Biovolume as a tool in biomass determination of Oligochaeta and Chironomidae

• 1 We used biovolume as a simple non-destructive means for estimating biomass for several tubificid and chironomid species. Biovolumes were determined by treating the organisms as cylinders and measuring body lengths and diameters; estimates were verified by measuring the displacement of water by live organisms in a 5-ml burette. In addition, factors were determined for the conversion of biovolume (V) into wet weight (WW), dry weight (DW) and ash-free dry weight (AFDW).
• 2 For six tubificid species, regression functions between the diameter of segment XI (D₁₁) and the biovolume enabled the prediction of any biovolume merely by measuring D₁₁. This method, however, underestimated biovolumes of Branchiura sowerbyi by 38–47% compared with burette measurements. This difference is largely attributable to the mountant we used during identification.
• 3 For ten chironomid species a linear relation was found between body length and the diameter of abdominal segment 5. The biovolume of Chironomus muratensis was underestimated by an average of 12% compared with burette measurements.
• 4 Specific gravity (WW:V) amounted to 1.07 and 1.05, DW:WW ratios were 0.20 and 0.142 and AFDW:WW ratios were 0.182 and 0.129 for Oligochaeta and Chironomidae, respectively.
• 5 The biovolume method is not yet very accurate for Oligochaeta, but to our knowledge, it is the only practical method that can be used in natural polyspecific communities that need to be treated with elucidating media for identification. For those Chironomidae that need no elucidation for identification, this method is time saving and just as accurate as the direct body shape—biomass method.

     

Changes in algal assemblages along observed and experimental phosphorus gradients in a subtropical wetland, U.S.A.

• 1 We wanted to determine if changes in algae in the Everglades were due to increased phosphorus (P) loading. Epiphytic algae, water chemistry, and surface sediment chemistry were characterized from 32 sloughs along a P gradient in the Everglades and changes in the algal assemblages along the P gradient were compared with those along an experimental P gradient of in situ mesocosms. The sloughs are the wettest open water habitats characterized by floating and submerged aquatic plants in the Everglades.
• 2 Algal species composition was much more sensitive to P concentration than algal biomass. The diatom species variance among sloughs, captured by 1st ordination axis, was more highly correlated with total P (TP) in surface sediments (r = ‐ 0.79), than soluble reactive P (SRP) (r = ‐ 0.08) and TP (r = ‐ 0.48) in the water column. Algal biomass (µg chl a cm^‐2) was not significantly correlated with P (SRP: r = 0.22, TP: r = 0.19, sediment TP: r = 0.07) along the P gradient in the Everglades. Cluster analysis classified diatom species assemblages in 32 sloughs into three groups (TWIN I, II, III), which corresponded to three zones along the P gradient. Dominant diatom species shifted from Mastogloia smithii (40.3%), Cymbella scotica (22.3%), and Fragilaria synegrotesca (21.8%) in TWIN I to Nitzschia amphibia (22.4%) and C. microcephala (12.4%) in TWIN III. TP in surface sediments and TP in epiphyton assemblages increased 4‐ and 5‐fold from TWIN I to TWIN III, respectively.
• 3 Patterns in epiphytic assemblages along the experimental P gradient in the mesocosms were very similar to those along the Everglades P gradient. Shannon diversity indices and species richness significantly increased along both P gradients. TN : TP ratio in epiphyton assemblages significantly decreased as sediment TP increased along both P gradient. Ordination analysis showed that diatom assemblages in the impacted zone (TWIN III) were ordinated closely to the assemblages from the highest P treatments in the mesocosms. The assemblages from the less impacted zone (TWIN I) were ordinated closely to the assemblages from controls in the mesocosms.
• 4 Concurrence between results of our survey and experiments suggest that changes in epiphytic assemblages along the P gradient in the Everglades are caused by increases in P concentrations.

     

Calanoid copepod grazing on phytoplankton: seasonal experiments on natural communities

Calanoid copepods are major components of most lacustrine ecosystems and their grazing activities may influence both phytoplankton biomass and species composition. To assess this we conducted four seasonal, in situ, grazing experiments in eutrophic Lake Rotomanuka, New Zealand. Ambient concentrations of late stage copepodites and adults of calanoid copepods (predominantly Calamoecia lucasi, but with small numbers of Boeckella delicata) were allowed to feed for nine days on natural phytoplankton assemblages suspended in the lake within 1160 litre polyethylene enclosures. The copepods reduced the total phytoplankton biomass of the dominant species in all experiments but were most effective in summer (the time of highest grazer biomass) followed by spring and autumn. In response to grazing pressure the density of individual algal species showed either no change or a decline. There were no taxa which increased in density in the presence of the copepods. The calanoid copepods suppressed the smallest phytoplankton species (especially those with GALD (Greatest Axial Linear Dimension) < µm) and there appeared to be no selection of algae on the basis of biovolume. Algal taxa which showed strong declines in abundance in the presence of the copepods include Cyclotella stelligera, Coelastrum spp., Trachelomonas spp., Cryptomonas spp., and Mallomonas akrokomos. Calanoid copepods are considered important grazers of phytoplankton biomass in this lake. The study supports the view that high phytoplankton:zooplankton biomass ratios and large average algal sizes characteristic of New Zealand lake plankton may, at least partly, be caused by year round grazing pressure on small algae shifting the competitive balance in favour of larger algal species.     

Development of the Periphytic Community on Artificial Substrates in Fish Ponds

The development of the periphytic algae and macrofauna was examined in two fish ponds. 43 genera of algae (mainly diatoms) were found on the substrates, and the maximum of algae was reached on the 10th day. The periphytic macrofauna consisted of 37 taxonomical groups (mainly Chironomidae). Larvae of Cricotopus intersectus were the most abundant species. Since the 2nd day of exposure, the number of Cricotopus larvae strongly increased by immigration of 2nd instars until the maximum was reached on the 15th day. No further significant oscillations were found in either the algal or animal component until the 75th day of exposure. The field observations and laboratory experiments confirmed that:

• (1) The distribution of frequencies of Cricotopus larvae found on 200 cm² surfaces could be approximated by the normal distribution.
• (2) The density of the algal periphyton is controlled by abiotic factors, not by grazing by chironomid larvae.
• (3) The Cricotopus larvae of the 2nd instar colonize the substrate only after the algal film has been formed. Later instars are sedentary and do not colonize new substrate (except under stress conditions).
• (4) Food and predation do not seem to be the factors controlling the Cricotopus population density. The main factor is considered to be the territorial behaviour of the larvae.

     

The effect of tubificids and chironomids on particle redistribution of lake sediment

The effects of chironomid larvae,Chironomus plumosus, and tubificid worms,Limnodrilus spp., on particle redistribution in lake sediment were investigated experimentally using pots containing sediments obtained from Lake Suwa, Japan. The chironomids and tubificids increased the water content of surface sediment. The chironomid larvae had no effect on particle size distribution, while tubificids continuously accumulated small particles on the surface sediment through their selective feeding activity. Particles larger than 0.125 mm were buried at a sediment depth of 6 cm. In Lake Suwa, long diatom frustules, large plant debris and blue-green algal flocs were found to accumulate in the deeper layer of the lake sediment inhabited by tubificids at high density.     

Biology of epiphytic Chironomidae (Diptera:Nematocera) in chalk streams

Submerged macrophytes are a conspicuous feature of chalk stream ecosystems, supporting large populations of diatoms and invertebrates, including larvae of the nematocerous family Chironomidae. Close temporal and spatial association is evident between chironomid larvae and diatoms, and diatoms are frequently a major component of the food of midge larvae. Larvae provided with food that is rich in diatoms survive better and grow and develop more quickly than larvae that are supplied with food that is predominantly fine organic detritus. First instar larvae selectively feed on diatoms but it is likely that selection is on the basis of particle size, rather than for diatoms per se. Three species of epiphytic larvae (2 Cricotopus spp. and Eukiefferiella ilkleyensis) transfer to a diet that is predominantly of fresh plant material (Ranunculus calcareus leaves) in the third and fourth instar. The life cycle strategies of many species of Orthocladiinae equip them to exploit temporarily favourable environmental conditions very rapidly and effectively. This fact helps to explain the coexistence of species with similar strategies of resource utilization, as part of the normal epiphytic fauna of chalk streams.     

Spatio-temporal effects of selected physico-chemical variables of water, algae and sediment chemistry on the larval community of nuisance Chironomidae (Diptera) in a natural and a man-made lake in central Florida

Spatio-temporal distributions of Chironomus crassicaudatus, Chironomus decorus, Glyptotendipes paripes, Cryptochironomus fulvus and Tanypodinae midge larvae and selected associated environmental variables (physico-chemical variables of water, sediment chemistry and algal composition) were studied for one year in natural Lake Monroe and man-made Konomac Lake in central Florida. Ordination analysis (CCA with variation partitioning) showed that in each lake, sediment variables were the most important environmental variables. However, the most important proportion of species variability in pooled data from both lakes was explained by lake-specific combinations of water, sediment and algal variables. Chironomid larvae were ordinated with increasing depth as follows: G. paripes, C. fulvus, C. crassicaudatus, Tanypodinae, and C. decorus. This trend was similar for both lakes individually as well as for the pooled data. As water depth increased, organic matter content and associated metals concentrations in sediment increased. Glyptotendipes paripes displayed significant, negative correlation with water depth and sediment total carbon content, while C. decorus showed a significant positive correlation with these variables; C. crassicaudatus did not show any significant correlation with either of these variables. The algal composition in the pooled data from both lakes was another important factor affecting the larval distributions. The proportion of G. paripes and C. decorus larvae increased with filamentous algal density, and C. crassicaudatus larvae with increasing Cyanobacteria. Although both study lakes were very shallow, the effect of water depth (alone or shared with environmental variables) on chironomid larval community composition was substantially higher than the seasonality (sampling month) effect.     

Larval Chironomid Community Organization in Four Tropical Rivers: Human Impacts and Longitudinal Zonation

Chironomid (Diptera) larvae were collected between February 1997 and December 1998 from four Trinidadian rivers, two relatively impacted (the Arima and Guanapo Rivers), and two comparatively pristine (the Marianne and Paria Rivers), in order to assess community changes as a result of both land-use and the natural longitudinal gradient. Multivariate analyses indicated changes in chironomid community composition at the impacted sites, with the most dramatic changes occurring in the low-reaches of the Arima and Guanapo Rivers, which were subjected to nutrient enrichment and general urban runoff. For example, genus richness, measured using Marglef’s Index, was lower in the low-reaches of both the Arima and Guanapo Rivers (0.9 and 1.1, respectively), compared with the low-reaches of the Marianne and Paria Rivers (1.8 and 2.8, respectively). The average chironomid densities in the low-reaches of both the Arima and Guanapo Rivers (1346 and 1029 chironomids/1 m², respectively) were also much higher compared with those of the Marianne and Paria Rivers (130 and 123 chironomids/1 m², respectively), most likely being the result of nutrient enrichment. Furthermore, the low-reaches of both the Arima and Guanapo Rivers demonstrated a shift in community structure, favouring those taxa more tolerant of non-point source pollution, including Thienemanniella spp., Paratrichocladius sp., Corynoneura spp., Polypedilum spp., Chironomus spp., Saetheria sp., Rheotanytarsus sp., and Thienemannimyia sp. In terms of natural longitudinal changes, the chironomid community shifted from one numerically dominated by Orthocladiinae in the headwaters to one numerically dominated by Chironominae in the low-reaches. Overall, this study shows that land-use can have a greater influence on the structure and diversity of chironomid communities than the natural longitudinal gradient.     

Phycoperiphyton in selected reaches of the Upper Mississippi River: community composition,architecture, and productivity

Attached algal communities were studied during ice-free periods along the borders of the main channel and in backwaters of the Upper Mississippi River. Diatoms strongly dominated the phycoperiphyton except during late June through August when the green alga Stigeoclonium was abundant. Two distinct assemblages were apparent: a diverse, complex assemblage during spring and late fall annd a less complex, adnate, two-dimensional summer assemblage dominated by Cocconeis placentula var. euglypta and Navicula tripunctata var. schizonemoides. Simultaneous studies revealed two-dimensional periphytic colonization in the main channel and more complex communities in backwaters. Greater physical turbulence (e.g., surface waves) in the main channel may have favored adnate taxa and two-dimensional architecture, whereas lesser turbulence (e.g. protected backwaters) favored the more diverse, complex community. Community architecture and species composition were similar among communities on artificial substrates within each navigation pool (median SIMI0.87), but communities on artificial substrates were not taxonomically very similar (median SIMI=0.44) to epiphytic communities on Cladophora.Accrual of algal cells, chlorophyll a, and aufwuchs ash-free dry weight was usually greater in Pool 5 than in Pool 9. This may have been due to differences in discharges and/or sampler placement. The greatest accrual of cells and chlorophyll a occurred during summer and early fall. Chironomid and tricopteran larvae were common at that time and are known to affect algal accumulation by grazing.     

Does light intensity modify the effect mayfly grazers have on periphyton?

1. A factorial experiment was conducted in artificial outdoor streams to quantify the effects of irradiance (two levels) and two mayfly grazers (four densities of each) on periphytic community structure. The mayflies were Ecdyonurus venosus (Heptageniidae), a grazer using brushing mouthparts, and Baetis spp. (Baetidae) a grazer which uses mandibles and maxilla to scrape and gather periphyton. The experiment ran for 16 days. 2. Grazer densities in channels approximated those existing in a shoreline habitat in the River Sihl, Switzerland. Light treatments were natural (daily mean = 810 μmol m^–2 s^–1) and shaded (daily mean = 286 μmol m^–2 s^–1). 3. Higher irradiance increased total algal abundance by a factor of 4. Algae most affected were prostrate/motile and erect diatoms, filamentous chlorophytes and Hydrurus foetidus. 4. Both species of mayfly reduced periphytic and algal biomass. Mayfly–mayfly interactions, however, were associated with statistical increases in algal biovolume and chlorophyll-a content, indicating that the two grazers may have interfered with one another as their densities increased. The mayfly–mayfly interaction did not influence periphytic ash-free dry mass (AFDM). Light modified the influence of Ecdyonurus such that this mayfly produced greater reductions in algal biovolume under high irradiance. 5. Despite efforts to exclude other grazers, chironomids colonized experimental channels. Chironomid biomass was approximately eight times less than mayflies across treatments and was positively correlated with all measures of periphytic abundance, suggesting that these grazers were responding to periphyton rather than controlling it. Chironomids were also associated with an increase in the abundance of diatoms having a prostrate/motile physiognomy. The only physiognomy to show a negative relationship with chironomid biomass was the thallus type, a form which comprised less than 1% of the algal biovolume across channels. 6. Ecdyonurus and Baetis had distinct influences on algal physiognomy. Ecdyonurus, for example, reduced adnate, stalked and Achnanthes-type physiognomies, but was associated with a significant increase in the abundance of filamentous chlorophytes (primarily Ulothrix sp.). Baetis reduced erect, Achnanthes-type and thallus physiognomies. Neither mayfly influenced the abundance of prostrate/motile diatoms; a physiognomy that comprised 21% of the algae in channels. 7. Light and mayfly interactions affected algal community structure. The interaction of Ecdyonurus with light had a negative effect on erect diatoms, filamentous chlorophytes and the thallus physiognomy, but a positive effect on stalked and Achnanthes-type physiognomies. Baetis interacting with light had a positive effect on adnate diatoms. 8. Although both mayfly taxa influenced periphytic community structure, physiognomy was not a good predictor of algal susceptibility to grazing. The type of substratum to which an alga is attached (detritus or algal filaments vs hard surfaces) and location within the periphytic matrix may be better indicators of vulnerability to grazing than physiognomy.     

Distribution of Chironomidae (Insecta: Diptera) Head Capsules in Recent Sediments of Canadian Arctic Lakes

Thirty-two taxa of chironomid larvae were collected from the sediments of 50 lakes from across the Canadian Arctic Islands. Most chironomid taxa living in the Arctic have wide distributions, with only one taxon, Abiskomyia, showing a clear geographic limitation in this region. Many of these taxa have habitat preferences, among which lake morphometry, pH, nutrients and temperature are important. Due to the complex environmental patterns in the Arctic, lakes in both the northern and southern portion of the Canadian Arctic Archipelago have warmer temperatures and the chironomid assemblages of these two regions resemble each other more than those of the intervening central islands. Chironomid diversity is lowest in the central arctic islands, primarily Devon and Cornwallis Island, where the combination of low nutrients and cold temperatures provide the most severe environment for chironomid survival.     

Feeding electivity of two epiphytic chironomids in a subtropical lake

Summary Feeding electivity of two epiphytic orthoclad chironomid species, Psectrocladius sp. and Thienemanniella cf. fusca, was investigated using gut content analysis of larvae collected from Typha stems in Lake Padgett, Florida. Electivity values, computed using Strauss's Food Selection Index, were strongly positive for Cosmarium and negative for Oedogonium and Bulbochaete. Diatoms either were avoided or grazed in proportion to their abundance in the environment. Patterns of electivity were similar for both chrionomid species during all seasons studied. Pairwise food preference experiments were conducted in the laboratory using the algal species, Cosmarium impressulum, Navicula pelliculosa, Selenastrum capricornuatum, Oedogonium cardiacum, and Synedra sp. Preferences were hierarchical and consistent for both larval genera. Preference ranking for the algae offered were CosmariumSynedra>Navicula>Oedogonium>Selenastrum. Larvae seemed to be feeding electively based upon algal genus, size, position in the epiphytic community, and possibly extracellular chemistry.     

Rotifer–crustacean interactions in a pseudokarstic lake: influence of hydrology

Zooplankton abundance was related to hydrological and environmental variables in a hydrologically dynamic lake fed by a pseudokarstic aquifer. The study period (2002–2006) in Lake Tovel covered different hydrological situations with water residence time (WRT) having the lowest values in 2002 and the highest values in 2003. WRT was negatively correlated with silica concentrations and algal biovolume. Furthermore, the biovolume of small algae was highest in spring and summer, while large algae did not show any pattern. In multivariate analysis, high abundance of crustacean species in autumn and winter was positively related to WRT and negatively to algal biovolume, while high abundance of rotifer species in spring and summer was negatively related to WRT and positively to algal biovolume. With the exception of Keratella cochlearis and Gastropus stylifer, rotifers showed a pattern of crustacean avoidance, and three groups were distinguished: (i) Ascomorpha ecaudis and Polyarthra dolichoptera, (ii) Asplanchna priodonta and Synchaeta spp., and (iii) Filinia terminalis and Keratella quadrata. These groups were associated with different food sources and depths. We suggest that WRT influenced the rotifer–crustacean relationship by wash-out effects and competition for food resources. The dynamics of single rotifer species were attributable to specific feeding requirements and adaptations. In summary, WRT determined the platform for abiotic and biotic interactions that influenced population dynamics of crustaceans and rotifers.     

Microscale measurements reveal contrasting effects of photosynthesis and epiphytes on frictional drag on the surfaces of filamentous algae

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The structure of diversity in an epiphytic chironomid community

The structure of diversity in a chironomid community inhabiting submerged macrophytes was analysed, including the relationship between predation/competition and chironomid diversity. Diversity as expressed by the Shannon functionH was found to be strongly associated with equitabilityJ but not with species richnessS in this community. Chironomid species richness was correlated with the abundance of diatoms. DiversityH and equitabilityJ were significantly correlated with chironomid density through the year. Invertebrate predators were generally rare and occurred sporadically throughout the year in this habitat, with only three species (Chaetogaster diaphanus, Rhyacophila dorsalis andZavrelimyia sp.) attaining >25% habitat occupancy. Neither these predators nor non-chironomid competitors encountered in the same habitat (Stylaria lacustris, Ophidonais serpentina, Hydroptila sp.,Simulium spp. andHydropsyche siltalai) appeared to affect diversity measures of the chironomid community under study, apart from a weak tendency of highSimulium density negatively affecting the total chironomid abundance. In conjunction with other analyses, this chironomid community seemed to be stochastically dynamic and was little influenced by biotic factors such as predation and competition.     

Estimating phytoplankton carbon from microscopic counts: an application for riverine systems

Algal biomass, in addition to cell numbers, is a measure of the successful conversion of inorganic to organic carbon. Consequently, carbon is the main currency used in aquatic models and in flux and budget studies. On the other hand, microscopic observation and counts remain the only means for determining species composition and biomass, which is relevant to many aspects of aquatic ecology. In this study, we focus on the way to convert biovolume to carbon biomass for algal assemblages of two rivers, using a computerized system that records dimensions of phytoplankton (Gosselain & Hamilton, 2000). We first compare different equations found in the literature for converting algal cell volume to cellular carbon content. We then evaluate the accuracy of a biomass estimate based on less time-consuming measurements, using pre-determined biovolume values instead of measuring cells in all samples. Biovolume/carbon equations are evaluated using total phytoplankton carbon biomass determined from measured chlorophyll a. Equations established for freshwater taxa seem to provide better estimates of algal biomass in the two case studies presented here, the Rideau and Meuse rivers (Canada and Belgium, respectively) than do more numerous equations defined for marine taxa. Furthermore, equations that make a distinction between diatoms and other algae appear more appropriate than those considering all algal groups as a whole. Finally, mean values of algal biovolumes, determined using sufficient measurements of cell dimensions from representative sampling series, may prove sufficient for carbon estimates of taxa in relatively homogenous size ranges. The careful choice of appropriate volumetric shapes and taxa categories remains of prime importance to get precise results.     

Deriving nutrient targets to prevent excessive cyanobacterial densities in U.S. lakes and reservoirs

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Effects of gastropod grazers on recruitment and succession of an estuarine assemblage: a multivariate and univariate approach

Grazers have been shown to affect assemblages of species in many habitats. Here we studied the effects of the gastropod grazers, Austrocochlea porcata and Bembicium auratum, on intertidal estuarine assemblages in a sheltered bay in New South Wales, Australia. We examined the effects of gastropods on individual species and on the assemblage as a whole. The multivariate response was compared with data on succession in these assemblages to estimate potential effects of grazers on succession. The experiment was repeated several times to determine the generality of grazer effects in the light of possible variation in the timing or intensity of recruitment. There were different responses of individual species to the presence of grazers. Grazers reduced the abundance of ephemeral algal species, bryozoans, copepods, insect larvae and Balanus spp. barnacles. They had a positive effect on oysters and spirorbids and no effect on the barnacles Elminius covertus and Hexaminius spp. These effects were consistent through time. Multivariate analyses confirmed that grazers caused significant changes to whole assemblages and that these effects were far-reaching and not only caused by changes to algal species. The removal of grazers appeared to neither speed up nor slow down succession, but rather caused a completely different assemblage to develop. Apparent important mechanisms affecting the composition of animal species when grazers were removed included accumulation of sediments and detritus and pre-emption of space by algae. Received: 13 May 1996 / Accepted: 1 September 1996     

Responses of phytoplankton to fish predation and nutrient loading in shallow lakes: a pan-European mesocosm experiment

1. The impacts of nutrients (phosphorus and nitrogen) and planktivorous fish on phytoplankton composition and biomass were studied in six shallow, macrophyte‐dominated lakes across Europe using mesocosm experiments. 2. Phytoplankton biomass was more influenced by nutrients than by densities of planktivorous fish. Nutrient addition resulted in increased algal biomass at all locations. In some experiments, a decrease was noted at the highest nutrient loadings, corresponding to added concentrations of 1 mg L^?1 P and 10 mg L^?1 N. 3. Chlorophyll a was a more precise parameter to quantify phytoplankton biomass than algal biovolume, with lower within‐treatment variability. 4. Higher densities of planktivorous fish shifted phytoplankton composition toward smaller algae (GALD < 50 μm). High nutrient loadings selected in favour of chlorophytes and cyanobacteria, while biovolumes of diatoms and dinophytes decreased. High temperatures also may increase the contribution of cyanobacteria to total phytoplankton biovolume in shallow lakes.