Crustacean zooplankton assemblages in freshwaters of tropical Australia

Throughout tropical Australia eulimnetic zooplankton is composed of 7 calanoid copepods, 5 cyclopoid copepods and 12 cladocerans. A further 10 cyclopoids and 9 cladocerans occur as littoral strays, making 43 species in all. Dominants include Diaptomus lumholtzi, Mesocyclops notius, Thermocyclops decipiens, Diaphanosoma excisum, Ceriodaphnia cornuta, and Moina micrura. Momentary species composition averages 1.0 calanoids, 1.3 cyclopoids and 2.0 cladocerans. These assemblages are not only less complex than in temperate Australia, but also are not as rich as in most other tropical regions. The main contributors to these differences are calanoids and cladocerans respectively. Nevertheless, as elsewhere, most zooplankters in tropical Australia are eurytropic, widely distributed and small.     

The freshwater zooplankton of Thailand (Rotifera and Crustacea)

A list is given of all zooplankton species hitherto reported from Thailand, based on the author's own observations and on the literature.From a comparison with the fauna of some neighbour countries, it appears that important gaps remain to be filled-in.     

Abundance,Species Composition and Spatial Distribution of Planktonic Rotifers and Crustaceans in Lake Ziway (Rift Valley,Ethiopia)

Species composition, abundance, and spatial distribution of rotifer and crustacean zooplankton were studied in Lake Ziway from late April to early July 2004. A total of 49 rotifer species was recorded, with Anuraeopsis fissa, Brachionus angularis, Filinia novaezealandiae, and Trichocerca ruttneri being numerically dominant. Variation in abundance was extremely high, ranging from 2 to 1000+ individuals per litre. There was no significant difference in the distribution of rotifer species between inshore and offshore regions. Crustacean species richness was low, with only five cladoceran and three copepod species occurring in the open water. Moina micrura and Diaphanosoma excisum dominated the cladoceran community, whereas Thermocyclops decipiens was the dominant copepod. Although numerically dominant (75%), rotifers accounted for less than 30% of mean total zooplankton biomass. Peak abundance of crustaceans was observed in May and June, following the onset of the rainy season and increased phytoplankton production. Variation in the spatial distribution of crustacean species was neither observed horizontally between inshore and offshore areas nor vertically in the highly turbid and wind exposed deeper part of the lake. On the other hand, Moina micrura varied significantly in size between inshore and offshore areas. Adult M. micrura dominated offshore, whereas juveniles were more abundant inshore, suggesting a predominantly littoral selective predation on large and adult crustaceans by fish. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Zooplankton species diversity in Lake St. Clair,Ontario, Canada

Zooplankton species diversity and selected chemical parameters were investigated at three stations in Lake St. Clair, Ontario, Canada, from 15 June–26 August, 1971. Primary productivity and zooplankton species diversity were greatest at stations 1 and 2 which were enriched by the Thames River drainage. No significant correlation between total zooplankton diversity and chlorophyll a was found, however, within the Cladocera and Copepoda, positive correlations with chlorophyll a, reactive silicate and nitrate were shown at stations 2 and 3. Rotifer species diversity showed negative correlation with chlorophyll a, nitrate and reactive silicate.     

The zooplankton of a small tropical reservoir (Solomon Dam,North Queensland)

This paper examines seasonal changes in the density and taxonomic composition of the zooplankton of a small tropical impoundment, in relation to factors of water temperature, food supply and reservoir flushing. The response of the zooplankton to management techniques designed to regulate the density of cyanobacteria in the dam are also considered. Cyclopoid copepods were the dominant zooplankters, although Cladocera became much more significant following the introduction of measures to control cyanobacteria. Planktonic Rotifera were a diverse but generally unimportant fraction of the total biomass, except following seasonal or management induced environmental perturbations, when the Rotifera often recovered most rapidly.     

Spatial and seasonal variation of the zooplankton in the coastal zone and main khors of Lake Nasser (Egypt)

A prominent feature of Lake Nasser is the presence of khors (dendritic side extensions). We studied the zooplankton of the larger khors and coastal zone of the main lake in 1996 and 1997, and found an assemblage of rotifers, cladocerans and copepods that was partly tropical, partly temperate, at relatively high biomasses. Spatial differences were weak, but the upstream khors (Toushka and Korosko) were consistently richer than the downstream khors (El-Ramla and Kalabsha), with a rather sudden transition around km 150 at El Madiq. Summer standing crops were higher than those in winter by a factor 2–3. The zooplankton of the littoral of the main channel showed the same spatial pattern as that in the khors, being more abundant in spring (average 82300 ind m^–3) than in autumn (average 72700 ind m^–3). Zooplankton dry weight increased from 4 g m^–2 at khor El-Ramla to 7 g m^–2 at khor Toushka. These rather high values had low variation. The number of species, diversity and evenness all showed a high degree of similarity among the khors and in the littoral of the main lake. The lake fish fauna is poor, lacking a pelagic planktivore. The predominance of medium-sized Copepoda (one calanoid, two cyclopoids) in the zooplankton suggests that fish predation is moderate. This is confirmed by the persistence of two Daphnia species at low abundance, although rather strong variations in time suggest that Cladocera suffer from summer predation by invertebrates (copepods) as well as vertebrates (mostly larval fish). Because the zooplankton is underutilised by higher trophic levels, we suggest to assess the benefits of introducing a pelagic zooplanktivorous fish.     

Improved protocols to accelerate the assembly of DNA barcode reference libraries for freshwater zooplankton

Currently, freshwater zooplankton sampling and identification methodologies have remained virtually unchanged since they were first established in the beginning of the XX century. One major contributing factor to this slow progress is the limited success of modern genetic methodologies, such as DNA barcoding, in several of the main groups. This study demonstrates improved protocols which enable the rapid assessment of most animal taxa inhabiting any freshwater system by combining the use of light traps, careful fixation at low temperatures using ethanol, and zooplankton‐specific primers. We DNA‐barcoded 2,136 specimens from a diverse array of taxonomic assemblages (rotifers, mollusks, mites, crustaceans, insects, and fishes) from several Canadian and Mexican lakes with an average sequence success rate of 85.3%. In total, 325 Barcode Index Numbers (BINs) were detected with only three BINs (two cladocerans and one copepod) shared between Canada and Mexico, suggesting a much narrower distribution range of freshwater zooplankton than previously thought. This study is the first to broadly explore the metazoan biodiversity of freshwater systems with DNA barcodes to construct a reference library that represents the first step for future programs which aim to monitor ecosystem health, track invasive species, or improve knowledge of the ecology and distribution of freshwater zooplankton.     

Degradation and rehabilitation of wetlands in the Alligator Rivers Region of northern Australia

The wetlands of the Alligator Rivers Region of northern Australia have been recognized as having high national and international conservation value. The diversity and productivity of these habitats is, however, under current and future threat from invasive feral animals (Asian water buffalo and pigs) and naturalized alien plants (mimosa, salvinia and para grass) and also from climate change and sea level rise. Some habitats have already been severely degraded and require rehabilitation. In response to this situation feral animal management has centered on eradicating the buffalo population and introducing measures to control pigs. Weed management has focused on control of mimosa and salvinia with an increasing emphasis on integrated control measures. The vulnerability of the freshwater wetlands to climate change and sea level rise is considerable, although the exact nature of environmental change has not been determined.Rehabilitation of the degraded wetlands has centered on controlling the cause of the problem (e.g., the invasive species) and allowing subsequent natural succession to occur. It is recommended that further monitoring and assessment of successional change is undertaken to ascertain if this is sufficient. An integrated monitoring program for detecting the extent and rate of ecological change because of climate change and sea level rise is also proposed. Specific management and research tasks for each of the major broad causes of wetland degradation within the region are made. It is then strongly recommended that all rehabilitation and monitoring activities, including related research, are conducted within a holistic management framework that takes into account the different land jurisdictions within the region and also within the broader landscape context. The utilization of existing management and research structures and processes is stressed as one means of achieving an integrated approach.     

Zooplankton community composition of lakes in the Yukon and Northwest Territories (Canada): relationship to physical and chemical limnology

We analysed associations between zooplankton species composition and local abiotic factors in 30 lakes located along a 900 km south-north transect from Whitehorse (Yukon Territory) to Inuvik (Northwest Territories). The lakes were situated in three broadly defined vegetation zones: (i) Boreal forest (between Whitehorse and Dawson City), (ii) alpine tundra (Ogilvie mountains north of Dawson City) and (iii) subarctic forest-tundra (near Inuvik). Lakes in the alpine tundra were characterised by lower conductivity, temperature, chlorophyll a and nutrients than those in the other two zones. Those in the forest-tundra were generally small and shallow, and had higher chlorophyll a concentrations than lakes further south. Lakes in forested catchments spanned a larger latitudinal range and exhibited a greater variety of physical and chemical characteristics. However, they were generally deeper, with higher conductivity, temperature and ionic concentrations. Forty-one zooplankton taxa were identified from the 30 lakes, of which the most frequently occurring were the rotifers Conochilus unicornis, Kellicottia longispina, Keratella cochlearis and Polyarthra vulgaris, the cladocerans Daphnia middendorffiana and Bosmina longirostris, and the copepods Leptodiaptomus pribilofensis, Heterocope septentrionalis and Cyclops spp. The lakes contained between two and fifteen species (mean = 6.9). Alpine tundra lakes contained slightly less species (mean = 5.8) than those at lower elevations; in particular the cladoceran fauna was depauperate or absent. Relationships among the lakes, species and environmental factors were examined using canonical correspondence analysis, with forward selection and associated Monte Carlo permutation tests. Chloride, silica and temperature showed statistically significant relationships with species distribution, and together these abiotic factors explained 25% of the variation in zooplankton communities within Yukon and Northwest Territories lakes.     

Observations on the zooplankton in the reedbelt area of the Neusiedlersee

Weekly sampling and simultaneous measurements of temperature, pH, and conductivity were made at three stations in the reedbelt, between 1980–82. 20 cladoceran and 14 copepod species were encountered, of whichCyclops vicinus vicinus was found in the lake for the first time. Of the measured environmental features, temperature showed the greatest seasonal changes; pH and conductivity were less variable. There were, both quantitatively and qualitatively, constant differences between the three stations, although they lay close to each other.     

Ecological studies of Cladocera in the ricefields of Tanjung Karang,Malaysia, subjected to pesticide treatment

Temporal changes in the population densities of four dominant Cladocera (Moina micrura, Diaphanosoma excisum, Alona guttata and Macrothrix spinosa) were studied in untreated and pesticide treated rice plots over a growing season. M. micrura was the first dominant species to occur in all the plots which were initially devoid of vegetation except for the newly transplanted rice seedlings. With the growth of the rice seedlings and the appearance of aquatic macrophytes, open water ricefields were transformed into vegetated littoral conditions precipitating the disappearance of M. micrura and the appearance of the littoral A. guttata and M. spinosa, and the eurytopic D. excisum. The cladoceran community was affected by spraying of the pesticide FMC35001, an analogue of Furadan®. The response of the four dominant species to the pesticide treatment is discussed.     

Structure and dynamics of zooplankton communities in the littoral zone of some North Carolina lakes

Species composition and seasonal, dynamics of zooplankton in the littoral zone were studied in three piedmont North Carolina lakes for one year. Nygaard's compound index indicated oligotrophic conditions in Belews Lake and eutrophic conditions in Salem Lake and Lake 150. A total of 32 species of zooplankton were found in the samples. Significantly fewer species of truely littoral zooplankton were present in the oligotrophic lake regardless of season (P < 0.05). Eutrophication appears to favor increased diversity in zooplankton of the littoral zone. Habitat heterogeneity, provided by a well developed littoral zone containing aquatic macrophytes, may be the major factor contributing to the maintenance of more taxa of zooplankton in eutrophic systems.Distinct taxa of Cladocera and Copepoda are present in the littoral zone, exhibiting seasonal dynamics that are largely different from the limnetic fauna. Such dynamics may result from predation by characteristically limnetic species of cyclopoid copepods which seek prey in the littoral zone. The numerical and seasonal abundance of predators and prey are inversely related and the true littoral taxa, represented in the present study by the genera Alona, Chydorus, Pleuroxus, Sida, Simocephalus, and Eucyclops, contained no predaceous species. The seasonal dynamics of these genera are very similar even in widely separated geographical regions, indicating that the factor(s) responsible operate independently of climatic and chemical variables. Intrazooplankton predation appears to be a more plausable explanation than segregation along depth which, although consistent with data from studies of limnetic waters, cannot be related to populations of zooplankton in shallow littoral areas.     

Studies on the ectocommensal ciliate,Trachelostyla tani nov. spec. (Protozoa: Ciliophora: Hypotrichida) from the mantle cavity of the scallop Chlamys farrei

A total of 33 sites (27 temporary pools, five dune slacks and one shallow lake) were sampled during January 1998. Forty two taxa (one ctenopoda, 19 anomopoda and 22 copepoda) are recorded. Data from the varied habitats types (temporary pools, dunary ponds, shallow lakes) are compared and biotic and abiotic factors influencing the spatial and temporal distribution of local zooplankton are discussed. The paper concludes with comments why local conservation efforts need to be directed towards temporary pools and dune slacks, two much-neglected habitats.     

The nature and origin of the crustacean zooplankton of Sahelian Africa,with a note on the Limnomedusa

The zooplankton of the major Sahel river basins Nile, Shari (Chad), Niger, and Senegal, is different from that found in the Sahara and in Equatorial Africa. Similarities and differences between the individual basins are numerous as well. Many species are shared by the Nile and Lake Chad, by Lake Chad and the Niger (plus Senegal), or occur in all four basins, or are restricted (endemic) to only one basin.These patterns are identical to patterns found in fish, molluscs, and macrophytes and show that crustacean zooplankton obeys the same laws of dispersal as these groups, in spite of its apparent preadaptation to passive dispersal.The patterns can be explained by the climatic fluctuations of the Upper Pleistocene and,Holocene. Following a general dry period over Africa between 20 000 and 13 000 BP, high river and lake levels prevailed between 12 500 and 8 400 BP. This was the period of maximum faunal interchange between all basins, and even with the Zaire basin. After a regression (8 000–7 000 BP), wetter conditions returned around 6 000 BP, but the Sahel itself remained dry, although its rivers and lakes, fed by waters of southern origin, showed higher levels than today. They flooded large areas of the southern Sahara, permitting aquatic animals and plants to reach the Adrar of Mauretania, the Tibesti, and the Ennedi mountains.Since 3 000 BP, present day conditions developed. This last period is characterized by species extinctions, as exemplified by the droughts in Lake Chad in historical times, and in spite of the tremendous diversity still extant here today. Between 6 000 BP and the present, however, very little speciation took place, and faunal exchange between basins was very limited.     

Distribution and abundance of zooplankton in the Waikato River,New Zealand

Potamoplankton is often a well developed component in large lowland rivers, yet little is known about its structure in New Zealand's longest river, the Waikato River. To redress this gap we sampled bimonthly at seven sites along the length of the river over 12 months. Rotifers were the dominant zooplankton in the Waikato River making up 85% of the total densities. Cladocerans represented 9% and copepods only 6%. Rotifers were also the most taxonomically rich group with 41 species in 20 genera identified throughout the study. Thirty rotifer species and nine genera represent new records for the river – two cladoceran species were also recorded for the first time. The highest densities of crustaceans and rotifers were found in the hydro lakes. Densities of crustaceans decreased with increasing distance downstream and densities of rotifers were on average 15 times greater than crustaceans in the lower river. The seasonality of Crustacea was similar to that in New Zealand lakes and rivers with high densities in summer and minimum densities over the winter period. Total rotifer densities showed a similar trend although there were marked seasonal differences between individual species.     

Mangrove zooplankton of North Queensland,Australia

Measurements of plankton community structure and trophic resourcespotentially available to planktonic copepods were made in the mangroveestuaries of six rivers in Northeastern Australia. The Pascoe, Claudie,Lockhart, McIvor and Daintree Rivers represent wet tropical systems on CapeYork, whereas the Haughton River estuary has restricted freshwater inflowbecause of a drier climate and freshwater diversion for agriculture. TheHaughton River was sampled approximately monthly between October 1992 andMay 1994, and had a mean abundance of zooplankton >37 μm of 200l⁻¹ (range 60–500 l⁻¹). The Cape Yorkrivers were sampled infrequently, and zooplankton abundances ranged between0.4 and 1400 l⁻¹. The zooplankton of all rivers was dominatedby copepods, particularly representatives of the genus Oithona which werecharacteristic of a distinct mangrove fauna. Physical forcing influencedthe zooplankton of mangrove estuaries much more than the measured biologicalvariables. The water column was characterised by high concentrations ofparticulate matter, up to 3.3 mg l⁻¹ C and 1.1 mgl⁻¹ N, of low food quality (as indicated by the C:N ratio).Phytoplankton biomass (as chlorophyll a) in all six rivers was on averagefour-fold greater than in neighbouring coastal waters (1.1–12.6μg l⁻¹), and 25% of this chlorophyll a wasderived from cells >10 μm, and thus potentially available tocopepods. The degree of mixing, determined by the combination of tidal stateand the extent of freshwater input, appears to drive both the quantity andquality of particulate material available to higher consumers and thedistribution of zooplankton communities within mangrove estuaries. This revised version was published online in July 2006 with corrections to the Cover Date.     

A review of systematics,distribution and ecology of tropical freshwater zooplankton

Studies on tropical freshwater zooplankton which commenced in the mid-19th century have been intensified during the past twenty years or so. The whole region, barring a few areas, has been investigated, including very recently tropical Australia. The widely scattered literature is briefly summarized with comments. Some general distributional patterns are emerging. There is a dearth of ecological studies especially on seasonality and production. Systematics lags behind the North Temperate zone in most tropical regions.     

Summer zooplankton communities of selected borrow-pit ponds in Northern Illinois,U.S.A.

Zooplankton samples were collected from 7 borrow-pit ponds during the summer months of 1975 in northern Illinois. Species diversity indices and evenness values were used to characterize the ponds zooplankton community structure. Thirty-one plankton species are reported. Older borrow-pit ponds contained more species and had higher mean densities than did the newer ponds. The number of dominant species reported per pond varied from 1 to 4. Species diversity indices are higher in older ponds, and there was a general tendency for species diversity to increase with pond age. No correlations between physicochemical measurements and the structure of the zooplankton communities were found. Factors possibly governing zooplankton community structure in borrow-pits are speculated upon.     

Composition,density and feeding of crustacean zooplankton community in a shallow,temperate lake (Lake Balaton,Hungary)

Composition density and filtering rates of crustacean zooplankton were studied in the open water and among the macrophytes of the oligo-mesotrophic part of Lake Balaton from 1981 to 1983. From the individual filtering rates of the different populations and the densities community grazing rates were derived.Copepoda made up 79–90% of crustacean plankton community in the open lake and 95–97% of it in littoral zone. Among them the nauplii dominated. At the end of summer 1982, when Anabaenopsis was in bloom, the filter-feeding species (Eudiaptomus, Daphnia) practically disappeared, being replaced by cyclopoids. Daphnia had the highest filtering rates followed by those of Eudiaptomus and Diaphanosoma. Among copepods, the filtering rates in decreasing order were: ovigerous > all adults > copepodites > nauplii. > . The filtering rates of the different species varied both seasonally as well as from year to year. In 1983, when the concentration of organic seston decreased, filtering rate increased compared with those in the earlier years. During the water bloom in 1982, the rates decreased by 70% on the average.The community grazing rate was very low (3% per day) in the open lake and among macrophytes, both in 1981 and 1982; also the share of crustacean zooplankton in grazing was very low. In 1983, together with the improving of water quality, the community grazing rate increased 4-fold. In 1981 and 1983 the rates were influenced by water temperature but in 1982 by seston concentration.     

The freshwater zooplankton of Central America and the Caribbean

So far mainly sporadic studies have been made on the freshwater zooplankton of this region. We studied material from Costa Rica, Cuba, Bahamas, El Salvador, Haiti and Trinidad and listed unpublished species data from Jamaica. In all 183 species of Rotifera; 104 of Cladocera; 64 Calanoida and Cyclopoida and a few Ostracoda are known from the region which includes Central America, the Caribbean Islands from the Bahamas to Trinidad and the islands off South America and Central America. Records from individual countries are generally low except for Cuban Cladocera and Copepoda. The total number of Copepoda and Cladocera recorded for the whole regions appears to be reasonably comprehensive. Daphnia is rare or absent from the equatorial regions and it is likely that the low species diversity may be due partly to the lack of a range of habitat types.