The structure of phytoplankton assemblages in Sicilian reservoirs: some hyphoteses on the driving factors

Abstract

From the analysis of the results of several researches carried out into Sicilian reservoirs to investigate their phytoplankton assemblages, it was highlighted that there is not any clear relationship between the trophic spectrum and the structure and composition of phytoplankton. Only a general increase of total biomass is detectable as the trophic state rises up. Anyway, such increase may cause several secondary modifications in the physical and chemical environment that may act as multidimensional segregating factors for phytoplankton organisms. In these secondary modifications, coupled with the peculiar morphology and hydrology of the water bodies, have to be sought the mechanisms governing the structure of phytoplankton assemblages.     

Applicability of phosphorus budget models to southern African man-made lakes

An investigation of the phosphorus loading characteristics of 31 southern African man-made was lakes made. The lakes were characterized by low water retention times, with most of the lakes having retention times of less than one year. Catchment phosphorus export rates showed wide variation (1–162 mg P m^-2 y^-1) with those lakes experiencing excessive municipal wastewater inputs having export rates in excess of 53 mg m^-2 y^-1. The phosphorus data were tested against the Vollenweider (1976) and Dillon & Rigler (1974) phosphorus budget models which predict in-lake steady state concentrations of phosphorus. It was found that both models displayed good potential for the prediction of steady state concentrations of phosphorus, with better results being obtained from the Dillon & Rigler (1974) model. However, because phosphorus concentrations within these lakes may not necessarily be related to trophic status the use of these models as a predictive tool for eutrophication control still requires further development.     

Trophic Structure of Fish Assemblages in Five Permanent Lagoons of the High Paraná River Floodplain, Brazil

We evaluated fish assemblage diet and trophic structure in five lakes (Patos, Zé do Paco, Fechada, Ressaco do Pau Véio and das Garças), connected or not with the river. Trophic structure analysis was based on the species whose number of sampled digestive tracts was greater or equal to 10 and ordinated according to a detrended correspondence analysis. We identified seven trophic guilds with the following representatives: (1) Detritivorous–ileophagous: Cyphocharax modestus, Prochilodus lineatus, Steindachnerina insculpta and Loricariichthys platymetopon; (2) Herbivorous: Schizodon borellii and Leporinus lacustris; (3) Benthophagous: Iheringichthys labrosus, Satanoperca pappaterra and Trachydoras paraguayensis; (4) Insectivorous: Astyanax altiparanae, Moenkhausia intermedia and Parauchenipterus galeatus; (5) Piscivorous: Hoplias cf. malabaricus and Serrasalmus marginatus; (6) Carnivorous–carcinophagous: Pimelodus maculatus and (7) Insectivorous–lepidophagous: Roeboides paranensis. The detritivorous–ileophagous guild was the predominant one in the five lakes.     

Phytoplankton assemblages in twenty-one Sicilian reservoirs: relationships between species composition and environmental factors

Data collected in a limnological survey, carried out between 1987 and 1988 on 21 Sicilian reservoirs of varying trophic state, were ordinated using CANOCO 3.1 to generalise the way in which the structure of phytoplankton assemblage is conditioned by both physical and chemical variables. The results showed that in these man-made lakes, characterised by conspicuous water-level fluctuations, the annual and interannual variability in the abundance and composition of phytoplankton may be strongly influenced by their peculiar hydraulic regimes rather than by nutrient availability. In particular, it was highlighted that, from the early summer, water abstraction often leads to increased circulation and to the deepening of the mixed layer. In this way, an increase of the ratio of mixing depth to euphotic depth is forced, with the result that phytoplankton cells experience longer periods in darkness as they are carried through the mixed layer. Phytoplankton assemblages change in species composition in response to the environmental variation. Both the raising of the trophic state, with an increase in phytoplankton biomass and a decrease in transparency, and the intensified abstraction enhance the role of light availability in promoting the development of specific phytoplankton assemblages adapted to the modified physical environment. Light climate is an important influence on the species structure of the phytoplankton, especially in the higher part of the trophic gradient. In contrast, the influence of nutrients on the structure of the assemblages appears to be higher in the lower part of the trophic spectrum or in those environments characterised by a higher hydrological stability during the year.     

Trophic level assessment of profundal sediments of the artificial Lake Campotosto (Central Italy), using midge larval community (Diptera: Chironomidae)

A study on the profundal chironomids of the artificial Lake Campotosto (Central Italy) was carried out during the summer/early autumn of 1983 and 1984, in order to analyse their composition and community structure in relation to the lake trophic level assessed by water chemical analysis.A total of about 2000 specimens belonging to 15 taxa were collected during the study.Chironomus plumosus group andTanytarsus spp. dominated in 1983 and 1984, respectively, showing a competitive relationship probably due to the larval size. The functional feeding organization was mostly composed of collectors (percentages greater than 90%), revealing the presence of abundant fine organic deposits (FPOM). Diversity and evenness appeared to be negatively affected by the monotony of food, which seems to constitute the key factor in governing both the taxonomic and the trophic structure of chironomid fauna.A clear discrepancy between water chemical data and profundal chironomid analyses was observed in the assessment of the lake trophic level. Sediments exhibited eutrophicated conditions, whereas overlying waters indicated an oligotrophic status. The relevance of profundal macrobenthic investigations in detecting eutrophication is stressed.     

Dynamics of feeding and growth of bluegill (Lepomis macrochirus) in Lake Wingra and Lake Mendota,Wisconsin

Adult bluegil grew faster in Lake Mendota than in Lake Wingra. Once and two year old fish from both lakes had similar growth patterns and grew at a rate similar to that of fish from other lakes. Small fish from the two lakes (averaging 10 g) had comparable rations in July but larger fish (averaging 50 g) had daily ration of 3% in Lake Mendota compared to 1% for Lake Wingra fish. Mean number of benthic organisms varied from 364 to 80 per m² in Lake Wingra as opposed to 1560 to 450 organisms per m² in Lake Mendota. Fish in Lake Wingra fed selectively on Daphnia and Cyclops, which, although small in size, were relatively larger than the other plankton species. Bluegill from Lake Mendota, on the other hand, fed mainly on large macroinvertebrates such as Hyalella and insects.     

鲢、鳙在天然条件下的摄食强度 (Ⅰ) 鲢、鳙鱼种在夏季的摄食强度

测定鲢(Hypophthalmichthy molitrix)、鳙(Aristichthys nobilis)鱼种在天然条件下肠管饱满度指数与水温及溶解氧的关系,在实验条件下鱼的排空率。根据修正后的Bajkov公式(D=C24·A/n)估计鱼的日摄食量。两种鱼在天然条件下具昼夜摄食节律,它们的摄食高峰在下午16—19时,低谷在清晨4—7时。鲢日粮为其体重12.81—23.08%;鳙为8.91—14.63%。它们的摄食强度随溶解氧的升高而加强,反之则下降。     

Estimation of the Consumption of Nekton and Plankton by the Minke Whale Balaenoptera acutorostrata

This is a review of the data available on the population subdivision and life cycle of the Minke whale, the most abundant whalebone whale in the World Ocean. Different methods of estimation and calculation of the rate of food consumption by this species, the latter including those developed for the Sea of Okhotsk, are compared.     

Feeding Patterns in Different Size Larvae of Walleye Pollack, Theragra chalcogramma (Pallas, 1814) on the Shelf of Western Kamchatka

The stomach contents were examined in 373 walleye pollack larvae of different sizes. The diet of pollack larvae included more than 20 plankters of different sizes. Phytoplankton was the major food source of 4- to 6-mm-long larvae. The proportion of phytoplankton in the larval diet decreased as the larvae grew, and the late larval stages shifted entirely to a diet of zooplankton. As the larvae increased in size, the spectrum of food organisms changed from smaller to larger sizes. In the larvae 4 to 31 mm long, the length of prey varied from 0.1 (Coscinodiscus) to 6.0 mm (Neocalanus plumchrus). The average daily repleteness of pollack larvae varied from 32 to 210. The minimum repleteness was registered in 4- to 6-mm-long larvae with mixed feeding (endogenous and exogenous); in 30- to 35-mm-long fish the repleteness was the greatest. The daily food rations calculated for the most abundant size groups of larvae ranged from 4.3 to 6.6% of their body weight.     

Seasonal variations in the density of a small West African lake

The seasonal variation in the vertical density profile of Lake Asejire waters was investigated from February 1974 to February 1976.The range of density was of the magnitude of 2.0 mg/cc, at the temperatures of Lake Asejire (21°C–32°C). Water densities were generally lower in the dry season when aquatic temperatures were high and generally higher in the rainy season when aquatic temperatures were low.During the dry season, the pycnocline was observed at 3m–7m in 1974 and 6 m–9 m in 1975. During periods of density stratification, the water body was clearly layered.Seasonal longitudinal differences in water density were such that during the floods of 1975 the inflow station waters had a higher density than the dam-site waters which however had a concomitantly higher conductivity. This suggests the insignificance of conductivity in water density changes in a lake with rather low conductivity values.     

The trophic state ‘chain of relationships’ in ponds: does size matter?

In contrast to shallow lakes, factors affecting trophic state in ponds are not well described, and may include unique effects related to pond size. We examined the interdependence of ambient N and P, phytoplankton biomass, light penetration and stratification in 13 ponds of varying area and mean depth in Chester County, PA (USA) during March, May and July of 2002. Seven of the ponds had primarily residential watersheds, and six were farm ponds. The ponds were all eutrophic or hypereutrophic based on Carlsons Trophic State Index, but varied widely in nutrient content (from 20 to 179 g total P/L and from 683 to 3895 g total N/L) and size (surface areas from 0.1 to 1.7 ha, mean depths from 0.6 to 1.8 m). Although total N (TN) typically declined while total P (TP) rose from March to July, the ratio TN/TP remained sufficiently high that algal growth was probably limited by P during the study period. Phytoplankton biomass (as chlorophyll-a) was positively correlated with TP and negatively correlated with Secchi depth on all three sampling dates. Despite their shallow nature, the ponds were frequently stratified with near-anoxic hypolimnia later in the study period; mixing depth was greater in ponds with greater light penetration. Residual variation in chlorophyll-a unexplained by TP, and in Secchi depth unexplained by chlorophyll-a, was related to either mean depth or surface area, suggesting that trophic state in ponds may be controlled differently than in much larger, shallow lakes.     

Feeding ecology of King George whiting Sillaginodes punctatus (Perciformes) recruits in seagrass and unvegetated habitats. Does diet reflect habitat utilization?

This study investigated the feeding ecology of King George whiting Sillaginodes punctatus recruits to determine how diet composition varies between habitat types (seagrass and unvegetated habitats), and between sites separated by distance. Broad-scale sampling of seagrass and unvegetated habitats at nine sites in Port Phillip Bay (Australia) indicated the diet composition varied more by distance into the bay than by habitat. Near the entrance to the bay the diet was dominated by harpacticoids and gammarid amphipods, in the middle reaches of the bay the diet was completely dominated by harpacticoids, while at sites furthest into the bay, mysids and crab zoea were also important. Abundances of prey in guts was significantly higher between 1000 and 2200 hours compared with other times, indicating diurnal feeding. Laboratory determined gut evacuation rate (based on an exponential model) was estimated to be -0·54. Daily rations were highly variable among sites and habitat types. Sillaginodes punctatus recruits consumed much higher quantities of prey on unvegetated habitat than seagrass habitat at some middle reach sites; with prey consumption of harpacticoid copepods on unvegetated habitat approaching 3000 individuals per day at one site. The results of this study provide insight into why habitat associations of S. punctatus recruits within mosaics of seagrass and unvegetated habitat show high spatial variation.     

Primary productivity and trophic status of a Kashmir Himalayan Lake

The paper deals with general limnology, phytoplankton production and trophic status of a Himalayan lake of Kashmir. The primary production as measured by in situ ¹⁴C istope technique ranged from 36 to 906 mgC.m^–2 d^–1 with characteristic seasonal variation. The photosynthetic efficiency was from 0.02 to 0.48% during the same period. The yearly (1975–1976) production was estimated at 134 gC.m^–2 m^–2, which shows that the lake has not yet reached a high level of eutrophication. The waterbody has been classified as mesotrophic.Formed part of thesis for which Ph. D. was awarded to MAK by Kashmir University, India