Microzooplankton Grazing Impact Research Articles

Mesozooplankton prey preference and grazing impact in the western Arctic Ocean

Abstract The role of mesozooplankton as consumers and transformers of primary and secondary production in the Beaufort and Chukchi Seas was examined during four cruises in spring and summer of both 2002 and 2004 as part of the western Arctic Shelf–Basin Interactions (SBI) program. Forty-seven grazing experiments using dominant mesozooplankton species and life stages were conducted at locations across the shelf, slope, and basin of the Chukchi and Beaufort Seas to measure feeding rates on both chlorophyll and microzooplankton and to determine mesozooplankton prey preferences. Mesozooplankton biomass was at all times dominated by life stages of four copepod taxa: Calanus glacialis , Calanus hyperboreus , Metridia longa , and Pseudocalanus spp. Significant interannual, seasonal, regional, between species and within species differences in grazing rates were observed. Overall, the dominant zooplankton exhibited typical feeding behavior in response to chlorophyll concentration that could be modeled using species and life-stage specific Ivlev functions. Microzooplankton were preferred prey at almost all times, with the strength of the preference positively related to the proportion of microzooplankton prey availability. Average mesozooplankton grazing impacts on both chlorophyll standing stock (0.6±0.5% d −1 in spring, 5.1±6.3% d −1 in summer) and primary production (12.8±11.8% d −1 in spring, 27.6±24.5% d −1 in summer) were quite low and varied between shelf, slope, and basin. Coincident microzooplankton grazing experiments [Sherr, E.B., Sherr, B.F., Hartz, A.J., 2009. Microzooplankton grazing impact in the Western Arctic Ocean. Deep-Sea Research II] were conducted at most stations. Together, microzooplankton–mesozooplankton grazing consumed only 44% of the total water-column primary production, leaving more than half directly available for local export to the benthos or for offshore transport into the adjacent basin.

Zooplankton community structure, micro-zooplankton grazing impact, and seston energy content in the St. Johns river system, Florida as influenced by the toxic cyanobacterium Cylindrospermopsis raciborskii

Zooplankton can influence the phytoplankton community through preferential grazing. In turn, nuisance cyanobacteria may affect zooplankton community structure by allowing certain species to out-compete others. We examined zooplankton-phytoplankton interactions, micro-zooplankton (< 200 μm) grazing, and biochemical components of the seston in the St. Johns River System (SJR), Florida in the presence and absence of the toxin-producing cyanobacterium Cylindrospermopsis raciborskii. We tested whether this cyanobacterium would cause a decrease in the size structure of the zooplankton community and postulated a resultant decline in the metabolic energy and carbon available to higher consumers (i.e. fish). When numbers of C. raciborskii were low or undetectable, zooplankton were more diverse and were comprised of larger species. Rotifers were the dominant zooplankton, and their numbers relative to other zooplankton increased as C. raciborskii concentrations increased. Micro-zooplankton grazing was higher in times of C. raciborskii abundance, suggesting competitive and predatory exclusion by larger zooplankton in times of higher phytoplankton diversity. Total caloric content of the seston was higher in times of C. raciborskii abundance. However, essential fatty acids and phosphorus may be lacking in the seston, or nutrients may potentially be sequestered by the cyanobacteria and remain as organic matter in the water column. In such cases, higher trophic levels would not be able to obtain optimal energy requirements. Overall, there was a greater impact of micro-grazers on phytoplankton in the presence of C. raciborskii and apparent negative effects on the larger zooplankton species, suggesting a potential for changes in zooplankton and higher trophic level community structure.

Microzooplankton grazing in Phaeocystis and diatom-dominated waters in the southern North Sea in spring

The impact of microzooplankton grazing upon phytoplankton production was quantified in surface waters of the Southern Bight of the North Sea, during April 1998. Two sites were studied in order to examine the impact of microzooplankton grazing on phytoplankton communities dominated by either Phaeocystis globosa and large phytoplankton or small phytoplankton taxa. The nearshore site was characterised by a phytoplankton community comprised mainly of P. globosa and chains of diatoms with high productivity (av. 346 ± 185 μgC l −1 d −1) and biomass (280 ± 171 μgC l −1 d −1). In contrast, in the offshore waters relatively small diatoms dominated the phytoplankton where productivity and biomass were more than ca. five times lower than in nearshore waters. Contrary to expectations, the nearshore site supported a high biomass of microzooplankton (av. 22.4 ± 10.6 μgC l −1 d −1) which was dominated by large heterotrophic dinoflagellates, mostly Gyrodinium cf. spirale. Offshore the microzooplankton community contained one-third the biomass of the nearshore community and was dominated by smaller individuals, in particular oligotrich ciliates, Strombidium spp. Dilution experiments were conducted in order to quantify phytoplankton growth and losses due to microzooplankton grazing in the <200 μm size fraction. Phytoplankton specific growth rates (<200 μm) ranged between 0.13 and 0.67 d −1 with highest values associated with offshore waters. In contrast, phytoplankton mortality due to microzooplankton grazing (0.27 to 1.14 d −1) was highest at the nearshore site and exceeded the growth rates of the <200 μm phytoplankton. Biomass specific grazing rates were three-fold higher in nearshore (av. 0.33 ± 0.23 d −1) waters compared to those offshore (av. 0.11 ± 0.09 d −1). These results show that microzooplankton were grazing more vigorously nearshore than offshore and were consistently cropping the production of the <200 μm phytoplankton. This high grazing pressure is likely to drive a shift in community composition from smaller to larger cells, in particular colonies of P. globosa. The high grazing rates on smaller phytoplankton demonstrated in this study illustrate that microzooplankton grazing may be one of the driving forces behind the evolution of the Phaeocystis life-history strategy that involves a transition between solitary and colonial cells.

Relative grazing impact of microzooplankton and mesozooplankton on a bloom of the toxic dinoflagellate Alexandrium minutum

Grazing can be a substantial loss factor for harm- ful algal blooms (HABs) and a possible cause of their termina- tion. There is, however, a considerable gap in our knowledge of the relative grazing impact of the different components of the planktonic community on a red tide. In this study, we examine the importance of grazing control on a naturally occurring bloom of the toxic dinoflagellate Alexandrium minu- tum. We estimated the grazing impact of microzooplankton (by the dilution method) and copepods (by 24 h incubations with cultured populations of Acartia grani and Oithona davisae) on a bloom of A. minutum. Grazing by microzooplankton (0.84 d -1 ) was equal to and even exceeded A. minutum growth rates (0.79 d -1

Microplankton community structure and the impact of microzooplankton grazing during an Emiliania huxleyi bloom, off the Devon coast

Phytoplankton and microzooplankton community structure and the impact of microzooplankton grazing were investigated during a one-day study of an Emiliania huxleyi bloom off the coast of Devon during July 1999. Vertical profiles were undertaken at four stations, along a transect which crossed from a low reflectance to a high reflectance area as seen by satellite imagery. Microzooplankton dilution grazing experiments, coupled with pigment analysis to determine class specific grazing rates, were performed at two of these stations.Highest concentrations of chlorophyll-a (5·3 mg m−3) and accessory pigments were measured inside the area of high reflectance. Phytoplankton standing stocks ranged between 1588 and 5460 mg C m−2 and were also highest in the area of high reflectance. The phytoplankton community was dominated by coccolithophores and diatoms in low reflectance waters and by photosynthetic dinoflagellates in high reflectance areas. Microzooplankton standing stocks ranged between 905 and 2498 mg C m−2. Protozoa dominated the microzooplankton community. The protozoan community comprised a relatively even mixture of heterotrophic dinoflagellates, non-choreotrich and choreotrich ciliates in low reflectance waters. However, non-choreotrich ciliates dominated the communities inside the high reflectance area. Of the heterotrophic ciliates, a predatory ciliate Askenasia sp. dominated both non-choreotrich abundance and biomass.Results from grazing experiments showed that 60–64% of the chlorophyll-a biomass was consumed daily by the microzooplankton. Highest grazing mortality was associated with peridinin (dinoflagellates) and alloxanthin (cryptophytes). Lower grazing rates were found on fucoxanthin (diatoms and prymnesiophytes). Our results indicate that grazing on E. huxleyi in the area of remotely sensed high reflectance was low and highest grazing was on photosynthetic dinoflagellates and cryptophytes.

Grazing impact of microzooplankton on a diatom bloom in a mesocosm as estimated by pigment-specific dilution technique

To investigate the impact of microzooplankton grazing on phytoplankton bloom in coastal waters, an enclosure experiment was conducted in Saanich Inlet, Canada during the summer of 1996. Daily changes in the microzooplankton grazing rate on each phytoplankton group were investigated with the growth rates of each phytoplankton group from the beginning toward the end of bloom using the dilution technique with high-performance liquid chromatography (HPLC). On Day 1 when nitrate and iron were artificially added, chlorophyll a concentration was relatively low (4.3 μg l −1) and 19′-hexanoyloxyfucoxanthin-containing prymnesiophytes were predominant in the chlorophyll biomass. However, both the synthetic rates and concentrations of 19′-hexanoyloxyfucoxanthin declined before bloom, suggesting that 19′-hexanoyloxyfucoxanthin-containing prymnesiophytes weakened. Chlorophyll a concentration peaked at 23 μg l −1 on Day 4 and the bloom consisted of the small chain-forming diatoms Chaetoceros spp. (4 μm in cell diameter). Diatoms were secondary constituents in the chlorophyll biomass at the beginning of the experiment, and the growth rates of diatoms (fucoxanthin) were consistently high (>0.5 d −1) until Day 3. Microzooplankton grazing rates on each phytoplankton group remarkably increased except on alloxanthin-containing cryptophytes after the nutrient enrichments, and peaked with >0.6 d −1 on Day 3, indicating that >45% of the standing stock of each phytoplankton group was removed per day. Both the growth and mortality rates of alloxanthin-containing cryptophytes were relatively high (>1 and >0.5 d −1, respectively) until the bloom, suggesting that a homeostatic mechanism might exist between predators and their prey. Overall, microzooplankton grazing showed a rapid response to the increase in phytoplankton abundance after the nutrient enrichments, and affected the magnitude of the bloom significantly. High grazing activity of microzooplankton contributed to an increase in the abundance of heterotrophic dinoflagellates with 7–24 μm in cell size, the fraction of large-sized (>10 μm) chlorophyll a, and stimulated the growth of larger-sized ciliates after the bloom.

DMSP and DMS dynamics and microzooplankton grazing in the Labrador Sea: application of the dilution technique

We adapted the dilution technique to study microzooplankton grazing of algal dimethylsulfoniopropionate (DMSP) vs. Chl a, and to estimate the impact of microzooplankton grazing on dimethyl sulfide (DMS) production in the Labrador Sea. Phytoplankton numbers were dominated by autotrophic nanoflagellates in the Labrador basin, but diatoms and colonial Phaeocystis pouchetii contributed significantly to phytomass at several high chlorophyll stations and on the Newfoundland and Greenland shelfs. Throughout the region, growth of algal Chl a and DMSP was generally high (0.2–1 d − 1), but grazing rates were lower and more variable, characteristic of the early spring bloom period. Production and consumption of Chl a vs. DMSP followed no clear pattern, and sometimes diverged greatly, likely because of their differing distributions among algal prey taxa and size class. In several experiments where Phaeocystis was abundant, we observed DMS production proportional to grazing rate, and we found clear evidence of DMS production by this haptophyte following physical stress such as sparging or filtration. It is possible that grazing-activated DMSP cleavage by Phaeocystis contributes to grazer deterrence: protozoa and copepods apparently avoided healthy colonies (as judged by relative growth and grazing rates of Chl a and DMSP), and grazing of Phaeocystis was significant only at one station where cells were in poor condition. Although we hoped to examine selective grazing on or against DMSP-containing algal prey, the dilution technique cannot differentiate selective ingestion and varying digestion rates of Chl a and DMSP. We also found that the dilution method alone was poorly suited for assessing the impact of grazing on dissolved sulfur pools, because of rapid microbial consumption and the artifactual release of DMSP and DMS during filtration. Measuring and understanding the many processes affecting organosulfur cycling by the microbial food web in natural populations remain a technical challenge that will likely require a combination of techniques to address.

Spring microzooplankton composition, biomass and potential grazing in the central Cantabrian coast (southern Bay of Biscay)

Microzooplankton abundance, biomass and composition were investigated in the coastal waters of Asturias (southern Bay of Biscay) in May 1996. Abundance ranged from 0.7×10 3 to 8.5×10 3 cell·L −1. The protists community was dominated by aloricate ciliates averaging 82 % of microheterotrophs. Small aloricate ciliates, below 20 μm in size, contributed 63 % to total ciliate abundance. Carbon biomass ranged from 2.4 to 15.4 mgC·m −3, averaging 23 % of phytoplankton biomass. Aloricate ciliates were also the dominant component of biomass (56.2 %), but the importance of copepod nauplii increased in terms of carbon, averaging 28.5 % of total biomass. Microzooplankton biomass was significantly correlated with Chl a concentration in the water column. Theoretical estimates of the grazing impact of the microzooplankton community on phytoplankton were calculated and resulted in an average value of 28.3 % of phytoplankton standing stock potentially consumed per day. Choreotrich ciliates were the most important potential grazers in the study (13.7 % of standing stock) followed by metazoan nauplii (6.3 %). The potential microzooplankton impact on phytoplankton was consistent with the large size of primary producers during diatom spring blooms, like the one found in this study. The validity of theoretical estimates of microzooplankton grazing impact, as well as the importance of including metazoan larvae in coastal microzooplankton community studies are discussed. © 2000 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS microzooplankton / ciliates / biomass / grazing / southern Bay of Biscay

Impact of microzooplankton on the progression and fate of the spring bloom in fjords of northern Norway

The objective of the study was to determine the role of microzooplankton in the fate of primary production and progression of the spring phytoplankton bloom in high latitude fjords. The 3 fjords, Balsfjord, Malangen and Ullsfjord (Norway), varied in oceanic influence and in the rate of development of the spring bloom. The abundance of Phaeocystis pouchetii was relatively low in the spring of 1997 compared to previous years, and diatoms dominated the biomass of the phytoplankton assemblage in all 3 fjords. The mean biomass of microzooplankton in the top 20 m averaged 72, 66 and 80 mg C m -3 and values integrated to 170 m averaged 4560, 4450 and 6820 mg C m -2 in Balsfjord, Malangen and Ullsfjord, respectively. The composition of the microzooplankton was consistent among the fjords and over time, with the proportion of biomass split evenly between nanoflagellates, dinoflagellates and ciliates. Grazing rates of the microzooplankton community were measured with the dilution technique. The impact of microzooplankton grazing was similar among the fjords, accounting for on average 68, 63 and 55% of the production of the < 200 µm phytoplankton in Bals- fjord, Malangen and Ullsfjord, respectively. When integrated to 20 m, based on a microzooplankton biomass-specific ingestion rate, microzooplankton grazing accounted for an estimated 12 to 26% of the gross primary production. However, this does not account for the carbon requirements of a sub- stantial proportion of the microzooplankton that occurred below 20 m. Clearance rates by ciliates of nanophytoplankton cells of a similar size to the single cells of P. pouchetii were determined from the uptake rates of fluorescently labelled algae (FLA). Generally, the taxa of ciliates that were found to ingest FLA accounted for ♢ 50% of the abundance of the ciliate population in each fjord. Taxon-spe- cific ciliate clearance rates of FLA in surface waters varied with ciliate size from 5.6 to 1.3 µl cell -1 h -1 . The FLA-consuming ciliate population cleared a total of 27 〈 10 3 to 141 〈 10 3 µl l -1 d -1 in surface waters. The ingestion rates of the FLA-consuming ciliates were equivalent to between 11 and 29% of the total microzooplankton consumption. It is possible that the grazing pressure exerted by the micro- zooplankton on single cells and small colonies was high enough to decrease the overall competitive- ness of the P. pouchetii populations and contribute to their low abundance.

Picophytoplankton dynamics and production in the Arabian Sea during the 1995 Southwest Monsoon

Phytoplankton community structure is expected to shift to larger cells (e.g., diatoms) with monsoonal forcing in the Arabian Sea, but recent studies suggest that small primary producers remain active and important, even in areas strongly influenced by coastal upwelling. To better understand the role of smaller phytoplankton in such systems, we investigated growth and grazing rates of picophytoplankton populations and their contributions to phytoplankton community biomass and primary productivity during the 1995 Southwest Monsoon (August–September). Environmental conditions at six study stations varied broadly from open-ocean oligotrophic to coastal eutrophic, with mixed-layer nitrate and chlorophyll concentrations ranging from 0.01 to 11.5 μM NO 3 and 0.16 to 1.5 μg Chl a. Picophytoplankton comprised up to 92% of phytoplankton carbon at the oceanic stations, 35% in the diatom-dominated coastal zone, and 26% in a declining Phaeocystis bloom. Concurrent in situ dilution and 14C-uptake experiments gave comparable ranges of community growth rates (0.53–1.05 d −1 and 0.44–1.17 d −1, to the 1% light level), but uncertainties in C:Chl a confounded agreement at individual stations. Microzooplankton grazing utilized 81% of community phytoplankton growth at the oligotrophic stations and 54% at high-nutrient coastal stations. Prochlorococcus (PRO) was present at two oligotrophic stations, where its maximum growth approached 1.4 d −1 (two doublings per day) and depth-integrated growth varied from 0.2 to 0.8 d −1. Synechococcus (SYN) growth ranged from 0.5 to 1.1 d −1 at offshore stations and 0.6 to 0.7 d −1 at coastal sites. Except for the most oligotrophic stations, growth rates of picoeukaryotic algae (PEUK) exceeded PRO and SYN, reaching 1.3 d −1 offshore and decreasing to 0.8 d −1 at the most coastal station. Microzooplankton grazing impact averaged 90, 70, and 86% of growth for PRO, SYN, and PEUK, respectively. Picoplankton as a group accounted for 64% of estimated gross carbon production for all stations, and 50% at high-nutrient, upwelling stations. Prokaryotes (PRO and SYN) contributed disproportionately to production relative to biomass at the most oligotrophic station, while PEUK were more important at the coastal stations. Even during intense monsoonal forcing in the Arabian Sea, picoeukaryotic algae appear to account for a large portion of primary production in the coastal upwelling regions, supporting an active community of protistan grazers and a high rate of carbon cycling in these areas.

Grazing impact of microzooplankton on different size classes of algae in the North Sea in early spring and mid-summer

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 180:93-104 (1999) - doi:10.3354/meps180093 Grazing impact of microzooplankton on different size classes of algae in the North Sea in early spring and mid-summer B. R. Kuipers*, H. J. Witte Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands *E-mail: bouwe@nioz.nl ABSTRACT: The impact of microzooplankton community grazing on different size classes of algae was investigated at 11 stations between Dogger Bank and the Shetlands in early spring (March-April) and in summer (July-August). This work is part of a larger study designed to test the hypothesis that size-differential grazing of phytoplankton populations plays a crucial role in regulating food web structure. Dilution experiments, in which loss rates of the algae due to microzooplankton grazing can be estimated from the relation between growth rate of the prey and dilution, failed in many cases due to high variance. The present paper analyses the problem and puts forward a solution which involved pooling data from comparable stations into 1 average grazing estimate per algal size class. In early spring, estimates of grazing from measurements of chlorophyll a (chl a) were obtained only for algae >5 µm, and average grazing rate was 0.23 d-1 at the deeper stations. At the shallower more southern stations where a phytoplankton bloom was in progress the average grazing rate on algae >5 µm was 0.5 d-1. Flow cytometry was more successful in the <5 µm algal fraction, yielding grazing rates of 0.25 d-1 for the southern and 0.31 d-1 for the northern stations. In summer, microzooplankton grazing incubations yielded significant results only when flow cytometry was used, and only when results were pooled for different areas. Grazing rates ranged from 0.07 d-1 in the 1-2 µm algal size class to 0.74 d-1 for algae of 3-4 µm and were 0.25 d-1 for the <5 µm cluster as a whole. KEY WORDS: Microzooplankton · Grazing · Dilution · Chlorophyll · Flow cytometry · North Sea Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 180. Publication date: May 03, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Microzooplankton grazing in different water masses associated with the subtropical convergence round the south island, New Zealand

Grazing rates by microzooplankton feeding on bacteria, picophytoplankton and total phytoplankton were measured in subtropical, Subtropical Convergence and subantarctic waters in winter and spring 1993. Water samples were collected simultaneously for determinations of nutrient concentrations and biological parameters. Bacteria, phytoplankton and microzooplankton abundance were generally higher in spring than winter. Picophytoplankton were a large proportion of the phytoplankton populations in subantarctic waters. Microzooplankton grazing impact on total chlorophyll a standing crop and phytoplankton production ranged from 10–92% to 71–194% in winter and 4–57% to 20–126% in spring, respectively. The only major difference between grazing impacts in winter and spring was in subtropical waters, where grazing impacts on both chlorophyll a and picophytoplankton were higher in winter. Grazing impact was generally greater in subantarctic water and on picophytoplankton than on total phytoplankton. Grazing balanced growth of phytoplankton in all water masses in winter, but in subtropical waters in spring, growth of total phytoplankton exceeded grazing and grazing exceeded growth in picophytoplankton populations. This decoupling of growth of the larger phytoplantion and grazing by microzooplankton contributed to the spring bloom and potential flux of carbon out of the surface waters in subtropical water masses. These findings are further discussed in relation to spatial and seasonal trends in other parts of the STC.

Preliminary Investigation of the Ecological Role of Microzooplankton in the Kariega Estuary, South Africa

A preliminary investigation of the ecological role of microzooplankton (20–200μm) was conducted in the Kariega Estuary along the south coast of South Africa during summer (November) 1994. Microzooplankton grazing impact on phytoplankton was estimated at 15 and 20°C in the laboratory using the dilution technique. Size-fractionated chlorophyll studies showed that the nano- and picophytoplankton dominated phytoplankton standing stock, comprising between 53 and 78% of total chlorophyll. During the entire investigation, the microzooplankton were numerically dominated by protozooplankton with densities ranging between 900 and 2850cells l−1. Based on biovolume: carbon estimates, microzooplankton contributed between 13 and 43% of the total biological seston in the size range 2–200μm. Amongst the protozoans, ciliates and dinoflagellates numerically dominated. Microzooplankton densities co-varied with chlorophyll concentrations (r2=0·45;P<0·05). Analysis of variance indicated that the grazing impact of microzooplankton was not significantly different between the two temperatures (F=12·68;P>0·05). The instantaneous grazing rates of microzooplankton on nanophytoplankton varied from 0·010 to 0·105day−1, and those on microphytoplankton from 0·007 to 0·091day−1. This level of grazing corresponds to a daily loss of about 5 and 2% of the initial standing stock and about 50 and 65% of the potential production of the two size fractions, respectively. During this study, the grazing rates of microzooplankton correlated with the growth rates of nanophytoplankton (r2=0·51;P<0·05) reflecting tight coupling between these two fractions. These data suggest that microzooplankton are important consumers of phytoplankton production in the Kariega Estuary.

Role of microplankton in the diet and daily ration of Antarctic zooplankton species during austral summer

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 143:15-23 (1996) - doi:10.3354/meps143015 Role of microplankton in the diet and daily ration of Antarctic zooplankton species during austral summer Froneman PW, Pakhomov EA, Perissinotto R, McQuaid CD Predation rates of the 9 most abundant Antarctic meso- (4 copepods) and macrozooplankton (3 euphausiids, 1 hyperiid and 1 salp) species on microplankton (20 to 200 µm) were estimated using in vitro incubations during the fourth cruise of the South African Antarctic Marine Ecosystem Study (SAAMES IV) to the ice-edge region of the Lazarev Sea during austral summer (Dec/Jan) 1994/1995. Chlorophyll a concentrations during the incubations ranged between 0.187 and 1.410 µg l-1 and were dominated by ice-associated chain-forming microphytoplankton (>20 µm) of the genera Nitzschia and Chaetoceros. The microplankton assemblages were entirely dominated by protozoans comprised of ciliates and dinoflagellates. Densities of protozoans ranged from 1375 to 2690 cells l-1. Based on previously published results, meso- and macrozooplankton species generally consumed >120% of their minimum daily ration, i.e. minimum carbon uptake (MCU), when offered microplankton. Exceptions were Euphausia crystallorophias and Vibilia antarctica for which microplankton carbon contributed 68 and 30% of MCU, respectively. Microplankton carbon contributed between 17 and 24% of the total carbon requirements for the 4 copepod species examined and between 21 and 73% for the macrozooplankton. The daily rations of juveniles were, however, twice those of the adults, suggesting that the relative importance of microzooplankton to the daily ration of macrozooplankton shifts with life stage. Carnivory by metazoan grazers may, therefore, potentially reduce the high grazing impact of microzooplankton on the local phytoplankton stock. Antarctica · Carnivory · Zooplankton · Microzooplankton Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 143. Publication date: November 14, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

A refined dilution technique for measuring the community grazing impact of microzooplankton, with experimental tests in the central equatorial Pacific

A refined dilution technique for measuring the community grazing impact of microzooplankton, with experimental tests in the central equatorial Pacific

Growth and grazed rates of bacterial communities in a bog as determined by the dilution method using a continuous culture system

The population dynamics of bacterial communities in Matsumi-ike Bog located in the campus of the University of Tsukuba was studied by the dilution method with a chemostat. The apparent growth rates of bacteria (total cells, rods, cocci and commas) was linearly proportional to the dilution factor and the growth and grazed rates could be estimated. The micro-zooplankton grazing impact was 14.6% bacterial standing stock hr−1 and 19.8% bacterial production hr−1.

Microzooplankton herbivory on the Grand Bank (Newfoundland, Canada): A seasonal study

Grazing impact of microzooplankton on phytoplankton was investigated on the Grand Bank, Newfoundland, Canada, in April, July and October 1984, using a seawater dilution method. In April a large proportion of chlorophylla was in the microplankton size fraction (> 20µm) while in mid-summer and fall most was in the nanoplankton size fraction (< 20µm). Diatoms were the dominant phytoplankters in April, while undetermined flagellates and coccolithophores were abundant in other seasons. Major grazers were oligotrichous ciliates in all seasons. Instantaneous grazing rates on nanophytoplankton, as measured by changes in chlorophylla, varied from 0.12 to 0.43 d−1 and those on microphytoplankton from 0.19 to 0.68 d−1. Grazing rates did not change over 24 and 48 h intervals. This level of grazing corresponded to a daily loss of about 20 and 30% of standing stock of chlorophylla and about 50 and 70% loss of potential production in the two size fractions respectively. Taxon-specific grazing rates, calculated from microscopic enumeration, showed that small diatoms were grazed heavily, and their growth was controlled by grazing in late spring. In late summer and fall, undetermined flagellates and coccolithophores were also grazed at high rates but their growth rates were higher than the grazing rates, and therefore, were not controlled by microzooplankton. In general, microzooplankton grazed on whatever appropriate sized food was dominant in the experimental water. Their potential ability to control the growth of certain food species may be one of the causes determining the species composition of phytoplankton communities.

Estimating the grazing impact of marine micro-zooplankton

This paper describes a dilution technique for estimating the micro-zooplankton grazing impact on natural communities of marine phytoplankton. Experiments performed in coastal waters off Washington, USA (October, 1980), yield estimates of micro-zooplankton impact equivalent to 6 to 24% of phytoplankton standing biomass and 17 to 52% of production per day. Indirect evidence suggests that most of this impact is due to the feeding of copepod nauplii and tintinnids; in contrast, non-loricate ciliates, comprising 80 to 90% of numerical abundance, appeared to contribute little to phytoplankton mortality.