Functional responses of juvenile herring and sprat in relation to different prey types

The relationship between particulate-feeding rates and prey concentrations (functional response) of juvenile herring and sprat (5–9 cm total length) was investigated in controlled feeding experiments monitored by an underwater camera system. A special tank system was developed allowing the regulation and quantification of low prey concentrations (1–160 L^?1). Non-evasive Artemia nauplii was used as prey to estimate the maximum biting rate of both predators. In contrast, Acartia tonsa with a high escape ability was used as a realistic prey type. Herring and sprat showed a type II functional response for both prey types. Nonlinear mixed effects model revealed no significant difference between the functional responses of both predators, except that herring showed significantly higher biting rates than sprat at A. tonsa concentrations below ~40 L^?1. For both predators feeding rates were significantly higher with Artemia nauplii than with A. tonsa. Video analysis indicated that sprat, unlike herring, is an obligate particulate-feeder.     

Vulnerability of the copepod Acartia tonsa to predation by the scyphomedusa Chrysaora quinquecirrha : effect of prey size and behavior

Although scyphomedusae have received increased attention in recent years as important predators in coastal and estuarine environments, the factors affecting zooplankton prey vulnerability to these jellyfish remain poorly understood. Current models predicting feeding patterns of cruising entangling predators, such as Chrysaora quinquecirrha (Desor, 1948), fail to account for the selection of fast-escaping prey such as copepods. Nevertheless, our analysis of gastric contents of field-collected medusae showed that this scyphomedusa fed selectively on the calanoid copepod Acartia tonsa (Dana, 1846) and preferentially ingested adult over copepodite stages. We measured feeding rates in a planktonkreisel while simultaneously videotaping predator–prey interactions. C. quinquecirrha consumed adult A. tonsa ten times faster than copepodites. Differences in prey behavior, in the form of predator–prey encounter rates or post-encounter escape responses, could not account for the elevated feeding rates on adults. Prey size, however, had a dramatic impact on the vulnerability of copepods. In experiments using heat-killed prey, feeding rates on adults (1.5 times longer than copepodites) were 11 times higher than on copepodites. In comparison, medusae ingested heat-killed prey at only two to three times the rate of live prey. These results suggest that during scyphomedusan–copepod interactions, prey escape ability is important, but ultimately small size is a more effective refuge from predation. Received: 26 September 1997 / Accepted: 20 May 1998     

Effects of prey escape ability,flow speed,and predator feeding mode on zooplankton capture by barnacles

Experimental studies of feeding on zooplankton often involve the use of non-evasive Artemia spp. to represent zooplanktonic prey. Some zooplankton, however, such as copepods, are potentially evasive due to possession of effective predator-avoidance mechanisms such as high-speed escape swimming. In the present study, we compared the efficiencies with which non-evasive (A. salina) and evasive (copepods) zooplankton were captured by a sessile, suspension feeder, the coral-inhabiting barnacle Nobia grandis (Crustacea, Cirripedia). N. grandis specimens and zooplankton used in the present study were collected near Eilat, Israel in 1993. The effect of different flow speeds (from 0 to 14 cm s^-1) on captures of the two preys was also investigated. Additionally, we examined the effect of a flow-induced barnacle behavioral switch from active to passive suspension feeding, on zooplankton capture. Two video cameras were used to make close-up, three dimensional recordings of predator-prey encounters in a computer-controlled flow tank. Frame-by-frame video analysis revealed a highly significant difference (P< 0.001) in the efficiency with which A. salina and copepods were caught (A. salina being much more readily captured than copepods). After an encounter with cirri of feeding barnacles, copepods were usually able to swim out of the barnacles capture zone within one video frame (40 ms), by accelerating from a slow swimming speed (approximately 1.85 cm s^-1) to a mean escape swimming speed of 18.11 cm s^-1 (ca. 360 body lengths s^-1). This was not the case for A. salina nauplii, which usually remained in contact with cirri before being transferred to the mouth and ingested. Thus, experimental studies addressing the methodology of organisms feeding on zooplankton should consider that slow-swimming prey like Artemia sp. nauplii may only represent the non-evasive fraction of natural mesozooplankton assemblages.     

Effects of symbiotic status,flow speed,and prey type on prey capture by the facultatively symbiotic temperate coral <Emphasis Type="Italic">Oculina</Emphasis><Emphasis Type="Italic">arbuscula</Emphasis>

Symbiotic temperate corals can supplement prey capture by the coelenterate host with autotrophic carbon production by endosymbiotic zooxanthellae. To test the relationship between heterotrophic consumption and photosynthetic energy, prey capture by symbiotic and aposymbiotic specimens of the temperate scleractinian coral Oculina arbuscula (Verrill) was measured in January-April 2001. Corals were tested in a laboratory flume at five flow speeds, using Artemia franciscana cysts and nauplii as prey. Per-polyp capture rate and feeding efficiency were independent of symbiotic condition. Capture rate increased with flow speed, while capture efficiency declined. The location of capture shifted from the upstream to downstream side of the coral as flow speed increased. Differences in capture rate, location, and feeding efficiency for cysts and live brine shrimp nauplii were likely due to prey size rather than swimming ability.     

Calanoid copepod escape behavior in response to a visual predator

Calanoid copepods typically exhibit escape reactions to hydrodynamic stimuli such as those generated by the approach of a predator. During the summers of 2000, 2001 and 2004, two small calanoid species, Temora turbinata Dana, 1849 and Paracalanus parvus Claus, 1863 were exposed to a visual predatory fish, the blenny Acanthemblemaria spinosa Metzelaar, 1919, and their predator–prey interactions were recorded using both high-speed and standard videographic techniques. Copepod escape reaction components, including swimming pattern, reactive distance, turning rate, and jump kinetics, were quantified from individual predation events using motion analysis techniques. Among the observed escape reaction components, differences were noted between the species’ swimming patterns prior to attack and their response latencies. Temora turbinata was a continuous cruiser and P. parvus exhibited a hop-and-sink swimming pattern. During periods of sinking, P. parvus stopped beating its appendages, which presumably reduced any self-generated hydrodynamic signals and increased perceptual abilities to detect an approaching predator. Response latency was determined for each copepod species using a hydrodynamic stimulus produced by a 1 ms acoustic signal. Response latencies of T. turbinata were significantly longer than those of P. parvus. Despite some apparent perceptual advantages of P. parvus, the blenny successfully captured both species by modifying its attack behavior for the targeted prey.     

Relative importance of prey size and concentration in determining the feeding behaviour of the herringClupea harengus

The feeding behaviour ofClupea harengus L. in the light is dependent primarily on prey concentration. In the laboratory the fish feed by biting at low prey concentrations and by filtering at high concentrations. With the brine shrimpArtemia sp. as prey, the concentration required for the onset of filter-feeding was directly dependent on prey size, but the concentration at which 50% of feeding fish were filtering differed little between three sizes of brine shrimp (nauplii, and 2 and 4 mm larvae). When fed onCalanus finmarchicus, however, 50% of fish fed by filtering at concentrations at least six times lower than on any size of brine shrimp. Filter-feeding thresholds forC. finmarchicus were six to ten times lower than for any size ofArtemia sp. and, on the basis of biomass, approximately eight times lower than for equivalent sizedArtemia sp.     

Predator shoaling moderates the confusion effect in blue-green chromis,Chromis viridis

Summary In experiments, blue-green chromis [Chromis viridis (Cuvier 1830)] were fed on either scattered or aggregated swarms of brine shrimp (Artemia sp.). Ten runs with each prey dispersion treatment were performed with shoals of one, two, five and ten chromis. The mean lag in reaching peak feeding rate for fish fed on aggregated prey was significantly shorter in the larger chromis shoals. In contrast, with the scattered treatment all such lags were similar and very short. As foraging proceeded, higher feeding rates were observed in the larger feeding shoals, regardless of prey dispersion. Prey capture success (i.e. the rate of retention of intercepted prey) declined with time, but was significantly higher in groups of ten fish. Two main conclusions emerge. Firstly, grouping facilitated initiation of feeding by individuals preying on concentrated swarms and reduced the delay in reaching a maximum feeding level. This may have been due to a suppression of the confusion effect through reduced reliance upon vigilance. Secondly, reduced vigilance allowed larger shoals of chromis to feed effectively over more extended periods. Trends of increasing shoal cohesion and decreasing prey retention rate with time were consistent with a postulated increase in antipredator vigilance with declining feeding motivation.     

Nitrogen balance in marine fish larvae: influence of developmental stage and prey density

The utilization and fate of nitrogen in larvae of plaice (Pleuronectes platessa), blenny (Blennius pavo) and herring (Clupea harengus), from the stage of first-feeding to metamorphosis, was examined under laboratory conditions. Rates of ammonia excretion, primary amine defaecation, and growth in terms of protein-nitrogen were monitored throughout larval life. Data were used to calculate daily ration, the coefficient of nitrogen utilization (absorption efficiency), and gross and net growth efficiencies. The developmental pattern of nitrogen balance was similar for plaice and blenny larvae. These species showed increasing growth efficiency (k₁: 55 to 80%) with decreasing weight-specific waste nitrogen losses with age. Absorption efficiencies. were high (83 to 98%) in plaice and blenny larvae, and tended to increase with development in the former species. Ration relative to body weight decreased with growth in both species. Herring larval development, although at a slower rate than blenny and plaice, appeared normal up to 33 d, after which high mortality occurred. Absorption efficiency in this species tended to decline (83 to 43%) with age, until metabolic costs exceeded the absorbed ration and growth ceased. Artemia sp. nauplii proved a suitable food source for the rearing of plaice and blenny larvae, but this diet may have long-term toxicity or deficiency effects on herring. Availability and density of food affected nitrogen balance in the larvae of all three species. Feeding stimulated the output of wastes in excretion and defaecation by a factor of up to ten times the 12-h non-feeding basal rates. Waste nitrogen output reached a peak some 2 to 3 h after commencement of feeding and returned slowly to the baseline in 5 to 10 h after cessation of feeding. There was an asymptotic increase in ration, ammonia output and growth of larvae as prey density increased. Ration saturated at a higher prey density (>4 prey ml^-1) than either growth or excretion rate (1 prey ml^-1). Thus the efficiency with which food is absorbed and utilized for growth must eventually decline in response to high prey density. The idea that larval fish are adapted to maximize ingestion and growth rate, rather than optimize growth efficiency and thus to respond to prey occurring in either low density or in occasional patches, is supported by these results.     

On the post-glacial history of Acartia tonsa (Copepoda: Calanoida) in the gulf of maine and the gulf of St. Lawrence

Acartia tonsa Dana is thought to have invaded summer-warm estuarine headwaters north of Cape Cod, USA in modern times. However, these northern populations are relict ones, derived from a distribution which was once continuous from Cape Cod to the Northumberland Strait. The conclusion is based on: (1) the presence of other relict warm-water faunal elements; (2) the reproductive ecology of A. tonsa; (3) present and post-glacial oceanographic conditions. A. tonsa is not a relict holoplankter. Because of its dormant winter eggs, the species is analogous to a meroplanktonic species having high fecundity and a long pelagic larval stage. The disjunction of A. tonsa in its present refuges may make it useful for studies on rates of speciation in marine calanoid copepods.Ira C. Darling Center Contribution No. 153     

Marker technique for investigating gut throughput rates in coral reef fishes

Artemia sp. shells were evaluated to determine their accuracy for tracing the passage of algal filaments through the gut of the damselfish Pomacentrus amboinensis Bleeker, 1868 (family Pomacentridae), an omnivorous coral reef fish. An automatic faeces-collection apparatus enabled the quantitative collection of markers and faeces in the laboratory. Defecation rates were similar for light and heavy doses of Artemia sp. shells and controls, indicating no detrimental effects of Artemia sp. shells on the gut throughput rate of P. amboinensis. In addition, similar rates and patterns of the passage of Artemia sp. shells and the algal markers Enteromorpha sp. and Lyngbya sp. indicated that Artemia sp. shells provide a reliable representation of the throughput rate of algal filaments. The mean throughput time of P. amboinensis was 4.6 h ±0.3 SE, with a modal recovery time of 4 h. Laboratory throughput estimates were validated by comparing the distribution patterns of Artemia sp. shells in the dissected gut of specimens administered markers in the laboratory and field. In addition, the retention of markers in the stomach of P. amboinensis suggested a likely site of prolonged processing. Received: 24 October 1996 / Accepted: 18 March 1997     

Strain-related physiological and behavioral effects of <Emphasis Type="Italic">Skeletonema marinoi</Emphasis> on three common planktonic copepods

Three strains of the chain-forming diatom Skeletonema marinoi, differing in their production of polyunsaturated aldehydes (PUA) and nutritional food components, were used in experiments on feeding, egg production, hatching success, pellet production, and behavior of three common planktonic copepods: Acartia tonsa, Pseudocalanus elongatus, and Temora longicornis. The three different diatom strains (9B, 1G, and 7J) induced widely different effects on Acartia tonsa physiology, and the 9B strain induced different effects for the three copepods. In contrast, different strains induced no or small alterations in the distribution, swimming behavior, and turning frequency of the copepods. 22:6(n-3) fatty acid (DHA) and sterol content of the diet typically showed a positive effect on either egg production (A. tonsa) or hatching success (P. elongatus), while other measured compounds (PUA, other long-chain polyunsaturated fatty acids) of the algae had no obvious effects. Our results demonstrate that differences between strains of a given diatom species can generate effects on copepod physiology, which are as large as those induced by different algae species or groups. This emphasizes the need to identify the specific characteristics of local diatoms together with the interacting effects of different mineral, biochemical, and toxic compounds and their potential implications on different copepod species.     

Ultraviolet photosensitivity and feeding in larval and juvenile coral reef fishes

The ability of young coral reef fishes to feed using solely ultraviolet-A (UV-A) radiation during ontogeny was examined using natural prey in experimental tanks. Larvae and juveniles of three coral reef fish species (Pomacentrus amboinensis, Premnas biaculeatus and Apogon compressus) are able to feed successfully using UV-A radiation alone during the later half of the pelagic larval phase. The minimum UV radiation intensities required for larval feeding occur in the field down to depths of 90–130 m in oceanic waters and 15–20 m in turbid inshore waters. There was no abrupt change in UV sensitivity after settlement, indicating that UV photosensitivity may continue to play a significant role in benthic juveniles on coral reefs. Tests of UV sensitivity in the field using light traps indicate that larval and juvenile stages of 16 coral reef fish families are able to detect and respond photopositively to UV wavelengths. These include representatives from families that are unlikely to possess UV sensitivity as adults due to the UV transmission characteristics of the ocular media. Functional UV sensitivity may be more widespread in young coral reef fishes than in the adults, and may play a significant role in detecting zooplanktonic prey.     

Trypsin content in intestines of herring larvae,Clupea harengus,ingesting inert polystyrene spheres or live crustacea prey

In 1986, at the Danish Institute of Fisheries and Marine Research, Denmark, Clupea harengus L. larvae from three different herring stocks were offered either non-biodegradable polystyrene spheres, nauplii and copepodites of Acartia tonsa or Artemia ssp. nauplii. Ingestion of polystyrene spheres induced trypsin secretion to a higher level than in non-feeding fish. Larvae ingesting live food of the same width as the polystyrene spheres exhibited the highest trypsin content in the intestines. Mechanisms responsible for the regulation of pancreatic enzyme secretion are discussed.     

Role of the free amino acid pool of the copepod Acartia tonsa in adjustment to salinity change

The free amino acid pool of the calanoid copepod Acartia tonsa was reduced in proportion to the decrease in external salinity within 24 h, with a corresponding increase in ammonia excretion and a transient rise in oxygen consumption. The free amino acid pool was not increased in response to increased salinity. Catabolism of free amino acids is important in the reduction of cellular osmotic pressure in reduced salinities. Antagonistic demands of osmotic preservation and nutritional metabolism on the free amino acid pool may limit the production of the species in waters of higher salinity.     

A continuous recirculating culture system for planktonic copepods

The calanoid copepods, Acartia clausi Giesbrecht and Acartia tonsa Dana, are maintained at high densities in continuous culture at 15°C. Synthetic sea-water medium is recirculated through filters and a foam tower which limits accumulation of dissolved wastes and various metabolites. The ciliate Euplotes vannus Müller is associated in culture with the copepods, and effectively controls bacterial population and accumulation of algal debris. The copepods graze upon the ciliates as well as upon the phytoflagellates Isochrysis galbana Parke and Rhodomonas baltica Korsten.Contribution No. 119 from the Institute of Marine and Atmospheric Sciences, University of Miami.     

Demographic and temporal structure of an allele frequency cline in the mussel Mytilus edulis

Feeding rates, patterns of prey selection, and starvation tolerance were investigated for adult males and females of the cyclopoid copepod Corycaeus anglicus collected from the waters of Friday Harbor, Washington, USA. Selection by C. anglicus was determined largely by prey body-size, but was also affected by species and developmental stage. Small developmental stages of all prey species were fed upon at relatively low rates. The small calanoid species Acartia clausii was increasingly vulnerable to predation by C. anglicus as it progressed through successive developmental stages. Larger prey species, Pseudocalanus sp. and Calanus pacificus, were more vulnerable in intermediate stages, the C3 and N6 stages, respectively. Larger and smaller prey were characteristically attacked at different sites on their bodies; however, attack sites fell within a similar range of body widths, 130 to 170 m. Males of Corycaeus anglicus killed a maximum of 1.4 prey d^-1 when feeding on the optimally-sized adult females of Acartia clausii, which are approximately equivalent to its own body length. Males fed at approximately double the rates of females. Despite its small size and apparent lack of metabolic stores, this cyclopoid is highly tolerant of starvation conditions. Median survival time without food is at least 2 wk for both males and females. In its predatory behavior, C. anglicus employs an ambush-type strategy and seems to be adapted for infrequent encounters with relatively large prey.Contribution No. 1412 from the School of Oceanography, University of Washington, Seattle     

Trophic modification of essential fatty acids by heterotrophic protists and its effects on the fatty acid composition of the copepod Acartia tonsa

To test whether heterotrophic protists modify precursors of long chain n−3 polyunsaturated fatty acids (LCn−3PUFAs) present in the algae they eat, two algae with different fatty acid contents (Rhodomonas salina and Dunaliella tertiolecta) were fed to the heterotrophic protists Oxyrrhis marina Dujardin and Gyrodinium dominans Hulbert. These experiments were conducted in August 2004. Both predators and prey were analyzed for fatty acid composition. To further test the effects of trophic upgrading, the calanoid copepod Acartia tonsa Dana was fed R. salina, D. tertiolecta, or O. marina that had been growing on D. tertiolecta (OM-DT) in March 2005. Our results show that trophic upgrading was species-specific. The presence of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the heterotrophic protists despite the lack of these fatty acids in the algal prey suggests that protists have the ability to elongate and desaturate 18:3 (n−3), a precursor of LCn−3PUFAs, to EPA and/or DHA. A lower content of these fatty acids was detected in protists that were fed good-quality algae. Feeding experiments with A. tonsa showed that copepods fed D. tertiolecta had a significantly lower content of EPA and DHA than those fed OM-DT. The concentration of EPA was low on both diets, while DHA content was highest in A. tonsa fed R. salina and OM-DT. These results suggest that O. marina was able to trophically upgrade the nutritional quality of the poor-quality alga, and efficiently supplied DHA to the next trophic level. The low amount of EPA in A. tonsa suggests EPA may be catabolized by the copepod.     

Electrophoretic survey of genetic variation in Pecten maximus,Chlamys opercularis,C. varia and C. distorta from the Irish Sea

Food selection by young larvae of the gulf menhaden (Brevoortia patronus) was studied in the laboratory at Beaufort, North Carolina (USA) in 1982 and 1983; this species is especially interesting, since the larvae began feeding on phytoplankton as well as microzooplankton. When dinoflagellates (Prorocentrum micans), tintinnids (Favella sp.), and N1 nauplii of a copepod (Acartia tonsa) were presented to laboratory-reared, larval menhaden (3.9 to 4.2 mm notochord length), the fish larvae ate dinoflagellates and tintinnids, but not copepod nauplii. Larvae showed significant (P<0.001) selection for the tintinnids. Given the same mixture of food items, larger larvae (6.4 mm notochord length) ate copepod nauplii as well as the other food organisms. These feeding responses are consistent with larval feeding in the northern Gulf of Mexico, where gulf menhaden larvae between 3 and 5 mm in notochord length frequently ate large numbers of dinoflagellates (mostly P. micans and P. compressum) and tintinnids (mostly Favella sp.), but did not eat copepod nauplii. As larvae grew, copepod nauplii and other food organisms became important, while dinoflagellates and tintinnids became relatively less important in the diet. Since the tintinnids and nauplii used in the laboratory feeding experiments were similar in size as well as carbon and nitrogen contents, the feeding selectivity and dietary ontogeny that we observed were likely due to a combination of prey capturability and larval fish maturation and learning.Contribution No. 5575 of the Woods Hole Oceanographic Institution     

Water flow and prey capture by three scleractinian corals, Madracis mirabilis, Montastrea cavernosa and Porites porites, in a field enclosure

Scleractinian corals experience a wide range of flow regimes which, coupled with colony morphology, can affect the ability of corals to capture zooplankton and other particulate materials. We used a field enclosure oriented parallel to prevailing oscillatory flow on the forereef at Discovery Bay, Jamaica, to investigate rates of zooplankton capture by corals of varying morphology and polyp size under realistic flow speeds. Experiments were carried out from 1989 to 1992. Particles (Artemia salina cysts) and naturally occurring zooplankton attracted into the enclosures were used as prey for the corals Madracis mirabilis (Duchassaing and Michelotti) (narrow branches, small polyps), Montastrea cavernosa (Linnaeus) (mounding, large polyps), and Porites porites (Pallas) (wide branches, small polyps). This design allowed corals to be used without removing them or their prey from the reef environment, and avoided contact of zooplankton with net surfaces. Flow speed had significant effects on capture rate for cysts (M. mirabilis), total zooplankton (M. mirabilis, M. cavernosa), and non-copepod zooplankton (M. mirabilis). Zooplankton prey capture increased with prey concentration for M. mirabilis and M. cavernosa, over a broad range of concentrations, indicating that saturation of the feeding response had not occurred until prey density was over 10⁴ items m⁻³, a concentration at least an order of magnitude greater than the normal range of reef zooplankton concentrations. Location of cyst capture on coral surfaces was not uniform; for M. cavernosa, sides and tops of mounds captured most particles, and for P. porites, capture was greatest near branch tops, but was close to uniform for M. mirabilis branches in all flow conditions. The present study confirms laboratory flume results, and field results for other species, suggesting that many coral species experience particle flux and encounter rate limitations at low flow speeds, decreasing potential zooplankton capture rates. Received: 17 September 1996 / Accepted: 22 November 1997     

Ingestion and incorporation of coral-mucus detritus by reef zooplankton

The copepod Acartia tonsa and the reef mysid Mysidium integrum ingest stained coral mucus. Ingestion rates determined with radioisotope-labeled mucus ranged from 4 to 81% body carbon · 24 h^-1 for the copepods and I to 70% body carbon · 24 h^-1 for the mysids. Incorporation was measured by comparing the organic composition of fecal material and by the incorporation of isotope-labeled mucus. A. tonsa incorporated 47% of ingested ash-free material, 68% of carbon and 36% of nitrogen. M. integrum incorporated 44% of ingested ash-free matter, 57% of carbon and 55% of nitrogen. Incorporation estimates using ¹⁴C-labeled mucus were 65% and 39% for incorporation by A. tonsa and M. integrum respectively. A. tonsa and M. integrum incorporated both the mucus substrate and the epiphytic bacteria of the mucus-detritus.