Short communication. Biomass and production characteristics of the first red tide noticed in Kuwait Bay, Arabian Gulf

Observations on the first red tide off Kuwait, Arabian Gulf, yielded high biomass [55.4-262.7 g chlorophyll (Chl) a l^-1] and primary production (507.9-571.2 g C h^-1l^-1), comparable with some of the highest values reported. There were contrasting changes in the carbon assimilation ratios, composition of the phytoplankton and the contribution of nanoplankton (<20 m) between 11 and 12 May. On 11 May, carbon assimilation by nanoplankton was 2.2 g C (g Chl a)^-1 h^-1, but increased to 9.2 g C (g C (g Chl a)^-1 h^-1 the following day. Nanoplankton contributed 56 and 9% of Chl a and production, respectively, on 11 May, while net plankton (>20 m) accounted for >65% of the biomass and primary production on 12 May. Picoplankton (<3 m) contributed <8% of Chl a and <3% of production. Frequent sampling will be necessary to capture such dynamic changes and ephemeral events in these waters.      

Spatial variability of the photosynthetic parameters and biomass of the Gulf of California phytoplankton

Spatial variability of the central Gulf of California (CGC) phytoplankton biomass and photosynthetic parameters in relation to physical forcing was studied. Sampling was carried out in November, and the surface TC range was 20-27.5°C. Strong tidal mixing in the midrift islands regions injects relatively cool, nutrient-rich waters to the euphotic zone. Some of this water is transported via jets and cool filaments throughout the Gulf. In general, chlorophyll a (Chl) of small phytoplankton (<8 m) (up to >2.5 mg m^-3) was higher than that of large phytoplankton. Highest values of phytoplankton assimilation numbers (P^Bm) [3.17 mg C (mg Chla)^-1 h^-1], and photosynthetic efficiency ^B) [0.23 mg C (mg Chl a)^-1 h^-1 (W m^-2)^-1] were determined for the large phytoplankton cells (>8 m). Our hypothesis that P^Bm values increase from cooler to warmer waters is not supported by the data. We found a 27-fold spatial difference of Chl, compared with a 10-fold difference of P^Bm and a 6-fold difference of ^B. Thus, in our study area, the major source of variability for primary productivity (PP) comes from Chl, and not from P^Bm and ^B. Therefore, we propose that it is possible to estimate late-fall PP for the CGC using average photosynthetic parameters. Average values for P^Bm and ^B of total phytoplankton were 0.72 mg c (mg Chl a)^-1 h^-1 and 0.12 mg C (mg Chl a^-1 h^-1, (W m^-2)^-1, with standard errors of 0.07 and 0.03, respectively.      

Short communication. Determination of generation time and asexual fecundity of doliolids (Tunicata, Thaliacea)

The goal of this study was to provide temporal information on the generation time of Dolioletta gegenbauri and some of the life cycle's components. At 20C and 90 g C l^-1 of ingestible phytoplankton. D.gegenbauri's life cycle is completed in 20.5 days. Phorozooids 5 mm produce on average 11.0 gonozooids day^-1 over a period of 8-18 days. Utilizing field data on the abundance and size distribution of an assemblage of phorozooids and nurses, in conjunction with experimentally obtained rates, indicates that asexual production per cubic meter by phorozooids with that of nurses should result in rapid colonization of a wide shelf by doliolids, as observed during July and August 1981 on the southeastern continental shelf of the USA.      

Impact of natural metazooplankton assemblage on planktonic microbial communities in a newly flooded reservoir

The grazing impact of a natural assemblage of metazoan zooplankton on pigmented flagellates (PF), heterotrophic nanoflagellates (HNF), ciliates, and non-flagellate algae and microcyanobacteria (NFAM) was measured in situ during the period of thermal stratification in a newly flooded reservoir (Reservoir de la Sep, France). Experiments were conducted with diffusion chambers in the meta- and epilimnion over a period of 7 h. The mean mortalities of PF in the epi- and metalimnion (0.08 0.02 and 0.06 ± 0.03 h^-1, respectively), of HNF (0.04 ± 0.02 and 0.05 ± 0.02 h^-1) and ciliates (0.09 ± 0.04 and 0.11 ± 0.04 h^-1) demonstrate the impact of the metazoan zooplankton, and particularly of the rotifer Asplanchna priodonta, on the components of the microbial loop. The mortality of NFAM, accounting for 14 and 18% of total mortality, remained low throughout the study. The taxa with the highest mortality were pigmented flagellates of 4-19 m, HNF, and small-sized ciliates such as Halteria sp. (0.10 ± 0.02 h^-1 at 1 m and 0.30 ± 0.38 h^-1 at 7 m) and Urotricha furcata (0.11 ± 0.05 h^-1 at 1 m and 0.12 ± 0.06 h^-1 at 7 m). Large-sized ciliates (Paradileptus elephantinus) and sessile ciliates (Suctorida, Vorticella sp.) had a very low mortality (>0.04 h^-1). After reservoir flooding, the organisms in the microbial trophic loop, favoured by the high quantities of allochthonous organic matter, are subject to a higher mortality than the phytoplankton.      

Effect of irradiance and temperature on the growth rate of Thalassiosira curviseriata Takano (Bacillariophyceae), a bloom diatom in Bahia Blanca estuary (Argentina)

Long-term phytoplankton studies in the Bahí Blanca estuary showed a seasonal pattern characterized by a winter-early spring bloom of diatoms dominated by Thalassiosira curviseriata. Laboratory experiments were carried out to elucidate the influence of irradiance, temperature and salinity on the growth rate of T.curviseriata. The maximum daily growth rate was 1.93 divisions at 20C. The compensation point (Ic) varied from approaching zero to 3.08 mol m^-2 s^-1, values were -0.020-0.070 divisions mol^-1, and the calculated Ik (the irradiance at which initial slope line reaches the maximum rate of growth) varied between 32 and 36 mol m^-2 s^-1. Growth became light saturated (when max) between 70 and 80 mol m^-2 s^-1, and was inhibited at -150 mol m^-2 s^-1 at all temperatures (5-20°C). The range of temperatures at which T.curviseriata can grow (5-20°C) coincides with the temperature range over which it is found in the field. In contrast, the thermal optimum for growth, 20°C, was higher than the range of temperatures (between 5 and 10°C) characteristic of the winter-early spring bloom in Bahí Blanca estuary. The mean specific growth rate of T.curviseriata was not affected by salinity over the tested range between 25 and 40 p.p.t. Field observations and experimental data support the characterization of T.curviseriata as a eurythermal and euryhaline species adapted to growth at relatively low light intensity. These characteristics may explain the ability of T.curviseriata to flourish seasonally when light conditions are apparently limiting and its presence almost year round under variable conditions of temperature and salinity.      

Bacterial growth and losses due to bacterivory in a mesotrophic lake

Bacterial secondary production and rates of bacterivory weredetermined from samples collected from mesotrophic Lake Arlington.Bacterial production and losses were determined by comparingthe growth of natural bacterial assemblages in the presenceof predators (unfiltered samples) to growth in the absence ofpredators (water filtered through 1.0 (im porosity filters).Growth rates of heterotrophic nanoflagellates (HNF) were estimatedfrom growth in the absence of predators (water filtered through5.0 µm porojity filters). Bacterial growth rates rangedbetween 0.002 and 0.069 h^–1 and averaged 0.026 h^–1.HNF grew at rates ranging between 0.003 and 0.107 h^–1and averaged 0.028 h^– Grazing rates ranged between 0.002and 0.043 h^–1, and averaged 0.018 h. The annual averagerate of bacterial biomass synthesis was 3.2 –g Cl^–h^–1 and {small tilde}69% of this production was grazed.Temporal changes in growth and grazing rates suggest a tightlycoupled predator-prey linkage in this lake. ¹Present address: Hydrobiological Institute, Czech Academy ofSciences, Na sddkach 7, 370 05 teski Budjovice, Czech Republic     

Seasonal variation of particulate organic carbon, dissolved organic carbon and the contribution of microbial communities to the live particulate organic carbon in a shallow near-bottom ecosystem at the Northwestern Mediterranean Sea

Microbial planktonic communities (i.e. bacteria and protozoa), phytoplankton, dissolved organic carbon (DOC) and particulate organic carbon (POC) were seasonally examined at Medes Islands (Northwestern Mediterranean) to assess their variation in abundance and composition throughout the year in a near-bottom littoral ecosystem. From October 1995 to November 1996, samples were collected between two and six times per month at 0.5 m above the bottom. Mean DOC and POC values throughout the year were 2560 180 (SE) and 387 ± 35 g C l^-1, respectively. All year, detrital organic carbon (detrital=total POC - live carbon) represented the main POC fraction, and mean live carbon was 24 ± 9 g C l^-1. Winter and spring had maximum values of POC, and spring and summer had maximum values of DOC. Heterotrophic bacteria, with a mean abundance of 5.16 ± 0.08 x 10⁵ cells ml^-1, were the main contributor to live carbon (26 ± 7%). During winter, heterotrophic bacterial biomass decreased 40% due to a decrease in mean biovolume per cell. Synechococcus sp. and Prochlorococcus sp. abundance were 2.24 ± 0.09 x 10⁴ and 1.05 ± 0.07 x 10⁴ cells ml^-1, respectively. However, while Synechococcus sp. were present all year, Prochlorococcus sp. were not observed from April to July. Mean phytoplankton (i.e. diatoms and dinoflagellates) abundance was 2.06 ± 0.40 x 10⁴ cells l^-1 with biomass at a maximum during the winter months, the period with the lowest temperature and the highest nutrient concentration. The size composition of live carbon showed two clearly distinct periods: from December to March, live carbon was dominated in biomass by microplankton, while from April to November, pico- and nanoplankton cells were dominant. Overall, the dynamics of the near-bottom planktonic communities was characterized by a low biomass of heterotrophic and autotrophic bacteria, phytoplankton and ciliates in contrast to previous water column studies. This pattern and the high temporal heterogeneity of the different planktonic communities are discussed in relation to the physical and chemical characteristics of the environment, as well as to the potential role that benthic communities may be exerting in the control of the near-bottom planktonic communities.      

Short communication. The effect of temperature, food concentration and female size on the egg production of the planktonic copepod Acartia bifilosa

Egg production of a brackish water calanoid copepod Acartia bifilosa was measured in the laboratory in different chlorophyll (Chl) a concentrations (0-24 mgr; l^-1) and temperatures 4-24C), and the cephalothorax length and carbon content of females were determined. Egg production was positively correlated both with Chl a concentration and with temperature; highest egg production was obtained with 14-20 g Chl a l^-1 and at 13-18°C. There was also a significant positive correlation between egg production and female length-specific carbon content (g C m^-1). However, no correlation was observed between egg production and cephalothorax length of females. Female carbon content changed during the 3 day experiments; carbon content was positively related to Chl a concentration and negatively related to temperature. We conclude that food availability (Chl a concentration), rather than temperature, limits the egg production of A.bifilosa in the present study area in the northern Baltic Sea. Further, both food concentration and temperature affect egg production not only through the direct effect on the numbers of eggs produced per female, but also through their effect on female carbon content.      

Limnological and ecophysiological aspects of Aphanizomenon ovalisporum bloom in Lake Kinneret, Israel

The first appearance of Aphanizomenon ovalisporum in Lake Kinneret in August 1994 was apparently boosted by relatively high concentrations of total dissolved phosphorus (12 g P l^-1 as compared to an average of 8 g P l^-1). The increasing Aphanizomenon biomass in a lake in which phytoplankton are generally phosphate limited in summer and autumn was accompanied by high enzymatic activity of alkaline phosphatase, reaching values of 2830 nmol MU l^-1 h^-1, suggesting a great demand for phosphorus. In addition, the nitrogen requirement of the developing population of Aphanizomenon was partly provided by nitrogen fixation, as indicated by a high percentage of heterocysts. Laboratory experiments demonstrated that filtrate from an old Peridinium gatunense culture enhanced Aphanizomenon growth. Thus, it is postulated that the degradation of the massive Peridinium bloom in spring and early summer supported the development of A.ovalisporum. The high pH and alkalinity during the bloom of Aphanizomenon indicate that A.ovalisporum is probably a HCO3^- user. After 1994, akinetes of A.ovalisporum were left in sediments and the water column, and could be a source for the next year's bloom. This possibility was demonstrated by inoculation of lake water and sediments into nitrogen-depleted BG-11 medium, resulting in the dominance of A.ovalisporum.      

Assimilation and release of 14C in a tropical strain of Cryptomonas obovata (Cryptophyceae) exposed to several irradiances

Carbon assimilation (¹⁴C) and dissolved organic carbon (DO¹⁴C) release by a tropical strain of Cryptomonas obovata was studied. Cells were exposed to a range of irradiances (0-2000 mol m^-2 s^-1) using axenic batch cultures in the laboratory (Ek = 180 mol m^-2s^-1). At up to 2000 mol m^-2s^-1, carbon assimilation was not inhibited and an acclimation to low irradiances was observed. DO¹⁴C release was dependent on carbon fixation and no increase was detected under high irradiances. To determine particulate organic carbon (PO¹⁴C) loss and CO¹⁴C release cells acclimated to 350 mol m^-2 s^-1 were incubated during 4 h at 35, 350, 850 and 1900 mol m^-2 s^-1. DO¹⁴C release was responsible for 30% of the PO¹⁴C loss at 1900 mol m^-2s^-1. High- and low-molecular-weight (HMW, LMW) compounds were released by C.obovata under all irradiance conditions. However, increased release with exposure time was observed only for the HMW compounds.      

Comparative ecophysiology of the harmful alga Chattonella marina (Raphidophyceae) form South Australian and Japanese waters

The raphidophyte flagellate Chattonella marina was successfully cultured from Boston Bay (South Australia), coincident with mass mortality of farmed bluefin tuna (Thunnus maccoyii) in April 1996. Grown under laboratory conditions at 150 mol m^-2 s^-1 irradiance, optimal growth (>0.5 day^-1) occurred at a temperature of 25C and a salinity of 30 p.s.u., but good growth (>0.3 day^-1) also occurred between a temperature of 10 and 30°C and at a salinity of 15-45 p.s.u. However, cultures grow much faster at an irradiance of 450 mol m^-2 s^-1 (1.08 day^-1). While Australian C.marina had similar temperature and salinity requirements as well-studied Japanese cultures from the Seto Inland Sea, the Australian strains exhibited a light saturation level for growth four times higher than that reported from Japan (150 mol m^-2 s^-1). An adaptation to higher light intensities was reflected in higher concentrations of microsporine-like amino acids in the Australian strains. The different light adaptation phenotypes were still apparent after long-term culturing under similar physiological conditions. Potential growth habitats for this ichthyotoxic flagellate in the Australian region and implications for finfish aquaculture industries are discussed.      

Effects of UVB radiation on freshwater autotrophic and heterotrophic picoplankton in a subalpine lake

The effects of UVB radiation on the activity of heterotrophic (HPP) and autotrophic (APP) picoplankton (0.2-2 m) and of autotrophic assemblages >2 m has been measured and compared. Under natural UVB irradiance in a large, deep, oligotrophic subalpine lake (Lago Maggiore, 4555N) with mean dissolved organic carbon (DOC) concentrations of 1 mg Cl^-1, the microorganisms of the two size fractions were not significantly photoinhibited in their autotrophic and heterotrophic activities. The vertical attenuation coefficient (Kd) for irradiance at 305 nm ranged from 1.45 to 1.67 during spring and summer. The mixing layer extended to a greater depth than the layer affected by UVB radiation (z1% < zmix), thus enabling the microorganisms living there to photoadapt. As the assimilation numbers of APP and nanoplankton were higher at 2 m depth than near the surface, we suspected that the influence of longer wavelength (UVA, photosynthetically active radiation) could be stronger than UVB in affecting the photosynthetic efficiency of natural populations. The artificial increase in UVB irradiance had a higher detrimental effect on HPP due to their smaller size, less protection and indirect effects through autotrophic cell inhibition. Picocyanobacteria were percentually more affected by UVB than nanoplankton during April due to the presence of diatoms, which are more resistant than other algal groups to solar UVB irradiance. Furthermore, picocyanobacteria had lower assimilation numbers with respect to larger phytoplankton in the quartz tubes during stratification.      

A preliminary study of tintinnid diversity in the NW Mediterranean Sea

Tintinnid diversity in surface waters was investigated in the Bay of Villefranche in March, before the formation of the seasonal thermocline, and in May, following water column stratification. Tintinnid abundance was much greater in March (500 cells l^-1), corresponding to a bloom of Stensomella nivalis compared to May (30 cells l^-1). Nonetheless, high numbers of species were encountered on both dates: 32 in March and 39 in May, respectively. Diversity was higher (H2.5) for the May date with low tintinnid concentrations. We examined taxonomic diversity and morphological diversity. Variance of lorica length was correlated with taxonomic diversity, in contrast to variance of lorica diameter, which was nearly invariant. We suggest that either species with similar lorica diameters exploit different prey items or competition for prey items is not the dominant factor in structuring tintinnid communities.      

Short communication. Carbon:nitrogen ratios of Baltic Sea copepods-indication of mineral limitation?

The carbon (C) and nitrogen (N) content and the C:N ratio of two common calanoid copepods, Eurytemora affinis and Acartia bifilosa were measured during spring and summer at the SW coast of Finland, northern Baltic Sea. The C:N ratio of both copepod species was slow and stable (4-4.5), irrespective of sampling time, which implies N limitation at least during intermediate to high food concentrations in spring and early summer. In addition, experiments were conducted to reveal whether the diet of copepods affects their C and N content. Adding green algae Brachiomonas submarina in concentrations of 50-500 g C l^-1 to <100-m-filtered sea water did not significantly increase copepod C or N content in 3 day experiments. However, the C and N contents of E.affinis eggs were 2 times higher in high food concentration, which may increase survival of eggs and nauplii.      

Seasonal and spatial distribution of bacterial biomass and the percentage of viable cells in a reservoir of Alabama

Spatial community dynamics of bacterioplankton were evaluatedalong the length of the former stream channel of Elledge Lake,a small reservoir in western Alabama. The reservoir was stronglystratified from April to October with up to a 10°C temperaturedifference across the 1 m deep metalimnion. Bacterial biomasswas highest during late summer, with a general pattern of increasingabundance from the inflowing river (10 µg C l^-1) to thedam (20–30 µg C l^-1). Bacterial numbers also increasedfollowing a >10-fold increase in turbidity associated witha major precipitation event, although only 10% of these cellswere viable. The percentage of viable cells generally increasedthrough the stratified period with 50–70% viable cellsin late summer. Overall, an average of 38% of bacterial cellswere viable, with a range from <20 to 70%. Although thesevalues were similar to those found by others, additional patternswere identified that have not been previously observed: a markeddecline in viable cells was found following turbid storm inflowsand increases in the percentage of viable cells occurred duringspring warming and following autumnal mixing events. Althougha modest increase in abundance occurred along the gradient frominflow down-reservoir to the dam, bacterial abundance did notincrease near the dam in a pattern coincident with the commonlyobserved increased algal biomass in the lacustrine portion ofreservoir ecosystems. The increases observed in bacterial viabilitymoving from the inflowing rivers towards the dam and later instratified periods stress the importance of differences in environmentalconditions in time and space in regulating bacterial biomassand development, as well as of shifts that would be anticipatedaccompanying altered hydrological regimes under climatic change.     

Short communication. First record of larval Brama brama (Pisces: Bramidae) and Corphaena hippurus (Pisces: Coryphaenidae) in the Adriatic Sea

The occurrence of early larval stages of Brama brama and Coryphaena hippurus is reported for the first time in Adriatic waters. Two larvae of B.brama between 4.36 and 5.00 mm, and two larvae of C.hippurus between 4.75 and 4.95 mm standard length, were found in ichthyoplankton collections taken off the River Neretva estuary (43010N, 17°250E) and station Stoncica, island Vis (43°000N, 16°20E) (eastern middle Adriatic), respectively. The capture of both species (B.brama) in August 1998; C.hippurus in May 1998) is in agreement with their proposed seasonal life cycle in the Adriatic Sea.      

Interspecific variability and environmental influence on particulate organic carbon {delta}13C in cultured marine phytoplankton

The stable carbon isotope composition of particulate organicmatter expressed as ¹³C was measured in cultures of 13 speciesof marine microalgae in different phylogenetic groups. The effectsof salinity variations and changes in photoperiod were alsoassayed for three of them (i.e. Skeletonema costatum, Amphidiniumopercularum and Isochrysis galbana); the effect of nature ofnitrogen supply (nitrate. ammonium) was studied for one (S.costatum).These environmental parameters were chosen because of theirvariability in the ocean and their possible effects on ¹³C valuesof phytoplankton organic carbon. Batch culture conditions andsampling time after inoculum were strongly controlled in orderto provide cells in good physiological state which were comparablefrom one culture to the other. In the same way, sampling waslimited to the first 2 days of exponential growth, in orderto avoid a possible dissolved inorganic carbon (DIC) limitation.Carboxylase activities [of the enzyme ribulose 1,5-bisphosphatecarboxylase oxygenase (Rubisco), and the three ß carboxylases:phosphoenolpyruvate carboxylase (PEPC), phosphoenolpyruvatecarboxykinase (PEPCK) and pyruvate carboxylase (PC)] and totalchlorophyll a concentrations were assayed simultaneously. The¹³C values observed were between –30.2 and –12.7i.e. comparable to those observed in the world's oceans. Theisotopic composition of phytoplankton organic carbon was shownto be under the influence of the parameters tested but ¹³C variationsare specific to the species considered. The nature of ßcarboxylase found in each species, or systematic position, couldnot be linked to the isotopic composition of organic carbon.No linear or single correlation between ¹³C variations and environmentalmodifications were observed and there is no evidence for a simpleand universal relation between ¹³C of phytoplankters and theirenvironment. In monospecific cultures as in the field, ¹³C fractionationby Rubisco (and eventually by PEPCK) may be counterbalancedby other mechanisms.     

The influence of temperature and light on the upper limit of Microcystis aeruginosa production in a hypertrophic reservoir

Primary production was measured for 7 years, using the in situ¹⁴C-method in hypertrophic Hartbeespoort Dam, South Africa,to examine the influence of light and water temperature on theupper limit of Microcystis aeruginosa production. Water temperaturesvaried from 11 to >25°C and chlorophyll concentrationsreached 6500 mg m^–3. The maximum volumetric rate of production(A_max) was 12->8800 mg C m^–3 h^–1 with areal productions(A) of 69->3300 mg C m^–2 h^–1 for euphotic zonedepths of <0.5–8.4 m. The intrinsic parameters of phytoplanktonproduction (, A_max/B, I_k) indicated that the phytoplankton populationwas adapted to high light levels. Both A_max/B and I_k were correlatedwith temperature. Under optimal conditions, , the theoreticalupper limit of A, was calculated to be 2.8 g Cm^–2 h^–1,while the measured rate was 2.5 g Cm^–2 h^–1. Measuredareal rates exceeding were overestimated due to methodologicalproblems when working with Microcystis scums. Light and watertemperature interacted to yield high production rates: watertemperature through its direct effect on photosynthetic ratesand indirectly in the formation of diurnal mixed layers; lightindirectly through water temperature and directly through itsattenuation and induction of light-adapted physiology in Microcystis.     

A comparison of nitrogen and carbon metabolism in the shallow and deep-water phytoplankton populations of a subalpine lake: response to photosynthetic photon flux density

Rates of , and CO₂ assimilationby the organisms in the shallow and deepchlorophyll layers ofCastle Lake were measured over a gradient of photosyntheticphoton flux densities (PPFD) during the 1979–1980 ice-freeseasons. The results of these experiments could be fitted witha hyperbolic function in the manner of the Michaelis-Mentenequation (excluding rates of dark assimilation) up to –40%of the surface PPFD after which photon inhibition occurred.The half saturation constants relative to incidence PPFD (K_LT)for assimilation ( = 1.1 E m^–2d^–2) were about twice those for ( = 0.5 E m^–2d^–1).All of the K_LT values correspond to depths in thelakerangingfrom 17–29 m(–1% of surface PPFD). Dark assimilationof both and was –50% of the assimilation at saturating PPFD implying that part ofthe immediate energy required for inorganic nitrogen assimilationmay come from intermediary metabolism. This contention was supportedfor assimilation by the results of experiments performed with specific inhibitors of non-cyclic photophosphorylationand oxidative phosphorylation. The K_LT values for the assimilationof CO₂ were from 2–10 times higher than those for inorganicnitrogen. These values for CO₂ assimilation were not significantlyaltered by the addition of either or during 12 h incubations.     

Assimilation of Fe and carbon by marine copepods from Fe-limited and Fe-replete diatom prey

Previous studies have demonstrated that growth of marine phytoplankton, bacteria and protozoa can be limited by the availability of Fe. We report evidence that the amount of Fe assimilated by crustacean grazers is affected by the Fe status of their pry. ⁵⁹Fe and ¹⁴C radiotracers were used to follow the fate of Fe and carbon during trophic transfer from diatoms to copepods. Fe assimilation efficiency was higher for copepods ingesting Fe-limited Thalassiosira weissflogii (17%) compared to diatoms that were not limited by Fe (10%), but assimilated Fe was lost more rapidly by copepods ingesting Fe-limited prey. Fe:C assimilation ratios were lower in copepods (5-12 mol Fe:mol C) than the cellular ratios of the phytoplankton prey (17-35 mol Fe:mol C), suggesting that copepods do not accumulate Fe relative to C during grazing. The largest single fate for Fe and C after grazing was regeneration to dissolved pools. Fe:C ratios in dissolved pools were approximately equal to the ratios in the original prey, but Fe:C ratios were higher in particular pools (largely fecal pellets), which should facilitate the export of Fe from the euphotic zone relative to C. Although copepod grazing does recycle cellular Fe and C, our results indicate that grazing may also tend to enhance Fe stress for lower trophic levels by removing Fe from the euphotic zone faster than C.