83 research outputs found

    77-4 Hydrographic and Biological Observations at an Anchor Station Off St. Augustine, Florida (Eastward Cruise E-1G-75)

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    The intrusion of deep, nutrient-rich Gulf Stream water into the shelf waters off the southeastern United States is probably the major source of nutrients in the shelf waters and consequently intrusions have a major impact on the biota. This particular cruise was one of the first to be designed to find the front that represents the interface between intruding Gulf Stream waters and normal shelf water. Once the front was delineated an anchor station was occupied to observe the time change at a particular location as the front moved back and forth past the station. The methods used and resultant data from that cruise are presented to aid others in the analyses of intrusions and related phenomena

    Modeling the Effects of Doliolids on the Plankton Community Structure of the Southeastern US Continental Shelf

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    A model of the lower trophic levels that consists of a system of coupled ordinary differential equations was developed to investigate the time-dependent behavior of doliolid populations associated with upwelling features on the outer southeastern US continental shelf. Model equations describe the interactions of doliolids with two phytoplankton size fractions, five copepod developmental stages and a detrital pool. Additional equations describe nitrate and ammonia. Model dynamics are based primarily upon data obtained from field and laboratory experiments for southeastern US continental shelf plankton populations. Variations on a reference simulation, which represents average upwelling conditions without doliolids, were carried out to determine the effect of inclusion of doliolids, temperature and nutrient variations, and variations in ambient food concentrations on the basic plankton community structure. These simulations provide a measure of the role of environmental versus biological interactions in structuring the planktonic food web on the southeastern US continental shelf. Simulations show that the copepod population is significantly reduced when doliolids are present. This happens primarily as a result of direct predation of the doliolids on copepod eggs and juveniles as opposed to an increase in competition for phytoplankton, the primary food source. Additional simulations show that the cooler temperatures associated with the newly upwelled water temporarily decrease the growth rates of the doliolids and copepods, bestowing an even greater advantage on the rapidly reproducing doliolids

    The Role of Feeding Behavior in Sustaining Copepod Populations in the Tropical Ocean

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    A fundamental question regarding marine copepods is how the many species coexist and persist in the oligotrophic environment (i.e. Hutchinson’s paradox). This question is addressed with a stochastic, object-oriented Lagrangian model that explicitly simulates the distinct foraging behaviors of three prominent tropical species: Clausocalanus furcatus, Paracalanus aculeatus and Oithona plumifera. The model also individually tracks all prey cells. Each particle’s motion combines sinking, turbulent diffusion and active swimming when applicable. The model successfully simulates observed size partitioned carbon uptake rates. Based on the model results, the wide-ranging translational ambit employed by C. furcatus is best suited for the acquisition of passive prey while the relatively stationary behavior of O. plumifera promotes the capture of larger, quickly sinking cells. The model results further suggest that the slow velocities and feeding current employed by P. aculeatus are best suited for acquiring the smallest cells though it also has a slight advantage over C. furcatus in acquiring the largest prey. A resource threshold, at a prey concentration of 530 cells mL–1,is consistently exhibited by all three modeled species. Overall, these results imply that the size-partition preferences due to their different foraging behavior contribute to the coexistence of these three species. (c) The Author 2005

    Vertical distribution and diel patterns of zooplankton abundance and biomass at Conch Reef, Florida Keys (USA)

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    Zooplankton play an important role in the trophic dynamics of coral reef ecosystems. Detailed vertical and temporal distribution and biomass of zooplankton were evaluated at four heights off the bottom and at six times throughout the diel cycle over a coral reef in the Florida Keys (USA). Zooplankton abundance averaged 4396 ± 1949 SD individuals m−3, but temporal and spatial distributions varied for individual zooplankton taxa by time of day and by height off the bottom. Copepods comprised 93–96% of the abundance in the samples. Taxon-based zooplankton CHN values paired with abundance data were used to estimate biomass. Average daily biomass ranged from 3.1 to 21.4 mg C m−3 and differed by both height off the bottom and by time of day. While copepods were the numerically dominant organisms, their contribution to biomass was only 35% of the total zooplankton biomass. Our findings provide important support for the new emerging paradigm of how zooplankton are distributed over reefs

    Grazing Rates of Calanus finmarchicus on Thalassiosira weissflogii Cultured under Different Levels of Ultraviolet Radiation

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    UVB alters photosynthetic rate, fatty acid profiles and morphological characteristics of phytoplankton. Copepods, important grazers of primary production, select algal cells based upon their size, morphological traits, nutritional status, and motility. We investigated the grazing rates of the copepod Calanus finmarchicus on the diatom Thalassiosira weissflogii cultured under 3 levels of ultraviolet radiation (UVR): photosynthetically active radiation (PAR) only (4 kJ-m−2/day), and PAR supplemented with UVR radiation at two intensities (24 kJ-m−2/day and 48 kJ-m−2/day). There was no significant difference in grazing rates between the PAR only treatment and the lower UVR treatment. However, grazing rates were significantly (∼66%) higher for copepods feeding on cells treated with the higher level of UVR. These results suggest that a short-term increase in UVR exposure results in a significant increase in the grazing rate of copepods and, thereby, potentially alters the flow rate of organic matter through this component of the ecosystem
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