Primary production of phytoplankton and periphyton in two humic lakes of a South American wetland

Seasonal primary productivities of periphyton and phytoplankton were compared in Grande Lake (GL) and a relict oxbow lake (ROL) in winter 2006 and summer 2007. GL was free of floating plants on the sampling dates and covered over 80 and 100% of the ROL surface in winter and summer, respectively. The ¹⁴C assimilation technique was used to obtain the P–E curves of phytoplankton and periphyton on artificial substrata. The periphytic maximum photosynthetic rate (P _max) was higher in the ROL in winter and summer, being better adapted to low irradiances than those in the GL. Phytoplankton and periphytic algae were light-limited in the ROL in summer due to complete coverage by floating macrophytes. In summer, P _max and α values for periphyton in the ROL were higher than those for phytoplankton, and were even higher than in GL. In turn, P _max and α values for phytoplankton in Grande Lake were higher than those for periphyton due to improved light conditions and the presence of algae that were adapted to movement through the water column. These results suggest that the complete coverage by floating macrophytes restricted phytoplankton productivity and allowed the development of a periphytic community that was better adapted to low-light conditions.     

Driving forces shaping phytoplankton assemblages in two subtropical plateau lakes with contrasting trophic status

1. We studied driving forces shaping phytoplankton assemblages in two subtropical plateau lakes with contrasting trophic status, the oligotrophic deep Lake Fuxian and the eutrophic shallow Lake Xingyun. 2. Phytoplankton samples were taken monthly for a year and phytoplankton species were sorted into the main taxonomic groups and associations proposed by Reynolds. A canonical correspondence analysis (CCA) was used to test the occurrence of these classification schemes and to determine their discriminatory power. 3. The results suggest that the major driving forces in Lake Fuxian were physical variables, and particularly the underwater light climate, whereas, nutrients were the important driving force in Lake Xingyun. 4. Top–down control through zooplankton grazing in Lake Fuxian was hardly ever a significant determinant itself, because of the scarcity of zooplankton and their low grazing efficiency of predation while a dominance of inedible cyanobacteria throughout the year rendered top–down controls ineffective failing in Lake Xingyun. Hence phytoplankton communities in both lakes appear to be regulated primarily by bottom–up controls.     

Nutrient balances and phytoplankton dynamics in two agriculturally loaded shallow lakes

The impact of agriculture was estimated on two shallow, eutrophic lakes, Lake Kotojärvi and Lake Villikkalanjärvi in southern Finland. The main emphasis was on phosphorus and nitrogen budgets and on the phytoplankton dynamics. Special attention was paid to internal P loading and blue-green algal blooms. The mean Tot-P load from agricultural land was 1.2 kg ha^-1 a^-1 in both basins and Tot-N loads were 19 kg ha^-1 a^-1 in L. Villikkalanjärvi and 12 kg ha^-1 a^-1 in L. Kotojärvi. The Tot-P input to L. Kotojärvi was on an average 0.62 g m^-2 a^-1 (per lake surface area), and the Tot-N input 9.1 g m^-2 a^-1. The corresponding inputs to L. Villikkalanjärvi were 3.1 and 57 g m^-2 a^-1, respectively. The annual variation followed the runoff volumes. About half of the Tot-P and one third of the Tot-N load was retained in L. Kotojärvi. In L. Villikkalanjärvi the retention was only 24% for Tot-P and 19% for Tot-N. The difference was very probably due to a longer theoretical retention time in L. Kotojärvi. In L. Villikkalanjärvi the mean concentration of Tot-P was 120 µg 1^-1 and that of Tot-N 1700 µg 1^-1 and the corresponding figures in L. Kotojärvi 67 and 990 µg 1^-1, respectively. The mean chlorophyll a concentration was, however, higher in L. Kotojärvi (26 µg 1^-1) than in L. Villikkalanjärvi (20 µg 1^-1). This was probably due to an internal P load in L. Kotojärvi: in 1988 the internal load of dissolved P was estimated to be as much as twofold the external load. In L. Villikkalanjärvi the internal dissolved P load was only up to 50% of the external input. In L. Kotojärvi the high internal P load coupled with a low DIN:DIP ratio resulted in a strong blue-green algal bloom in the summer of 1988. In L. Villikkalanjärvi blue-green algae were observed only in small amounts. Even in August 1990, when the DIN:DIP ratio was low enough to favor the occurrence of blue-green algae, they contributed only up to 10–15% of the total phytoplankton biomass.     

An experimental investigation of phytoplankton nutrient limitation in two contrasting low arctic lakes

We investigated whether phytoplankton communities in two lakes in SW Greenland were phosphorus or nitrogen limited. The study lakes have contrasting water chemistry (mean conductivities differ ten fold) and are located near Kangerlussuaq, SW Greenland (~67°N, 51°W). A microcosm nutrient enrichment experiment was performed in June 2003 to determine whether nitrate or phosphate addition stimulated phytoplankton growth. Samples were analysed for species composition, biomass, and alkaline phosphatase activity (APA). Initially, both lakes had extremely low total phosphorus but high total nitrogen concentrations and high APA, suggesting that the phytoplankton were phosphorus limited prior to the start of the experiment. The phytoplankton composition and biomass (mainly Ochromonas spp.) responded to phosphate but not to nitrate addition. In both lakes, chlorophyll a increased significantly when phosphate was added. Furthermore, APA was significantly lower in the two lakes when phosphate was added compared to the control and the nitrogen addition treatment. The dominance of mixotrophic phytoplankton and high DOC values suggest that these lakes may be regulated by microbial loop processes.     

Primary production studies in two linked but contrasting Welsh lakes

SUMMARY. Llyn Padarn and Llyn Peris have distinct phytoplankton populations. During 1975–76, the standing crop measured as chlorophyll- a was 5.5 times greater in Padarn than in Peris and the production rate, determined by the ¹⁴CO₂ method, was faster by 3.4 times. These differences were attributed to the higher concentrations of phosphorus in the lower lake caused by treated sewage effluent. Incident light intensity, which was slightly lower in Peris due to mountain shading, and temperature, which was 1–4°C higher in Padarn, made little significant contribution to these differences during the summer. The reduced transparency of Padarn water, compared with that of Peris, resulted from denser phytopiankton crops in Padarn. During the summer, Padarn exhibited carbon dioxide depletion which correlated with the chlorophyll concentration. Light inhibition at the surfaces of both lakes correlated with solar radiation intensity. However, the relationship between pigment content and maximum photosynthetic rate was poor. Extracellular products accounted for about 16% of the total production in the lakes. Uptake of ¹⁴C-labelled acetate was low compared with that of ¹⁴CO₂ uptake.     

Populations and production of bacteria in the plankton of two shallow lakes

The troglobitic amphipod crustacean Crangonyx antennatus populates two distinct habitats in southern Appalachian caves, mud-bottom pools and gravel-bottom streams. An investigation was conducted to determine if stream populations possess behavioral adaptations to lotic conditions. Observations on the thigmotactic behavior of C. antennatus were made seasonally in six Lee Co., Virginia caves, three containing pool habitats and three with stream habitats. Stream-dwelling amphipods were found to exhibit more cryptic behavior than those inhabiting pools under natural conditions and when disturbed. Artificial stream experiments indicate that stream-dwelling C. antennatus are better adapted behaviorally to lotic conditions than pool-dwelling amphipods.     

The importance of bacterial utilization of released phytoplankton photosynthate in two humic forest lakes in southern Finland

Bacterial utilization of photosynthetically fixed dissolved organic carbon (PDOC) released from natural phytoplankton assemblages was studied in two small, extremely humic, forest lakes in southern Finland. Bacterial activity (measured as uptake of ¹⁴C-glucose) and phytoplankton photosynthesis (measured as light uptake of ¹⁴CO₂) could be most effectively separated using Nuclepore filters of pore size 1–2 μm. Released PDOC was 10–67% of total phytoplankton carbon fixation during in situ experiments, and represented about 0.1% of total DOC. Net uptake of PDOC by bacteria was found to be about 20% during 24 hour laboratory incubations, although about 40% of PDOC present at the start of an experiment could be utilized by bacteria during a 24 hour period. PDOC does not provide a quantitatively important substrate supply for bacterial respiration in humic forest lakes.     

Nutrient limitation of bacterioplankton and phytoplankton in humic lakes in northern Sweden

1. Two small humic lakes in northern Sweden with concentrations of dissolved organic carbon (DOC) between 15 and 20 mg L^–1 were fertilized with inorganic phosphorus (P) and inorganic nitrogen (N), respectively. A third lake was unfertilized and served as a control. In addition to this lake fertilization experiment, data from different regional surveys were used to assess the role of different limiting factors.
2. The P fertilization had no effects on bacterioplankton or phytoplankton, while phytoplankton were significantly stimulated by N fertilization. Inorganic nutrient limitation of bacterioplankton was a function of DOC concentration in water of the investigated region and nutrient-limited bacteria were found only in lakes with DOC concentrations less than around 15 mg L^–1
3. The fertilization experiments demonstrated that the DOC-rich experimental lakes contained a bioavailable pool of P that was not utilized to its full potential under natural conditions. The overall mobilization of energy (bacterioplankton plus phytoplankton) in the experimental lakes was restricted by lack of inorganic N.     

Bacterial chitin hydrolysis in two lakes with contrasting trophic statuses

Chitin, which is a biopolymer of the amino sugar glucosamine (GlcN), is highly abundant in aquatic ecosystems, and its degradation is assigned a key role in the recycling of carbon and nitrogen. In order to study the significance of chitin decomposition in two temperate freshwater lakes with contrasting trophic and redox conditions, we measured the turnover rate of the chitin analog methylumbelliferyl-N,N'-diacetylchitobioside (MUF-DC) and the presence of chitinase (chiA) genes in zooplankton, water, and sediment samples. In contrast to the eutrophic and partially anoxic lake, chiA gene fragments were detectable throughout the oligotrophic water column and chiA copy numbers per ml of water were up to 15 times higher than in the eutrophic waters. For both lakes, the highest chiA abundance was found in the euphotic zone--the main habitat of zooplankton, but also the site of production of easily degradable algal chitin. The bulk of chitinase activity was measured in zooplankton samples and the sediments, where recalcitrant chitin is deposited. Both, chiA abundance and chitinase activity correlated well with organic carbon, nitrogen, and concentrations of particulate GlcN. Our findings show that chitin, although its overall contribution to the total organic carbon is small (~0.01 to 0.1%), constitutes an important microbial growth substrate in these temperate freshwater lakes, particularly where other easily degradable carbon sources are scarce.     

Live labeling technique reveals contrasting role of crustacean predation on microbial loop in two large shallow lakes

We tested the hypotheses that the ciliate assemblages in moderately eutrophic lake are controlled by the effective crustacean predation, and the high abundances of planktonic ciliates in highly eutrophic and turbid lake are due to insufficient regulation by crustacean zooplankton. A food tracer method coupled with natural assemblage of microciliates labeled with fluorescent microparticles was used to measure the cladoceran and copepod predation rates on planktonic ciliates and to estimate the carbon flow between the ciliate–crustacean trophic links. The results revealed that the microciliates (15–40 μm) were consumed by all dominant cladoceran and copepod species in both the lakes studied, mainly by Chydorus sphaericus and cyclopoid copepods in Lake Võrtsjärv, and by Daphnia spp. and Bosmina spp. in Lake Peipsi. The grazing loss in moderately eutrophic Peipsi indicated strong top-down control of ciliates mainly by cladocerans. The extraordinary abundant population of planktonic ciliates having a predominant role in the food web in highly eutrophic and turbid Võrtsjärv is explained by the measured low crustacean predation rates on ciliates. The estimated carbon flow from the ciliates to crustaceans suggest that in eutrophic lakes majority of the organic matter channeled via metazooplankton to higher trophic levels may originate from the microbial loop.     

Structure, biomass, production and depth distribution of periphyton on artificial substratum in shallow lakes with contrasting nutrient concentrations

1. To examine how the vertical distribution of periphytic biomass and primary production in the upper 0–1 m of the water column changes along an inter‐lake eutrophication gradient, artificial substrata (plastic strips) were introduced into the littoral zones of 13 lakes covering a total phosphorus (TP) summer mean range from 11 to 536 μg L^?1. Periphyton was measured in July (after 8 weeks) and September (after 15 weeks) at three water depths (0.1, 0.5 and 0.9 m). 2. Periphyton chlorophyll a concentration and dry weight generally increased with time and the communities became more heterotrophic. Mean periphytic biomass was unimodally related to TP, reaching a peak between 60 and 200 μg L^?1. 3. The proportion of diatoms in the periphyton decreased from July to September. A taxonomic shift occurred from dominance (by biovolume) of diatoms and cyanobacteria at low TP to dominance of chlorophytes at intermediate TP and of diatoms (Epithemia sp.) in the two most TP‐rich lakes. 4. The grazer community in most lakes was dominated by chironomid larvae and the total biomass of grazers increased with periphyton biomass. 5. Community respiration (R), maximum light‐saturated photosynthetic rate (P_max), primary production and the biomass of macrograzers associated with periphyton were more closely related to periphyton biomass than to TP. Biomass‐specific rates of R, P_max and production declined with increasing biomass. 6. Mean net periphyton production (24 h) was positive in most lakes in July and negative in all lakes in September. Net production was not related to the TP gradient in July, but decreased in September with increasing TP. 7. The results indicate that nutrient concentrations alone are poor predictors of the standing biomass and production of periphyton in shallow lakes. However, because periphyton biomass reaches a peak in the range of phosphorus concentration in which alternative states occur in shallow lakes, recolonisation by submerged macrophytes after nutrient reduction may potentially be suppressed by periphyton growth.     

Primary production and phytoplankton in two small,polyhumic forest lakes in southern Finland

Primary production and phytoplankton in polyhumic lakes showed a very distinct seasonal succession. A vigorous spring maximum produced by Chlamydomonas green algae at the beginning of the growing season and two summer maxima composed mainly of Mallomonas caudata Iwanoff were typical. The annual primary production was ca. 6 g org. C · m^–2 in both lakes. The mean epilimnetic biomass was 1.1 in the first lake and 2.2 g · m^–2 (ww) in the second one. The maximum phytoplankton biomass, 14 g · m^–2, was observed during the vernal peak in May.     

Zooplankton spatial patterns in two lakes with contrasting fish community structure

Horizontal and temporal patterns in crustacean zooplankton communities were analyzed in two small, oligotrophic lakes which were morphologically and chemically similar, but had contrasting fish communities. Ranger Lake was dominated by two bass species and the planktivores numbered < 25 ind. ha^–1. Mouse Lake had no large piscivores and planktivores numbered > 1200 ind. ha^–1. There were significant differences in the distribution of zooplankton taxa and size classes between sampling stations. In Ranger Lake, the smallest size classes were more abundant at the deeper stations and the larger individuals were more abundant at the shallower stations. In Mouse Lake, the smaller individuals were more common at the shallow stations and the larger individuals were more common at the deeper stations. These differences suggest medium scale patterns induced by vectorial forces, but modified by species specific migration patterns. We tested the hypothesis that horizontal heterogeneity should be influenced by planktivore density and found that none of the taxa showed significant between-lake differences in the variance-mean regressions. We also tested the hypothesis that larger taxa should be more heterogeneous and we found that cladocerans were more heterogeneous than copepods and nauplii. In terms of sampling methodology our data suggest that the between-station variability was so high that a single mid-lake sample would certainly lead to completely unacceptable errors in the estimation of population densities and biomasses.     

Cladoceran and rotifer grazing on bacteria and phytoplankton in two shallow eutrophic lakes: in situ measurement with fluorescent microspheres

Metazooplankton grazing on bacteria and on the phytoplanktonof various sizes was estimated in shallow eutrophic lakes Kaiavereand Võrtsjärv (Estonia) by in situ feeding experimentswith fluorescent microspheres (diameters 0.5 µm for bacteriaand 3, 6 and 24 µm for phytoplankton). Zooplankton communitycomposition, abundance and food density were important factorsdetermining grazing rates in these lakes. Cladocerans and rotifersfiltering rates (FR) and ingestion rates (IR) on bacteria andphytoplankton were several times higher in Lake Kaiavere wherebacterivorous rotifers and Daphnia contributed more to zooplanktonassemblage. While cladocerans were generally the main phytoplanktonconsumers, both lakes differed with respect to the groups ofbacterivores. Based on consumption of fluorescent microspheres,the metazooplankton grazing rates were relatively low and hadlow impact on production and standing stock of bacteria andingestible phytoplankton (<30 µm). On average, 0.5and 0.1% of standing stock of bacteria and 2.6 and 1.0% of standingstock of ingestible phytoplankton was grazed daily by metazooplanktonin lakes Kaiavere and Võrtsjärv, respectively. Thatcorresponded to daily grazing of 4.1% of the bacterial productionand 0.43% of the total primary production (PP) by metazooplanktonin Lake Kaiavere compared with 4.3 and 0.06% in Lake Võrtsjärv,respectively. The results suggest that the majority of consumptionof the bacterial and phytoplankton PP is most likely channelledthrough the microbial loop.     

Relationship between epipelon,epiphyton and phytoplankton in two limnological phases in a shallow tropical reservoir with high Nymphaea coverage

Macrophytes and phytoplankton are recognized as having roles in determining alternative stable states in shallow lakes and reservoirs, while the role of periphyton has been poorly investigated. Temporal and spatial variation of phytoplankton, epipelon and epiphyton was examined in a shallow reservoir with high abundance of aquatic macrophytes. The relationships between algae communities and abiotic factors, macrophyte coverage and zooplankton density were also analyzed. Monthly sampling was performed in three zones of the depth gradient of the reservoir. Two phases of algal dominance were found: a phytoplankton phase and epipelon phase. The phase of phytoplankton dominance was characterized by high macrophyte coverage. Rotifera was the dominant zooplankton group in all the zones. Flagellate algae were dominant in phytoplankton, epipelon and epiphyton. Macrophyte coverage was found to be a predictor for algal biomass. Changes in biomass and species composition were associated with macrophyte cover variation, mainly the Nymphaea. In addition to the abiotic factors, the macrophyte coverage was a determining factor for changes to the algal community, contributing to the alternation between dominance phases of phytoplankton and epipelon. The macrophyte–phytoplankton–periphyton relationship needs to be further known in shallow reservoirs, especially the role of epipelon as an alternate stable state.

     

Productivity of clear and humic lakes: nutrients,phytoplankton, bacteria

The relationships between long-term surface average concentrations of humic acids measured as water colour, dissolved organic carbon (DOC) or Secchi disk transparency and trophic state variables were studied with literature data from more than 600 freshwater lakes. The geometric means of summer surface average nutrient (phosphorus and nitrogen) concentration, phytoplankton biomass (chlorophyll concentration), and hypolimnetic anoxia (anoxic factor) were significantly higher in coloured than in clear lakes. The regressions of colour or DOC on these trophic state variables were positive and significant throughout a range of three orders of magnitude. Phytoplankton or primary productivity was higher in coloured lakes, when expressed per volume of epilimnion. Annual integral primary productivity expressed on an areal basis was smaller in coloured lakes, probably a reflection of shallower phototrophic depths in these lakes. There is evidence that annual integral bacteria productivity is much higher in coloured lakes for two reasons: first, epilimnetic bacteria production was ca. four times higher in coloured lakes, second, other studies have shown that hypolimnetic bacteria production is commonly higher than epilimnetic production, especially in anoxic hypolimnia that are frequent in coloured lakes. All volumetrically expressed variables indicated higher productivity in coloured lakes. In addition, high bacteria productivity reflects a different food chain involving mixotrophs, possibly compensating for low light conditions. Our analyses indicate that primary and secondary productivity is as high as or higher than in clear lakes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Vertical distribution of primary production and phytoplankton in two small lakes with different humus concentration in southern Finland

Vertical distribution of primary production and phytoplankton was studied in a polyhumic brownwater lake and in an oligo-mesohumic lake. During summer both lakes were thermally, chemically and biologically stratified. In the brownwater lake primary production was restricted to the uppermost layer of 1–1.5 m of epilimnion. In the oligo-mesohumic lake noticeable primary production was detected down to depths of 2–3 m. The ice-free period primary production was about 20% higher in the oligo-mesohumic lake, though occasionally the surface production was 2–3 times higher in the brownwater lake. Epilimnetic total phosphorus and total nitrogen concentrations were higher in the brownwater lake, while nitrate-nitrite, ammonium and phosphate concentrations were very low in both lakes.
Phytoplankton was confined to the uppermost productive layer in the brownwater lake. In the oligo-mesohumic lake phytoplankton was distributed more evenly, though the mean maximum biomass was at the depth of 3–4 m. Below the oxic water layer biomass decreased abruptly in both lakes. In the oligo-mesohumic lake chlorophyll concentration was extremely high (max. 320 mg chl a m⁻³) in the anoxic hypolimnion, due to green sulphus bacteria.
Flagellated chlorophytes and thrysophytes dominated in the brownwater lake; in spring Chlamydomonas species, followed by Mallomonas caudata . In the oligo-mesohumic lake small coccal green algae, such as Oocystis, Scenedesmus and Westella -like species, dominated in mid-summer, and chrysophytes and cryptomonads in autumn.     

Winter phytoplankton community structure in three shallow temperate lakes during ice cover

The general model of seasonal phytoplankton succession in temperate lakes suggests that winter phytoplankton growth is minimal under ice-cover. However, some studies have found diverse phytoplankton communities during winter. The primary objectives of this study were to determine the species composition and the changes in the winter phytoplankton community structure under the ice. For 2 consecutive winters, phytoplankton samples were collected under ice-cover at 4 sites on 3 lakes in Arrowwood National Wildlife Refuge (ANWR), near Pingree, North Dakota. Ninety taxa were identified and enumerated. Densities of several of these taxa frequently exceeded 10⁶ cells l^–1. The winter phytoplankton communities in these lakes were dominated by flagellates, principally cryptomonads, a synurophyte (Synura uvella), small chrysophytes (Chrysococcus spp., Kephyrion spp.) and a dinoflagellate (Peridinium aciculiferum), as well as non-flagellate microchlorophytes (Monoraphidium spp., Ankistrodesmus spp., and Pseudodictyosphaerium sp.), a cyanobacterium (Gloeocapsa aeruginosa) and centric diatoms (Stephanodiscus minutulus, S. parvus and Cyclotella meneghiniana).     

Effect of grazers and viruses on bacterial community structure and production in two contrasting trophic lakes

Background

Over the last 30 years, extensive studies have revealed the crucial roles played by microbes in aquatic ecosystems. It has been shown that bacteria, viruses and protozoan grazers are dominant in terms of abundance and biomass. The frequent interactions between these microbiological compartments are responsible for strong trophic links from dissolved organic matter to higher trophic levels, via heterotrophic bacteria, which form the basis for the important biogeochemical roles of microbial food webs in aquatic ecosystems. To gain a better understanding of the interactions between bacteria, viruses and flagellates in lacustrine ecosystems, we investigated the effect of protistan bacterivory on bacterial abundance, production and structure [determined by 16S rRNA PCR-DGGE], and viral abundance and activity of two lakes of contrasting trophic status. Four experiments were conducted in the oligotrophic Lake Annecy and the mesotrophic Lake Bourget over two seasons (early spring vs. summer) using a fractionation approach. In situ dark vs. light incubations were performed to consider the effects of the different treatments in the presence and absence of phototrophic activity.

Results

The presence of grazers (i.e. < 5-μm small eukaryotes) affected viral production positively in all experiments, and the stimulation of viral production (compared to the treatment with no eukaryotic predators) was more variable between lakes than between seasons, with the highest value having been recorded in the mesotrophic lake (+30%). Viral lysis and grazing activities acted additively to sustain high bacterial production in all experiments. Nevertheless, the stimulation of bacterial production was more variable between seasons than between lakes, with the highest values obtained in summer (+33.5% and +37.5% in Lakes Bourget and Annecy, respectively). The presence of both predators (nanoflagellates and viruses) did not seem to have a clear influence upon bacterial community structure according to the four experiments.

Conclusions

Our results highlight the importance of a synergistic effect, i.e. the positive influence of grazers on viral activities in sustaining (directly and indirectly) bacterial production and affecting composition, in both oligotrophic and mesotrophic lakes.     

Patterns of microbial food webs in Mediterranean shallow lakes with contrasting nutrient levels and predation pressures

Hygraula nitens is a New Zealand native moth with aquatic larvae that feed on submerged aquatic plants. The larvae have been mainly observed using native Potamogeton and Myriophyllum species as a food source, although some studies reported larvae feeding on the alien macrophytes Hydrilla verticillata, Lagarosiphon major and Ceratophyllum demersum. Experimental mesocosm studies showed larvae had a major effect on H. verticillata, C. demersum, L. major, Elodea canadensis and Egeria densa. In both no choice and choice experiments H. nitens larvae showed a clear preference for and the highest consumption of C. demersum, while the native macrophyte Myriophyllum triphyllum ranked fourth out of five alien and two native plant species, indicating a preference of the larvae for alien macrophytes. Additional choice experiments using C. demersum, sampled from different waters in NZ, illustrated that there was a clear difference in H. nitens preference for plants based on their source. However although C. demersum had the lowest leaf dry matter content (LDMC) compared with the other macrophytes, neither the LDMC nor leaf carbon, nitrogen, phosphorus or total phenolic contents alone could explain the preferences of H. nitens, and we conclude that food choice is based on a combination of these and/or additional factors.