184
R. A. Ribeiro Filho et al.
(Mcqueen, 1990; Carpenter and Kitchell 1993), indicating a
bottom-up effect.
The last trophic level examined, confirming the bottomup effect, was the chlorophyll–nutrient interaction, where
increased concentrations of chlorophyll-a were positively
related to the concentrations of total phosphorus. In
temperate environments this ratio is positive (Mcqueen 1990;
Carpenter and Kitchell 1993), and nutrient concentrations
control chlorophyll-a concentrations.
Hambright et al. (1991) point out that a complicating factor for the functioning of the trophic cascade hypothesis is
the assumption that all populations of planktivorous fish are
susceptible to increased biomass of piscivores. Hambright
(1994) also shows that the morphological characteristics
(such as mouth opening of predators) and prey refuges are
factors of extreme importance for the development of the
trophic cascade hypothesis.
Indirect relationships indicate that omnivores, insectivores and detritivores control chlorophyll and cyanobacteria.
These three groups of fish can be used to control the quality
of water in the reservoir, and laboratory and in situ experiments may provide answers for the management of this environment. The iliophagous and zooplanktivorous fish showed
positive relations with chlorophyll-a and cyanobacteria,
respectively. These results indicate that both groups of fish
somehow stimulated the development of primary productivity. Measures such as the encouraging of catchment of these
species in both artisanal and sport fisheries would bring beneficial results in the control of water quality in the reservoir.
Insectivores and herbivores were the only groups of fish
that were somehow related to the concentration of total phosphorus. Both showed negative relationships with phosphorus, indicating that an increase of the biomass of these causes
a reduction in the total phosphorus concentration. These results imply that management of these species (increase of
stock) may have a greater control of total phosphorus in the
reservoir.
Persson (1997) compared the rate of excretion of phosphorus in zooplanktivorous fish, with estimates of internal
and external loads in a eutrophic lake (Lake Finjasjon, Sweden). The experiments were performed in the laboratory
using two prey species (one benthic and one pelagic), and the
results were extrapolated to the entire lake, using the calculation of consumption of prey by the fish, based on field data
on community structure, growth rate of excretion and diet
of the fish. The phosphorus rate excreted by the fishes was
on average 0.53 mg P/m²/d, which had a 110 % increase of
external load and 42 % of internal load. Most of the phosphorus released by the fish is recycled within the water column,
that is, more than 18 % of phosphorus released in the water
comes from the benthic food, thus representing the transportation of phosphorus from the sediment to the water column.
Phosphorus excreted by the fishes became available for phyments. These results corroborate the work of Lazzaro (1997)
and Lazzaro et al. (2003), which emphasize the effect of
omnivores and the detritivore chains in these environments.
The only guild of fishes that showed some relationship
with the macrozooplankton was the one composed by iliophagous, and the relations were positive and not negative
as they occur in temperate ecosystems (Mcqueen et al. 1990;
Carpenter and Kitchell 1993). These results suggest that the
increase in iliophagous biomass causes an increase in herbivorous zooplankton communities, indicating that the pressure
of fishes does not affect the zooplankton community, which
is capable of consuming the phytoplankton, what appears to
be a bottom-up effect.
The low pressure the fishes cause on zooplankton implies
the dominance of small individuals in the zooplankton communities in tropical and subtropical lakes (Lazzaro 1997).
The omnivorous copepods biomass usually dominates in
oligomesotrophic systems, whereas microzooplankton prevails in more eutrophic systems. At higher temperatures, the
daily fluctuations of the physical or chemical conditions or
sudden environmental changes (due to heavy rain, for example) may affect the zooplankton community (increasing
the number of protozoa and rotifers), but it has the ability to
recover very quickly. The classic control of phytoplankton
by macrozooplankton in temperate lakes is not as often seen
in tropical lakes (Lazzaro 1997; Jeppesen et al. 2005; Rejas
et al. 2005). This absence of predation pressure on zooplankton may represent an additional limitation on the difficulty of
biomanipulation in tropical and subtropical lakes.
While studying mesocosms Baca and Drenner (1995)
found that the predator causes a strong impact on the planktivore community, but the interactions of the trophic levels
below these communities did not show a strong effect on the
phytoplankton and zooplankton communities. The results
described above can explain the increased biomass of the
zooplankton community, with regard to the macrozooplankton analyses (cladocerans and copepods), in this study. The
results show that there is no predatory pressure of fish on
zooplankton. Studies in 31 reservoirs in the state of Paraná
showed the same positive relationship between chlorophylla and macrozooplankton. According Lazzaro (1997), in
tropical environments prey are not strictly zooplanktivorous,
but omnivorous, having no direct effect on zooplankton
community.
The macrozooplankton (cladocerans and copepods)
showed a positive relationship with chlorophyll, indicating that the former had no control over the latter. These results corroborate the work by Lansac-Tôha et al. (2005) and
Piana et al. (2005), held in reservoirs of Paraná, in which
positive relationships were also found between zooplankton
and chlorophyll-a. This type of relationship is opposite to
what is commonly found in temperate lakes and reservoirs
R. A. Ribeiro Filho et al.
(Mcqueen, 1990; Carpenter and Kitchell 1993), indicating a
bottom-up effect.
The last trophic level examined, confirming the bottomup effect, was the chlorophyll–nutrient interaction, where
increased concentrations of chlorophyll-a were positively
related to the concentrations of total phosphorus. In
temperate environments this ratio is positive (Mcqueen 1990;
Carpenter and Kitchell 1993), and nutrient concentrations
control chlorophyll-a concentrations.
Hambright et al. (1991) point out that a complicating factor for the functioning of the trophic cascade hypothesis is
the assumption that all populations of planktivorous fish are
susceptible to increased biomass of piscivores. Hambright
(1994) also shows that the morphological characteristics
(such as mouth opening of predators) and prey refuges are
factors of extreme importance for the development of the
trophic cascade hypothesis.
Indirect relationships indicate that omnivores, insectivores and detritivores control chlorophyll and cyanobacteria.
These three groups of fish can be used to control the quality
of water in the reservoir, and laboratory and in situ experiments may provide answers for the management of this environment. The iliophagous and zooplanktivorous fish showed
positive relations with chlorophyll-a and cyanobacteria,
respectively. These results indicate that both groups of fish
somehow stimulated the development of primary productivity. Measures such as the encouraging of catchment of these
species in both artisanal and sport fisheries would bring beneficial results in the control of water quality in the reservoir.
Insectivores and herbivores were the only groups of fish
that were somehow related to the concentration of total phosphorus. Both showed negative relationships with phosphorus, indicating that an increase of the biomass of these causes
a reduction in the total phosphorus concentration. These results imply that management of these species (increase of
stock) may have a greater control of total phosphorus in the
reservoir.
Persson (1997) compared the rate of excretion of phosphorus in zooplanktivorous fish, with estimates of internal
and external loads in a eutrophic lake (Lake Finjasjon, Sweden). The experiments were performed in the laboratory
using two prey species (one benthic and one pelagic), and the
results were extrapolated to the entire lake, using the calculation of consumption of prey by the fish, based on field data
on community structure, growth rate of excretion and diet
of the fish. The phosphorus rate excreted by the fishes was
on average 0.53 mg P/m²/d, which had a 110 % increase of
external load and 42 % of internal load. Most of the phosphorus released by the fish is recycled within the water column,
that is, more than 18 % of phosphorus released in the water
comes from the benthic food, thus representing the transportation of phosphorus from the sediment to the water column.
Phosphorus excreted by the fishes became available for phyments. These results corroborate the work of Lazzaro (1997)
and Lazzaro et al. (2003), which emphasize the effect of
omnivores and the detritivore chains in these environments.
The only guild of fishes that showed some relationship
with the macrozooplankton was the one composed by iliophagous, and the relations were positive and not negative
as they occur in temperate ecosystems (Mcqueen et al. 1990;
Carpenter and Kitchell 1993). These results suggest that the
increase in iliophagous biomass causes an increase in herbivorous zooplankton communities, indicating that the pressure
of fishes does not affect the zooplankton community, which
is capable of consuming the phytoplankton, what appears to
be a bottom-up effect.
The low pressure the fishes cause on zooplankton implies
the dominance of small individuals in the zooplankton communities in tropical and subtropical lakes (Lazzaro 1997).
The omnivorous copepods biomass usually dominates in
oligomesotrophic systems, whereas microzooplankton prevails in more eutrophic systems. At higher temperatures, the
daily fluctuations of the physical or chemical conditions or
sudden environmental changes (due to heavy rain, for example) may affect the zooplankton community (increasing
the number of protozoa and rotifers), but it has the ability to
recover very quickly. The classic control of phytoplankton
by macrozooplankton in temperate lakes is not as often seen
in tropical lakes (Lazzaro 1997; Jeppesen et al. 2005; Rejas
et al. 2005). This absence of predation pressure on zooplankton may represent an additional limitation on the difficulty of
biomanipulation in tropical and subtropical lakes.
While studying mesocosms Baca and Drenner (1995)
found that the predator causes a strong impact on the planktivore community, but the interactions of the trophic levels
below these communities did not show a strong effect on the
phytoplankton and zooplankton communities. The results
described above can explain the increased biomass of the
zooplankton community, with regard to the macrozooplankton analyses (cladocerans and copepods), in this study. The
results show that there is no predatory pressure of fish on
zooplankton. Studies in 31 reservoirs in the state of Paraná
showed the same positive relationship between chlorophylla and macrozooplankton. According Lazzaro (1997), in
tropical environments prey are not strictly zooplanktivorous,
but omnivorous, having no direct effect on zooplankton
community.
The macrozooplankton (cladocerans and copepods)
showed a positive relationship with chlorophyll, indicating that the former had no control over the latter. These results corroborate the work by Lansac-Tôha et al. (2005) and
Piana et al. (2005), held in reservoirs of Paraná, in which
positive relationships were also found between zooplankton
and chlorophyll-a. This type of relationship is opposite to
what is commonly found in temperate lakes and reservoirs