Lake salinization drives consistent losses of zooplankton abundance and diversity across coordinated mesocosm experiments (original) (raw)
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Hydrobiologia, 2018
Changes in zooplankton community structure and function were analyzed in 24 lakes covering a wide salinity gradient (from 0.5 to 115 g l-1) in a semiarid region in northwest China. We hypothesized that species richness (S), species diversity (H), functional diversity (FD), biomass, and size of zooplankton would decrease with increasing salinity. We found that S, H, and FD did decrease with increasing salinity, whereas zooplankton sizes, size range, and biomasses did not. In fact, the sizes of microcrustaceans were mainly regulated by the abundance of small fish. Besides the impoverishment of FD, the zooplankton functional groups also varied along the salinity gradient. A shift occurred from selective raptorial to more generalist microphagous rotifers, from selective to more generalist filter feeder cladocerans, and from dominance of microphagous herbivorous copepods to microphagous carnivores. Our study indicates that the ongoing salinization of lakes with climate warming will result in important changes in the zooplankton, affecting not only the structure but also the functioning of this community. A weakened top-down control by zooplankton on phytoplankton at moderate high salinities may be an indirect consequence, leading to a worsening of eutrophication symptoms. Loss of fish at high salinities may, however, counteract this effect.
Hydrobiologia
Quantifying the interactions between functional diversity and environmental change is important for understanding the effects of biodiversity on ecosystem processes. This study aims to evaluate zooplankton secondary production and biomass in an experiment with different levels of functional diversity and environmental stress in the form of increased salinity. It is expected that communities that are more functionally diverse will present higher secondary production and biomass, even under conditions of environmental stress. To test this hypothesis, a mesocosm experiment with two factors was performed: low and high diversity and with and without salt totaling four possible combinations of treatments over the duration of 4 weeks. The high functional diversity treatments showed higher zooplankton secondary production and biomass than those of the low diversity treatments, even under salt addition. The salinity decreased zooplankton production and functional diversity, but its effects were more pronounced in the low than in the high diversity communities. However, in the low diversity treatments the zooplankton biomass and production were maintained due to the dominance of species with certain traits. In summary, our study contributed to understanding the role of zooplankton functional diversity on ecosystem processes in the face of environmental changes promoted by increased salinity.
Experimental Mesocosm Studies of Salinity Effects on the Benthic Algal Community of a Saline Lake
Journal of Phycology, 1998
As closed-basin systems, saline lakes are prone to fluctuate in level and salinity with climate change and hydrologic alterations. Loss of many Great Basin lakes has resulted from the diversion of tributary streams for agricultural or municipal uses. At Mono Lake, an alkaline salt lake in eastern California, salinities have risen from 50 to 100 g·L Ϫ1 in just 50 years. Experimental mesocosms were established to simulate some of the potential ecological effects that could have accompanied this change. The influence of salinity on diatom diversity, taxonomic structure, and primary production was tested using mesocosms deployed at Mono Lake. Mesocosm tanks were 500 L in volume, 1 m square, and 0.5 m deep, with open tops covered by 1 mm mesh net. Five treatments (50, 75, 100, 125, and 150 g·L Ϫ1) with four replicates per treatment were used over a 2-month period. The diatom-dominated benthic algae were reduced both in standing crop (from 6 to Ͻ0.1 g·m Ϫ2) and diversity (from 30 to 12 taxa) with increased salinity, with most loss occurring in salinities Ն75 g·L Ϫ1 . Photosynthetic oxygen production also was significantly lower at salinities Ն75 g·L Ϫ1 . Diatom indicator taxa for these shifts included Denticula sp., Nitzschia frustulum, N. monoensis, N. communis, and Stephanodiscus oregonicus increasing in relative abundance in higher salinity treatments, accompanied by decreases in Achnanthes minutissima, Cymbella minuta, N. dissipata, and Rhoicosphenia abbreviata. Exhibiting dominance at moderate salinity levels (75 to 125 g·L Ϫ1) were Nitzschia frustulum, N. communis, N. palea, and Navicula crucialis. These latter species may be limited by both physiological stress at high salinity and grazing and competition at low salinity. The filamentous chlorophyte, Ctenocladus circinnatus, and cyanobacteria (Oscillatoria spp.) occurred only in salinity treatments from 50 to 100 g·L Ϫ1 . Diversion of tributary stream flow and resulting salinity increases in this lake threaten sustained benthic primary production and algal species diversity relative to conditions prior to stream diversion. The 1994 decision of the California State Water Resources Control Board to return stream flows to Mono Lake will raise the lake level and reduce salinity to around 75 g·L Ϫ1 and is expected to increase the diversity and productivity of the benthic algae of this ecosystem.
Aquatic Ecology, 2017
Lentic ecosystems act as sentinels of climate change, and evidence exists that their sensitivity to warming varies along a latitudinal gradient. We assessed the effects of nutrient and water level variability on zooplankton community composition, taxonomic diversity and size structure in different climate zones by running a standardised controlled 6-months (May to November) experiment in six countries along a European north-south latitudinal temperature gradient. The mesocosms were established with two different depths and nutrient levels. We took monthly zooplankton samples during the study period and pooled a subsample from each sampling to obtain one composite sample per mesocosm. We found a significant effect of temperature on the community composition and size structure of the zooplankton, whereas no effects of water depth or nutrient availability could be traced. The normalised size spectrum became flatter with increasing temperature reflecting higher zooplankton size diversity due to higher abundance of calanoid copepods, but did not
Freshwater …, 2004
1. Responses of zooplankton to nutrient enrichment and fish predation were studied in 1998 and 1999 by carrying out parallel mesocosm experiments in six lakes across Europe. 2. Zooplankton community structure, biomass and responses to nutrient and fish manipulation showed geographical and year-to-year differences. Fish had a greater influence than nutrients in regulating zooplankton biomass and especially the relative abundances of different functional groups of zooplankton. When fish reduced the biomass of large crustaceans, there was a complementary increase in the biomasses of smaller crustacean species and rotifers. 3. High abundance of submerged macrophytes provided refuge for zooplankton against fish predation but this refuge effect differed notably in magnitude among sites. 4. Large crustacean grazers (Daphnia, Diaphanosoma, Sida and Simocephalus) were crucial in controlling algal biomass, while smaller crustacean grazers and rotifers were of minor importance. Large grazers were able to control phytoplankton biomass even under hypereutrophic conditions (up to 1600 lg TP L )1 ) when grazer biomass was high (>80-90 lg dry mass L )1 ) or accounted for >30% of the grazer community. 5. The littoral zooplankton community was less resistant to change following nutrient enrichment in southern Spain, at high temperatures (close to 30°C), than at lower temperatures (17-23°C) characterising the other sites. This lower resistance was because of a greater importance of nutrients than zooplankton in controlling algal biomass. 6. Apart from the reduced role of large crustacean grazers at the lowest latitude, no consistent geographical patterns were observed in the responses of zooplankton communities to nutrient and fish manipulation.
Freshwater Biology, 2004
1. Shallow lake ecosystems are normally dominated by submerged and emergent plants. Biological stabilising mechanisms help preserve this dominance. The systems may switch to dominance by phytoplankton, however, with loss of submerged plants. This process usually takes place against a background of increasing nutrient loadings but also requires additional switch mechanisms, which damage the plants or interfere with their stabilising mechanisms. 2. The extent to which the details or even major features of this general model may change with geographical location are not clear. Manipulation of the fish community (biomanipulation) has often been used to clear the water of algae and restore the aquatic plants in northerly locations, but it is again not clear whether this is equally appropriate at lower latitudes. 3. Eleven parallel experiments (collectively the International Mesocosm Experiment, IME) were carried out in six lakes in Finland, Sweden, England, the Netherlands and Spain in 1998 and 1999 to investigate the between-year and large-scale spatial variation in relationships between nutrient loading and zooplanktivorous fish on submerged plant and plankton communities in shallow lakes. 4. Comparability of experiments in different locations was achieved to a high degree. Cross-laboratory comparisons of chemical analyses revealed some systematic differences between laboratories. These are unlikely to lead to major misinterpretations. 5. Nutrient addition, overall, had its greatest effect on water chemistry then substantial effects on phytoplankton and zooplankton. Fish addition had its major effect on zooplankton and did not systematically change the water chemistry. There was no trend in the relative importance of fish effects with latitude, but nutrient addition affected more variables with decreasing latitude. 6. The relative importance of top-down and bottom-up influences on the plankton differed in different locations and between years at the same location. The outcome of the Correspondence: Brian Moss,
Controlling factors in planktonic communities over a salinity gradient in high-altitude lakes
Annales de Limnologie - International Journal of Limnology, 2015
This study aimed to determine the factors affecting plankton structure along a salinity gradient during the summer in high-altitude endorheic lakes in Catamarca Province (Argentina). During the summer 2013, eight lakes located between 3000 and 4300 meters above sea level were sampled in a 6-day period being analysed plankton, limnological variables and flamingo abundance. Principal Component Analysis explained 80% of the system variability, permitting lakes to be ordered by salinity: subhaline (SH), hypohaline (HH) and mesohaline (MH). A total of 101 phytoplankton taxa were registered, having Bacillariophyceae the highest richness (43 species registered). HH lakes were dominated by Bacillariophyceae (between 65 and 100%), while Chlorophyceae and Euglenophyceae were more abundant in SH and MH lakes. Zooplankton was poorly represented in richness (only 21 species were registered). MH lakes were dominated by Copepoda ( > 85% of total abundance) and HH lakes by Rotifera ( > 51% of total abundance). It was not found a clear pattern in SH lakes. The redundancy analysis explained 70.7% of phytoplankton variability and 75.7% of zooplankton variability. Bacillariophyceae presence was associated with availability of dissolved silica (Si), while Euglenophyceae and Chlorophyceae were associated with a higher nitrogen:phosphorus ratio. Cladocera and Copepoda abundance were linked to Euglenophyceae abundance and the area of lakes while Rotifera displayed a positive relation with the concentration of dissolved organic matter. We conclude that both phytoplankton and zooplankton abundance are mainly controlled by Bottom-Up forces including dissolved Si for Bacillariophyceae, and availability of Euglenophyceae for zooplankton while salinity and altitude have an effect on plankton richness distribution.
Hydrobiologia, 2009
We quantify the role of zooplankton in nutrient cycles in Lake Kinneret, Israel, using field data and a numerical model. A coupled ecological and hydrodynamic model (Dynamic Reservoir Model (DYRESM)-Computational Aquatic Ecosystem Dynamics Model (CAEDYM)) was validated with an extensive field data set to simulate the seasonal dynamics of nutrients, three phytoplankton groups and three zooplankton groups. Parameterization of the model was conducted using field, experimental and literature studies. Sensitivity of simulated output was tested over the full parameter space and established that the most sensitive parameters were related to zooplankton grazing rates, temperature responses and food limitation. The simulated results predict that, on average, 51% of the carbon from phytoplankton photosynthesis is consumed by zooplankton. Excretion of dissolved nutrients by zooplankton accounts for 3-46 and 5-58% of phytoplankton uptake of phosphorus and nitrogen, respectively. Comparison of nutrient fluxes attributable to zooplankton with nutrient loads from inflows and release from bottom sediments shows that the relative contribution by zooplankton to inorganic nutrients in the photic zone varies seasonally in response to the annual hydrodynamic cycle of stratification and mixing. As a percent of total dissolved organic sources relative contributions by zooplankton excretion are highest (62%) during periods of stratification and when inflow nutrient loads are low, and lowest (2%) during the breakdown of stratification and when inflow loads are high. The results illustrate the potential of a lake ecosystem model to extract useful process information to complement field data collection and address questions related to the role of zooplankton in nutrient cycles.
A comparison of zooplankton communities in saline lakewater with variable anion composition
Hydrobiologia, 2003
Although salinity and aquatic biodiversity are inversely related in lake water, the relationship between types of salts and zooplankton communities is poorly understood. In this study, zooplankton species were related to environmental variables from 12 lakes: three saline lakes with water where the dominant anions were SO4 and CO3, four saline lakes with Cl-dominated water, and five dilute, subsaline (0.5–3 gl−1 total dissolved solids) lakes of variable anion composition. Although this study comprised only 12 lakes, distinct differences in zooplankton communities were observed among the two groups of chemically defined saline lakes. Canonical correspondence analysis identified total alkalinity, sulphate, chloride, calcium, sodium, potassium, and total phosphorus as all contributing to the first two ordination axes (λ1 = 0.97 and λ2 = 0.62, PBrachionus plicatilis and the harpactacoid copepod Cletocamptus sp. prevailed lakes with Cl-dominated water. In contrast, the calanoid copepods Leptodiaptomus sicilis and Diaptomus nevadensis were dominant in the SO4/CO3-dominated lake water with elevated potassium (79–128 mg l−1) and total phosphorus concentrations (1322-2915 μg l−1). The contrasting zooplankton species distribution among these two saline lake types is likely explained by variable selective pressure on zooplankton and their predators from differing physiological tolerances to salt stress and specific ions. While inland saline lakes with Cl as the dominant anion are relatively rare in Canada and SO4/CO3 are the common features, our study provided an opportunity to compare zooplankton communities across the two groups of lakes.
Zooplankton Seasonal Abundance of South AmericanSaline Shallow Lakes
International Review of Hydrobiology, 2006
The central provinces of Argentina are characterized by the presence of a high number of shallow lakes, located in endorheic basins, many of which have elevated salinities as well as eutrophic or hypereutrophic condition. The zooplankton of four saline shallow lakes of the province of La Pampa was studied on a monthly basis during a 2-year period to determine its temporal and spatial variation.