Jean Louis Valentin

Numerical modelling of phytoplankton bloom in the upwelling ecosystem of Cabo Frio (Brazil)

Abstract The phenomenon of phytoplankton bloom during upwelling events in the coastal region of Cabo Frio (Brazil), is investigated using a 1 1 2 ocean model including the physics of coastal waters and the biological changes of the marine primary biomass. The vertical structure of the coupled, physical–biological model is described by an active layer overlaying a deep inert layer where the pressure gradient is set to zero. The physical model describes the changes of momentum, mass and heat in the dynamic layer and is forced by wind acting at the surface. The biological model describes the changes of its three components (nutrients, phytoplankton and zooplankton) and is forced by the primary biomass concentration injected into the upper layer as a consequence of upwelling favorable winds and by the light producing the photosynthesis of the phytoplankton. Coupling is established by the horizontal-velocity, layer-thickness and upwelling velocity fields from the physical solution. The equations are solved numerically in space and time by the finite difference method. Model results forced by transient winds are arranged initially for a standard run causing coastal upwelling. During the spin-up of winds, the nutrient, phytoplankton and zooplankton concentrations are injected into the upper layer by upwelling. Consequently a maximum of nutrients takes place (generated by the nutrient injection), decreasing from the increasing assimilation by phytoplankton and by reduction of nutrients supply (spin-down stage of winds). One day after the maximum of nutrients takes place, the phytoplankton bloom occurs with amplitude and duration similar to that observed in this region. This bloom is very short due the increase of grazing by zooplankton. The results of the standard run, reproduce observed features of physical and biological fields during upwelling events; in particular, the time dependent pattern of the short-lived phytoplankton bloom, suggesting that the physical–biological model presented here, contains much of this important time-dependent phenomenon. Experiments indicate that the change of transient wind duration affects the time response of the biological components, changing the instant of the maximum of nutrients concentration, but keeping unchanged the instant of maximum of phytoplankton. The reduction of the constant of optimum photosynthesis rate affects the bloom of phytoplankton delaying it and reducing its amplitude. Experiments indicate that the maximum grazing rate is an important factor in limiting the persistence and amplitude of the phytoplankton bloom.

Spatial structure of the zooplankton community in the Cabo Frio region (Brazil) influenced by coastal upwelling

Cabo Frio area (Central-southern Brazilian littoral) is characterized by a coastal upwelling due to prevailing E-NE winds, mainly during the spring-summer season.The geographic distribution of the zooplankton was described in order to separate ecological areas in terms of specific communities. Cluster analysis by weighted pair-group method (WPGA) and principal component (PC) analysis was performed on the most important hydrological parameters and zooplankton taxa. The first PC, explaining 38% of the total zooplankton variability, represented the influence of the nearshore-offshore gradient. Zooplankton communities and ecological areas were defined as follows:i)nearshore neritic: the richest region with more than 5 000 org. m-3. In this very narrow nearshore region we observed 3 groups of taxa deliminated by upwelling effects and trophic conditions: a) Ctenocalanus vanus, Penilia avirostris, Calanoides carinatus and Copepod larva, all herbivorous species associated with the phytoplankton blooms in the upwelling zone; b) Creseis acicula and Temora stylifera; c) Siphonophora, Chaetognaths and a high diversity of Copepoda dominated by Coryceus amazonicus, C. giesbrechti, Eucalanus pileatus, Clausocalanus acuicornis, all carnivorous or omnivorous feeders representing a high degree of complexity of the ecosystem.ii)offshore neritic: characterized by appendicularians, this region constitutes an intermediate zone between coastal and oceanic waters.iii)oceanic: occupied by the Brazil Current where zooplankton is poor, but diversified, with typical copepods from tropical warm water: Clausocalanus furcatus, Mecynocera clausi, Corycella gracilis, Oithona setigera, Coryceus typicus, Oncea conifera, Undinula vulgaris, Calocalanus pavo, Haloptilus longicornis, Lucicutia flavicornis.

Structuring of bacterioplankton diversity in a large tropical bay.

Structuring of bacterioplanktonic populations and factors that determine the structuring of specific niche partitions have been demonstrated only for a limited number of colder water environments. In order to better understand the physical chemical and biological parameters that may influence bacterioplankton diversity and abundance, we examined their productivity, abundance and diversity in the second largest Brazilian tropical bay (Guanabara Bay, GB), as well as seawater physical chemical and biological parameters of GB. The inner bay location with higher nutrient input favored higher microbial (including vibrio) growth. Metagenomic analysis revealed a predominance of Gammaproteobacteria in this location, while GB locations with lower nutrient concentration favored Alphaproteobacteria and Flavobacteria. According to the subsystems (SEED) functional analysis, GB has a distinctive metabolic signature, comprising a higher number of sequences in the metabolism of phosphorus and aromatic compounds and a lower number of sequences in the photosynthesis subsystem. The apparent phosphorus limitation appears to influence the GB metagenomic signature of the three locations. Phosphorus is also one of the main factors determining changes in the abundance of planktonic vibrios, suggesting that nutrient limitation can be observed at community (metagenomic) and population levels (total prokaryote and vibrio counts).

Environmental and Sanitary Conditions of Guanabara Bay, Rio de Janeiro.

Guanabara Bay is the second largest bay in the coast of Brazil, with an area of 384 km2. In its surroundings live circa 16 million inhabitants, out of which 6 million live in Rio de Janeiro city, one of the largest cities of the country, and the host of the 2016 Olympic Games. Anthropogenic interference in Guanabara Bay area started early in the XVI century, but environmental impacts escalated from 1930, when this region underwent an industrialization process. Herein we present an overview of the current environmental and sanitary conditions of Guanabara Bay, a consequence of all these decades of impacts. We will focus on microbial communities, how they may affect higher trophic levels of the aquatic community and also human health. The anthropogenic impacts in the bay are flagged by heavy eutrophication and by the emergence of pathogenic microorganisms that are either carried by domestic and/or hospital waste (e.g., virus, KPC-producing bacteria, and fecal coliforms), or that proliferate in such conditions (e.g., vibrios). Antibiotic resistance genes are commonly found in metagenomes of Guanabara Bay planktonic microorganisms. Furthermore, eutrophication results in recurrent algal blooms, with signs of a shift toward flagellated, mixotrophic groups, including several potentially harmful species. A recent large-scale fish kill episode, and a long trend decrease in fish stocks also reflects the bay’s degraded water quality. Although pollution of Guanabara Bay is not a recent problem, the hosting of the 2016 Olympic Games propelled the government to launch a series of plans to restore the bay’s water quality. If all plans are fully implemented, the restoration of Guanabara Bay and its shores may be one of the best legacies of the Olympic Games in Rio de Janeiro.

Dynamic of decapod crustacean larvae on the entrance of Guanabara bay

In the present study, we observed seasonal variations in the density of decapod larvae as well as changes in density related to diurnal and tidal cycles. Among the decapod larvae collected, portunids and grapsids were the most abundant, especially during nocturnal ebb tides and near the surface. The same results were obtained in late winter (September) and late summer (March). These results demonstrated a flow of decapod larvae from Guanabara Bay to adjacent coastal waters. Luciferid (Lucifer faxoni) was the only group with high densities during flood tides and we suggest this is an evidence of L. faxoni larvae entering Guanabara Bay in late winter. Probably these changes in distribution of Lucifer faxoni among winter and summer were related to reproductive cycle in the bay. For the portunids, grapsids and ocypodids, a similar dispersion strategy was observed towards adjacent coastal waters in the surface during nocturnal ebb tides.

Seasonal variation in fish larvae at the entrance of Guanabara Bay, Brazil

Devido a crescente acao antropica a qual esta sujeita e sua importância socio-economica, a baia de Guanabara vem despertando grande interesse na comunidade cientifica. O presente trabalho objetivou analisar a variacao quali-quantitativa temporal das larvas de peixes, relacionar a densidade das larvas com o ciclo nictemeral e verificar a influencia dos ciclos de mare. Foram realizadas coletas, em um ponto localizado na entrada da baia, em setembro de 1995 e marco de 1996. As coletas ocorreram nas mares de enchente e vazante ao longo de tres dias. Os arrastos foram obliquos, utilizando uma rede do tipo bongo com malhas de 500 µm. Foi coletado um total de 42 taxons. As familias Engraulidae (Cetengraulis edentulus e Anchoa lyolepis) e Clupeidae (Harengula jaguana) ocorreram em grandes densidades e dominaram nas duas campanhas. As maiores densidades de larvas de peixes ocorreram durante a campanha de marco, que apresentou altas temperaturas e baixas salinidades. Observou-se um padrao nictemeral em relacao a abundância de larvas, com altas densidades durante a noite e baixas durante o dia. Os altos indices de diversidade encontrados ressaltam a importância desse ecossistema para varias especies de peixes.

Modelling maximum chlorophyll in the Cabo Frio (Brazil) upwelling: a preliminary approach

Abstract The Cabo Frio area (Central-southern Brazilian littoral) is characterized by a coastal upwelling due to prevailing E-NE winds, mainly during the spring-summer season. This upwelling which has been studied for the last 15 years, is a local phenomenon with phytoplankton bloom of less than 1 day, and low intensity (max. 6 μg 1 −1 of chlorophyll a ) but relatively important for this tropical region. The objective of this study is to start the development of an upwelling model for the Cabo Frio ecosystem. Our approach was to simulate a chlorophyll peak during an upwelling event. Measurements of wind, current, water temperature, nitrate and chlorophyll a were made during 5 days at a fixed station every four hours. All simulations were performed on a McIntosh Plus computer, using the Stella program. A conceptual diagram included as state variables chlorophyll amount (values ranging from 0.48 to 5.50 μg 1 −1 ), nitrate (11.0−0.4 μM 1 −1 ) and water temperature (15.5–21.5°C). The flows used were growth rate ( V max ) as a Michaelis-Menten function of nitrate, and a sinusoidal function of time ( V max ranging from 0 to 0.15 h −1 ), and mortality rate varying from 0 to 0.10 h −1 . These values were obtained from the literature or calculated from data of Cabo Frio upwelling. The model simulated accurately the chlorophyll maximum observed after 3 days. The best results of simulation are obtained by considering the advection factor and the mortality rate (grazing) as function of zooplankton abundance.

Spatial and temporal variations of Penilia avirostris and Evadne tergestina (Crustacea, Branchiopoda) in a Tropical Bay, Brazil

We analysed monthly samples collected in Guanabara Bay, with a conical net of 200 μm mesh during 1985. The bay was divided into three areas: an outer region (area A), influenced by oceanic waters; an inner region (area C), influenced by fluvial inflow; and a transition region (area B) with intermediate features. Penilia avirostris and Evadne tergestina were observed in the three areas, with greatest densities, however, in the outermost region, which had the highest salinities and lowest temperatures. Penilia avirostris was more abundant in summer (March), a period with the greatest relative densities of nanoplankton. Evadne tergestina was also abundant in summer, but its peak fell in November, a period with a relative increase in microphytoplankton density in the bay. The two species disappeared in winter: Penilia avirostris was absent from May to August, whereas Evadne tergestina disappeared in August and September.

DISTRIBUTION OF HNA AND LNA BACTERIAL GROUPS IN THE SOUTHWEST ATLANTIC OCEAN

Um estudo do bacterioplâncton foi realizado numa area extensa do Oceano Atlântico Sudoeste entre 13 e 25oS e 28 e 42oW. As amostras foram coletadas em 108 estacoes oceanograficas a 20 m de profundidade. A abundância bacteriana foi determinada por citometria de fluxo apos coloracao dos acidos nucleicos com Syto13. Dois grupos de bacterias foram enumerados e distinguidos: bacterias com alto conteudo de acidos nucleicos (HNA) e bacterias com baixo conteudo de acidos nucleicos (LNA). O numero de bacterias variou de 0,37 a 5,53 105 celulas mL-1. As celulas HNA representaram de 15 a 70% da abundância total enquanto as celulas LNA representaram de 30 a 85%. A producao bacteriana foi determinada por incorporacao de leucina tritiada e variou de 2,7 a 171,07 ng C L-1 h-1. A correlacao entre abundância e producao bacterianas nao foi significativa. Entretanto uma analise multivariada realizada entre abundância, producao, clorofila a e outros dados oceanograficos revelou que a distribuicao dos dois grupos em diferentes provincias oceânicas pode ser atribuida a disponibilidade de nutrientes. As bacterias HNA foram responsaveis pelo maior percentual de celulas na area ao norte de 19oS e estiveram relacionadas as aguas quentes e aos nutrientes de origem pluvial. As bacterias LNA foram dominantes ao sul dessa latitude e estiveram relacionadas a disponibilidade de nitrato cujos valores foram mais altos nessa regiao.

Factors influencing spatial patterns of molluscs in a eutrophic tropical bay

r.a.f. neves, c.a. echeverria, l.a. pessoa, p.c. paiva, r. paranhos and j.l. valentin Programa de Pós-Graduação em Ecologia, Departamento de Ecologia, Instituto de Biologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, CEP 21941-902, Brazil, Laboratório de Pesquisas Costeiras e Estuarinas, Núcleo Interdisciplinar UFRJ-Mar, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil, Instituto Virtual Internacional de Mudanças Globais (IVIG–COPPE, UFRJ), Instituto Alberto Luiz Coimbra de Pós-Graduação e Pesquisa de Engenharia, Universidade Federal do Rio de Janeiro, Brazil, Programa de Pós-Graduação em Biologia Marinha, Departamento de Biologia Marinha, Instituto de Zoologia, Universidade Federal Fluminense, Laboratório de Polychaeta, Departamento de Zoologia, Instituto de Biologia, Universidade Federal do Rio de Janeiro, Laboratório de Hidrobiologia, Departamento de Biologia Marinha, Instituto de Biologia, Universidade Federal do Rio de Janeiro, Laboratório de Zooplâncton Marinho, Departamento de Biologia Marinha, Instituto de Biologia, Universidade Federal do Rio de Janeiro