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.

Feeding, reproduction and accumulation of cyanobacterial toxins by the calanoid copepods Acartia bifilosa and Eurytemora affinis were studied during a cruise in the northern Baltic Sea. The experiments were carried out using both mixtures of natural plankton communities, mixtures containing the toxic Nodularia spumigena, and diets containing only the toxic cyanobacterium. Both copepod species had a high survival and fed actively on N. spumigena, both as a single food source and when offered in mixtures. Feeding on N. spumigena resulted in the detection of nodularin equivalents in the animals. However, there was a negative relationship between the gross growth efficiency and accumulated toxins, which indicates that the food quality was not ideal, possibly related to a high metabolic cost to cope with ingested toxins. Overall low egg production rates by both species and low egg hatching success by A. bifilosa in natural seawater suggested that the copepods were food-limited in the environment. The presence of Brachiomonas submarina offered in combination with N. spumigena enhanced A. bifilosa egg production, but not egg hatching success. Egg hatching success was not affected by increasing concentrations of N. spumigena in the diet. Instead, lack of food seemed to be a more important factor. Similar responses by E. affinis populations from sites with different history of toxin occurrence suggest that tolerance to cyanobacterial toxins has evolved in the Baltic Sea. This has possibly been guaranteed by genetic exchange between the 2 populations. These results suggest that N. spumigena is not directly harmful to copepods if an alternative food source is available, even though reproduction is not sustained if the species is offered as a single diet. Moreover, even if both copepods might act as a link transporting toxins to higher trophic levels, a very small fraction of the estimated ingested toxin was found in the animals, therefore the relative importance of this pathway seems limited.

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The Imboassica lagoon, located in the Municipality of Macaé (RJ), is separated from the sea by a sand bar, and its surroundings are partially occupied by residential areas. This coastal lagoon has undergone environmental degradation due to sewage input and artificial sand bar openings. The temporal and spatial variation of environmental variables and zooplankton were studied monthly for four years. There were five artificial openings of the sand bar during the period of study, mostly in the rainy season. Besides osmotic changes, these events caused the drainage of the water of the lagoon into the sea, loss of total organic nitrogen, and an increase of total phosphorus. The zooplankton community of Imboassica lagoon included freshwater and marine taxa, holoplanktonic, meroplanktonic and nectobenthonic forms. Polychaeta, Bivalvia and Gastropoda larvae, and the taxa of Rotifera Hexarthra spp., Lecane bulla, Synchaeta bicornis, nauplii of Cyclopoida and Calanoida copepods were considered constant taxa. Distinct zooplankton assemblages were found during zooplankton spatial surveys in oligohaline and mesohaline conditions. The successful zooplankton populations were either favored by the disturbance of the sand bar opening, such as the veligers of the gastropod Heleobia australis, or capable of fast recovery after the closing of the sand bar, during the succession from a marine into an oligohaline environment, such as Hexarthra spp.. Such populations seemed well adapted to the stress conditions usually found in the lagoon due to osmotic changes, column mixing, nutrient input, and high fish predation pressure. Rare species in the community, such as Moina minuta, presented population increases all over the lagoon under oligohaline conditions. Keywords: zooplankton community, coastal lagoon, sand bar opening, Hexarthra spp., Moina minuta.Mudanças ambientais e variação temporal e especial do zooplâncton em uma lagoa costeira brasileira submetida a distúrbios ResumoA Lagoa Imboassica, localizada no Município de Macaé (RJ), é separada do mar por uma barra de areia e se encontra cercada parcialmente por áreas residenciais. Esta lagoa costeira tem sofrido intensa degradação ambiental devido à afluência de esgotos domésticos e a aberturas artificiais da barra de areia. Neste estudo foram acompanhadas, mensalmente ao longo de quatro anos, as variações temporais e espaciais de variáveis ambientais e do zooplâncton. Durante o período estudado foram realizadas cinco aberturas artificiais da barra de areia, sendo a maioria efetuada na época chuvosa. Além das alterações osmóticas, estas aberturas causaram a drenagem da água da lagoa para o mar, diminuição dos valores de nitrogênio total e aumento da concentração de fósforo total. A comunidade zooplanctônica da lagoa incluiu táxons de água doce e marinhos e formas holoplanctônicas, meroplanctônicas e nectobentônicas. Foram considerados constantes na comunidade larvas de Polychaeta, Bivalvia e Gastropoda, os táxons de Rotifera Hexarthra spp., Lecane bulla, Synchaeta bicornis e...

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Toxic cyanobacterial blooms are a common phenomenon in the Baltic Sea. The fate of the toxin in the food web is largely unknown. We studied the effect of algal diets on production of pellets and toxin content of the calanoid copepod Eurytemora affinis in the northern Baltic Sea. Fieldcollected copepods were fed with (1) cultured toxic cyanobacteria Nodularia spumigena; (2) cultured non-toxic flagellates Brachiomonas submarina; and (3) a natural phytoplankton assemblage. Natural phytoplankton was dominated by non-toxic cyanobacteria Aphanizomenon flos-aquae, but also remnants of toxic N. spumigena were found. Pellet production was highest on cultured B. submarina, second highest on N. spumigena and lowest on natural phytoplankton. Because pellets were produced on cultured N. spumigena, this shows that toxic cyanobacteria are consumed if no other food is available. The toxin content of E. affinis was highest in copepods fed with cultured N. spumigena, but toxin was also found in lower concentrations in animals fed with natural phytoplankton. Results indicate that an accumulation of toxins mainly occurs during a growing phase of cyanobacterial blooms. The toxin concentration in the pellets was approximately 6 to 12 times lower than in the copepods. We suggest that a large part of the ingested toxin accumulates in copepod tissues, although some is egested with pellets. This may lead to transport and, possibly, accumulation of cyanobacterial toxin in higher pelagic trophic levels in the Baltic Sea. KEY WORDS: Cyanobacterial toxin · Nodularia spumigena · Toxin transfer · Copepods · Faecal pelletsResale or republication not permitted without written consent of the publisher

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