A review of regulation mechanisms of metazoan plankton in riverine ecosystems: aquatic habitat versus biota

Abstract

This review summarizes the key factors of a series of articles about animal plankton in rivers, a topic that remains poorly investigated. Running water, in which sampling processes are variable and often difficult, acts as a constraint as well as a resource for plankton. Assessment of the potamoplankton reveals that good swimmers of the true plankton are mixed with numerous poor swimmers among littoral and epibenthic forms. Small taxa dominate communities in most of rivers all over the world and, in comparison with crustaceans; the successful development of rotifers rests on their shorter development times. According to hydraulic and geomorphological features, the diversity of the habitats and the ability of individuals to avoid washout was examined, decrease in flow creating standing zones favourable to zooplankton development. Many species can find suitable conditions for the development of dense populations in stream habitats and examples of taxa-specific response, regardless of the habitat structure, are observed. While the challenge for riverine plankton remains 'eat to be fruitful and multiply', their activities have been poorly investigated in turbulent conditions, those able to continue growing in a current of 20 cm s À1, such as brachionid species, being usually dominant in rivers. Examination of the distribution of plankton populations, in the Middle Loire and in other rivers, showed that the flow regime, which plays a central role in organizing river habitats, explains the presence/absence of these fast-growing organisms. While reservoirs are major sources of crustaceans, lateral exchanges as well as downstream transport are important in determining the plankton. These ecosystems are primarily governed by abiotic factors, biological control taking place after physical control has happened. Because animals arrive by chance in any habitat during dispersion, zooplankton in rivers remains primarily governed by unpredictable physical processes and depends on the age of the water and the availability of habitats. In this way, the hydro-dynamics of river habitats need to be more documented with regard to their key role in the planktonic life. Preservation of the lentic areas remaining at the heart of the matter, the contrasting ecology of the rotifers should be a reliable tool with which to estimate the changes in habitats diversity of main channels, particularly during droughts, while crustacean's diversity would be more representative of flood plain annexes, particularly during flood events.

Zooplankton communities of two lake outlets in relation to abiotic factors

“…Little is known about zooplankton communities found in flowing water bodies. The majority of authors concerned with this subject studied large or relatively large rivers [4][5][6][7] in which the density of zooplankton is greater than in small rivers. In lake outlets, the number of zooplankton species, their density and their body length decreases with increasing distance downstream along rivers [8,9].…”

“…Perhaps planktivorous fish attacked plankters ineffectively, because of low transparency and high number of zooplankton refugees. Although planktivorous fish and macro-invertebrates control the zooplankton community in the rivers, the most important controlling factors of zooplankton production are physical, particularly river hydrology [4,31].…”

Effect of sampling effort and sampling frequency on the composition of the planktonic crustacean assemblage: a case study of the river Danube

“…This is partly due to the relatively short generation time of cladocerans. The present study is only confined to planktonic crustaceans; however, rotifers are characterised with shorter generation times (Akopian et al 2002;Lair 2006) Thorp et al 1994-Ohio River). Therefore, additional research is needed when sampling strategies of zooplankton can be evaluated.…”

The diversity and longitudinal changes of zooplankton in the lower course of a large, regulated European river (the lower Vistula River, Poland)

“…Whereas about half as many species were identified in the Rhine -35 (van Dijk & van Zanten 1995) and in the Danube River -30 (Reckendorfer et al 1999). Some authors (Welker & Walz 1998;Lair 2006) emphasize that the fluvial zooplankton is usually a community poor in species, when you compare its structure with the richness of species in lakes and dam reservoirs.…”