Cyanotoxins: Bioaccumulation and Effects on Aquatic Animals

Cyanobacteria are photosynthetic prokaryotes with wide geographic distribution that can produce secondary metabolites named cyanotoxins. These toxins can be classified into three main types according to their mechanism of action in vertebrates: hepatotoxins, dermatotoxins and neurotoxins. Many studies on the effects of cyanobacteria and their toxins over a wide range of aquatic organisms, including invertebrates and vertebrates, have reported acute effects (e.g., reduction in survivorship, feeding inhibition, paralysis), chronic effects (e.g., reduction in growth and fecundity), biochemical alterations (e.g., activity of phosphatases, GST, AChE, proteases), and behavioral alterations. Research has also focused on the potential for bioaccumulation and transferring of these toxins through the food chain. Although the herbivorous zooplankton is hypothesized as the main target of cyanotoxins, there is not unquestionable evidence of the deleterious effects of cyanobacteria and their toxins on these organisms. Also, the low toxin burden in secondary consumers points towards biodilution of microcystins in the food web as the predominant process. In this broad review we discuss important issues on bioaccumulation and the effects of cyanotoxins, with emphasis on microcystins, as well as drawbacks and future needs in this field of research

Effects of toxin-producing phytoplankton on copepods: feeding, reproduction and implications to the fate of toxins

Phytoplankton growth and loss rates are governed by several factors and in many cases, when growth control fails, algal blooms are established. Such blooms can be formed by different phytoplankton species and some of them have harmful impacts on marine ecosystems. One of these negative impacts by some bloom-forming phytoplankton is the ability to produce toxic or inhibitory compounds with broad effects on aquatic organisms. Harmful effects can also reach humans if food or water contaminated with toxins is consumed. Copepods are one of the most numerous consumers of phytoplankton in marine environments. These invertebrates can also obtain their nutrition from other food resources such as single cell animals (e.g. ciliates), which could be an important alternative under bloom conditions. The aims of this thesis were to assess 1) to which extent toxic or inhibitory phytoplankton is consumed (or avoided) by copepods; 2) whether ciliates and other food types could contribute to the diets of copepods when toxic food is present; 3) if copepods accumulate toxins and excrete them with faecal pellets when toxic phytoplankton is ingested; and 4) the effect of toxic diets on the reproductive success of copepods. Based on some of the results obtained, the role of cellular mechanisms in the detoxification of toxins from the ingested toxic diets was investigated. In addition, the importance of the transport of toxins via copepods to higher consumers such as fish was evaluated. In some cases, toxic phytoplankton was not consumed by copepods. In other cases, copepods fed actively upon toxic phytoplankton. Reproduction was not sustained if toxic phytoplankton was the only food available, or when compared to an adequate diet. This was related to a decrease in the numbers of oocytes produced or in the degree of maturation of these cells. Toxins were detected in copepods and in their faecal pellets after ingestion of the toxic cyanobacterium Nodularia spumigena. However, the amount of toxins found in the copepods was far lower than the amount of ingested toxins, which could indicate that copepods might have metabolic mechanisms to get rid of these compounds. High metabolic activity (GSH transferase activity) was, however, detected in well-fed copepods and not related with the ingestion of toxic food. More sensitive studies (e.g. at the molecular level) are needed. Calculations indicated that part of the phytoplankton toxins detected in the copepods could be transferred to fish populations in the Baltic Sea. In some cases, this toxin transfer could be low, but in others it could considerable and threaten both fish and humans. Therefore, frequent monitoring of phytoplankton toxins in fish stocks is needed to assure safe consumption of fish by us

Resilience of a zooplankton community subjected to marine intrusion in a tropical coastal lagoon

One of the main disturbances on Imboassica Lagoon is the occasional artificial opening of its sand bar. Following two such events, two environmental gradients were observed. One was directly related to entry of marine water ( salinity gradient); and the other to a decrease in dilution of the nutrient load, because of water level reduction ( trophic status gradient). Two stations were sampled. At Station 1, located near the sand bar, salinity increase caused a decrease in the total zooplankton density and a shift in community composition due to a loss of relatively small individuals (i.e. rotifers) and the subsequent entrance of larger ones (i.e. copepods). High diversity was related to salinity increases. At Station 2, located near the mouth of a sewage canal, the total zooplankton abundance and dominance were related to the salinity increase, while the highest richness and the lowest dominance were obtained at a high trophic state. The zooplankton community showed high persistence and resilience, which together with other ecological features in the system, returned to the pre-disturbance state 2 months after the sand bar was closed. Canonical correspondence analysis was a useful tool to assess system resilience

Rotifers from a humic coastal lagoon of Rio de Janeiro State, Brazil

A four-year study of species composition of the zooplankton community was conducted at Lagoa Comprida, a coastal lagoon. Forty-two species of rotifers were recorded and illustrated. All rotifer species, except Lecane boettgeri Koste, 1986 and Macrochaetus kostei, Jose de Paggi, Branco & Kozlowsky-Suzuki, 2000, have already been found in other areas of Brazil. Some factors, which probably favored the dominant richness and density of rotifers in the zooplankton community, are discussed

Food selectivity and grazing impact on toxic Dinophysis spp. by copepods feeding on natural plankton assemblages

Food selectivity and grazing impact by Acartia bifilosa, Temora longicornis and Centropages typicus on Dinophysis spp. plankton assemblages were experimentally investigated in the Baltic Sea. Toxin analyses were carried out on phyto- and zooplankton-dominated size fractions from field-collected samples to assess if toxins produced by Dinophysis spp. would end up in the zooplankton. All copepod species fed,actively on toxic Dinophysis spp. (Dinophysis acuta and Dinophysis norvegica). Despite the non-selective feeding behaviour by T longicornis and C. typicus, selectivity coefficients on D. acuta progressively decreased as food availability increased. Similar response was not observed for A. bifilosa, which displayed an even less selective behaviour. A. bifilosa had no significant negative effect on the net growth of D. norvegica at the lowest food concentration offered, whereas T longicornis and C typicus had significant negative effects on the net growth of D. acuta at low concentrations, similar to those observed in situ. Both species could potentially contribute as a substantial loss factor for Dinophysis spp. provided they are abundant at the onset of the blooms. The estimated grazing impact by the copepod populations was only considerable when C typicus abundance was high and D. acuta population in sharp decline. Our results suggest that when high abundance of grazers and poor growth condition of prey populations prevail, grazing impact by copepods can contribute considerably to prevent Dinophysis spp. populations to grow or to cause the populations to decline. Okadaic acid was detected in the zooplankton size fraction at one occasion, but the concentration was far lower than the one expected from the ingested toxins. Thus, even if copepods may act as vectors of DSP-toxins to higher trophic levels, the amount of these toxins transported in the food web by copepods seems limited. (C) 2005 Elsevier B.V. All rights reserved

Rotifers from a humic coastal lagoon of Rio de Janeiro State, Brazil

A four-year study of species composition of the zooplankton community was conducted at Lagoa Comprida, a Brazilian coastal lagoon. Forty-two species of rotifers were recorded and iIIustrated. Ali rotifer species, except Lecane boettgeri Koste, 1986 and Macrochaetus kostei, José de Paggi, Branco & Kozlowsky-Suzuki, 2000, have already been found in other areas of Brazil. Some factors, which probably favored the dominant richness and density of rotifers in the zooplankton community, are discussed. Keywords: Rotifer assemblage, zooplankton, humic coastal lagoon, Comprida Lagoon, Neotropics, Hexanhra longicorniculaFil: Branco, Christina W. C.. Universidade Federal Do Estado Do Rio de Janeiro.; BrasilFil: Kozlowsky-Suzuki, Betina. Lund University; SueciaFil: Jose, Susana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentin

Comprehensive Meta-Analysis of Pathways to Increase Biogas Production in the Textile Industry

The textile industry is one of the largest environmental polluters in the world. Although waste management via anaerobic digestion (AD) is a sustainable strategy to transform waste into clean energy and water recovery, the efficiency of the AD process is reduced by the presence of recalcitrant materials, chemicals, and toxic contents. This study aims to investigate the performance of several chemical, physical, and biological pretreatments applied to improve the biodegradability of textile waste. We performed a meta-analysis with 117 data extracted from 13 published articles that evaluated the efficiency of pretreatments applied to textile waste prior to AD to increase biogas production measured as methane (CH4) yield. Even though the majority of the studies have focused on the effect of chemical and physical pretreatments, our results showed that the application of biological pretreatments are more efficient and eco-friendlier. Biological pretreatments can increase CH4 yield by up to 360% with lower environmental risk and lower operating costs, while producing clean energy and a cleaner waste stream. Biological pretreatments also avoid the addition of chemicals and favor the reuse of textile wastewater, decreasing the current demand for clean water and increasing resource circularity in the textile industry.Funding Agencies|Swedish Energy Agency [35624-2]; Formas [2021-02429]; Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior-Brasil (CAPES) [001]</p

Predicting temporal variation in zooplankton beta diversity is challenging

<div><p>Beta diversity, the spatial variation in species composition, has been related to different explanatory variables, including environmental heterogeneity, productivity and connectivity. Using a long-term time series of zooplankton data collected over 62 months in a tropical reservoir (Ribeirão das Lajes Reservoir, Rio de Janeiro State, Brazil), we tested whether beta diversity (as measured across six sites distributed along the main axis of the reservoir) was correlated with environmental heterogeneity (spatial environmental variation in a given month), chlorophyll-<i>a</i> concentration (a surrogate for productivity) and water level. We did not found evidence for the role of these predictors, suggesting the need to reevaluate predictions or at least to search for better surrogates of the processes that hypothetically control beta diversity variation. However, beta diversity declined over time, which is consistent with the process of biotic homogenization, a worldwide cause of concern.</p></div