A 2‐year experimental study on nutrient and predator influences on food web constituents in a shallow lake of north‐west Spain

Abstract

A 2-year study was carried out on the roles of nutrients and fish in determining the plankton communities of a shallow lake in north-west Spain. Outcomes were different each year depending on the initial conditions, especially of macrophyte biomass. In 1998 estimated initial 'per cent water volume inhabited' (PVI) by submerged macrophytes was about 35%. Phytoplankton biomass estimated as chlorophyll a was strongly controlled by fish, whereas effects of nutrient enrichment were not significant. In 1999 estimated PVI was 80%, no fish effect was observed on phytoplankton biomass, but nutrients had significant effects. Water temperatures were higher in 1998 than in 1999. 2. In the 1998 experiment, cladoceran populations were controlled by fish and cyanobacteria were the dominant phytoplankton group. There were no differences between effects of low (4 g fresh mass m )2 ) and high (20 g fresh mass m )2 ) fish density on total zooplankton biomass, but zooplankton biomass was higher in the absence of fish. With the high plant density in 1999, fish failed to control any group of the zooplankton community. 3. Total biovolume of phytoplankton strongly decreased with increased nutrient concentrations in 1998, although chlorophyll a concentrations did not significantly change. At higher nutrient concentrations, flagellate algae became more abundant with likely growth rates that could have overcompensated cladoceran feeding rates. This change in phytoplankton community composition may have been because of increases in the DIN : SRP ratio. Both chlorophyll a concentration and total phytoplankton biovolume increased significantly with nutrients in the 1999 experiment. 4. A strong decline of submerged macrophytes was observed in both years as nutrients increased, resulting in shading by periphyton. This shading effect could account for the plant decline despite lower water turbidity at the very high nutrient levels in 1998.

State of the art in the functioning of shallow Mediterranean lakes: workshop conclusions

“…Pronounced water level changes may act as catastrophic disturbances leading to state shifts and affecting the functioning of the biotic components (Chow-Fraser et al, 1998;Gafny & Gasith, 1999;Ferná ndez-Alá ez et al, 1999;Coops et al, 2003;Naselli-Flores & Barone, 2003;Romo et al, 2004;Beklioglu et al, 2004;Tan & Beklioglu, 2005Van Geest et al, 2005;Beklioglu et al, 2006). Low water levels may enhance submerged plant biomass and coverage in SMLs Ferná ndez-Alá ez et al, 2004;Mitraki et al, 2004;. The impact of water depth in determining the extent of the littoral zone is dependent also on lake morphometry and bathymetry .…”

“…Dense macrophyte beds significantly increased water clarity at low and intermediate nutrient levels in mesocosm experiments carried out in Spanish lakes Ferná ndez-Alá ez et al, 2004). However, at high nutrient levels (TP > 0.25 mg L -1 ) submerged plants did not prevent deterioration in water transparency in some SMLs Tan & Beklioglu, 2005;Karapinar, 2005).…”

“…Plant-associated rotifers and salinity-tolerant calanoid copepods can predominate during low water level periods taking advantage of the structure offered by macrophytes (Tan, 2002;Romo et al, 2004;Ferná ndez-Alá ez et al, 2004). Salinity may limit the presence of Cladocera, copepods gaining competitive advantage at salinities above 0.5& (Jeppesen et al, 1994).…”

Typology, classification and management issues of Greek lakes: implication of the Water Framework Directive (2000/60/EC)

“…Zooplankton community in almost all lakes is characterized by the small-sized species (i.e. rotifers) as it happens in many Mediterranean lakes (Beklioglu et al 2003;Romo et al 2004;Fernández-Aláez et al 2004) while in lakes at high ecological status (Megali Prespa) there is a larger proportion of Cladocera. Regarding at the macrophytes coverage, it seems that Greek lakes shift from the macrophyte dominance state to the algal dominance state since in many lakes macrophyte coverage is limited, presumably they declined last years (Papastergiadou et al 2002).…”

How Submerged Macrophyte Restoration Promotes a Shift of Phytoplankton Community in a Shallow Subtropical Lake

“…For example, Bachmann et al [24] found that no significant correlations exist between the abundance of submerged macrophyte and phytoplankton biomas in a set of lakes in southern Florida in the United States. Moreover, studies in the Mediterranean and subtropical South American lakes, in contrast, found a significant negative relationship between submerged macrophyte and phytoplankton biomass [25][26][27]. Therefore, more studies and field experiments should be conducted to explore the interactions between macrophyte and phytoplankton communities in subtropical/tropical lakes.…”