Across-shelf predatory effect of Pleurobrachia bachei (Ctenophora) on the small-copepod community in the coastal upwelling zone off northern Chile (23{degrees} S)

To estimate the predation effect of the predominant ctenophorePleurobrachia bachei on the small-copepod community in the upwellingarea off Mejillones (23°S), northern Chile, a series ofoceanographic cruises and predation experiments were conductedin the austral springs 2000, 2001 and 2002. The daily consumptionrates and predatory effect of P. bachei on the small copepods(in terms of % of standing stock and biomass removed daily)were determined at three stations located in relation to theshelf-break (coastal, shelf-break and oceanic) reaching valuesup to 4.5% per day of the <1500 µm copepod standingstock. Our results indicate that the ctenophores were most abundantat the coastal station, that small copepods dominated the copepodcommunity (being more abundant nearshore), and that the relativefrequency of ctenophores with copepods in their guts was alsohigher near the coast. The predatory effect of P. bachei onthe small-copepod community was also higher in the coastal zone.However, the effect of this predation on the copepod biomassin terms of carbon did not decrease steadily seawards, whichmay be due to the larger sized copepods consumed at the offshorestations. Determinations of predatory effect on the secondaryproduction of the more abundant small-copepod populations (i.e26% daily in 2000) suggest that this single species of Pleurobrachiais modulating the population growth rate of the small copepods,the copepod community size structure, and maybe even the alternanceof key species in the Mejillones coastal upwelling zone.     

Grazing of copepod assemblages in the north-east Atlantic: the importance of the small size fraction

The North Atlantic was the site for the 1989 JGOFS Pilot Study,an international study of ocean fluxes in relation to the carboncycle. In this paper we present preliminary estimates of thegrazing pressure by copepod assemblages at four stations 60,56, 52 and 47°N, along the JGOFS 20°W transect, duringJune–July. Three major size fractions of mesoplanktoniccopepods were considered, small (200–500 µm), medium(500–1000 µm) and large (1000–2000 µm).At each station, copepod composition and abundance were analysedand the gut fluorescence method was used to estimate ingestionrates. The results support the importance of the small sizefraction relative to the other fractions, in terms of numericalabundance and their grazing impact. However, the total grazingpressure of copepods on phytoplankton was relatively minor duringthe period of sampling since the fraction of phytoplankton standingstock and primary production consumed by the copepods was onaverage <1 and 2% respectively. The implications of theseresults as well as the potential sources of bias involved inthese types of measurements and estimations are discussed.     

The importance of protozooplankton as prey for copepods in the coastal areas of the central Irish Sea

This study evaluates food supply for copepods, highlighting the trophic relationship between copepods and protozooplankton. To test the hypotheses that protozooplankton prey are capable of sustaining the copepod standing stock in the western Irish Sea, the taxonomic and size composition of these two groups and the size-specific predation of copepods on protozooplankton were investigated. Protozooplankton and copepod samples were collected off the southwest coast of the Isle of Man using 1.7 l Niskin water bottles and two nets (64 and 280 μm meshes), respectively. Copepod predation on protozooplankton was calculated using weight-specific clearance rates from the literature, considering the availability of prey that was accessible to a given size of copepod. Low protozooplankton biomass was dominated by small cells (<60 μm), and high copepod biomass was dominated by small species, which were more efficiently collected by a 64-μm mesh net. However, large copepods were only collected by a 280-μm mesh net, suggesting that the combination of the two nets provided a better estimate of copepod biomass. Predation by the copepod assemblage in the Irish Sea removed 1–47% and 0.5–22% of ciliates and dinoflagellates standing stock, respectively, resulting in 1–40% of the copepod feeding requirement per day. Contrary to our hypothesis, copepods could not meet their feeding requirements by grazing only on the microzooplankton prey (15–200 μm), and other food sources (i.e. nanoplankton) must be important additional dietary components to copepods in the Irish Sea. Handling editor: S. M. Thomaz     

Zooplankton Community During the Transition from Spring Bloom to Oligotrophy in the Open NW Mediterranean and Effects of Wind Events. 2. Vertical Distributions and Migrations

Vertical distribution of zooplankton was investigated over a3-week period at a fixed station in the open NW Mediterraneanduring the DYNAPROC cruise (May 1995). The observational periodcoincided with the transition from spring bloom to oligotrophyin this area. Vertical distribution and migration in the 0–1000m water column are described in detail for the main speciesof copepods (>500 µm). Ontogenetic migration is reportedfor Neocalanus gracilis, Euchaeta acuta and Pleuromamma abdominalis.This study also documented the downwards seasonal migrationof Calanus helgolandicus. Short-term changes in the verticaldistribution of the small-sized organisms (>50 µm)in the upper 100 m are discussed in relation to the two majorwind events that occurred during the cruise. The naupliar stagesof copepods and euphausiids appeared unable to counter the upwardsvertical advection and the wind-induced mixing, while no markedchanges were observed for Oithona spp. and Microsetella spp.     

Contribution of nanoprotists to metazooplankton diet in a mesocosm experiment in the coastal northern Baltic

Grazing by a metazooplankton community on nanoprotists <10µm was studied four times during a 21 day enclosure experimentcarried out off the SW coast of Finland in late summer. Duringthe study, the pelagic community was manipulated through nutrientenrichment (N + P) and through predation by stickleback fry.Grazing experiments were conducted in the laboratory using 5µm prefiltered, ³H-labelled nanoplankton as tracer food. Grazing by mesozooplankton (Meso) and metazaan microplankton(Micro), screened through 140 and 100 µm mesh, was studied.Owing to enrichment effects and weak predation control by fish,the biomass of Meso and Micro increased during the study peridMeso biomass consisted mostly of the copepod Eurytemora affinisand the cladoceran Bosmina longispims maritima, and Micro biomassof copepod nauplii NIII–NVI. The community clearance rateof Meso usually exceeded that of Micro when feeding on nanoprotistsThe opposite was found for the biomass-smc clearance rate, revealingnanoprotists to be a more important f d source for Micro thanfor Meso. Metazmplankton were not able to control nanoprotists,because Meso and Micro were estimated to remove on average 4and 2% of nanoprotowan biomass daily. When integrated throughthe study period, grazing on nanoprotists could meet 5 and 17%of the carbon need for Meso and Micro, 3 and 12% of their productionbeing estimated to consist of bacterial carbon transferred bynanoprotists Micro were estimated to be more closely Linkedto the microbial food web than Meso, suggesting that the trophicpusition of copepods changes slightly during their maturationfrom nauphi to larger copepodites. ¹ Present address: Department of Ecology and Systematics, Divkionof Hydrobiology, University of Helsinki, FIN-00014, Helsinki,Finland     

Vertical distribution of protozoan and microcopepod communities in the South Adriatic Pit

The qualitative composition, numerical abundance and verticaldistribution of radiolarians, tintinnines, nauplii and smallcopepod assemblages were studied in the central area of theSouthern Adriatic Pit at three stations during 10 cruises fromOctober 1985 to May 1990. The samples were collected with aplankton net of 53 µm mesh size equipped with a closingsystem in eight vertical layers. Data are presented for 53 radiolarians,61tintinnines and for the first time for 22 poecilostomatoidspecies in the Adriatic Sea. According to the numerical abundanceof assemblages and the frequency of occurrence of the bulk ofthe individual species population in the water column, fourcommunities could be defined: the surface (0–50 m), thesubsurface (50–100m), the midwater (100–600 m) andthe deep-sea community (below 600 m). The euphotic layer wascharacterized by tintinnines, copepod nauplii, cyclopoids andjuvenile calanoid copepods, while radiolarians and poecilostomatoidcopepods dominated in the deeper layers. The highest numericaldifferences between stations and seasons were noted only onthe surface. Towards the deeper layers, the differences wereconstantly smaller, and below400 m there was a uniform distributionof all assemblages. This research, on the basis of the numericalabundance of protozoans and micrometazoans, shows that the centralpart of the South Adriatic Pit is considerably richer than mentionedby earlier authors.     

Vertical distributions of zooplankton across the Almeria-Oran frontal zone (Mediterranean Sea)

The vertical distribution of zooplankton in the upper 700 mof the water column was investigated across the Almeria–Oranfront (Alboran Sea) during winter 1997/98 (Almofront 2 cruise).Eight sites corresponding to three hydrodynamic structures (theAtlantic jet, an anticyclonic gyre and the surrounding Mediterraneanwaters) were explored, by day and at night, using multiple-netsampling. Results are presented for the major species of copepods(>500 µm), macroplankton and microplankton. Speciesinhabiting the surface layer or occupying it at night extendeddeeper in the gyre. On the other hand, mesopelagic species (e.g.Pleuromamma borealis, Pleuromamma abdominalis, Euphausia krohniand Cyclothone braueri) were found to live deeper, at leastby day for the migrants, in the Mediterranean waters comparedwith the two other structures. These changes in preferentialdepths across the front are discussed in relation to environmentalfeatures, such as light level, abundance of food and mixed layerdepth. This study also documented the vertical distributionof some overwintering copepod species (Calanus helgolandicus,Eucalanus hyalinus and Eucalanus monachus).     

Zooplankton species composition is linked to ocean transport in the Northern California Current

In the Northern California Current (NCC), zooplankton communities show interannual and multiyear shifts in species dominance that are tracked by survival of salmon populations. These zooplankton community changes correlate with the Pacific Decadal Oscillation (PDO) index: a ‘warm‐water’ copepod species group is more abundant during warm (positive) phases of the PDO and less abundant during cold (negative) phases; the reverse occurs for a ‘cold‐water’ species group. The observed relationship led to the hypothesis that the relative dominance of warm/cold‐water copepods in the NCC is driven by changes in the horizontal advection of surface water over different phases of the PDO. To test this hypothesis, variation in surface water advection to coastal regions of the NCC over the period of 1950–2008 was investigated using a Regional Ocean Modeling System (ROMS) and passive tracer experiments, then was compared with zooplankton collected off Oregon since 1996. Results showed that surface water advection varied with the phase of the PDO; the low‐frequency component of advection anomalies strongly correlated with copepod species composition (R>0.9). During positive phases of the PDO, current anomalies were northward and onshore, resulting in transport of warmer waters and the associated copepods into the region. During negatives phases, increased equatorward current anomalies led to a copepod community that was dominated by cold‐water taxa. Our results support the hypothesis that climate‐driven changes in basin‐scale circulation controls copepod community composition in the NCC, and demonstrate that large‐scale climate forcings downscale to influence local and regional ecosystem structure.     

Copepod grazing impact on the trophic structure of the microbial assemblage of the San Pedro Channel, California

In August 2002 and March 2003 the trophic structure of the microbialassemblage from the San Pedro Channel, California was studiedfollowing the experimental alteration of the number of copepods.Changes in the abundance/biomass of microorganisms <80 µmduring 3-day incubations were monitored in (i) the absence ofmetazoa >80 µm, (ii) the presence of natural abundancesof metazoa and (iii) the presence of an elevated number of copepods.Prokaryotes and small-sized eukaryotes (<4 µm) dominatedplankton biomass during both experimental months. Diatoms numericallydominated the 10–80 µm plankton in August 2002,but ciliate and heterotrophic dinoflagellate biomass generallyexceeded diatom biomass on both dates. Ingestion of protozooplankton(predominantly ciliates) contributed substantially to copepoddaily carbon rations. The adult copepod assemblage removed 4.6and 36% per day of the microzooplankton standing stocks (10–80µm size fraction) in August and March, respectively. Elevatedcopepod grazing pressure on protozooplankton resulted in increasedbiomass of nanoplankton (<5 µm) presumably via a trophiccascade. Accordingly, the copepod–protozoan trophic linkappears to be a key factor structuring the planktonic microbialassemblage in the San Pedro Channel. This paper is one of six on the subject of the role of zooplanktonpredator–prey interactions in structuring plankton communities.     

Copepod communities off Franz Josef Land (northern Barents Sea) in late summer of 2006 and 2007

Copepods are considered to be the main component of the Arctic marine zooplankton. We examined the copepod distribution and diversity off Franz Josef Land (northern Barents Sea) in August 2006 and 2007. A total of 18 and 14 copepod taxa were identified from the sampling layers (100–0 m or bottom–0 m) in 2006 and in 2007, respectively. There were no significant differences in the total copepod abundance between the years (means ± SE: 118,503 ± 24,115 individuals m⁻² in 2006 vs. 113,932 ± 28,564 individuals m⁻² in 2007). However, the copepod biomass in 2006 (4,518 ± 1,091 mg C m⁻²) exceeded clearly the value in 2007 (1,253 ± 217 mg C m⁻²). The copepod community showed low species richness and diversity in both years (Simpson index D: 0.34 and 0.38, respectively). Biomass of the large and small copepod species strongly decreased from 2006 to 2007. The total abundance of copepods was negatively correlated with water temperature in 2006 and positively correlated with salinity in 2007. The patchiness in copepod distribution was associated with local hydrography and temperature conditions.     

Seasonal variation and longitudinal distribution of copepods in the main river area of the Three Gorges Reservoir

The ecosystem of the Three Gorges in the Yangtze River was changed into an artificial lake (reservoir) ecosystem after impoundment in June 2003. We surveyed the seasonal variation and spatial distribution of copepods from April 2004 to January 2005 in order to provide data for clarifying the successional pattern of the ecosystem. From Jiangjin to Maoping, eight copepod species were collected and classified into Calanoida (2), Harpacticoida (1), and Cyclopoida (5). Among them, Mesocyclops pehpeiensis, M. leuckarti and Sinocalanus dorrii had a relatively wide distribution. No distinct difference in species number was found among the sampling sites, but the species composition was different. Species composition, distribution and density of copepods showed significant seasonal variations. In addition, copepod density showed an obvious gradient with the distance from the reservoir dam: the nearer to the dam, the denser the copepods. __________ Translated from Biodiversity Science Sinica, 2007, 15(3): 300–305 [译自: 生物多样性]     

The seasonal abundance and production of Oithona nana (Copepoda:Cyclopoida) in Southampton Water

Recent studies indicate that Oithona spp. contribute significantlyto total copepod biomass. Little is known, however, about theirecological significance, particularly in the case of the estuarineOithona nana. A study comprising three sites within SouthamptonWater was conducted to evaluate the late-stage copepodite/adult(stages IV–VI) O. nana community, using 120-µm meshnets. Although present throughout the estuary, there was a strikingspatial gradient with O. nana most common in the upper estuary.A clear seasonal pattern was observed with O. nana as the mostabundant copepod species from late summer until early winter.It comprised 61% of all copepods recorded, with a biomass of757.22 mg C m^–3. Production estimates of O. nana werederived from the ‘instantaneous-growth’ approach,using appropriate growth equations. The estimated productionof O. nana ranged from 1.50 mg C m^–3 year^–1 withinthe lower estuary to 146.77 mg C m^–3 year^–1 in theupper estuary. In the upper estuary, this compares with productionrates of 187.47 mg C m^–3 year^–1 for all Acartiacongeners (excluding nauplii), the most common calanoid genus.Throughout the estuary, O. nana annual production represented18% of total copepod production clearly indicating that, atleast in the upper estuary, O. nana production may be directlycomparable with calanoid production.     

Weak 'top-down' control of dinoflagellate growth in the coastal Skagerrak

Effects of planktivorous fish (Sprattus sprartus), copepods(mainly Oithona sp.) and benthic filter feeders (Mytilus edulis)on the biomass and species composition of a natural marine planktoncommunity, dominated by dinoflagellates, was studied experimentallyin September 1988. Plastic 300 I cylinders were filled withSkagerrak surface water, filtered through a 90 µm nylonnet in order to remove mesozooplankton. Copepods were addedin three different concentrations (0, 1x and 6x the ambientdensity) with and without nutrient additions (nitrate, silicateand phosphate). In two nutrient-enriched cylinders with addedcopepods (1x and 6x), 5 cm sprats were also added (10 per cylinder).In two nutrient-enriched cylinders without added copepods. bluemussels (20 per cylinder. 3 cm length) were introduced. Chlorophylla. inorganic nutrients and densities of phytoplankton, ciliatesand copepods were measured throughout the experimental periodof 10 days. Gyrodinium aureolum increased in cell numbers inall but the mussel cylinders, while the other dominating dinoflagellate,Ceratium furca, decreased. This decrease was not due to grazing,but probably a container artefact. Diatoms, Rhizosolenia fragilissinia,Leptocylindrus danicus and Chaetoceros spp., increased slowlyin treatments without fish. In the fish treatments, diatomshad appreciably higher growth rates and cell numbers, probablydue to predation by fish on the copepods. Gyrodiniun aureolunalso had a somewhat higher growth rate in the presence of fish.although this was probably not due to reduction of copepod grazing.The results show that planktivorous fish can affect the biomassand species composition of natural phytoplankton communitiesin marine waters, but that the effect on the late summer-autumndinoflagellate dominated community is weak. Blue mussels areefficient grazers of the whole phytoplankton community and arenot particularly selective with respect to either size or species.     

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.     

Copepod community structure and abundance in a tropical mangrove estuary,with comparisons to coastal waters

Zooplankton, sampled at five stations from the upper Sangga estuary (7 km upstream) in Matang Mangrove Forest Reserve (MMFR), Malaysia, to 16 km offshore, comprised more than 47% copepod. Copepod abundance was highest at nearshore waters (20,311 ind m⁻³), but decreased toward both upstream (15,572 ind m⁻³) and offshore waters (12,330 ind m⁻³). Copepod abundance was also higher during the wetter NE monsoon period as compared to the drier SW monsoon period, but vice versa for copepod species diversity. Redundancy analysis (RDA) shows that copepod community structure in the upper estuary, nearshore and offshore waters differed, being influenced by spatial and seasonal variations in environmental conditions. The copepods could generally be grouped into estuarine species (dominantly Acartia spinicauda Mori, Acartia sp1, Oithona aruensis Früchtl, and Oithona dissimilis Lindberg), stenohaline species (Acartia erythraea Giesbrecht, Acrocalanus gibber Giesbrecht, Paracalanus aculateus Giesbrecht, and Corycaeus andrewsi Farran) and euryhaline species (Parvocalanus crassirostris Dahl, Oithona simplex Farran, and Bestiolina similis (Sewell)). Shifts in copepod community structure due to monsoonal effects on water parameters occurred at the lower estuary. Copepod peak abundance in mangrove waters could be associated with the peak chlorophyll a concentration prior to it. Evidence of copepod consumption by many species of young fish and shrimp larvae in the MMFR estuary implies the considerable impact of phytoplankton and microphytobenthos on mangrove trophodynamics.     

Annual Zooplankton Succession in Coastal NW Mediterranean Waters: The Importance of the Smaller Size Fractions

Zooplankton abundance, biomass (biovolume) and taxonomic compositionwere studied within an annual cycle (August 1995–October1996) in the Bay of Blanes (northwest Mediterranean). Weeklyzooplankton sampling included oblique tows made with a 200 µmJuday–Bogorov net, and vertical tows made with a 53 µmnet, to adequately sample both mesoplankton and the smallerzooplankton fractions. Total zooplankton abundance showed highvariability, lacking any clear seasonal pattern. However, thedifferent species within the zooplankton community displayeda clear succession throughout the year. In general, cyclopoidcopepods (Oithona spp.) and cladocerans (Peniliaavirostris)dominated the summer and autumn communities, whereas in winterand spring, calanoid copepods (Clausocalanus spp., Paracalanussp. and Centropages typicus) were predominant. The zooplanktonannual cycle in the Bay of Blanes does not resemble those ofother Mediterraneanlittoral areas, probably due to the inherentparticularity and variability associated with open coastal environments.On average, the abundance of organisms estimated with a traditional200 µm Juday–Bogorov net was 8.1 times lower thanthe values obtained with a 53 µm net. Even if only organisms>200 µm collected in the 53 µm tows were considered,the total abundance within the 53 µm net was still 4.4times higher than the estimates from the Juday–Bogorovnet. These results suggest the need for accurate samplings ofthe entire zooplankton assemblage when characterizing the structureand dynamics of zooplanktonic communities.     

Transition zones in small lakes: the importance of dilution and biological uptake on lake-wide heterogeneity

Community structure and diversity patterns of pelagic copepods were investigated for the coastal areas and in the marine lakes of the Palau islands in the West Pacific. We conducted field surveys during 2004–2007 and collected zooplankton samples from eight coastal areas and 16 marine lakes. The marine lakes in the islands of Palau are limnologically classified into two types, meromictic and holomictic lakes. Species diversity indices (Margalef’s species richness d′, Shannon–Wiener index H′, and Simpson’s dominance) were measured at each sampling site. The copepod community structure was analyzed using multivariate analyses, hierarchical cluster analysis, and non-metric multidimensional scaling (MDS) from the PRIMER package. A total of 36 copepod taxa were identified to the genus or species level from Calanoida, Cyclopoida, Harpacticoida, and Poecilostomatoida. Multivariate analysis based on the Bray–Curtis similarity index revealed that copepod assemblages could be classified into three different groups according to their habitat: (I) meromictic lakes, (II) holomictic lakes with an exceptionally shallow and flat basin (type A holomictic lakes), (III) holomictic lakes with a deep basin (type B holomictic lakes), and all coastal areas. The meromictic lakes were characterized by markedly decreased species diversity (d′ = 0.15, H′ = 0.41) in which only two brackish-water species, Bestiolina similis and Oithona dissimilis, were dominant. Type A holomictic lakes were characterized by relatively low levels of species diversity (d′ = 1.25, H′ = 1.35). In contrast, type B holomictic lakes were characterized by relatively high levels of species diversity, which was comparable to that of coastal areas. This result indicated that zooplankton assemblages in the type B holomictic lakes were closely related to a coastal community. The present study showed that the species diversity of pelagic copepods varies according to the level of isolation and the local environmental conditions for each marine lake.     

Seasonal variations in copepod size: effects of temperature, food abundance, and vertebrate predation

Seasonal dry weights of female and male Cyclops bicuspidatusthomasi, Diaptomus ashlandi and Diaptomus minutus were studiedin southeastern Lake Michigan during 1975–1981. Smallestanimals occurred during summer and early fall, and largest animalsin winter and spring, a pattern reported for other copepods.The range of weights for the species and sexes decreased fromwinter to summer, and converged in summer to a value of approximately2 µg/animal. Surface water temperature and abundancesof young-of-the-year (YOY) fish were inversely correlated withweights of males and females of the three copepod species. Standingstocks of important phytoplankton groups, especially pennatediatoms and flagellates, were positively correlated with copepodweight. Seasonal change of copepod body size appears to be morethan simply a function of temperature; seasonal predation byYOY fish may be a factor influencing sizes of adult copepods.     

Trophodynamics of the plankton community at Dogger Bank: predatory impact by larval fish

The trophodynamics of a coastal plankton community were studied,focusing on fish larvae and their copepod prey. The major objectiveswere to describe distributional overlap and evaluate the predatoryimpact by larval fish. The study was carried out across DoggerBank in the North Sea, August-September 1991. Sampling transectscrossed tidal fronts off the Bank and plankton at all trophiclevels showed peak abundance within frontal zones. Also Verticallythere was a significant overlap in distributional patterns ofthe plankton. Seven species of fish larvae were abundant, ofthese sprat (Sprattus sprattus) dominated. The abundance ofone group of fish larvae peaked in the shallow water close tothe Bank, whereas other species, including sprat, were foundin deeper water. Prey preference and predation pressure of fishlarvae were assessed using information on prey sizes and growthrates of larvae and the copepod prey. We estimated larval removalof preferred prey sizes to 3–4% day^–1, counterbalancedby a 3–7% day^–1' replenishment from copepod productionand growth. Additional predation pressure on copepods by aninvertebrate predator was estimated to 1–3%day^–1.In conclusion, the dynamics of fish larvae and other zooplankterswere closely linked. At peak abundances of fish larvae (>35mg dry weight m^–2), the accumulated predation on specificsize ranges of copepods, exerted by larvae and other predators,could exceed the ability of copepod replenishment and intra-/interspecificcompetition among predators might take place.     

Vertical distribution of subtropical epiplanktonic copepods

The goal of our project is to increase our knowledge about theco-existence of the numerous small copepod species in the subtropicaland tropical open oceans by combining experimental and fieldstudies. In this paper we present the vertical distributionof the copepod assemblages collected in the upper 100 m of thewater column during a diel cycle at an oceanic site off Bermudain summer 2000. Our quantitative analysis ranged from the grossfeatures of the community to order, genus, species and sex,ending with the population structure for one representativecalanoid (Mecynocera clausii). Total abundance of copepods sampledwith both 63 and 200 µm meshes increased from near thesurface to 100 m depth. Of the four orders, the Calanoida andCyclopoida increased slightly with depth, whereas the Poecilostomatoidahardly occurred in the upper 30 m and then increased by morethan one order of magnitude towards 100 m depth. Harpacticoidashowed even abundance through the vertical column during thenight. Some abundant genera/species displayed hardly any orsmall differences in abundance over the upper 100 m (e.g. Calocalanus,Oithona); that distribution also showed that genera with entirelydifferent motion and feeding behaviour can occupy the same verticalenvironment. A second group appeared to avoid the upper mixedlayer and upper thermocline almost completely (e.g. Oncaea,Mecynocera clausii, Clausocalanus pergens, Eucalanus hyalinus,Haloptilus longicornis). A third limited group seemed to preferthe upper mixed layer (e.g. Clausocalanus furcatus). Some generawere characterized by a paucity of males whereas others hadas many males as females. Our results showed that quantifyingthe distribution and abundance of genera, species and theircopepodid stages seems to be the preferable approach, leadingtowards an understanding of the functioning of the epipelagialcopepod community. We hypothesize that a combination of variables,including feeding behaviour, temperature preference and alsopredation, could determine the ranges of vertical distribution,which would be flexible because of the effect of each of thevariables. It is reasoned that predation was of minor impactin these oligotrophic waters because of the very low abundanceof carnivorous species.