Zooplankton Feeding Rates Research Articles

Light climate and dissolved organic carbon concentration influence species-specific changes in fish zooplanktivory

Dissolved organic carbon (DOC) in lakes reduces light penetration and limits fish production in low nutrient lakes, reportedly via reduced primary and secondary production. Alternatively, DOC and light reductions could influence fish by altering their visual feeding. Previous studies report mixed effects of DOC on feeding rates of zooplanktivorous fish, but most investigators tested effects of a single concentration of DOC against clear-water, turbid, or algal treatments. We used a controlled laboratory study to quantify the effects of a DOC gradient (3–19 mg L−1) on average light climate and the zooplankton feeding rate of 3 common, north temperate fishes. Light availability, which was inversely related to DOC concentration, had a positive and linear effect on zooplankton consumption by juvenile largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus), explaining 22% and 28% of the variation in consumption, respectively. By contrast, zooplankton feeding rates by fathead minnow (Pimephales promelas) were best predicted by a nonlinear, negative influence of light (R2 = 0.13). In bluegill feeding trials we found a general trend for positive selection of larger zooplankton (Cladocera and Chaoboridae); however, the light climate did not influence the selection of prey type. Largemouth bass selected for larger-bodied zooplankton, with weak evidence that selectivity for large Cladocera changed from negative to neutral selection based on electivity values across the light gradient. Our results suggest that the effect of DOC on the light climate of lakes may directly influence fish zooplanktivory and that this influence may vary among fish species.

Partial diel vertical migrations in pelagic fish

1. Field studies on diel vertical migration (DVM) usually report uniform behaviour with population-wide ascents and descents during crepuscular periods. This contrasts partial seasonal migrations of many animal populations, where individuals choose either the resident or the migrant strategy depending on population density, feeding opportunity and predation risk in the resident and migrant habitats. 2. We tested whether DVM of freshwater zooplanktivorous fish (Coregonus spp.) resembles partial migrations. Twenty-eight hydroacoustic surveys were performed in the deep Lake Stechlin (Germany) between 2000 and 2010, with samplings encompassing all months between March and December. Zooplankton samples were simultaneously taken in epilimnetic and hypolimnetic layers. Fish obtained from depth-stratified samplings by a midwater trawl were used to test for individual differences between residents and migrants. 3. We show for the first time that DVMs of freshwater fish resemble patterns of partial migrations often found in seasonal environments. Across all samplings, 7-33% of fish did not ascend at dusk, but exhibited the resident strategy. The proportion or residents increased at low zooplankton feeding rates in the daytime habitat and during months when the temperature difference between daytime and night-time habitats was minor. 4. Slightly larger size and higher caloric density of migrants over residents in one of the coexisting Coregonus species suggested that individual differences contributed to the migration strategy performed. However, these results were based on one sample only, and extrapolation to the entire data set is not possible. 5. Our results are indirect evidence that the balance between migrants and residents may primarily depend on the trade-off between feeding gains and metabolic and predation costs of migration. However, the results also suggest that the global fitness consequences for the resident and migrant strategies may not be identical, rendering the importance of individual traits in the 'decision to migrate' likely.

Differences in zooplankton feeding rates and isotopic signatures from three temperate lakes

Bacteria and phytoplankton are integral in the mobilization and transfer of organic matter to higher trophic levels. Hence, we examined their role in zooplankton diets and assessed trends in their nitrogen isotopic variability. We performed feeding experiments with natural particulate organic matter (POM) and four zooplankton groups (Daphnia, Holopedium, large calanoids and small calanoids) to (1) examine whether there are differences in consumption (presented as clearance and ingestion rates) of phytoplankton and bacteria, and (2) determine whether differences in zooplankton clearance and ingestion rates are correlated with their δ15N isotopic signatures. In general, phytoplankton and bacteria clearance rates and biomass ingested per animal varied significantly among different zooplankton groups within lakes and between lakes for a given zooplankton group. Within a given lake, Daphnia and Holopedium had the highest phytoplankton and bacteria clearance and ingestion rates, followed by large calanoids, and then small calanoids. For a given zooplankton group, bacteria and phytoplankton clearance rates varied among lakes. In contrast, phytoplankton ingestion rates were consistently highest in Dickie Lake for all taxa, whereas bacteria ingestion rates were more variable among lakes for the different zooplankton taxa. The percentage contribution of different phytoplankton taxa to the biomass of phytoplankton ingested also varied significantly among lakes for a given taxa, but there were few differences within a given lake among zooplankton. Zooplankton δ15NDOMC values were correlated with their size adjusted phytoplankton and bacteria clearance and ingestion rates. The correlations were stronger with (1) phytoplankton compared to bacteria, and (2) clearance rates compared to ingestion rates of biomass. Together our results suggest that zooplankton taxa with low phytoplankton and bacteria clearance and ingestion rates and higher δ15NDOMC are likely exploiting food sources from higher trophic levels.

Molecular detection of algal prey in copepod guts and fecal pellets

The ability to obtain information about feeding selectivity and rates in situ for key organisms such as copepods and other zooplankton is vital for understanding the mechanisms structuring marine ecosystems. Copepods feed on a wide range of prey, and there are presently no methods available to directly quantify zooplankton feeding on all different prey types in situ. Therefore, the development of a new nonintrusive direct method is necessary to gain a better understanding of the trophic interactions in aquatic ecosystems. Molecular methods based on the polymerase chain reaction have recently become an important tool to study predation by arthropods, particularly insects. Here we present the first results of successful molecular detection of a specific prey consumed by calanoid copepods from gut and fecal material. Using the calanoid copepod species Calanus finmarchicus consuming the haptophyte alga Emiliania huxleyi as a model system, 18S ribosomal DNA originating from E. huxleyi was unambiguously detected in whole DNA extracts from copepods and from their fecal pellets. The results also suggest that prey DNA may be quantified for determination of prey‐specific zooplankton feeding rates. However, significantly more research under controlled laboratory and field conditions will be required to achieve these objectives. We hypothesize that molecular methods will become an important tool with the potential to quantify undisturbed trophic interactions between individual predators and all their prey in the complex natural plankton.

Zooplanktivory by Praunus flexuosus (Crustacea:Mysidacea):functional responses and prey selection in relation to prey escape responses

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 174:77-87 (1998) - doi:10.3354/meps174077 Zooplanktivory by Praunus flexuosus (Crustacea: Mysidacea): functional responses and prey selection in relation to prey escape responses Markku Viitasalo*, Milla Rautio Tvärminne Zoological Station, FIN-10900 Hanko, Finland and Department of Ecology and Systematics, Division of Hydrobiology, PO Box 17, FIN-00014 University of Helsinki, Finland *Address for correspondence: Department of Ecology and Systematics, Division of Hydrobiology, PO Box 17, FIN-00014 University of Helsinki, Finland. E-mail: markku.viitasalo@helsinki.fi ABSTRACT: Zooplankton feeding rates and prey selection of the mysid shrimp Praunus flexuosus were studied in single and multiple prey species experiments. Functional responses of P. flexuosus were determined for 2 copepod species, Acartia spp. (adults) and Eurytemora affinis (adult females), and 2 cladoceran species, Pleopsis polyphemoides and Bosmina longispina maritima. Feeding rates were highest with P. polyphemoides, intermediate with B. longispina maritima and Acartia spp. and lowest with E. affinis. Videofilming of the prey species subjected to an artificial water flow confirmed that E. affinis displays a stronger escape response than Acartia spp., and that cladocerans cannot withstand a water current. In a prey selection experiment with Acartia spp. and E. affinis, P. flexuosus' clearance rates of Acartia spp. were suppressed in the presence of E. affinis, suggesting an interference effect from E. affinis. In another multiple prey species experiment with Acartia spp. and P. polyphemoides, the mysids fed intensively on cladocerans, regardless of whether the cladocerans occurred alone or with copepods. In contrast, predation on Acartia spp. significantly declined when cladocerans were offered as alternative food (at high concentration). We suggest that P. flexuosus can capture cladocerans by creating a suspension feeding current, whereas the evasive copepods need to be perceived and attacked individually. At low prey concentration, P. flexuosus feeds opportunistically by using both feeding modes, and the apparent 'selectivity' mainly reflects the escape capabilities and morphological defences of the prey species; at high prey concentration, P. flexuosus may show true selection by switching from omnivorous feeding to suspension feeding on cladocerans. KEY WORDS: Mysid shrimps · Praunus flexuosus · Zooplanktivory · Functional response · Prey selection · Prey switching · Escape reaction · Baltic Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 174. Publication date: November 26, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.

Pelagic and benthic ecology of the lower interface of the Eastern Tropical Pacific oxygen minimum zone

The distributions of pelagic and benthic fauna were examined in relation to the lower boundary of the oxygen minimum zone (OMZ) on and near Volcano 7, a seamount that penetrates this feature in the Eastern Tropical Pacific. Although the broad, pronounced OMZ in this region is an effective barrier for most zooplankton, zooplankton abundances, zooplankton feeding rates, and ambient suspended particulate organic carbon (POC) peaked sharply in the lower OMZ (about 740–800 m), in association with the minimum oxygen concentration and the increasing oxygen levels just below it. Zooplankton in the lower OMZ were also larger in size, and the pelagic community included some very abundant, possibly opportunistic, species. Elevated POC and scatter in the light transmission data suggested the existence of a thin, particle-rich, and carbon-rich pelagic layer at the base of the OMZ. Gut contents of planktonic detrifvores implied opportunistic ingestion of bacterial aggregates, possibly from this layer. Benthic megafaunal abundances on the seamount, which extended up to 730 m, peaked at about 800 m. There was a consistent vertical progression in the depth of first occurrence of different megafaunal taxa in this depth range, similar to intertidal zonation. Although the vertical gradients of temperature, salinity, and oxygen were gradual at the lower OMZ interface (in contrast to the upper OMZ interface at the thermocline), temporal variability in oxygen levels due to internal wave-induced vertical excursions of the OMZ may produce the distinct zonation in the benthic fauna. The characteristics of the lower OMZ interface result from biological interactions with the chemical and organic matter gradients of the OMZ. Most zooplankton are probably excluded physiologically from pronounced OMZs. The zooplankton abundance peak at the lower interface of the OMZ occurs where oxygen becomes sufficiently high to permit the zooplankton to utilize the high concentrations of organic particles that have descended through the OMZ relatively unaltered because of low metazoan abundance. A similar scenario applies to megabenthic distributions. Plankton layers and a potential short food chain (bacteria to zooplankton) at OMZ interfaces suggest intense utilization and modification of organic material, localized within a thin midwater depth zone. This could be a potentially significant filter for organic material sinking to the deep-sea floor.

Feeding by a Lotic Mayfly Grazer as Quantified by Gut Fluorescence

It is often of interest in ecological research to quantify the feeding of study animals. Approaches used previously with grazing aquatic insects have been either labor-intensive (algal cell counts of gut contents), lacking in sensitivity (AFDM, relative gut fullness), or involve radioactive tracers (dual isotope method). A method developed and applied by marine biologists to study zooplankton feeding rates uses the amount of plant pigment in the gut as a feeding index. We have modified this technique to assess feeding by larvae of a grazing mayfly, Baetis bicaudatus (Ephemeroptera: Baetidae) in a western Colorado stream. Gut pigments include chlorophyll from ingested algae, which is rapidly degraded to phaeophorbide and passes unassimilated through the gut, thereby acting as a tracer of feeding activity. Our experiments showed that the optimum dissection and pigment extraction procedure entailed macerating whole Baetis individuals and extracting the gut pigments for 24 hr in 90% ethanol. Pigment levels (c...

Zooplankton feeding rates in relation to suspended sediment content: potential influences on community structure in a turbid reservoir

SUMMARY. 1. Changes in zoopiankton composition and abundance in Lake le Roux, a turbid subtropical reservoir on the Orange River in South Africa, were correlated with changes in water transparency (related to suspended sediment levels) during a 7 year field study. Results of radiotracer studies of the effect of mineral turbidity on zooplankton feeding rates which potentially influence competitive ability, and thus community structure, are reported here.2. Feeding rates of five zooplankters were very variable, but consistently declined with rising turbidity: rates of decline differed between species. A regression estimate of the critical turbidity threshold at which food intake matched the estimated respiratory need was derived for each species. This yielded the following “turbidity‐tolerance” ranking: Moina brachiata Jurine > Metadiaptomus meridianus (van Douwe) ×Daphnia gibba Methuen > D. barbata Weltner > D. longispina O. F. Muller. The consistency between this ranking and one based upon abundance‐transparency relationships in the field study suggests that community structure is related to differential feeding capabilities, although other influences are not excluded.3. Tests on D. gibba and M. meridianus failed to reveal any detectable feeding rate saturation (incipient limiting food level) below 1.2mg 1−1 C. The relative reduction in feeding rates at elevated turbidity was nearly 3 times greater for the daphnid than the copepod over a range of food concentrations, and considerably reduces the competitive ability of this (and other) daphnids. The turbidity tolerance disparity between Moina and the daphnids demonstrates a more complex situation than a simple copepod/cladoceran dichotomy. These findings and their implieations are discussed in relation to wider features of zooplankton ecology.

The effect of inorganic turbidity on zooplankton feeding rates and its related implications to community structure: an experimental analysis

The effect of inorganic turbidity on zooplankton feeding rates and its related implications to community structure: an experimental analysis