ECOLOGY PROGRESS - PDF document

ECOLOGY PROGRESS planktonic prey prey densities replicate bottle as prey as prey) shrimp Arfemia Flagellate Paraphysomonas Diatom Thalassiosira weissflogii Flagellate Paraphysomonas phase, 1.9 Flagellate Paraphysomonas Cyanobacterium Synechococcus bacterial cells), filtrate activity ment was centric diatom Prey cells by centrifugation (10 This process carried out times before were resuspended suspension was subdivided equally control bottles (Table filter activity filtrate activity (dissolved activity) determined using liquid scintillation Assimilation efficiencies were determined as outlined below, except that was determined assimilation efficiencies were measured grazer assemblages Expts 3 a 333 net. Grazers being used in experiments. monospecific collection the grazers Prey in Expts 3 4 consisted or a flagellated graphic Institute). groups can be crustacean grazers ocean (Stoecker Capuzzo 1990). carried out using labeled stationary growth trace metals based on growth diatom species used as prey these experi- late species Expts 3 in Expt a cell with Aquil trace metals 1989). Cultures fluorescent lights a photon Log-phase cultures harvested after 3 d bottles; prey Flagellate cultures strain 1334) which had been planktonic prey initial isotope diatom prey found dissolved fraction represent the dissolved Fe activity bottles with brine shrimp control bottles (labeled diatoms without rapid rise dissolved activity during the the experi- ment, suggesting a fast initial cells similar Fisher (1993) 10 in Expt ment. The the grazers represented a significant fraction activity. Only size fraction diatom prey data (Fig. 2A). which Monterey trace metals during grazing dissolved metal isotope bottles comprised total activity originally added as the amount control bottles (2 over controls; Fig. over controls; Fig. consistent with diatom prey dissolved isotope only slowly linearly, without release observed 3 elements prey, al- and Evadne dissolved fraction (0.2 bottles with cladoceran grazers. bars have been since prey contained bacteria, dissolved isotope levels in grazing ence in the ized after This strongly driving remineralization although bac- material already processed a relatively slow 1979, Lee when the microbial community enriched (Lee crustacean grazing experiments sented here Fisher (1994) they used metals, grazers, prey, more important trace metal be the process driving euphotic zone upon 2 have suggested phytoplankton production, has been coastal and waters (Laws et 1988, Smith 1989, Frost 1991, et al. phytoplankton production grazing rates cases, however, surface waters. laboratory investigations that bacteria play a minor nutrient regeneration (1979) also concluded that bacterial remineralization acidic conditions in most exceptionally well trace metals. guts can the pH the feeding protozoans may (Fok et demonstrated that homogenate became available They hypothesized that grazers role in iron cling largely their acidic digestion ingested proteins digestion could highly soluble (Fe2+), depending initial acidic zoan grazers egestion (Fok Moriarty 1983). Under these would likely iron oxyhydroxides. can become available through thermal ents during grazing trace metal in these grazing experiments. crustacean grazers 30 min material may 10 h that carbon lost from fecal pellets observed a fecal pellets, gested that responsible. The increases in the experiments presented here acidic digestive processes a significant influence on metal those found unnaturally high bottles could the true alization. Because and Mn (and lesser extent Bruland: Grazer planktonic prey highly particle-reactive, fecal pellets levels originating activity. Nolan labeled phytoplankton observed that the minutes, supporting the grazing experiments during grazing that scavenging metals onto surfaces metal chelator bias opposite that mentioned weakly bound sites associated fecal pellets. Because potentially conflicting tion efficiency, while Expt experiments probably somewhere between because inorganic with major lower effective surface ocean, the chemical speciation (Bruland 1989) Cu (Coale strong natural organic The extent in the present unknown, although some marine organisms producing very strong (Trick 1989, potentially play trace metals fecal pellets before their removal chelation is, natural ligands rather than ligands such as the in these experiments. play only role in Mn Variations in isotopes remineralized during grazing. the amount known that instance, grazers fed N-limited phyto- compare regeneration metal-replete prey. prey grown be expected substantially less metal regeneration than the metal concentrations. phase makes these elements short time periods. elements ingested another mechanism nutrients in surface waters (Fisher et be excreted, making them available into zooplankton biomass also required nutrients available secondary pro- trophic levels. incorporated into feeding period in these exper- in Expt (Zn in These percentages although in some cases they do associated with fecal pellets dissolved levels. these experiments non-required particle-reactive elements measured Fisher (1991). typical assimilation efficiencies obtained in nutrient elements such in this from 12 reported a value was least higher than particle-reactive metals. experimental organisms