Temporal dynamics of deep inflalittoral macrobenthic fauna inside a subtropical estuarine environment

Seasonal and inter-annual patterns of hydrological variation determine different salinity regimes inside the Patos Lagoon estuarine region, southern Brazil. Throughout two environmentally distinct years (2000 and 2006), macrobenthic samples were taken seasonally from a 14 m deep main channel region, at nine monitoring sites, using a van Veen grab (0.078 m2). In order to keep the Patos Lagoon main access channel at constant navigable depths, the Rio Grande Harbour Superintendence periodically executes maintenance dredging operations on this infralittoral area, but our multivariate analyses evidenced no significant difference between dredged and non-dredged sites regardless the year. Among the abiotic parameters analyzed here(temperature, percentage of fine sediments and salinity), the later was evidenced to be highly correlated to the biological data. Reductions in density and/or changes in the species composition could both be attributed to a natural macrobenthic response related to environmental variations. Along the year 2000 high salinity values decreased constantly through seasons to almost limnetic condition in spring, reducing diversity and abundance of marine species and densities of the dominant gastropod species Heleobia australis. On the other hand, salinity values along the year 2006 revealed the maintenance of brackish waters throughout seasons, favoring the input and survival of marine species from coastal adjacent areas inside the estuary, raising its macrobenthic diversity mainly by mollusks and polychaete worms

The tricky task of fisher-gardener research in conservation paleobiology

The study of sambaquis (ancient shell mounds) in conservation paleobiology is a complicated subject, especially when comparing body sizes of current and past mollusk valves to observe possible changes. There is a lack of information regarding how ancient fisher-gardeners collected these shellfish. Another obstacle is finding the hypothesis tests and data that can be used to compare current and past body sizes. To this end, we use the t-test (tt), Mann-Whitney (mw), and Bootstrap (bt) analyses to determine data scenarios for yellow clam (Amarilladesma mactroides) shells from two sambaquis units, and from two transects along the beaches of Rio Grande do Sul in southern Brazil. The study finds that the average body size of an Amarilladesma mactroides adult specimen is greater in sambaquis than the current valves across all tests (tt, p = 0.0005; mw, p = 0.006; bt, p = 0.04), even after reducing the sample number. However, when the comparison is only between valves that are larger than average, this does not hold true for two of the statistics (tt, p = 0.24; mw, p = 0.04; bt, p = 0.25). By refining the comparison for recent valves from different levels in the swash zone (upper, middle, and lower levels) with the past valves, we find that body sizes only differ at the middle level of the swash zone (tt, p = 0.004; mw, p = 0.004; bt, p = 0.005), where smaller adults, recruits, and juveniles live. This result could indicate that fisher-gardeners collected large organisms at distinct levels depending on the season (i.e., adults are collected in the upper level during summer and in the lower level during winter)

A estrutura do macrozoobentos em uma praia arenosa no extremo sul do Brasil: a influência da morfodinâmica, de feições geomorfológicas e de eventos meteorológicos

Tese (Doutorado)A influência da morfodinâmica, de feições geomorfológicas e eventos meteorológicos na estrutura da comunidade macrozoobentônica foi investigada ao longo de uma praia arenosa exposta no extremo sul do Brasil (~32ºS). As principais relações tróficas e os fluxos de matéria nos diferentes compartimentos biológicos foram revisados, sendo comparada a estrutura das comunidades macrozoobentônicas em regiões de praia com distintos estados morfodinâmicos. Expedições de monitoramento/amostragem foram sazonalmente realizadas - durante quatro semanas consecutivas - na primavera 2010 e no verão, outono e inverno 2011. Amostragens biológicas foram executadas em áreas de cúspides praiais, sangradouros e áreas de embancamentos sempre que detectados, sendo posteriormente comparados com áreas controle. Variáveis ambientais foram registradas com o objetivo de caracterizar o ambiente praial, as feições geomorfológicas (cúspides e sangradouros) e as áreas de embancamento. Densas concentrações da diatomácea Asterionellopsis glacialis sustentam consumidores até o nível terciário, principalmente Amarilladesma mactroides, Donax hanleyanus e Emerita brasiliensis. Caranguejos, gastrópodes, poliquetas carnívoros, aves e peixes podem estar presentes e ocupam níveis tróficos superiores, dependendo da morfodinâmica praial. A presença de sistemas cúspide/baía foi sazonalmente associada às estações quentes, com predomínio de estados morfodinâmicos intermediários. Bivalves A. mactroides e D. hanleyanus ocorreram em densas concentrações associadas às baías enquanto elevadas densidades de E. brasiliensis e Excirolana armata foram associadas às cúspides. A presença de sangradouros foi sazonalmente influenciada pelas taxas de precipitação, mais elevadas nas estações frias. Uma maior concentração de sangradouros foi observada em áreas urbanizadas e de lagoas costeiras/banhados. A precipitação influenciou a vazão dos sangradouros e a salinidade na costa, determinando alterações significativas na composição e estrutura do macrozoobentos. Elevadas densidades de A. mactroides, D. hanleyanus e Spio gaucha foram registradas nas áreas afastadas dos sangradouros (i.e., áreas controle), um padrão também observado para a riqueza de espécies. Situações específicas favoreceram a ocorrência de S. gaucha, E. brasiliensis e E. armata próximo aos sangradouros. Ciclones extratropicais foram mais frequentes durante a primavera e o inverno, quando sistemas frontais foram frequentes. Ventos fortes de SW-E influenciaram no empilhamento de água na costa, independentemente da estação. Quinze táxons macrozoobentônicos foram registrados em dez áreas de embancamentos, principalmente registrados nas estações quentes. A ação de ventos fortes (SW) em períodos de recrutamento aumenta significativamente o risco de embancamentos. Elevadas perdas em densidade e alterações na composição da comunidade podem afetar o equilíbrio ecológico das associações de macroinvertebrados bentônicos, especialmente na relação entre A. mactroides e seus principais competidores, D. hanleyanus e E. brasiliensis. Podemos concluir que as comunidades macrozoobentônicas que habitam o extremo sul do Brasil são controladas por fatores físicos e interações ecológicas. Os estados morfodinâmicos são capazes de influenciar as relações tróficas e a distribuição horizontal da macrofauna pela presença de cúspides praiais. Fenômenos estocásticos (ENSO) e os cenários de mudança climática global também podem influenciar negativamente o macrozoobentos, tanto em função das alterações na distribuição espaço-temporal de sangradouros (influenciando sua vazão e a salinidade na costa), como pela maior frequência e intensidade de embancamentos.The influence of beach morphodynamics, geomorphological features and extreme weather events upon the structure of the macrobenthic community was investigated along the southernmost Brazilian sandy shores (~32ºS). The main trophic relationships and flows of matter through different biological compartments were reviewed and the structure of macrobenthic communities along beaches with distinct morphodynamic states was compared. Monitoring/sampling expeditions were seasonally executed – along four consecutive weeks – in spring 2010, summer, autumn and winter 2011. Biological samplings were performed along beach cusps, washouts and stranding areas whenever detected, being therefore compared with control areas. Environmental variables were registered in order to characterize the beach environment, the geomorphological features (beach cusps and washouts) and the stranding areas. Dense concentrations of the diatom Asterionellopsis glacialis sustain consumers up to the tertiary level, mainly Amarilladesma mactroides, Donax hanleyanus and Emerita brasiliensis. Crabs, whelks, carnivorous polychaetes, seabirds and fishes may be present and occupy superior trophic levels based on the beach morphodynamics. The presence of cusp/bay systems was seasonally associated with the warm seasons along intermediate morphodynamic states. Clams A. mactroides and D. hanleyanus were found in dense concentrations along cusp bays while high densities of E. brasiliensis and Excirolana armata were associated with cusp horns. The presence of washouts was seasonally influenced by the precipitation rates, which were higher during the cold seasons. A higher concentration of washouts was related to urbanized areas and to coastal lagoons/wetlands. Rainfall rates influenced the washout flows and the salinity values along the coast, causing significant changes in both macrobenthic composition and structure. High densities of A. mactroides, D. hanleyanus and S. gaucha were found in those areas far from the washouts (i.e., the control areas), a pattern also observed for the species richness. Particular circumstances further favored the occurrence of S. gaucha, E. brasiliensis and E. armata near the washouts. Extratropical cyclones were commonly registered during the spring and winter, when frontal systems were also frequent. Strong winds from SW-E influenced a piling-up of water towards the shore regardless of the season. Fifteen macrobenthic taxa were recorded in ten different stranding areas mainly related to the warm seasons. The action of strong SW winds during recruitment periods significantly increases the risk of strandings. High density 4 losses and changes in the community composition affect the ecological equilibrium of the macrobenthic assemblages, especially the relationship between A. mactroides and its main competitors D. hanleyanus and E. brasiliensis. We conclude that macrobenthic communities inhabiting the southernmost Brazilian shores are controlled by physical factors and ecological interactions. Beach morphodynamics influence those trophic relationships and also the horizontal distribution of the macrobenthic fauna by the presence of beach cusps. Stochastic phenomena (ENSO) and the global climate change scenarios may negatively affect the macrobenthic fauna due to alterations in the spatial- temporal distribution of washouts (influencing its flow and salinity along the coast), and due to the increasing frequency and intensity of stranding events

Temporal dynamics of deep infralittoral macrobenthic fauna in a subtropical estuarine environment

Seasonal and inter-annual patterns of hydrological variation determine different salinity regimes inside the Patos Lagoon estuarine region, southern Brazil. Throughout two environmentally distinct years (2000 and 2006), macrobenthic samples were taken seasonally from a 14 m deep main channel region, at nine monitoring sites, using a van Veen grab (0.078 m2). In order to keep the Patos Lagoon main access channel at constant navigable depths, the Rio Grande Harbour Superintendence periodically executes maintenance dredging operations on this infralittoral area, but our multivariate analyses evidenced no significant difference between dredged and non-dredged sites regardless the year. Among the abiotic parameters analyzed here (temperature, percentage of fine sediments and salinity), the later was evidenced to be highly correlated to the biological data. Reductions in density and/or changes in the species composition could both be attributed to a natural macrobenthic response related to environmental variations. Along the year 2000 high salinity values decreased constantly through seasons to almost limnetic condition in spring, reducing diversity and abundance of marine species and densities of the dominant gastropod species Heleobia australis. On the other hand, salinity values along the year 2006 revealed the maintenance of brackish waters throughout seasons, favoring the input and survival of marine species from coastal adjacent areas inside the estuary, raising its macrobenthic diversity mainly by mollusks and polychaete worms

Temporal dynamics of deep inflalittoral macrobenthic fauna inside a subtropical estuarine environment

Seasonal and inter-annual patterns of hydrological variation determine different salinity regimes inside the Patos Lagoon estuarine region, southern Brazil. Throughout two environmentally distinct years (2000 and 2006), macrobenthic samples were taken seasonally from a 14 m deep main channel region, at nine monitoring sites, using a van Veen grab (0.078 m2). In order to keep the Patos Lagoon main access channel at constant navigable depths, the Rio Grande Harbour Superintendence periodically executes maintenance dredging operations on this infralittoral area, but our multivariate analyses evidenced no significant difference between dredged and non-dredged sites regardless the year. Among the abiotic parameters analyzed here(temperature, percentage of fine sediments and salinity), the later was evidenced to be highly correlated to the biological data. Reductions in density and/or changes in the species composition could both be attributed to a natural macrobenthic response related to environmental variations. Along the year 2000 high salinity values decreased constantly through seasons to almost limnetic condition in spring, reducing diversity and abundance of marine species and densities of the dominant gastropod species Heleobia australis. On the other hand, salinity values along the year 2006 revealed the maintenance of brackish waters throughout seasons, favoring the input and survival of marine species from coastal adjacent areas inside the estuary, raising its macrobenthic diversity mainly by mollusks and polychaete worms

Temporal variability of the bivalve Erodona mactroides BOSC, 1802 during and after the El Ni\uf1o phenomenon (2002/2003) in a subtropical lagoon, southern Brazil

The aim of this work was to study the relationships between temporal variability of Erodona mactroides and abiotic parameters of the water column and the substrate in a shallow embayment of the Patos Lagoon estuarine region in southern Brazil; Methods: Samples were taken with a PVC corer (10 cm diameter) buried 10 cm into the sediment between October 2002 and December 2004. Each month 18 biologic samples were taken, six substrate samples were analyzed for sediment grain size and organic matter content and sediment deposition rates were determined by 12 sediment traps every two weeks. Salinity, water temperature, water level and estuarine freshwater discharge were measured daily. Abiotic parameters and bivalve densities were tested among months with registered mortality events by ANOVA (One-way, p = 0.05), being the E. mactroides seasonal variability tested by Kruskal-Wallis (p = 0.05). Regression analyses among abiotic parameters and Spearman’s “R” correlation analyses between biological and environmental data were both performed; Results: Two periods were identified with distinct features: one at the beginning of the study when observed limnetic conditions in the estuarine region were caused by the ENSO - El Niño 2002/2003 phenomenon when an absence of E. mactroides was registered as well as a higher percentages of fine sediments and lower percentages of organic matter. The second period was characterized by a decreasing influence of the El Niño and predominance of mixohaline conditions, recruitments and increasing densities of E. mactroides with a successive decrease of mean densities due to three mortality events, lower percentages of fine sediments and higher percentages of organic matter; Conclusions: The present study provides evidences that the occurrence of E. mactroides in the southern estuarine region depends on the water flow regime from the drainage basin, which characterizes species recruitment as temporally unpredictable and affects its persistence through time due to adverse conditions that influence species development like events of fine sediment deposition.O objetivo do presente trabalho foi avaliar as relações entre a variabilidade temporal de Erodona mactroides e os parâmetros abióticos da coluna d’água e do substrato em uma enseada rasa da região estuarina da Lagoa dos Patos, sul do Brasil; Métodos: As amostras foram coletadas com um extrator de PVC (10 cm de diâmetro), enterrado a 10 cm no interior do sedimento, entre Outubro/02 e Dezembro/04. Em cada mês foram coletadas 18 amostras biológicas, seis réplicas de sedimento para análises granulométricas e teor de matéria orgânica, além de 12 réplicas quinzenais de experimentos de deposição de sedimentos. A salinidade, temperatura da coluna d’água, profundidade e vazão do estuário foram medidas diariamente. Os parâmetros abióticos e densidades do bivalve entre os meses em que foram observados eventos de mortalidade foram testados através de ANOVA (Uma via, p = 0,05), e a variabilidade sazonal de E. mactroides foi testada através da análise de Kruskal-Wallis (p = 0,05). Foi aplicada análise de Regressão entre os dados abióticos e Correlação de Spearman “R” entre os dados biológicos de densidade e parâmetros ambientais;Resultados: Foram identificados dois períodos com características distintas: no início do estudo foram registradas condições limnéticas na região estuarina devido ao fenômeno ENSO – El Niño 2002/2003, quando foi registrada a ausência de E. mactroides, maiores percentuais de sedimento finos e menores percentuais de matéria orgânica. O segundo período foi caracterizado pela diminuição da influência do El Niño e predominância de condições mixohalinas, recrutamentos e pelo aumento das densidades médias de E. mactroides com sucessivos decréscimos no número de organismos devido a três eventos de mortalidade, menores percentuais de sedimentos finos e maiores percentuais de matéria orgânica; Conclusões: O presente estudo evidencia que a ocorrência de E. mactroides na porção sul da região estuarina, que depende do regime de vazão da laguna, caracteriza os recrutamentos como temporalmente imprevisíveis, e sua persistência é afetada por condições desfavoráveis a seu desenvolvimento como eventos de deposição de sedimentos finos

The Tricky Task of Fisher-Gardener Research in Conservation Paleobiology

The study of sambaquis (ancient shell mounds) in conservation paleobiology is a complicated subject, especially when comparing body sizes of current and past mollusk valves to observe possible changes. There is a lack of information regarding how ancient fisher-gardeners collected these shellfish. Another obstacle is finding the hypothesis tests and data that can be used to compare current and past body sizes. To this end, we use the t-test (tt), Mann-Whitney (mw), and Bootstrap (bt) analyses to determine data scenarios for yellow clam (Amarilladesma mactroides) shells from two sambaquis units, and from two transects along the beaches of Rio Grande do Sul in southern Brazil. The study finds that the average body size of an Amarilladesma mactroides adult specimen is greater in sambaquis than the current valves across all tests (tt, p = 0.0005; mw, p = 0.006; bt, p = 0.04), even after reducing the sample number. However, when the comparison is only between valves that are larger than average, this does not hold true for two of the statistics (tt, p = 0.24; mw, p = 0.04; bt, p = 0.25). By refining the comparison for recent valves from different levels in the swash zone (upper, middle, and lower levels) with the past valves, we find that body sizes only differ at the middle level of the swash zone (tt, p = 0.004; mw, p = 0.004; bt, p = 0.005), where smaller adults, recruits, and juveniles live. This result could indicate that fisher-gardeners collected large organisms at distinct levels depending on the season (i.e., adults are collected in the upper level during summer and in the lower level during winter).</jats:p

Data_Sheet_1_The Tricky Task of Fisher-Gardener Research in Conservation Paleobiology.csv

The study of sambaquis (ancient shell mounds) in conservation paleobiology is a complicated subject, especially when comparing body sizes of current and past mollusk valves to observe possible changes. There is a lack of information regarding how ancient fisher-gardeners collected these shellfish. Another obstacle is finding the hypothesis tests and data that can be used to compare current and past body sizes. To this end, we use the t-test (tt), Mann-Whitney (mw), and Bootstrap (bt) analyses to determine data scenarios for yellow clam (Amarilladesma mactroides) shells from two sambaquis units, and from two transects along the beaches of Rio Grande do Sul in southern Brazil. The study finds that the average body size of an Amarilladesma mactroides adult specimen is greater in sambaquis than the current valves across all tests (tt, p = 0.0005; mw, p = 0.006; bt, p = 0.04), even after reducing the sample number. However, when the comparison is only between valves that are larger than average, this does not hold true for two of the statistics (tt, p = 0.24; mw, p = 0.04; bt, p = 0.25). By refining the comparison for recent valves from different levels in the swash zone (upper, middle, and lower levels) with the past valves, we find that body sizes only differ at the middle level of the swash zone (tt, p = 0.004; mw, p = 0.004; bt, p = 0.005), where smaller adults, recruits, and juveniles live. This result could indicate that fisher-gardeners collected large organisms at distinct levels depending on the season (i.e., adults are collected in the upper level during summer and in the lower level during winter).</p