Pigment destruction by Calanus pacificus: impact on the estimation of water column fluxes

Measurements of gut pigment made prior to fecal pellet productionin Calanus pacificus females and CV copepodites suggest that(i) chlorophyll a and/or its pheopigment derivatives are degradedinto molecules that are not detectable by the standard fluorometrictechnique; and (ii) the percentage of ingested chlorophyll awhich degrades into fluorometrically undetected molecules isnot constant. Thus, measurements of chlorophyll and pheopigmenta in the guts of zooplankton can only yield minimum estimatesof in situ grazing rates. Estimates of the vertical flux ofprimary particulates based on chlorophyll and pheopigment abudgets may also be underestimated.     

Short-term feeding rates of A carrier grani in natural conditions: diurnal variation

Short-term in situ diel grazing activity of adult male and femalesofAcania graniSars. were investigated at a coastal station inthe Alboran sea (SE of Spain). Gut pigment contents were measuredfluorometrically, and the ingestion rates, filtration ratesand daily ratios were calculated from gut fullness, evacuationrates and pigment concentrations in sea water. The results indicatethat there were size-related differences in the amount of foodingested by males and females. Gut contents of females wereon average >1.5 times that for males. Body-volume-specificfeedingestimates were, however, the same for both sexes. Gutpassagetimes, estimated from animals collected at the time of day whengut pigments were maximal, were shorter in females. Both sexesshowed diel changes in feeding activity and faecal pellet productionof about one order of magnitude;the maximum rates were observedat dusk, the minimum rates at midday. There was a directrelationshipbetween copepod grazing and pigment concentration in sea waterwhen a time lag was considered. Daytime and night-time in situincubations using natural sea water enriched withlaboratorycultured algae provided evidence of non-continuous feeding andof light intensity control of the diel patterns. The possibleadaptive advantages of differences in sexual size on feedingbehaviour and diurnal variability are discussed.     

Diel variations in gut pigment content, diel vertical migration and estimates of grazing impact for copepods in the southern Benguela upwelling region in October 1987

The gut fluorescence technique was used to estimate ingestionand filtration rates of the adult female copepods Paracalanusparvus, Cenlropages brachiatus and Calanus austrails, and copepoditestages 3, 4 and 5 of C.australis in the southern Benguela upwellingregion. During the study period chlorophyll concentrations withinthe upper 20 m of the water column were high, 5 µg I^–1in mid-shelf waters and 15–30 µg I^–1 in innershelf waters. Copepod gut pigment content was low and constantduring the day then increased sharply during the first 2 h aftersunset. Gut pigment content was 2–6 times higher duringthe night compared with daytime values. Small non-migratingcopepods (Paracalanus parvus) showed the smallest diel differencein gut pigment content and large migrating copepods (Centropagesbrachiatus and Calanus australis) the largest difference. Eggproduction rates were 20 and 50% of maximum at the mid-shelfand inner shelf stations respectively, suggesting food-limitation.Comparison of ingestion rates calculated from egg productiondata with ingestion rates calculated from gut pigment data suggestedthat the copepods were feeding omnivorously at the inner shelfstations but herbivorously at the mid-shelf stations. Assumingthat all of the phytoplankton was available as food, the nearshorecopepod assemblage grazed {small tilde}1% of the standing cropeach day, and the mid-shelf assemblage grazed 5% day^–1.Because of errors and uncertainties associated with the gutfluorescence technique, the feeding impact could be underestimatedby 2–4-fold. We discuss several approaches which couldlead to more precise estimates of feeding rates. ³Present address: Marine Sciences, SUNY, Stony Brook, NY, 11794-5000,USA     

In situ diel variation in gut pigment contents of Ceriodaphnia sp. in stratification and destratification periods

The short-term, in situ diel grazing of Ceriodaphnia sp. duringperiods of stratification and mixing was investigated usingthe technique of fluorimetric analysis of the gut pigments.There were considerable seasonal differences in feeding behaviourIn mixing, when the concentration of chlorophyll a in the watercolumn was high and Ceriodaphnia abundance was low, gut pigmentcontents showed clear diel variation patterns, probably dueto diel variations of the high values of feeding activity observedin the 24 hour cycle The maximum values were found at dawn.On the other hand, no diel variations in gut pigment were observedduring periods of stratification and while the amounts of pigmentsin the water and in the gut were very low, species abundancewas high. Taking into account the ambient conditions, the authorsdiscuss the possibility that the change of feeding of the Ceriodaphniasp. observed when the environment changed from a mixing periodto one of stratification represents a change from herbivorousto detritivorous behavior.     

Zooplankton feeding ecology: clearance and ingestion rates of the salps Thalia democratica, Cyclosalpa affinis and Salpa cylindrica on naturally occurring particles in the Mid-Atlantic Bight

Aggregate stages of the salps Thalia democratica, Cyclosalpaaffinis and Salpa cylindrica collected by SCUBA diving in theMid-Atlantic Bight were fed with naturally occurring food assemblages.This is one of the few studies where salps have been fed withnatural food assemblages. The estimated clearance rate for allspecies based on disappearance of chlorophyll varied from 82to 444 mL individual^–1 day^–1. Cell counts showedthat T. democratica mostly ingested carbon from autotrophicnanoflagellates and autotrophic dinoflagellates. Ingestion byS. cylindrica was primarily on larger prey, such as dinoflagellates,while C. affinis ingested auto- and heterotrophic nanoflagellates.All main prey types ingested by salps corresponded to thosethat contributed most to biomass at each experimental station.Thus, salps fed on naturally occurring particles primarily inproportion to prey biomass and to their mechanical capacityto be retained and ingested. Feeding by salps on dinoflagellatesand ciliates implies that they may act not only as potentialcompetitors with microzooplankton, but also as consumers ofthem.     

Pigment ingestion and egg production rates of the calanoid copepod Temora longicornisr. implications for gut pigment loss and omnivorous feeding

We examined the relationship between egg production rate (E)and pigment ingestion rate (I, from gut content corrected for33% loss) for adult female Temora longicornis in Long IslandSound on 47 occasions. Linear regression of E on I [both variablesexpressed in mass of nitrogen (N) female^–1 day^–1]was: E_N = 0.0016 + 0.770 x I_N. The slope, 0.77, is the apparentgross efficiency of egg production, equivalent to the grossgrowth efficiency (GGE) assuming that females partition allnitrogen for growth into egg production. Published work suggeststhat a GGE of 0.37 would be expected for herbivorous copepods.The discrepancy between the expected value of 0.37 and observedvalue of 0.77 could result from unquantified losses of gut pigmentor because T.longicomis ingested a significant amount of nitrogenby feeding as a carnivore. We suggest that if T.longicomis femalesderive all of their nitrogen for growth by feeding on phytoplankton,and if no correction for pigment loss is employed, then thegut pigment method underestimates pigment ingestion by no morethan a factor of two.     

Temporal variability in copepod fecundity during two different spring bloom periods in coastal waters off Plymouth (SW England)

The temporal variation in egg production of the planktonic copepodsCalanus helgolandicus, Temora longicornis and Pseudocalanuselongatus was studied during two different spring bloom periodsin 1989 and 1990 by weekly sampling at two permanent stationsin coastal waters off Plymouth (SW England). Copepod egg productionwas estimated in situ by incubating individual adult femalesin filtered seawater for 24 h (72 h until hatching for P.elongatus)at the field surface temperature. The relationship between copepodegg production rates and: (i) chlorophyll a concentration (totaland >10 µm size fraction), (ii) temperature and (iii)initial copepod gut pigment content was investigated. The springbloom periods were very different in both years, with the occurrenceof a Phaeocystis sp. bloom in 1990, which negatively affectedthe feeding and fecundity of copepods. Egg production ratesin spring 1989 were significantly correlated with chlorophylla concentration (particularly with the >10 µm fraction),field temperature and copepod gut pigment contents. In spring1990, egg production rates were also correlated with copepodgut pigment contents, but no significant correlations were obtainedwith temperature or with chlorophyll a concentration, as a consequenceof the lower egg production rates obtained during the Phaeocystissp. dominance period. These results show that food availabilityis the factor which mainly affects the fecundity of neriticcopepods in short time periods.     

Comparison of main emissions at--196?C from phycobilisomes of two blue-green algae Anabaena cylindrica and Anacystis nidulans

Main emissions at—196?C from phycobilisomes of two blue-greenalgae Anabaena cylindrica and Anacystis nidulans were studiedwith special reference to allophycocyanin (APC) B content. Supplementaryexperiments were done with Anabaena variabilis (M-2 and M-3).The main emission from phycobilisome of Anacystis nidulans richin APC B was located at 681 nm. The location was identical tothat of the main emission from APC B but at a shorter wavelengththan that of in vivo emission (685 nm). Results indicate thatAPC B acts as the energy output of phycobilisomes, but thatthe in vivo 685 nm emission is not attributed to APC B. The main emission of the phycobilisome of Anabaena cylindricawas always located at 685 nm irrespective of the preparationmethod; 0.75 M phosphate buffer [Plant Physiol., 63: 615–620(1979)] or 30% polyethylene glycol [Special Issue of Plant &Cell Physiol., No. 3, p. 23–31 (1977)]. This alga alsocontained a special form of APC, but its content was very low.The location of its emission band (681 nm) was identical tothat of APC B, but shorter than that of the main band of phycobilisomes(685 nm). The 685 nm emitter in phycobilisomes showed a charactersimilar to chlorophyll a but not phycobiliproteins in treatmentsfor aqueous extraction or methanol extraction. Results indicatethat the pigment is probably chlorophyll a as we assumed previously.The 685 nm emission from phycobilisomes of Anabaena variabilis(M-2 and M-3) showed the same character. Results were interpreted as indicating that (i) the contentof the special form of APC varies with the species or strainof blue-green algae and (ii) the energy at the phycobilin levelis transferred directly from APC to pigment system II chlorophylla when the amount of the special form of APC is low. (Received October 24, 1979; )     

The effects of food deprivation, prey density and volume on clearance rates and ingestion rates of Diacyclops thomasi

The ingestion rates of the copepod, Diacyclops thomasi, on thesoft-bodied rotifer, Synchaeta pectinata, increased 10-fold(0.07–0.77 Synchaeta h^–1) over the range 50–250prey l^–1. The saturating functional response curve appearedsigmoid but was statistically indistinguishable from a parabola.The response curve was more linear and 10 times lower over thesame range of density when Diacyclops was offered Kerarellacochleans, a species having a stiffened lorica. Diacyclops maximizedits ingestion rate on Synchaeta as a function of the availablegut space. Predation effort, measured as clearance rates, waslinked tentatively to changes in swimming speed of Diacyclopsand was a function of hunger level. Diacyclops, which were starvedfor varying periods of time, increased their ingestion rateson Synchaeta up to a maximum (-3.0 h^–1) after 7–10h of food deprivation. The gut passage time of Diacyclops wasestimated to be 7–8 h. Therefore, ingestion rates (andclearance rates) appeared to be strongly correlated to the volumeof food in the gut.     

Pigment gut contents of copepods and deep phytoplankton maximum in the Western Mediterranean

The feeding activity of Centropages typicus in the Western Mediterraneanwas evaluated during the summer stratification period, whena deep phytoplankton and chlorophyll maximum (DCM) develops.The lack of significant day-night differences in gut contentssuggests continuous phytoplankton ingestion, despite nictemeralmigration of this species. Copepods captured in the DCM hadgreater phytoplankton gut contents, both in nocturnal and diurnalsamples. The observed pattern of phytoplankton ingestion andvertical migration implies copepod-mediated upward transportof nutrients, which might contribute to the maintenance of primaryproduction in the photic layers.     

Gut fluorescence in herbivorous copepods: an attempt to justify the method

Recently the gut fluorescence technique has been critisized because of the possible degradation of chlorophyll into nonfluorescent derivatives during passage through copepod guts and changes of the gut passage time with food concentration. Here pigment budgets have been calculated in 6 experiments with Calanus finmarchicus CIV caught 2 km offshore of the Murmansk Marine Biological Institute (the Barents Sea, Dalnije Zelentsi) in September 1992. Copepods were fed with culture of Platymonas viridis at different concentrations. Gut pigment and ingestion rate increased with food concentration in a similar way. On average between 78% and 89% of ingested chlorophyll was recovered in the guts and faecal pellets. No trend for a greater loss of fluorescence at low food concentration than at high was observed. Pigment content of faecal pellets incubated in filtered seawater decreased by 20–30% in the first 7–12 h and by up to 60% in 48 h. The decline of pigment content was accompanied by a rapid bacterial growth (by a factor of 3 in 48 h). Gut passage time increased with decreasing food concentration (from 40 min at 9 µg pigm l^–1 to 64 min at 0.9 µg pigm l^–1). These results together with some data by other authors suggest that the gut fluorescence method can be used to estimate in situ grazing rate providing gut passage time is measured properly and there are no losses of faecal material. However, careful consideration should be given to the previous feeding history of copepods.     

Copepod feeding behavior and the measurement of grazing rates in vivo and in vitro

In this paper some aspects of the use of the gut fluorescence method for estimating ingestion rates have been, examined. One assumption is that gut turnover time in feeding copepods is equal to the gut clearance time in filtered seawater. When arctic Pseudocalanus were pre-fed on Thalassiosira weisflogii, and then given a trace addition of the same C¹⁴-labelled culture, or were transferred to filtered seawater, results suggested that this assumption was probably justified. In another experiment in which Pseudocalanus were fed at the same concentration of either melted ice algae, or pelagic under ice algae, there were significant differences in both gut clearance times and gut pigment levels in the two cases.Pigment: biogenic silica ratios in epontic algae were higher than those in faecal pellets produced by Pseudocalanus feeding on the algae, suggesting that pigment destruction was occurring during grazing. In a 28 hr time course experiment ingestion rates determined by rate of disappearance of particulate chlorophyll were higher than those simultaneously determined by the gut fluorescence method, which also supports the idea of pigment destruction in copepods guts.     

Influence of phytoplankton composition and stratification degree on gut pigment content of Ceriodaphnia sp. at dawn

Very short-term feeding activity of the cladoceran Ceriodaphniasp. was investigated in situ in a eutrophic reservoir in thesouth of Spain, using fluorimetric analysis of the gut pigmentcontent in periods when the water column was relatively mixedor strongly stratified. The results obtained in the mixed watercolumn showed a clear increase in gut pigment content at dawn,a period sampled with high frequency. The accumulation of thecladoceran at the depth of maximum concentration of phytoplankton,and the high gut pigment concentration in cladocerans at thatdepth just after dawn, suggested active feeding of Ceriodaphniaon phytoplankton at that time. During stratification, the abundanceof Ceriodaphnia was higher, but the gut pigment contents werevery low and they did not reflect any clear feeding patterns,with either time or depth. Changes in phytoplankton concentrationand composition between the relatively mixed and the stratifiedwater column suggest a shift in feeding activity from herbivorousto.     

HPLC analysis of phytoplankton pigments from Lake Kinneret with special reference to the bloom-forming dinoflagellate Peridinium gatunense (Dinophyceae) and chlorophyll degradatio products

Photosynthetic pigments extracted from the paniculate materialof the water column of Lake Kinneret were studied throughoutthe periods of May 1988-June 1989, and November 1993-November1994, by means of HPLC. The temporal and vertical variationof the pigment suite found agreed with the microscopically determinedphytoplankton record. The regression calculations of taxon-specificbiomass with the corresponding signature pigments suggest thatpigment analysis may be a useful tool for the monitoring ofbloom-forming species, e.g. the dinoflagellate Peridinium gatunenseNygaard. The HPLC pigment analysis permitted the identificationand quantification of chlorophyll degradation products, providingfor the first time information about their composition in LakeKinneret. Chlorophyllide a was the major detectable degradationproduct of chlorophyll a, varying between 1 and 9% of the chlorophylla concentration. Other chlorophyll a derivatives appeared mostlyin minor quantities. Pheophytin a was virtually lacking in allthe samples. Removal rates of pigments, measured by sedimentationtraps, indicated that the degradation of chlorophyll a via chlorophyllidea is a dynamic process that continues during the sedimentationof the phytoplankton particles.     

Copepod feeding study in the upper layer of the tropical South China Sea

The South China Sea (SCS) is the world’s largest marginal sea being notable for vertical mixing at various scales resulting in a sequence of chemical and biological dynamics in surface waters. We investigated the ingestion, gut content, evacuation and clearance rates of copepods collected from six stations (including a South East Asia Time Series station) along a transect line in the tropical of a SCS cruise during September 27, 1999 to October 2, 1999. The goal of the present study was to understand the feeding ecology of copepods in the upper water layers (0–5 m) of the northern SCS during autumn. We measured the gut pigment contents of 33 copepod species by the gut fluorescence method. The gut chlorophyll a values of most small size copepods (<1 mm) were lower than 1.00 ng Chl a individual⁻¹. The highest gut pigment content was recorded in Scolecithrix danae (7.07 ng Chl a individual⁻¹). The gut pigment contents of 33 copepod species (including 70 samples and 1,290 individuals) estimated is negatively correlated with seawater temperature (Pearson correlation r = −0.292, P = 0.014) and is positively correlated with the chlorophyll a concentration of ambient waters (Pearson correlation r = 0.243, P = 0.043). Mean gut pigment content, ingestion and clearance rates (from 80 samples and 1,468 individuals) show that larger copepods (>2 mm) had significantly higher values than medium sized copepods (1–2 mm) and smaller sized copepods. The present study shows that the performance of feeding on phytoplankton was variable in different sized copepod groups, suggesting that copepods obtained in the tropical area of the southeastern Taiwan Strait might be opportunistic feeders.     

Estimation of phosphorus metabolic rates of Daphnia galeata using a three-compartment model

A compartment model to estimate the different phosphorus metabolicrates in Daphnia galeata is presented. The model has three compartments:gut, metabolic pool and structural pool. Existing two-compartmentmodels used for carbon and phosphorus turnover in Daphnia donot allow estimation of ingestion and egestion rates. We extendedexisting two-compartment models with one more compartment, thegut, which allowed us to estimate both the ingestion and theegestion rates. Parameters of the model are estimated from asingle experiment of feeding unlabelled Daphnia with ³²P-labelledScenedesmus obliquus. Separate experiments with juvenile andadult daphnids were carried out in order to compare their metabolisms.This model permits a reliable estimation of the different metabolicrates of Daphrna in a single experiment and discriminates clearlybetween animals of different sizes.     

Grazing experiments with two freshwater zooplankters:fate of chlorophyll and carotenoid pigments

In order to evaluate the validity of the gut pigment methodto assess grazing and diet in two freshwater zooplankters, experimentswere carried out to check chlorophyll a and xanthophyll conservationduring feeding. For both animals, two sets of experiments wereconducted by incubating animals in the laboratory, either isolatedfrom a reservoir (the calanoid copepod, Eudiaptomus gracilis)or cultured under high-food conditions (the cladoceran, Daphniagaleata). For both animals, gut pigments and clearance rateson different types of algae were determined from the same incubations.Chlorophyll a and derivatives, as well as major algal carotenoids,were analysed by High Performance Liquid Chromatography (HPLC).In copepods, the pigment profiles from the gut extracts reflectedthe diet of the animals poorly. The animal extracts containedalmost exclusively alloxanthin (or an alloxanthin-like pigment)in large amounts, whereas the other pigments were lost in highproportions (>70% for lutein and fucoxanthin; 57 and 78%for a-phorbins). The cladocerans fed on the main types of algaeabundant in the suspensions, with a preference, however, forsmall cells. Although the main xanthophylls from these algaewere detected in the Daphnia extracts, some destruction of luteinand fucoxanthin may have occurred (18.7 and 30%). The loss ratefor alloxanthin seemed more variable (0 and 68%), possibly dependingon food concentration. As for the transformation of a-phorbins,E.gracilis and D.galeata behaved quite differently. The HPLCprofiles of copepod extracts always showed a very small chlorophylla peak, along with phaeophytin a and pyrophaeophytin a. Thosefrom the cladoceran exhibited a large phaeophorbide a peak,along with some chlorophyll a and phaeophytin a. In fact, D.galeatadid not destroy a-phorbins under our experimental conditionsbut converted chlorophyll a mainly into phaeophorbide. Froma comparison of our results with data from other studies, itseems that in these two zooplankters, use of gut pigment datafor quantitative grazing assessment should be considered withcaution.     

Chlorophyll a conversion and gut passage time for the pelagic tunicate Oikopleura vanhoeffeni (Appendicularia)

We determined the chlorophyll (Chl) a conversion efficiency,defined as the conversion of Chi a into pheopigments and non-fluorescentproducts, for the cold-water appendicularian Oikopleura vanhoeffeniusing ⁶⁸Ge as conservative tracer. In both laboratory experimentsand in freshly collected animals, there was enough undegradedChi a present in the gut to provide an index of feeding activityfor individual animals. In laboratory experiments with diatoms,Chi a conversion efficiency was predictable with an averageof 79%. The mean gut passage time (0.8 h) determined using cornstarch and diatoms as markers was not influenced by food concentrationor animal size over a trunk length range of 1.8–5 mm.When experimentally determined Chi a conversion efficiency andgut passage times were applied to O.vanhoeffeni from Logy Bay(Newfoundland), the estimated clearance rates were in closeagreement with previously published values using several differenttechniques. We therefore suggest that the modified gut pigmenttechnique is a useful tool to assess in situ ingestion ratesof O.vanhoeffeni.     

Gut pigment destruction by the copepod Acartia clausi

The extent of chlorophyll (Chi) a degradation into colorlessproducts by the copepod Acartia clausi was determined by measuringgut fluorescence prior to fecal pellet production. The efficiencyof pigment degradation of animals fed at different concentrationsof Thalassiosira weiss-fiogii varied between 30.56 and 94.05%,and the quantity of pigments lost during gut passage was directlyrelated to total ingestion. The role of feeding history in pigmentdestruction was tested. The fraction of ingested Chi a degradedby copepods acclimated to a high food concentration (15 ng Chla ml^–1) was greater than the fraction degraded by thoseacclimated to a low food concentration (1.5 ng Chl a ml^–1).The percentage of ingested Chl a that A.clausi transformed intofluorometrically undetected compounds was not constant. At present,knowledge of the pigment destruction process indicates thatChi a and Chi --derived pigments are not considered useful quantitativetracers of the feeding activity of copepods. The results ofthis study suggest a reassessment of the application of thegut fluorescence method to evaluate grazing activity of thecopepod A.clausi     

Further Investigations of Liposoluble Fluorescent Compounds in Senescing Plant Cells

The accumulation of liposoluble fluorescent compounds with excitationand emission fluorescent maxima in the bands of 350–370nm and 410–440 nm respectively has been observed in thedegrading (the late stationary phase) blue-green algae Anabaenavariabilis K?tz and Anabaena cylindrica Lemm. cells, in thedark-senescing cotyledons from Phaseolus vulgaris L., and inmore than 1-year-old leaves of evergreen plants (Ligustrum japonicumThunb. and Osmanthus fortunei Carr.)- Spectral and chromatographicproperties of the compounds are rather similar to those previouslydescribed in the cells of other senescing plant species. Therole of lipid peroxidation in the formation of fluorescent pigmentsand in the ageing of plant cells is discussed. Key words: Fluorescent pigment, Anabaena sp, Senescence