Copepod Prey Research Articles

Nutritional Status and Diet Composition Affect the Value of Diatoms as Copepod Prey

The role of diatoms as key food for copepods at the base of pelagic food chains has been questioned recently on the grounds of toxicity. We show, using unialgal versus mixed algal diets of different nutritional status (i.e., nitrogen:carbon ratio) fed to Acartia tonsa, that diatoms per se are not toxic but that single-diatom diets are inadequate. Additionally, the nutritional state of the phytoplankton has a profound effect on copepod growth and growth efficiency. The ecological significance of laboratory demonstrations of diatom toxicity needs to be reconsidered.

Summer and fall habitat of North Atlantic right whales (Eubalaena glacialis) inferred from satellite telemetry

Satellite-monitored radio tags were attached to North Atlantic right whales (Eubalaena glacialis) in Grand Manan Basin of the lower Bay of Fundy during the summer and early fall seasons of 1989–1991 and 2000. Monte Carlo tests were used to examine the distribution of the tagged whales in space and time and with respect to a variety of environmental variables to characterize right whale habitat on their northern feeding grounds. These environmental variables included depth, depth gradient, climatological surface and bottom hydrographic properties, and remotely sensed surface temperature, chlorophyll concentration, and their respective horizontal gradients. Site fidelity in the Bay of Fundy was very low during 1989–1991 and high during 2000. When the tagged animals left the Bay, they did not frequently visit the deep basins of the Gulf of Maine and Scotian Shelf, where abundances of their primary copepod prey, Calanus finmarchicus, are thought to be high. Instead, right whales visited areas characterized by low bottom water temperatures, high surface salinity, and high surface stratification. No evidence was found that the tagged right whales associated with oceanic fronts or regions with high standing stocks of phytoplankton.

Diet of the chaetognaths Sagitta setosa and S. elegans in relation to prey abundance and vertical distribution

The chaetognaths Sagitta setosa and S. elegans and their potential prey organisms were collected from 6 different depth strata on 6 day and night occasions in the Gullmar fjord, west Sweden. The chaetognaths were analysed for gut contents and predation impact estimated. Number of prey per chaetognath (NPC) ranged from 0.2 to 1.0 for S. setosa and 0.4 to 0.9 for S. elegans, with significantly higher values at night. For S. setosa, small copepods dominated gut contents, with the addition of the appendicularian Oikopleura dioica and chaetognaths later in the season. For S. elegans, the great majority of prey were Calanus copepodites. Predation impact was strong on single copepod species, increasing from 0.4 to a maximum of 48 % of the individuals removed daily by S. setosa at the end of October. S. elegans consumed 5 to 18 % of the deeper dwelling Calan us community daily. Cannibalism was pronounced in S. setosa; in October, 74 to 84 % of the population could potentially be removed each day, Selective feeding was observed in S. setosa by estimating clearance rates for different prey. Pseudocalanus sp. was over-represented in the guts (clearance 120 ml ind.(-1) d(-1)) as well as S, setosa (124 ml ind.(-1) d(-1)) and Paracalanus parvus (40 ml ind.(-1) d(-1)). S. setosa was able to maintain a daily ration of 11 to 17 % of body weight despite a rapid decline in copepod prey abundance, and this was possible through cannibalism and intense predation on O. dioica.

Distribution and transport of bay anchovy ( Anchoa mitchilli) eggs and larvae in Chesapeake Bay

Mechanisms and processes that influence small-scale depth distribution and dispersal of bay anchovy ( Anchoa mitchilli) early-life stages are linked to physical and biological conditions and to larval developmental stage. A combination of fixed-station sampling, an axial abundance survey, and environmental monitoring data was used to determine how wind, currents, time of day, physics, developmental stage, and prey and predator abundances interacted to affect the distribution and potential transport of eggs and larvae. Wind-forced circulation patterns altered the depth-specific physical conditions at a fixed station and significantly influenced organism distributions and potential transport. The pycnocline was an important physical feature that structured the depth distribution of the planktonic community: most bay anchovy early-life stages (77%), ctenophores (72%), copepod nauplii (>76%), and Acartia tonsa copepodites (69%) occurred above it. In contrast, 90% of sciaenid eggs, tentatively weakfish ( Cynoscion regalis), were found below the pycnocline in waters where dissolved oxygen concentrations were <2.0 mg l −1. The day–night cycle also influenced organism abundances and distributions. Observed diel periodicity in concentrations of bay anchovy and sciaenid eggs, and of bay anchovy larvae >6 mm, probably were consequences of nighttime spawning (eggs) and net evasion during the day (larvae). Diel periodicity in bay anchovy swimbladder inflation also was observed, indicating that larvae apparently migrate to surface waters at dusk to fill their swimbladders. Overall results suggest that wind-forced circulation patterns, below-pycnocline dissolved oxygen conditions, and diel changes in vertical distribution of larvae and their copepod prey have important implications for potential transport of bay anchovy early-life stages.

Functional response and potential predatory impact of Tortanus dextrilobatus, a carnivorous copepod recently introduced to the San Francisco Estuary

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 277:167-179 (2004) - doi:10.3354/meps277167 Functional response and potential predatory impact of Tortanus dextrilobatus, a carnivorous copepod recently introduced to the San Francisco Estuary Rian C. Hooff1,2,*, Stephen M. Bollens1,3 1Romberg Tiburon Center for Environmental Studies and Department of Biology, San Francisco State University, 3150 Paradise Drive, Tiburon, California 94920, USA 2Present address: Hatfield Marine Science Center, Oregon State University, 2030 SE Marine Science Drive, Newport, Oregon 97365, USA 3Present address: School of Biological Sciences, Washington State University Vancouver, 14204 NE Salmon Creek Avenue, Vancouver, Washington 98686, USA *Email: rian.hooff@oregonstate.edu ABSTRACT: Despite a dramatic increase in the introduction of non-indigenous estuarine zooplankton in recent decades, the trophic implications of such introductions have rarely been quantified. Here we investigate predation rates of Tortanus dextrilobatus, a carnivorous copepod recently introduced to the San Francisco Estuary that achieves peak abundances in excess of 1000 ind. m-3. The functional response of T. dextrilobatus feeding upon 2 copepod prey types‹the non-indigenous cyclopoid Oithona davisae, and the Œnative¹ calanoid Acartia (Acartiura) sp.‹was described by a type II functional response (Ivlev function) at 2 experimental temperatures. In 3 of these 4 treatments, 90% Imax was achieved within a naturally occurring range of prey densities. Taxon-specific seasonal size variation was identified, and carbon-based consumption values were used to determine temperature-dependent rates of predation on both prey types. These empirically derived consumption rates and temperature dependence values were then applied to broadscale surveys (1997 to 1999) of zooplankton community composition in order to estimate the predatory impact of T. dextrilobatus upon prey populations in the San Francisco Estuary. Predatory impact estimates (% population consumed d-1) greater than 1% occurred on a regular basis when T. dextrilobatus was abundant, with maxima exceeding 20, 65, and 25% for O. davisae, Acartia (Acartiura) sp. and all Copepoda, respectively. These observations support the hypothesis that non-indigenous invertebrate zooplanktivores can play a significant role, at least seasonally or episodically, in the secondary production dynamics of aquatic ecosystems. KEY WORDS: Zooplankton ecology · Feeding · Predation · Copepods · Tortanus dextrilobatus · Non-indigenous · Invasion · San Francisco Estuary Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 277. Online publication date: August 16, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

Behavioral adaptations of the cubozoan medusa Tripedalia cystophora for feeding on copepod (Dioithona oculata) swarms

The cubozoan medusa Tripedalia cystophora preys on dense swarms of the copepod Dioithona oculata in the mangrove prop-root habitat of Puerto Rico. The copepod swarms form in shafts of sunlight that penetrate the mangrove canopy during the day. T. cystophora are found primarily within the same illuminated areas, feeding heavily on the dense swarms of copepods. Laboratory studies were conducted to examine the behavioral adaptations of T. cystophora that allow them to remain within these dense copepod swarms. In the presence of vertical light shafts, T. cystophora showed both a significant change in swimming speed and a significant increase in turning rate. T. cystophora turn abruptly when they leave a vertical shaft of light and quickly re-enter. The presence or absence of copepod prey, either in swarms or dispersed, had no significant effect on T. cystophora swimming speed or turning behavior. Feeding rates of T. cystophora on the copepod D. oculata increase rapidly with copepod density, and maximum rates are not achieved until the high densities associated with swarms are reached. It seems doubtful that these small medusae could survive without their ability to encounter and exploit these dense swarms of copepods.

Associations between North Atlantic right whales and their prey, Calanus finmarchicus, over diel and tidal time scales

Temporal variability in the distribution and abundance of North Atlantic right whales Eubalaena glacialis and their copepod prey, late-stage Calanus finmarchicus, was monitored at an oceanographic station in Grand Manan Basin of the lower Bay of Fundy for 29 h on 2 separate occa- sions. The vertical distribution of C. finmarchicus was measured at 1 /2 h intervals with an optical plankton counter (OPC) and at 6 or 12 h intervals with a MOCNESS. Right whale abundance was estimated from periodic point scans. Late-stage C. finmarchicus exhibited diel vertical migration in the upper 100 m of the water column, but the bulk of the population remained at depths below 100 m throughout both the day and night and was likely in diapause. Diel vertical migration is unlikely to be influenced by right whales, but may instead be motivated by abundant, near-surface food resources and avoidance of visual predators. Right whale sighting rate was correlated with OPC- detected C. finmarchicus fifth copepodite (C5) abundance at mid-depths (90-140 m); variability in both right whale sighting rate and C. finmarchicus C5 abundance in this depth stratum appeared to have similar periodicity to that of the tide. Energetic considerations suggest that right whales continue to feed on deep, diapausing layers of C. finmarchicus during the night, but the occasional presence of exploitable near-surface concentrations of C. finmarchicus suggests that nighttime near-surface feeding might sometimes occur.

Effect of heterotrophic versus autotrophic food on feeding and reproduction of the calanoid copepod Acartia tonsa: relationship with prey fatty acid composition

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 31:267-278 (2003) - doi:10.3354/ame031267 Effect of heterotrophic versus autotrophic food on feeding and reproduction of the calanoid copepod Acartia tonsa: relationship with prey fatty acid composition Elisabetta Broglio1,*, Sigrún H. Jónasdóttir2, Albert Calbet1, Hans H. Jakobsen2,3, Enric Saiz1 1Departament de Biologia Marina i Oceanografia, Institut de Ciències del Mar, CSIC, Passeig Marítim de la Barceloneta 37-49, 08003 Barcelona, Catalunya, Spain 2Department of Marine Ecology and Aquaculture, Danish Institute for Fisheries Research, Kavalergaarden 6, 2920 Charlottenlund, Denmark 3Present address: Western Washington University Shannon Point Marine Center, 1900 Shannon Point, Anacortes Road, Washington 98221, USA *Email: broglio@icm.csic.es ABSTRACT: We determined the egg production efficiency (EPE: egg production/ingestion) and egg viability of the copepod Acartia tonsa Dana under different heterotrophic and autotrophic diets. EPE was estimated in adult females either as the slope of the linear relationship between specific egg production (EPR) and ingestion rates, or as the quotient: EPR/ingestion rate. The diets, offered in monoculture, were the heterotrophic ciliates Strombidium sulcatum or Mesodinium pulex, the heterotrophic dinoflagellate Gymnodinium dominans, the autotrophic cryptophyte Rhodomonas salina and the autotrophic dinoflagellate Gymnodinium sanguineum. The diets were also analyzed for fatty acid contents and composition, relationships with EPE and reproductive success were determined. Clear differences were found in the fatty acid contents and the composition of the different diets offered, but these differences did not correspond with variability in EPE. However, egg viability was correlated with ingestion of certain prey essential fatty acids; interestingly, our data do not show that ciliates and heterotrophic dinoflagellates are nutritionally superior prey for marine copepods, contrary to general expectations. KEY WORDS: Copepod · Acartia tonsa · Ciliate · Dinoflagellate · Egg production · Food quality · Fatty acids · Egg production efficiency · Hatching success Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 31, No. 3. Online publication date: April 03, 2003 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2003 Inter-Research.

Optimal foraging in patchy turbulent environments

The problem of what strategy a predator should adopt when foraging in a turbulent and spatially patchy environment is investigated using simple mathematical models. The study was moti- vated by the need to understand the behaviour of marine fish larvae searching for copepod prey. It is demonstrated that optimal swimming speed should decrease with increasing turbulence, and that in a patchy turbulent environment it is best to concentrate swimming activity within patches of prey until a threshold of turbulence is exceeded and swimming ceases to be energetically favourable. If the predator is unaware of its global environment, or is only able to make foraging decisions based on temporally and spatially local knowledge, then its ability to forage in a near-optimal manner is severely reduced.

Comparative assimilation of Cd, Cr, Se, and Zn by the barnacle Elminius modestus from phytoplankton and zooplankton diets

Assimilation from the diet is established as a key factor in the accumulation of very high trace metal concentrations by the barnacle Elminius modestus. Assimilation efficiencies (AE) of Cd, Cr, Se and Zn were measured from a diet of different phytoplankton (2 diatoms, a dinoflagellate, a prasinophyte and a chlorophyte) and of zooplankton (the copepod Acartia spinicauda with metal accumulated from solution or diet). AEs of Cd, Se and Zn (but not Cr) varied greatly with phyto- plankton type, and for Cd and Se the AE was correlated with the percentage of metal burden held in the cytoplasm of the phytoplankton diet. AE was generally higher from the zooplankton diet than from a phytoplankton diet. Variation in AEs of Cd, Se and Zn was not explained by any correlation with the percentage of copepod metal burden held in the soft tissues, nor was there variation for either Cd or Zn according to whether the copepod prey had accumulated metal from dissolved or food sources. Comparisons of the assimilation and efflux of accumulated metals by the archaeo- balanid barnacle E. modestus and literature data for (phylogenetically younger) balanid species of the genus Balanus indicate some differences in digestive physiology of barnacles from the 2 families, tending towards higher AEs in the balanids. Modeling of the accumulation of Cd and Zn by E. mod- estus predicts that for each metal >97% of accumulated metal has been derived from dietary inges- tion. The dominance of dietary ingestion in trace metal accumulation is a function of the conspicu- ously high assimilation efficiencies and high ingestion activity of barnacles. This study adds to the small but growing list of examples highlighting the significance of trophic transfer in metal accumu- lation by aquatic invertebrates.

Modelling the attack success of planktonic predators: patterns and mechanisms of prey size selectivity

A mathematical model of the attack success of planktonic predators (fish larvae and carnivorous copepods) is proposed. Based on a geometric representation of attack events, the model considers how the escape reaction characteristics (speed and direction) of copepod prey affect their probability of being captured. By combining the attack success model with previously published hydrodynamic models of predator and prey perception, we examine how predator foraging behaviour and prey perceptive ability affect the size spectra of encountered and captured copepod prey. We examine food size spectra of (i) a rheotactic cruising predator, (ii) a suspension-feeding hovering copepod and (iii) a larval fish. For rheotactic predators such as carnivorous copepods, a central assumption of the model is that attack is triggered by prey escape reaction, which in turn depends on the deformation rate of the fluid created by the predator. The model demonstrates that within a species of copepod prey, the ability of larger stages to react at a greater distance from the predator results in increased strike distance and, hence, lower capture probability. For hovering copepods, the vorticity field associated with the feeding current also acts in modifying the prey escape direction. The model demonstrates that the reorientation of the prey escape path towards the centre of the feeding current's flow field results in increased attack success of the predator. Finally, the model examines how variability in the kinetics of approach affects the strike distance of larval fish. In cases where observational data are available, model predictions closely fit observations.

Serological estimation of prey-protein gut-residence time and quantification of meal size for grass shrimp consuming meiofaunal copepods.

A series of experiments using serological reagents was conducted to examine predation, ingestion and digestion in a model predator-prey system. The harpacticoid copepod Amphiascoides atopus, obtained from mass culture, was used as prey and the grass shrimp, Palaemonetes pugio, as predator. Bulk-gut passage time in P. pugio was measured by visualization of latex beads and ranged from 0.5 to 4 h in starved and continuously-fed grass shrimp. A polyclonal antibody was prepared from crude extracts of A. atopus; cross reactions with P. pugio and three other crustaceans were either negligible or not detected using slide agar-gel-double-immunodiffusion (AGID) and Western blot preparations. The presence of A. atopus antigens was detected with great sensitivity (e.g., seven copepods, 35 µg dry weight, gave positive results) in grass shrimp gut contents even when proteins of other crustacean prey were present. Prey-proteins could be detected for as long as 4 h with AGID and 8 h with Western blot techniques. Individual grass shrimp that were fed A. atopus and consumed from 0 to 98 copepods h(-1) were subjected to Western-blot preparation with chemiluminescence detection and densitometric evaluation. There was a significant curvilinear relationship between protein content and the number of copepod prey ingested. Results suggest that serological techniques can be modified to estimate the mass or abundance of standard-sized prey ingested by field-collected predators.

Response of life history traits to food conditions in a cyclopoid copepod from an oligotrophic environment

The Cyclops sp. responses of life history traits (growth, development, and reproduction) to food conditions from oligotrophic Lake Toya were analyzed by rearing animals individually under four food regimes:three densities of the alga Cryptomonas tetrapyrenoidosa and nauplii of the calanoid copepod Eurytemora affinis as prey in an algal suspension. Cyclops sp. grew successfully from newborn nauplii to adults when algal density was ≥4 × 103 cells ml‐1 . Development time was shorter and body length larger in the high‐density (H) treatment (4 × 104 cells ml‐1 ) than in medium‐density (M) treatment (4 × 103 cells ml−1) until the early copepodite stages. In late copepodite stages, females tended to grow more slowly but tended to be larger in the M treatment than in the H treatment. However, stage‐specific growth rates were similar among treatments during development, suggesting a trade‐off between body size and development time. Although the egg production rate was higher in the M treatment than in the H treatment, it depended on female body size regardless of the food regime. Furthermore, the weight‐specific egg production rate was the same among treatments, indicating egg production was not affected by the algal concentrations tested. Addition of copepod prey influenced neither postembryonic development time nor body size, and egg production rates were comparable to those reared with an algal diet. These results reveal that even older copepodites and adults, which are generally thought to be predacious, do not necessarily require animal prey for growth and reproduction, and that Cyclops sp. can complete its life cycle on an algal diet alone. For female Cyclops sp., reduction of algal density resulted in slow development and large body size, which might be an adaptation to the oligotrophic environment, the original habitat of the copepod.

Transfer of Cd, Cr and Zn from zooplankton prey to mudskipper Periophthalmus cantonensis and glassy Ambassis urotaenia fishes

Assimilation efficiency (AE) of metals from ingested food is critical for understanding trace metal accumulation and trophic transfer in aquatic animals. Most recent measurements of metal AEs have been on aquatic invertebrates, whereas relatively few studies have examined metal assimilation in fishes. In this study we determined the AEs of Cd, Cr and Zn in 2 fishes (pelagic glassy Ambassis urotaenia, Ambassidae, and the intertidal mudskipper Periophthalmus cantonensis, Gobiidae) feeding on 2 zooplankton prey (brine shrimp Artemia larvae and copepods). Zooplankton were radiolabeled either by feeding on radiolabeled phytoplankton or by direct exposure to radiotracers in the dissolved phase. Fishes were then fed with radiolabeled zooplankton prey for < 1 h, and the retention of ingested metals in the fishes was followed for 2 d. The measured AEs of Cd, Cr and Zn were 14 to 33, 4 to 12, and 5 to 17% in glassy fish, and 10 to 26, 4 to 19, and 11 to 31% in mudskipper, respectively. Routes of radiolabeling in copepod prey did not affect metal AEs in either mudskipper or glassy, whereas metal AEs differed by up to 10-fold in glassy fish feeding on Artemia larvae labeled from different routes. There was little difference in the gut passage time of metals for different food types and metals or between fishes. AE was not significantly related to metal gut passage time or metal distribution in the soft tissues of zooplankton prey, for each metal. However, AE in mudskippers was significantly correlated with metal distribution in the prey's soft tissues when all 3 metals were considered. Our study demonstrated that marine fishes can appreciably assimilate trace metals, and trophic transfer should be considered as a source for metal accumulation in fishes.

Effects of bottom-layer hypoxia on abundances and depth distributions of organisms in Patuxent River, Chesapeake Bay

Oxygen depletion, seasonally common in bottom waters of many stratified aquatic systems, may have strong effects on abundances, distributions, and interactions among organisms, and therefore community dynamics. To examine effects of bottom-layer hypoxia on densities and vertical distributions in a stratified subestuary, fish larvae, their gelatinous predators, and copepod prey were surveyed near-surface, within the pycnocline, and near-bottom in the Patuxent River (Chesapeake Bay) under a range of near-bottom dissolved oxygen (DO) conditions. Overall abundances of fish larvae and copepod nauplii were lower throughout the water column when bottom-layer DO was low (≤2 mg DO 1 -1 ). When bottom-layer DO was low ( 2 mg 1 -1 ) DO conditions, and overall density of copepod nauplii declined by >50%. Depth-distributions of several organisms also were affected by bottom-oxygen depletion: fish larvae, scyphomedusae, and copepods were much less common near the bottom when bottom-layer DO was low than when it was >2 mg 1 -1 . The ctenophore Mnemiopsis leidyi occurred in high densities at DO as low as 1.3 mg 1 -1 , but was nearly absent at <1 mg 1 -1 . The results indicate the potential for substantial differences in organism interactions, especially predator-prey relationships, between times of hiqh and low bottom-layer DO.

The effect of prey mobility, prey contrast, turbidity and spectral composition on the reaction distance of Gobiusculus flavescens to its planktonic prey

The reaction distance of Gobiusculus flavescens to mobile and immobile copepod prey of different transparency was studied in water conditions with different turbidity levels or spectral composition. Both prey contrast (red or transparent Calanus spp.) and prey mobility caused reaction distance of G. flavescens to increase. The effect of prey mobility or prey transparency on reaction distance was independent of turbidity level. Longest reaction distances were measured for mobile and red prey at intermediate turbidity levels (10–20 JTU). Contrast threshold decreased with increasing turbidity. Although contrast of red and transparent copepod prey increased with increasing wavelength, longest reaction distances were observed at shorter wavelengths (blue–green). Lowest contrast threshold was found at shorter wavelengths. Visual pigments of G. flavescens are adapted to its natural environment. Both turbidity and spectral composition influenced G. flavescens contrast threshold.

Predatory Promesostoma species (Plathelminthes, Rhabdocoela) in the Wadden Sea

Laboratory experiments were performed on the food ecology of four congeneric species of free-living plathelminths, Promesostoma caligulatum, P. marmoratum, P. rostratum, and P. meixneri, all inhabiting an intertidal sandflat near the island of Sylt (North Sea). Their prey spectrum is within the microcrustaceans: P. caligulatum preferred ostracods, while the other three species favoured copepods, with species-specific differences for copepod species and size classes. Daily consumption of prey species varied with the size of both the predator and the prey. On average, P. marmoratum consumed 0.76 Harpacticus flexus per day while this rate decreased to 0.06 in P. meixneri, the smallest predator. When these Promesostoma species were fed with Tachidius discipes, a smaller prey species, their predation rates were about 25% higher. While the larger predators preferred the larger harpacticoids as prey, the small P. meixneri preferred small cyclopoids over larger harpacticoids. In terms of biomass, P. marmoratum's mean consumption of T. discipes per day was about half the predator's own weight. This average varied with prey density and temperature. A comparison of these consumption rates with the field densities of the predators and their prey shows that the plathelminth predators may consume as much as 10% per day of their copepod prey populations, thus strongly influencing these prey populations on these sandflats. The predation pressure of P. caligulatum on ostracods was about 1% per day of the prey population. Since ostracods usually have fewer generations per year, the total effect on the population dynamics may be similar to that on copepods. Therefore, nocturnal swimming of copepods in the water column may be interpreted as an attempt to escape plathelminth predators.

Predator and prey perception in copepods due to hydromechanical signals

Copepods can perceive moving predators and prey by means of the hydrodynamical disturbances these generate. We formulate a simplified, general model of the fluid disturbance generated by a plankter that is moving or generating a feeding current and we estimate the magnitude and attenuation of the different components of the fluid disturbance. We use this model to argue that prey perception depends on the absolute magnitude of the fluid velocity generated by the moving prey, while predator perception depends on the magnitude of one or several of the components of the fluid velocity gradients (deformation rate, vorticity, acceleration) generated by the predator. On the assumption that hydrodynamic disturbances are perceived through the mechanical bending of sensory setae, we estimate the magnitude of the signal strength due to each of the fluid disturbance components. We then derive equations for reaction distances as a function of threshold signal strength and the size and velocity of the prey or predator. We provide a conceptual framework for quantifying threshold signal strengths and, hence, perception distances. The model is illustrated by several examples, and we demonstrate for example, (1) how larval fish behaviour is adapted to allow their undetected approach up to the strike distance of their copepod prey, (2) that prey velocity is much more significant for prey encounter rates than traditionally assumed, even for cruising predators, (3) that prey perception is strongly biased towards large and rapidly swimming/sinking prey particles, and (4) that the model can accommodate the 3 orders of magnitude variation in clearance rates observed in the copepod Oithona similis feeding on motile protists and sinking particles. We finally discuss the implications of hydromechanical predator and prey perception to trophic interactions and vertical particle fluxes, and suggest important research questions that may be addressed.

Annual production of fish larvae and their prey in relation to size-fractionated primary production (Scotian Shelf, NW Atlantic)

The annual cycles of abundance of fish larvae and their zooplankton prey were analysed in relation to the biomass and production of size-fractionated phytoplankton on the Scotian Shelf (North-west Atlantic). Outside the spring bloom of large (>5 μm) phytoplankton (February to April), the small-sized fraction of phytoplankton (<5 μm) contributed the bulk of total primary production. The production of copepod nauplii and copepodites was sustained throughout the year and fish larvae specializing on copepod prey occurred year-round. Species feeding on a mixed diet of copepods, cladocerans and/or appendicularians were restricted to periods of maximum temperature in summer and early autumn. Two short trophic pathways (two links) from primary producers to fish larvae were identified: the herbivorous food chain (large phytoplankton→calanoid copepods→fish larvae) and the large-microphage shunt of the microbial food web (small phytoplankton→appendicularians/pteropods→fish larvae). The year-round production of fish larvae and the fact that several of their major prey (appendicularians, thecosome pteropods, cladocerans, and cyclopoid copepods) exploit the microbial food web, challenge the tenet that the feeding of marine fish larvae depends primarily on the reproduction of herbivorous calanoid copepods grazing the spring and autumn blooms of large phytoplankton.

Euphausiid predation on copepods in coastal waters of the Northeast Atlantic

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 172:149-168 (1998) - doi:10.3354/meps172149 Euphausiid predation on copepods in coastal waters of the Northeast Atlantic Ulf Båmstedt*, Karin Karlson University of Bergen, Department of Fisheries and Marine Biology, The High Technology Center, N-5020 Bergen, Norway *E-mail: ulf.baamstedt@ifm.uib.no ABSTRACT: Quantitative analyses of copepod mandibles in stomach contents of the 4 most dominant euphausiid species from the Skagerrak and the northwest coast of Norway were used to evaluate trophic interactions between copepods and krill and to develop a new method to estimate degree of carnivory in the diet. Copepods were an important food item and, based on the new method, gave a ranking in degree of carnivory mainly as Meganyctiphanes norvegica >= Thysanoessa inermis = T. longicaudata >> T. raschii. M. norvegica preying on Calanus finmarchicus had similar predation rates in both laboratory studies and field samples (average 1.2 copepods ind.-1 h-1, 12.7% daily ration) and showed that (1) copepod mandibles were not accumulated in the predator stomach, (2) there was no diel predation rhythm, and (3) ca 20% of copepods caught by the predator were only partly eaten, with no strong preference for the front or back part of the copepods. Carnivory was less important in the Skagerrak than in the northern area for all 3 species occurring in both areas. T. inermis from the Skagerrak seldom fed on copepods, whereas average carnivory in stations from the northern area ranged from 8 to 35%. T. raschii usually had high stomach fullness but almost never took copepod prey. C. finmarchicus was by far the most dominant prey, making up 85% of the copepod prey mass for small M. norvegica (<50 mg dry weight) and 93 to 95% for the larger M. norvegica. Similar prey species dominated the other krill species. Peak size of C. finmarchicus prey corresponded to copepodid II for small (5 to 7.5 mm carapace length) M. norvegica, copepodid III for the larger ones, with no differences between predator sexes. Similar size distributions of C. finmarchicus prey were shown for T. inermis and T. longicaudata. The high daily ration on C. finmarchicus for M. norvegica, T. inermis and T. longicaudata, in combination with the commonly high abundance for both prey and predators, indicates that krill predation may contribute significantly to the mortality of C. finmarchicus. Furthermore, because of the pronounced importance of krill for many pelagic fish, seabirds and marine mammals in high-latitude areas, krill species may be of utmost importance in transferring copepod production to food yield for man. KEY WORDS: Meganyctiphanes · Thysanoessa · Carnivory · Ingestion · Digestion · Gut contents · Predatory impact · Pelagic food chains Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 172. Publication date: October 22, 1998 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1998 Inter-Research.