Effects of Environmental Concentrations of Total Phosphorus on the Plankton Community Structure and Function in a Microcosm Study.

The excessive nutrients in freshwater have been proven to promote eutrophication and harmful algae blooms, which have become great threats to water quality and human health. To elucidate the responses of the plankton community structure and function to total phosphorus (TP) at environmental concentrations in the freshwater ecosystem, a microcosm study was implemented. The results showed that plankton communities were significantly affected by the TP concentration ≥ 0.1 mg/L treatments. In terms of community structure, TP promoted the growth of Cyanophyta. This effect was transmitted to the zooplankton community, resulting in the promotion of Cladocera growth from day 42. The community diversities of phytoplankton and zooplankton had been continuously inhibited by TP. The principal response curve (PRC) analysis results demonstrated that the species composition of phytoplankton and zooplankton community in TP enrichment treatments significantly (p ≤ 0.05) deviated from the control. For community function, TP resulted in the decline in phytoplankton photosynthesis. The chlorophyll fluorescence parameters were significantly inhibited when TP concentration reached 0.4 mg/L. In TP ≥ 0.1 mg/L treatments, the reductions in total phytoplankton abundances led to a continuous decrease in pH. This study can directly prove that the plankton community changes significantly when TP concentrations are greater than 0.1 mg/L and can help managers to establish specific nutrient management strategies for surface water.

Bottom-up and top-down effects on phytoplankton communities in two freshwater lakes.

The relative importance of bottom-up versus top-down effects in aquatic ecosystems remains a longstanding and ongoing controversy. To investigate these effects on phytoplankton communities in freshwater lakes, phytoplankton and zooplankton were sampled, and physical-chemical variables were measured during spring and summer in two important freshwater lakes in northern China: Nansi Lake and Dongping Lake. The redundancy analysis results showed that phytoplankton density and biomass were regulated by physical-chemical variables (bottom-up effects) and predation (top-down effects) together, and the former was more prominent in both lakes. However, the correlation analysis indicated that the top-down effects of zooplankton on phytoplankton were not significant in spring and summer in both lakes, while the bottom-up regulation of physical-chemical variables on phytoplankton had different patterns in the two lakes. In Nansi Lake, the bottom-up effects of physical-chemical variables on phytoplankton were weaker in summer than that in spring due to the abundant nutrients in summer. In Dongping Lake, the bottom-up effects of physical-chemical on phytoplankton were significant both in spring and summer, and the dominant bottom-up control factor shifted from total nitrogen in spring to total phosphorus in summer, with an increased ratio of nitrogen to phosphorus due to changes in limiting factors. In the two studied lakes, with fish culture, the bottom-up effects of phytoplankton on zooplankton were more important than the top-down effects of zooplankton on phytoplankton. These results demonstrate the interactions between phytoplankton and zooplankton and highlight the importance of phytoplankton regulation in freshwater lakes, which has implications for the effective management of freshwater lake ecosystems.

Probabilistic modeling to estimate jellyfish ecophysiological properties and size distributions.

While Ocean modeling has made significant advances over the last decade, its complex biological component is still oversimplified. In particular, modeling organisms in the ocean system must integrate parameters to fit both physiological and ecological behaviors that are together very difficult to determine. Such difficulty occurs for modeling Pelagia noctiluca. This jellyfish has a high abundance in the Mediterranean Sea and could contribute to several biogeochemical processes. However, gelatinous zooplanktons remain poorly represented in biogeochemical models because uncertainties about their ecophysiology limit our understanding of their potential role and impact. To overcome this issue, we propose, for the first time, the use of the Statistical Model Checking Engine (SMCE), a probability-based computational framework that considers a set of parameters as a whole. Contrary to standard parameter inference techniques, SMCE identifies sets of parameters that fit both laboratory-culturing observations and in situ patterns while considering uncertainties. Doing so, we estimated the best parameter sets of the ecophysiological model that represents the jellyfish growth and degrowth in laboratory conditions as well as its size. Behind this application, SMCE remains a computational framework that supports the projection of a model with uncertainties in broader contexts such as biogeochemical processes to drive future studies.

Microplastics ingestion in the ephyra stage of Aurelia sp. triggers acute and behavioral responses.

For the first time, we report a correspondence between microplastics (MP) ingestion and ecotoxicological effects in gelatinous zooplankton (Cnidarian jellyfish). The ephyra stage of the jellyfish Aurelia sp. was exposed to both environmental and high concentrations of fluorescent 1-4 µm polyethylene MP (0.01-10 mg/L). After 24 and 48 h, MP accumulation, acute (Immobility) and behavioral (Frequency pulsation) endpoints were investigated. MP were detected by confocal and tomographic investigations on gelatinous body and mouth, either attached on the surface or ingested. This interaction was responsible for impairing ephyrae survival and behavior at all tested concentrations after 24 h. Acute and behavioral effects were also related to mechanical disturbance, caused by MP, triggering a loss of radial symmetry. Contaminated ephyrae exposed to clean seawater showed full recovery after 72 h highlighting the organisms without the microspheres, attached on body jellyfish surface around the mouth and lappets. In conclusion, short-term exposure to MP affects ephyrae jellyfish health, impairing both their survival and behavior. Polyethylene MP temporarily affect both Immobility and Frequency of pulsation of Aurelia sp. jellyfish. This study provides a first step towards understanding and clarifying the potential impacts of MP contamination in gelatinous zooplankton.

Augmenting biologging with supervised machine learning to study in situ behavior of the medusa Chrysaora fuscescens.

Zooplankton play critical roles in marine ecosystems, yet their fine-scale behavior remains poorly understood because of the difficulty in studying individuals in situ Here, we combine biologging with supervised machine learning (ML) to propose a pipeline for studying in situ behavior of larger zooplankton such as jellyfish. We deployed the ITAG, a biologging package with high-resolution motion sensors designed for soft-bodied invertebrates, on eight Chrysaora fuscescens in Monterey Bay, using the tether method for retrieval. By analyzing simultaneous video footage of the tagged jellyfish, we developed ML methods to: (1) identify periods of tag data corrupted by the tether method, which may have compromised prior research findings, and (2) classify jellyfish behaviors. Our tools yield characterizations of fine-scale jellyfish activity and orientation over long durations, and we conclude that it is essential to develop behavioral classifiers on in situ rather than laboratory data.

The impact of giant jellyfish Nemopilema nomurai blooms on plankton communities in a temperate marginal sea.

This study focused on the bloom-developing process of the giant jellyfish, Nemopilema nomurai, on phytoplankton and microzooplankton communities. Two repeated field observations on the jellyfish bloom were conducted in June 2012 and 2014 in the southern Yellow Sea where blooms of N. nomurai were frequently observed. We demonstrated that the bloom was made up of two stages, namely the developing stage and the mature stage. Total chlorophyll a increased and the concentrations of inorganic nutrients decreased during the developing stage, while both concentrations maintained stable and at low levels during the mature stage. Our analysis revealed that phosphate excreted by growing N. nomurai promoted the growth of phytoplankton at the developing stage. At the mature stage, size compositions of microzooplankton were altered and tended to be smaller via a top-down process, while phytoplankton compositions, affected mainly through a bottom-up process, shifted to be less diatoms and cryptophytes but more dinoflagellates.

Macroscale abundance patterns of hydromedusae in the temperate Southwestern Atlantic (27°-56° S).

Gelatinous organisms are crucial components of marine ecosystems and some species imply social and economic consequences. However, certain geographic areas, such as the temperate Southwestern Atlantic (SWA, 27° - 56° S), remain understudied in terms of jellyfish ecological data. We analyzed 3,727 plankton samples collected along ~6.7 million km2 over a 31-year period (1983-2014) to determine the occurrence, abundance, and diversity patterns of hydromedusae in the SWA. Analyses were made at both community and species levels. Two abundance hot spots of hydromedusae were identified, where values up to 2,480 ind. m-3 were recorded between 2003 and 2014. Liriope tetraphylla and Obelia spp. were the main responsible for recurrent peaks. Diversity indexes were in the range of those published for temperate areas worldwide, and some coastal zones showed values that can be considered moderate to high for a temperate neritic region. The community analysis yielded 10 groups following previously determined biogeographic schemes throughout the study area. This work enhances the knowledge of hydromedusae in the SWA and provides essential information about the current global warming context and the gelatinous zooplankton data necessity.

Do magnetic phosphorus adsorbents used for lake restoration impact on zooplankton community?

Magnetic microparticles (MPs) have been recently proposed as innovative and promising dissolved inorganic phosphorus (DIP) adsorbents. However, before using them in a whole-lake restoration project, it is essential to assess their toxicological effects (direct and indirect) on aquatic biota. In the present study we hypothesized that zooplankton community is affected by MPs used for lake restoration. To test our hypothesis we designed a microcosms experiment (n = 15) containing lake water and surface sediment from a hypertrophic lake. Temporal changes (70 days) on physico-chemical conditions and on zooplankton structure (rotifers, copepods and branchiopods) were monitored under different scenarios. In particular, three different treatments were considered: no addition of MPs (control) and MPs addition (1.4 g MPs L-1) on the surface water layer (T-W) and on the sediment (T-S). After 24 h of contact time, MPs were removed with a magnetic rake. A total of 15 zooplankton species (12 rotifers, 1 branchiopod and 2 copepods) were recorded and a high abundance of zooplankton was registered during the experiment for all treatments. No significant differences (RM-ANOVA test; p > 0.05) in total abundance, species richness and species diversity among treatments were found. The absence of any effect of MPs on zooplankton can be explained because MPs did not significantly alter any of its physico-chemical (e.g. temperature, pH, O2) or biological (e.g. food quantity and quality) drivers. These results confirm the suitability of MPs as a promising tool for removing DIP in eutrophic aquatic ecosystems.

Fish-mediated plankton responses to increased temperature in subtropical aquatic mesocosm ecosystems: Implications for lake management.

Although it is well established that climate warming can reinforce eutrophication in shallow lakes by altering top-down and bottom-up processes in the food web and biogeochemical cycling, recent studies in temperate zones have also shown that adverse effects of rising temperature are diminished in fishless systems. Whereas the removal of zooplanktivorous fish may be useful in attempts to mitigate eutrophication in temperate shallow lakes, it is uncertain whether similar mitigation might be achieved in warmer climates. We compared the responses of zooplankton and phytoplankton communities to climate warming in the presence and absence of fish (Aristichthys nobilis) in a 4-month mesocosm experiment at subtropical temperatures. We hypothesized that 1) fish and phytoplankton would benefit from warming, while zooplankton would suffer in fish-present mesocosms and 2) warming would favor zooplankton growth but reduce phytoplankton biomass in fish-absent mesocosms. Our results showed significant interacting effects of warming and fish presence on both phytoplankton and zooplankton. In mesocosms with fish, biomasses of fish and phytoplankton increased in heated treatments, while biomasses of Daphnia and total zooplankton declined. Warming reduced the proportion of large Daphnia in total zooplankton biomass, and reduced the zooplankton to phytoplankton biomass ratio, but increased the ratio of chlorophyll a to total phosphorus, indicating a relaxation of zooplankton grazing pressure on phytoplankton. Meanwhile, warming resulted in a 3-fold increase in TP concentrations in the mesocosms with fish present. The results suggest that climate warming has the potential to boost eutrophication in shallow lakes via both top-down (loss of herbivores) and bottom-up (elevated nutrient) effects. However, in the mesocosms without fish, there was no decline in large Daphnia or in total zooplankton biomass, supporting the conclusion that fish predation is the major driver of low large Daphnia abundance in warm lakes. In the fishless mesocosms, phytoplankton biomass and nutrient levels were not affected by temperature. Our study suggests that removing fish to mitigate warming effects on eutrophication may be potentially beneficial in subtropical lakes, though the rapid recruitment of fish in such lakes may present a challenge to success in the long-term.

Impact of anthropogenic activities on water quality and plankton communities in the Day River (Red River Delta, Vietnam).

Planktons are a major component of food web structure in aquatic ecosystems. Their distribution and community structure are driven by the combination and interactions between physical, chemical, and biological factors within the environment. In the present study, water quality and the community structure of phytoplankton and zooplankton were monthly investigated from January to December 2015 at 11 sampling sites along the gradient course of the Day River (Red River Delta, northern Vietnam). The study demonstrated that the Day River was eutrophic with the average values of total phosphorus concentration 0.17 mg/L, total nitrogen concentration 1.98 mg/L, and Chl a 54 µg/L. Microscopic plankton analysis showed that phytoplankton comprised 87 species belonging to seven groups in which Chlorophyceae, Bacillariophyceae, and Cyanobacteria accounted for the most important constituents of the river's phytoplankton assemblage. A total 53 zooplankton species belonging to three main groups including Copepoda, Cladocera, and Rotatoria were identified. Plankton biomass values were greatest in rainy season (3002.10-3 cell/L for phytoplankton and 12.573 individuals/m3 for zooplankton). Using principal correspondence and Pearson correlation analyses, it was found that the Day River was divided into three main site groups based on water quality and characteristics of plankton community. Temperature and nutrients (total phosphorus and total nitrogen) are key factors regulating plankton abundance and distribution in the Day River.

Effect of excess food nutrient on producer-grazer model under stoichiometric and toxicological constraints.

Accurately assessing the risks of contaminants requires more than an understanding of the effects of contaminants on individual organism, but requires further understanding of complex ecological interactions, elemental cycling, and the interactive effects of natural stressors, such as resource limitations, and contaminant stressors. There is increasing evidence that organisms experience interactive effects of contaminant stressors and food conditions, such as resource stoichiometry, availability and excess of nutrient. Here, we develop and analyze the first producer-grazer population model that incorporates the effects of excess nutrients, as well as nutrient limitations on grazer exposed to toxicants. We use analytical, numerical and bifurcation analysis to reduce and exploremodel parameterized for an aquatic system of algae and zooplankton exposed to methylmercury under varying phosphorus conditions. Under certain environmental conditions, our models predict higher toxicity than previous models that neglect the consequences excess nutrient conditions can have on grazer populations.

Comparative study of the effects of a small-scale trout farm on the macrozoobenthos, potamoplankton, and epilithic diatom communities.

Trout farms are one of the major sources of pollution of highland streams and rivers, which are very sensitive ecosystems otherwise scarcely influenced by human activities. A trout farm with low annual production was chosen for comparative monitoring of its effects on the macrozoobenthos, epilithic diatom, and potamoplankton communities in the receiving stream. Research was conducted every 2 months during a period of 1 year (one control point and three localities downstream from the farm). The fish farm discharge induced moderate alteration of environmental factors in the receiving watercourse, viz., significant increase of the ionized and un-ionized ammonia fraction, dissolved oxygen concentration, and biological oxygen demand. Species richness and Simpson's diversity index did not change in any of the communities. Correspondent analysis of potamoplankton community composition clearly showed trout farm effects, thereby indicating the need for reevaluation of saprobic valence values for potamoplankton species. The complete lack of influence of the trout farm discharge on the epilithic diatom community is probably due to absence of significant changes of phosphorus concentration in the receiving stream. Effects of the trout farm on the macrozoobenthos community were further characterized by 14 additional indices. The percentages of Chironomidae larvae, shredders, and total collectors; ratio of shredders to collectors; and the family biotic index are suggested as candidates for future multimetric index for measuring of trout farm influence.

The combined influence of two agricultural contaminants on natural communities of phytoplankton and zooplankton.

Concentrations of glyphosate observed in the environment are generally lower than those found to exert toxicity on aquatic organisms in the laboratory. Toxicity is often tested in the absence of other expected co-occurring contaminants. By examining changes in the phytoplankton and zooplankton communities of shallow, partitioned wetlands over a 5 month period, we assessed the potential for direct and indirect effects of the glyphosate-based herbicide, Roundup WeatherMax(©) applied at the maximum label rate, both in isolation and in a mixture with nutrients (from fertilizers). The co-application of herbicide and nutrients resulted in an immediate but transient decline in dietary quality of phytoplankton (8.3 % decline in edible carbon content/L) and zooplankton community similarity (27 % decline in similarity and loss of three taxa), whereas these effects were not evident in wetlands treated only with the herbicide. Thus, even at a worst-case exposure, this herbicide in isolation, did not produce the acutely toxic effects on plankton communities suggested by laboratory or mesocosm studies. Indirect effects of the herbicide-nutrient mixture were evident in mid-summer, when glyphosate residues were no longer detectable in surface water. Zooplankton abundance tripled, and zooplankton taxa richness increased by an average of four taxa in the herbicide and nutrient treated wetlands. The lack of significant toxicity of Roundup WeatherMax alone, as well as the observation of delayed interactive or indirect effects of the mixture of herbicide and nutrients attest to the value of manipulative field experiments as part of a comprehensive, tiered approach to risk assessments in ecotoxicology.

Ecomorphological variability of Arthrospira fusiformis (Cyanoprokaryota) in African soda lakes.

The filamentous spirally coiled cyanoprokaryote Arthrospira fusiformis is found in extremely high densities in tropical soda lakes acting as driving force of the food web. We studied pronounced temporal morphological changes of Arthrospira in Kenyan soda lakes, Nakuru and Bogoria, and identified underlying key factors. Cell (diameter and height) and filament (height of coil, coil diameter, and number) dimensions were measured from weekly samples collected over a period of 16 months. In both lakes, medium-sized cells and large, widely coiled filaments prevailed most. Percentage of large, widely coiled filaments was promoted by elevated levels of soluble reactive phosphorus, wind speed, temperature and conductivity and the opposite for small filaments. Large, narrow-coiled filaments were associated with an increase in mainly Arthrospira-grazing zooplankton and cyanophage infections. Widely coiled spirals were promoted by increased turbulences. Based on fluorescence measurements, we found widely coiled filaments representing high vitality. From this study we were able to demonstrate for the first time morphological patterns of Arthrospira in nature. Arthrospira morphotypes are suitable for indicating the biological status in soda lakes as they are subjective and therefore reflective of what is happening in its habitat. Additionally, this outcome might be also of interest for commercial 'Spirulina' farms in enhancing high-quality production.

Stimulation of fecal bacteria in ambient waters by experimental inputs of organic and inorganic phosphorus.

Fecal microbial pollution of recreational and shellfishing waters is a major human health and economic issue. Microbial pollution sourced from stormwater runoff is especially widespread, and strongly associated with urbanization. However, non-point source nutrient pollution is also problematic, and may come from sources different from fecal-derived pollution (i.e. fertilization of farm fields, lawns and gardens, and ornamental urban areas). Fecal bacteria require nutrients; thus the impact of such nutrient loading on survival and abundance of fecal coliform bacteria in ambient waters was experimentally investigated in a constructed wetland in coastal North Carolina, USA. A series of nutrient-addition bioassays testing impacts of inorganic and organic nitrogen and phosphorus demonstrated that additions of neither organic nor inorganic nitrogen stimulated fecal coliform bacteria. However, phosphorus additions provided significant stimulation of fecal coliform growth at times; on other occasions such additions did not. Dilution bioassays combined with nutrient additions were subsequently devised to assess potential impacts of microzooplankton grazing on the target fecal bacteria populations. Results demonstrated grazing to be a significant bacterial reduction factor in 63% of tests, potentially obscuring nutrient effects. Thus, combining dilution experiments with nutrient addition bioassays yielded simultaneous information on microzooplankton grazing rates on fecal bacteria, fecal bacterial growth rates, and nutrient limitation. Overall, when tested against a non-amended control, additions of either organic or inorganic phosphorus significantly stimulated fecal coliform bacterial growth on 50% of occasions tested, with organic phosphorus generally providing greater stimulation. The finding of significant phosphorus stimulation of fecal bacteria indicates that extraneous nutrient loading can, at times, augment the impacts of fecal microbial pollution of shellfishing and human contact waters.

Impacts of an uncontrolled phosphogypsum dumpsite on summer distribution of phytoplankton, copepods and ciliates in relation to abiotic variables along the near-shore of the southwestern Mediterranean coast.

In connection with the Taparura Project, studies of spatial distribution of the crustacean zooplankton community, nutrients, phytoplankton and ciliates were conducted in July 2007 at 45 stations spread over fifteen transects along the coast north of Sfax. The results showed that the N/P ratio was lower than the Redfield ratio, suggesting potential N limitation. Phytoplankton was characterised by the proliferation of several diatoms, while ciliates were largely dominated by spirotrichs. Copepods were the most abundant zooplankton present during the entire study period, comprising 61% of the total zooplankton community. Twelve copepod families were identified at every station, with a high percentage of Oithonidae (77% of copepods) dominated by Oithona nana. The abundance of this species was correlated with that of diatoms, Cocoolithophorideae and ciliated Colpodea, suggesting that O. nana may feed on a wide range of prey. Despite human pressure and industrial activities, the coastal waters north of Sfax showed a wide diversity of phytoplankton, ciliates and zooplankton.

Extracoelenteric zooplankton feeding is a key mechanism of nutrient acquisition for the scleractinian coral Galaxea fascicularis.

Internal and external feeding on zooplankton may provide scleractinian corals with important nutrients. However, the latter process has never been properly quantified. To quantify the dynamics of zooplankton capture, digestion and release for a scleractinian coral, we performed detailed video analyses of Galaxea fascicularis feeding on Artemia nauplii. A highly dynamic process of prey capture, digestion and release was observed. A single G. fascicularis polyp (N=3) captured 558±67 and released 383±75 Artemia nauplii over a 6 h interval. On average, 98.6% of prey captured was not ingested. Instead, prey items were clustered into aggregates that were digested externally by mesenterial filaments. In addition, we employed carbon, nitrogen and phosphorus analysis of zooplankton before and after digestion by G. fascicularis colonies (N=6). For total organic carbon, 43.1% (0.298±0.148 µg Artemia(-1)) was lost after 6 h of digestion. For total organic nitrogen, total organic phosphorus and orthophosphate (PO(4)(3-)), these values were 51.3% (0.059±0.028 µg Artemia(-1)), 50.9% (0.009±0.004 µg Artemia(-1)) and 84.6% (0.0019±0.0008 µg Artemia(-1)), respectively. For extracoelenteric zooplankton feeding alone, total estimated nutrient inputs for G. fascicularis colonies were 76.5±0.0 µg organic carbon, 15.2±0.0 µg organic nitrogen, 2.3±0.2 µg organic phosphorus and 0.5±0.8 µg inorganic phosphorus per cm(2) coral tissue per day. These values exceed calculations based on intracoelenteric feeding by up to two orders of magnitude. Our results demonstrate that extracoelenteric zooplankton feeding is a key mechanism of nutrient acquisition for a scleractinian coral. These results are of importance to coral aquaculture and our understanding of benthic-pelagic coupling on coral reefs.

Heterotrophy in tropical scleractinian corals.

The dual character of corals, that they are both auto- and heterotrophs, was recognized early in the twentieth Century. It is generally accepted that the symbiotic association between corals and their endosymbiotic algae (called zooxanthellae) is fundamental to the development of coral reefs in oligotrophic tropical oceans because zooxanthellae transfer the major part of their photosynthates to the coral host (autotrophic nutrition). However, numerous studies have confirmed that many species of corals are also active heterotrophs, ingesting organisms ranging from bacteria to mesozooplankton. Heterotrophy accounts for between 0 and 66% of the fixed carbon incorporated into coral skeletons and can meet from 15 to 35% of daily metabolic requirements in healthy corals and up to 100% in bleached corals. Apart from this carbon input, feeding is likely to be important to most scleractinian corals, since nitrogen, phosphorus, and other nutrients that cannot be supplied from photosynthesis by the coral's symbiotic algae must come from zooplankton capture, particulate matter or dissolved compounds. A recent study showed that during bleaching events some coral species, by increasing their feeding rates, are able to maintain and restore energy reserves. This review assesses the importance and effects of heterotrophy in tropical scleractinian corals. We first provide background information on the different food sources (from dissolved organic matter to meso- and macrozooplankton). We then consider the nutritional inputs of feeding. Finally, we review feeding effects on the different physiological parameters of corals (tissue composition, photosynthesis and skeletal growth).

[Biological process of phosphorus turnover in surface water body of Xiamen Harbor. II: Grazing pressure of copepod on phytoplankton].

To understand the roles of copepod in the biogeochemical cycling of phosphorus, gut fluorescence method was applied to examine in situ the grazing rate of copepod on the phytoplankton in Xiamen Time Station (XMTS) in May, August and November 2005 and March 2006. In the meanwhile, the abundance and species composition of copepod were investigated, and the grazing pressure of copepod on the phytoplankton was estimated. The results showed that the annual average grazing rate of copepod was 55.53 microg x m(-3) x d(-1), being the highest (108.98 microg x m(-3) x d(-1)) in autumn and the lowest (7.18 microg x m(-3) x d(-1)) in summer. Based on the estimation from our experimental data, the daily grazing rate of copepod populations on the phytoplankton in Xiamen Harbor was, on annual average, about 1.81% of the phytoplankton's standing stock, with the values in spring, summer, autumn, and winter being 3.22%, 0.06%, 3.52% and 0.46%, respectively.

Zooplankton biodiversity and lake trophic state: explanations invoking resource abundance and distribution.

While empirical studies linking biodiversity to local environmental gradients have emphasized the importance of lake trophic status (related to primary productivity), theoretical studies have implicated resource spatial heterogeneity and resource relative ratios as mechanisms behind these biodiversity patterns. To test the feasibility of these mechanisms in natural aquatic systems, the biodiversity of crustacean zooplankton communities along gradients of total phosphorus (TP) as well as the vertical heterogeneity and relative abundance of their phytoplankton resources were assessed in 18 lakes in Quebec, Canada. Zooplankton community richness was regressed against TP, the spatial distribution of phytoplankton spectral groups, and the relative biomass of spectral groups. Since species richness does not adequately capture ecological function and life history of different taxa, features which are important for mechanistic theories, relationships between zooplankton functional diversity (FD) and resource conditions were examined. Zooplankton species richness showed the previously established tendency to a unimodal relationship with TP, but functional diversity declined linearly over the same gradient. Changes in zooplankton functional diversity could be attributed to changes in both the spatial distribution and type of phytoplankton resource. In the studied lakes, spatial heterogeneity of phytoplankton groups declined with TP, even while biomass of all groups increased. Zooplankton functional diversity was positively related to increased heterogeneity in cyanobacteria spatial distribution. However, a smaller amount of variation in functional diversity was also positively related to the ratio of biomass in diatoms/chrysophytes to cyanobacteria. In all observed relationships, a greater variation of functional diversity than species richness measures was explained by measured factors, suggesting that functional measures of zooplankton communities will benefit ecological research attempting to identify mechanisms behind environmental gradients affecting diversity.