Community structure of sponges (Porifera) in three reefs at Morrocoy National Park, Venezuela and its correspondence with some environmental variables. Sponges have an important ecological role in coral reef ecosystems. However, when compared to other benthic Phyla, it has been little researched. This research was focused in the variability of the community structure of sponges in three locations at Morrocoy National Park (Cayo Sombrero, Playa Mero and Punta Brava) exposed to different environmental conditions (transparency and currents intensity) and affected in different degree of severity by a mass mortality event in 1996. A total of 15 transects (10m long and 1m wide) were evaluated in three strata (between 3 and 15m depth) in each site, where all the individuals were counted by species. Relative abundance by species, diversity and evenness were calculated. Locations showed differences respect turbidity, wave and current intensity. 27 species were found in Morrocoy; Cayo Sombrero (23), Playa Mero (18) and Punta Brava (15). Agelas sceptrum, Amphimedon erina and Niphates erecta were the most common in first location; Niphates erecta and Dysidea etheria in Playa Mero and Dysidea etheria, Niphates erecta and Amphimedon erina in Punta Brava. The species composition showed statistical differences between all three locations; Cayo Sombrero resulted the most diverse and even, followed by Playa Mero and Punta Brava. According to Sorensen Similarity Index results, Cayo Sombrero and Playa Mero were more similar, while Punta Brava resulted the most different. The variability in environmental conditions and the differential mass mortality effects of 1996 in all three reefs, were probably the main causes of the differences between their sponge communities. Nevertheless, we cannot conclude about the weight of these factors. Rev. Biol. Trop. 61 (3): 1229-1241. Epub 2013 September 01.
Soil physico-chemical characteristics of oodplains, particularly hydrology, in uence microbiological activity. As such, each river oodplain system has a unique physico-chemical dynamic that in turn supports the microbial community. The Mapire River oodplain is a complex system in which seasonal ood pulses cause changes in the soil physico-chemical variables. We examined how these temporal and spatial differences are associated with the microbiological activity along a seasonally ooded gradient at the mouth of the Mapire River (Lower Orinoco, Venezuela). Soil samples were collected during three different seasons by a systematic sampling at 4 points of the gradient, de ned by the intensity of ooding. The physico-chemical parameters of the soil were determined and related by the density and physiological pro le of the microbial community through multivariate permutation analysis and gradient analysis. The results indicate that there is a spatial gradient determined by soil clay content and a temporal gradient in uenced by moisture and total organic carbon. Signi cant differences were found among soil zones and seasons, with the interaction of both factors also signi cant. It was observed that microbial activity is decisive in phosphorus dynamics, even during ooding. It is concluded that amid the complex interactions between biotic and abiotic factors, microbial communities are able to respond to changes in the physico-chemical soil environment and maintain their activity throughout the hydroperiod.
Soil physico-chemical characteristics of floodplains, particularly hydrology, influence microbiological activity. As such, each river floodplain system has a unique physico-chemical dynamic that in turn supports the microbial community. The Mapire River floodplain is a complex system in which seasonal flood pulses cause changes in the soil physico-chemical variables. We examined how these temporal and spatial differences are associated with the microbiological activity along a seasonally flooded gradient at the mouth of the Mapire River (Lower Orinoco, Venezuela). Soil samples were collected during three different seasons by a systematic sampling at 4 points of the gradient, defined by the intensity of flooding. The physico-chemical parameters of the soil were determined and related by the density and physiological profile of the microbial community through multivariate permutation analysis and gradient analysis. The results indicate that there is a spatial gradient determined by soil clay content and a temporal gradient influenced by moisture and total organic carbon. Significant differences were found among soil zones and seasons, with the interaction of both factors also significant. It was observed that microbial activity is decisive in phosphorus dynamics, even during flooding. It is concluded that amid the complex interactions between biotic and abiotic factors, microbial communities are able to respond to changes in the physico-chemical soil environment and maintain their activity throughout the hydroperiod.
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