Short-term stability of estuarine benthic assemblages: are storms pattern-defining events?

Storms, associated with strong winds and heavy rains, are often the most severe physical disturbances in shallow coastal areas causing instability to sedimentary environments. We hypothesized herein that if storms influence short-term assemblage structure of macrofauna, then assemblages should change after storms, while remaining relatively stable over calm weather conditions. The study was conducted at the subtropical Paranaguá Bay, in southern Brazil. We selected four 700 m² sites, at the estuarine outlet, to monitor changes in number of species, number of individuals and Shannon diversity. Sampling was arranged considering the weather forecast so that both before and after conditions could be recorded. Data of each site was tested separately to access the significance of specific (before/after) comparisons using t tests. There were no clear effects of storms on macrofaunal species richness, abundance and diversity at the four sampled sites. Conversely, we showed that short-term variation in abundances occurred regardless of weather conditions. Increased dispersal may be the most common process associated with storms instead of mortality. Storms that intermittently affect the southern coast of Brazil can be thus seen as minor driving forces of shallow-water estuarine macrofauna. Effects of extreme meteorological events remain to be assessed.

Short-term stability of estuarine benthic assemblages: are storms pattern-defining events?

Storms, associated with strong winds and heavy rains, are often the most severe physical disturbances in shallow coastal areas causing instability to sedimentary environments. We hypothesized herein that if storms influence short-term assemblage structure of macrofauna, then assemblages should change after storms, while remaining relatively stable over calm weather conditions. The study was conducted at the subtropical Paranaguá Bay, in southern Brazil. We selected four 700 m² sites, at the estuarine outlet, to monitor changes in number of species, number of individuals and Shannon diversity. Sampling was arranged considering the weather forecast so that both before and after conditions could be recorded. Data of each site was tested separately to access the significance of specific (before/after) comparisons using t tests. There were no clear effects of storms on macrofaunal species richness, abundance and diversity at the four sampled sites. Conversely, we showed that short-term variation in abundances occurred regardless of weather conditions. Increased dispersal may be the most common process associated with storms instead of mortality. Storms that intermittently affect the southern coast of Brazil can be thus seen as minor driving forces of shallow-water estuarine macrofauna. Effects of extreme meteorological events remain to be assessed.

Short-term stability of estuarine benthic assemblages: are storms pattern-defining events?

Storms, associated with strong winds and heavy rains, are often the most severe physical disturbances in shallow coastal areas causing instability to sedimentary environments. We hypothesized herein that if storms influence short-term assemblage structure of macrofauna, then assemblages should change after storms, while remaining relatively stable over calm weather conditions. The study was conducted at the subtropical Paranaguá Bay, in southern Brazil. We selected four 700 m² sites, at the estuarine outlet, to monitor changes in number of species, number of individuals and Shannon diversity. Sampling was arranged considering the weather forecast so that both before and after conditions could be recorded. Data of each site was tested separately to access the significance of specific (before/after) comparisons using t tests. There were no clear effects of storms on macrofaunal species richness, abundance and diversity at the four sampled sites. Conversely, we showed that short-term variation in abundances occurred regardless of weather conditions. Increased dispersal may be the most common process associated with storms instead of mortality. Storms that intermittently affect the southern coast of Brazil can be thus seen as minor driving forces of shallow-water estuarine macrofauna. Effects of extreme meteorological events remain to be assessed.

A new look into the small-scale dispersal of free-living marine nematodes

We tested experimentally the hypothesis that prevailing locomotion/feeding strategies and body morphology may lead to more active dispersal of free-living marine nematodes, besides passive transport. Neutral Red was applied to the sediment inside cores and the red plume formed during the flood tide was divided into near, middle, and distant zones. At 0.5 m and 1 m from the stained cores, sampling nets were suspended 5 and 10 cm above the sediment-water interface. Dispersion behaviors were defined as a function of a) the numbers of stained recaptured nematodes in comparison to their mean densities in the sediment, b) movement in the sediment or swimming in the water column, and c) body morphology. Tidal currents with average velocities of 9 cm/s resuspended the numerically dominant nematode taxa Sabatieria sp., Terschellingia longicaudata de Man, 1907, Metachromadora sp. and Viscosia sp. The recapture of stained nematodes as far as 2 m from the original stained cores showed that, despite their small body size, they can disperse through relatively large distances, either passively or actively, via the water column during a single tidal event. Recapture patterns in the sediment and in the water column indicate that nematode dispersal is directly influenced by their body morphology and swimming ability, and indirectly by their feeding strategies, which ultimately define their position in the sediment column. Besides stressing the role played by passive transport in the water column, our experiment additionally showed that mobility and feeding strategies also need to be considered as determinant of short-scale nematode dispersal.

A new look into the small-scale dispersal of free-living marine nematodes

We tested experimentally the hypothesis that prevailing locomotion/feeding strategies and body morphology may lead to more active dispersal of free-living marine nematodes, besides passive transport. Neutral Red was applied to the sediment inside cores and the red plume formed during the flood tide was divided into near, middle, and distant zones. At 0.5 m and 1 m from the stained cores, sampling nets were suspended 5 and 10 cm above the sediment-water interface. Dispersion behaviors were defined as a function of a) the numbers of stained recaptured nematodes in comparison to their mean densities in the sediment, b) movement in the sediment or swimming in the water column, and c) body morphology. Tidal currents with average velocities of 9 cm/s resuspended the numerically dominant nematode taxa Sabatieria sp., Terschellingia longicaudata de Man, 1907, Metachromadora sp. and Viscosia sp. The recapture of stained nematodes as far as 2 m from the original stained cores showed that, despite their small body size, they can disperse through relatively large distances, either passively or actively, via the water column during a single tidal event. Recapture patterns in the sediment and in the water column indicate that nematode dispersal is directly influenced by their body morphology and swimming ability, and indirectly by their feeding strategies, which ultimately define their position in the sediment column. Besides stressing the role played by passive transport in the water column, our experiment additionally showed that mobility and feeding strategies also need to be considered as determinant of short-scale nematode dispersal.

A new look into the small-scale dispersal of free-living marine nematodes

We tested experimentally the hypothesis that prevailing locomotion/feeding strategies and body morphology may lead to more active dispersal of free-living marine nematodes, besides passive transport. Neutral Red was applied to the sediment inside cores and the red plume formed during the flood tide was divided into near, middle, and distant zones. At 0.5 m and 1 m from the stained cores, sampling nets were suspended 5 and 10 cm above the sediment-water interface. Dispersion behaviors were defined as a function of a) the numbers of stained recaptured nematodes in comparison to their mean densities in the sediment, b) movement in the sediment or swimming in the water column, and c) body morphology. Tidal currents with average velocities of 9 cm/s resuspended the numerically dominant nematode taxa Sabatieria sp., Terschellingia longicaudata de Man, 1907, Metachromadora sp. and Viscosia sp. The recapture of stained nematodes as far as 2 m from the original stained cores showed that, despite their small body size, they can disperse through relatively large distances, either passively or actively, via the water column during a single tidal event. Recapture patterns in the sediment and in the water column indicate that nematode dispersal is directly influenced by their body morphology and swimming ability, and indirectly by their feeding strategies, which ultimately define their position in the sediment column. Besides stressing the role played by passive transport in the water column, our experiment additionally showed that mobility and feeding strategies also need to be considered as determinant of short-scale nematode dispersal.

Morphological variations caused by fixation techniques may lead to taxonomic confusion in Laeonereis (Polychaeta: Nereididae)

The nereidid polychaete Laeonereis acuta (Treadwell, 1923) is either considered to be a valid species, or a synonym of Laeonereis culveri (Webster, 1879). The species epithet, acuta, refers to the acuminate anterior region of the body followed by a widening that is visible up to the 10th setiger. The relative width of the anterior region of the body, however, has been reported in the taxonomic literature as variable for Laeonereis Hartman, 1945, a genus known from the eastern coast of North America to Patagonia (southern South America). To test whether variations in this character are real, or whether they correspond to an artifact, we analyzed morphological changes associated with different anesthesia and fixation techniques regularly used to prepare specimens of Laeonereis from southern Brazil (formerly reported as L. acuta). Six treatments, including combinations of anesthetics and fixative agents, and a control, were evaluated in groups of 25 adult animals. A simple model II regression analysis on living specimens showed that the growth is approximately isometric. One-way ANOVA was used to compare the treatment effect on the ratio of peristome width: setiger 6 width. This ratio was smaller in non-anesthetized individuals, especially when prepared in formalin and freshwater. When anesthetized with menthol and fixed in formalin with sea water, individuals retained a shape that was closest to their in vivo shape. Consequently, our results suggest that fixation without prior anesthesia is not recommended for morphological and taxonomical studies. Since morphology and morphometrics of the anterior region are consistently influenced by preparation techniques, it is likely that inadequate fixation routines have introduced several errors in the taxonomic and ecological literature of Laeonereis.

Morphological variations caused by fixation techniques may lead to taxonomic confusion in Laeonereis (Polychaeta: Nereididae)

The nereidid polychaete Laeonereis acuta (Treadwell, 1923) is either considered to be a valid species, or a synonym of Laeonereis culveri (Webster, 1879). The species epithet, acuta, refers to the acuminate anterior region of the body followed by a widening that is visible up to the 10th setiger. The relative width of the anterior region of the body, however, has been reported in the taxonomic literature as variable for Laeonereis Hartman, 1945, a genus known from the eastern coast of North America to Patagonia (southern South America). To test whether variations in this character are real, or whether they correspond to an artifact, we analyzed morphological changes associated with different anesthesia and fixation techniques regularly used to prepare specimens of Laeonereis from southern Brazil (formerly reported as L. acuta). Six treatments, including combinations of anesthetics and fixative agents, and a control, were evaluated in groups of 25 adult animals. A simple model II regression analysis on living specimens showed that the growth is approximately isometric. One-way ANOVA was used to compare the treatment effect on the ratio of peristome width: setiger 6 width. This ratio was smaller in non-anesthetized individuals, especially when prepared in formalin and freshwater. When anesthetized with menthol and fixed in formalin with sea water, individuals retained a shape that was closest to their in vivo shape. Consequently, our results suggest that fixation without prior anesthesia is not recommended for morphological and taxonomical studies. Since morphology and morphometrics of the anterior region are consistently influenced by preparation techniques, it is likely that inadequate fixation routines have introduced several errors in the taxonomic and ecological literature of Laeonereis.

Morphological variations caused by fixation techniques may lead to taxonomic confusion in Laeonereis (Polychaeta: Nereididae)

The nereidid polychaete Laeonereis acuta (Treadwell, 1923) is either considered to be a valid species, or a synonym of Laeonereis culveri (Webster, 1879). The species epithet, acuta, refers to the acuminate anterior region of the body followed by a widening that is visible up to the 10th setiger. The relative width of the anterior region of the body, however, has been reported in the taxonomic literature as variable for Laeonereis Hartman, 1945, a genus known from the eastern coast of North America to Patagonia (southern South America). To test whether variations in this character are real, or whether they correspond to an artifact, we analyzed morphological changes associated with different anesthesia and fixation techniques regularly used to prepare specimens of Laeonereis from southern Brazil (formerly reported as L. acuta). Six treatments, including combinations of anesthetics and fixative agents, and a control, were evaluated in groups of 25 adult animals. A simple model II regression analysis on living specimens showed that the growth is approximately isometric. One-way ANOVA was used to compare the treatment effect on the ratio of peristome width: setiger 6 width. This ratio was smaller in non-anesthetized individuals, especially when prepared in formalin and freshwater. When anesthetized with menthol and fixed in formalin with sea water, individuals retained a shape that was closest to their in vivo shape. Consequently, our results suggest that fixation without prior anesthesia is not recommended for morphological and taxonomical studies. Since morphology and morphometrics of the anterior region are consistently influenced by preparation techniques, it is likely that inadequate fixation routines have introduced several errors in the taxonomic and ecological literature of Laeonereis.

Species of Terebellides (Polychaeta, Terebellidae, Trichobranchinae) from the Brazilian coast

Terebellides sepultura sp. nov. is described from the continental shelf bottoms off southern Brazil. Terebellides carmenensis Solis-Weiss, Fauchald & Blankensteyn, 1991 is newly recorded for the Brazilian coast and notes on T. anguicomus F. Müller, 1858 and T. klemani Kinberg, 1867 are provided. A key to 28 species of Terebellides is given.

Nereididae (Annelida, Polychaeta) da costa nordeste do Brasil: II. Gêneros Namalycastis, Ceratocephale, Laeonereis e Rullierinereis

Six polychaete species belonging to the genera Namalycastis Hartman, 1959, Ceratocephale Malmgren, 1867, Laeonereis Hartman, 1945, and Rullierinereis Pettibone, 1970 were recorded as part of a systematic survey of the family Nereididae in estuaries, exposed sandy beaches, shelly soft bottoms, atolls and coral reefs of the Brazilian northeastern coast. Two new species, Rullierinereis auxiliadorae, from Ceará coast and Ceratocephale rocaensis, from Atol das Rocas, are described.

Nereididae (Annelida, Polychaeta) da costa nordeste do Brasil: II. Gêneros Namalycastis, Ceratocephale, Laeonereis e Rullierinereis

Six polychaete species belonging to the genera Namalycastis Hartman, 1959, Ceratocephale Malmgren, 1867, Laeonereis Hartman, 1945, and Rullierinereis Pettibone, 1970 were recorded as part of a systematic survey of the family Nereididae in estuaries, exposed sandy beaches, shelly soft bottoms, atolls and coral reefs of the Brazilian northeastern coast. Two new species, Rullierinereis auxiliadorae, from Ceará coast and Ceratocephale rocaensis, from Atol das Rocas, are described.

Species of Terebellides (Polychaeta, Terebellidae, Trichobranchinae) from the Brazilian coast

Terebellides sepultura sp. nov. is described from the continental shelf bottoms off southern Brazil. Terebellides carmenensis Solis-Weiss, Fauchald & Blankensteyn, 1991 is newly recorded for the Brazilian coast and notes on T. anguicomus F. Müller, 1858 and T. klemani Kinberg, 1867 are provided. A key to 28 species of Terebellides is given.