Estudo comparativo de métodos de amostragem de comunidades de Costão

Abstract

Sampling methods for rocky shoresThis study compares three sampling methodologies of rocky shore communities: visual estimation, point intercept quadrats and destructive sampling. Visual estimation was performed in two sizes of sampling device and, point intercept quadrats was done with different numbers of marked dots. The sampling took place on the rocky shore of Forno beach, Búzios, RJ, in two different algae belts; one whose the landscape is characterized by Amphiroa sp., the other, Sargassum furcatum was the most conspicuous species. The data were analyzed by ANOVA and Kruskal-Wallis tests. Number of species, total percent cover, diversity and evenness indices were the variables used. The results shown that in general the methods compared were not statistically different one from the other in this community. There were significative differences between the methods when comparison was made between nondestructive and destructive sampling. However, smaller areas of sampling devices and fewer intercept points decreased the sampling power in respect of sampling species richness. All of the methods studied were considered similar in concern of total cover index and of diversity and evenness indices, with some exceptions. Present data are useful only for rocky communities with similar profiles. The choice of method must be made in regard of each situation.Key words: sampling methods, rocky shore, phytobenthos, Búzios, RJ. RESUMOO presente estudo compara três metodologias de amostragem de costão rochoso: estimativa visual, pontos de interseção e raspagem total do substrato. No método de estimativa visual, variou-se o tamanho do amostrador e, no de pontos de interseção, o número de pontos marcados. As amostras foram coletadas no costão da praia do Forno, Búzios, RJ, em duas faixas, uma dominada fisionomicamente por Amphiroa sp. e a outra, por Sargassum furcatum. Foram aplicados testes de ANOVA e KruskalWallis aos resultados encontrados, utilizando-se como variáveis os índices bionômicos de número de espécies, porcentagem total de recobrimento, índice de diversidade e índice de uniformidade. Os resultados provaram que nenhuma metodologia de amostragem semelhante mostrou-se estatisticamente diferente da outra. Existe diferença quando se comparam os métodos não-destrutivos ao método destrutivo. No entanto, amostradores com menor área ou menor número de pontos não amostram bem o índice número de espécies. Os métodos não apresentaram diferença significativa em relação à cobertura total e aos índices de diversidade e uniformidade, salvo algumas exceções. Os resultados do presente trabalho são aplicáveis apenas a comunidades de costão rochosos com perfis similares ao da comunidade estudada. A escolha do método deve ser considerada para cada situação.Palavras-chave: metodologia de amostragem, costão rochoso, fitobentos, Búzios, RJ.

Comparison of rocky itertidal community sampling methods at northern coast of Rio de Janeiro State, Brazil

“…However, richness and species percentage values at each height did not show significant differences among the methods. Meese & Tomich (1992) and Sabino & Villaça (1999) compared different sampling techniques to estimate the coverage percentage on rocky intertidal shores and verified that no method was considerably better, reaching the same conclusion as this study.…”

“…Since conclusions of field studies rest partly on how data was collected, sampling issues have been given considerable attention in ecology (Miller & Ambrose, 2000). There has been some extent work on collecting data methods (Foster et al, 1991;Dethier et al, 1993;Sabino & Villaça, 1999) and sampling schedule for environmental impact assessments (e.g. Green, 1979;Underwood, 1994).…”

“…In order to understand the species distribution and abundance patterns, it is supposed that the applied methods give accurate estimates of the number of organisms. The precise patterns description is then essential to understand the ecological processes (Andrew & Mapstone, 1987;Sabino & Villaça, 1999).…”

“…Little attention has been given to methodological problems involving such community (Villaça, 1991;Sabino & Villaça, 1999).…”

Method for monitoring intertidal communities in a steep rocky shore: a combination of digital image technology and field operational strategy

“…Point intersect estimation of percent cover, while being more precise in the estimation, is limited by the time available during sampling at low tide. This limitation leads to a decrease of precision by reducing the number of samples or intersections used (Sabino & Villaça, 1999;Meese & Tomich, 1992). Photographic methods take little time per sample, allowing multiple samples that lead to a more precise abundance estimation and yield a permanent record that can be later achieved (Murray et al, 2006).…”