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 Aim We investigated the relationship between ecological attributes of the zooplankton community and its secondary production. Methods Samples were taken from lakes in the floodplain of the Upper Paraná River (Brazil), in low and high-water periods, and in a manipulative experiment realized in mesocosms. Results The highest amount of production was related to the dominance of few species. Secondary production of larger and long-lived organisms, such as copepods, had been most associated with the biomass, whereas smaller ones, such as rotifers, with the abundance. Conclusions These attributes of the zooplankton community (biomass and abundance) can be used as proxies to estimate the zooplankton secondary production in the floodplain, supporting the studies on monitoring and conservation of these ecosystems. Brazil, Brazil , (Brazil) highwater high water periods mesocosms species longlived long lived organisms copepods biomass ones rotifers abundance ecosystems (Brazil

Resumo Objetivo Nós investigamos a relação entre atributos ecológicos da comunidade zooplanctônica e a produção secundária. Métodos Amostras foram coletadas em lagos da planície de inundação do Alto Rio Paraná (Brasil), em períodos de águas baixas e altas, e em um experimento manipulativo realizado em mesocosmos. Resultados A maior produção secundária esteve relacionada à dominância de poucas espécies. A produção secundária de organismos de maior tamanho e maior ciclo de vida, como os copépodes, foi mais associada à biomassa, enquanto os menores, como os rotíferos, à abundância. Conclusões Esses atributos da comunidade zooplanctônica (biomassa e densidade) podem ser usados como proxies para estimar a produção secundária de zooplâncton na planície de inundação, subsidiando os estudos de monitoramento e conservação desses ecossistemas. Brasil, Brasil , (Brasil) altas mesocosmos espécies vida copépodes biomassa menores rotíferos abundância densidade ecossistemas (Brasil

ABSTRACT Biomass is a valuable indicator of biological production in any ecosystem and represents a proxy of secondary production in the case of zooplankton. This short communication aims to report zooplankton biomass values in the waters of the Campeche Canyon, southern Gulf of Mexico, during the “Nortes” storm season of 2011 and to explore their relationship with the hydrography and the circulation pattern. The results showed the presence of cyclonic and anticyclonic eddies associated with high and low water density at the base of the pycnocline. The highest values of zooplankton biomass (>40 g 100 m-3) were observed in regions that presented higher water density values (~26.1 kg m-3). In comparison, the lowest zooplankton biomass values (<5 g 100 m-3) were associated with low water densities (<25.6 kg m-3). The results presented here contribute to elucidating the role that physical forcing plays on the zooplankton biomass of the region, particularly during a season in which the passage of extreme storms is widespread.

Abstract: Aim Zooplankton functional groups play an important role in lake functioning and can readily respond to environmental changes and may be associated with phytoplankton changes. In warmer regions, zooplankton species have a smaller body size, which decreases their grazing capacity, attenuating top-down control throughout phytoplankton. We evaluated changes in density and biomass of zooplankton functional groups and their relationship with algal groups in horizontal reservoir zonation (pelagic, sublittoral, and eulittoral zones) of the shallow reservoir. We hypothesize that the density and biomass of zooplankton functional groups are associated with fluctuations in the phytoplankton groups in horizontal reservoir zonation. Methods Changes in the structure of the zooplankton functional group and the controlling limnological variables were verified at three sampling stations: pelagic, sublittoral, and eulittoral zones in a mesotrophic reservoir. Results Zooplankton species were distributed in seven functional groups. The density and biomass of zooplankton functional groups were not clearly associated with biomass variations of phytoplankton groups. However, the zooplankton functional groups were associated with horizontal reservoir zonation, where specific groups were found in the pelagic, sublittoral, and eulittoral zones. Conclusions The zooplankton functional groups were related to the horizontal zonation of the reservoir but were not associated with changes in the phytoplankton groups due to the dominance of small organisms. Abstract regions size capacity topdown top down pelagic (pelagic sublittoral stations However organisms

Resumo: Objetivo Os grupos funcionais do zooplâncton desempenham um papel importante no funcionamento dos lagos, são capazes de responder prontamente às mudanças ambientais e podem estar associados às mudanças no fitoplâncton. Em regiões mais quentes, as espécies de zooplâncton apresentam pequeno tamanho corporal, o que diminui sua capacidade de pastejo e atenua o controle de cima para baixo sobre o fitoplâncton. Avaliamos as mudanças na densidade e biomassa de grupos funcionais do zooplâncton e sua relação com grupos de algas na zonação horizontal de um reservatório raso (zona pelágica, sublitoral e eulitoral). Nossa hipótese é que a densidade e biomassa dos grupos funcionais do zooplâncton estão associadas a flutuações nos grupos do fitoplâncton no zoneamento horizontal do reservatório. Métodos Em um reservatório mesotrófico, as alterações na estrutura do grupo funcional do zooplâncton e nas variáveis limnológicas foram avaliadas em três zonas de amostragem: pelágica, sublitoral e eulitoral. Resultados As espécies de zooplâncton foram distribuídas em sete grupos funcionais. Evidenciou-se que a densidade e a biomassa dos grupos funcionais do zooplâncton não foram claramente associadas às variações da biomassa dos grupos do fitoplâncton. No entanto, os grupos funcionais do zooplâncton foram associados à zonação horizontal do reservatório, onde grupos específicos foram encontrados na zona pelágica, sublitoral e eulitoral. Conclusões Os grupos funcionais do zooplâncton foram relacionados com a zonação horizontal do reservatório, mas não foram associados às mudanças nos grupos do fitoplâncton devido à dominância de organismos de pequeno porte. Resumo lagos quentes corporal pelágica eulitoral . eulitoral) mesotrófico amostragem Evidenciouse Evidenciou se entanto porte

Resumen. Los copépodos, como uno de los principales grupos que componen el zooplancton marino, juegan un papel importante por su posición en la red trófica. Se evaluó la biomasa de copépodos en un vórtice ciclónico durante 2 estaciones climáticas contrastantes en la bahía de La Paz, al sur del golfo de California, la cual se caracteriza por una alta productividad biológica. Durante 2 campañas oceanográficas en invierno de 2006 y verano de 2009, se determinó la estructura física de la columna de agua mediante un CTD y se recolectaron muestras de zooplancton mediante arrastres oblicuos. Se utilizaron datos de satélite para visualizar los patrones de distribución de clorofila a (Cla). Los resultados mostraron un vórtice ciclónico en ambas estaciones, con un diámetro de ~25 km y velocidades geostróficas >50 cm·s-1 en su periferia, con elevada Cla (~3 mg·m-3 en invierno). La máxima biomasa de calanoides ocurrió en invierno, con hasta 6.6 mg·100 m-3 en el oeste de la bahía, cerca de la costa; además, su distribución coincidió con el patrón de Cla y circulación, ya que formó un anillo siguiendo la periferia del vórtice, con un segundo pico cerca de la conexión con el golfo. Los valores medios de biomasa de copépodos mostraron un patrón de alternancia calanoides-ciclopoides entre invierno y verano dentro del vórtice ciclónico, con más biomasa de calanoides que ciclopoides en invierno y lo contrario en verano. Los resultados resaltan el impacto del vórtice en el ecosistema planctónico a través de su influencia sobre las condiciones hidrográficas en la columna de agua. Otros factores, como las interacciones ecológicas, la dinámica poblacional y los hábitos alimenticios, también pueden jugar un papel importante. El comportamiento alimentario es afectado por altas concentraciones de Cla, que representan una fuente de alimento para copépodos observados alrededor del vórtice.

Abstract. As one of the main groups comprising marine zooplankton, copepods play an important role due to their position in the trophic web. We assessed the copepod biomass in a cyclonic eddy during 2 contrasting seasons in the Bay of La Paz, southern Gulf of California, which is characterized by high biological productivity. Two oceanographic expeditions took place in the winter of 2006 and the summer of 2009; a CTD probe was used to determine the physical structure of the water column, and oblique zooplankton hauls collected zooplankton samples. Satellite data were used to visualize the chlorophyll a (Chla) distribution patterns. The results showed a well-defined cyclonic eddy in both seasons, with a diameter of ~25 km and geostrophic velocities >50 cm·s-1 in its periphery. At the edges of the eddy, Chla was high, reaching ~3 mg·m-3 in winter. The maximum calanoid copepod biomass occurred in winter, reaching 6.6 mg·100 m-3 in the western bay close to the coast; moreover, their distribution corresponded well with the Chla and circulation patterns, forming a belt shape following the periphery of the eddy, with a second peak close to the connection with the gulf. The mean values of copepod biomass exhibited a pattern with alternating calanoids-cyclopoids between winter and summer within the cyclonic eddy, with calanoid biomass higher than cyclopoid biomass in winter, which was the opposite of summer. The results highlight the impacts of the eddy on the planktonic ecosystem through its influence on the hydrographic conditions in the water column. Other factors, such as ecological interactions, population dynamics, and feeding habits, may also play a role. Feeding behavior is affected by the high concentrations of Chla, which represent a source of food for copepods observed around the eddy.

Resumen Introducción: Las proliferaciones de cianobacterias en los cuerpos de agua tropicales son cada vez más comunes, debido a la eutrofización y al aumento de las temperaturas. En consecuencia, muchos sistemas de agua dulce se ven afectados por la reducción de la calidad del agua, la biodiversidad y los servicios de los ecosistemas. Con el aumento de la frecuencia de la proliferación de algas nocivas, el desarrollo de herramientas biológicas para mejorar la calidad del agua es urgente. Objetivo: Evaluar los efectos de una macrófita sumergida y un cladócero sobre la cianobacteria productora de microcistina llamada Microcystis aeruginosa (NPLJ-4) y la clorofita Raphidocelis subcapitata (BMIUFRPE-02) en cultivos mixtos. Métodos: Se realizaron dos experimentos paralelos durante diez días para evaluar los efectos de la macrófita sumergida Ceratophyllum demersum y el cladócero Moina micrura sobre las interacciones microalgales. Se cultivaron cepas de microalgas en el medio de cultivo ASM1, en condiciones controladas de laboratorio. El primer experimento presentó cuatro tratamientos: M (C. demersum), Z (M. micrura), MZ (C. demersum y M. micrura) y C (control). El segundo experimento consistió en cinco tratamientos, en el que las microalgas se cultivaron juntas en diferentes proporciones de Microcystis:Raphidocelis: 1:0, 3:1, 1:1, 1:3 y 0:1. La biomasa y las tasas de crecimiento de las cepas se evaluaron cada dos días, y se trataron estadísticamente con ANOVA de medidas repetidas de dos o tres factores. Resultados: En el primer experimento, M. aeruginosa se inhibió significativamente en los tratamientos M y MZ a partir del segundo día, y en Z a partir del cuarto, mientras que R. subcapitata no mostró reducción de su biomasa en ningún tratamiento. Por otro lado, R. subcapitata fue estimulada a partir del octavo y décimo día en el tratamiento M y solo en el octavo día en el tratamiento Z. En el segundo experimento, M. aeruginosa se inhibió significativamente cuando se cultivó con R. subcapitata en proporciones bajas (proporción de Microcystis:Raphidocelis de 1:3) durante todo el experimento, mientras que la clorófita se estimuló en ese tratamiento. Conclusiones: La coexistencia de una cianobacteria con un alga verde no alteró la principal respuesta negativa de M. aeruginosa a la macrófita sumergida y al zooplancton, sino que estimuló al alga verde. En consecuencia, la introducción de macrófitos y cladóceros sumergidos ya adaptados a las condiciones eutróficas, tanto aislados como combinados, resultó ser un buen método para controlar las proliferaciones de cianobacterias sin afectar negativamente a otras especies de fitoplancton coexistentes.

Abstract Introduction: Cyanobacterial blooms in tropical water bodies are increasingly common, because of eutrophication and rising temperatures. Consequently, many freshwater systems are affected, by reducing water quality, biodiversity, and ecosystem services. With the increased frequency of harmful algal blooms, the development of biological tools to improve water quality is an urgent issue. Objective: To evaluate the effects of a submerged macrophyte and a cladoceran on the microcystin-producing cyanobacteria Microcystis aeruginosa (NPLJ-4) and the chlorophyte Raphidocelis subcapitata (BMIUFRPE-02) in mixed cultures. Methods: Two parallel experiments were carried out for ten days to evaluate the effects of the submerged macrophyte Ceratophyllum demersum and the cladoceran Moina micrura on microalgal interactions. Microalgal strains were cultivated in the ASM1 culture medium, under controlled laboratory conditions. The first experiment presented four treatments: M (C. demersum), Z (M. micrura), MZ (C. demersum and M. micrura), and C (control). Meanwhile, the second experiment consisted of five treatments, in which the microalgae were cultivated together at different Microcystis:Raphidocelis ratios: 1:0, 3:1, 1:1, 1:3, and 0:1. Biomass and growth rates of the strains were evaluated every two days, which were statistically treated with three-way or two-way repeated-measures ANOVA. Results: In the first experiment, M. aeruginosa was significantly inhibited in M and MZ treatments from the second day, and Z from the fourth, while R. subcapitata showed no reduction in its biomass in any treatment. On the other hand, R. subcapitata was stimulated from the eighth and tenth days in M treatment and only on the eighth day in Z treatment. In the second experiment, M. aeruginosa was significantly inhibited when cultivated with R. subcapitata in low ratios (Microcystis:Raphidocelis ratio of 1:3) throughout the experiment, while the chlorophyte was stimulated in that treatment. Conclusions: The coexistence of a cyanobacterium with a green alga did not alter the main negative response of M. aeruginosa to the submerged macrophyte and zooplankton but stimulated the green alga. Accordingly, the introduction of submerged macrophytes and cladocerans already adapted to eutrophic conditions, both isolated and combined, proved to be a good method to control cyanobacterial blooms without negatively affecting other coexisting phytoplankton species.

RESUMEN Entender las relaciones entre las comunidades planctónicas en un embalse nos permite inferir posibles cambios en la redistribución de los flujos de materia y energía en este sistema. Este trabajo propone un modelo dinámico para representar la red trófica del embalse tropical Riogrande II, donde se integran las cadenas tróficas de pastoreo y detritus y se limitan las interacciones entre predadores, presas y recursos al introducir un factor limitante de encuentro con la presa (pmf). El modelo dinámico se enfoca en el balance de masas sustentado en una amplia búsqueda bibliográfica. Los datos usados para validar el modelo se colectaron de datos previamente reportados para el embalse durante los años 2010 y 2013. Los valores de pmf obtenidos en cada simulación, sugieren que el predador dominante puede acceder a su presa principal a ciertas concentraciones de fósforo total, con una probabilidad de encuentro que va desde 9,3 % hasta 17,7 %. Nuestros resultados indican que la mayor parte de la producción primaria es poco aprovechada por los consumidores en la zona fótica, sin embargo, ingresa en el flujo de la cadena detrítica de manera que soporta la producción de zooplancton casi por completo. Las relaciones causales asumidas en este modelo explican en gran medida las densidades de biomasa reportadas en estudios previos.

ABSTRACT The understanding of the relationships between the planktonic communities in a reservoir allows us to infer possible changes in the redistribution of matter and energy flows in these systems. This work proposes a dynamic model for the trophic network of the Riogrande II tropical reservoir, which integrates the planktonic trophic chains of detritus and grazing, limiting the prey-predator interactions by introducing the prey meeting factor (pmf). We built a dynamic model of mass balance supported by an extensive bibliographic search. The limitations of consumers and resources were represented simultaneously by means of the pmf. The data used to validate the model were compiled from previous investigations carried out in this reservoir from 2010 to 2013. The values of pmf that we found in each simulation suggest that the top predator can access its main prey in certain concentrations of total phosphorus, with a probability of encounter ranging from 9.3 % to 17.7 %. Our simulations indicate that most of the primary production is poorly used by the primary consumers in the photic zone, however, it enters in the flows of the detrital chain and supports the production of zooplankton almost entirely. According to this finding, the biomass densities obtained in the previous studies can be better explained by the causal relationships assumed in this model.

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.

Resumen Introducción: Los ecosistemas costeros alrededor del mundo están bajo la influencia de tensores locales, regionales y globales, como la contaminación, la eutroficación y el cambio climático. El Golfo Dulce es un profundo ecosistema tropical relativamente inalterado y accesible, que provee oportunidades para la investigación comparativa y colaborativa. Objetivo: Resumir los informes publicados sobre investigaciones pasadas realizadas en el ecosistema, identificar tópicos para estudios futuros y sugerir nuevas áreas de investigación. Métodos: Se hizo una búsqueda en la red de informes basados en investigaciones hechas en Golfo Dulce y publicadas en revistas científicas. Fueron incluidos aquellos informes sobre parámetros ambientales y la biota. Resultados: Un total de 123 estudios que incluyen datos sobre Golfo Dulce son citados. Los cuatro tópicos citados con más frecuencia fueron: Los resultados de la expedición del R/V Victor Hensen (1993-1994) y estudios de seguimiento sobre microbiología, informes sobre parámetros acuáticos, investigaciones sobre vertebrados y estudios sobre zooplancton. Los informes sobre perfiles de oxígeno y temperatura son presentados con mayor detalle, seguidos por aquellos sobre la biota. Conclusiones: Golfo Dulce tiene bajas concentraciones de oxígeno por debajo de 50 m y es usualmente anóxico a 200 m en el fondo, con formación ocasional de H2S. Sin embargo, el ecosistema contiene una diversidad de organismos identificados relativamente alta, desde bacterias hasta ballenas. De relevancia particular para futuros estudios es, entre otros, la conducción, de muestreos multidisciplinarios orientados a obtener datos sobre productividad primaria, la diversidad y biomasa de los principales grupos de organismos planctónicos, demersales y bénticos, así como la frecuencia y magnitud del flujo de agua oceánica hacia el interior. Estos datos, así como los obtenidos en el pasado, son esenciales para actualizar el modelo trófico desarrollado hace más de 25 años, o en apoyo de nuevos modelos predictivos de funcionamiento del ecosistema.

Abstract Introduction: Coastal ecosystems worldwide are under the influence of local, regional and global stressors, such as pollution, eutrophication and climate change. Golfo Dulce is a relatively pristine and accessible deep tropical ecosystem that provides opportunities for comparative and collaborative research. Objective: To summarize published reports on past research conducted in this ecosystem, identify topics for further study, and suggest new research issues. Methods: A search was made on the web for reports based on research conducted in Golfo Dulce and published in scientific journals. Reports focusing on environmental parameters and on the biota were included. Results: A total of 123 studies that include data from Golfo Dulce are cited. The four topics more frequently addressed were reports based on the results of the R/V Victor Hensen expedition (1993-1994) and follow-up work on microbiology, studies on water parameters, research on vertebrates, and zooplankton studies. The reports focusing on vertical profiles of oxygen and temperature are discussed in detail, followed by those on the biota. Conclusions: Golfo Dulce has low oxygen concentrations below 50 m and is frequently anoxic at the 200 m deep basin with occasional formation of H2S. However, the ecosystem contains a relatively high diversity of identified organisms, from bacteria to whales. Of particular relevance for future studies are multidisciplinary surveys aiming at obtaining data on primary productivity, the diversity and biomass of the main groups of planktonic, demersal and benthic organisms, and the frequency and magnitude of the influx of deep offshore waters over the sill into the basin. These data, as well as the information gathered in the past, are essential for updating the trophic model developed more than 25 years ago and in support of new predictive models on the functioning of the ecosystem.

Abstract Aquatic humic substances (HS) represent about 60-95% of the dissolved organic carbon (DOC) present in coastal environments of northern Rio de Janeiro state, Brazil. Although they are important regulators of processes involving aquatic communities, the response of the zooplankton community to their presence remains poorly understood, especially in natural tropical environments. Therefore, our objective was to elucidate zooplankton community responses along a natural gradient of HS. Such natural humic gradient was obtained in coastal freshwater environments with distinct DOC concentrations (20-200 mg L-1). Results show a decrease in zooplankton density and biomass along the HS gradient. However, microphages organisms (e.g. non-predatory rotifers and smaller testate amoeba, such as Difflugia) were most present in environments with higher concentration of HS, probably due to a stronger importance of the microbial-loop in these environments. Some species – such as Scapholeberis armata (Cladocera) and Lecane boettgeri (Rotifera) were only accounted for environments with high HS concentration, illustrating their potential as bioindicators for HS presence. Nevertheless, we were able to observe the effects of HS on the structure and composition of primary consumers and how these substances might indirectly affect species dynamics. We point out to new findings in highly humic tropical environments, which are still poorly studied and understood.

Abstract Studies considering the functional traits of organisms, populations, and communities functional indices increase the understanding of many factors on ecosystem functioning. Here, we analyze the predation effect (by fish) on zooplankton functional diversity and the effects of biomass and density of periphytic algae on zooplankton feeding type trait and body size. We expect that intense predation by fish on zooplankton leads to higher values of zooplankton functional diversity and that food resource will be positively related to the abundance of zooplankton trait and body size. For that, microcosms were established (T1- fish-absence, and T2- fish-presence, both with periphytic algae as food). We observed that fish presence decreased zooplankton functional diversity through modifications in the availability of nutrients and algae, through the middle-out effect. We also observed that body size had a negative relationship with the food resource, reaffirming that high food availability in subtropical lakes is linked to small-bodied zooplankton. The raptorial copepods covariate positively with the periphytic algae, which was an alternative food resource and, in this case, the main form of carbon input into the system. In this study, omnivorous fish reduced zooplankton functional traits, which can alter the energy stock and energy flow in aquatic ecosystems.

Resumo: Objetivo Testar a hipótese de que o zooplâncton altera a estrutura do fitoplâncton em reservatórios tropicais, reduzindo a biomassa de espécies de algas susceptíveis a herbivoria. Métodos Avaliamos experimentalmente as respostas espécie-específicas do fitoplâncton ao zooplâncton em reservatórios eutróficos com diferentes estruturas da comunidade fitoplanctônica no nordeste do Brasil. Amostras de água foram coletadas da subsuperfície nas regiões costeiras dos reservatórios Apipucos e Mundaú em janeiro/2012 e novembro/2014, respectivamente, e transportadas para o laboratório. Os experimentos foram realizados em frascos Erlenmeyer (1 litro) cheios de água dos locais das amostras e mantidos por cinco dias nas condições laboratoriais. Dois tratamentos foram mantidos (1) com fitoplâncton e presença do zooplâncton nativo e (2) sem zooplâncton nativo. Resultados O zooplâncton provou ser um fator importante, modificando a estrutura da comunidade fitoplanctônica, principalmente no reservatório de Apipucos. Neste reservatório, observamos uma redução significativa na biomassa de Cyclotella meneghiniana e Chlamydomonas sp., e um incremento na biomassa de Raphidiopsis raciborskii. No reservatório Mundaú, observamos uma redução significativa de C. meneghiniana e R. raciborskii, enquanto a cianobactéria Microcystis aeruginosa aumentou sua biomassa na presença de zooplâncton. Conclusões Estes resultados mostram a importância da estrutura da comunidade de microalgas nas interações fitoplancton-zooplâncton para as cadeias alimentares em ambientes tropicais, bem como, apoiam o papel do zooplâncton na promoção do crescimento de cianobactérias e na manutenção da proliferação de algas.

Abstract: Aim To test the hypothesis that zooplankton changes the structure of phytoplankton in tropical reservoirs by reducing the biomass of algal species susceptible to herbivory. Methods We experimentally evaluated the species-specific responses of phytoplankton to zooplankton within eutrophic reservoirs with different phytoplankton community structure in northeastern of Brazil. Water samples were collected from the subsurface in coastal regions of the Apipucos and Mundaú reservoirs in January/2012 and November/2014, respectively, and transported to the laboratory. The experiments were performed in Erlenmeyer flasks (1 liter) filled with water from the sample sites and were maintained for five days in the laboratory conditions. Two treatments were maintained (1) with phytoplankton and the presence of the native zooplankton and (2) without native zooplankton. Results Zooplankton proved to be an important factor, modifying the structure of the phytoplankton community, especially in the Apipucos reservoir. In this reservoir, we observed a significant reduction of biomass in diatom Cyclotella meneghiniana, and the chlorophyte Chlamydomonas sp., and an increase in the biomass of Raphidiopsis raciborskii. In the Mundaú reservoir, we observed a significant reduction of C. meneghiniana and R. raciborskii, while cyanobacteria Microcystis aeruginosa increased their biomasses in the presence of zooplankton. Conclusions These results show the importance of the microalgae community structure in phytoplankton-zooplankton interactions for food webs in tropical environments, as well as support the role of zooplankton in fostering cyanobacterial growth and maintain algal blooms.

Abstract In this study we analyzed the holoplanktonic mollusk fauna in neritic waters of Mahahual, Mexican Caribbean Biosphere Reserve, to test the hypothesis that faunae are distributed homogenously across the internal and external zones due to a narrow continental shelf. Zooplankton sampling was carried out with 2 conical nets of 333 and 505 µm mesh size over 33 sampling stations. In the laboratory, zooplankton biomass was estimated as wet weight and the holoplanktonic mollusks were separated from samples and identified. The biomass values recorded (0.02 to 7.51 g 100 m-3) are typical of the oligotrophic waters of the Caribbean. Eight species of mollusks were identified, which in decreasing order of abundance are: Creseis acicula, Heliconoides inflatus, Atlanta lesueurii, Diacavolinia longirostris, Limacina trochiformis, Limacina lesueurii, Firoloida desmarestia, and Limacina bulimoides. Results of the Anosim statistical test showed that there were no differences in the fauna distribution between the internal and external shelf probably due to the strong influence of oceanic waters over the neritic environment. The information provided here is of great importance to the consideration of pelagic biota in future conservation plans for the reserve.

Resumen En este estudio se analizó la fauna de moluscos holoplanctónicos en aguas neríticas de Mahahual, Reserva de la Biosfera Caribe Mexicano, bajo la hipótesis de encontrar una homogeneidad en la distribución de la fauna en las plataformas interna y externa debido a la estrecha plataforma continental. Los muestreos de zooplancton se efectuaron con 2 redes cónicas de apertura de malla de 333 y 505 µm en 33 estaciones de muestreo. En el laboratorio se estimó la biomasa de zooplancton en peso húmedo y se separaron e identificaron los moluscos holoplanctónicos. Los valores de biomasa registrados (0.02 a 7.51 g 100 m-3) son típicos de las aguas oligotróficas del Caribe. Se identificaron 8 especies de moluscos, que en orden decreciente de abundancia son: Creseis acicula, Heliconoides inflatus, Atlanta lesueurii, Diacavolinia longirostris, Limacina trochiformis, Limacina lesueurii, Firoloida desmarestia y Limacina bulimoides. Los resultados de la prueba estadística Anosim mostraron que no hubo diferencias en la distribución de la fauna entre las plataformas interna y externa, probablemente debido a la fuerte influencia de aguas oceánicas sobre las neríticas. La información aquí proporcionada es de gran importancia en la generación de eventuales planes de conservación de la biota pelágica de la reserva.

RESUMEN En el Caribe sur se presentan dos áreas principales de surgencia, la Guajira colombiana y el oriente de Venezuela; sin embargo, la producción pesquera es muy desigual, a pesar de que en la Guajira la intensidad del viento es mayor y teóricamente la surgencia es más intensa. Por esta razón, debería tener una producción pesquera mayor que la venezolana, lo que no ocurre. Se plantean las posibles causas de esta notable diferencia y se comentan aspectos relacionados con el viento, la hidrografía, la concentración de nutrientes, la biomasa del fitoplancton, la plataforma continental, el aporte de ríos, la presencia de islas y otros factores. El oriente de Venezuela tiene mayor fertilidad y producción pesquera porque la masa de Agua Subsuperficial Subtropical es la que abastece la surgencia durante los primeros meses del año (sequía). En el segundo semestre, cuando la surgencia se relaja, el área se enriquece con materia orgánica del río Orinoco y el aporte de biomasa fitoplanctónica proveniente de lagunas costeras, golfos y bahías semicerradas. También juega un papel fundamental la amplitud de la plataforma continental con la presencia de archipiélagos, islas mayores y menores que causan enriquecimientos locales y la concentración y retención del plancton. Esto último aumenta la productividad biológica y propicia la reproducción de esos organismos. En la Guajira, la surgencia podría estar influenciada por la contracorriente del Darién, que por su origen debe contener baja concentración de nutrientes inorgánicos; además, en esta zona no están presentes grandes ríos que aporten materia orgánica y la plataforma continental es poco amplia y no contiene islas que propicien el aumento de la productividad acuática. Para la comprensión de la surgencia en la Guajira, se sugieren estudios para el seguimiento in situ de la hidrografía, nutrientes inorgánicos, clorofila y la abundancia de fito y zooplancton.

ABSTRACT In the southern Caribbean, there are two main upwelling areas, the Colombian Guajira and eastern Venezuela. However, fishing production is highly dissimilar, even though in the Guajira the wind intensity is stronger and theoretically the upwelling is more intense. For this reason, it should have a higher fishing production than Venezuela, which is not the case. The possible reasons for this important difference are presented, detailing aspects related to wind, hydrography, nutrient concentration, phytoplankton biomass, continental shelf, river contribution, island presence and other factors. Eastern Venezuela has greater fertility and fishing production because the Subtropical Subsuperficial Water mass is what supplies the water upwelling during the first months of the year (dry season). In the second semester, when the upwelling relaxes, the area is enriched with organic matter from the Orinoco River and the contribution of phytoplankton biomass from coastal lagoons, inlets, and partially closed bays. The wide extension of the continental shelf, with the presence of archipelagos, large islands, and islets that cause local enrichment and the plankton concentration and retention also plays a fundamental role. The latter increases biological productivity and support plankton reproduction. On the other hand, Colombian Guajira upwelling water may be influenced by the Darien Countercurrent, which, by its origin, should be poor in inorganic nutrients; furthermore, this region lacks important rivers that contribute organic matter and the Guajira continental shelf is rather narrow and does not contain islands that may help to increase aquatic productivity. In order to understand Guajira upwelling it is necessary to follow its hydrography in situ, as well as inorganic nutrients, chlorophyll, and phytoplankton and zooplankton abundances.

ABSTRACT. The seasonal variability of gelatinous zooplankton (siphonophores, medusae, and thaliaceans) abundance was investigated at Cabo Pulmo National Park (CPNP) from weekly zooplankton samples collected throughout 2014. The Gulf of California had prolonged warming during 2009-2019, with 2014 as the anomalously warm year preceding El Niño 2015-2016 compared to the 2003-2020 SST time series. Gelatinous zooplankton accounted <1% of the entire zooplankton community abundance at CPNP during 2014, suggesting a low influence of predation pressure upon their zooplanktonic and micronekton preys. Siphonophores (57%), thaliaceans (42%), and medusae (1%) were present throughout the year. The abundance of gelatinous zooplankton had a significant negative association with sea surface temperature and a positive association with sea surface chlorophyll-a concentration and velocity and direction of the wind, increasing their abundance during October after the hurricane season. The gelatinous zooplankton species assemblage at the coastal CPNP was similar but less abundant than the gelatinous zooplankton species assemblage observed in the oceanic region of the southern Gulf of California during summer 2014. Tropical species Diphyes dispar, Abylopsis tetragona, Chelophyes contorta, and Thalia spp. numerically dominated the gelatinous zooplankton community associated with a regional heatwave period recorded during 2014. A high proportion of tropical zooplankton indicates that mesotrophic conditions sustain the current high biomass and diversity of nektonic and benthonic planktophagous fauna inhabiting CPNP. However, prolonged warming events might decrease zooplankton biomass in the southern region of the Gulf of California in the future.