Sérgio Henrique Gonçalves da Silva

Succession in rocky intertidal benthic communities in areas with different pollution levels at Guanabara Bay (RJ-Brazil)

The aim of this study was to describe and compare the succession of intertidal benthic communities in two areas at Guanabara Bay, RJ, Brazil: Urca, an area submitted to moderated organic pollution and Catalao, an extremely polluted area. Three transects in each area were scraped one month before the beginning of this study in order to evaluate the recruitment (recruitment-treatments). Three other transects were monitored without manipulation (monitoring treatments). Species composition and relative abundance were evaluated monthly between September and December, 2000. A total of 26 species was found at Urca and 13 at Catalao. The percent cover of the most abundant organisms was not similar between treatments at Urca after four months, while in Catalao, the similarity was 72% in the second month. The faster community development and recovery at the most polluted area was probably related to the existence of simple and resilient communities in more impacted areas.

A comparative study of the methods used to evaluate the activity of Teredinidae molluscs

Abstract Different methodologies are usually employed to evaluate Teredinidae wood-boring activity. Many authors using panels made of solid wood, estimated density by counting Teredinidae punctures on the wood surface or using x-ray techniques. However this technique does not allow the identification of species. A second approach, employing a collecting device made of sheets of wood, can be more effective for quantitative and qualitative analyses. The present paper compares density, species composition and diversity when using both solid and sheet panels. In addition different methods of estimating density were analysed. The results show that the evaluation of Teredinidae activity can change according to the methodology employed.

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

This paper introduces a method for temporal studies of steep rocky intertidal communities. It combines the use of digital image technology with field methodology, so that a wide area of the community can be sampled in a short time. Two current nondestructive percent cover estimation methods (visual estimation and point intersection) were compared in terms of cost, operational advantages and data quality, with a proposed method for a sucessional study . The proposed method used sequential photos to sample multiple fixed vertical transects over time. Reproduction of the mid-intertidal transect over time was possible by overlaying temporal transects in an image editing program. This method was similar to the point intersection quadrat method used to estimate percent cover. Benefits included reduced time on field work, economic advantages and other advantages of using digital photography, such as recording. Temporal photography of transects provided measurements of recruitment, mortality and population growth, and made it possible to manufacture an animation of sucessional stages. We suggest that this is the best method for providing information and understanding on the process of succession and for monitoring benthic invertebrate intertidal communities on steep rocky shores.

How Much Is Too Little to Detect Impacts? A Case Study of a Nuclear Power Plant

Several approaches have been proposed to assess impacts on natural assemblages. Ideally, the potentially impacted site and multiple reference sites are sampled through time, before and after the impact. Often, however, the lack of information regarding the potential overall impact, the lack of knowledge about the environment in many regions worldwide, budgets constraints and the increasing dimensions of human activities compromise the reliability of the impact assessment. We evaluated the impact, if any, and its extent of a nuclear power plant effluent on sessile epibiota assemblages using a suitable and feasible sampling design with no ‘before’ data and budget and logistic constraints. Assemblages were sampled at multiple times and at increasing distances from the point of the discharge of the effluent. There was a clear and localized effect of the power plant effluent (up to 100 m from the point of the discharge). However, depending on the time of the year, the impact reaches up to 600 m. We found a significantly lower richness of taxa in the Effluent site when compared to other sites. Furthermore, at all times, the variability of assemblages near the discharge was also smaller than in other sites. Although the sampling design used here (in particular the number of replicates) did not allow an unambiguously evaluation of the full extent of the impact in relation to its intensity and temporal variability, the multiple temporal and spatial scales used allowed the detection of some differences in the intensity of the impact, depending on the time of sampling. Our findings greatly contribute to increase the knowledge on the effects of multiple stressors caused by the effluent of a power plant and also have important implications for management strategies and conservation ecology, in general.

The effect of low salinity on teredinids

Teredinids survival in low salinities was determined in aquaria. Panels previously immersed in Ponta de Leste, Ilha Grande Bay, Rio de Janeiro, were transferred to aquaria with salinities ranging from 5.0 to 15.0 Practical Salinity Unities (PSU). The waters of Ilha Grande Bay receive a large amount of wood from the marginal rainforest vegetation, being suitable for the development of teredinids. The coastal areas of the bay are subjected to wide salinity fluctuations due to strong and sudden tropical storms. Eleven different species of teredinids were found in the panels. The critical salinity concentration for the survival of the two most common species was 11.93 PSU for Lyrodus floridanus and 12.90 PSU for Teredo furcifera. The effect of time on the mortality of teredinids at low salinities is also discussed.

Avaliação da infestação e diversidade de Teredinidae (Mollusca - Bivalvia) ao longo da costa do estado do Rio de Janeiro, Brasil

In order to evaluate the diversity and infestation level of Teredinidae wood-boring molluscs, ten satations were chosen along the coast of Rio de Janeiro State. Using five pine-wood panels in each station, it was possible to distinguish five areas according to species dominance. Ilha Grande Bay is characterized by the dominance of Lyrodus floridanus (Bartsch, 1922); Sepetiba Bay, by Bankia fimbriatula Moll & Roch, 1931, Tijuca Lagoon by Teredo navalis Linnaeus, 1758; Guanabara Bay by Notoredo knoxi (Bartsch, 1917) and Araruama Lagoon by Teredo furcifera Martens, 1894. Specific composition and dominance of these species were due mainly to abiotic factors such as salinity whereas infestation level was associated not only to salinity but also to other factors such as the quantity and quality of fouling, the presence of larval dispersion focus and the wood supply in each area.

Distribuição vertical de Teredinidae (Mollusca, Bivalvia) em Portogallo, Angra dos Reis, Rio de Janeiro, Brasil

In order to study the vertical distribution of Teredinidae at Angra dos Reis, State of Rio de Janeiro, Brazil, 30 collectors of wood sheets (Araucaria sp.) were submerged (10 at each depth) at 0,2, 2 and 4 m, respectively. Among the species collected, Lyrodus floridanus was the only one that did not whow significant variation in number of individuals in relation to depth. All the other species were unaffected, in number of individuals, by the different depths tested.

Spatial distribution of bivalvia (Mollusca) in the soft-bottoms of Ilha Grande Bay, Rio de Janeiro, Brazil

A distribuicao espacial dos bivalves e sua relacao com a granulometria e os teores de materia orgânica e silte-argila foram estudados no Saco do Ceu. Obteve-se amostras de fauna e sedimento em 39 estacoes nos meses de janeiro e julho de 1992, utilizando-se um busca-fundo de Petersen de 0,1 m2. O sedimento variou de areia fina a areia grossa. Foram quantificadas 19 especies sendo que 14 ocorreram nos dois periodos do ano. Os fundos de areia media e fina no verao e areia grossa no inverno apresentaram os maiores valores de diversidade e uma maior heterogeneidade estrutural. Evidenciou-se a existencia de uma comunidade dominada por Anomalocardia brasiliana em fundos grossos e outra dominada por Corbula caribaea em fundos finos, ricos em materia orgânica. Ambas distribuiram-se em continuo, ao longo de um gradiente sedimentologico.