Abstract This study aimed to characterize seasonal changes in microphytoplankton composition and abundance on Bahia continental shelf, a region with upwelling events. Semi-annual sampling was conducted during summer and winter from 2017 to 2021 at nine points. Microphytoplankton was sampled using a conical plankton net through horizontal subsurface drags, using a flowmeter coupled to the net, to measure the total volume of filtered water. Temperature and salinity were measured in situ, presenting typical values of tropical waters. In addition, dissolved inorganic nutrient concentration corroborated a tropical marine oligotrophic pattern. A total of 144 taxa were identified in the region, with the phyla Heterokontophyta and Dinoflagellata being the most representative, as is typically recorded in tropical coastal regions. The density ranged from 6.08 × 104 to 3.38 × 108 cells L-1, with higher average values in summer. Although cyanobacteria accounted for only 3.2% of species richness in the region, due to summer blooms of Trichodesmium erythraeum (2018, 2019, and 2021), it was the most abundant group throughout the study. It was observed that upwelling events do not seem to establish favorable conditions for marked seasonal changes in microphytoplankton composition and abundance. Trichodesmium erythraeum blooms are closely related to physiology and ecological capacity of this species. Except for bloom periods, the study area presented a high species richness and diversity throughout the analyzed time series.

Resumen El objetivo del presente estudio fue caracterizar los cambios estacionales en la composición y abundancia del microfitoplancton en la plataforma continental de Bahía, una región con presencia de eventos de surgencia. Se realizaron muestreos semestrales durante los veranos e inviernos de 2017 a 2021 en nueve puntos. El microfitoplancton se muestreó utilizando una red cónica de plancton en arrastres horizontales debajo de la superficie, utilizando un medidor de corriente acoplado a la red, para medir el volumen total de agua filtrada. La temperatura y la salinidad fueron medidas in situ, presentando valores típicos de aguas tropicales. Además, las concentraciones de nutrientes inorgánicos disueltos corroboraron el patrón oligotrófico marino tropical. Se identificaron un total de 144 taxones en la región, siendo los phyla Heterokontophyta y Dinoflagellata los más representativos, como se registra típicamente en las regiones costeras tropicales. La densidad varió de 6,08 × 104 a 3,38 × 108 células L-1, con valores promedio más altos en verano. Aunque las cianobacterias representaron solo el 3,2% de la riqueza de especies en la región, debido a las floraciones de verano de Trichodesmium erythraeum (2018, 2019 y 2021), fue el grupo más abundante a lo largo del estudio. Se observó que los eventos de surgencia no parecen establecer condiciones favorables para cambios estacionales marcados en la composición y abundancia del microfitoplancton. Las floraciones de Trichodesmium erythraeum están estrechamente relacionadas con la fisiología y la capacidad ecológica de esta especie. Con excepción de los períodos de floración, el área de estudio presentó patrones de alta riqueza y diversidad de especies a lo largo de la serie temporal analizada.

Abstract Bioseston is a heterogeneous assemblage of bacterioplankton, phytoplankton, zooplankton, and planktonic debris. A detailed knowledge of biosestons is essential for understanding the dynamics of trophic flows in marine ecosystems. The distributional features of seston biomass in plankton (micro- and mesoplankton) in the Southwest Atlantic Ocean (Rio de Janeiro State, Brazil) were analyzed using stratified samples gathered to a depth of 2,400 m during night time. The horizontal pattern of biomass distribution was analyzed vis-a-vis station depth during both wet and dry periods, with higher values recorded in the continental shelf than in the slope, confirming the terrestrial contribution of nutrient sources to the marine environment. This horizontal variation reinforces the occurrence of seasonal vortices in Cabo Frio and Cabo de São Tomé on the central coast of Brazil. Environmental variables reflect the hydrological signatures of the water masses along the Brazilian coast. The largest seston biomass was related to high temperatures, salinities, and low inorganic nutrient concentrations in tropical and South Atlantic central waters. The observed distribution patterns suggest that seston biomass in plankton in the region may be structured based on partitioned horizontal and vertical habitats and food resources. bacterioplankton phytoplankton zooplankton debris ecosystems micro (micro mesoplankton Rio State Brazil 2400 2 400 2,40 time visavis vis periods slope environment temperatures salinities waters resources 240 40 2,4 24 4 2,

Abstract We evaluated the seasonal phosphorus (P) status of the plankton community in the Ombla Estuary (OE) by using its specific alkaline phosphatase activity (sAPA). Microphytoplankton (MICRO) indicated a substantially higher P deficiency than nanophytoplankton (NANO) and picoplankton (PICO). We found that the prolonged increase in the temperature of the surface estuarine water supported a notable growth of the dinoflagellate Prorocentrum spp. in late spring-early summer (June). In the summer (August), we found the maximum microphytoplankton sAPA (MICRO sAPA) (307.8 nmol μg C-1 h-1) in the surface water, in which (84%) dinoflagellates predominated within MICRO with the maximum alkaline phosphatase activity (APA) in all size fractions, including free enzymes. Persistently low discharge of Ombla during summer-early autumn caused a transition from phosphorus- to potentially nitrogen-limited MICRO in the surface water in early autumn (October). Nutrient stress disappeared in winter, in which a significant amount of dissolved orthosilicate, dissolved inorganic nitrogen (DIN), and soluble reactive phosphorus (SRP) enriched the estuary via maximal river discharge and inflow of nutrient-rich coastal waters. MICRO (coccolithophorids and diatoms) had very low APA (surface water) and quantitatively undetectable APA (bottom water) in the nutrient-rich water column in January. This study shows a more significant impact of nutrient concentrations on MICRO than other size classes of the plankton community. Because of the similarity in seasonal hydrological features, we assume that the general pattern of switching from P- to N-limitation of phytoplankton growth also occurs in other highly stratified estuaries along the coastal karst of the eastern Adriatic Sea during the lowest river discharges and groundwater activities in summer-early autumn before the rainy season. This study indicates that a common highly stratified estuary on the eastern Adriatic coast can serve as a natural laboratory to explore connections between nutrient limitations and phytoplankton successions. (P OE (OE sAPA. . (sAPA) NANO (NANO PICO. PICO (PICO) spp springearly spring June. June (June) August, August , (August) 307.8 3078 307 8 (307. C1 C 1 C- h1 h h-1 84% 84 (84% (APA fractions enzymes summerearly nitrogenlimited limited October. October (October) winter orthosilicate DIN, DIN (DIN) SRP (SRP nutrientrich rich waters coccolithophorids diatoms bottom January features Nlimitation N limitation season successions (sAPA (PICO (June (August 307. 30 (307 h- (84 (October (DIN 3 (30 (8 (3 (

Resumo Os cladóceros representam um importante grupo de zooplâncton, devido ao seu destaque sazonal em termos de abundância e à sua contribuição no controlo da produção primária (fitoplâncton). Em escala global, há poucos estudos com Cladocera em ambientes hipersalinos. O presente trabalho tem como objetivo avaliar a variação espaço-temporal da assembleia de Cladocera em um gradiente de salinidades da Lagoa de Araruama. As amostras foram coletadas em meses aleatórios, durante um período de quatro anos, em 12 estações fixas na Lagoa de Araruama, utilizando uma rede de plâncton WP2 equipada com um fluxômetro. Os nossos resultados não revelam uma influência significativa da maré e da variação sazonal como fatores que afetam a assembleia de Cladocera. Cinco espécies de Cladocera foram encontradas na Lagoa de Araruama. A assembleia apresentou maior densidade absoluta estações 12 e 11, atingindo uma a média de 1.799 ± 3.103 inds-3. A média do Índice de Diversidade de Shannon foi de 0,45 ± 0,2. As espécies que se destacaram em termos de frequência e abundância foram: Penilia avirostris (frequência de ocorrência: 71%), seguida de Pseudevadne tergestina (41%). As mesmas espécies também se destacaram em termos de abundância relativa Penilia avirostris (87%) e Pseudevadne tergestina (11%). A ausência de Cladocera nas partes mais interiores da lagoa sugere que a sua entrada nestes locais é possivelmente inibida pela salinidade e gradiente de temperatura da lagoa, sendo os principais fatores que influenciam a dinâmica da assembleia de Cladocera.

Abstract Cladocera represent an important zooplankton group because of their seasonal prominence in terms of abundance and their contribution in controlling primary production (phytoplankton). On a global scale, there are few studies on Cladocera in hypersaline environments. The present work aims to evaluate the spatio-temporal variation of the Cladocera assemblage across a salinity gradient in the habitats of the Araruama Lagoon. Samples were collected in random months over a period of four years at 12 fixed stations in the Araruama Lagoon using a WP2 plankton net equipped with a flow meter. Our results do not reveal significant influence of the tide and seasonal variation as factors affecting the Cladocera assemblage. Five Cladocera species were found in the Araruama Lagoon, only in stations 11 and 12 where they reached an average of 1,799 ± 3,103 ind. m-3. The mean of the Shannon Diversity Index was 0.45 ± 0.2. The species that stood out in terms of frequency and abundance were: Penilia avirostris (frequency of occurrence: 71%), followed by Pseudevadne tergestina (41%). The same species also stood out in terms of relative abundance, Penilia avirostris (87%) and Pseudevadne tergestina (11%). The absence of Cladocera in the innermost parts of the lagoon suggests that their entrance to these locations is possibly inhibited by the salinity and temperature gradient of the lagoon, being the main factors influencing the dynamics of the Cladocera assemblages.

Resumo Objetivo O reservatório Owalla, um dos maiores e mais antigos lagos artificiais do estado de Osun, fornece água potável para muitas cidades, incluindo a capital do Estado, Osogbo. Atividades de pesca também ocorrem no lago. Apesar da importância do reservatório, as informações sobre a comunidade planctônica e a qualidade físico-química da água são escassas. Portanto, este estudo investigou a qualidade da água e a composição do plâncton do Reservatório Owalla, Estado de Osun, Nigéria, de outubro de 2012 a novembro de 2013, com o objetivo de fornecer informações das características Limnológicas do reservatório. Métodos Sete estações de amostragem (designadas Estações 1-7) foram estabelecidas como representantes das zonas e regiões do reservatório e a amostragem foi realizada trimestralmente. Nas Estações 1 e 3, foram coletadas apenas amostras de água superficial, enquanto para as demais estações, foram coletadas amostra de água na superfície, em meia profundidade e próximo ao fundo. Amostras de plâncton total e qualidade físico-química da água foram analisadas usando métodos padrões. Resultados O resultado do estudo mostrou que as concentrações médias do oxigênio dissolvido (P <0,001), a demanda bioquímica de oxigênio, a condutividade elétrica, o pH (P <0,001) e a alcalinidade foram maiores na superfície do reservatório. Com relação à variação sazonal, a alcalinidade e a demanda bioquímica de oxigênio apresentaram os maiores valores médios durante o período chuvoso. Além disso, acidez, oxigênio dissolvido e pH apresentaram valores significativamente (P <0,001) maiores durante a estação chuvosa. Cento e trinta e sete (137) taxa de fitoplâncton e 39 taxa de zooplâncton foram registradas no reservatório. O padrão horizontal de variação mostrou um aumento na abundância média da maioria dos grupos de fitoplâncton da entrada para a área da barragem, enquanto a variação vertical mostrou uma diminuição na abundância média da superfície para o fundo do reservatório. Os taxas de fitoplâncton e zooplâncton foram mais abundantes durante a estação seca do que na estação chuvosa. Conclusões O estudo concluiu que todas as variáveis físico-químicas monitoradas de qualidade da água estavam dentro da faixa de nível de referência da Organização Mundial da Saúde (OMS) para água potável. O Reservatório Owalla é qualitativamente rico em fitoplâncton e zooplâncton e o reservatório pode suportar uma comunidade aquática viável e uma produção pesqueira sustentável.

Abstract Aim Owalla Reservoir, one of the largest and oldest man-made lakes in Osun State supplies potable water to many towns in the state including the state capital, Osogbo. Active fishing activities also takes place in the lake. Inspite of the importance of the reservoir, information on the planktonic community and physico-chemical water quality are scarce. Therefore, this study investigated the water quality and plankton composition of Owalla Reservoir, Osun State, Nigeria, from October 2012 to November 2013 with a view to providing baseline information on limnology of the reservoir. Methods Seven sampling stations (designated Stations 1-7) were established as representatives of the zones and regions of the reservoir and sampling was conducted quarterly. At Stations 1 and 3, only surface water samples were collected while water samples were collected from the surface, mid-depth and close to the bottom at other stations. Samples for total plankton and physico-chemical water quality were analyzed using standard methods. Results The result of the study showed that mean dissolved oxygen (P<0.001), biochemical oxygen demand, conductivity, pH (P<0.001), and alkalinity were higher at the surface of the reservoir. As regards seasonal variation, alkalinity, biochemical oxygen demand had the higher mean values during the rainy season. Also, acidity, dissolved oxygen, and pH showed significantly (P<0.001) higher values during the rainy season. One hundred and thirty-seven (137) taxa of phytoplankton and 39 taxa of zooplankton were recorded from the reservoir. The horizontal pattern of variation showed an increase in the mean abundance of most of phytoplankton groups from inflow to the dam area while vertical variation showed a decrease in mean abundance from surface to the bottom of the reservoir. Most of the phytoplankton and zooplankton taxa were more abundant during the dry season than in the rainy season. Conclusions The study concluded that all the monitored physico-chemical water quality parameters were within the guide level range as of the World Health Organisation (WHO) for drinking water, Owalla Reservoir is qualitatively rich in both phytoplankton and zooplankton and the reservoir can support a viable aquatic community and sustainable fishery production.

Abstract Patterns of beta diversity of plankton communities in rivers have been mainly determined by hydrological factors that alter the dispersion and composition of species and traits. Rotifers in the Guamá River (eastern Amazonian River) were sampled (monthly between October 2017 and June 2019) to analyze the temporal variation of taxonomic and functional beta diversity and its partitions (turnover and nestedness) as well as the effects of temporal, environmental, and seasonal dissimilarities. Taxonomic turnover and functional nestedness over time were observed as well as functional homogenization, which was arguably due to the hypereutrophic condition of the river. There were no seasonal differences in taxonomic and functional beta diversity probably due the low environmental dissimilarity. This study demonstrated that this Guamá River stretch presented low environmental dissimilarity and hypereutrophic waters, which benefited the establishment of a community of species with high taxonomic turnover over time, but with low functional dissimilarity and loss of some functions related to the functional traits evaluated in the ecosystem. It is important to point out that temporal studies should evaluate both taxonomic and functional aspects of communities, mainly because the effect of environmental changes may be more noticeable at the functional level of communities.

Resumen Introducción: La identificación de hábitats críticos para especies vulnerables de elasmobranquios es crucial para tomar medidas de conservación efectivas. La manta diablo o raya de Munk (Mobula munkiana) es endémica del Pacífico Oriental y se sabe poco sobre su biología, ecología y uso de hábitat. Como filtradores, se asume que se concentran en regiones de afloramiento con alta productividad; sus poblaciones se consideran en disminución y requieren información urgente para fundamentar medidas de conservación. Objetivo: El estudio se realizó para obtener información sobre un comportamiento de alimentación observado en juveniles de M. munkiana, con el fin de proporcionar más información sobre las primeras etapas de vida de esta especie considerada vulnerable a la extinción. Métodos: De junio a setiembre de 2017 y en agosto de 2018, se observó el comportamiento de alimentación de los juveniles de M. munkiana en dos bahías poco profundas de Punta Descartes, en el Pacífico norte de Costa Rica. Los individuos fueron capturados utilizando un método no letal para obtener datos sobre el tamaño, peso y sexo. Se tomaron 100 muestras de plancton en las bahías para inferir la composición de la dieta. Resultados: Las rayas mostraron un comportamiento de natación repetitivo paralelo a la playa, alimentándose exclusivamente en la zona de rompimiento de las olas en marea baja, a menos de 50 cm de profundidad. Un total de 12 rayas M. munkiana (11 vivas y una encontrada muerta) indicaron una agregación de juveniles para alimentarse. Los anchos de disco variaron de 490 a 610 mm y el peso entre 1400 a 2300 g. La proporción sexual (machos: hembras) fue de 3:1. En la zona donde rompían las olas se encontró principalmente el orden Mysidaceae. Conclusiones: El comportamiento específico y la ocurrencia estacional de M. munkiana en la zona de estudio parecen estar impulsados por la abundancia de presas. Se necesita más investigación para concluir la presencia de adultos reproductivos a mayor profundidad y sobre el uso de hábitat en los alrededores de Punta Descartes durante todo el año. Esta área se encuentra amenazada por un desarrollo insostenible y requiere estrategias de manejo realistas para garantizar la supervivencia de especies vulnerables y sus hábitats críticos.

Abstract Introduction: Identifying critical habitats for vulnerable elasmobranch species is crucial for effective conservation measures. The Munk’s devil ray (Mobula munkiana) is endemic to the Eastern Pacific, but yet little is known about its biology, ecology, and habitat use. As filter feeders, it is assumed that this species concentrates at high-productive upwelling regions, such as the Costa Rican Dome. Like many elasmobranchs, its populations are highly depleted and require urgent information to inform better conservation measures. Objective: The study was conducted to gain information on a unique behavior observed in juvenile M. munkiana, so further information can be provided on early life stages of this vulnerable species. Methods: From June to September 2017 and in August 2018, the feeding behavior of juvenile Mobula munkiana was observed in two shallow bays located at Punta Descartes, North Pacific Costa Rica. Individuals were captured using a non-lethal method to obtain data on size, weight, and sex distribution. Plankton samples (n = 100) were taken at both bays throughout the months to infer diet composition. Results: Munk’s devil rays showed a repetitive swimming movement parallel to the beach, feeding exclusively in the shallow breaking zone of the low tide waves at depth <50cm. A total of 12 M. munkiana (11 live and one found dead) indicated a juvenile feeding aggregation ranging from 490 - 610mm in disk width and 1400 - 2300gr in weight. The sex ratio (males to females) was 3:1. Zooplankton of the order Mysidacae was found in the highest abundance in the breaking zone. Conclusions: The specific behavior and seasonal occurrence of juvenile Munk’s devil rays in this area seem to be driven by prey abundance. More research is needed to conclude the presence of reproductive adults at deeper depths and the year-round habitat use of Punta Descartes. The area is threatened by unsustainable development and requires realistic management strategies to guarantee the survival of vulnerable species and their critical habitats.

Resumen Introducción: El Pacífico Norte de Costa Rica se caracteriza por presentar una variación de la temperatura subsuperficial del mar (TSSM) modulada por vientos superficiales de componente este, con variaciones estacionales e intra-estacional. La TSSM es fundamental para las interacciones de la interfase océano-atmósfera y de gran influencia en los procesos biológicos marinos. Los estudios de zooplancton en el Pacífico Norte son escasos y se han enfocado en la composición, abundancia y biomasa de macro y mesozooplanctonen en Bahía Culebra. No se han realizado trabajos sobre zooplancton al norte del Golfo de Papagayo. Objetivo: Analizar la variación del zooplancton de Bahía Salinas a diferentes escalas como respuesta a condiciones oceanográficas-atmosféricas. Métodos: durante algunos meses de los años 2011, 2012 y 2013, el mesozooplancton fue muestreado en siete estaciones siguiendo un gradiente costero-oceánico para determinar su abundancia, biomasa y composición de la comunidad. Se realizaron lances de CTD en cada estación, y se recopilaron datos horarios de la TSSM desde junio de 2003 a diciembre de 2017. Resultados: La temperatura superficial anual en Bahía Salinas es menor en diciembre-abril con un mínimo secundario en julio y mayor en mayo-junio, y agosto-octubre. Los eventos fríos, neutros y cálidos determinados por anomalías en la TSSM, presentaron una distribución de la temperatura en la columna de agua con estratificación horizontal, de mezcla vertical y homogénea, respectivamente. La distribución espacial del zooplancton no presentó diferencias significativas y la variación del promedio total de abundancia y biomasa mostró un comportamiento similar durante el período de estudio, con menor variación en el primer año en comparación con el segundo, siendo los copépodos la categoría predominante para todas las fechas. A escala estacional no se observó un patrón general de variación entre estación seca y lluviosa y, copépodos y otros grupos del zooplancton fueron las categorías que presentaron diferencias. A escala intra-estacional la abundancia y biomasa presentaron una relación inversa con la TSSM y se vieron afectadas de manera diferencial. Los copépodos y zooplancton gelatinoso se diferenciaron en todos los eventos. Conclusiones: El zooplancton de Bahía de Salinas responde de manera diferencial en las diferentes escalas a las condiciones climáticas que afectan la TSSM de la región. La clasificación de las fechas de muestreo en eventos permite caracterizar diferentes perfiles en la columna de agua, así como permite definer patrones de variación para el mesozooplancton, que refleja la adaptación a corto plazo en función de la variación de las condiciones ambientales. El conocimiento generado ayuda a comprender mejor los fenómenos oceanográficos y su efecto sobre las poblaciones de plancton y la biota en general, especialmente en el escenario de cambio climático y las manifestaciones modernas de su impacto, p. e. la acidificación oceánica y pérdida de biodiversidad marina.

Abstract Introduction: The North Pacific of Costa Rica is characterized by presenting a variation of the subsurface temperature of the sea (SSST) modulated by surface winds with east component, with seasonal and intra-seasonal variations. The SSST is fundamental for the interactions of the ocean-atmosphere interface and influence marine biological processes. Zooplankton studies in the North Pacific are scarce and have been focused on the composition, abundance and biomass of macro and mesozooplankton in Culebra Bay. No works on zooplankton has been carried out northward of Papagayo Gulf. Objective: To analyze the variation of the zooplankton in Bahía Salinas at different scales in response to oceanographic-atmospheric conditions. Methods: during 2011, 2012 and 2013, mesozooplankton was collected in seven stations following a coastal-ocean gradient to determine abundance, biomass, and community composition. CTD casts were also carried out in each station. Hourly data of the Sea Subsurface Temperature (SSST) were obtained from June 2003 to December 2017. Results: The annual surface temperature in Bahía Salinas was lower in December-April with a secondary minimum in July and higher in May-June and August-November. The cold, neutral and warm events determined by anomalies in the SSST, presented a distribution of the temperature in the water column with horizontal stratification, vertical mixture and homogeneous, respectively. The spatial distribution of zooplankton did not show significant differences and the variation of the total average abundance and biomass showed a similar behavior during the study period, with less variation in the first year compared to the second one, being the copepods the predominant category for all the dates. On a seasonal scale, a general pattern of variation between dry and rainy seasons was not observed, and copepods and others zooplankton groups were the categories that presented differences. On an intra-seasonal scale, abundance and biomass showed an inverse relationship with SST. Copepods and gelatinous zooplankton (GZ) were differentiated in all events. Conclusions: The zooplankton of Bahía Salinas respond differentially at different scales to the climatic conditions that affect the SSST of the region. The classification of the sampling dates into events allows characterizing different profiles in the water column it also allows to define the variation patterns for mesozooplankton that reflects short-term adaptation as a function of variation in environmental conditions. These findings help to understand how oceanographic processes determine plankton community composition and biota in general. This is relevant in times of climate change and the manifestation of its impact through processes such as ocean acidification and loss of marine biodiversity.

Resumo Objetivos Neste trabalho investigamos como fatores espaciais e dinâmica sazonal influenciaram a comunidade de diatomáceas em um reservatório tropical, profundo e de baixa produtividade no Brasil. Métodos Nós usamos as características físicas e químicas da água e as diatomáceas presentes no plâncton em 9 estações de amostragem durante os períodos seco (inverno austral) e chuvoso (verão austral) (N = 18) como base para avaliação da qualidade da água, e das características espaciais e dos padrões sazonais do reservatório. Para avaliar espacialmente e temporalmente os eventos integrados do passado recente (aproximadamente 5 anos antes da data de amostragem), e as espécies provenientes dos diversos hábitats do ecossistema, foram analisadas diatomáceas presentes nos sedimentos superficiais (primeiros 2 cm, N = 9). A amostragem sazonal do sedimento não foi necessária, já que os 2 cm de sedimento superficial utilizados contêm as carapaças de diatomáceas depositadas no passado recente do reservatório. Resultados durante a estação seca, diatomáceas longas, coloniais e altamente silicificadas, associadas com aumento da profundidade de mistura, pH e transparência da água, dominaram o ambiente planctônico, enquanto na estação úmida, o reservatório se tornou estratificado, favorecendo diatomáceas planctônicas solitárias com alta razão superfície volume. No sedimento superficial, um padrão geral foi observado, onde espécies planctônicas foram dominantes nas amostras de regiões mais profundas da represa, enquanto a abundância de espécies bentônicas aumentou nas estações mais rasas, próximas aos tributários. Conclusões A assembleia de diatomaceas foi influenciada principalmente pela sazonalidade e regime de mistura. O sedimento superficial forneceu informação de longo prazo, e revelou que a comunidade de diatomáceas é moldada de acordo com a diferenciação de hábitats. No geral, a espécie planctônica, cêntrica e pequena Aulacoseira tenella (Nygaard) Simonsen destacou-se como a mais abundante do reservatório tanto no plâncton como no sedimento, indicando que tamanho e forma provavelmente servem como estratégias adaptativas favorecendo flutuabilidade e absorção de nutrientes, e representam vantagem competitiva em ambientes profundos de baixa produtividade.

Abstract: Aim in this paper we investigated how spatial factors and seasonal dynamics influenced the diatom community in a tropical deep environment of low productivity waters in Brazil. Methods we used physical and chemical characteristics of the water and planktonic diatoms from 9 sampling stations during dry (austral winter) and wet (austral summer) seasons (N = 18) as the outline to identify water quality, spatial and seasonal patterns. To evaluate spatially and temporally integrated events from the recent past (approximately the last 5 years before sampling), and the species from diverse habitats of the system, we used diatoms from the surface sediment (top 2 cm, N = 9). Since we used the top 2 cm of surface sediment containing the dead diatoms that were deposited over recent past of the reservoir, seasonal sampling of the sediment was not needed. Results during the dry season heavily silicified long colonial planktonic diatom species associated mainly with higher mixing depth, pH, and transparency dominated the plankton, whereas in the wet season the reservoir became stratified, favoring planktonic solitary diatoms with high surface volume ratios. For the sediment, a general pattern emerged where planktonic species dominated in the deep sections of the reservoir, and the abundance of benthic species in shallow areas near the tributaries increased. Conclusions the diatom assemblages was mainly influenced by seasonal variations and mixing regime. Surface sediment samples provided longer-term information, and revealed habitat differentiation shaping diatom assemblages. Overall, the small centric planktonic Aulacoseira tenella (Nygaard) Simonsen stood out as the most abundant species in the entire reservoir in both, the plankton and the sediment, indicating that size and shape serve as adaptive strategies for buoyancy and nutrient uptake stand as a competitive advantage in deep low productivity environments.

ABSTRACT Although planktonic diatoms are one of the most abundant taxonomic groups in coastal wetlands, their assemblages have not been used to determine the environmental health of these ecosystems. Studies of ecosystem environmental health have been based on other taxonomic groups; we propose that diatom genera diversity represents a viable alternative for this purpose. Thus, our aim was to determine the alpha and beta diversities of the planktonic diatom assemblage present in Caulín Bay, Chiloé Island (41° 49’S; 73° 38’W), southern Chile, during the austral winter and spring of the years 2012 and 2014. Caulín Bay is an important site for aquatic bird observation and conservation, hunting is prohibited on a national scale and, internationally, the site has been declared an Important Bird and Biodiversity Area (IBA). Our results indicate different diversities between sampling stations, but not between the years studied. In total, we recorded 53 diatom genera, of which the most abundant were Coscinodiscus (21.99%) and Cocconeis (16.23%). The study area presented high genera diversity (i.e., H’(log2) >3.74) and beta diversity indicated that Caulín presents a low level of heterogeneity and is a low genera replacement environment. Consequently, we infer that Caulín Bay is a productive and environmentally stable ecosystem. This leads us to conclude that diatom diversity determination is a viable alternative to establish aquatic ecosystem environmental health and we recommend that future conservation strategies be established for Caulín Bay.

RESUMEN Si bien las diatomeas planctónicas son uno de los grupos taxonómicos más abundantes de los humedales costeros, sus ensambles no se han utilizado para determinar el estado ambiental de estos ecosistemas. Aunque se han realizado estudios de la salud ambiental de un ecosistema utilizando otros grupos taxonómicos, nosotros proponemos que la diversidad de géneros de diatomeas representa una alternativa viable. Por lo tanto, el objetivo de este estudio fue determinar las diversidades alfa y beta del ensamble de diatomeas planctónicas presentes en la Bahía de Caulín, Isla de Chiloé (41° 49’S; 73° 38’O), sur de Chile, durante las temporadas de invierno y primavera austral de los años 2012 y 2014. Bahía Caulín es un sitio importante para la observación y conservación de aves acuáticas por lo que a nivel nacional se ha prohibido la caza y a nivel internacional fue decretada un Área Importante para la Conservación de Aves, AICA. Los resultados de este estudio indicaron diferencias en las diversidades entre las estaciones de muestreo, pero no entre los años estudiados. En total, se identificaron 53 géneros de diatomeas; los más abundantes fueron Coscinodiscus (21,99%) y Cocconeis (16,23%). El área de estudio presentó una alta diversidad de géneros (i.e., H’(log2) >3,74) y la diversidad beta indicó que Caulín presentó bajo nivel de heterogeneidad y es un entorno con bajo reemplazo de géneros. Así, inferimos que Bahía Caulín es un ecosistema productivo y ambientalmente estable, por lo cual concluimos que la determinación de las diversidades de diatomeas es una alternativa viable para establecer la salud ambiental de los ecosistemas acuáticos y recomendamos establecer futuras estrategias de conservación para Bahía Caulín.

ABSTRACT Background: Bahía de la Paz, Mexico have seasonal blooms of planktonic prey that support a range of marine species including whale sharks (Rhincodon typus). Goals: This study includes the first sampling cycle that covers all climatic seasons, to know changes in the abundance and composition of zooplankton in the coastal waters off the El Mogote Sandbar, in Bahía de La Paz, BCS, Mexico. Methods: A total of 96 plankton samples were collected at predetermined field stations, spanning the entire length of the El Mogote from June 2016 to May 2017. Results: Total biomass was significantly different between seasons (Kruskal-Wallis chi-squared = 29.993, p = 0.000001385), with the lowest biomass recorded in spring (176.28 ml 100 m-3, 10.1%); and highest observed for winter (703.04 ml 100 m-3, 40.4%). Zooplankton composition was largely comprised of two main taxonomic groups: Copepoda (396,234 organisms100 m-3, 43.1%) and Chaetognatha (196,986 organisms100 m-3, 21.4%). The total number of individuals (sum of all taxonomic groups) per season showed significant differences (Kruskal-Wallis chi-squared = 29.78, p = 0.000001533) with the highest concentrations recorded in winter (292,429 organisms100 m-3, 31.8%) and lowest in spring (162,995 organisms100 m-3; 17.7%). Conclusions: This information provides the first work focused solely in the El Mogote area as a main foraging site for whale sharks, with clear changes in plankton communities with respect to shifting climatic seasons, and the importance of certain taxonomic groups to the diet of whale sharks.

RESUMEN Antecedentes: En la Bahía de la Paz, México se presentan proliferaciones de plancton estacionales que son presas potenciales de varias especies marinas incluyendo tiburón ballena (Rhincodon typus). Objetivos: En este estudio se presenta el primer ciclo de muestreo que cubre todas las temporadas climáticas, para conocer cambios en la abundancia y composición de zooplancton en aguas costeras de la barra de arena El Mogote en Bahía de La Paz, BCS, Mexico. Metodología: De junio 2016 a mayo 2017 se recolectaron 96 muestras de plancton en estaciones predeterminadas que cubren todo el largo de El Mogote. Resultados: La biomasa de zooplancton fue significativamente diferente entre temporadas (Kruskal-Wallis chi-cuadrada = 29.993, p = 0.000001385), la biomasa más baja se registró en primavera (176.28 ml 100 m-3, 10.1%) y la más alta en invierno (703.04 ml 100 m-3, 40.4%). El zooplancton estuvo compuesto principalmente por dos grupos taxonómicos: Copépodos (396,234 organismos100 m-3, 43.1%) y Quetognatos (196,986 organismos100 m-3, 21.4%). El número total de individuos (suma de todos los grupos taxonómicos) entre temporadas fue significativamente diferente (Kruskal-Wallis chi-cuadrada = 29.78, p = 0.000001533), las concentraciones más altas se registraron en invierno (292,429 organismos100 m-3, 31.8%) y las más bajas en primavera (162,995 organismos100 m-3; 17.7%). Conclusiones: Este es el primer trabajo enfocado exclusivamente al área de El Mogote como principal sitio de alimentación del tiburón ballena, con cambios estacionales claros en las comunidades de plancton y la importancia de ciertos grupos taxonómicos en la dieta del tiburón ballena.

RESUMEN En los lagos tropicales, los cambios estacionales en la dinámica del plancton son mínimos e irregulares, ya que las condiciones climáticas son bastante estables durante todo el año, en la mayoría de los casos solamente estudios a largo plazo permiten observar patrones en la dinámica del plancton. El lago de Río Cuarto es un lago meromícto tipo maar localizado en las llanuras del norte de Costa Rica, en el pasado se han realizado estudios limnológicos no mayores a un año de muestreo, en este trabajo presentamos datos de la composición del fitoplancton y del zooplancton a lo largo de cuatro años, del 2013 al 2017, con el fin de analizar cambios en la comunidad del plancton en un periodo de tiempo mayor, asociados a variables ambientales. Para el fitoplancton se tomaron muestras subsuperficiales y se fijaron con lugol, y para el zooplancton se hicieron arrastres verticales de 20 m con una red con 64 µm de poro, que se preservaron con formalina y luego se pasaron a alcohol de 95 %. El fitoplancton incluyó 54 taxa, la mayoría fue Chlorophyta, seguidos por Cyanobacteria y Bacillariophyta. Las taxa más comunes fueron: Synechococcus spp., Aphanocapsa sp. Coenochloris fotii, Chlorella sp. y Discostella stelligera. La abundancia total del fitoplancton disminuyó de 2013 a 2017, principalmente debido a una disminución en las Cyanobacteria. El zooplancton estuvo compuesto por 14 taxa: 5 cladóceros, 4 copépodos, 1 díptero y 4 rotíferos. Los más abundantes fueron: Keratella americana, Brachionus falcatus, Eubosmina tubicen y Arctodiaptomus dorsalis. Se observó un cambio en la diversidad y abundancia del zooplancton, al principio (2013-2014) K. americana y E. tubicen se alternaron en dominancia, y luego (2015-2016) A. dorsalis, Diaphanosoma sp. y Ceriodaphnia sp. fueron dominantes, con un regreso de K. americana en el 2017. Los cambios observados en el periodo de estudio parecen estar relacionados con cambios en la condición del lago, pues la termoclina se hundió y el lago se volvió más trasparente durante el estudio. La abundancia, de rotíferos y del cladócero Eubosmina tubicen, disminuyó asociada a una disminución de Cyanobacterias. Esos cambios no siguieron un ciclo anual, más bien parecen cambios que ocurren a largo plazo, tal y como se ha propuesto en la literatura sobre lagos tropicales.

Abstract In tropical lakes, seasonal changes in plankton dynamics are minimal and irregular, since climatic conditions are fairly stable throughout the year, in most cases only long-term studies allow observing patterns in the dynamics of the plankton. Lake Río Cuarto is a maar-type meromic lake located in the plains of Northern Costa Rica, in the past there have been no limnological studies more than a year of sampling, in this work we present data on the composition of phytoplankton and zooplankton over four years, from 2013 to 2017, with the aim of analyzing changes in the plankton community in a longer period, associated with environmental variables. Phytoplankton was studied from subsurface samples, preserved in Lugol’s solution and zooplankton from 20 m vertical hawls of a 64 µm mesh net, and preserved with formaline and later transferred to 95 % ethanol. Phytoplankton composition included 54 taxa, most of them were Chlorophyta, followed by Cyanobacteria and Bacillariophyta. The most abundant were: Synechococcus spp., Aphanocapsa sp. Coenochloris fotii, Chlorella sp. and Discostella stelligera. Total phytoplankton decreased from 2013 to 2017, mainly due to a decrease in Cyanobacteria. Zooplankton comprised 14 taxa, 5 cladocerans, 4 copepods, 1 diptera and 4 rotifers. The most abundant were: Keratella americana, Brachionus falcatus, Eubosmina tubicen and Arctodiaptomus dorsalis. There was a substitution of dominant species through time, at first (2013-2014) K. americana and E. tubicen alternated in dominance, and later (2015-2016), A. dorsalis, Diaphanosoma sp. and Ceridaphnia sp. became dominant, with a return of K. americana by 2017. The changes that occurred during the time of the study seem to be related to changes in the conditions of the lake, since its thermocline deepened with time and became more transparent. The abundance, of rotifers and Eubosmina tubicen, decreased associated to a decrease of Cyanobacteria. Those changes were not cyclical on an annual basis, but seemed to occur more on a long-term basis, as has been recognized earlier in the literature about tropical lakes.

Resumo Objetivo: Este estudo teve como objetivo caracterizar a estrutura do zooplâncton em rios de montanha no sul do Brasil, sub-bacia do rio Pelotas, bem como, as respectivas relações com as condições ambientais nas diferentes estações do ano. Métodos O zooplâncton foi coletado usando uma rede de plâncton (malha de 68 μm) e concentrado em um volume de 50 ml para posterirormente ser analisado em laboratório. As amostragens ocorreram durante o inverno (agosto de 2013), primavera (novembro de 2013), verão (fevereiro de 2014) e outono (maio de 2014). Resultados Os rotíferos e as amebas testáceas foram os grupos predominantes. Os valores médios de abundância, diversidade e equitabilidade variaram consideravelmente entre as diferentes estações do ano. A variabilidade do zooplâncton foi correlacionada com as condições ambientais (condutividade, sólidos em suspensão, pH, temperatura e oxigênio dissolvido). Conclusão A variação sazonal da comunidade zooplanctônica possibilitou elucidar algumas questões que envolvem a ecologia desses organismos em rios de montanhas no sul do Brasil. Esses ecossistemas únicos merecem maiores esforços de pesquisa e monitoramento, incluindo estudos dos seus padrões hidrológicos, diversidade biológica e mecanismos adaptativos da comunidade zooplanctônica.

Abstract Aim: This study aimed to characterize the zooplankton structure in highland streams in southern Brazil, Pelotas River sub-basin, as well as the respective relationships with the environmental conditions in the different seasons. Methods Zooplankton was collected using a plankton net (68 µm mesh) and concentrated into a volume of 50 ml for later analysis in the laboratory. Sampling occurred during the winter (August 2013), spring (November 2013), summer (February 2014) and autumn (May 2014). Results Rotifers and testate amoebae were the predominant groups. Mean abundance, diversity and evenness varied considerably between the different seasons. The variability of zooplankton was correlated to environmental conditions (conductivity, suspended solids, pH, temperature and dissolved oxygen). Conclusions The seasonal variation of the zooplankton community made it possible to elucidate some questions involving the ecology of these organisms in highland streams in southern Brazil. These unique ecosystems warrant further research and monitoring efforts, including studies of their hydrological patterns, biological diversity and adaptive mechanisms of the zooplankton community.

Abstract Background: The tropics are centers of high biodiversity of Rotifera that are highly variable and abundant. They play a key role since they are a link in the interaction network with members of other communities. Temporal changes in the community structure of the Rotifera assemblage is related to hydrologic phases. Goals: In this study, we focus on testing the hypothesis that the seasonal changes in alpha diversity and abundance (standing stocks) of Rotifera (Monogononta), considering also limnological variables, are mainly related to rainfall patterns. We consider four seasons based on rainfall: rainy, very rainy, dry, and very dry. Methods: Between 2008 and 2009, rotifers were sampled monthly with a plankton net in qualitative and quantitative sampling, and seven limnological variables were recorded at three sampling stations along Lake Amapá. Results: We found approximately 23% of all Rotifera listed for the Amazonia. The high Menhinick index revealed a high species dominance, except in the rainy season. The Shannon index did not show a greater distribution of organisms (0.3844 to 0.8886) independent of the layer and time season. In general, the equability index showed that all species were equally abundant in all seasons, with higher values at the surface and in the middle of the water column. The limnological variables also showed differences between all seasons in at least a layer of the water column. Conclusions: The seasons influenced the fluctuations in the communities of Rotifera of Lake Amapá, which led to a different species distribution pattern over time.

Resumen Antecedentes: Los trópicos son centros de alta biodiversidad donde los rotíferos son muy variables y abundantes. Estos organismos desempeñan un papel clave en el ecosistema, ya que son eslabones en la red de interacciones con los miembros de otras comunidades. Objetivos: En este estudio nos enfocamos en probar la hipótesis de que los cambios estacionales, incluyendo los patrones de lluvias y las variables limnológicas, influyen en la diversidad y la abundancia de los rotíferos monogonontos del lago Amapá. Métodos: En total se consideraron cuatro períodos estacionales basados en la precipitación: lluvioso, muy lluvioso, seco y muy seco. Entre el año 2008 y 2009, se realizaron muestreos mensuales de plancton y se tomaron siete variables limnológicas en tres estaciones establecidas a lo largo del lago Amapá. Las muestras fueron analizadas de forma cualitativa y cuantitativa en laboratorio. Resultados: Se encontró cerca del 23% de rotíferos registrados en la Amazonia. El índice de Menhinick reveló una alta dominancia de las especies, excepto en la época de lluvias. Independientemente de la profundidad de la columna de agua y la estación del año; el índice de Shannon no mostró una mayor distribución de organismos (0.3844 a 0.8886) independientemente de la profundidad de la columna de agua y la temporada de colecta. En general, el índice de equidad mostró que todas las especies fueron igualmente abundantes en todos los períodos estacionales, los valores más altos se observaron en la porción superficial y media de la columna del agua. En al menos una capa de la columna de agua se encontraron diferencias entre las variables limnológicas de todas las estaciones. Conclusiones: Las fluctuaciones en las comunidades de rotíferos de lago Amapá, estuvo influenciado por los períodos estacionales, lo cual determinó un patrón diferencial en la distribución de las especies a través del tiempo.

The composition and abundance of the zooplankton of El Morro lagoon on the island of Margarita, Venezuela, during the upwelling period (March-May 2011) and relaxation (June-August 2011) were analyzed. Samples were collected at 6 stations in different areas of the lagoon. Sampling was performed with a 333 μm plankton net for 10 minutes. Water Temperature, salinity and dissolved oxygen were measured in situ, in addition to nutrients. Average water temperature values of 29.7 °C, a salinity of 36 ups, and dissolved oxygen of 5.9 mg.L-1 were found. The concentration of nutrients was low (averages of 0.12, 0.04, 0.03 mg.L-1 for nitrate, nitrite and phosphate, respectively). Significant seasonal differences were detected with greater records in the relaxation season, whereas spatially did not show differences, although in the internal stations a greater abundance was recorded. Fifteen zooplankton groups were identified, identifying nine species of Copepoda, two of Cladocera, one of Decapoda, Tunicada and Rotifera and different larval forms of different taxa. Crustacean larvae showed the highest average and relative abundance (47738 ind.m-3 y 46.83%, respectively), followed by copepod O. nana (31740 ind.m-3 and 25.94%, respectively) and P. quasimodo (12958 ind.m-3 and 8.47%, respectively). This lagoon involves the emergence-relaxation seasonality as an important effect on the distribution and abundance of zooplankton.

Se analizó la composición y abundancia del zooplancton de la laguna El Morro en la isla de Margarita, Venezuela, durante el periodo de surgencia (marzo-mayo 2011) y de relajación (junio-agosto 2011). Las muestras fueron recolectadas en 6 estaciones de las diferentes zonas de la laguna. Se realizaron calados con una red de plancton de 333 µm durante 10 minutos. Se midió in situ la temperatura, salinidad y oxígeno disuelto, además de nutrientes. Se registraron valores medios de temperatura de 29.7 ºC, salinidad de 36 ups, oxígeno disuelto de 5.9 mg.L-1. La concentración de nutrientes fue baja (medias de 0.12; 0.04; 0.03 mg.L-1 para nitrato, nitrito y fosfato, respectivamente). Se detectaron diferencias significativas temporales con mayores registros en la temporada de relajación, mientras que espacialmente no mostró diferencias, a pesar que en las estaciones internas (Est. 4,5,6) se obtuvo mayor abundancia. Se identificaron quince grupos zooplanctónicos, determinándose nueve especies del grupo Copepoda, dos de Cladocera, una de Decapoda, Tunicada y Rotifera y diferentes formas larvarias de distintos taxa. Las larvas de crustáceos presentaron la abundancia media y relativa más alta (47738 ind.m-3 y 46.83%, respectivamente), seguido del copépodo Oithona nana (31740 ind.m-3 y 25.94%, respectivamente) y Paracalanus quasimodo (12958 ind.m-3 y 8.47%, respectivamente). Esta laguna involucra la estacionalidad surgencia-relajación como un efecto importante en la distribución y abundancia del zooplancton.