Zooplankton community size structure and taxonomic composition affects size-selective grazing in natural communities

Abstract

The body size of an individual zooplankton is well related to its grazing rate and to the range of particle sizes it can ingest, and since cladocerans and copepods feed differently, they follow different relationships. Based on these general patterns in individual organisms, we tested whether the size structure and taxonomic composition of more complex natural zooplankton communities are related to their in situ grazing rate and to the range of algal sizes they graze. We compared community grazing rates on individual algal taxa in two communities dominated by small cladocerans, three communities dominated by large cladocerans and three copepod-dominated communities. Small algae were usually grazed most intensively, but grazing rates were poorly related to algal size alone. The range in size of grazed algae increased with increasing mean zooplankton body size, but differed systematically with their taxonomic composition. Communities dominated by Ceriodaphnia or Holopedium grazed a narrower size range of algae [maximum greatest axial length dimension (GALD)=16-36 μm)] than communities with large biomasses of Bosmina or Daphnia (maximum GALD=28-78 μm). Copepod-dominated communities followed the same general relationship as cladocerans. Daphnia-dominated communities grazed the broadest range of algal sizes, and their total grazing rates were up to 2.4 times their grazing rates on small (<35 μm) "highly edible" algae, a difference of similar magnitude to those found in successful trophic cascade biomanipulations.

Cascading effect of exotic fish fry on plankton community in a tropical Andean high mountain lake: a mesocosm experiment

“…The abundance of herbivores, mainly C. brandorffi, the largest and most abundant zooplankter, decreased in trout fry treatments, causing a reduction in grazing pressure and of average size of Peridinium. These results are consistent with the size-efficiency hypothesis (SEH), which postulates that the minimum and maximum size of the food particles ingested by zooplankton depends on body size, and that the larger organisms consume a wider size range of particles (Hall et al, 1976;Cyr and Curtis, 1999;Humphries, 2007). However, our results conflict with other research where algae with GALD>30 µm are considered less vulnerable or inedible for herbivorous zooplankton (Attayde and Hansson, 2001;Benndorf et al, 2002;Zhao et al, 2016).…”

Grazer-diatom size relationships in an epiphytic community

“…We suggest that GALD probably summarizes the size limits for both handling and ingestion and therefore represents a simple and effective parameter to describe food for consumption studies. Cyr and Curtis (1999) reported an inconsistency between laboratory results with artificial particles and field observation of maximum algal size ingested by Daphnia-dominated communities (Fig. 3).…”

“…These authors reported zooplankton grazing on both Ceratium (mean GALD 237 m) and Oscillatoria (mean GALD 146 m), which greatly exceed the size range predicted by plankton-based equations but are within the size range of diatoms ingested by grazers in our study. Laboratory studies with simplified assemblages of one or a few algal species or with particles (beads or pollen grains) thus appear to underestimate the size of algae actually available to zooplankton (Cyr and Curtis 1999) and benthos. The prediction of grazing selectivity will require the development of more realistic models based on natural food size and shape.…”

The Response of Zooplankton Communities in Montane Lakes of Different Fish Stocking Histories to Atmospheric Nitrogen Deposition Simulations

“…Therefore, lakes with fish present may have zooplankton communities that are altered to better buffer against increases in acidity, while fishless lake zooplankton communities may be less resilient due to a greater abundance of sensitive taxa. Rotifers and smaller-bodied crustacean taxa are typically less efficient grazers with lower grazing rates compared to communities dominated by large Daphnia (Cyr and Curtis 1999), thus it would be expected that increased algal biovolume due to nitrogen addition could be more likely to lead to algal blooms in communities present with fish. As aquatic montane systems receive inputs of atmospheric nitrogen deposition these stressors could interact with one another to increase pressure on native biota through decreases in food availability and quality, as well as acute and chronic mortality.…”

“…Water for chlorophyll analysis was divided into two fractions, one passing through a 35µm filter to represent the highly edible algal fraction (Cyr and Curtis 1999), and one unfiltered to represent total algae, using chlorophyll a (chl a) as a proxy of algal biomass. Each fraction was then filtered through a 1.2μm pore size glass fiber filter and frozen.…”