Temporary pools are seasonal wetland habitats with specifically adapted biota, including annual Nothobranchiuskillifishes that survive habitat desiccation as diapausing eggs encased in dry sediment. To understand the patterns in the structure of Nothobranchius assemblages and their potential in wetland conservation, we compared biodiversity components (alpha, beta, gamma) between regions and estimated the role and sources of nestedness and turnover on their diversity. We sampled Nothobranchius assemblages from 127 pools across seven local regions in lowland Eastern Tanzania over two years, using dip net and seine nets. We estimated species composition and richness for each pool, and beta and gamma diversity for each region. We decomposed beta diversity to nestedness and turnover components. We tested nestedness in three main regions (Ruvu, Rufiji, Mbezi) using the number of decreasing fills metric and compared the roles of pool area, isolation and altitude on nestedness. A total of 15 species formed assemblages containing 1-6 species. Most Nothobranchius species were endemic to one or two adjacent regions. Regional diversity was highest in the Ruvu, Rufiji and Mbezi regions. Nestedness was significant in Ruvu and Rufiji, with shared core (N. melanospilus, N. eggersi, N. janpapi) and common (N. ocellatus, N. annectens) species, and distinctive rare species. Nestedness apparently resulted from selective colonization rather than selective extinction and local species richness was negatively associated with altitude. The Nothobranchius assemblages in the Mbezi region were not nested, had many endemic species and the highest beta diversity driven by species turnover. Overall, we found unexpected local variation in the sources of beta diversity (nestedness, turnover) within the study area. The Mbezi region contained the highest diversity and many endemic species, apparently due to repeated colonisations of the region rather than local diversification. We suggest that annual killifish can serve as a flagship taxon for small wetland conservation.

Data collected in the wild from 127 killifish communitites using dipnets and seine nets. Presence absence data. Fish determined on the bank and released, vouchers taken.