Heterotrophic Pico Research Articles

Diet of sardine Sardina pilchardus: an ‘end-to-end’ field study

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 453:173-188 (2012) - DOI: https://doi.org/10.3354/meps09656 Diet of sardine Sardina pilchardus: an ‘end-to-end’ field study N. Nikolioudakis1,3,*, S. Isari1, P. Pitta2, S. Somarakis1 1Institute of Marine Biological Resources and 2Institute of Oceanography, Hellenic Centre for Marine Research, Thalassocosmos, Heraklion 71003, Crete, Greece 3Department of Biology, University of Crete, Heraklion 71409, Crete, Greece *Email: niknikos@hcmr.gr ABSTRACT: The diet of sardines was analyzed from samples collected at a coastal site in the North Aegean Sea (eastern Mediterranean) in July 2007 and July 2008 (stratification periods), and in December 2007 (early phase of the mixing period) and February 2009 (late phase of the mixing period). Concurrent measurements of environmental and planktonic community variables (from bacteria to mesozooplankton) were carried out to infer major trophic pathways in the pelagic food web and determine how these pathways are related to sardine prey selection. The bulk of the dietary carbon in adults was derived from calanoid copepods, >1 mm total length, although the diet was numerically dominated by phytoplankton. In juveniles, phytoplankton consumption was negligible. The diet composition and prey selection seemed to be driven by the availability of large prey. During summer, microbial processes prevailed (the ratio of autotrophs <20 µm:>20 µm was 13 to 15, and the ratio of autotrophic to heterotrophic pico- and nanoplankton biomass was <0.5), the mean size of mesozooplankton was smaller, and filter-feeding cladocerans and appendicularians were very abundant. In February 2009, autotrophs >20 µm dominated the carbon budget, and the abundance of larger copepods (e.g. Centropages) was high. In December 2007, when waters were mixed but still relatively warm, both the ‘microbial’ and ‘classical’ (herbivorous) trophic pathways seemed to be important. The mean size of mesozooplankton (copepods and cladocerans) in sardine stomachs was highly correlated with their mean size in the field, and the latter was in turn highly positively correlated with the concentration of diatoms. Finally, a strong negative relationship between the Shannon-Wiener diversity index and average size of mesozooplankton prey in the stomachs was found, which could be explained in terms of the interplay of feeding modes, i.e. filter (non-selective) and particulate (selective) feeding. KEY WORDS: Sardine · Sardina pilchardus · Diet · Food web · End-to-end Full text in pdf format Supplementary material PreviousNextCite this article as: Nikolioudakis N, Isari S, Pitta P, Somarakis S (2012) Diet of sardine Sardina pilchardus: an ‘end-to-end’ field study. Mar Ecol Prog Ser 453:173-188. https://doi.org/10.3354/meps09656 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 453. Online publication date: May 07, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Structure of the summer under fast ice microbial community near Syowa Station, eastern Antarctica

Temporal variations in the microbial community structure of plankton, which is composed of autotrophic and heterotrophic pico-, nano- and microplankton, were investigated during the austral summer of 2005/2006 under fast ice near Syowa Station, eastern Antarctica. Autotrophic algal populations were composed almost entirely of diatoms followed by phytoflagellates such as autotrophic dinoflagellates and cryptophytes. Among the microbial community, heterotrophic biomass was dominated by heterotrophic dinoflagellates and naked ciliates and finally exceeded autotrophic biomass. Qualitative microscopic analysis revealed that heterotrophic dinoflagellates were ingesting large number of diatoms. Synchronizing fluctuation of naked ciliates with phytoflagellates suggested a predator–prey relationship between them. Our results suggest that the pelagic food webs under the extensive ice-covered areas in coastal Antarctic regions are not short but complex.

Spatial variability in bacterial abundance and other microbial components in the NW Iberian margin during relaxation of a spring upwelling event

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 43:255-266 (2006) - doi:10.3354/ame043255 Spatial variability in bacterial abundance and other microbial components in the NW Iberian margin during relaxation of a spring upwelling event F. G. Figueiras1,*, M. K. Zdanowski2, B. G. Crespo1 1Instituto de Investigacións Mariñas (CSIC), Eduardo Cabello 6, 36208 Vigo, Spain 2Department of Antarctic Biology, Polish Academy of Sciences, 02-141 Warsaw, Ustrzycka 10, Poland *Email: paco@iim.csic.es ABSTRACT: The spatial distribution of heterotrophic bacterioplankton abundance (BA) and bacterial colony forming units (CFU) plus additional biological (abundance of autotrophic and heterotrophic pico- and nanoplankton, diatoms and chlorophyll a concentration), physical (temperature and salinity) and chemical (nutrient concentrations) variables were investigated along the Galician coast (NW Iberia) after the cessation of a strong spring upwelling event. BA and abundance of autotrophic and heterotrophic pico- and nanoplankton tended to increase with distance from the coast, while diatoms were more abundant near to the coast. Over 70% of the variance in BA could be explained by a regression equation with 3 variables, in which abundance of autotrophic nanoflagellates (61%) and abundance of heterotrophic nanoflagellates (7%) accounted for 68% of the total explained variability. The remaining 2% was related to chlorophyll a variations. Variability in CFU abundance (67%) was attributable to a negative relationship with salinity and to a lesser but significant degree by a positive relationship with diatom abundance. These data suggest that a number of mechanisms regulated bacterial abundance in the NW Iberian margin after spring upwelling: CFU was related to continental influence and diatoms, and BA was associated with the biomass of autotrophic nanoflagellates. The relationships between BA, autotrophic nanoflagellates (ANF) and chlorophyll a (Chl) in the oceanic samples suggest that a change from bottom-up to top-down control of BA would occur at concentrations higher than 2500 ANF ml–1 and 1.72 mg Chl m–3. KEY WORDS: Bacterial abundance · Phytoplankton · Upwelling relaxation · NW Iberia Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 43, No. 3. Online publication date: July 19, 2006 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2006 Inter-Research.

Photo- and heterotrophic pico- and nanoplankton in the Mississippi River plume: distribution and grazing activity

The abundance of pico- and nanophytoplankton, bacteria and heterotrophic nanoflagellates, and grazing rates on phototrophic pico- and nanoplankton and bacterioplankton were assessed along a salinity gradient (0.2–34.4) in the Mississippi River plume in May 2000. Grazing rates were established by serial dilution experiments, and analysis by flow cytometry allowed differentiation of grazing rates for different phytoplankton subpopulations (eukaryotes, Synechococcus spp., Prochlorococcus spp.). Grazing rates on phytoplankton tended to increase along the salinity gradient and often approached or exceeded 1 day−1. Phytoplankton net growth rates (growth – grazing) were mostly negative, except for positive values for eukaryotic nanoplankton in the low-salinity, high-chlorophyll region. Grazing pressure on bacteria was moderate (∼0.5 day−1) and bacteria gained positive net growth rates of ∼0.3 day−1. Eukaryotic nanophytoplankton were the major phototrophic biomass and protozoan food source, contributing 30–80% of the total consumed carbon. Bacteria were the second most important food source at 9–48% of the total consumed carbon. Synechococcus spp. and Prochlorococcus spp. remained an insignificant portion of protozoan carbon consumption, probably due to their low contribution to the total pico- and nanoplankton biomass. Group-specific grazing losses relative to standing stocks suggest protozoan prey preference for eukaryotes over bacteria. Protozoan grazers exerted a major grazing pressure on pico- and nanophytoplankton, but less so on bacteria.

Particulate matter and plankton dynamics in the Ross Sea Polynya of Terra Nova Bay during the Austral Summer 1997/98

The structure and variability of the plankton community and the distribution and composition of suspended particulate matter, were investigated in the polynya of Terra Nova Bay (western Ross Sea) during the austral summer 1997/1998, with the ultimate objective of understanding the trophic control of carbon export from the upper water column. Sampling was conducted along a transect parallel to the shore, near the retreating ice edge at the beginning of December, closer to the coast at the beginning of February, and more offshore in late February. Hydrological casts and water sampling were performed at several depths to measure total particulate matter (TPM), particulate organic carbon (POC), biogenic silica (BSi), chlorophyll a (Chl a) and phaeopigment (Phaeo) concentrations. Subsamples were taken for counting autotrophic and heterotrophic pico- and nanoplankton and to assess the abundance and composition of microphyto- and microzooplankton. Statistical analysis identified two major groups of samples: the first included the most coastal surface samples of early December, characterized by the prevalence of autotrophic nanoplankton biomass; the second included all the remaining samples and was dominated by microphytoplankton. With regard to the relation of the plankton community composition to the biogenic suspended and sinking material, we identified the succession of three distinct periods. In early December Phaeocystis dominated the plankton assemblage in the well-mixed water column, while at the retreating ice-edge a bloom of small diatoms (ND) was developing in the lens of superficial diluted water. Concentrations of biogenic particulates were generally low and confined to the uppermost layer. The very low downward fluxes, the near absence of faecal pellets and the high Chl a/Phaeo ratios suggested that the herbivorous food web was not established yet or, at least, was not working efficiently. In early February the superficial pycnocline and the increased water column stability favoured the development of the most intense bloom of the season, essentially sustained by micro-sized diatoms (MD). The shift of the autotrophic community toward this size component produced major changes in the composition of particulate matter and determined its export to depth. The particulate organic carbon (POC)/chlorophyll a (Chl a) and Chl a/Phaeo ratios more than halved, biogenic silica (BSi)/POC and BSi/Chl a strongly increased. Downward fluxes were greatly enhanced (reaching the yearly maximum) and essentially occurred via faecal pellets, underscoring the high efficiency of the herbivorous food web. In late February the deepening of the pycnocline, together with the decrease in light intensity, contributed to halting the diatom bloom. The biomass of small heterotrophs (HNF and MCZ) significantly increased relative to the previous period, favouring the shift toward a mistivorous food web (sensu [Ophelia 41 (1995) 153]) and resulting in the retention of biogenic matter in the superficial layer. Only in early February, with the increase in the size of primary producers (essentially represented by micro-sized diatoms), did the grazing food web become efficient [S. Afr. J. Mar. Sci. 12 (1992) 477], fuelling the long-lived carbon pool and enhancing export to depth (and hence carbon sequestration) via the sinking of large diatoms and high amounts of faecal pellets. The conditions predominating in the Terra Nova Bay polynya in mid-summer probably increased the efficiency of the CO 2 pump, possibly causing the Bay to act as a carbon sink.

Biomass, Production and Grazing Rates of Pico- and Nanoplankton in Coral Reef Waters (Miyako Island, Japan)

Concentrations of phytoplankton (cyanobacteria, autotrophic flagellates, and microphytoplankton) and planktonic microorganisms (bacteria, heterotrophic flagellates, and ciliates) were measured in the water over a fringing coral reef at Miyako Island (Japan). Their in situ growth and production rates, as well as their grazing rates, were estimated using diffusion chambers. Bacteria dominated the heterotrophic biomass (37–73% of total C), whereas nanoflagellates dominated the autotrophic biomass (65–75% of total autotropic C). Growth and production rates showed that these microbial populations over the reef were in a very dynamic state: growth rates ranged between 2 and 4 doublings day−1 for the bacteria, and between 1.5 and 3 doublings day−1 for the auto- and heterotrophic pico- and nanoplankton. This led to high production rates (10–25 μg C liter−1 day−1 for bacteria and flagellates). The microbial biomass was removed rapidly, since 60–70% of the bacterial production and 30–50% of the autotrophic production were grazed by the heterotrophic flagellates and ciliates, which themselves were grazed (50–70% of the production) by the higher trophic levels. These results suggest that dissolved organic matter was continuously channeled through the microbial loop to the higher trophic levels and the microbes had an important trophic role in terms of nutrient for the benthic organisms.

The origin of sedimenting detrital matter in a coastal system

Total sedimentation and the fraction due to copepod fecal pellets were measured during the growth season (March–October 1989) in the southern Kattegat, Denmark. In this period the sedimentation of detritus made up 52 g C m−2, equal to 82% of the sedimenting matter from the euphotic zone, but fecal pellets (11 g C m−2) constituted only a minor fraction. The remaining detrital matter was produced by other heterotrophs than copepods. Published data on heterotrophic biomass and grazing obtained during the investigation in the Kattegat are reviewed in order to relate the sedimentation to processes in the pelagic system. Copepod defecation nearly equaled the sedimentation of fecal pellets, indicating that retention of this matter in the pelagic system was insignificant. A considerable fraction (10–24%) of the carbon flow processed by heterotrophic pico‐, nano‐, and microplankton was converted to detritus that was lost from the mixed system by sedimentation. The microbial food web is thus not an exclusively regenerating system.

Phototrophic and heterotrophic pico- and nanoplankton in anoxic depths of the central Baltic Sea

Phototrophic and heterotrophic pico- and nanoplankton in anoxic depths of the central Baltic Sea

On the Importance of Planktonic Protozoans in the Eutrophication Process of the Baltic Sea

AbstractAnalysing the results of various authors recent studies in the pelagic region of the Baltic revealed that protozoan biomass is in the same range or even higher than metazooplankton biomass. The dominant groups of planktonic protozoans are heterotrophic pico‐ and nanoflagellates (various taxonomic groups), large heterotrophic flagellates (mainly dinoflagellates) and ciliates. Regularly the spring bloom of phytoplankton is accompanied by a maximum of protozoan biomass which declines in early summer as a result of intensive grazing pressure by metazooplankton and changing food conditions. The analysis of results from different stations indicated that biomasses of protozoans increase with an increasing degree of eutrophication. Several trophic levels within the microbial web should be added to the traditional view on the pelagic food web of the Baltic. Our knowledge regarding the quantitative aspect of the microbial matter flux of the Baltic is very limited up to now and complex ecological (and taxonomical) studies using standardized methods including all protozoan components are necessary. Protozoans (various trophic groups and levels), besides bacteria, should be viewed as the metabolically most active heterotrophic component in the pelagic region of the Baltic, their activity should increase with an increasing degree of eutrophication.

Productivity of the southern ocean: a closer look

1. 1. This paper reviews present knowledge of the standing crop and productivity of Antarctic phytoplankton and of the factors that govern primary production. 2. 2. Investigations have shown that (a) productivity of Antarctic waters varies by at least one to two orders of magnitude; and (b) generally, these waters display their richness mainly in the coastal regions. 3. 3. Recent studies of the autotrophic and heterotrophic pico- and nanoplankton are reviewed, and new data are presented. 4. 4. The relative abundances of these very small-sized classes of organisms are discussed, and their potentially important role in the emerging paradigm of the Antarctic food web is considered.