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Journal ArticleDOI

Distribution and abundance of thaliaceans and copepods off the southeastern U.S.A. during winter

TL;DR: It is assumed that thaliacea due to their high rates of feeding, individual and population growth could impact zooplankton communities two-fold: indirectly, by reducing phytoplankon concentrations rapidly thus affecting reproduction of certain calanoid taxa, and directly, by consuming copepod eggs.
Abstract: The abundance and distribution of planktonic copepods and tunicates were studied in relation to physical and biological variables from late January to early February 1990 on the middle and outer shelf off South Carolina, U.S.A. The inner and part of the middle shelf were vertically mixed throughout the study period, the middle and outer shelf only after passage of a storm on 4 and 5 February. Subtidal currents at the 40 m isobath were highly correlated with local alongshore winds, whereas at the 75 m isobath the currents showed a mixed response to wind and Gulf Stream events. Chlorophyll concentrations in the study area usually surpassed 0.5 and reached levels of 3 μg l−1. Zooplankton was characterized by high abundances of doliolids (Tunicata, Thaliacea) and relatively low concentrations of calanoid and cyclopoid copepods. When doliolids were very abundant the vertical distribution of doliolids was inversely related to those of the calanoids. We hypothesized that this inverse relationship could be the result of (a) doliolids removing food particles, thus reducing food particle concentrations, and through that calanoid reproduction rates; (b) doliolids ingesting calanoid eggs and nauplii, thereby reducing copepod recruitment; (c) active avoidance of doliolids by downward migration of copepods; and (d) vertical shear between the upper and lower part of the stratified water column. At stations on the middle shelf the abundance of photo- and heterotrophic nanoplankton was inversely related to the abundance of doliolids. The frequency of occurrence of thaliacea in neritic regions is evaluated in relation to hydrographic regimes and the availability of seed populations. From previous and present observations we assume that thaliacea due to their high rates of feeding, individual and population growth could impact zooplankton communities two-fold: indirectly, by reducing phytoplankton concentrations rapidly thus affecting reproduction of certain calanoid taxa, and directly, by consuming copepod eggs.
Citations
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Journal Article
TL;DR: Inadequate understanding of the true abundance, biomass, trophic ecology, and role of small copepods in biogenic fluxes precludes properUnderstanding of the ecology of the sea.
Abstract: Small planktonic marine copepods (< 1 mm in length) are the most abundant metazoans on Earth. Included are adults and copepodites of calanoid genera such as Paracalanus, Clausocalanus, and Acartia; cyclopoid genera such as Oithona, Oncaea, and Corycaeus; planktonic harpacticoids of the genus Microsetella; and nauplii of almost all copepod species. Despite the abundance of small copepods, they have historically been undersampled due to the use of nets with meshes > 200- 333 μm. Recent studies have shown, however, that when appropriate net meshes of 100 μm or less are used, small copepods vastly exceed the abundance and sometimes the biomass of larger ones. Failure to adequately account for small copepods may cause serious underestimations of zooplankton abundance and biomass, the copepod grazing impact on phytoplankton primary production, zooplankton-mediated fluxes of chemicals and materials, and trophic interactions in the sea. The feeding ecology of small copepods is less well-known than that of adults of larger copepod species, such as members of the genus Calanus. Further, most feeding information for small copepods is for coastal genera such as Acartia, rather than for offshore taxa. Although it is generally assumed that small copepods, including nauplii, feed primarily upon small-sized phytoplankton cells, most such information comes from rearing or feeding studies on limited laboratory diets. There have been few examinations of actual copepod feeding on mixed diets of natural phytoplankton and microzooplankton found in the sea, but some of those have produced surprises. For instance, some species of Oithona and Paracalanus and even nauplii of Arctic Calanus spp. may feed primarily as predators upon heterotrophic protists, rather than as grazers of phytoplankton. Also, nauplii of various tropical copepod species have been shown to feed upon bacterioplankton. Thus, numerous basic questions remain as to the feeding ecology and grazing/predation impact of small copepods in the sea. Despite limited knowledge of what small copepods eat, it is clear that many higher-trophic-level consumers eat them. Numerous studies have shown that copepod nauplii, Oithona spp., and other small copepods are important prey of fish larvae and other planktivores. Small copepods exhibit a variety of reproductive strategies to compensate for losses to their populations due to predation. These include having high fecundity and growth rates, when not limited by insufficient food; having high reproduction and growth rates at warmer temperatures; having limited motion and low respiration rates, allowing the investment of more energy in reproduction; and having extended longevity to maximize lifetime reproductive output. Thus, small copepods are important links in marine food webs, serving as major grazers of phytoplankton, as components of the microbial loop, and as prey for ichthyoplankton and other larger pelagic carnivores. Our present inadequate understanding of the true abundance, biomass, trophic ecology, and role of small copepods in biogenic fluxes precludes proper understanding of the ecology of the sea.

647 citations


Cites background from "Distribution and abundance of thali..."

  • ...…and Strickler 1996), others have examined feeding by adults of small copepod genera, including Acartia (Paffenhöfer and Stearns 1988), Paracalanus (Paffenhöfer et al. 1995b), Oithona (Hwang and Turner 1995, Paffenhöfer et al. 1996, Paffenhöfer and Mazzocchi 2002), and Clausocalanus (Mazzocchi and…...

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  • ...…1985) of the northeastern US, the Sargasso Sea (Roman et al. 1993), the continental shelf off the southeastern United States (Paffenhöfer 1985 1993, Paffenhöfer et al. 1995a), coastal and oceanic waters of Jamaica (Chisholm and Roff 1990, Webber and Roff 1995a b, Hopcroft et al. 1998a, Hopcroft…...

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Journal ArticleDOI
TL;DR: An evaluation of data and published results on abundances of doliolids and salps from ocean margins reveals that a considerable degree of prediction is possible, based upon meteorological and boundary current intrusion dynamics.
Abstract: The occurrence of large patches of gelatinous zooplankton has for decades been considered to be unpredictable. An evaluation of our own data and published results on abundances of doliolids and salps from ocean margins reveals that a considerable degree of prediction is possible, based upon meteorological and boundary current intrusion dynamics.

88 citations

Journal ArticleDOI
01 May 2006
TL;DR: The salps demonstrated a strong pattern of diel vertical migration, moving to depth (mostly 600-800m) during the day and aggregating in the epipelagic (100 m ) at night.
Abstract: Sampling during four summers over a twenty-seven year period has documented dense populations of Salpa aspera in the Slope Water south of New England, northeastern United States. The salps demonstrated a strong pattern of diel vertical migration, moving to depth (mostly 600–800 m) during the day and aggregating in the epipelagic ( 100 m ) at night. Filtration rates determined from both gut pigment analysis and direct feeding experiments indicated that both the aggregate and solitary stages filtered water at rates ranging from 0.5 to 6 l h - 1 ml - 1 biovolume. Maximum displacement volumes of salps measured were 5.7 l m - 2 in 1986 and 1.6 l m - 2 in 1993. Depending on the year, the sampled salp populations were calculated to clear between 8 and 74% of the upper 50 m during each 8 h night. Total fecal output for the same populations was estimated to be between 5 and 91 mg C m - 2 night - 1 . These results, and other observations, suggest this region is a salp “hot spot”, with swarms of S. aspera developing seasonally on a frequent basis.

82 citations

Journal ArticleDOI
TL;DR: It is hypothesized that in the absence of control by meta- zooplankton, protozoa control their own abundance by predation/cannibalism.
Abstract: A common approach to divide zooplankton into groups has been by size or size fractiona- tion (micro-, meso- and macrozooplankton) Whereas almost all zooplankton retained by 200 um mesh are metazoa, those not retained are proto- and metazoa Even so, the variability of major taxa among those retained by 200 (jm mesh can range widely between samples, that of passing 200 urn can vary even more when considering the grazing impact If heavily weighted towards protozoa, the 50 um3 in volume, ie those which could be actively perceived It is hypothesized that in the absence of control by meta- zooplankton, protozoa control their own abundance by predation/cannibalism

61 citations

Journal ArticleDOI
TL;DR: The results suggest that doliolid feeding and growth rates are a function of environmental food concentrations and temperatures, and imply that they can be important consumers in a changing neritic environment.
Abstract: The goal of this research is to enhance our knowledge of the contributions of doliolids to the planktonic community as consumers and secondary producers. The objectives are to quantify feeding and growth rates of Dolioletta gegenbauri gonozooids at four food concentrations and four temperatures in order to determine their impact as grazers throughout the water column. Although doliolids are abundant in numerous regions of the coastal ocean, and are considered to be major planktonic grazers, data on rates of feeding and growth are scarce. Laboratory experiments were conducted at 16.5, 20, 23.5 and 26.5°C to quantify removal of a 50:50 volumetric concentration of Thalassiosira weissflogii and Rhodomonas sp. at four different food concentrations of 20, 60, 160 and 390 µg C l -1 . Results from these experiments suggest that clearance rates are similar at concentrations from 20 to 60 µg C l -1 , and decrease as the food concentrations increase to 160 and 390 µg C l -1 . The ingestion rates increase over a range of phytoplankton concentrations from 20 to 160 µg C l -1 , then decrease when abnormally high concentrations of 390 µg C l -1 are offered. Clearance and ingestion rates increase as temperature increases from 16.5 to 26.5°C. The exponential growth rates range from k = 0.2-0.7, with the lowest rates occurring at the highest food concentration. Growth rates increase with increasing temperature from K = 0.1-0.3 at 16.5°C to 0.45-0.7 at 26.5°C. In each case, the small- and medium-sized zooids had higher growth rates than the larger gonozooids. These results suggest that doliolid feeding and growth rates are a function of environmental food concentrations and temperatures, and imply that they can be important consumers in a changing neritic environment.

57 citations

References
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Journal ArticleDOI
TL;DR: In this article, the concentration of chlorophyll and phaeophytin was measured in 85% acetone extracts using a sensitive fluorometer. The method is very sensitive in the 10 fluorescence units are equal to 0·001 O.D. 665 mμ 10 cm.

1,823 citations

BookDOI
02 May 2018
TL;DR: This work focuses on the isolation and culture of Marine Protists from Estuarine, Littoral, Psammolittoral and Sublittoral Waters and the identification, Enumeration, and Diversity of Anaerobic and Microaerobic Protists.
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Cloning, and Axenic Culturing of Marine Ciliates (AT Soldo and SA Brickson) Isolation and Laboratory Culture of Marine Oligotrichous Ciliates (DJ Gifford) Extraction of Protists in Aquatic Sediments via Density Gradient Cetrifugation (DM Alongi) Identification, Enumeration, and Diversity: Statistical Analysis of Direct Counts of Microbial Abundance (DL Kirchman) Enumeration and Isolation of Viruses (CA Suttle) Total Count of Viruses in Aquatic Environments (G Bratbak and M Heldal) Improved Sample Preparation for Enumeration of Aggregated Aquatic Substrate Bacteria (MI Velji and LJ Albright) Direct Estimates of Bacterial Numbers in Seawater Samples without Incurring Cell Loss Due to Sample Storage (CM Turley) Total and Specific Bacterial Counts by Simultaneous Staining with DAPI and Fluorochrome-Labeled Antibodies (KA Hoff) Use of RFLPs for the Comparison of Marine Cyanobacteria (SE Douglas) Use of High-Resolution Flow Cytometry to Determine the Activity and Distribution of Aquatic Bacteria (DK Button and BR Robertson) Phytoplankton Analysis Using Flow Cytometry (RJ Olson, ER Zettler, and MD DuRand) Enumeration of Phototrophic Picoplankton by Autofluorescence Microscopy (EA MacIsaac and JG Stockner) Estimating Cell Concentration and Biomass of Autotrophic Plankton Using Microscopy (BC Booth) Preservation and Storage of Samples for Enumeration of Heterotrophic Protists (EB Sherr and BF Sherr) Staining of Heterotrophic Protists for Visualization via Epifluorescence Microscopy (EB Sherr, DA Caron, and BF Sherr) A Quantitative Protargol Stain (QPS) for Ciliates and Other Protists (DJS Montagnes and DH Lynn) Preparation of Pelagic Protists for Electron Microscopy (BSC Leadbeater) A Rapid Technique for the Taxonomy of Methanogenic Bacteria: Comparison of the Methylreductase Subunits (PE Rouviere and CH Kuhner) Extraction of DNA from Soils and Sediments (RM Atlas) Detecting Gene Sequences Using the Polymerase Chain Reaction (RM Atlas) Quantitative Description of 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1,446 citations

Journal ArticleDOI

829 citations

Journal ArticleDOI
TL;DR: The behavioral variation documented here confirms that diel vertical migration is dynamic rather than a fixed, invariant behavioral trait within a population, and predator avoidance by Pseudocalanus newmani confers a fitness advantage upon a population that migrates across a thermocline.
Abstract: Three types of diel vertical migration behavior were expressed within a fjord population of the calanoid copepod Pseudocalanus newmani: (1) reverse migration (nocturnal descent), (2) normal migration (nocturnal ascent), and (3) no detectable migration. Reverse migration by P. newmani occurred in all three study years, but only at a deep (185 m) station at times of year when normally migrating predatory zooplankton (the copepod Euchaeta elongata, the chaetognath Sagitta elegans, and the omnivorous euphausiid Euphausia pacifica) were abundant. A predator—exclusion "natural experiment" tested the hypothesis that the reverse migration is a predator avoidance mechanism: at a shallow (55 m) station within the same fjord, large predatory zooplankton were absent or reduced markedly in abundance. In conditions of reduced nocturnal predation by predatory zooplankton, no reverse migration by P. newmani was detected on any of 11 cruises, consistent with the hypothesis. Instead, at the shallow station, where diurnal predation by planktivorous fish was of increased importance, normal diel vertical migration by P. newmani was observed on several occasions. No migration was detectable at either the deep station or the shallow station at times of year of low feeding activity of predators in surface waters. The predominant migration behavior (reverse, normal, or no migration) varied depending whether the primary source of mortality was predation by nocturnally feeding zooplankton or visually hunting planktivorous fish, and appeared unrelated to resource distributions or temperature gradients. The relative advantage of the three migration behaviors is explored with theoretical life table analyses. Re—examination of the demographic advantage hypothesis proposed by McLaren (1974) illustrates that vertical migration across a thermocline carries a fitness cost, not a benefit. The realized rate of increase of a migrant population of Pseudocalanus is found to be lower than a nonmigrant population for all combinations of surface temperatures, positive thermal stratification, and ratios of mortality for early and late developmental stages. However, avoidance of predators by vertical migrants reverses the outcome of this analysis. Predator avoidance by Pseudocalanus, accompanied by reduced mortality rates, confers a fitness advantage upon a population that migrates across a thermocline. Remarkably small reductions in mortality rates (as little as 12%) confer this advantage, whether migrants avoid nonvisually hunting predatory zooplankton by night or visually hunting planktivorous fish by day. The behavioral variation documented here confirms that diel vertical migration is dynamic rather than a fixed, invariant behavioral trait within a population. In environments where predation pressure and other factors vary through time, studies of limited scope and short duration are unlikely to illuminate the ultimate causes for diel vertical migration. The heritability of the vertical migration trait is unclear. The different phenotypic responses reflected within this single populations of P. newmani may reflect altered behavior of individuals. Alternatively, this behavioral variation may represent a balanced polymorphism maintained by differential mortality of genotypes experiencing selection pressures that vary through time.

307 citations