Photoprotective compounds in weakly and strongly pigmented copepods and co-occurring cladocerans

1. The prevalence of mycosporine‐like amino acids (MAAs) – a group of potential ultraviolet (UV)‐photoprotective compounds – was surveyed across 11 species of freshwater copepods from 20 lakes of varying ultraviolet radiation (UVR) transparency in North America, New Zealand and Argentina. Co‐occurring cladocerans were also analysed (seven species from 12 lakes). Many of the calanoid copepod populations were red with carotenoid pigmentation, allowing comparison of MAA and carotenoid accumulation as photoprotective strategies. 2. In two Pennsylvania (U.S.A.) lakes, MAA and carotenoid contents were followed during the early spring to mid‐summer period of lake warming. A pronounced seasonal pattern of higher carotenoid/low MAA content in spring, shifting to low carotenoid/higher MAA content in summer, was observed in calanoids from the more UV transparent lake. 3. All copepod samples contained MAAs. Visibly red calanoids, especially southern Hemisphere Boeckella, often had moderate to high concentrations (2.5–11 μg MAA mg^?1 dw), but low concentrations (0.04–1 μg MAA mg^?1 dw) in some N. American red calanoids show that high carotenoid pigmentation (e.g. 5–10 μg carotenoid mg^?1 dw) does not necessarily imply high MAA content. 4. No cladoceran sample had more than trace amounts of MAAs (<0.05 μg mg^?1 dw). Therefore, MAA accumulation does not seem to be a photoprotective strategy utilized by Daphnia (five species from nine lakes) or other cladocerans. 5. Seven identifiable MAAs were widely distributed among both calanoids and cyclopoids. Shinorine was ubiquitous and was usually the most abundant MAA in N. American samples. In contrast, porphyra‐334 was the predominant MAA in the southern Hemisphere Boeckella. 6. Copepods from higher UVR lakes tended to have a higher MAA content, but this relationship was statistically weak overall and taxon‐specific when found.     

Energetics and feeding dynamics of Euphausia superba in the South Georgia region during the summer of 1994

Measurements of adult Antarctic krill (Euphausia superba) gutcontents, evacuation and egestion rates, as well as digestiveefficiency, were carried out during February-March 1994 in thevicin ity of South Georgia to estimate in situ daily ration.These were combined with acoustically derived biomass data tocalculate the grazing impact of Antarctic krill and its contributionto the carbon flux in the region. Individual levels of gut pigmentconcentrations and evacuation rates ranged from 27 to 1831 ngchlorophyll a-eq. ind.^–1 and from 0.133 to 0.424 h^–1,respectively. Losses of pigment fluor escence during digestionwere very high, ranging from 58 to 98% of the total pigmentdigested. Daily carbon consumption estimated using the gut fluorescencemethod varied from 0.234 to 0.931 mg C ind.^–1 day^–1(or 0.4–1.7% of body carbon), compared to {small tilde}2.73mg C ind.^–1 day^–1 (or {small tilde}5% of body carbon)using the faecal pellet production data. The 3-fold higher dailyration estimated using egestion rate data may be explained bypredation on micro-and mesozooplankton. Maximum krill grazingimpact ranged from 0.4 to 1.9% of the total phytoplankton stockor from 10 to 59% of the total daily primary production. However,grazing impact on the microphytoplankton (>20 µm) wassubstantially higher, at times exceeding 100% of the daily microphytoplanktonproduction. It is suggested that to meet its energetic demands,kriil must consume a substantial proportion of heterotrophiccarbon. ³Present address Zoology Department, University of Fort Hare,P/Bag X1314, Alice, 5700, South Africa     

Growth and feeding rates of the newly hatched larval ctenophore Mnemiopsis leidyi A. Agassiz (Ctenophora, Lobata)

Mnemiopsis leidyi: larvae depend on microplankton (<200 µm) prey duringthe first few days following hatching until larvae are >0.5mm in length and can successfully capture and consume mesozooplanktonprey. Feeding and growth rates of newly hatched M. leidyi larvaewere measured in controlled laboratory experiments. When fednatural microplankton assemblages, newly hatched larvae consumedsignificant quantities of both autotrophic and heterotrophicprey, including diatoms, phototrophic, heterotrophic and mixotrophicdinoflagellates, euglenoid flagellates, aloricate and tintinnidciliates, and rotifers. Average per capita clearance rates were1.99–7.59 mL individual^–1 h^–1 ( = 4.01 mL individual^–1 h^–1; SD = 1.95)and total per capita ingestion was 0.01–4.70 µgC individual^–1 day^–1 x 10² ( = 0.83 µg C individual^–1 day^–1 x 10²; SD =1.89). Larval growth rates were –0.13 to 0.56 mm individual^–1day^–1 (equivalent to –1.72 to 4.33 µg C individual^–1day^–1) over a range of larval sizes from 0.5 (<0.5µg C) to 5 mm (85 µg C). A diet consisting entirelyof microplankton prey supported larval growth for >2 weeks,and growth rate decreased when larvae reached 4–5 mm inlength, corresponding to the beginning of their morphologicaltransition from tentaculate to lobate feeding mode. The grossgrowth efficiency of larvae fed natural microplankton assemblageswas 3%.     

Predicting chlorophyll vertical distribution in response to epilimnetic nutrient enrichment in small stratified lakes

Light-limited metalimnetic phytoplankton communities are thoughtto be negatively impacted by epilimnetic nutrient enrichmentbecause of shading by increased epilimnetic phytoplankton biomass.We tested this expectation with a dynamic simulation model thatwas calibrated to three lakes undergoing whole-lake nutrientand food web manipulations. Total areal chlorophyll increaseddue to nutrient enrichment in each lake, but the magnitude ofthe response varied between lakes. Modeling experiments, whichallowed analysis of separate components of each lake's responseto nutrient enrichment, indicated that the response to enrichmentdepended on lake water color and food web structure. In weaklystained lakes ({small tilde}10 mg Pt 1^–1, k₄ = 0.4 m^–1),metalimnetic chlorophyll was stimulated by nutrient enrichmentup to moderate levels (1 µg Pt1^–1 day^–1).In more strongly colored lakes (25 mg Pt 1^–1, k₄ = 1.0),metalimnetic chlorophyll responded negatively to nutrient enrichmentat all P loading rates. Food web structure, as expressed byrates of zooplanktivory, interacted with water color in twoways. One impact was through direct grazing losses on metalimneticchlorophyll. The other process involved was indirect impactfrom grazing on epilimnetic phytoplankton, which reduced shadingon metalimnetic chlorophyll. Vertical redistribution of chlorophyllbetween the epilimnion and the metalimnion led to little accumulationof areal chlorophyll with increased P loading over limited rangesof water color and nutrient input rates. Model predictions maybe most effectively tested with whole-lake experiments contrastingfood web structure, water color and nutrient loading.     

Microplankton and primary production in the Sea of Okhotsk in summer 1994

Phytoplankton composition, density, vertical distribution andprimary production were investigated in the Sea of Okhotsk andin the adjacent northern north Pacific in July–August1994, together with measurements of density and distributionof planktonic microheterotrophs: bacteria, nanoheterotrophsand ciliates. Different phases of phytoplankton seasonal successionwere encountered during the period of investigation in variousregions of this sea. Primary production measured at 144 stationswas found to be greatest (1.5–4 g C m^-2day^-1) in areasof spring-phase succession along the Sakhalin shelf and theKashevarov bank. Periodic relapses of the spring blooms of ‘heavy’diatoms during the whole growth season were recorded over thisbank. The summer phase of the phytoplankton minimum prevailedin the central and eastern parts of the sea, manifested by thedominance of nanoflagellates in terms of phytoplankton biomass.Primary production was 0.5–1 g C m^-2 day^-1. The earlyautumn phase of succession was typical of the Kurile straitarea and the adjacent north Pacific. Primary production therevaried from 0.7 to 2 g C m^-2 day^-1. The integrated phytoplanktonbiomass in the water column varied from 9–12 g m^-2 inzones supporting the summer minimum assemblage to 15–20g m^-2 in zones of early autumn recovery of phytoplankton growth,and up to 40–70 g m^-2 in areas of remnant or relapseddiatom blooms. The numerical density of bacterioplankton wasbetween 1 x 10⁶ and 3 x 10⁶ cells ml^-1 and its wet biomass wasbetween 100 and 370 mg m^-3. In deep waters it was 8–15mg m^-3. The integrated bacterioplankton biomass in the upperwater column varied from 6 to 29 g m^-2. The numerical densityof zooflagellates varied in the upper layer between 0.8 x 10⁶and 4 x 10⁶ l^-1 and their biomass was between 20 and 50 mg m^-3.In deep waters they were still present at a density of 0.05x 10⁶ to 0.2 x 10⁶ cells l^-1. The biomass of planktonic ciliatesvaried between stations from 20 to 100 mg m^-3. The joint biomassof planktonic protozoa in the water column was between 3 and12 g m^-3 at most of the stations.     

Mycosporine-like amino acids in planktonic organisms living under different UV exposure conditions in Patagonian lakes

Mycosporine-like amino acids (MAAs) were studied in zooplanktonfrom 13 Argentinian lakes covering a broad range in altitude,maximum depth and physico-chemical properties of the water.Four to nine different MAAs (predominantly porphyra-334 andshinorine) were found in the copepods Boeckella gibbosa, B.gracilipes, B. meteoris and Parabroteas sarsi, and in the ciliateStentor amethystinus, while MAAs were undetectable in the cladoceranDaphnia middendorffiana. Among the different copepods, maximumMAA concentrations accounted for 0.25–1.31% of the dryweight, and contents were generally about three to seven times(up to 43 times) higher in the animals living in the clearestlakes compared to those occurring in low-UV systems. This variabilityin the content of MAAs was related to the lake altitude (r²= 0.71), and the fraction of the water column to which 1% ofthe surface UV radiation at 320 nm penetrated (r² = 0.57). Ourdata therefore underscore the role of MAAs as sunscreens todecrease the potential negative effects of solar radiation,but they also indicate that other environmental factors besidesUV transparency play a role in determining MAA concentrations.One lake was selected to obtain additional information on thequalitative composition of MAAs in seston of <100 µmbetween two sampling sites and over a 2 month study period (australsummer). Six different MAAs were detected in the samples, withporphyra-334 and palythine being predominant. In the copepodscollected simultaneously, there was low variation in MAA concentrationsbetween the two sites and over time. Thus, our results suggestthat under similar UV exposure conditions MAA contents of planktonicorganisms show low temporal variation.     

Pigment-specific rates of phytoplankton growth and microzooplankton grazing in a subtropical lagoon

Phytoplankton growth and microzooplankton grazing rates wereevaluated in one station in Bahía Concepción,located in the middle region of the Gulf of California, México.We used high-performance liquid chromatography (HPLC) estimationsof phytoplankton pigment signatures to evaluate the annual variationof taxon-specific grazing and growth rates obtained with thedilution technique. Chlorophyll-a (Chl-a) concentrations variedwidely (0.34–3.32 µg L^–1) and showed two maxima,during late spring and autumn, associated with the transitionbetween mixed and stratified conditions. Phytoplankton growthrates varied seasonally with the lowest rates during summer(range: 0.01–2.55 day^–1 for Chl-a; 0.00–3.84day^–1 for Chl-b; 0.26–3.29 day^–1 for fucoxanthin;0.00–6.27 day^–1 for peridinin; 0.00–4.35 day^–1for zeaxanthin). Microzooplankton grazing was an important lossprocess (range: 0.0–1.89 day^–1 for Chl-a; 0.00–3.12day^–1 for Chl-b; 0.26–3.29 day^–1 for fucoxanthin;0.00–2.03 day^–1 for peridinin; 0.00–3.51 day^–1for zeaxanthin). Average grazing rates accounted 68–89%of estimated average phytoplankton pigment-specific growth rates.The analysis of pigment signatures indicates that diatoms anddinoflagellates were the dominant groups, and contrary to expectationfor typical subtropical lagoons, the specific growth rates inBahía Concepción showed a pronounced seasonalvariability, linked to transitional hydrographic conditions.Our results indicate a close coupling between the communitymicrozooplankton grazing and phytoplankton growth rates, withoutselective feeding behavior. These results suggest that microzooplanktonplay a critical role and may significantly modify the availabilityand efficiency of transfer of energy to higher trophic levels.     

Daily irradiance governs growth rate and colony formation of Phaeocystis (Prymnesiophyceae)

Phaeocystis was cultured at a range of ecologically significantdaily irradiances under nutrient-replete conditions. Below athreshold of 100 W h m^–1 day^–1, the cells were smalland flagellated, and remained solitary. Above this threshold,the cells were larger and able to form colonies. Growth rateand colony formation were maximum at sea surface irradiances(>700 W h m^–2 day^–2). Presumably, colonial growthis a strategy to maintain optimum growth rates in the watercolumn. Sinking, nutrient-stressed colonies reach low irradiancesand colonial cells can transform into small solitary flagellatedcells. These observations are important in understanding theecology and life cycle of Phaeocystis.     

Polyamine Content in Relation to Embryo Growth and Dedifferentiation in Barley (Hordeum vulgare L.)

Putrescine, spermidine, and spermine content were analysed inzygotic embryos of barley (Hordeum vulgare L.). Changes in polyaminecontent were observed during zygotic embryo growth. In two cultivars,‘Bomi’ and ‘Golden Promise’, the totalpolyamine content in the embryos was 2.6–2.9 nmol mg^–1fresh weight 10 d after anthesis, the highest content observed.It dropped to 1.3 nmol mg^–1 fresh weight 14 d after anthesis.This drop was caused by decreases in all three polyamine concentrations.From 14 to 35 d after anthesis the putrescine content continuedto decrease while the spermidine and spermine content increased,thus the total polyamine content remained constant until 35d after anthesis. The mutant ‘Ris? 1508’ showeda constant polyamine content around 1.3 nmol mg^–1 freshweight from 14 to 35 d after anthesis. The polyamine patternwas conserved in all three lines throughout the period of investigationshowing a spermidine content higher than putrescine contentwhich was, in turn, higher or equal to the spermine content.The polyamine content measured as nmol µg^–1 proteindecreased from 14 to 21 d post anthesis in all three lines,because the protein content (µg mg^–1 fresh weight)increased during the period. In dedifferentiating zygotic embryoscultured in vitro the putrescine content (nmol mg^–1 freshweight) rose by a factor of nine and the spermidine contentdoubled within the first week of cultivation, whereas sperminecontent did not change. For embryoderived calli a repeated patternof change in polyamine content was observed throughout the subculturingperiod. Key words: Polyamines, Hordeum vulgare L., embryo development     

Photosynthetic algal production, accumulation and release of phytoplankton storage carbohydrates and bacterial production in a gradient in daily nutrient supply

In a mesocosm experiment providing a gradient of semi-continuousaddition of mineral nutrient, production rates and mortalityof phytoplankton were estimated. Heterotrophic bacterial biomassand production rates and their responses to the mineral nutrientsadditions were also estimated. The purpose of the experimentwas to establish responses of the major biological factors asa function of nutrient amendments. Initial primary productionwas 0.47 µg C L^–1 day^–1. In the most fertilizedmesocosm, phytoplankton biomass increased at a specific rateof 0.4 day^–1 during the first week of the experiment,and on day 9 primary production reached a peak at 1027 µgC L^–1 day^–1. The responses in the other fertilizedmesocosms were intermediate, and in an unfertilized controlthe variables measured stayed almost constant throughout theexperiment. The termination of the blooms in the fertilizedmesocosms was a consequence of nitrogen limitation, and nitrogenlimitation subsequently induced storage of intracellular organicmaterial in the phytoplankton. In the mesocosm receiving thehighest daily dose of nutrients, strong post-bloom nutrientlimitation resulted in high phytoplankton mortality, and releaseof organic material from the algae supported the gradient’shighest heterotrophic bacterial production.     

Trophic links in the lowland River Meuse (Belgium): assessing the role of bacteria and protozoans in planktonic food webs

Trophic interactions within the plankton of the lowland RiverMeuse (Belgium) were measured in spring and summer 2001. Consumptionof bacteria by protozoa was measured by monitoring the disappearanceof ³H-thymidine-labelled bacteria. Metazooplankton bacterivorywas assessed using 0.5-µm fluorescent microparticles (FMPs),and predation of metazooplankton on ciliates was measured usingnatural ciliate assemblages labelled with FMPs as tracer food.Grazing of metazooplankton on flagellates was determined throughin situ incubations with manipulated metazooplankton densities.Protozooplankton bacterivory varied between 6.08 and 53.90 mgC m^–3 day^–1 (i.e. from 0.12 to 0.86 g C^–1bacteria g C^–1 protozoa day^–1). Metazooplankton,essentially rotifers, grazing on bacteria was negligible comparedwith grazing by protozoa (1000 times lower). Predation of rotiferson heterotrophic flagellates (HFs) was generally low (on average1.77 mg C m^–3 day^–1, i.e. 0.084 g C^–1 flagellatesg C^–1 rotifers day^–1), the higher contribution ofHF in the diet of rotifers being observed when Keratella cochleariswas the dominant metazooplankter. Predation of rotifers on ciliateswas low in spring samples (0.56 mg C m^–3 day^–1,i.e. 0.014 g C^–1 ciliates g C^–1 rotifers day^–1)in contrast to measurements performed in July (8.72 mg C m^–3day^–1, i.e. 0.242 g C^–1 ciliates g C^–1 rotifersday^–1). The proportion of protozoa in the diet of rotiferswas low compared with that of phytoplankton (<30% of totalcarbon ingestion) except when phytoplankton biomass decreasedbelow the incipient limiting level (ILL) of the main metazooplantonicspecies. In such conditions, protozoa (mainly ciliates) constituted50% of total rotifer diet. These results give evidence thatmicrobial organisms play a significant role within the planktonicfood web of a eutrophic lowland river, ciliates providing analternative food for metazooplankton when phytoplankton becomesscarce.     

Biomass, feeding and production of Noctiluca scintillans in the Seto Inland Sea, Japan

The abundance and biomass of the large heterotrophic dinoflagellateNoctiluca scintillans, together with the changes in its potentialprey items, were monitored in the Seto Inland Sea, Japan, duringsummer 1997 (17 July-11 August). Growth and grazing rates ofNscintillans fed natural plankton populations were also measuredeight and seven times, respectively, during the survey period.The abundance and biomass of N scintillans averaged over thewater column (19 m) were in the range 1–345 cells 1^–1(temporalaverage = 93 cell1^–1) and 0.1–49.6 µg C l^–1(temporalaverage = 13.8 µg C l^–1; three times higher thanthat of calanoid copepods during the same period). Noctilucascintillans populations followed the changes in phytoplankton:N.scintillans biomass was increasing during the period of diatomblooms and was at a plateau or decreasing during periods oflow chlorophyll a. The growth rates of N.scintillans (µ)were also consistent with the wax and wane of the N.scintillanspopulation: N.scintillans showed highest growth rates duringdiatom blooms. A simple relationship between µ and chlorophylla concentration was established, and the production of N.scintillanswas estimated using this relationship and the measured biomass.The estimated production averaged over the water column wasin the range >0.1–5.2 µg C l^–1 day^–1(temporalaverage = 1.4 µg C l^–1 day^–1; 64% of the productionof calanoid copepods during the same period). Diatom clearancerates by N.scintillans were in the range 0.10–0.35 mlcell^–1 day^–1, and the phytoplankton population clearanceby N.scintillans was >12% day^–1. Thus, although thefeeding pressure of N.scintillans on phytoplankton standingstock was low, N.scintillans was an important member of themesozooplank-ton in terms of biomass and production in the SetoInland Sea during summer.     

Bacterial biomass and production in a shallow bay

Bacterial biomass (BB, acridine orange) and bacterial secondaryproduction (BSP, [³H]thymidine incubations) were measured forthe first time in Concepción Bay (37°35'S, 73°01'W).BB ranged from 1.8x10⁶ to 22.5x10⁶ cells ml^–1 (the lattervalue observed near to an industrial effluent), BSP from 0.27x10⁶to 2.5x10⁶ cell ml^–1 day^–1 and heterotrophic turnoverrates between 0.15 and 1.0 doublings day^–1.     

A case of thermal pollution limited primary productivity in a southwestern U.S.A. Reservoir

North Lake, a small (330 ha. surface area) southwestern U.S.A. cooling water reservoir was found to contain less phytoplankton production (104.0 mg C m⁻³ day⁻¹), lower annual mean total organic carbon (3.7 mg l⁻¹) and phytoplankton standing crops (0.9 ml m⁻³) than other local area reservoirs. Concentrations of inorganic P and N were at or below test detection limits during the study year 1973–1974.In situ ¹⁴C non-filtration primary productivity techniques demonstrated significant (≃13 percent) stimulation of planktonic primary productivity due to power plant entrainment. Optical counts showed no destruction of entrained phytoplankters. Populations of Cyanophyta were never dominant, although they frequently bloom in most other local reservoirs. Thermal loading at North Lake is thought to ultimately depress phytoplankton primary production and standing crop by causing nutrient limitation.     

The annual cycle of Mesodinium rubrum in the waters surrounding the Isles of Shoals, Gulf of Maine

Mesodinium rubrum was collected in Kemmerer bottles, fixed inBouin's solution and protargol stained. Cell volume showed aseasonal change of over an order of magnitude, being largest(3.25x10⁴ µm³) in the early spring and smallest in thesummer. Cell abundance was highest in the spring and lowestin the summer. Biomass followed a similar trend ranging from{small tilde}1 to 147 J m^–3 Production, estimated by amultiple regression that incorporated ambient temperature andcell volume, was 2.5 kJ m^–3 day^–1 This is {smalltilde}0.3% of the primary production.     

Microzooplankton grazing in a coastal embayment off Concepcion, Chile, (~36{degrees} S) during non-upwelling conditions

The impact of grazing by natural assemblages of microzooplanktonwas estimated in an upwelling area (Concepción, Chile)during the non-upwelling season in 2003 and 2004. Seawater dilutionexperiments using chlorophyll a (Chl a) as a tracer were usedto estimate daily rates of phytoplankton growth and microzooplanktongrazing. Initial Chl a concentrations ranged from 0.4 to 1.4mg Chl a m^–3 and phytoplankton prey biomass and abundancewere numerically dominated by components <20 µm. Phytoplanktongrowth and microzooplankton grazing rates were 0.19–0.25day^–1 and 0.26–0.52 day ^–1, respectively.These results suggest that microzooplankton exert a significantremoval of primary production (>100%) during the non-upwellingperiod.     

Copepod abundance in the western Irish Sea: relationship to physical regime, phytoplankton production and standing stock

The distinct patterns of stratification in the North Channeland stratified region of the western Irish Sea influence theseasonal abundance of phytoplankton. The 3–4 month productionseason in the stratified region was characterized by productionand biomass peaks in the spring (up to 2378 mg C m² day^–1and 178.4 mg chlorophyll m^–2) and autumn (up to 1280 mgC m^–2 day^–1 and 101.9 mg chlorophyll m^–2).Phytoplankton in the North Channel exhibited a short, late productionseason with a single summer (June/July) peak in production (4483mg Cm^–2 day^–1) and biomass (–160.6 mg chlorophyllm^–2). These differences have little influence on copepoddynamics. Both regions supported recurrent annual cycles ofcopepod abundance with similar seasonal maxima (182.8–241.810³ind. m^–2) and dominant species (Pseudocalanus elongatusand Acartia clausi). Specific rates of population increase inthe spring were 0.071 and 0.048 day¹ for the North Channel andstratified region, respectively. Increased copepod abundancein the stratified region coincided with the spring bloom, andwas significantly correlated with chlorophyll standing stock.Increased copepod abundance preceded the summer production peakin the North Channel. This increase was not correlated withchlorophyll standing crop, suggesting that a food resource otherthan phytoplankton may be responsible for the onset of copepodproduction prior to the spring bloom. Hetero-trophic microplanktonas an alternative food source, and advection of copepods fromthe stratified region, are proposed as possible explanationsfor copepod abundance increasing in advance of the summer peakin primary production.     

Dense sub-ice bloom of dinoflagellates in the Baltic Sea, potentially limited by high pH

The phytoplankton community, carbon assimilation, chlorophylla (Chl a), pH, light and attenuation and inorganic nutrientswere monitored under the ice in the coastal Gulf of Finland,Baltic Sea. Maximum ice and snow thickness was 40 and 15 cm,respectively. Freshwater influence had created a halocline 1–2m below the ice–water interface, and above this halocline,a dense bloom of dinoflagellates developed (max: >300 µgChl a L^–1). The photosynthetic uptake of carbon dioxideby this "red tide" increased the pH to a maximum of 9.0. Thesub-ice phytoplankton community was dominated by the dinoflagellateWoloszynskia halophila (max: 3.6 x 10⁷ cells L^–1). ThepH tolerance of this species was studied in a monoculture andthe results indicate that pH >8.5 limits growth of this speciesat ambient irradiance. This study shows that primary productivitymay raise the pH to growth limiting levels, even in marine,low-light environments where pH normally is not considered important.     

Zooplankton fecal pellet fluxes and vertical transport of particulate organic material in the pelagic environment

Fecal pellet fluxes were determined using a series of multireplicatetraps set at 35, 65, 150, 500, 750 and 1500 m in the northeastPacific. Fecal pellets appear to be important contributors to total carbonfluxes. In near-surface waters (35–150 m), pellet fluxesranged from 2–3 x 10⁵ pellets m^–2 day^–1. Minimumpellet fluxes were observed at 500m({small tilde}0.4x 10⁵ pelletsm^–2day^–1). In contrast, the 1500 m pellet flux valueincreased to approximately 0.8 x 10⁵ pellets m^–2 day^–1relative to the 500 m depth, and is probably the result of insitu repackaging. Analyses of pellet content suggest multiplesources of "large" particle input throughout the water column.The implications of this phenomenon are discussed in terms ofthe detrital rain and ladder of migration theories.     

Dynamics of inorganic phosphorus in pelagic communities of the Sea of Okhotsk

Inorganic phosphorus uptake and regeneration in the OkhotskSea waters were investigated in July–August 1994 withthe use of radioisotopic techniques. The rates of PO₄-P uptakeby microplankton in the upper mixed layer were between 1.5 and6.6 µg P l^-1 day^-1 (average 2.75) in areas of diatom dominance,and between 0.68 and 1.68 µg P l^-1 day^-1 (average 1.16)in areas of intense warming and summer phytoplankton minimum.The residence time of PO₄-P standing stock in water at differentstations varied between 1.5 and 24 days (mean 9 days). The shareof bacterioplankton contributing to total PO₄-P uptake was 50%in areas of the summer phytoplankton minimum and 20–30%in areas of diatom dominance. The PO₄-P regeneration rate wasmeasured first time experimentally in the temperate sea. Itsrates varied from 0.30 to 1.65 µg P l^-1 day^-1. In areasof diatom dominance, it compensated with 30–60% of PO₄-Puptake. In zones of summer phytoplankton minimum and in thelayers of deep chlorophyll maxima at 10–25 m depths, thePO₄-P regeneration rate often exceeded its uptake. Primary phytoplanktonproduction correlated well with PO₄-P uptake values in the uppermixed layer, while no correlation was found between primaryproduction and the ambient PO₄-P content in water.