Taxonomic, phylogenetic, and functional diversity of mollusk death assemblages in coral reef and seagrass sediments from two shallow gulfs in Western Cuban Archipelago.

Mollusk death assemblages are formed by shell remnants deposited in the surficial mixed layer of the seabed. Diversity patterns in tropical marine habitats still are understudied; therefore, we aimed to investigate the taxonomic, phylogenetic, and functional diversity of mollusk death assemblages at regional and local scales in coral reef sands and seagrass meadows. We collected sediment samples at 11 sites within two shallow gulfs in the Northwestern Caribbean Sea and Southeastern Gulf of Mexico. All the shells were counted and identified to species level and classified into biological traits. We identified 7113 individuals belonging to 393 species (290 gastropods, 94 bivalves, and nine scaphopods). Diversity and assemblage structure showed many similarities between gulfs given their geological and biogeographical commonalities. Reef sands had higher richness than seagrasses likely because of a more favorable balance productivity-disturbance. Reef sands were dominated by epifaunal herbivores likely feeding on microphytobenthos and bysally attached bivalves adapted to intense hydrodynamic regime. In seagrass meadows, suspension feeders dominated in exposed sites and chemosynthetic infaunal bivalves dominated where oxygen replenishment was limited. Time averaging of death assemblages was likely in the order of 100 years, with stronger effects in reef sands compared to seagrass meadows. Our research provides evidence of the high taxonomic, phylogenetic, and functional diversity of mollusk death assemblages in tropical coastal sediments as result of the influence of scale-related processes and habitat type. Our study highlights the convenience of including phylogenetic and functional traits, as well as dead shells, for a more complete assessment of mollusk biodiversity.

Evaluation of remodeling and geometry on the biomechanical properties of nacreous bivalve shells.

Mollusks have developed a broad diversity of shelled structures to protect against challenges imposed by biological interactions(e.g., predation) and constraints (e.g., [Formula: see text]-induced ocean acidification and wave-forces). Although the study of shell biomechanical properties with nacreous microstructure has provided understanding about the role of shell integrity and functionality on mollusk performance and survival, there are no studies, to our knowledge, that delve into the variability of these properties during the mollusk ontogeny, between both shells of bivalves or across the shell length. In this study, using as a model the intertidal mussel Perumytilus purpuratus to obtain, for the first time, the mechanical properties of its shells with nacreous microstructure; we perform uniaxial compression tests oriented in three orthogonal axes corresponding to the orthotropic directions of the shell material behavior (thickness, longitudinal, and transversal). Thus, we evaluated whether the shell material's stress and strain strength and elastic modulus showed differences in mechanical behavior in mussels of different sizes, between valves, and across the shell length. Our results showed that the biomechanical properties of the material building the P. purpuratus shells are symmetrical in both valves and homogeneous across the shell length. However, uniaxial compression tests performed across the shell thickness showed that biomechanical performance depends on the shell size (aging); and that mechanical properties such as the elastic modulus, maximum stress, and strain become degraded during ontogeny. SEM observations evidenced that compression induced a tortuous fracture with a delamination effect on the aragonite mineralogical structure of the shell. Findings suggest that P. purpuratus may become vulnerable to durophagous predators and wave forces in older stages, with implications in mussel beds ecology and biodiversity of intertidal habitats.

Osmoionic homeostasis in bivalve mollusks from different osmotic niches: Physiological patterns and evolutionary perspectives.

Physiological knowledge gained from questions focused on the challenges faced and strategies recruited by organisms in their habitats assumes fundamental importance about understanding the ability to survive when subjected to unfavorable situations. In the aquatic environment, salinity is particularly recognized as one of the main abiotic factors that affects the physiology of organisms. Although the physiological patterns and challenges imposed by each occupied environment are distinct, they tend to converge to osmotic oscillations. From a comparative perspective, we aimed to characterize the osmoregulatory patterns of the bivalve mollusks Corbicula largillierti (purple Asian cockle), Erodona mactroides (lagoon cockle), and Amarilladesma mactroides (white clam) - inhabitants of different osmotic niches - when submitted to hypo- and/or hyperosmotic salinity variations. We determined the hemolymph osmotic and ionic concentrations, tissue hydration, and the intracellular isosmotic regulation (IIR) from the use of osmolytes (organic and inorganic) after exposure to species-specific salinity intervals. Additionally, we incorporated phylogenetic perspectives to infer and even broaden the understanding about the patterns that comprise the osmoionic physiology of Bivalvia representatives. According to the variables analyzed in the hemolymph, the three species presented a pattern of osmoconformation. Furthermore, both ionic regulation and conformation patterns were observed in freshwater, estuarine, and marine species. The patterns verified experimentally show greater use of inorganic osmolytes compared to the participation of organic molecules, which varied according to the osmotic niche occupied in the IIR for the mantle, adductor muscle, and gills. This finding widens the classic vision about the preferential use of certain osmolytes by animals from distinct niches. Our phylogenetic perspective also indicates that environmental salinity drives physiological trait variations, including hemolymph osmolality and the ion composition of the extracellular fluid (sodium, chloride, magnesium, and calcium). We also highlight the important role played by the shared ancestry, which influences the interspecific variability of the hemolymph K+ in selected representatives of Bivalvia.

Changes in abundance and composition of a Caribbean coral reef zooplankton community after 25 years / Cambios en abundancia y composición de una comunidad de zooplancton arrecifal en el Caribe 25 años después

Abstract:Coral reef zooplankton represents a key community in coral ecosystems, as they are involved in trophic and biogeochemical dynamics, and recruitment processes. Zooplankton abundance, composition and biomass were surveyed at six stations within the coral reef at Cahuita National Park, Limon, Costa Rica, in order to compare with the only previous study conducted during 1984. Samples were collected monthly (September 2010-August 2011). Seston biomass (0.49-85.87 mg/m3) and total abundance (1 145-112 422 ind./ m3) fluctuated among the months and the stations. Higher values of these two variables were found in the rainiest months (November 2010 and May 2011). A total of 38 taxa were identified, of which calanoid copepods abundance dominated year round (66 %), followed by appendicularians (12 %). Zooplankton mean abundance in this survey resulted 20 times higher (13 184 ± 4 104 ind./m3) than in 1984 (645 ± 84 ind./m3). Copepods and appendicularians were the groups that differed the most, relative to the 1984 study, resulting in 63 and 170 times more abundant overall, respectively. An increase in terrestrial runoff and nutrient input during the past 30 years could explain these differences. High abundances of zooplankton may constitute an important food source for coral reef organisms in Cahuita ecosystem. In addition, zooplankton abundances here reported for Cahuita are among the worldwide highest coral reef zooplankton abundances, and further trophic models can help elucidate its role in coral reef resilience in the Caribbean Coast of Central America.

ResumenEl grupo de zooplancton representa una comunidad clave en los arrecifes de coral. Está involucrado en dinámicas tróficas y biogeoquímicas, y en procesos de reclutamiento. La abundancia, composición y biomasa del zooplancton fueron estudiadas en seis estaciones dentro del arrecife coralino del Parque Nacional Cahuita, para compararlas con el único estudio realizado durante 1984. Las muestras se recolectaron mensualmente (Septiembre 2010-Agosto 2011). La biomasa del seston (0.49-85.87 mg/m3) y la abundancia total (1 145-112 422 ind./m3) fluctuaron entre meses y estaciones. Los valores más altos se encontraron durante los meses más lluviosos (Noviembre 2010 y Mayo 2011). Treinta y ocho taxones fueron identificados, copépodos calanoidos (66 %) y apendicularias (12 %) dominaron la abundancia durante todo el año. La abundancia promedio en este estudio fue 20 veces más alta (13 184 ± 4 104 ind./m3) que en 1984 (645 ± 84 ind./m3). Copépodos y apendicularias fueron los grupos con mayor discrepancia con respecto al estudio de 1984. Un aumento en la descarga de nutrientes de origen terrestre, podría explicar estas grandes diferencias. Abundancias tan altas de zooplancton podrían constituir una importante fuente de alimento para los organismos del arrecife en Cahuita. Las abundancias aquí reportadas colocan al arrecife de Cahuita entre los arrecifes de coral con mayor abundancia de zooplancton en el mundo y estudios futuros en redes tróficas podrían elucidar el papel de esta comunidad en procesos de resiliencia en los arrecifes del Caribe centroamericano.

Reproductive periods of Lucina pectinata (BIVALVE; LUCINIDAE) in the Paranaguá Estuarine Complex, Paraná - Brazil / Período reprodutivo de Lucina pectinata (BIVLAVE; LUCINIDAE) no Complexo Estuarino de Paranaguá, PR - Brasil

Abstract The objectives of the present study is to describe the size for exploitation and gonadal maturation of L. pectinata in Peças Island in Paraná coast. Twenty two individuals were sampled every month, from an intertidal flat of the Peças River, Municipality of Guaraqueçaba, during two periods summer/autumn and winter of the 2009. Environmental parameter data was obtained at the same time of the biological sampling: temperature, salinity and seawater transparency at the Peças River mouth. The animals height, length, width, gross weight, wet weight of meat and dry weight of meat were measured at the lab. The gonad development stages (GDS), condition index (CI) and yield index (Y) were calculated. Sex identification was conducted by direct observation of the gonads and gametes under an optic microscope. Individuals were classified as males (M), females (F) or undetermined (U). The medium height observed was of 49.62 ± 6.84 mm. Period of more expressive gonad repletion were observed in summer when water temperature was higher. Results of GDS in both periods showed a predominance of partially filled gonad stages. This may be related with the fact that L. pectinata has intense gametogenesis activity, that is, the organisms do not have a resting interval, but go back to gonad restructuring rapidly after releasing the gametes. The continuity of the reproductive cycle of the specimens found in both studied periods could demonstrate a possible continuous reproduction of the species and a size for exploitation above 40.00 mm of height.(AU)

Resumo O presente estudo tem como objetivo descrever o tamanho de exploração e a maturação gonadal de L. pectinata na Ilha das Peças no litoral do Paraná. Vinte e dois indivíduos foram amostrados mensalmente na região entre-marés no Rio das Peças, Município de Guaraqueçaba, durante 2 períodos verão/outono e inverno de 2009. Paralelamente às amostragens, foram obtidos dados dos parâmetros ambientais: temperatura, salinidade e transparência da água do mar na foz do Rio das Peças. A altura, comprimento, largura, peso bruto, peso úmido da carne e peso seco da carne dos animais foram medidos no laboratório. Foram calculados os estágios de desenvolvimento gonadal (EDG), índices de condição (IC) e de rendimento (R). A Identificação do sexo foi realizada por observação direta das gônadas e gametas sob microscópio óptico. Os indivíduos foram classificados como: machos (M), fêmeas (F) ou indeterminados (I). A altura média observada foi de 49,62 ± 6,84 mm. O período de maior repleção gonadal foi observado no verão, quando a temperatura da água foi mais elevada. Resultados dos EDG em ambos os períodos mostrou um predomínio de gônadas parcialmente cheias. Isso pode estar relacionado com o fato de que L. pectinata tem atividade gametogênese intensa, ou seja, os organismos não têm um intervalo de repouso, mas voltam a reestruturação das gônadas rapidamente após liberação dos gametas. A continuidade do ciclo reprodutivo dos espécimes encontrados em ambos os períodos estudados, pode demonstrar possível reprodução contínua da espécie e tamanho de exploração superior a 40,00 mm de altura.(AU)

Changes in abundance and composition of a Caribbean coral reef zooplankton community after 25 years.

Coral reef zooplankton represents a key community in coral ecosystems, as they are involved in trophic and biogeochemical dynamics, and recruitment processes. Zooplankton abundance, composition and biomass were surveyed at six stations within the coral reef at Cahuita National Park, Limon, Costa Rica, in order to compare with the only previous study conducted during 1984. Samples were collected monthly (September 2010-August 2011). Seston biomass (0.49-85.87 mg/m3) and total abundance (1 145-112 422 ind./m3) fluctuated among the months and the stations. Higher values of these two variables were found in the rainiest months (November 2010 and May 2011). A total of 38 taxa were identified, of which calanoid copepods abundance dominated year round (66 %), followed by appendicularians (12 %). Zooplankton mean abundance in this survey resulted 20 times higher (13 184 ± 4 104 ind./m3)than in 1984 (645 ± 84 ind./m3). Copepods and appendicularians were the groups that differed the most, relative to the 1984 study, resulting in 63 and 170 times more abundant overall, respectively. An increase in terrestrial runoff and nutrient input during the past 30 years could explain these differences. High abundances of zooplankton may constitute an important food source for coral reef organisms in Cahuita ecosystem. In addition, zooplankton abundances here reported for Cahuita are among the worldwide highest coral reef zooplankton abundances, and further trophic models can help elucidate its role in coral reef resilience in the Caribbean Coast of Central America.

An intimate link between antimicrobial peptide sequence diversity and binding to essential components of bacterial membranes.

Antimicrobial peptides and proteins (AMPs) are widespread in the living kingdom. They are key effectors of defense reactions and mediators of competitions between organisms. They are often cationic and amphiphilic, which favors their interactions with the anionic membranes of microorganisms. Several AMP families do not directly alter membrane integrity but rather target conserved components of the bacterial membranes in a process that provides them with potent and specific antimicrobial activities. Thus, lipopolysaccharides (LPS), lipoteichoic acids (LTA) and the peptidoglycan precursor Lipid II are targeted by a broad series of AMPs. Studying the functional diversity of immune effectors tells us about the essential residues involved in AMP mechanism of action. Marine invertebrates have been found to produce a remarkable diversity of AMPs. Molluscan defensins and crustacean anti-LPS factors (ALF) are diverse in terms of amino acid sequence and show contrasted phenotypes in terms of antimicrobial activity. Their activity is directed essentially against Gram-positive or Gram-negative bacteria due to their specific interactions with Lipid II or Lipid A, respectively. Through those interesting examples, we discuss here how sequence diversity generated throughout evolution informs us on residues required for essential molecular interaction at the bacterial membranes and subsequent antibacterial activity. Through the analysis of molecular variants having lost antibacterial activity or shaped novel functions, we also discuss the molecular bases of functional divergence in AMPs. This article is part of a Special Issue entitled: Antimicrobial peptides edited by Karl Lohner and Kai Hilpert.

Análise sensorial para controle de qualidade do pescado: método de índice de qualidade (miq)

No setor de alimentos e bebidas,em geral, a análise sensorial é de grande relevância por avaliar a aceitabilidade mercadológica e a qualidade do produto, sendo parte inerente ao plano de controle de qualidade de uma indústria. É por meio dos órgãos dos sentidos que se procedem tais avaliações, e, como estas são executadas por pessoas, é importante um criterioso preparo das amostras testadas e uma adequada aplicação dos testes tradicionais de análise sensorial para se evitara interferência de diversos fatores que podem remeter a conceitos pré-formados.

Análise sensorial para controle de qualidade do pescado: método de índice de qualidade (miq)

No setor de alimentos e bebidas,em geral, a análise sensorial é de grande relevância por avaliar a aceitabilidade mercadológica e a qualidade do produto, sendo parte inerente ao plano de controle de qualidade de uma indústria. É por meio dos órgãos dos sentidos que se procedem tais avaliações, e, como estas são executadas por pessoas, é importante um criterioso preparo das amostras testadas e uma adequada aplicação dos testes tradicionais de análise sensorial para se evitara interferência de diversos fatores que podem remeter a conceitos pré-formados.

Molluscs associated with the macroalgae of the genus Gracilaria (Rhodophyta): importance of algal fronds as microhabitat in a hypersaline mangrove in Northeastern Brazil / Moluscos associados a macroalgas do gênero Gracilaria (Rhodophyta): importância das frondes algais como microhabitat em um manguezal hipersalino no Nordeste do Brasil

The fronds of marine macroalgae play an important role in coastal ecosystems because the algae banks are utilized as a microhabitat by different taxa, including molluscs, one of the most abundant and diverse animals of marine ecosystems. In this study, we characterized the malacofauna associated with the macroalgae Gracilaria domingensis (Kützing) Sonder ex Dickie 1874 and Gracilaria cuneata Areschoug 1854 of a hypersaline mangrove on the northern coast of the state of Rio Grande do Norte, Northeastern Brazil. The first alga dominates in the rainy season and it is substituted by second one in the dry period. A total of 1,490 molluscs were surveyed, representing 56 species in 29 families: 1,081 were associated with G. domingensis and 409 with G. cuneata, the latter showing the greater diversity (H′=1.25). Columbellidae, Neritidae, Pyramidellidae and Cerithiidae were among the most representative families in the number of species and individuals. The micromolluscs were dominant in the algal microhabitat, constituting 74.63% of the malacofauna recorded. The columbellid Parvanachis obesa (C. B. Adams, 1845) was the dominant species followed by the neritid Neritina virginea (Linnaeus, 1758) in both algae. In spite of the annual alternated succession of the algae species, at least 15 mollusc species are common for these algae. Furthermore, juveniles of P. obesa were recorded in both seasons, indicating a continuous reproduction. Possible reasons for difference in abundance, diversity and dominance of molluscs living on these algae are discussed. Both species of substrate-algae represent an important microhabitat for refuge, feeding and the reproduction of small-sized mollusc species during rainy and dry seasons.

As frondes de macroalgas marinhas exercem um importante papel nos ecossistemas costeiros, tendo em vista que os bancos de algas são utilizados como microhabitat por diferentes táxons, incluindo os moluscos, que estão entre os mais abundantes e diversos animais dos ecossistemas marinhos. Neste estudo, caracterizou-se a malacofauna associada às macroalgas Gracilaria domingensis (Kützing) Sonder ex Dickie 1874 e Gracilaria cuneata Areschoug 1854 de um manguezal hipersalino da costa norte do estado do Rio Grande do Norte, Nordeste do Brasil. A primeira alga domina no período chuvoso e é substituída pela segunda no período seco. Foram inventariados 1.490 moluscos, representando 56 espécies em 29 famílias: 1.081 estavam associados a G. domingensis e 409 a G. cuneata, esta última apresentando maior diversidade (H′=1,25). Columbellidae, Neritidae, Pyramidellidae e Cerithiidae estiveram entre as famílias mais representativas em número de espécies e indivíduos. Os micromoluscos foram dominantes no microhabitat algal, constituindo 74,63% da malacofauna registrada. O columbelídeo Parvanachis obesa (C. B. Adams, 1845) foi a espécie dominante, seguida pelo neritídeo Neritina virginea (Linnaeus, 1758) em ambas as algas. Apesar da sucessão alternada anual das espécies de algas, pelo menos 15 espécies de moluscos são comuns a estas algas. Além disso, os jovens de P. obesa foram registrados em ambas as estações, indicando uma reprodução contínua. São discutidas possíveis razões para a diferença na abundância, diversidade e dominância dos moluscos habitantes destas algas. Ambas as espécies de alga-substrato representam um importante microhabitat para refúgio, alimentação e reprodução para pequenas espécies de moluscos durante as estações chuvosa e seca.

Molluscs associated with the macroalgae of the genus Gracilaria (Rhodophyta): importance of algal fronds as microhabitat in a hypersaline mangrove in Northeastern Brazil / Moluscos associados a macroalgas do gênero Gracilaria (Rhodophyta): importância das frondes algais como microhabitat em um manguezal hipersalino no Nordeste do Brasil

The fronds of marine macroalgae play an important role in coastal ecosystems because the algae banks are utilized as a microhabitat by different taxa, including molluscs, one of the most abundant and diverse animals of marine ecosystems. In this study, we characterized the malacofauna associated with the macroalgae Gracilaria domingensis (Kützing) Sonder ex Dickie 1874 and Gracilaria cuneata Areschoug 1854 of a hypersaline mangrove on the northern coast of the state of Rio Grande do Norte, Northeastern Brazil. The first alga dominates in the rainy season and it is substituted by second one in the dry period. A total of 1,490 molluscs were surveyed, representing 56 species in 29 families: 1,081 were associated with G. domingensis and 409 with G. cuneata, the latter showing the greater diversity (H′=1.25). Columbellidae, Neritidae, Pyramidellidae and Cerithiidae were among the most representative families in the number of species and individuals. The micromolluscs were dominant in the algal microhabitat, constituting 74.63% of the malacofauna recorded. The columbellid Parvanachis obesa (C. B. Adams, 1845) was the dominant species followed by the neritid Neritina virginea (Linnaeus, 1758) in both algae. In spite of the annual alternated succession of the algae species, at least 15 mollusc species are common for these algae. Furthermore, juveniles of P. obesa were recorded in both seasons, indicating a continuous reproduction. Possible reasons for difference in abundance, diversity and dominance of molluscs living on these algae are discussed. Both species of substrate-algae represent an important microhabitat for refuge, feeding and the reproduction of small-sized mollusc species during rainy and dry seasons.(AU)

As frondes de macroalgas marinhas exercem um importante papel nos ecossistemas costeiros, tendo em vista que os bancos de algas são utilizados como microhabitat por diferentes táxons, incluindo os moluscos, que estão entre os mais abundantes e diversos animais dos ecossistemas marinhos. Neste estudo, caracterizou-se a malacofauna associada às macroalgas Gracilaria domingensis (Kützing) Sonder ex Dickie 1874 e Gracilaria cuneata Areschoug 1854 de um manguezal hipersalino da costa norte do estado do Rio Grande do Norte, Nordeste do Brasil. A primeira alga domina no período chuvoso e é substituída pela segunda no período seco. Foram inventariados 1.490 moluscos, representando 56 espécies em 29 famílias: 1.081 estavam associados a G. domingensis e 409 a G. cuneata, esta última apresentando maior diversidade (H′=1,25). Columbellidae, Neritidae, Pyramidellidae e Cerithiidae estiveram entre as famílias mais representativas em número de espécies e indivíduos. Os micromoluscos foram dominantes no microhabitat algal, constituindo 74,63% da malacofauna registrada. O columbelídeo Parvanachis obesa (C. B. Adams, 1845) foi a espécie dominante, seguida pelo neritídeo Neritina virginea (Linnaeus, 1758) em ambas as algas. Apesar da sucessão alternada anual das espécies de algas, pelo menos 15 espécies de moluscos são comuns a estas algas. Além disso, os jovens de P. obesa foram registrados em ambas as estações, indicando uma reprodução contínua. São discutidas possíveis razões para a diferença na abundância, diversidade e dominância dos moluscos habitantes destas algas. Ambas as espécies de alga-substrato representam um importante microhabitat para refúgio, alimentação e reprodução para pequenas espécies de moluscos durante as estações chuvosa e seca.(AU)

Rebuilding biodiversity of Patagonian marine molluscs after the end-Cretaceous mass extinction.

We analysed field-collected quantitative data of benthic marine molluscs across the Cretaceous-Palaeogene boundary in Patagonia to identify patterns and processes of biodiversity reconstruction after the end-Cretaceous mass extinction. We contrast diversity dynamics from nearshore environments with those from offshore environments. In both settings, Early Palaeogene (Danian) assemblages are strongly dominated by surviving lineages, many of which changed their relative abundance from being rare before the extinction event to becoming the new dominant forms. Only a few of the species in the Danian assemblages were newly evolved. In offshore environments, however, two newly evolved Danian bivalve species attained ecological dominance by replacing two ecologically equivalent species that disappeared at the end of the Cretaceous. In both settings, the total number of Danian genera at a locality remained below the total number of late Cretaceous (Maastrichtian) genera at that locality. We suggest that biotic interactions, in particular incumbency effects, suppressed post-extinction diversity and prevented the compensation of diversity loss by originating and invading taxa. Contrary to the total number of genera at localities, diversity at the level of individual fossiliferous horizons before and after the boundary is indistinguishable in offshore environments. This indicates an evolutionary rapid rebound to pre-extinction values within less than ca 0.5 million years. In nearshore environments, by contrast, diversity of fossiliferous horizons was reduced in the Danian, and this lowered diversity lasted for the entire studied post-extinction interval. In this heterogeneous environment, low connectivity among populations may have retarded the recolonisation of nearshore habitats by survivors.

Molluscs associated with the macroalgae of the genus Gracilaria (Rhodophyta): importance of algal fronds as microhabitat in a hypersaline mangrove in Northeastern Brazil.

The fronds of marine macroalgae play an important role in coastal ecosystems because the algae banks are utilized as a microhabitat by different taxa, including molluscs, one of the most abundant and diverse animals of marine ecosystems. In this study, we characterized the malacofauna associated with the macroalgae Gracilaria domingensis (Kützing) Sonder ex Dickie 1874 and Gracilaria cuneata Areschoug 1854 of a hypersaline mangrove on the northern coast of the state of Rio Grande do Norte, Northeastern Brazil. The first alga dominates in the rainy season and it is substituted by second one in the dry period. A total of 1,490 molluscs were surveyed, representing 56 species in 29 families: 1,081 were associated with G. domingensis and 409 with G. cuneata, the latter showing the greater diversity (H'=1.25). Columbellidae, Neritidae, Pyramidellidae and Cerithiidae were among the most representative families in the number of species and individuals. The micromolluscs were dominant in the algal microhabitat, constituting 74.63% of the malacofauna recorded. The columbellid Parvanachis obesa (C. B. Adams, 1845) was the dominant species followed by the neritid Neritina virginea (Linnaeus, 1758) in both algae. In spite of the annual alternated succession of the algae species, at least 15 mollusc species are common for these algae. Furthermore, juveniles of P. obesa were recorded in both seasons, indicating a continuous reproduction. Possible reasons for difference in abundance, diversity and dominance of molluscs living on these algae are discussed. Both species of substrate-algae represent an important microhabitat for refuge, feeding and the reproduction of small-sized mollusc species during rainy and dry seasons.

Phylogenetic patterns and phenotypic plasticity of molluscan sexual systems.

Molluscs show a wide diversity of sexual systems and strategies. There are both gastropod and bivalve families that are each primarily dioecious, simultaneous hermaphrodites, or sequential hermaphrodites, and other families in which almost every sexual strategy occurs. The multiple evolutionary transitions of sexual systems within molluscs would allow comparative analyses of the associated ecological factors, but data on all but a few groups are too sparse to draw many solid conclusions. The phylogenetic distribution of sexual systems in the Mollusca shows that gastropods and bivalves demonstrate different patterns, possibly associated with the presence/absence of copulation. The distribution of change of sex suggests that, in gastropods, sequential hermaphrodites do not evolve from simultaneous hermaphrodites, and that sex reversal (flip-flopping) occurs in free-spawners but not in copulators. Three well-studied protandrous gastropod groups (calyptraeids, coralliophilids, and patellogastropods) show similar responses to environmental conditions and associations with conspecifics. They all have the following attributes: (1) they are sedentary, (2) they live in groups, patches, or aggregates, and (3) size at sex change varies among sites and among aggregates. In addition the available experimental evidence suggests that (4) the presence of females or large individuals represses growth and sex change of males, and (5) behavior seems to mediate the repressive influence of large females. Available data from other species tend to support these patterns. Finally, the repression of growth of males by females in protandry likely facilitates the evolution of dwarf males.

Does the trematode Centrocestus formosanus affect the locomotory activity of the mollusc Melanoides tuberculatus?

BACKGROUND: Melanoides tuberculatus (Müller, 1774) (Thiaridae), an introduced gastropod mollusc with a wide geographical distribution in the Neotropics, is the intermediate host of the trematode Centrocestus formosanus (Nishigori, 1924) (Heterophyidae). This parasite is considered to be pathogenic to humans. The aim of the present work was to evaluate the locomotory activity of uninfected M. tuberculatus compared with those naturally infected with C. formosanus. FINDINGS: The locomotory activity of each mollusc was recorded using an image analysis biomonitoring system, Videomex-V, to evaluate and quantify the parameters of 'Stereotypic' and 'Resting time'. The Generalized Estimating Equation analysis of locomotory activity of M. tuberculatus infected with C. formosanus revealed significant differences compared with uninfected molluscs for the parameters 'Stereotypic time' and 'Resting time' with a reduction of movement. The variations in the values of the monitoring intervals recorded showed a significant difference for the infected molluscs in the case of Stereotypic time, with an irregular locomotory activity pattern, as compared to that of uninfected molluscs. The analysis of the standard length of all molluscs did not exhibit any correlation with locomotory activity, showing that C. formosanus is able to alter the locomotory activity of its snail host regardless of the standard length. CONCLUSIONS: The trematode C. formosanus affects the locomotory activity of the mollusc M. tuberculatus by reducing its movement and causing it to exhibit an irregular pattern of activity, both of which are independent of the snail's standard length.

Interspecific competition for shelters in territorial and gregarious intertidal grazers: consequences for individual behaviour.

Experiments have shown that interspecific interactions within consumer guilds can alter patterns of distribution, abundance and size of species. Plastic behavioural responses can be modulated by agonistic interactions. In many cases, consumers compete for space and shelters, and these interactions change the manner in which they exploit food. This study investigates the consequences of competition in the spatial and temporal organization of behaviour of intertidal grazers, which share algal resources and the use of rock crevices while resting, but exhibit different body sizes, spatial behaviour and foraging modes. We evaluate interaction strength between small gregarious Siphonaria lessoni and the larger territorial keyhole limpet Fissurella crassa and between S. lessoni and the medium-size gregarious chiton Chiton granosus. Using field manipulations and artificial arenas in the laboratory, we tested whether the use of crevices, micro-spatial distribution and activity are modified by the density of conspecifics and the presence of heterospecifics. Our results show that small-scale spatial segregation observed in the field between S. lessoni and C. granosus result from species-specific differences in habitat use. In turn, we found evidence that spatial segregation between F. crassa and S. lessoni results from highly asymmetric interference competition in the use of shelters. The presence of F. crassa reduced the use of crevices and growth rates of S. lessoni. Effects on growth rates are assumed to result from exposure to harsh environmental conditions rather than food limitation. Thus, neither gregarious behaviour nor differences in activity were sufficient to prevent competition with the larger grazer. Our study illustrates the importance of competition for shelters, which results in behavioural changes of the smaller-sized species, and how these plastic responses can translate into differences in growth rates. Use of shelters can thus be modulated by environmental conditions in a species-specific as well as an interactive manner within consumers' guilds.

Disentangling diversity patterns in sandy beaches along environmental gradients.

Species richness in sandy beaches is strongly affected by concurrent variations in morphodynamics and salinity. However, as in other ecosystems, different groups of species may exhibit contrasting patterns in response to these environmental variables, which would be obscured if only aggregate richness is considered. Deconstructing biodiversity, i.e. considering richness patterns separately for different groups of species according to their taxonomic affiliation, dispersal mode or mobility, could provide a more complete understanding about factors that drive species richness patterns. This study analyzed macroscale variations in species richness at 16 Uruguayan sandy beaches with different morphodynamics, distributed along the estuarine gradient generated by the Rio de la Plata over a 2 year period. Species richness estimates were deconstructed to discriminate among taxonomic groups, supralittoral and intertidal forms, and groups with different feeding habits and development modes. Species richness was lowest at intermediate salinities, increasing towards oceanic and inner estuarine conditions, mainly following the patterns shown for intertidal forms. Moreover, there was a differential tolerance to salinity changes according to the habitat occupied and development mode, which determines the degree of sensitivity of faunal groups to osmotic stress. Generalized (additive and linear) mixed models showed a clear increase of species richness towards dissipative beaches. All taxonomic categories exhibited the same trend, even though responses to grain size and beach slope were less marked for crustaceans and insects than for molluscs or polychaetes. However, supralittoral crustaceans exhibited the opposite trend. Feeding groups decreased from dissipative to reflective systems, deposit feeders being virtually absent in the latter. This deconstructive approach highlights the relevance of life history strategies in structuring communities, highlighting the relative importance that salinity and morphodynamic gradients have on macroscale diversity patterns in sandy beaches.

Spatial distribution of epibenthic molluscs on a sandstone reef in the Northeast of Brazil.

The present study investigated the distribution and abundance of epibenthic molluscs and their feeding habits associated to substrate features (coverage and rugosity) in a sandstone reef system in the Northeast of Brazil. Rugosity, low coral cover and high coverage of zoanthids and fleshy alga were the variables that influenced a low richness and high abundance of a few molluscan species in the reef habitat. The most abundant species were generalist carnivores, probably associated to a lesser offer and variability of resources in this type of reef system, when compared to the coral reefs. The results found in this study could reflect a normal characteristic of the molluscan community distribution in sandstone reefs, with low coral cover, or could indicate a degradation state of this habitat if it is compared to coral reefs, once that the significantly high coverage of fleshy alga has been recognized as a negative indicator of reef ecosystems health.

Spatial distribution of epibenthic molluscs on a sandstone reef in the Northeast of Brazil / Distribuição espacial de moluscos epibentônicos em um recife arenítico no Nordeste do Brasil

The present study investigated the distribution and abundance of epibenthic molluscs and their feeding habits associated to substrate features (coverage and rugosity) in a sandstone reef system in the Northeast of Brazil. Rugosity, low coral cover and high coverage of zoanthids and fleshy alga were the variables that influenced a low richness and high abundance of a few molluscan species in the reef habitat. The most abundant species were generalist carnivores, probably associated to a lesser offer and variability of resources in this type of reef system, when compared to the coral reefs. The results found in this study could reflect a normal characteristic of the molluscan community distribution in sandstone reefs, with low coral cover, or could indicate a degradation state of this habitat if it is compared to coral reefs, once that the significantly high coverage of fleshy alga has been recognized as a negative indicator of reef ecosystems health.

O presente estudo investigou a distribuição, a abundância e os hábitos alimentares de moluscos epibentônicos associados à cobertura e à rugosidade do substrato, em um sistema recifal arenítico no Nordeste do Brasil. A rugosidade, a baixa cobertura de corais e a alta cobertura de zoantídeos e algas frondosas foram as variáveis que influenciaram na baixa riqueza e na alta abundância de poucas espécies de moluscos no habitat recifal. As espécies mais abundantes foram classificadas em carnívoras generalistas, provavelmente associadas à baixa oferta e variabilidade de recursos nesse tipo de sistema recifal, quando comparado a recifes coralíneos. Os resultados encontrados neste estudo podem estar refletindo características normais para a distribuição dos moluscos em recifes areníticos, com baixa cobertura de coral, ou podem estar indicando um estado de degradação desse habitat, quando comparado aos recifes de corais, uma vez que a cobertura significativa de algas frondosas vem sendo reconhecida como um indicador negativo quanto à saúde dos ecossistemas recifais.

The invasion of five alien species in the Delta do Parnaíba Environmental Protection Area, Northeastern Brazil

Marine biological invasions have been regarded as one of the major causes of native biodiversity loss, with shipping and aquaculture being the leading contributors for the introductions of alien species in aquatic ecosystems. In the present study, five aquatic alien species (one mollusk, three crustaceans and one fish species) were detected during dives, shore searches and from the fisheries on the coast of the Delta do Parnaíba Environmental Protection Area, in the States of Piauí and Maranhão, Northeastern Brazil. The species were the bicolor purse-oyster Isognomon bicolor, the whiteleg shrimp Litopenaeus vannamei, the giant river prawn Macrobrachium rosenbergii, the Indo-Pacific swimming crab Charybdis hellerii and, the muzzled blenny Omobranchus punctatus. Ballast water (I. bicolor, C. hellerii, and O. punctatus) and aquaculture activities (L. vannamei and M. rosenbergii) in adjacent areas are the most likely vectors of introduction. All exotic species found have potential impact risks to the environment because they are able to compete against native species for resources (food and habitat). Isognomon bicolor share the same habitat and food items with the native bivalve species of mussels and barnacles. Litopenaeus vannamei share the same habitat and food items with the native penaeids such as the pinkspot shrimp Farfantepenaeus brasiliensis, the Southern brown shrimp Farfantepenaeus subtilis, and the Southern white shrimp Litopenaeus schmitti, and in the past few years L. vannamei was responsible for a viral epidemics in the cultivation tanks that could be transmitted to native penaeid shrimps. Charybdis hellerii is also able to cause impacts on the local fisheries as the species can decrease the populations of native portunid crabs which are commercialized in the studied region. Macrobrachium rosenbergii may be sharing natural resources with the Amazon River prawn Macrobrachium amazonicum. Omobranchus punctatus shares habit with the native redlip blenny Ophioblennius atlanticus and other fishes, such as the frillfin goby Bathigobius soporator. Some immediate remedial measures to prevent further introductions from ballast water and shrimp farm ponds should be: (i) to prevent the release of ballast water by ship/vessels in the region; (ii) to reroute all effluent waters from shrimp rearing facilities through an underground or above-ground dry well; (iii) to install adequate sand and gravel filter which will allow passage of water but not livestock; (iv) outdoor shrimp pounds located on floodable land should be diked, and; (v) to promote environmental awareness of those directly involved with ballast water (crews of ship/vessels) and shrimp farms in the region. Rev. Biol. Trop. 58 (3): 909-923. Epub 2010 September 01.

En el Área de Protección Ambiental del Delta Del Río Parnaíba, noreste de Brasil fueron detectadas cinco especies acuáticas invasoras (un molusco, tres crustáceos y un pez): la ostra de dos colores Isognomon bicolor, el camarón patiblanco Litopenaeus vannamei, el camarón gigante de río Macrobrachium rosenbergii, el cangrejo nadador del Indo-Pacifico Charybdis hellerii y el blenio hocicudo Omobranchus punctatus. El agua de lastre (I. bicolor, C. hellerii, y O. punctatus) y la acuicultura (L. vannamei y M. rosenbergii) en áreas adyacentes son los vectores de introducción más probables. Todas las especies exóticas encontradas son potencialmente riesgosas para el ambiente ya que son aptas para competir con las nativas por recursos como alimento y hábitat. Charybdis hellerii también podría causar impacto en el recurso pesquero local, al reducir las poblaciones de cangrejos portúnidos nativos, comercializados en el área de estudio.