Copepod Feeding Research Articles

How effective are Mesocyclops aspericornis (Copepoda: Cyclopoida) in controlling mosquito immatures in the environment with an application of phytochemicals?

We investigated the susceptibility of Mesocyclops aspericornis and Aedes aegypti larvae to mosquito larvicidal phytochemicals: piperine and eugenol and the predation efficiency of the adult female M. aspericornis on Ae. aegypti larval instar-I and late II at the sublethal concentration of piperine and eugenol. Both prey and predator were susceptible to both the phytochemicals; however, the lethal concentration of either phytochemicals recorded for Ae. aegypti did not exert mortality on the copepods. The predator’s latent time was significantly longer in the phytochemical medium than control. The encounter frequency was significantly higher in control than in the phytochemical medium. For instar-I larvae, the post-encounter attack probabilities were not affected by the tested phytochemicals. However, for instar-II, the post-encounter attack probability was lower in eugenol treatment than in either the control or piperine. The escape and post-escape survival probabilities of larvae were substantially lower in phytochemical treatments than in the control. However, the overall copepod-imposed mortality did not differ significantly between the control and the phytochemical medium. In conclusion, both the phytochemicals modify the copepod feeding behavior without affecting the copepod incurred total larval mortality. Therefore, application of these phytochemicals along with M. aspericornis for mosquito control is advisable.

Remains of the protozoan sticholonche zanclea in the faecal pellets of Paracalanus quasimodo, Parvocalanus crassirostris, Temora stylifera and Temora turbinata (copepoda, calanoida) in Brazilian coastal waters

Studies of copepod feeding have identified these organisms as key species in marine ecosystems, because they have a pivotal position in food webs: they control primary production through grazing, and are also a crucial link between the microbial food web and higher trophic levels, especially because they are able to predate on protozoa (STOECKER; CAPUZZO, 1990). The ingestion of protozoans has attracted particular attention, not only because it extends our understanding of the manifold energy pathways that structure aquatic food webs, but also because it involves an important behavioral aspect, i.e., what strategies are used to locate and capture preferred prey (AZEMAR et al., 2007). Copepods of the genera Paracalanus and Temora are believed to devote most of their time to filter feeding (VAN DUREN; VIDELER, 1995). The feeding habits of the copepods Paracalanus quasimodo , Temora stylifera and T. turbinata have shown that these species are omnivorous, but primarily opportunistic herbivores and that carnivory is infrequent (TURNER, 1984a, 1984b). Paracalanus quasimodo , Parvocalanus crassirostris , Temora stylifera and T. turbinata are abundant in Brazilian coastal waters, and are assumed to play a fundamental role in the control of primary production. Scanning electron microscopy analysis of the faecal pellets of these copepods was performed to assess the main food item ingested during the occurrence of different water masses in the Sao Sebastiao Channel (SSC), a coastal ecosystem located on the northeast coast of Sao Paulo State. Sampling was carried out every three months in the SSC, from January 1996 to July 1997 and also in July 1998 and January 1999, at two sampling points (map available in Eskinazi-Sant’Anna; Bjornberg, 2006). Surface (0.5 m) water samples (250 ml) for phytoplankton and protozooplankton analyses were taken with a Van Dorn bottle (5 L) and preserved in Lugol’s solution. Phytoplankton was enumerated using the inverted microscope method and carbon content determined using the volume:carbon conversions. Mesozooplankton was collected during 2-min surface tows with a 150-mm mesh net. Adult females of the copepods Parvocalanus crassirostris , Paracalanus quasimodo , Temora stylifera and Temora turbinata were sorted under a WILD M8 stereomicroscope, isolated within 20 min of collection, and transferred to Petri dishes containing collected surface sea water, and then left for 30 to 120 min to produce faecal pellets. The expelled faecal pellets (38 from P. crassirostris , 78 from P. quasimodo , 37 from T. stylifera and 21 from T. turbinata ) were individually removed by pipette and placed in petri dishes containing a mixture of filtered sea water (Nuclepore cellulose acetate membrane filters 20 mm) and 10 mm screened surface sea water. The pellets were then left for 24 h at 24

To eat and not be eaten: optimal foraging behaviour in suspension feeding copepods

Zooplankton feed on microscopic prey that they either entrain in a feeding current or encounter as they cruise through the water. They generate fluid disturbances as they feed and move, thus elevating their risk of being detected and encountered by predators. Different feeding modes generate different hydrodynamic signals to predators and different predator encounter speeds but may also differ in their efficiency; the optimal behaviour is that which maximizes the net energy gain over the predation risk. Here, we show by means of flow visualization and simple hydrodynamic and optimization models that copepods with a diversity of feeding behaviours converge on optimal, size-independent specific clearance rates that are consistent with observed clearance rates of zooplankton, irrespective of feeding mode, species and size. We also predict magnitudes and size-scaling of swimming speeds that are consistent with observations. The rationalization of the magnitude and scaling of the clearance rates of zooplankton makes it more suitable for development of models of marine ecosystems, and is particularly relevant in predicting the size structure and biomass of pelagic communities.

Marine snow, zooplankton and thin layers: indications of a trophic link from small-scale sampling with the Video Plankton Recorder

Marine aggregates of biogenic origin, known as marine snow, are considered to play a major role in the ocean's particle flux and may represent a concentrated food source for zoo- plankton. However, observing the marine snow−zooplankton interaction in the field is difficult since conventional net sampling does not collect marine snow quantitatively and cannot resolve so-called thin layers in which this interaction occurs. Hence, field evidence for the importance of the marine snow−zooplankton link is scarce. Here we employed a Video Plankton Recorder (VPR) to quantify small-scale (metres) vertical distribution patterns of fragile marine snow aggregates and zooplankton in the Baltic Sea during late spring 2002. By using this non-invasive optical sam- pling technique we recorded a peak in copepod abundance (ca. 18 ind. l −1 ) associated with a pro- nounced thin layer (50 to 55 m) of marine snow (maximum abundance of 28 particles l −1 ), a feature rarely resolved. We provide indirect evidence of copepods feeding on marine snow by computing a spatial overlap index that indicated a strong positively correlated distribution pattern within the thin layer. Furthermore we recorded images of copepods attached to aggregates and demonstrat- ing feeding behaviour, which also suggests a trophic interaction. Our observations highlight the potential significance of marine snow in marine ecosystems and its potential as a food resource for various trophic levels, from bacteria up to fish.

Zooplankton distribution and feeding in the Arctic Ocean during a Phaeocystis pouchetii bloom

In early summer 2007 we determined the vertical distribution of mesozooplankton (>200μm) and assessed the copepod feeding rates in 19 stations distributed along the East Greenland Current and the Fram Strait. The study coincided with a bloom of the haptophyte Phaeocystis pouchetii in the colonial form. Copepods dominated the zooplankton community numerically, and were mainly distributed within the upper 150m (except for Metridia longa and Oithona spp., that inhabited deeper waters), without showing a clear avoidance of the P. pouchetii layer. Copepod diet was diverse, ciliates having a relevant share (40% of the diet). Copepods also displayed active grazing upon the colonies of P. pouchetii. In general, feeding rates were low (on average, daily ration was 1.6% of body carbon), likely due to the scarcity of nano and microplankton during the study (<100μgCL−1). Consequently, the trophic impacts on both the nano- and microplankton standing stocks and on primary production were negligible. These results suggest that during the period of study the transfer of carbon and energy from lower trophic levels towards copepods was low.

Bioconversion of fatty acids at the basis of marine food webs: insights from a compound-specific stable isotope analysis

Polyunsaturated fatty acids (PUFA) are essential compounds that can limit the productivity of primary consumers in aquatic food webs, where the efficiency in energy transfer at the plant-animal interface has been related to food quality in terms of fatty acids (FA). At this interface, copepods play a pivotal role both as consumers of primary production and as a food source for higher trophic levels. Understanding the role of grazing copepods in the transfer of FA is therefore essential for our knowledge on the overall functioning of marine ecosystems. The harpacticoid copepod Microarthridion littorale grazed for 9 d on C-13 labelled diatoms and bacteria in the laboratory and was then subjected to FA-specific stable isotope analysis. The objective of this analysis was to inspect the copepod's ability to bioconvert short-chain FA (SC-PUFA, = 20 carbons) and the FA involved in the potential bioconversion pathways. Diatoms and bacteria were chosen as test diets because of their different FA composition, i.e. docosahexaenoic acid (DHA; 22: 6 omega 3) was absent in the bacteria, and eicosapentaenoic acid (EPA; 20: 5 omega 3) was <5% of the total FA weight of bacteria. The presence of labelled DHA in copepods feeding on bacteria showed that this PUFA must have been converted from other FA, possibly EPA. The FA composition of copepods in the laboratory was different from that of field copepods, which suggests the availability of more food sources in the field than those offered in the experiment. The weight proportion of C18 FA decreased in copepods feeding on either bacteria or diatoms relative to field copepods, while the proportion of both EPA and DHA increased. In contrast to planktonic calanoid copepods that have limited ability to bioconvert FA, benthic harpacticoid copepods apparently developed the ability to elongate FA and to exploit niches with poor quality food. Moreover, by improving the quality of the food they graze upon, especially in terms of EPA and DHA, harpacticoid copepods upgrade the nutritive value of food available to the higher trophic levels in marine food webs.

Ingestion rate, survival and growth of newly released seahorse Hippocampus reidi fed exclusively on cultured live food items

The main bottleneck for seahorse aquaculture is the low survival of newly released juveniles. Although the reasons for low survival are poorly understood, proper nutrition is considered crucial. This study therefore evaluated the ingestion rate (IR), survival and growth of newly released Hippocampus reidi reared under different management protocols. The indirect method was used to estimate the IR of different live food items (newly hatched Artemia nauplii, rotifers Brachionus plicatilis and the offspring of the copepod Tisbe biminiensis). A 14day-long rearing trial was conducted on 38L aquaria connected to a seawater recirculation system. Six treatments were tested: Art00h — newly hatched Artemia nauplii (5ind.mL−1); Art24h — 24-h enriched Artemia (5ind.mL−1); Rot+Art24h — rotifers (B. plicatilis; 10ind.mL−1) from day 1 until day 7 followed by enriched Artemia metanauplii (5ind.mL−1); Cop — Copepods (T. biminiensis; 2ind.mL−1); and Art24h+Cop — T. biminiensis (2ind.mL−1) and 24-h enriched Artemia (5ind.mL−1). In the treatment Starvation, no feed was provided. All treatments, except Starvation, received the microalgae Nannochloropsis oculata every other day. The IR trials indicated that the offspring of the copepod was the main live food ingested by the seahorses. Treatment Art24h+Cop resulted in a significantly higher survival (33.5±5.4%), followed by Cop (6.6±4.8%) and Art00h (6.0±8.3%) which were not significantly different from each other, but significantly higher than juveniles fed rotifers and Artemia (Rot+Art24h) with a survival of only 0.3% (±0.5). No survivors were observed in the remaining treatments. Growth parameters were significantly higher in Art24h+Cop and Art00h. Results showed that the feeding of copepods T. biminiensis combined with enriched Artemia increases growth and survival of H. reidi during the first two weeks of life.

Algal Toxins Alter Copepod Feeding Behavior

Using digital holographic cinematography, we quantify and compare the feeding behavior of free-swimming copepods, Acartia tonsa, on nutritional prey (Storeatula major) to that occurring during exposure to toxic and non-toxic strains of Karenia brevis and Karlodinium veneficum. These two harmful algal species produce polyketide toxins with different modes of action and potency. We distinguish between two different beating modes of the copepod’s feeding appendages–a “sampling beating” that has short durations (<100 ms) and involves little fluid entrainment and a longer duration “grazing beating” that persists up to 1200 ms and generates feeding currents. The durations of both beating modes have log-normal distributions. Without prey, A. tonsa only samples the environment at low frequency. Upon introduction of non-toxic food, it increases its sampling time moderately and the grazing period substantially. On mono algal diets for either of the toxic dinoflagellates, sampling time fraction is high but the grazing is very limited. A. tonsa demonstrates aversion to both toxic algal species. In mixtures of S. major and the neurotoxin producing K. brevis, sampling and grazing diminish rapidly, presumably due to neurological effects of consuming brevetoxins while trying to feed on S. major. In contrast, on mixtures of cytotoxin producing K. veneficum, both behavioral modes persist, indicating that intake of karlotoxins does not immediately inhibit the copepod’s grazing behavior. These findings add critical insight into how these algal toxins may influence the copepod’s feeding behavior, and suggest how some harmful algal species may alter top-down control exerted by grazers like copepods.

Short-term changes in population structure and vertical distribution of mesopelagic copepods during the spring phytoplankton bloom in the Oyashio region

To evaluate the responses to the spring phytoplankton bloom, short-term changes in population structure and vertical distribution of mesopelagic copepods (Gaetanus simplex, Gaidius variabilis, Pleuromamma scutullata, Paraeuchaeta elongata, P. birostrata, Heterorhabdus tanneri and Heterostylites major) were studied in the Oyashio region. Samples were collected with a 60μm mesh VMPS from 9 strata between 0 and 1000m both day and night on five occasions during March–April 2007. All the species except Heterorhabdidae species performed reproduction during the spring phytoplankton bloom, while no recruitment to copepodid stages was detected because the newly born individuals were eggs or nauplii. The shallower-living species, G. simplex, P. scutullata and P. elongata had nocturnal ascent diel vertical migration (DVM). While suspension feeding copepods cease DVM after 11 April (P. scutullata) or 23 April (G. simplex), carnivorous P. elongata continued DVM over the study period. Since the gut contents of G. simplex showed a nocturnal increment even in the period of no DVM (23 and 29 April), they might be feeding at depth without DVM. Thus, the cessation of DVM in mesopelagic suspension feeding copepods would be induced by the increase of sinking particles (e.g. food for suspension feeders) during the spring phytoplankton bloom.

Predation by Pseudodiaptomus annandalei (Copepoda: Calanoida) on rotifer prey: Size selection, egg predation and effect of algal diet

The brackish water calanoid copepod Pseudodiaptomus annandalei is considered to be primarily herbivorous, and being cultured as live feed for grouper fish larvae. In the present study we observed both males and females of P. annandalei preying on the rotifer, Brachionus rotundiformis and its eggs. In a series of laboratory experiments, P. annandalei was presented with neonates, ovigerous and non-ovigerous adult of B. rotundiformis to investigate rotifer predation, egg predation, prey consumption rates, size selection, and satiation level and duration. Prey consumption rates on neonate and adult rotifers were recorded in presence and absence of algae, the smaller Isochrysis galbana and the larger Tetraselmis chui. Both males and females of P. annandalei were able to successfully ingest the eggs, neonates and adults of B. rotundiformis. The prey consumption rates were significantly lower in males than in females of P. annandalei. Regardless of sex and reproductive state of the copepod, prey consumption rates were higher on rotifer neonates than on adults. The prey ingestion rates did not differ significantly between ovigerous and non-ovigerous adults of P. annandalei females. The ovigerous B. rotundiformis was ingested at lower rates than either non-ovigerous or neonates by both males and females of P. annandalei. Rejection of prey after getting entrained in the copepods feeding appendages was also recorded. Satiated P. annandalei rejected rotifers more often than hungry individuals. The presence of smaller algae I. galbana had no effect on rotifer consumption, whereas, the larger algae T. chui negatively influenced the rotifer consumption rates. The egg consumption rates in P. annandalei increased linearly with increasing numbers of egg bearing rotifers in the environment. From a combination of adults and neonates of B. rotundiformis, P. annandalei females preferred neonates over adult rotifers. The prey preference of copepods exhibited switching based on relative prey proportion in the environment. P. annandalei females reached to satiation level in 165min, ingesting 47.33±1.8 and 38.67±1.83 individuals of non-ovigerous and ovigerous rotifers respectively. The present study provides first information on predatory efficiency of P. annandalei, and attests its omnivory feeding habit. This study suggests that P. annandalei, being perennially abundant in many tropical brackish ponds and estuaries may be playing a major role in shaping the community structure through predation in its natural habitat.

Biogeographic effects of the Gulf of Mexico red tide dinoflagellate Karenia brevis on Mediterranean copepods

There may be biogeographic aspects of interactions between toxic phytoplankton and their zooplankton grazers. Grazers that naturally co-occur with a given species of toxic phytoplankton may have evolved mechanisms to counteract adverse effects of phytoplankton toxins. Conversely, grazers that have no co-evolutionary experience with a toxic phytoplankter may be more susceptible to its effects. This may also be true for toxic metabolites other than neurotoxins that adversely affect copepod reproduction and development such as the well-described diatom oxylipins. In order to test this hypothesis, we investigated interactions in terms of feeding, reproductive success and survival of a copepod feeding on a potentially toxic dinoflagellate species with which the copepod does not naturally co-occur: the red tide dinoflagellate Karenia brevis from the Gulf of Mexico and the copepod Calanus helgolandicus from the Mediterranean. We additionally compared interactions of these two allopatric plankters with various co-occurring sympatric ones, including the copepod Temora stylifera and a non-neurotoxic strain of the dinoflagellate Alexandrium tamarense, both from the Mediterranean, and as a control, the non-toxic dinoflagellate Prorocentrum minimum. Both Mediterranean copepods fed, reproduced and survived on diets of K. brevis from the Gulf of Mexico, but neither copepod did as well on this diet as on diets of A. tamarense from the Mediterranean or the control diet of P. minimum. Of the two copepods, T. stylifera fared worse on a diet of K. brevis than did C. helgolandicus. Egg hatching success for both copepods feeding on K. brevis was sharply diminished over the seven days of the experiments. This was surprising, since we subsequently discovered that our culture of K. brevis contained no brevetoxins. However, our culture appeared to contain another as yet unidentified compound. Similarly, we have previously demonstrated that our culture of A. tamarense, which contained no saxitoxins or aldehydes, did contain another unidentified compound that reduced egg hatching success by inhibiting sperm from fertilizing eggs. Thus, although diets of the dinoflagellate from the Gulf of Mexico (K. brevis) caused adverse effects on both of the Mediterranean copepods, T. stylifera was also adversely affected by the Mediterranean dinoflagellate (A. tamarense). The copepod T. stylifera which co-occurs in the Gulf of Mexico with the dinoflagellate K. brevis was far more adversely affected by feeding on a sole diet of this dinoflagellate than was the Mediterranean copepod (C. helgolandicus) which never naturally co-occurs with this dinoflagellate. Thus, any putative biogeographic effects of copepods feeding on allopatric versus sympatric dinoflagellates did not clearly emerge from our data. However, since both species of dinoflagellates appear to contain additional undescribed chemicals other than the neurotoxins for which they are best known, and these compounds are potentially related to the adverse effects we recorded, it appears that understanding of the biogeography must await further defining the biochemistry of some harmful algae:grazer interactions.

Fatty acid transformation in zooplankton: from seston to benthos

All organic matter, fatty acids (FA) in particular, is transformed in the pelagic plank- ton food web before reaching fishes or benthic organisms. Mesozooplankton (0.2 to 2 mm) is the main conduit for FA transfer, and FA profiles in sedimenting matter should therefore be signifi- cantly affected by its activity. To test this hypothesis, we sampled seston, zooplankton and sedi- ment trap material for FA analysis during 5 campaigns spanning 4 seasons at a coastal site on the west coast of Sweden. Saturated (SAFAs) and monounsaturated (MUFAs) FAs dominated seston and trap material, while copepods contained 75 to 90% polyunsaturated FAs (PUFAs). Sedimen- tation of bulk particulate organic carbon did not vary significantly with season (coefficient of vari- ation, CV = 33%), while pigment (CV = 49%) and in particular faecal pellet fluxes (CV = 100%) were highly variable as a result of copepod feeding activity. Copepod feeding, pellet production and egg production were all high after the spring bloom and in summer and autumn. Overall, 5 to 25% of the sedimenting FAs were affected by copepod feeding activities, and the supply of PUFAs to the benthos was significantly enhanced by copepod grazing activity. SAFAs and MUFAs were enriched by 5 to 10% in sediment traps, while the proportion of the most important PUFA, docosa- hexaenoic acid, was reduced by up to 15% in summer and autumn. In conclusion, the periods of significant input of PUFAs to the sediment coincide with the period of highest transformation by the mesozooplankton, which in the present study was summer and autumn.

Reassessment of copepod grazing impact based on continuous time series of in vivo gut fluorescence from individual copepods

Copepod grazing is a fundamental link between autotrophs and heterotrophs, affecting the particle size spectrum, modifying trophic interactions for a wide range of organisms, and playing a potentially significant role in the carbon cycle. A considerable amount of work has been done to quantify and understand feeding in copepods from a behavioral, physiological and ecological standpoint. An impressive body of knowledge has accumulated as a result. However, some of the methods used to experimentally determine copepod grazing have known, un-quantified problems. The small size of individual copepods requires the use of multiple animals, thereby introducing poorly understood variability. Digestion and gut dynamics in copepods are not fully understood either. Here we propose an approach to measure grazing that aims to be complementary to past contributions. Using a novel planar laser imaging technique, we have quantified grazing (pellet evacuation rates and gut clearance rates, K) in feeding copepods (Calanus pacificus). Highly resolved time series up to 5 h long were obtained from individual copepods at three different temperatures. K was found to be temperature-dependent, to vary in time and among copepods, and to be significantly higher during feeding than non-feeding, invalidating some assumptions of previous methods. Previous studies not accounting for the observed variations in K may have underestimated copepod ingestion by 15–70%. This suggests that copepods may exert a greater grazing pressure on phytoplankton than previously estimated, implying a higher copepodmediated vertical carbon transport, and a greater transfer rate of energy to higher trophic levels.

Copepod feeding and digestion rates using prey DNA and qPCR

Copepod feeding and digestion rates were measured using quantitative polymerase chain reaction (qPCR) to amplify the prey Thalassiosira weissflogii and Heterocapsa triquetra from the guts of Acartia tonsa. Using species-specific primers, prey 18S rDNA could be detected routinely and quantified in the guts and fecal pellets of A. tonsa. Recovery of gut contents DNA using two fixation methods was compared. Prey 18S copy numbers were .10-fold higher in copepods fixed in 95% ethanol (3260+ 822 copies copepod) compared with anesthetized and frozen copepods (210+ 19 copies copepod). Experiments using 95% ethanol fixation showed rapid prey DNA digestion rates during the initial 2 min after ingestion (0.7 min) after which they slowed 10-fold. Chlorophyll pigment disappearance rates were slower ( 0.015 min). Rates of gut filling measured by DNA and gut pigments differed, reaching 95% of the asymptote, Imax, in 3 and 58 min, respectively, likely reflecting differences in rates at which biomarkers were digested. Gut fullness measured by DNA increased with prey concentration, reaching Imax at 9760 copies copepod and a critical concentration (Icrit) at 1530 cells mL . These results demonstrate that qPCR analysis of prey DNA in copepod guts can be used to provide a quantitative index of feeding rates.

Grazing rates of Calanus finmarchicus on Thalassiosira weissflogii cultured under different levels of ultraviolet radiation.

UVB alters photosynthetic rate, fatty acid profiles and morphological characteristics of phytoplankton. Copepods, important grazers of primary production, select algal cells based upon their size, morphological traits, nutritional status, and motility. We investigated the grazing rates of the copepod Calanus finmarchicus on the diatom Thalassiosira weissflogii cultured under 3 levels of ultraviolet radiation (UVR): photosynthetically active radiation (PAR) only (4 kJ-m−2/day), and PAR supplemented with UVR radiation at two intensities (24 kJ-m−2/day and 48 kJ-m−2/day). There was no significant difference in grazing rates between the PAR only treatment and the lower UVR treatment. However, grazing rates were significantly (∼66%) higher for copepods feeding on cells treated with the higher level of UVR. These results suggest that a short-term increase in UVR exposure results in a significant increase in the grazing rate of copepods and, thereby, potentially alters the flow rate of organic matter through this component of the ecosystem.

지방 바이오마커를 활용한 북서태평양에서 요각류(Euchaeta sp. and Pleuromamma spp.)의 서식 위도별 영양상태 및 먹이원 연구

In order to ascertain latitudinal variation of lipid contents and compositions in copepods, we collected warm water copepod species (Euchaeta sp. and Pleuromamma spp.) from four different regions from low (sub-tropical) to mid (temperate) latitudes in the Northwest Pacific Ocean. Total lipid contents of Pleuromamma spp. were about 11 <TEX>$ug{\cdot}ind^{-1}$</TEX> with little latitudinal variation, whereas Euchaeta sp. showed slightly higher lipid content (20 <TEX>$ug{\cdot}ind^{-1}$</TEX>) than Pleuromamma spp. with latitudinal gradient (low at subtropic and high at temperate). Wax esters, known as the major storage lipid classes, were found to be the dominant lipid classes (accounting for more than 35% of total lipids) in Euchaeta sp., whereas in Pleuromamma spp., phospholipids, known as cellular membrane components, were the dominant lipid classes. However, the exception was specimens from warm pool region exhibiting dominance in storage of lipids as a form of triacylglycerols. Among fatty acids, polyunsaturated fatty acids (PUFA), especially docosahexaenoic acid (DHA : 22:6(n-3)) (about 35% of total fatty acids), were most abundant in Euchaeta sp., while saturated fatty acids (SAFA), specially hexadecanoic acid (16:0) (about 30% of total fatty acids), were most abundant in Pleuromamma spp.. Among the neutral fraction of lipids, phytol, originated from the side chain of chlorophyll, was found in all samples which generally indicate active copepods feeding on algae. While only trace amounts of short-chain fatty alcohols were found in Pleuromamma spp., significant amounts of fatty alcohols were found in Euchaeta sp.. Particularly, significant amounts of long chain monounsaturated fatty alcohols (20:1 and 22:1), generally found in cold water species, were found in Euchaeta sp. from low latitudes. The latitudinal variation of trophic lipid markers in these copepods could be significantly related with in-situ food availability and species-specific diet preference. The result of this study suggests that the lipid contents and compositions in copepods may not only indicate their nutritional condition and feeding ecology but also provide insight into species-specific living strategies under different environmental conditions (i.e. water temperature, food availability).

Food web dynamics in the Scotia Sea in summer: A stable isotope study

The pelagic food web of the Scotia Sea was studied by analysing natural abundances of nitrogen and carbon stable isotopes of primary producers and pelagic consumers, sampled from the seasonal ice edge in the south to the Antarctic Polar Front in the north. The analysis covered, within a single mid-summer period, particulate organic matter (POM) and 38 taxa, ranging from suspension feeding copepods and salps to omnivorous euphausiids, pelagic fish and higher, land-based predators including fur seals, penguins and flying birds. Spatial variation in δ 15N of POM correlated well with nutrient availability and primary productivity. Latitudinal differences in δ 13C of POM were closely linked to variations in temperature, nutrients and productivity depending on the frontal region sampled. This translated to equivalent (although smaller) regional δ 13C differences among higher trophic levels. The trophic positions of species based on isotope values broadly agreed with previously published dietary data with three important exceptions. First, the carnivorous amphipod Themisto gaudichaudii had anomalously low δ 15N values. Second, Euphausia superba had δ 15N values that were also surprisingly low, considering the abundant literature suggesting its omnivory. Third, the copepod Rhincalanus gigas, considered a suspension feeder, had unexpectedly high δ 15N values rather more in keeping with omnivorous feeding. The consumer δ 15N values ranged from 1.2‰ (min.) measured in Salpa thompsoni (designated here as trophic level (TL) 2 across all regions) to 15.2‰ (max.) measured in white-chinned petrels ( Procellaria aequinoctialis, calculated as TL5 relative to the TL2 of salps). Excluding seabirds, the resulting food chain length of 3.7 TL (above POM at TL1) was lower than in most other Southern Ocean and temperate marine pelagic ecosystems. The majority (60%) of vertebrate predators occupied only 1–1.5 trophic levels above the herbivorous suspension feeders such as krill. This indicates the existence of the classic short food chain of POM–suspension feeder–vertebrate predator. However the presence of trophic levels 4 and above indicates the existence of alternative trophic pathways, for example involving myctophid fish or carrion, and that some wide-ranging predators which breed at South Georgia also feed outside the region. This conclusion is supported first by the continuum of δ 15N values between krill, suspension feeding copepods and myctophid fish, and secondly by higher trophic levels in several of the myctophid species in the low-krill region of the northern Scotia Sea, suggesting latitudinal differences in food web structure and food chain length.

Effects of suspended sediments on copepods feeding in a glacial influenced sub-Arctic fjord

), while no effect was found for M. longa.ForC. finmarchicus, a rela-tively constant fecal pellet production (FPP) and fecal pellet volume suggestedingestion of sediment, which probably led to reduction in egg production rates(EPRs) at high sediment concentrations. For Pseudocalanus sp., FPP decreased withincreasing sediment concentrations, while no effect was observed on EPR. No sig-nificant difference was observed in FPP for M. longa feeding on the diatom T. weiss-flogii compared to the ciliate Strombidium sulcatum. The study shows that highsediment concentrations influence the capability of carbon turnover in C. finmarchi-cus and Pseudocalanus sp., while M. longa appears to be more tolerant to high sedi-ment loads. Therefore, high concentrations of SPM could potentially influence thespecies composition of glacially influenced fjords.KEYWORDS: grazing; copepoda; suspended sediment; Greenland

Effect of different live food on survival and growth of first feeding barber goby, Elacatinus figaro (Sazima, Moura &amp; Rosa 1997) larvae

One of the major challenges in marine fish culture is how to provide live food of adequate size and nutritional quality for first-feeding larvae. Commonly used live food organisms, rotifers and brine shrimp, may not always be the best option. To determine the suitability of different zooplankton in the larviculture of Elacatinus figaro, three diets were tested: RE – rotifers Brachionus sp. (10 ind mL−1)+ciliate Euplotes sp. (10 ind mL−1), enriched with fatty acids; RC – enriched rotifers (10 ind mL−1)+wild copepod nauplii (10 ind mL−1); and R – enriched rotifers (20 ind mL−1). Survival rates were estimated 10 days after hatch (DAH) for the three test groups, and growth rates were evaluated for RE and R at 10 and 20 DAH. Although survival rate was numerically higher for the RC diet (41.1±14.2%), no significant difference was detected between groups fed RE (20.5±18.1%), RC or R (32.1±16.5%). At 10 DAH, the growth rate was significantly higher in RC (5.7±0.6 mm) than in R (4.6±0.5 mm), a trend that was also observed at 20 DAH for RC (8.6±0.5 mm) and R (5.8±0.7 mm) (P<0.05). E. figaro larvae fed on ciliates did not show satisfactory results, whereas feeding copepod nauplii enhanced growth.

Copepod feeding in a coastal area of active tidal mixing: diel and monthly variations of grazing impacts on phytoplankton biomass

AbstractThis study examined monthly feeding rates and grazing impact on phytoplankton biomass, as well as diel feeding rhythms of four key copepod species in a tidally well mixed estuary (Asan Bay, Korean Peninsula). Monthly ingestion rates estimated based on gut pigment analysis were closely associated with their peak densities, but not with phytoplankton biomass, implying high ingestion may be related to reproductive output for population growth. The three smaller copepods, Acartia hongi, Acartia pacifica and Paracalanus parvus, showed feeding preference for smaller phytoplankton (&lt;20 μm) with higher clearance rates, whereas the larger Calanus sinicus preferred larger phytoplankton. Acartia pacifica and P. parvus showed distinct increased nocturnal feeding rates as measured with gut fluorescence, whereas A. hongi showed no significant day–night differences. Copepod diel feeding patterns were not associated with food quantity, and endogenous physiological rhythm might be hypothesized as responsible for the observed diel feeding patterns. Grazing impact on phytoplankton biomass by the four copepods in the estuary was on average 8% (range 0.2–29.8%) of the phytoplankton standing stock, similar to values reported in other coastal waters. Very high copepod abundances but low daily carbon ration (&lt;20% for all copepods) provided by feeding on phytoplankton indicate that copepods also grazed on other non‐phytoplankton foods in Asan Bay.