Effects of fertilization and planktivorous fish (yellow perch) predation on size distribution of particulate phosphorus and assimilated phosphate: Large enclosure experiments1

Abstract

Nutrients, planktivorous fish (1 + yellow perch), or both were added to eight large enclosures in a 2 x 2 factorial design. The size distributions of particulate phosphorus (PP) and assimilated 32P043-and POd3-turnover times were determined from June through August by filter fractionation. The amount of PP > 200 pm (mesoplankton) increased with fertilization and decreased with addition of fish, but the amount of PP in nanoplankton (3-20 pm) and large picoplankton (l-3 pm) showed opposite results. Fertilization and addition of fish had interacting effects on the PP in microplankton (20-200 pm). Microplankton phosphorus was higher with fish in unfertilized enclosures and lower with fish in fertilized enclosures. Slopes estimated from the relationship between the proportion of PP retained and the logarithm of filter size were used to characterize the size spectra of plankton and were lower with fertilization and steeper with addition of fish. They were negatively correlated with PO, 3-turnover time, reflecting that plankton communities dominated by small cells were more nutrient limited. The slope parameter was also significantly correlated with water clarity (Secchi depth) and algal biomass (Chl a), but particle size distribution contributed to water clarity independent of biomass or pigment concentration.This slope parameter can be used as a convenient indicator of plankton size spectra and trophic interactions in freshwater ecosystems. Manipulationof planktivorous fish causes significant changes in the size structure of zooplankton (e.g. Benndorf et al. 1984;Schoenberg and Carlson 1984; McQueen et al. 1986;Post and McQueen 1987) the biomass of algae (Shapiro 1980;Henssen et al. 1986), water clarity (Shapiro and Wright 1984), and total phosphorus (Wright and Shapiro 1984). A few studies have also considered the combined effects of fertilization and fish addition on algal biomass (e.g. Riemann and Ssndergaard 1986).The mechanisms proposed to explain the effect of fish addition have dealt primarily with the activities of large vs. small zooplankton, including nutrient regeneration (e.g. Bartell and Kitchell 1978; Bartell 198 1) and grazing (e.g. Nilssen 1978). It has also been suggested that an important difference between communities dominated by large and small zooplankton is in the amount of the total limiting nutrient and biomass sequestered in animals (Taylor 1984). Large zooplankton with relatively low metabolic rates can comprise a large fraction of the total phosphorus, but small zooplankton with high metabolic rates cannot. Furthermore, large zooplankton tend to pass on their nutrients to higher trophic levels or to the hypolimnion more readily, and total phosphorus may therefore decline more rapidly during stratification when zooplankton are large.Fertilization effects have been considered primarily from the viewpoint of increasing the overall biomass of plankton commu- 19 8 5), and it is possible that both effects must be studied simultaneously to avoid confusing the effects of fish addition w...

Interdependence of phosphorus, fish, and site effects on phytoplankton biomass and zooplankton

“…Vanni (1987a, b) found significant nutrient x fish interactions for abundances of large zooplankton and a few phytoplankton taxa. Mazumder et al (1988) detected a nutrient x fish interaction for the microplankton (20-200 pm). None of these studies found a nutrient x fish interaction on phytoplankton biomass.…”

“…One reason is that we detected a phosphorus x fish interaction only for rotifers, and probabilities associated with phosphorus x fish interactions for other response variables were Mazumder et al 1988). In these studies, two or three levels of nutrient addition were cross-classified with two levels of visually feeding zooplanktivore.…”

“…First, do nutrients and fish act as independent regulators of plankton communities or are there nutrient x fish interactions (Lynch and Shapiro 198 1;Vanni 1987a, b;Mazumder et al 1988)? A nutrient x fish interaction is an effect attributable to the combination of nutrient and fish variables beyond Notes that which can be predicted from the variables considered singly (Winer 197 1).…”

Whole‐lake experiments: The annual record of fossil pigments and zooplankton

“…Replacement of a small-bodied, inefficient herbivore assemblage by large, efficient grazers also reduces algal standing crop and leads to increased water transparency (Shapiro and Wright 1984;Carpenter et al 1987;Mazumder et al 1988). Changes in water clarity regulate the presence of deep bloom-forming algae (Pick et al 1984) and bacteria (Brown et al 1984).…”

National Center for Ecological Analysis and Synthesis, Santa Barbara, California 93101 and Center for Limnology,University of Wisconsin, Madison, Wisconsin 53706

“…Table 1. Expected changes in phytoplankton size structure due to increases in nutrient loading or mean length of crustacean zooplankton, derived from comparative studies, mesocosm experiments, models, and single-factor whole-lake experiments (including Kalff and Knoechel 1978;Gliwicz 1975;Nilssen 1978;Spodniewska 1978Spodniewska , 1979Harris 1980;Malone 1980;Watson and Kalff 1981;Sprules and Knoechel 1984;Sprules and Munawar 1986;McQueen 1990;Watson et al 1992;Mazumder 1994;Reynolds 1994;Benndorf 1995). Symbols: ϩ indicates an increase, -indicates a decrease, and nc indicates no change.…”