Can microcystins affect zooplankton structure community in tropical eutrophic reservoirs?

Abstract

The aim of our study was to assess whether cyanotoxins (microcystins) can affect the composition of the zooplankton community, leading to domination of microzooplankton forms (protozoans and rotifers). Temporal variations in concentrations of microcystins and zooplankton biomass were analyzed in three eutrophic reservoirs in the semi-arid northeast region of Brazil. The concentration of microcystins in water proved to be correlated with the cyanobacterial biovolume, indicating the contributions from colonial forms such as Microcystis in the production of cyanotoxins. At the community level, the total biomass of zooplankton was not correlated with the concentration of microcystin (r2 = 0.00; P > 0.001), but in a population-level analysis, the biomass of rotifers and cladocerans showed a weak positive correlation. Cyclopoid copepods, which are considered to be relatively inefficient in ingesting cyanobacteria, were negatively correlated (r2 = - 0.01; P > 0.01) with the concentration of cyanotoxins. Surprisingly, the biomass of calanoid copepods was positively correlated with the microcystin concentration (r2 = 0.44; P > 0.001). The results indicate that allelopathic control mechanisms (negative effects of microcystin on zooplankton biomass) do not seem to substantially affect the composition of mesozooplankton, which showed a constant and high biomass compared to the microzooplankton (rotifers). These results may be important to better understand the trophic interactions between zooplankton and cyanobacteria and the potential effects of allelopathic compounds on zooplankton.

Phytoplankton Community Response to Changes in Light: Can Glacial Rock Flour Be Used to Control Cyanobacterial Blooms?

“…Cyanophytes can be too large for many gape-limited grazers to consume, either because they form mucilaginous colonies or long filaments (Haney, 1987). The production of cyanotoxins can also be detrimental to grazers, though the magnitude of these effects are debated (Rohrlack et al, 2001;Paes et al, 2016). Conversely, cryptophytes are highly nutritious and are an important component of aquatic food webs (Stemberger and Gilbert, 1985;Sarnelle, 1993).…”

Influence of Biotope and Biotic Factors on Cyanobacteria Abundance, Genotype and Toxin Production

“…Temperature alone may only partly determine bloom formation and it is accepted that a combination of factors are responsible for a bloom to develop: increasing temperatures, decreasing nutrients and increased water column stability (40); temperature has the most pronounced effect on toxicity; the highest toxicity was found at 20°C, but reduced at temperatures in excess of 28°C. According to Paes and his colleagues (41), in all studied reservoirs that experienced toxic blooms water transparency was reduced. P. rubescens abundance appears to be strongly influenced by water transparency, at least in prealpine lakes (42).…”

“…Even if the cyanobacteria strain is nontoxic or toxic, at least in the case of B. calyciflorus , this type of diet suppresses the population growth; effects were less severe than that produced by toxic M. aeruginosa (73). Is was observed that in eutrophic systems higher abundance of rotifers is often observed with higher abundance of cyanobacteria, which indicates that not all cyanobacteria inhibit rotifer growth (41,74). Additionally, rotifers are affected by three selected forms (unicellular, filamentous, and colonial) of cyanobacteria (73).…”

“…Therefore, at times when these colonial forms dominate the phytoplankton, Daphnia populations might be expected to show decreased growth and fecundity in response to food limitation or toxicity. Is very probably that any effect of cyanobacteria on zooplankton could be influenced by evolutionary mechanisms in natural systems with a long history of cyanobacterial blooms: zooplankton that co-occur with dense biomass of cyanobacteria have better chance to adapt than others that were not exposed to these conditions (41). It was already demonstrated that, if the proportion of any toxic cyanobacteria and any edible algae studied is in concordance with tested microorganism needs, the survival rate is growing (64,(73)(74)(75)(76).…”

Изучение Вертикального Распределения Зоопланктона Запорожского Водохранилища Для Расчёта Зарыбления Пёстрым Толстолобиком

“…В данном месяце в нижней части водоёма перепад температуры в этом слое приводил к заметному снижению количественных показателей зоопланктона на горизонтах ниже 10 м. Ещё одним фактором, обуславливающим более низкую биомассу зоопланктона поверхностного слоя по сравнению с таковой на глубине 10 м, может быть цветение синезелёных водорослей, токсины которых, накапливаясь, оказывают аллелопатическое угнетающее воздействие на зоопланктон [16,20]. Несмотря на способность доминантных видов зоопланктона питаться как синезелёными водорослями, так и микроорганизмами, размножающимися в условиях детритной пищевой цепи, а также несмотря на резистентность к токсинам синезелёных водорослей [26], слишком высокая концентрация последних в условиях водохранилища летом [28] [24,29]. Преобладание в сообществе зоопланктона мелких видов и молоди веслоногих ракообразных, которые интенсивно развивались и концентрировались в поверхностном слое, приводило к огромной разнице, прежде всего по численности, между поверхностным слоем 0 м (170 тыс.…”