SALGA publications (with abstracts)

  1. Kruk, C., N. Mazzeo, G. Lacerot & C. S. Reynolds, 2002. Classification schemes for phytoplankton: a local validation of a functional approach to the analysis of species temporal replacement. J. Plankton Res. 24: 901-912.
    Abstract: During ecosystem succession, phytoplankton species composition is hard to predict and although it is tempting to use taxonomic groups for predictive purposes, the conditions favouring their development are often cross-phyletic and, frequently, overlap. Another alternative is to consider functional groups. Reynolds (1997) proposed phytoplankton associations according to functional criteria, based upon identified coherent morphological and ecological properties. Here we apply data from the phytoplankton community of Lake Rodo in Montevideo, Uruguay (small, shallow, polymictic and hypertrophic lake under restoration) to test and quantify the effectiveness of the approach. The phytoplankton species were sorted into their main taxonomic groups and into the associations proposed by Reynolds. A canonical variate analysis was use to test the non-random occurrence of these classification schemes and to determine their discriminatory power. Both classification schemes, taxonomic and functional, showed a significant result, but classification into functional associations had a higher discriminatory power. The eigenvalue for the canonical correspondence analysis first axis for the functional associations was 0.708 and the cumulative explained variance for the species-environmental relationship was 78.6%. The environmental factors showed similar patterns between associations and individual species. Our data indicate that the scheme using functional associations does indeed capture much of the ecology of the phytoplankton.

  2. Mazzeo, N., L. Rodriguez-Gallego, C. Kruk, M. Meerhoff, J. Gorga, G. Lacerot, F. Quintans, M. Loureiro, D. Larrea & F. Garcia-Rodriguez, 2003. Effects of Egeria densa Planch. beds on a shallow lake without piscivorous fish. Hydrobiologia 506: 591-602.
    Abstract: Submerged plants are thought to negatively affect phytoplankton crops in the temperate zone by a number of mechanisms, including nutrient and light limitation, and enhancement of top-down control by offering diurnal refuge for zooplankton against visual predation, and by favouring piscivores. In 1997-1998, Lake Blanca (34degrees54'S, 54degrees50' W), a yellow-brownish shallow lake in Uruguay, suffered a severe water level reduction (associated with El Nino events between 1995-1997) that resulted in a massive fish kill and an extensive colonisation by Egeria densa. A clear water phase is established nowadays in the system (Secchi depth > 1 m), despite a fish community restricted to two small ornnivorous-planktivorous fish: Jenynsia multidentata and Cnesterodon decemmaculatus. We studied the effects of E. densa on bottom-up and top-down controls on phytoplankton by comparing physical, chemical, and biological characteristics between submerged plant beds and sites without plants, from autumn 2000 to autumn 2001. The water column had low to intermediate nutrient concentrations, and phytoplankton community was highly diverse with a low to moderate biomass (mean Chl-a = 10.6 mug l(-1)). The water level, recovered during the study, promoted a dilution process that explained the temporal pattern of many chemical variables. Macrophyte PVI represented 28-39% of the lake volume (annual mean biomass = 174 g DW m(-2)). The zooplankton community was generally dominated by copepods in terms of biomass. Fish and zooplankton were significantly associated with submerged plant beds. In spite of the high biomass and density of ornnivorous-planktivorous fish (115 kg ha(-1), 13 ind m(-2)), zooplankton strongly affected phytoplankton spatial and temporal variation. The most important differences of algal biomass between zones coincided with a high herbivorous zooplankton biomass and/or with plants occupying the entire water column during the low level period. Medium-sized zooplankton declined with fish reproduction. The consequent stronger predation of juvenile fish seemed to decrease macrophyte efficiency as a zooplankton refuge in summer. E. densa bottom-up mechanisms would also be present, contributing to maintaining clear water. Besides the usually described nutrient and light limitation, the internal production of humic substances could enhance the observed top-down effect.

  3. Scasso, F., N. Mazzeo, J. Gorga, C. Kruk, G. Lacerot, J. Clemente, D. Fabian & S. Bonilla, 2001. Limnological changes in a sub-tropical shallow hypertrophic lake during its restoration: two years of a whole-lake experiment. Aquat. Conserv.-Mar. Freshw. Ecosyst. 11: 31-44.
    Abstract: 1. Lake Rodo is a turbid system, a condition attributed to algal biomass. The proximal source of the eutrophication was stormwater discharges from an ill-defined urban area. This paper describes an attempt to restore the water quality of Lake Rodo, the first time this has been done in Uruguay. In spring 1996 it was drained, sediments were removed and stream inputs were diverted. Groundwater was used to re-fill the lake. Due to its high nutrient concentration a re-circulation system was designed, pumping water from associated pools covered with free-floating plants. 2. After the lake was refilled, the system was characterized by oxygen saturation or over-saturation, neutral to basic pH, and high phosphorus, nitrogen and silicate concentrations. Ratios of total nitrogen (TN):total phosphorus (TP) and chlorophyll a (Chl a):TP indicated that phosphorus was the primary limiting nutrient during the period of groundwater supply. Once groundwater pumping had ceased, there was a decrease in TN:TP and Chl a:TP ratios, suggesting N-limiting conditions prevailed in some periods. 3. Before restoration, the phytoplankton community was dominated year-round by Planktothrix agardhii; since restoration the community has been more diverse. This change has favoured grazing by mesozooplankton, and the onset of clear-water phases in spring. 4. Abundant populations of small omnivorous fish maintained a high predation pressure on zooplankton, restricting the abundance of large-bodied herbivores, which, in turn, allowed an increase in phytoplanton biomass and a decrease in water transparency. Based on this observation, together with the phosphorus concentration and the low abundance of filamentous cyanobacteria compared with previous studies, we suggest that top-down control has played a key role in increasing transparency in Lake Rodo. 5. A nutrient reduction programme, by the mechanical harvest of floating plants, and a removal of small omnivorous fishes and stocking strictly with piscivores, could be key factors in the achievement of a stable clear-water phase. However, if blooms of Microcystis or other similar genera occur in summer, additional measures (e.g. reduction of the hydraulic residence time) will be needed to improve water transparency. Copyright (C) 2001 John Wiley & Sons, Ltd.

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