Eugregarine infection within the digestive tract of larval Antarctic krill, Euphausia superba

The infection rate of eugregarine parasites, Cephaloidophora pacifica, within the digestive tract of larval Antarctic krill, Euphausia superba, was examined using samples collected from the Indian sector of the Southern Ocean. Immature and mature eugregarine gamont stages were found at all larval stages older than Calyptopis I stage. Eugregarine infection in 14.0% (N = 108) of the first feeding stage (Calyptopis I) suggested that krill larvae are at risk from being infected during physiological transition from non-feeding to feeding stages. Eugregarine prevalence and intensity of infection at the three calyptopis stages increased with stage/krill length. Statistical analysis showed that the intensity of C. pacifica infection also increased with host density. Thus, krill density is probably a key determinant of the intensity of infection. We found gamont stage eugregarines in the host hind-gut, blocking the passage of food. Eugregarine infections in larval krill may have a negative impact on digestion and absorption in the host digestive tract.     

Understanding the trophic role of the Antarctic ctenophore,Callianira antarctica,using lipid biomarkers

To better understand the trophic role of ctenophores in Antarctica during austral fall and winter, a major species of cydippid ctenophore, Callianira antarctica, was collected during April/May (fall) and August/September (winter) 2002 in the vicinity of Marguerite Bay. Lipid content, lipid classes, fatty acids, fatty alcohols and sterols were analyzed in animals, together with lipid biomarkers in krill and copepod species representing potential ctenophore prey. Lipid content in ctenophores collected in winter was slightly higher than from animals in fall (4.8 and 3.5% of dry weight, respectively). Polar lipids were the dominant lipid class in ctenophores, accounting for over half of the lipid content, with significant amounts of free fatty alcohols (more than 10% of total lipid content) detected. Lipid-class composition, however, differed significantly between seasons, with significant amounts of neutral lipid (wax esters and triacylglycerols) only detected in animals from fall. Although the dominant lipid classes in ctenophores varied between fall and winter, individual lipids (i.e., fatty acids, alcohols and sterols) showed only minor changes between seasons. Specifically, long-chain polyunsaturated fatty acids [20:5(n-3) and 22:6(n-3)] found in high abundance in larval krill were also elevated in ctenophores collected in winter. Very high amounts of monounsaturated fatty alcohols, particularly 20:1(n-9) and 22:1(n-11), known to be important components of wax esters in calanoid copepods, were also observed. Multivariate analysis using the suite of lipids found indicated that copepods are an important diet item for ctenophores in the study area. Results further suggest that C. antarctica feed actively year-round, with larval krill providing a food resource during austral winter.     

Energetic demands of larval krill, Euphausia superba, in winter

Metabolic rates of larval and juvenile krill, Euphausia superba, were measured on board ship during three winter cruises west of the Antarctic Peninsula (June-July 1987, June 1993, and June 1994), and also under different temperature regimes and feeding conditions during long-term maintenance in the laboratory (Palmer Station, winter 1993). A mean oxygen consumption and nitrogen excretion ratio of 31.1 measured on board ship at ambient ocean temperatures suggested that larval and juvenile krill from ice-covered waters were primarily herbivorous. Results from both shipboard and laboratory experiments demonstrated that oxygen consumption increased with temperature, but that larvae subjected to acute temperature increases exhibited higher rates. Experiments conducted at near ambient water temperatures for winter were also conducted to test the effect of habitat on the energy requirements of larval and juvenile krill. A comparison of the field and laboratory studies conducted at −1.5 to −1.8 °C showed that larvae from ice-covered waters and fed larvae in the laboratory had oxygen consumption rates significantly higher than those of larvae collected from open, i.e. ice-free, water and those starved in the laboratory. Results of the comparison lend support to the concept that in winter, larval and juvenile krill are better fed in ice-covered waters than in open water, and to the hypothesis that ice biota in the pack ice are an important food resource in winter for larval and juvenile krill.     

The overwintering of Antarctic krill, Euphausia superba, from an ecophysiological perspective

A major aim of this review is to determine which physiological functions are adopted by adults and larvae to survive the winter season with low food supply and their relative importance. A second aim is to clarify the extent to which seasonal variation in larval and adult krill physiology is mediated by environmental factors with a strong seasonality, such as food supply or day light. Experimental studies on adult krill have demonstrated that specific physiological adaptations during autumn and winter, such as reduced metabolic rates and feeding activity, are not caused simply by the scarcity of food, as was previously assumed. These adaptations appear to be influenced by the local light regime. The physiological functions that larval krill adopt during winter (reduced metabolism, delayed development, lipid utilisation, and variable growth rates) are, in contrast to the adults, under direct control by the available food supply. During winter, the adults often seem to have little association with sea ice (at least until early spring). The larvae, however, feed within sea ice but mainly on the grazers of the ice algal community rather than on the algae themselves. In this respect, a miss-match in timing of the occurrence of the last phytoplankton blooms in autumn and the start of the sea ice formation, as has been increasingly observed in the west Antarctic Peninsula (WAP) region, will impact larval krill development during winter in terms of food supply and consequently the krill stock in this region.     

Interannual variation in the diet of non-breeding male Antarctic fur seals, <Emphasis Type="Italic">Arctocephalus gazella</Emphasis>, at Isla 25 de Mayo/King George Island

The diet of non-breeding male Antarctic fur seals, Arctocephalus gazella, was investigated at Stranger Point, King George Island, through the analysis of scats during three consecutive summer seasons (1996, 1997, 1998). Overall, fish and krill were the most frequent prey occurring, respectively, in an average of 82.9% and 78.8% of samples (n = 131), followed by penguins (22.8%) and cephalopods (17.8%). Myctophids constituted almost 90% of the fish predated, with Electrona antarctica and Gymnoscopelus nicholsi being the most abundant and frequent species consumed. All fish taxa identified were krill feeding species suggesting that seals foraged mainly on a krill and a fish community associated with krill aggregations. However, a seasonal change was observed in the relative proportions of the different prey taxa, with a progressive decrease with time in the occurrence of krill and a concomitant increase of fish, penguins and squid. Possible influence of the strong 1997/98 ENSO event is discussed.     

Real-time PCR as an effective technique to assess the impact of phoresy by Paenibacillus sp. bacteria on Steinernema diaprepesi nematodes in nature

Quantitative real‐time PCR (qPCR) is a powerful tool to study species of cryptic organisms in complex food webs. This technique was recently developed to detect and quantify several species of entomopathogenic nematodes (EPNs), which are widely used for biological control of insects, and some natural enemies of EPNs such as nematophagous fungi and the phoretic bacteria Paenibacillus sp. and Paenibacillus nematophilus. A drawback to the use of primers and TaqMan probes designed for Paenibacillus sp. is that the qPCR also amplified Paenibacillus thiaminolyticus and Paenibacillus popilliae, two closely related species that are not phoretically associated with EPNs. Here, we report that the detection of Paenibacillus sp. DNA in nematode samples was two orders of magnitude greater (P < 0.001) when the bacterium was added to soil together with its EPN species‐specific host Steinernema diaprepesi than when it was added concomitantly with other EPNs or with species of bacterial‐feeding nematodes. Just 6% of samples detected trace amounts of P. thiaminolyticus and P. popilliae exposed to the same experimental conditions. Thus, although the molecular assay detects Paenibacillus spp. DNA in nonphoretic associations, the levels are essentially background compared to the detection of Paenibacillus sp. in association with its nematode host.     

Abundance, sizes and developmental stages of larval krill, Euphausia superba, during winter in ice-covered seas west of the Antarctic Peninsula

Larval krill were sampled west of the Antarctic Peninsula duringthree winter cruises: September 1991, June 1993 and September1993. Larval abundances were estimated from net catches andcompared directly to visual counts (made by a SCUBA diver) oflarvae occupying the ice habitat at the same sampling stations.The number of larvae per square meter sampled with nets wasmore often greater than that observed by the diver, irrespectiveof the sampling period. However, comparisons of larval abundancewithin sampling periods were not statistically significant.Larval krill collected by divers were significantly larger thanthose collected with nets for each of the three cruises. Thestage composition of larval krill also depended on the collectionmethod: net-collected samples contained a disproportionatelyhigh number of early furcilia larvae in June 1993 (early winter),and a disproportionately low number of early juveniles duringSeptember 1991 and 1993 (late winter). These results lead usto suggest that larval/juvenile krill occupy both the watercolumn and sea ice habitat during the austral winter, and thatthere are often differences in the sizes and developmental stagesof the two groups. For larval krill that occupied the sea icehabitat, aggregations were larger and more numerous during latewinter than in early winter. In addition, larvae within aggregationsoccupied structurally complex microhabitats, provided by over-raftedice floes, more often than they occupied smooth, downward-facingice surfaces where ice was not over-rafted.     

Mycobiota associated with larval mines of Thrypticus truncatus and T. sagittatus (Diptera, Dolichopodidae) on waterhyacinth, Eichhornia crassipes, in Argentina

Thrypticus truncatus is a candidate agent for biocontrol of waterhyacinth; the larvae of this diptera mine in the petioles and feed on the phloem in the vascular bundles. The mycobiota associated with T. truncatus and T. sagittatus mines was investigated during two surveys undertaken in the spring and autumn in the Delta of the Paraná River, Argentina. Isolations were made from the mines and larval feeding points, as well as from the larvae, following dissection of the petioles, and plated onto agar. Young and upper parts of the petioles without Thrypticus mines were used as controls. Twenty eight fungal species were isolated from the mines. Pestalotiopsis guepinii, Mucor attenuatus, Phoma tropica, Achlya americana, Fusarium avenaceum, Cladosporium cladosporioides, Clonostachys rosea, Epicoccum purpurascens, Plectosporium tabacinum, Alternaria alternata, and Acremonium sp. were the most common fungi associated with mines and feeding points. Cladosporium cladosporioides, Cytospora sp., Mucor attenuatus, and Phoma tropica were associated with the larval body. The list of fungi in mines was compared with bibliographic information to determine if the species are known pathogens on waterhyacinth or other plant species. This is the first study on mycobiota associated with T. truncatus and T. sagittatus mines in waterhyacinth petioles in Argentina.     

Settlement, growth and survival of abalone, Haliotis discus hannai, in response to eight monospecific benthic diatoms

The settlement, early growth and survival of the larval abalone Haliotis discus hannai in response to eight monospecific benthic diatoms were examined in the laboratory. Postlarvae showed active settling and feeding behaviour in all diatom species and in naturally occurring diatoms. Larval settlement rates differed significantly between experimental substrata after 24 h and 48 h. Nitzschia sp. (96.67 %), Hantzschia amphioxys var. leptocephala (95.00 %) and Navicula seminulum (90.00 %) strongly induced larval settlement of H. discus hannai. Postlarvae could feed on benthic diatoms (< 36 μm in shell length) with both weak and strong adhesion on the 4th day after settlement. Greatest growth (shell length) occurred on Nitzschia sp. (786.84 μm ± 2.50 SE and 773.09 μm ± 2.09 SE). Survival of postlarvae was also greatest on Nitzschia sp. (95.33 % ± 1.45 SE). These results indicate the effectiveness of Nitzschia sp., H. amphioxys var. leptocephala, N. seminulum, Rhaphoneis surirella and Navicula corymbosa as single species over natural diatoms in larval settlement and postlarvae growth of H. discus hannai. Thus, Nitzschia sp. has the best potential diet for larval settlement and postlarvae growth of H. discus hannai. H. amphioxys var. leptocephala and N. seminulum can be used as cues to induce larvae settlement, and R. surirella and N. corymbosa can be used as food for growing postlarval.     

Food and feeding ecology of postlarval and juvenile Pleuragramma antarcticum (Pisces; Notothenioidei) in the seasonal pack ice zone off the Antarctic peninsula

Summary Stomach contents of 275 postlarval and 269 one year old juvenile Pleuragramma antarcticum caught in February 1982, March 1981 and November 1977 in the Bransfield Strait and adjacent waters were investigated. Juveniles in November 1977 fed mainly on calanoid copepods and Oithona spp. The principal food of postlarvae in February 1982 were Oncaea spp., eggs of calanoid copepods and tintinnids whereas the staple food of juveniles in February 1982 consisted of calanoid copepods of which copepodites of Calanus propinquus were most abundant. Eggs of Euphausia superba were frequently ingested by postlarvae and were the main component of the juvenile diet in the Antarctic Sound. Postlarvae in March 1981 preyed on Oncaea spp. and calanoid eggs. There was a shift from feeding on cyclopoid copepods by postlarvae to feeding on calanoids by juveniles. The food particle size increased as a function of fish length. Maximum prey size was controlled by mouth width up to at least 45 mm standard length. Prey selection was apparently food density dependent with an inverse relationship between food abundance and selective feeding. Density dependent size selection may have resulted in resource partitioning among postlarval and juvenile fishes in February. This specific feeding behaviour is likely to be an adaptation to the low zooplankton stocks of the high Antarctic shelf waters to minimize food competition among the youngest age classes. Predation on krill eggs indicated that the frequent association of one year old juvenile Pleuragramma antarcticum with the Antarctic krill is related to local spawning events.     

Occurrence of larval Pacific lamprey Entosphenus tridentatus from Japan, detected by random amplified polymorphic DNA (RAPD) analysis

Species identifications of the Pacific lamprey Entosphenus tridentatus from four other Japanese lampreys, Lethenteron japonicum, L. kessleri, and two undescribed Lethenteron species (L. sp. N and L. sp. S), were carried out on the basis of random amplified polymorphic DNA (RAPD) using the polymerase chain reaction (PCR) method. Of 65 RAPD loci, seven loci possessing species-specific fragments were obtained for E. tridentatus. Based on these RAPD loci, four larval individuals of E. tridentatus from the Naka River (eastern Honshu Island, Japan) were recognized in 2001 and 2002. The existence of larval individuals of E. tridentatus, as well as spawning adults previously reported from the same river, indicated the possibility of residence in that species.     

Larval host plants of two lizard beetles in the genus Tetraphala (Coleoptera,Erotylidae, Languriinae,Languriini) from Taiwan,with a host plant list of Languriini

Lizard beetles (Erotylidae, Languriinae, Languriini) are known as stem borers of plants and contain agricultural pests and endangered species, but their species–host plant associations have been poorly documented. Here we investigated the larval host plants of two species of the genus Tetraphala Strum, T. collaris (Crotch) and Tetraphala sp. occurring in Taiwan. Females of T. collaris excavated living leafstalks and stems of the herbaceous dicot, Sambucus chinensis (Adoxaceae) using their mandibles for oviposition. We observed the eggs and early-instar larvae inside and nearby oviposition holes and late-instar larvae inside stems, suggesting that T. collaris uses living leafstalks and stems of S. chinensis as oviposition substrate and the larvae tunnel into stems with feeding on the tissues. Similarly, females of Tetraphala sp. excavated living leafstalks of the fern, Pteris wallichiana (Pteridaceae) using their mandibles for oviposition. We observed the eggs and early-instar larvae inside and nearby oviposition holes. When reared in laboratory, a larva reached adulthood inside the leafstalk. These results indicated that Tetraphala sp. uses living leafstalks of Pt. wallichiana as oviposition substrate and the larvae complete their development within. This study revealed that the genus Tetraphala contains both fern- and dicot-users during larval period. Further study is needed to clarify the evolutionary process of host plant use of languriines. Additionally, the host plant list of Languriini is provided.     

Distribution,size frequencies and maturity stages of krill,Euphausia superba,in relation to sea-ice in the Northern Weddell Sea

Summary The spring (November) and early summer (December) distribution pattern and demography of Euphausia superba in the seasonally ice covered areas of the north-western Weddell Sea are described. Sampling with a Rectangular Midwater Trawl (RMT) and during SCUBA diving were undertaken in the pack-ice during the EPOS expedition 1988/1989 of RV Polarstern. These data were compared with former cruises during late winter (October) and summer (February). The biomass values of krill (1–27 g/m²) in the water column within the ice covered areas were of the same order of magnitude as earlier acoustic estimates in the ice-edge region of the same area. No significant correlation between percentage ice cover and krill abundance in the water column was found. Cluster analyses of size frequency distributions and maturity stage composition revealed the demography of the animals sampled. Samples obtained by SCUBA and RMT are compatible and results show a geographic and demographic separation of the krill. It is proposed that krill in the northern zone are largely emigrants from the Bellingshausen Sea, while the krill in the southern zone are of eastern Weddell Sea origin. Further studies concentrating on the under-ice distribution of krill are recommended.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation. Publication no 62 of the Alfred-Wegener-Institut für Polar- und Meeresforschung     

Description of Cydia piceicola,sp. nov. (Lepidoptera,Tortricidae), feeding on Picea jezoensis in Korea

The adult and the early stages of Cydia piceicola, sp. nov., are described and illustrated from Korea. Larvae of the new species feed on Picea jezoensis (Siebold et Zucc.) Carrière, The life history and larval feeding habits are briefly discussed.     

Essential krill species habitat resolved by seasonal upwelling and ocean circulation models within the large marine ecosystem of the California Current System

Due to their global distribution, high biomass and energy content, euphausiids (krill) are important prey for many mid and upper trophic level marine organisms. Understanding drivers of krill habitat is essential for forecasting range shifts, and to better understand the response of krill predators to climate change. We hypothesized that the distribution and abundance of krill species derived from ecosystem surveys in spring/summer relates to geomorphic features, coastal upwelling during the preceding winter, and spring mesoscale oceanographic conditions. To test this hypothesis, we used boosted regression trees with environmental data and ocean model output to quantify the habitat associations of two primary krill species (Euphausia pacifica and Thysanoessa spinifera) in the central California Current Ecosystem from 2002 to 2018. Models confirmed the neritic distribution of T. spinifera and pelagic, outer slope association of E. pacifica (deviance explained ~35%). Distribution of these species were influenced by depth and bottom rugosity; chlorophyll-a concentrations and increased winter upwelling conditions; and spring surface currents and wind stress. Thysanoessa spinifera and E. pacifica abundance responded negatively (positively) to warm (cold) climate events, confirming known relationships. As an independent evaluation of krill models, observations of krill predator (seabirds, marine mammals) distribution indicated they were present within habitats of predicted high krill species abundance. Our framework indicates species-specific habitat relationships for these foundational forage species and their negative response to large-scale climate variations, such as El Niño and marine heatwave conditions. The approach can be easily transferred to other ecosystems or krill species that respond to similar ocean and climate forcing.     

Diet of two icefish species from the South Shetland Islands and Elephant Island,<Emphasis Type="Italic"> Champsocephalus gunnari</Emphasis> and<Emphasis Type="Italic"> Chaenocephalus aceratus</Emphasis>

The summer diet of two species of icefishes (Channichthyidae) from the South Shetland Islands and Elephant Island, Champsocephalus gunnari and Chaenocephalus aceratus, was investigated from 2001 to 2003. Champsocephalus gunnari fed almost exclusively on krill (Euphausia superba) in all years. The importance of other taxa (Themisto gaudichaudii, mysids, myctophids) in the diet was negligible. The average feeding rate of Champsocephalus gunnari inferred from an exponential gastric evacuation model was between 1.0 and 1.5% body weight per day. Most of the stomachs of Chaenocephalus aceratus were empty. Stomachs with food contained mainly krill, mysids and fish. Among the fish taken, locally abundant species formed the bulk of the diet: Gobionotothen gibberifrons in 2001, Lepidonotothen larseni and Champsocephalus gunnari in 2002 and L. larseni in 2003. An ontogenetic shift in feeding preference of Chaenocephalus aceratus was observed: fish smaller than 30 cm fed on krill and mysids, while larger animals relied primarily on fish.     

Melatonin and its possible role in mediating seasonal metabolic changes of Antarctic krill, Euphausia superba

Melatonin, the chief secretory product of the vertebrate pineal gland is suspected to be a ubiquitous molecule principally involved in the transduction of photoperiodic information. Besides vertebrates, melatonin has been detected throughout phylogeny in numerous non-vertebrate taxa. In the present study, the occurrence of melatonin in Antarctic krill Euphausia superba and its possible role in mediating seasonal metabolic changes was evaluated. Melatonin was quantified by enzyme linked immunosorbent assay (ELISA) in high performance liquid chromatography (HPLC) purified extracts of eyestalks and hemolymph of krill sampled in the Lazarev Sea during the Antarctic winter and summer. In addition, oxygen uptake rates and the activities of the metabolic enzyme malate dehydrogenase (MDH) were recorded to assess the metabolic status of krill. Validation of melatonin measurements was carried out on the basis of three different extraction methods with parallel determination of melatonin by ELISA in crude extracts and in HPLC purified extracts, and after derivatization of melatonin under alkaline conditions in the presence of hydrogen peroxide. A significantly higher respiration rate and MDH activity was found in summer krill than in winter krill indicating that krill was in a state of reduced metabolic activity during winter. However, neither during winter nor during summer there were detectable melatonin concentrations in the visual system or hemolymph of krill. Based on these results, we question a mediating role of melatonin in the control of seasonal metabolic changes in Antarctic krill.     

Exotic sturgeons in the Vistula Lagoon in 2011, their occurrence,diet and parasites,with notes on the fishery background

The Siberian sturgeon Acipenser baerii and the sterlet Acipenser ruthenus were recorded for the first time in the Vistula Lagoon in 2011. Among 66 sturgeons collected between April and December 2011, the Siberian sturgeon was the most numerous species (77%); however, a significant seasonal variability was observed, with sterlet dominating in the catches in late autumn of the same year. The stomach contents of the two species differed widely: Siberian sturgeon (14.9–42.2 cm standard length, SL) fed on crustaceans (Cercopagis pengoi, Oithona sp., Neomysis integer) (10.7% IRI), larvae and pupas of insects (Chaoborus sp., Chironomus sp., Polypedilum sp., Procladius sp., Culex sp.) (88.9% IRI) and fishes (Neogobius melanostomus, Osmerus eperlanus) (0.5% IRI), whereas sterlet (24.0–34.4 cm SL) consumed crustaceans (N. integer) (64.3% IRI), larvae of insects (Chironomus sp., Polypedilum sp.) (20.3% IRI) and fish (N. melanostomus) (15.4% IRI). Single Siberian sturgeon (4.3%) were found to harbour the parasitic nematode (Raphidascaris acus).     

Oceanic micronektonic/macrozooplanktonic community structure and feeding in ice covered Antarctic waters during the winter (AMERIEZ 1988)

Summary Fifty-seven species of oceanic micronekton and macrozooplankton were collected under pack ice during the winter in the vicinity of the Weddell-Scotia Confluence with a modified opening-closing Tucker trawl. The majority of the 57 species did not vertically migrate and lived deeper during the winter than during the spring or fall. However, despite the short day length, several of the most common mesopelagic fish and crustaceans did migrate. Fish moved into shallower depths at night but apparently most did not continue into the near-freezing upper mixed layer, leaving that zone to the migratory crustaceans. In the upper 1000 m, the dominant species were, in order of decreasing biomass, Euphausia superba, the cnidarian Atolla wyvillei, the ctenophore Beroe sp., and the mesopelagic fish Electrona antarctica, Bathylagus antarcticus and Gymnoscopelus braueri. Thysanoessa macrura and Salpa thompsoni were biomass subdominants. The majority of the dominant species showed little seasonal differences in biomass. However, the biomass of gelatinous species varied considerably with A. wyvillei and Beroe sp. being most abundant and S. thompsoni least abundant during the winter. Incidence of food in the stomachs in several important species was low, suggesting a low impact on their Zooplankton prey. Specimens of S. thompsoni had high quantities of food in their guts but this species was uncommon so its net impact would also have been low. Euphausia superba and the three common mesopelagic fish had significantly lower stomach fullness ratings during the winter than during the fall, suggesting an overall decrease in feeding activity of dominant species during the winter.