Clumpy coexistence in phytoplankton : the role of functional similarity in community assembly

Emergent neutrality (EN) suggests that species must be sufficiently similar or sufficiently different in their niches to avoid interspecific competition. Such a scenario results in a transient pattern with clumps and gaps of species abundance along the niche axis (e.g. represented by body size). From this perspective, clumps are groups of coexisting species with negligible fitness differences and stochastic abundance fluctuations. Plankton is an excellent model system for developing and testing ecological theories, especially those related to size structure and species coexistence. We tested EN predictions using the phytoplankton community along the course of a tropical river considering 1) body size structure, 2) functional clustering of species in terms of morphology-based functional groups (MBFG) and 3) the functional similarity among species concerning their functional traits. Two main clumps in the body size axis (clump I and II) were conspicuous through time and were detected in different stretches of the river. Clump I comprised medium-sized species from the MBFGs IV, V and VI while clump II included large-bodied species from the MBFGs V and VI. Pairwise differences in species biovolume correlated with species functional similarity when the whole species pool was considered, but not among species within the same clump. Although clumps comprised multiple MBFGs, the dominant species within the clump belonged always to the same MBFG. Also, within-clump species biovolume increased with functional distinctiveness considering both seasons and stretches, except the lower course. These results suggest that species within clumps behave in a quasi-neutral state, but even minor shifts in trait composition may affect species biovolume. Our findings point that EN belongs to the plausible mechanisms explaining community assembly in river ecosystems.Peer reviewe

Downstream transport processes modulate the effects of environmental heterogeneity on riverine phytoplankton

Environmental heterogeneity (EH) in space and time promotes niche-partition, which leads to high variation in biological communities, such as in algae. In streams, EH is highly related to the intensity of the water flow and may lead to community variation mainly during the low flow conditions. Despite the wide knowledge on the responses of phytoplankton communities to EH in lentic and semi-lentic systems, studies of riverine phytoplankton community variation are still scarce. Here, we first investigated the relationship between phytoplankton community variation and EH in different courses of the river and between seasons. We expected that under low or intermediate flow conditions, there is a positive correlation between community variation and EH. Alternatively, we did not expect any relationship between EH and community variation under high flow condition because stronger downstream transport would mask environmental filtering. We sampled nine sites monthly (May 2012 to April 2013) in a tropical river of Brazilian Southeast. We calculated EH from abiotic data whereas for community variation, here community distinctiveness (CD), we used Sorensen (CDSor) and Bray-Curtis (CDBray) dissimilarities. Differences in EH, CDSor and CDBray were tested at between-season and among-course levels. We found lower distinctiveness during the dry season when EH was the highest. Contrastingly, phytoplankton CD was the highest even when EH was low during the wet season. We found that this pattern raised from the increasing in individuals dispersal during the wet season, promoting mass effects. Finally, our results thus reject the first hypothesis and show a negative relationship between EH and distinctiveness. However, results support our alternative hypothesis and show that during the wet season, distinctiveness is not driven by EH. These results provide new insights into how EH drives community variation, being useful for both basic research about riverine algal communities and biomonitoring programs using phytoplankton communities as bioindicators. (C). 2019 Elsevier B.V. All rights reserved.Peer reviewe

A CONTRIBUIÇÃO DA PALEONTÓLOGA LÉLIA DUARTE PARA A COLEÇÃO DE VEGETAIS FÓSSEIS DO DEPARTAMENTO DE BIOLOGIA DA UERJ

A coleção de vegetais fósseis do Departamento de Biologia Vegetal, no Instituto de Biologia Roberto Alcantara Gomes, da Universidade do Estado do Rio de Janeiro (UERJ) foi organizada e mantida por muitos anos pela professora e paleobotânica Lélia Duarte. Nesta coleção há exemplares fósseis procedentes de várias unidades litoestratigráficas do Brasil. Sugere-se aqui a criação da Coleção Paleobotânica Lélia Duarte em homenagem a esta ilustre pesquisadora, e neste trabalho pretende-se tornar acessível esta coleção de vegetais fósseis relacionando os principais exemplares depositados, dentre os 370 exemplares que a compõe. DOI:  http://dx.doi.org/10.14295/cad.cult.cienc.v14i2.105

FLORAÇÕES DE CIANOBACTÉRIAS TÓXICAS EM UMA LAGOA COSTEIRA HIPEREUTRÓFICA DO RIO DE JANEIRO/RJ (BRASIL) E SUAS CONSEQUÊNCIAS PARA SAÚDE HUMANA

revista vol 13 nº 2.indd The Jacarepaguá Basin, Rio de Janeiro, Brazil has over the last four decades undergone a disordered process of urban and industrial growth with direct consequences on water quality and incidence of cyanobacterial blooms in the Jacarepaguá Lagoon Complex (JLC). The present study combines data aiming to evaluate water quality in Jacarepaguá Lagoon (JL) from monitoring of physical variables (pH, water transparency, temperature), chemical variables (salinity, dissolved oxygen, chlorophyll), the planktonic community, and the concentration of microcystins in fish from the region. The data herein presented were divided into three periods according to seasonal cycles: PI (aug/96 to sep/97), PII (jan/99 to nov/99), and PIII (feb/07 to jan/08). Dominance by cyanobacteria characterized most of the study period, interspersed with sudden peaks (e.g. during PII and PIII) of high diversity of phytoplankton. Phytoplanktonic peaks were represented by Chlorophyta, diatoms, Prasinophyta and Criptophyta. Interestingly, the events observed in 1999 repeated almost 10 years later, suggesting roughly seasonal community structure dynamism in the JLC. Disappearance of the bloom coincided with the lowest recorded water temperatures, suggesting that temperature is an important factor in the observed dynamics. The JL had a high abundance of zooplankton, yet species diversity was relatively low. Concentrations of microcystins found in muscles of fish from JL often contained values above the levels recommended by OMS for human consumption.  revista vol 13 nº 2.indd La Cuenca de Jacarepaguá (RJ/Brasil) ha sufrido, en las últimas cuatro décadas, un proceso desordenado de ocupación urbana e industrial, que se refleja en un cambio en la calidad del agua y en la incidencia de floraciones de las cianobacterias en el Complejo Lagunar Jacarepaguá (CLJ). El presente estudio reúne una serie de datos con el objeto de evaluar la calidad del Lago Jacarepaguá (LJ), a través del monitoreo físico (pH, transparencia del agua y temperatura), químico (salinidad, O.D. y clorofila a) y de la comunidad planctónica. También fue analizada la concentración de microcistinas en pescados comercializados en la región. Los datos fueron divididos en tres períodos de acuerdo con los diferentes ciclos estacionales estudiados: PI (ago/96 a sept/07), PII (ene/99 a nov/99) y PIII (feb/07 a ene/08). La dominancia de cianobacterias ocurre en la mayor parte del período de estudio, intercalada con pulsos de mayor diversidad fitoplanctónica, observada desde 1999 (PII y PIII). Dicha diversidad estuvo representada por las clorofíceas, diatomeas, prasinoficeas y criptoficeas. Cabe destacar que la dinámica observada en 1999 se repitió casi 10 años después, lo que sugiere una tendencia estacional para la estructura de la comunidad del CLJ. La desaparición de la floración coincide con épocas de bajas temperaturas sugiriendo que ésta es un factor regulador importante de la dinámica observada. El LJ presentó una elevada abundancia zooplanctónica, con baja diversidad de especies. Durante algunos meses, las concentraciones de microcistinas encontradas en los músculos de los peces estuvieron por encima de los valores recomendados por la OMS para el consumo humano.A baixada de Jacarepaguá (RJ/Brasil) vem sofrendo há pelo menos quatro décadas um processo desordenado de ocupação urbana e industrial, o que tem se refletido em mudança na qualidade da água e na incidência de florações de cianobactérias no Complexo Lagunar de Jacarepaguá (CLJ). O presente estudo reuniu uma série de dados temporais objetivando avaliar a qualidade hídrica da Lagoa de Jacarepaguá (LJ) através do monitoramento físico (pH, transparência da água e temperatura), químico (salinidade, O.D. e clorofila a) e da comunidade planctônica. Foi também analisado a concentração de microcistinas no pescado comercializado na região. Os dados foram divididos em três períodos de acordo com os diferentes ciclos sazonais estudados: PI (ago/96 a set/97), PII (jan/99 a nov/99) e PIII (fev/07 a jan/08). Dominância de cianobactérias ocorreu na maior parte do tempo, intercalada por pulsos de maior diversidade fitoplanctônica, observados a partir de 1999 (PII e III). Esta diversidade foi representada pelas clorofíceas, diatomáceas, prasinoficeas e criptoficeas. Foi interessante notar que a dinâmica observada em 1999 tenha se repetido quase 10 anos depois, o que sugere uma tendência sazonal de estruturação da comunidade no CLJ. O desaparecimento da floração coincidiu com épocas de menores temperaturas, sugerindo ser esse um importante fator regulador da dinâmica observada. A LJ apresentou uma elevada abundância zooplanctônica, com baixa diversidade de espécies. Durante alguns meses, as concentrações de microcistinas encontradas nos músculos dos peixes estiveram acima dos valores recomendados pela OMS para consumo humano

Assessment of the Effects of Light Availability on Growth and Competition Between Strains of Planktothrix agardhii and Microcystis aeruginosa

In this study, we tested the hypothesis that Planktothrix agardhii strains isolated from a tropical water body were better competitors for light than Microcystis aeruginosa strains. These cyanobacteria are common in eutrophic systems, where light is one of the main drivers of phytoplankton, and Planktothrix is considered more shade-adapted and Microcystis more high-light tolerant. First, the effect of light intensities on growth was studied in batch cultures. Next, the minimum requirement of light (I*) and the effect of light limitation on the outcome of competition was investigated in chemostats. All strains showed similar growth at 10 μmol photons m−2 s−1, demonstrating the ability of the two species to grow in low light. The optimum light intensity was lower for P. agardhii, but at the highest light intensity, Microcystis strains reached higher biovolume, confirming that P. agardhii has higher sensitivity to high light. Nonetheless, P. agardhii grew in light intensities considered high (500 μmol photons m−2 s−1) for this species. M. aeruginosa showed a higher carrying capacity in light-limited condition, but I* was similar between all the strains. Under light competition, Microcystis strains displaced P. agardhii and dominated. In two cases, there was competitive exclusion and in the other two P. agardhii managed to remain in the system with a low biovolume (≈15 %). Our findings not only show that strains of P. agardhii can grow under higher light intensities than generally assumed but also that strains of M. aeruginosa are better competitors for light than supposed. These results help to understand the co-occurrence of these species in tropical environments and the dominance of M. aeruginosa even in low-light conditions

Assessment of possible solid-phase phosphate sorbents to mitigate eutrophication : Influence of pH and anoxia

Managing eutrophication remains a challenge to water managers. Currently, the manipulation of biogeochemical processes (i.e., geo-engineering) by using phosphorus-adsorptive techniques has been recognized as an appropriate tool to manage the problem. The first step in finding potential mitigating materials is conducting a sequence of upscaling studies that commence with controlled laboratory experiments. Here, the abilities of 10 possible solid–phase-sorbents (SPS) to adsorb P were examined. Four materials adsorbed P, and two of these materials were modified, i.e., a lanthanum-modified-bentonite (LMB) and an aluminum-modified-zeolite (AMZ), and had the highest adsorption capacities of 11.4 and 8.9 mg P g− 1, respectively. Two natural materials, a red soil (RS) and a bauxite (BAU), were less efficient with adsorption capacities of 2.9 and 3.4 mg P g− 1, respectively. Elemental composition was not related to P adsorption. Since SPS might be affected by pH and redox status, we also tested these materials at pH values of 6, 7, 8 and 9 and under anoxic condition. All tested materials experienced decreased adsorption capacities under anoxic condition, with maximum adsorptions of 5.3 mg P g− 1 for LMB, 5.9 mg P g− 1 for AMZ, 0.2 mg P g− 1 for RS and 0.2 mg P g− 1 for BAU. All materials were able to adsorb P across the range of pH values that were tested. The maximum adsorption capacities of LMB and RS were highest at pH 6, AMZ was higher at a pH of 9 and BAU at a pH of 8. Thus, pH influenced P adsorption differently. Given the effects of pH and anoxia, other abiotic variables should also be considered. Considering the criteria that classify a useful SPS (i.e., effective, easy to produce, cheap and safe), only the two modified materials that were tested seem to be suitable for upscaling to enclosure studies with anoxic sediments.</p

Increasing Temperature Counteracts the Negative Effect of UV Radiation on Growth and Photosynthetic Efficiency of Microcystis aeruginosa and Raphidiopsis raciborskii

High temperature can promote cyanobacterial blooms, whereas ultraviolet radiation (UVR) can potentially depress cyanobacterial growth by damaging their photosynthetic apparatus. Although the damaging effect of UVR has been well documented, reports on the interactive effects of UV radiation exposure and warming on cyanobacteria remain scarce. To better understand the combined effects of temperature and UVR on cyanobacteria, two strains of nuisance species, Microcystis aeruginosa (MIRF) and Raphidiopsis raciborskii (formerly Cylindrospermopsis raciborskii, CYRF), were grown at 24°C and 28°C and were daily exposed to UVA + UVB (PAR + UVA+UVB) or only UVA (PAR + UVA) radiation. MIRF and CYRF growth rates were most affected by PAR + UVA+UVB treatment and to a lesser extent by the PAR + UVA treatment. Negative UVR effects on growth, Photosystem II (PSII) efficiency and photosynthesis were pronounced at 24°C when compared to that at 28°C. Our results showed a cumulative negative effect on PSII efficiency in MIRF, but not in CYRF. Hence, although higher temperature ameliorates UVR damage, interspecific differences may lead to deviating impacts on different species, and combined elevated temperature and UVR stress could influence species competition.</p

Response of Natural Cyanobacteria and Algae Assemblages to a Nutrient Pulse and Elevated Temperature

Eutrophication (nutrient over-enrichment) is the primary worldwide water quality issue often leading to nuisance cyanobacterial blooms. Climate change is predicted to cause further rise of cyanobacteria blooms as cyanobacteria can have a competitive advantage at elevated temperatures. We tested the hypothesis that simultaneous rise in nutrients and temperature will promote cyanobacteria more than a single increase in one of the two drivers. To this end, controlled experiments were run with seston from 39 different urban water bodies varying in trophic state from mesotrophic to hypertrophic. These experiments were carried out at two different temperatures, 20 °C (ambient) and 25 °C (warming scenario) with or without the addition of a surplus of nutrients (eutrophication scenario). To facilitate comparisons, we quantified the effect size of the different treatments, using cyanobacterial and algal chlorophyll a concentrations as a response variable. Cyanobacterial and algal chlorophyll a concentrations were determined with a PHYTO-PAM phytoplankton analyzer. Warming caused an 18% increase in cyanobacterial chlorophyll-a, while algal chlorophyll-a concentrations were on average 8% higher at 25ºC than at 20ºC. A nutrient pulse had a much stronger effect on chlorophyll-a concentrations than warming. Cyanobacterial chlorophyll-a concentrations in nutrient enriched incubations at 20ºC or 25ºC were similar and , but had been increased 900% compared9 times higher than to in the incubations at 20ºC without nutrient pulse. Likewise, algal chlorophyll-a concentrations increased by 600%were 6 times higher. The results of this study confirm that warming alone yields marginally highermore cyanobacteria chlorophyll-a concentrations, yet that a pulse of additional nutrients is boosting blooms. The responses of seston originating from mesotrophic waters seemed less strong than those from eutrophic waters, which indicates that nutrient control strategies –catchment as well as in-system measures– could increase the resilience of surface waters to the negative effects of climate change

Cyanobacteria dominance drives zooplankton functional dispersion

Accelerated eutrophication reduces water quality and shifts plankton communities. However, its effects on the aquatic food web and ecosystem functions remain poorly understood. Within this context, functional ecology can provide valuable links relating community traits to ecosystem functioning. In this study, we assessed the effects of eutrophication and cyanobacteria blooms on zooplankton functional diversity in a tropical hypereutrophic lake. Phytoplankton and zooplankton communities and limnological characteristics of a tropical Brazilian Lake (Southeast, Brazil) were monitored monthly from April 2013 to October 2014. Lake eutrophication indicators were total phosphorus, total chlorophyll-a, and chlorophyll-a per group (blue, green, and brown). The variation of major phytoplankton taxonomic group biomass was calculated and used as a proxy for changes in phytoplankton composition. Zooplankton functional diversity was assessed through functional dispersion and the community-weighted mean trait value. Regressions were performed between the lake eutrophication indicators, the phytoplankton biomass variation, and zooplankton functional dispersion. Our results suggest that eutrophication and cyanobacterial dominance change the composition of zooplankton traits and reduce functional dispersion, leading to zooplankton niche overlap. These findings are important because they provide a meaningful view of phytoplankton-zooplankton trophic interactions and contribute to an improved understanding their functional effects on aquatic ecosystems.</p

Lanthanum in Water, Sediment, Macrophytes and chironomid larvae following application of Lanthanum modified bentonite to lake Rauwbraken (The Netherlands)

Lanthanum Modified Bentonite (LMB; Phoslock®) is used to mitigate eutrophication by binding phosphate released from sediments. This study investigated the fate of lanthanum (La) from LMB in water, sediment, macrophytes, and chironomid larvae in Lake Rauwbraken (The Netherlands). Before the LMB application, water column filterable La (FLa) was 0.02 µg L−1, total La (TLa) was 0.22 µg L−1. In sediment the total La ranged 0.03–1.86 g m−2. The day after the application the maximum FLa concentration in the water column was 44 µg L−1, TLa was 528 µg L−1, exceeding the Dutch Maximum Permissible Concentrations (MPC) of 10.1 µg L−1 by three to fourfold. TLa declined below the MPC after 15 days, FLa after 75 days. After ten years, FLa was 0.4 µg L−1 and TLa was 0.7 µg L−1. Over the post-application years, FLa and TLa showed statistically significant downward trends. While the LMB settled homogeneously on sediment, after 3 years it redistributed to 0.2–5.4 g La m−2 within shallow zones, and 30.7 g m−2 to 40.0 g La m−2 in deeper zones. In the upper 20 cm of sediment, La concentrations were 7–6702 mg kg −1 dry weight (DW) compared to 0.5–7.0 mg kg−1 before application. Pre-application anaerobic sediment release of FLa was 0.006 mg m−2 day−1. Three months after the application it was 1.02 mg m−2 day−1. Three years later it was 0.063 mg m−2 day−1. Before application La in plants was 0.8–5.1 mg La kg−1 DW, post-application values were up to 2925 mg La kg−1 DW. In chironomid larvae, La increased from 1.7 µg g−1 DW before application to 1421 µg g−1 DW after one month, 3 years later it was 277 µg g−1 DW. Filtration experiments indicate FLa is not truly dissolved free La3+ cations.</p