O fundo marinho da baía da Ilha Grande, RJ: evidências da ação de correntes e de ondas no canal central com base em formas de fundo observadas em registros de sonar (100kHz)
Abstract:Based on high-resolution seismic data (sub-bottom profiler 7,0kHz and side scan sonar 100kHz) and geological bottom samples, interesting aspects of the Ilha Grande bay seabed were investigated. The seabed along the eastern-central channel of the bay was characterized by eight bottom sedimentary patterns. Such patterns showed variations in the texture, in the bio-debris content and in the acoustic back-scattering of the sediments. Observed evidences of modern facies transitions from sub-environments dominated b… Show more
“…Two sites (IM1, BP3) are northern orientated (shoreward), whereas IM2 and BP4 are southern (seaward) and western orientated, respectively. The entrance of waves from the S-SE quadrant into Ilha Grande Bay is facilitated by the coastline configuration of the embayment, as reported by BELO (2002), and waves arriving from other quadrants are partially or totally obstructed. Therefore, regarding wave exposure, we considered IM1 and BP3 as protected sites and IM2 and BP4 as moderately exposed.…”
The structure of subtidal rocky bottom communities at Tamoios Ecological Station (TES), situated in Ilha Grande Bay, Rio de Janeiro State, as well as in other Brazilian marine protected areas, is insufficiently characterized. The present study describes the macroalgal assemblages of shallow subtidal rocky bottoms on two islands of the TES-Imboassica (IM) and Búzios Pequena (BP)adopting species and genera as observational units. Two sites were surveyed on each island in summer 2011. Random 30x30 cm quadrats (n=3) were scraped to collect all macroalgae except crustose species. The subtidal assemblages, in which 58 macroalgal species occurred, were characterized by the high frequency and percent cover of Sargassum vulgare C. Agardh (56.8±8.4%). The sites differed significantly in total number of species and Shannon-Weiner diversity index (PERMANOVA, p<0.05). According to SIMPER, the macroalgal genera that most contributed to the dissimilarities of cover between the sites (contribution >5%) were Sargassum, Laurencia, Wrangelia, Canistrocarpus, Asparagopsis, Hypnea, Ceratodictyon, Gayliella, Spyridia and Chondria.Dissimilarities within and between the islands, as shown by nMDS of the cover data, suggest that different spatial scales should be considered in monitoring the rocky bottom communities of Ilha Grande Bay.
“…Two sites (IM1, BP3) are northern orientated (shoreward), whereas IM2 and BP4 are southern (seaward) and western orientated, respectively. The entrance of waves from the S-SE quadrant into Ilha Grande Bay is facilitated by the coastline configuration of the embayment, as reported by BELO (2002), and waves arriving from other quadrants are partially or totally obstructed. Therefore, regarding wave exposure, we considered IM1 and BP3 as protected sites and IM2 and BP4 as moderately exposed.…”
The structure of subtidal rocky bottom communities at Tamoios Ecological Station (TES), situated in Ilha Grande Bay, Rio de Janeiro State, as well as in other Brazilian marine protected areas, is insufficiently characterized. The present study describes the macroalgal assemblages of shallow subtidal rocky bottoms on two islands of the TES-Imboassica (IM) and Búzios Pequena (BP)adopting species and genera as observational units. Two sites were surveyed on each island in summer 2011. Random 30x30 cm quadrats (n=3) were scraped to collect all macroalgae except crustose species. The subtidal assemblages, in which 58 macroalgal species occurred, were characterized by the high frequency and percent cover of Sargassum vulgare C. Agardh (56.8±8.4%). The sites differed significantly in total number of species and Shannon-Weiner diversity index (PERMANOVA, p<0.05). According to SIMPER, the macroalgal genera that most contributed to the dissimilarities of cover between the sites (contribution >5%) were Sargassum, Laurencia, Wrangelia, Canistrocarpus, Asparagopsis, Hypnea, Ceratodictyon, Gayliella, Spyridia and Chondria.Dissimilarities within and between the islands, as shown by nMDS of the cover data, suggest that different spatial scales should be considered in monitoring the rocky bottom communities of Ilha Grande Bay.
“…The presence of bedforms in Sepetiba Bay was first mentioned by Belo (2002) and later studied by Oliveira (2013). Belo (2002) described small bedforms in the entrance of the bay (height ranging from less than 0.2 until 0.55 m and wavelength between 8.6 and 60 m).…”
Sand ripples have been the subject of many studies. Numerous empirical formulas exist to describe their dimensions. In this paper, ripple height and length are studied at equilibrium state in a current flume. The impact of the grain size and grain shape are analysed. This work is the first stage to estimate ripple characteristics induced by a current, under simple configurations.
“…Environments of rocky shores, beaches and 365 islands are found in its greatest extension. It is considered to be a relatively well-preserved area, in which remnants of insular Atlantic forest occur (Belo 2003, Pires et al 2007. Its waters are characterized as oligotrophic, however, close to urban areas locations with domestic sewage discharges culminating in a eutrophic environment close to the coast can be observed (Mayer-Pinto andJunqueira 2003, Ignacio et al 2010).…”
Monitoring surveys provide data needed to assess ecosystem conditions in places where bioinvasion occurs. The collection of data by volunteer researchers (citizen science) is an alternative for scientists and research agencies that lack information but do not have sufficient financial resources. The objective of the study was to evaluate the potential of volunteer divers with different diving experiences and the use (or not) of an invasive marine species identification guide at eight diving sites distributed between the north of Ilha Grande and the municipality of Angra dos Reis in the Central Channel of Ilha Grande Bay, Rio de Janeiro state. During the three months of study, 207 questionnaires were evaluated. The results showed that the group of volunteer divers with more experience identified a greater number of invasive exotic species compared to the group of divers with less experience. No statistical difference was found in the number of species identified between the groups of volunteer divers with and without a species identification chart. As a recommendation for the use of citizen science, it is necessary to use divers with greater diving experience. Developing stricter protocols for the identification of invasive exotic marine species is essential for the collection of quality data. The improvement of monitoring programs based on citizen science can provide useful information for research on biodiversity in marine environments, significantly reducing financial costs and time in the field, in addition to contributing to the ecological knowledge, awareness and environmental education of participants.
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