Hábitat y historia de vida de Pachychelles laevidactylus (Crustacea, Anomura, Porcellanidae) en el intermareal rocoso de Mar del Plata, Argentina / Habitat and life's story of Pachychelles laevidactylus (Crustacea, Anomura, Porcellanidae) in the rocky shore of Mar del Plata, Argentina

Se analizó la estructura del hábitat, el crecimiento relativo, la heteroquelia, la estructura poblacional, la madurez morfométrica y la fecundidad de Pachycheles laevidactylus Ortmann, 1892, durante Abril, Mayo y Junio del 2005, en sustratos naturales de Mar del Plata, Argentina (38°02'S, 57°31'W). La cobertura algal, la exposición al oleaje y el tiempo de inmersión varió de manera significativa entre estratos y entre meses. La morfometría de las quelas no manifestó diferencias entre sexos. Las hembras mostraron el abdomen más grande que los machos. Si bien existió la heteroquelia, no se detectó lateralidad. Las tallas (ancho de caparazón) estuvieron comprendidas entre 0.67 mm a 9.3 mm para los machos, y entre 1.07 mm a 10.65 mm, para las hembras. La densidad de organismos varió entre meses y entre los estratos. La estructura poblacional, para el periodo de estudio, se explicó en función de la estructura del hábitat. La madurez morfométrica de las hembras fue registrada a los 4.38 mm de ancho de caparazón. El número de huevos se correlacionó positivamente con la talla de las hembras ovígeras con un mínimo de 2 huevos y un máximo de 160, pero esa relación dependió del avance en el desarrollo de los embriones.(AU)

Habitat structure, relative growth, the heterochely, population structure, morphometric maturity and fecundity of Pachycheles laevidactylus Ortmann, 1892 were analyzed during April, May and June 2005, in natural substrates of Mar del Plata, Argentina (38°02'S, 57°31'W). Algal cover, wave exposure and immersion time varied significantly between strata and between months. Chelae morphometry showed no differences between sexes. Females showed the greatest abdomen. While there was the heteroquelia, laterality not detected. The size (carapace width) ranged from 0.67 mm to 9.3 mm for males and from 1.07 mm to 10.65 mm, for females. The density of organisms varied among months and between strata. The population structure for the period of study explained depended on habitat structure. The morphometric maturity of females was recorded at the 4.38 mm of carapace width. The number of eggs was positively correlated with the size of the gravid females with a minimum of 2 eggs and a maximum of 160, but that relationship depended on progress in the development of embryos.(AU)

Hábitat y historia de vida de Pachychelles laevidactylus (Crustacea, Anomura, Porcellanidae) en el intermareal rocoso de Mar del Plata, Argentina / Habitat and life's story of Pachychelles laevidactylus (Crustacea, Anomura, Porcellanidae) in the rocky shore of Mar del Plata, Argentina

Se analizó la estructura del hábitat, el crecimiento relativo, la heteroquelia, la estructura poblacional, la madurez morfométrica y la fecundidad de Pachycheles laevidactylus Ortmann, 1892, durante Abril, Mayo y Junio del 2005, en sustratos naturales de Mar del Plata, Argentina (38°02'S, 57°31'W). La cobertura algal, la exposición al oleaje y el tiempo de inmersión varió de manera significativa entre estratos y entre meses. La morfometría de las quelas no manifestó diferencias entre sexos. Las hembras mostraron el abdomen más grande que los machos. Si bien existió la heteroquelia, no se detectó lateralidad. Las tallas (ancho de caparazón) estuvieron comprendidas entre 0.67 mm a 9.3 mm para los machos, y entre 1.07 mm a 10.65 mm, para las hembras. La densidad de organismos varió entre meses y entre los estratos. La estructura poblacional, para el periodo de estudio, se explicó en función de la estructura del hábitat. La madurez morfométrica de las hembras fue registrada a los 4.38 mm de ancho de caparazón. El número de huevos se correlacionó positivamente con la talla de las hembras ovígeras con un mínimo de 2 huevos y un máximo de 160, pero esa relación dependió del avance en el desarrollo de los embriones.

Habitat structure, relative growth, the heterochely, population structure, morphometric maturity and fecundity of Pachycheles laevidactylus Ortmann, 1892 were analyzed during April, May and June 2005, in natural substrates of Mar del Plata, Argentina (38°02'S, 57°31'W). Algal cover, wave exposure and immersion time varied significantly between strata and between months. Chelae morphometry showed no differences between sexes. Females showed the greatest abdomen. While there was the heteroquelia, laterality not detected. The size (carapace width) ranged from 0.67 mm to 9.3 mm for males and from 1.07 mm to 10.65 mm, for females. The density of organisms varied among months and between strata. The population structure for the period of study explained depended on habitat structure. The morphometric maturity of females was recorded at the 4.38 mm of carapace width. The number of eggs was positively correlated with the size of the gravid females with a minimum of 2 eggs and a maximum of 160, but that relationship depended on progress in the development of embryos.

Hábitat y historia de vida de Pachychelles laevidactylus (Crustacea, Anomura, Porcellanidae) en el intermareal rocoso de Mar del Plata, Argentina

RESUMEN Se analizó la estructura del hábitat, el crecimiento relativo, la heteroquelia, la estructura poblacional, la madurez morfométrica y la fecundidad de Pachycheles laevidactylus Ortmann, 1892, durante Abril, Mayo y Junio del 2005, en sustratos naturales de Mar del Plata, Argentina (38°02'S, 57°31'W). La cobertura algal, la exposición al oleaje y el tiempo de inmersión varió de manera significativa entre estratos y entre meses. La morfometría de las quelas no manifestó diferencias entre sexos. Las hembras mostraron el abdomen más grande que los machos. Si bien existió la heteroquelia, no se detectó lateralidad. Las tallas (ancho de caparazón) estuvieron comprendidas entre 0.67 mm a 9.3 mm para los machos, y entre 1.07 mm a 10.65 mm, para las hembras. La densidad de organismos varió entre meses y entre los estratos. La estructura poblacional, para el periodo de estudio, se explicó en función de la estructura del hábitat. La madurez morfométrica de las hembras fue registrada a los 4.38 mm de ancho de caparazón. El número de huevos se correlacionó positivamente con la talla de las hembras ovígeras con un mínimo de 2 huevos y un máximo de 160, pero esa relación dependió del avance en el desarrollo de los embriones.

Abstract Habitat structure, relative growth, the heterochely, population structure, morphometric maturity and fecundity of Pachycheles laevidactylus Ortmann, 1892 were analyzed during April, May and June 2005, in natural substrates of Mar del Plata, Argentina (38°02'S, 57°31'W). Algal cover, wave exposure and immersion time varied significantly between strata and between months. Chelae morphometry showed no differences between sexes. Females showed the greatest abdomen. While there was the heteroquelia, laterality not detected. The size (carapace width) ranged from 0.67 mm to 9.3 mm for males and from 1.07 mm to 10.65 mm, for females. The density of organisms varied among months and between strata. The population structure for the period of study explained depended on habitat structure. The morphometric maturity of females was recorded at the 4.38 mm of carapace width. The number of eggs was positively correlated with the size of the gravid females with a minimum of 2 eggs and a maximum of 160, but that relationship depended on progress in the development of embryos.

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.

Vertical distribution, segregation by size and recruitment of the yellow clam Mesodesma mactroides Deshayes, 1854 (Mollusca, Bivalvia, Mesodesmatidae) in exposed sandy beaches of the Rio Grande do Sul state, Brazil

The vertical distribution and the segregation by size of the yellow clam Mesodesma mactroides Deshayes, 1854 were investigated in the intertidal zone and its limits with the lower and upper shores at exposed sandy beaches of Rio Grande do Sul state, Brazil. The gathering was made throughout 12 months; from the Pinhal beach towards the south of the State, in six 15 km equidistant transects, determined through random selection. In these transects, the calculation of 30 consecutive waves was made in order to determine its average amplitude point (P0), from which two points were marked towards the lower shore (P-1 and P-2) and three towards the upper shore (P1, P2 and P3). A 30 by 50 cm cylinder was buried down to the depth of 40 cm, the material was separated with a 0.25 cm mesh and the specimens were quantified and measured in length. The yellow clam presented segregation by size, especially between recruit and adult individuals, with recruits occupying preferably the zones above P0 and adults from this point towards the sea. The young specimens are distributed through all zones, mixed with adult and recruit specimens, which dismisses the hypothesis of segregation by size in function of competition for space and food, once the burying depth is directly proportional to their length. However, the segregation between recruits and adults might be related to the filtering mechanism of the adults, which could ingest the larva, as well as the fact that the recruits, being small and light, are easily transported to the regions above P0. Seasonal migration was observed for adult individuals during winter and spring, probably associated to the reproduction period of the species, being that the peak of recruitment was greater in the end of the winter and the beginning of spring.

Foram investigadas a distribuição vertical e a segregação por tamanho no marisco branco Mesodesma mactroides Deshayes, 1854 na zona intermareal e seu limite com o infra e o supralitoral nas praias arenosas expostas do Rio Grande do Sul, Brasil. Ao longo de 12 meses, foram realizadas as coletas a partir da praia de Pinhal em direção ao sul do Estado, em seis transectos eqüidistantes 15 km, determinados mediante sorteio. Nestes, procedeu-se ao cálculo de 30 ondas consecutivas para avaliar o seu ponto médio de amplitude (P0), a partir do qual, foram assinalados dois pontos em direção ao infralitoral (P-1 e P-2) e três em direção ao supralitoral (P1, P2 e P3). Enterrou-se um cilindro de 30 x 50 cm até 40 cm de profundidade, sendo o material triado em malha de 0,25 cm com os exemplares quantificados e mensurados em comprimento. O marisco branco apresentou segregação por tamanho, em especial entre os indivíduos recrutas e os adultos, com os recrutas ocupando preferencialmente as zonas acima de P0 e os adultos, deste ponto em direção ao mar. Já os jovens estão distribuídos por todas as zonas, mesclados com os espécimes adultos e com os recrutas, o que descarta a hipótese de segregação por tamanho em função da competição por espaço e por alimento, uma vez que a profundidade em que se enterram é diretamente proporcional ao seu comprimento. Já a segregação entre os indivíduos recrutas e adultos, pode estar relacionada ao mecanismo de filtração dos adultos, que poderiam ingerir as larvas, como também, ao fato de que os recrutas, por serem pequenos e leves, são facilmente transportados para as regiões acima de P0. Foi constatada a migração sazonal por parte dos indivíduos adultos no inverno e na primavera, provavelmente associada, ao período de reprodução da espécie, pois o pico de recrutamento mais pronunciado foi no fim do inverno e no início da primavera.

Vertical distribution, segregation by size and recruitment of the yellow clam Mesodesma mactroides Deshayes, 1854 (Mollusca, Bivalvia, Mesodesmatidae) in exposed sandy beaches of the Rio Grande do Sul state, Brazil

The vertical distribution and the segregation by size of the yellow clam Mesodesma mactroides Deshayes, 1854 were investigated in the intertidal zone and its limits with the lower and upper shores at exposed sandy beaches of Rio Grande do Sul state, Brazil. The gathering was made throughout 12 months; from the Pinhal beach towards the south of the State, in six 15 km equidistant transects, determined through random selection. In these transects, the calculation of 30 consecutive waves was made in order to determine its average amplitude point (P0), from which two points were marked towards the lower shore (P-1 and P-2) and three towards the upper shore (P1, P2 and P3). A 30 by 50 cm cylinder was buried down to the depth of 40 cm, the material was separated with a 0.25 cm mesh and the specimens were quantified and measured in length. The yellow clam presented segregation by size, especially between recruit and adult individuals, with recruits occupying preferably the zones above P0 and adults from this point towards the sea. The young specimens are distributed through all zones, mixed with adult and recruit specimens, which dismisses the hypothesis of segregation by size in function of competition for space and food, once the burying depth is directly proportional to their length. However, the segregation between recruits and adults might be related to the filtering mechanism of the adults, which could ingest the larva, as well as the fact that the recruits, being small and light, are easily transported to the regions above P0. Seasonal migration was observed for adult individuals during winter and spring, probably associated to the reproduction period of the species, being that the peak of recruitment was greater in the end of the winter and the beginning of spring.

Foram investigadas a distribuição vertical e a segregação por tamanho no marisco branco Mesodesma mactroides Deshayes, 1854 na zona intermareal e seu limite com o infra e o supralitoral nas praias arenosas expostas do Rio Grande do Sul, Brasil. Ao longo de 12 meses, foram realizadas as coletas a partir da praia de Pinhal em direção ao sul do Estado, em seis transectos eqüidistantes 15 km, determinados mediante sorteio. Nestes, procedeu-se ao cálculo de 30 ondas consecutivas para avaliar o seu ponto médio de amplitude (P0), a partir do qual, foram assinalados dois pontos em direção ao infralitoral (P-1 e P-2) e três em direção ao supralitoral (P1, P2 e P3). Enterrou-se um cilindro de 30 x 50 cm até 40 cm de profundidade, sendo o material triado em malha de 0,25 cm com os exemplares quantificados e mensurados em comprimento. O marisco branco apresentou segregação por tamanho, em especial entre os indivíduos recrutas e os adultos, com os recrutas ocupando preferencialmente as zonas acima de P0 e os adultos, deste ponto em direção ao mar. Já os jovens estão distribuídos por todas as zonas, mesclados com os espécimes adultos e com os recrutas, o que descarta a hipótese de segregação por tamanho em função da competição por espaço e por alimento, uma vez que a profundidade em que se enterram é diretamente proporcional ao seu comprimento. Já a segregação entre os indivíduos recrutas e adultos, pode estar relacionada ao mecanismo de filtração dos adultos, que poderiam ingerir as larvas, como também, ao fato de que os recrutas, por serem pequenos e leves, são facilmente transportados para as regiões acima de P0. Foi constatada a migração sazonal por parte dos indivíduos adultos no inverno e na primavera, provavelmente associada, ao período de reprodução da espécie, pois o pico de recrutamento mais pronunciado foi no fim do inverno e no início da primavera.