Change in the meiofauna community structure of sandy beaches of the Nuevo Gulf (Chubut, Argentina)

La composición y distribución de la meiofauna bentónica del Golfo Nuevo (Chubut, Argentina) se describen en relación a las variables ambientales. La meiofauna y el sedimento de la zona intermareal de cuatro playas de arena con diferentes perturbaciones antrópicas fueron recolectadas en Junio de 2005. Las muestras se colectaron en 20 sitios de muestreo con tubos core de 2,5 cm de diámetro y 10 cm de profundidad. Fueron identificados 13 taxones de meiofauna, representados principalmente por nematodos, gastrotricos, ciliados y poliquetos y la abundancia de la meiofauna que fue desde 1,5 × 10³ a 6,5 × 10³ ind. 10 cm2. Los análisis univariado (ANOVA de una-vía) y multivariado (ANOSIM/MDS) indicaron diferencias significativas en las estructuras de la comunidad entre los sitios con efectos antrópicos y aquellos en condiciones prístinas, revelando que estas diferencias fueron entre las playas próximas y alejadas de una ciudad con la actividad portuaria. Los cambios en la estructura de la comunidad (abundancia y diversidad) pueden haber estado relacionados con gradientes ambientales próximos a la costa. El análisis BIOENV mostró que la profundidad de la discontinuidad del potencial redox puede ser el principal factor que influye en la distribución espacial de los organismos.

The composition and distribution of the benthic meiofauna assemblages of the Nuevo Gulf (Chubut, Argentina) are described in relation to abiotic variables. The meiofauna and sediment samples were collected in the intertidal zone of four sandy beaches with different anthropic disturbances in June 2005. The samples were obtained at 20 sampling sites using a 2.5 cm diameter core tube at a depth of 10 cm. A total of 13 meiofauna taxa were identified, with the meiofauna being primarily represented by nematodes, gastrotrichs, ciliates and polychaetes and the meiofauna abundances ranging from 1.5 × 10³ to 6.5 × 10³ ind. 10 cm2. Univariate (one-way ANOVA test) and multivariate (ANOSIM/MDS test) analyses showed clear dissimilarities in community structures between sites with anthropic effects and those in pristine condition, revealed by the significant differences were found between beaches near to and far way from a city with port activity. The meiofaunal assemblage varied in abundance and diversity, and these changes in the community structure may have been related to environmental gradients on the shore. The BIOENV analysis showed that the redox potential discontinuity depth might be the main factor in the spatial distribution of organisms.

Change in the meiofauna community structure of sandy beaches of the Nuevo Gulf (Chubut, Argentina)

La composición y distribución de la meiofauna bentónica del Golfo Nuevo (Chubut, Argentina) se describen en relación a las variables ambientales. La meiofauna y el sedimento de la zona intermareal de cuatro playas de arena con diferentes perturbaciones antrópicas fueron recolectadas en Junio de 2005. Las muestras se colectaron en 20 sitios de muestreo con tubos core de 2,5 cm de diámetro y 10 cm de profundidad. Fueron identificados 13 taxones de meiofauna, representados principalmente por nematodos, gastrotricos, ciliados y poliquetos y la abundancia de la meiofauna que fue desde 1,5 × 10³ a 6,5 × 10³ ind. 10 cm2. Los análisis univariado (ANOVA de una-vía) y multivariado (ANOSIM/MDS) indicaron diferencias significativas en las estructuras de la comunidad entre los sitios con efectos antrópicos y aquellos en condiciones prístinas, revelando que estas diferencias fueron entre las playas próximas y alejadas de una ciudad con la actividad portuaria. Los cambios en la estructura de la comunidad (abundancia y diversidad) pueden haber estado relacionados con gradientes ambientales próximos a la costa. El análisis BIOENV mostró que la profundidad de la discontinuidad del potencial redox puede ser el principal factor que influye en la distribución espacial de los organismos.

The composition and distribution of the benthic meiofauna assemblages of the Nuevo Gulf (Chubut, Argentina) are described in relation to abiotic variables. The meiofauna and sediment samples were collected in the intertidal zone of four sandy beaches with different anthropic disturbances in June 2005. The samples were obtained at 20 sampling sites using a 2.5 cm diameter core tube at a depth of 10 cm. A total of 13 meiofauna taxa were identified, with the meiofauna being primarily represented by nematodes, gastrotrichs, ciliates and polychaetes and the meiofauna abundances ranging from 1.5 × 10³ to 6.5 × 10³ ind. 10 cm2. Univariate (one-way ANOVA test) and multivariate (ANOSIM/MDS test) analyses showed clear dissimilarities in community structures between sites with anthropic effects and those in pristine condition, revealed by the significant differences were found between beaches near to and far way from a city with port activity. The meiofaunal assemblage varied in abundance and diversity, and these changes in the community structure may have been related to environmental gradients on the shore. The BIOENV analysis showed that the redox potential discontinuity depth might be the main factor in the spatial distribution of organisms.

Explaining dissimilarities in macroinvertebrate assemblages among stream sites using environmental variables

The relationship between community structure and environmental factors usually varies according to ecosystem type, group of organisms, and spatial scale. In this study I assessed whether dissimilarities among assemblages of stream macroinvertebrates are related to differences in environmental variables. Data consisted of macroinvertebrate samples of 10 stream sites during the dry season. Seven environmental variables were assessed. The relationship among dissimilarities in assemblage structure and dissimilarities in environmental variables was assessed using the BioEnv approach. Conductivity and measures related to stream size were the most important variables. However, part of the correlation with conductivity was due to the high value observed in a single stream site, which presented a relatively distinct macroinvertebrate fauna. There was an abrupt change in assemblage structure between 4th and 5th order streams. Although the study included a single 5th order site and thus only weak generalizations are possible, this finding corroborates scattered evidence observed in previous studies. The finding that nearby sites may harbor distinct macroinvertebrate assemblages implies whole-catchment conservation strategies. As most of the remaining Atlantic Rain Forest is restricted to small fragments, restoration projects near fragments should be implemented so as to properly conserve lotic ecosystems.

Explaining dissimilarities in macroinvertebrate assemblages among stream sites using environmental variables

The relationship between community structure and environmental factors usually varies according to ecosystem type, group of organisms, and spatial scale. In this study I assessed whether dissimilarities among assemblages of stream macroinvertebrates are related to differences in environmental variables. Data consisted of macroinvertebrate samples of 10 stream sites during the dry season. Seven environmental variables were assessed. The relationship among dissimilarities in assemblage structure and dissimilarities in environmental variables was assessed using the BioEnv approach. Conductivity and measures related to stream size were the most important variables. However, part of the correlation with conductivity was due to the high value observed in a single stream site, which presented a relatively distinct macroinvertebrate fauna. There was an abrupt change in assemblage structure between 4th and 5th order streams. Although the study included a single 5th order site and thus only weak generalizations are possible, this finding corroborates scattered evidence observed in previous studies. The finding that nearby sites may harbor distinct macroinvertebrate assemblages implies whole-catchment conservation strategies. As most of the remaining Atlantic Rain Forest is restricted to small fragments, restoration projects near fragments should be implemented so as to properly conserve lotic ecosystems.

Explaining dissimilarities in macroinvertebrate assemblages among stream sites using environmental variables

The relationship between community structure and environmental factors usually varies according to ecosystem type, group of organisms, and spatial scale. In this study I assessed whether dissimilarities among assemblages of stream macroinvertebrates are related to differences in environmental variables. Data consisted of macroinvertebrate samples of 10 stream sites during the dry season. Seven environmental variables were assessed. The relationship among dissimilarities in assemblage structure and dissimilarities in environmental variables was assessed using the BioEnv approach. Conductivity and measures related to stream size were the most important variables. However, part of the correlation with conductivity was due to the high value observed in a single stream site, which presented a relatively distinct macroinvertebrate fauna. There was an abrupt change in assemblage structure between 4th and 5th order streams. Although the study included a single 5th order site and thus only weak generalizations are possible, this finding corroborates scattered evidence observed in previous studies. The finding that nearby sites may harbor distinct macroinvertebrate assemblages implies whole-catchment conservation strategies. As most of the remaining Atlantic Rain Forest is restricted to small fragments, restoration projects near fragments should be implemented so as to properly conserve lotic ecosystems.