqueirao Beaches. The first two beaches were classified by Deans morphodynamic index (Ω) as intermediate, and the last as reflective. Slope, beach width and median grain size were significantly different among the beaches. Two-way analysis of variance revealed significant differences in species richness only among the beaches. No significant differences in density of the macrofauna between beaches and season were observed. However, Prainha Beach showed a higher temporal variation of the density of the macrofauna (and higher standard deviation) than the other two beaches. Emerita brasiliensis (Crustacea: Decapoda), Excirolana braziliensis (Crustacea: Isopoda), and Pseudorchestoidea brasiliensis (Crustacea: Amphipoda) were the most abundant species. Canonical correspondence analysis calculated the influence of the temporal variation as 27·5%; the influence of the environmental variation on community structure was 20·9%. The results suggest that in spite of the long-term fluctuations in species density, the beaches did not have temporal differences in the species richness and total density macrofauna during the study period.

Spatial and temporal changes in interstitial meiofauna on a sandy ocean beach of South America

Spatial and temporal patterns of meiofauna community from a Brazilian sandy beach were investigated. The objective of this work was to analyze the meiofauna distribution using a statistical model that considers the biological data as variables, and granulometric characteristics, organic matter, and temperature as covariables.Four zones were sampled throughout one year in a Brazilian sandy beach and three sediment cores were taken monthly from each zone. The meiofauna was composed by 12 taxa, with tardigrades and nematodes comprising 92% of the total fauna. The meiofauna mean density varied from 1556.25 to 13125.25 ind.10 cm-2, with the highest densities in December. The results of multiple regression showed that the mean effects of zones, vertical layers, and months on the organisms were significantly correlated with the principal taxa of meiofauna. The retention zone and the 0-10 cm layer presented the highest densities. The temporal distribution showed different patterns and some taxa were more abundant in the dry season, and others in the rainy season. Sedimentological variables had strong and significant effects on the meiofauna taxa. According to the results, physical variables at the retention zone create optimal living conditions for the meiobentos, making this zone an area that favors the basic and applied ecological studies.

Population Biology and Secondary Production of Excirolana braziliensis (Isopoda: Cirolanidae) in Two Sandy Beaches of Southeastern Brazil

Abstract The population dynamics and secondary production of the cirolanid isopod Excirolana braziliensis are compared between two distinct sandy beaches. Monthly sampling from June 1998 through July 2000 was carried out at Grumari (a reflective beach with coarse sand and steeper slope) and Restinga da Marambaia (an intermediate beach with fine sand and moderate slope), both located in Rio de Janeiro State (23° S), southeastern Brazil. Sampling was conducted according to a systematic design in which two transects (fixed 500 meters apart) were established, each with 10 equally spaced sampling strata. From each stratum, five replicates (0.04 square meters) were taken. Highest population abundances were observed in spring and summer on both beaches. The beaches differed significantly in physical parameters and the characteristics of their inhabitant populations: (1) Grumari Beach had a steeper slope, coarse sands, and a short swash period; (2) the abundance of total population, fecundity at length, and egg production potential were higher at Restinga da Marambaia; and (3) individual growth of males was higher at Grumari. Mean length at sexual maturity (L50%), mortality, growth of females, secondary production, and mean annual biomass did not show significant differences between beaches. Variations in population parameters of E. braziliensis might be regulated by phenotypic adjustment to local conditions, optimizing fitness, and especially enabling species to adapt to different physical conditions.

GROWTH, MORTALITY, AND REPRODUCTION OF EXCIROLANA BRAZILIENSIS RICHARDSON, 1912 (ISOPODA, CIROLANIDAE) ON THE PRAINHA BEACH, RIO DE JANEIRO, BRAZIL

[With the aim of estimating the growth parameters, mortality, and reproduction of a population of Excirolana braziliensis, monthly samplings were performed in the period from June 1993 to May 1995 at Prainha Beach, Rio de Janeiro, Brazil. The average size at first sexual maturity was estimated to be 6.9 mm (TL) with an average fecundity of 13 embryos per female. There was a significant linear regression between the clutch size and the length of the female. The growth analyses demonstrated that there is seasonality in growth with smaller rates coincident with lower temperatures. This paper discusses the existence of a size gradient, indicated by an increase in total length with decreasing temperatures.Com o objetivo de estimar os parâmetros de crescimento, mortalidade e reproducao de uma populacao de Excirolana braziliensis, amostragens mensais foram feitas no periodo entre Junho de 1993 e Maio de 1995 na Praia da Prainha (Rio de Janeiro, Brasil). O tamanho medio da primeira maturacao sexual foi estimado em 6,9 mm (CT) com fecundidade media de 13 embrioes por femea. Houve uma significativa regressao linear entre o tamanho da ninhada e o comprimento da femea. Foi observada sazonalidade no crescimento, com menores taxas coincidindo com temperaturas mais baixas. Este artigo discute a existencia de um gradiente de tamanho, indicado pelo aumento do comprimento total com a diminuicao da temperatura., With the aim of estimating the growth parameters, mortality, and reproduction of a population of Excirolana braziliensis, monthly samplings were performed in the period from June 1993 to May 1995 at Prainha Beach, Rio de Janeiro, Brazil. The average size at first sexual maturity was estimated to be 6.9 mm (TL) with an average fecundity of 13 embryos per female. There was a significant linear regression between the clutch size and the length of the female. The growth analyses demonstrated that there is seasonality in growth with smaller rates coincident with lower temperatures. This paper discusses the existence of a size gradient, indicated by an increase in total length with decreasing temperatures.Com o objetivo de estimar os parâmetros de crescimento, mortalidade e reproducao de uma populacao de Excirolana braziliensis, amostragens mensais foram feitas no periodo entre Junho de 1993 e Maio de 1995 na Praia da Prainha (Rio de Janeiro, Brasil). O tamanho medio da primeira maturacao sexual foi estimado em 6,9 mm (CT) com fecundidade media de 13 embrioes por femea. Houve uma significativa regressao linear entre o tamanho da ninhada e o comprimento da femea. Foi observada sazonalidade no crescimento, com menores taxas coincidindo com temperaturas mais baixas. Este artigo discute a existencia de um gradiente de tamanho, indicado pelo aumento do comprimento total com a diminuicao da temperatura.]

Atlantorchestoidea brasiliensis (Crustacea: Amphipoda) as an indicator of disturbance caused by urbanization of a beach ecosystem

Este trabalho e um estudo comparativo da densidade de Atlantorchestoidea brasiliensis (Crustacea: Amphipoda) no trecho urbanizado e no trecho preservado da praia do Pero, Cabo Frio, Rio de Janeiro. Foram realizadas coletas sazonais da populacao de talitrideos, assim como uma estimativa do numero de banhistas nessas areas. Na area preservada foi registrada a menor frequencia de banhista independente dos periodos amostrados, enquanto que no trecho urbanizado a maior frequencia ocorreu no mes de Janeiro (550 individuos/m-1). As analises estatisticas mostraram a ausencia de Atlantorchestoidea brasiliensis na area urbanizada em todos os periodos amostrados, indicando que essa especie e bastante sensivel a urbanizacao das praias. E discutida tambem a utilizacao da familia Talitridae como indicadora de impactos oriundos dos efeitos de urbanizacao nos ecossistemas de praias arenosas.