Abstract The accuracy of traditional methods to sample planktonic microcrustaceans depends on two assumptions: that organisms are alive during sampling and that all carcasses can be identified despite their degradation state, but fresh carcasses are not easy to distinguish by traditional methods. Previous studies about mortality have shown that neglecting dead organisms can provide biased ecological information. Thus, our objective was to determine the mortality rate and the proportion of dead microcrustacean in three tropical reservoirs. Sampling was carried out in 12 stations during two periods. The proportion of dead organisms was verified using aniline blue and it varied between 0.6% and 90.6%. The carcass decomposition period varied between 3 to 16 days and microcrustaceans mortality rate varied between 0.005 and 0.314 d-1. Traditional preservation techniques with formalin do not significantly overestimate species abundance. However, these values should not be disregarded, because corrected (disregarding organisms that were dead) and formalin-preserved abundances were correlated with distinct limnological descriptors. Therefore, the traditional formalin preservation technique could provide misleading ecological interpretations. Other studies over larger temporal scales in addition to experiments to evaluate the effects of viruses, parasitism and the toxic effects of cyanobacteria on zooplankton would enlighten mortality rate patterns in freshwater ecosystems.

Resumo O presente estudo objetivou inventariar a biodiversidade de microcrustáceos planctônicos (Cladocera e Copepoda) em 44 mananciais da região semiárida do Brazil, ampliando o conhecimento da comunidade zooplanctônica desta região, incluindo as espécies fitófilas. Os organismos foram coletados de modo não sistemático entre 2011 e 2017, nos estados do Rio Grande do Norte, Pernambuco, Ceará e Paraíba. Um total de 60 espécies de microcrustáceos planctônicos foram identificadas, sendo 52 de cladóceros e oito de copépodes. A bacia que apresentou maior riqueza foi a do rio Pajeú com 41 espécies. Mesmo assim, o número extrapolado de espécies mostra tendência de aumento para essa bacia. A composição dos gêneros foi diferente entre as bacias hidrográficas, sendo a bacia do Moxotó (Pernambuco) isolada das demais, talvez porque nesta bacia as lagoas foram o único tipo de ambiente amostrado. Os padrões de riqueza e de abundância se mostraram mais elevados para as bacias ondem a amostragem foi realizada principalmente em ambientes lênticos, como a do Pajeú e do Moxotó. Inventários de microcrustáceos e estudos de longa duração precisam ser maximizados para ampliação do conhecimento da biodiversidade dos ecossistemas aquáticos continentais da região semiárida brasileira.

Abstract The present study aimed to inventory the biodiversity of planktonic microcrustaceans (Cladocera and Copepoda) in 44 environments from the semiarid region of Brazil, increasing the knowledge about zooplankton community, including phytophilous species. Between 2011 and 2017, organisms were collected in a non - systematic way in the states of Rio Grande do Norte, Pernambuco, Ceará and Paraíba. A total of 60 species of planktonic microcrustaceans were identified, of which 52 were cladocerans and eight were copepods. The basin that presented the highest richness was Pajeú River with 41 species. Nevertheless, the extrapolated number of species shows an increasing tendency for this basin. The genus composition was different between the basins, with Moxotó basin (Pernambuco) being isolated from the others, probably since lagoons were the only type of environment sampled in this basin. Richness and abundance patterns were higher for the basins where sampling was mainly performed in lentic environments, such as Pajeú and Moxotó. Microcrustacean inventories and long-term studies need to be conducted more frequently to better understand the biodiversity of continental aquatic ecosystems in the semiarid region of Brazil.

RESUMO Hipóteses sobre a distribuição das comunidades de zooplâncton em vários ecossistemas são muitas vezes limitadas pela falta de dados sobre os seus mecanismos de dispersão. Muitas pesquisas sobre a dispersão passiva mediada por anuros têm sido desenvolvidas em bromélias, porém com foco em ostrácodes e anelídeos. Nós investigamos o potencial para a forésia externa do zooplâncton (rotíferos, cladóceros, copépodes) por anuros arbóreos em fitotelmos de bromélias. Nossa hipótese é que (1) a composição do zooplâncton presente na pele dos anuros e nos fitotelmos das bromélias é semelhante, e que (2) anuros com maior tamanho corporal carregam mais propágulos de invertebrados. Filtramos a água presente nos fitotelmos (10 a 150 mL) usando uma rede de plâncton (45 µm) e fixamos os invertebrados em formol a 4%. Os anuros foram coletados ativamente em torno das bromélias (até ~1,5 m de raio) e depois lavados com água destilada. Quatorze espécies de rotíferos e três de crustáceos foram registradas na água dos fitotelmos e no corpo dos anuros. Capturamos 17 anuros variando de 2 a 5 cm de SLV e pertencentes a cinco espécies: Pristimantis ramagii (Boulenger, 1888), Dendropsophus decipiens (A. Lutz, 1925), Scinax auratus (Wied-Neuwied,1821), S. pachycrus (Miranda-Ribeiro, 1937) e S. x-signatus (Spix, 1824). Entre eles, 12 (70,59%) tinham propágulos aderidos ao corpo, dos quais a maioria (dez indivíduos) apresentou formas ativas de zooplâncton, enquanto apenas dois apresentaram ovos dormentes. Dez rotíferos e duas espécies de microcrustáceos foram registrados aderidas aos anuros. A composição zooplanctônica diferiu entre os fitotelmos e a pele de anuros e, o tamanho do corpo do dispersor não explicou o número de propágulos transportados, refutando ambas as hipóteses. No entanto, ressaltamos que evidências de dispersão foram encontradas devido ao alto número de propágulos aderidos aos anuros. Nosso estudo fornece evidências de que os anuros podem ser potenciais dispersores de formas ativas e inativas de zooplâncton em bromélias, através de forésia externa.

ABSTRACT Assumptions about the distribution of zooplankton communities in various ecosystems are often limited by lack of data on dispersal mechanisms. Many studies on frog-mediated passive dispersal have been developed in bromeliads, but they usually focus on ostracods and annelids. We investigated the potential for external phoresy of zooplankton (rotifers, cladocerans, copepods) by treefrogs in bromeliad phytotelms. Our hypotheses are that (1) zooplankton composition on frogs’ skin and in phytotelm tanks is similar, and (2) frogs with larger body size carry more propagules of these invertebrates. We filtered phytotelm water (10 to 150 mL) using plankton net (45 µm), and fixed invertebrates with 4% formalin. Frogs were actively collected in and around bromeliads (up to ~1.5 m radius) and then washed with distilled water. Fourteen species of rotifers and three of crustaceans were registered in phytotelm water and frog bodies. We captured 17 frogs with a snout-vent length (SVL) ranging from 2 to 5 cm and belonging to five species: Pristimantis ramagii (Boulenger, 1888), Dendropsophus decipiens (A. Lutz, 1925), Scinax auratus (Wied-Neuwied,1821), S. pachycrus (Miranda-Ribeiro, 1937) and S. x-signatus (Spix, 1824). Among them, 12 (70.59%) had propagules adhered to their bodies, of which the majority (ten individuals) had active zooplankton forms, while only two had dormant eggs. Ten rotifer and two microcrustacean species were recorded adhered to frogs. The zooplankton composition differed between phytotelms and anuran skin, and frog body size does not explain the number of propagules carried, refuting both hypotheses. However, evidence of dispersal was found due to the high number of propagules adhered to anurans. Our study provides evidence that frogs may be potential dispersers of dormant and active forms of zooplankton in bromeliads, through external phoresy.

ABSTRACT This paper aims to compare alpha and beta diversities of planktonic microcrustaceans from three reservoirs located nearby in a tropical semiarid basin. Our hypothesis was that alpha and beta diversities of the community are different, although the ecosystems are located close to each other. We carried out two sampling campaigns: dry and rainy seasons. The sampling of microcrustaceans and environmental variables (dissolved oxygen, chlorophyll a and nutrient) was performed at twelve stations and were distributed throughout the three zones (river, transition, and lacustrine), using a plankton net (45 µm). The reservoirs showed different uses and types of nitrogen predominance: Cachoeira (supply/nitrate), Borborema (sewage/ammonia) and Saco (aquaculture/ammonia). Seventeen species were recorded whose richness was assessed as particularly specific to each one of the studied reservoirs. Seasonally, both reservoirs with high anthropogenic alteration showed greater richness in the dry season. The three reservoirs located in a same basin showed different richness and composition, but the diversity did not differ between the zones of the reservoirs. Although communities are close to each other, their composition and richness were found to be distinct for each reservoir. This may be in response to the peculiar particularities, such as nitrogen sources and the different uses.