Trends in planktonic copepod diversity in reservoirs and lotic stretches in a large river basin in South America

Abstract

Copepod assemblages were analysed across La Plata River basin, the second largest in South America. High values of species richness and Shannon–Wiener diversity were found in the lower Paraná River, the main and largest river of the basin, and in eutrophic reservoirs located in the upper basin. The species richness was negatively correlated with turbidity, probably because of the negative impact on filtration rates in calanoids. There was a trend of decreasing richness correlated with high water flow in reservoirs with short water-retention time (<40 days) and simple morphometric shape, and also in deeper oligo-mesotrophic reservoirs with very long water-retention time and dendritic shape (variables that occurred in combination in the present study). The number of copepod species (46) found in our study is only about half of the gamma diversity estimated using Jack1 non-parametric analysis for the basin (86 species). There are groups of copepod species typical of reservoirs and rivers, and others that can occur in both of these habitat types. Reservoir and lentic species are favoured by a deeper water column, higher temperatures and higher transparency, whereas the opposite is the case of typical riverine species. There is also a group of species that occur in both sets of conditions.

A new species of Notodiaptomus from the Amazon basin (Crustacea, Copepoda, Calanoida, Diaptomidae)

“…The Amazon basin is the richest area in the Neotropical region concerning the presence of diaptomid species, due in large part to its area extension (Perbiche-Neves et al 2014). It is expected that some new species will be described from this region, as well as in other large river basins in this zoogeographical area.…”

“…Even at present we still find new species in remote areas such as the Xingu and Tocantins river basins, nowadays the target of large reservoirs construction for hydropower generation. Other examples of gap areas in South America are reported in Perbiche-Neves et al (2014).…”

“…For example, no diaptomid species is shared between North and South America (Suárez-Morales et al 2005; Perbiche-Neves et al 2014). The endemicity of the South American species stands out for its high species richness, and is directly associated with the area of ecoregions (Perbiche-Neves et al 2014). …”

Regulation of the abundance and turnover of copepod species by temperature, turbidity and habitat type in a large river basin

“…There are similarities between Mexican and Nearctic species, but South American taxa are poorly represented in Mexico (only one genus in common) (Perbiche‐Neves et al . ). Boxshall and Jaume () inferred that there have been at least four waves of colonization by the Diaptomidae, and high mutation rates and genetic divergence between diaptomid populations have been suggested as factors contributing to the high diversity of these organisms (Thum & Harrison ; Willet & Ladner ).…”

“…Perbiche‐Neves et al . () examined the historical biogeographic processes that acted on the Neotropical diaptomids and showed that species are distributed among ecoregions in many river basins, highlighting the patterns of endemism in this group.…”