Pleurobrachia Bachei Research Articles

DNA Methylation in Basal Metazoans: Insights from Ctenophores.

Epigenetic modifications control gene expression without altering the primary DNA sequence. However, little is known about DNA methylation in invertebrates and its evolution. Here, we characterize two types of genomic DNA methylation in ctenophores, 5-methyl cytosine (5-mC) and the unconventional form of methylation 6-methyl adenine (6-mA). Using both bisulfite sequencing and an ELISA-based colorimetric assay, we experimentally confirmed the presence of 5-mC DNA methylation in ctenophores. In contrast to other invertebrates studied, Mnemiopsis leidyi has lower levels of genome-wide 5-mC methylation, but higher levels of 5-mC methylation in promoters when compared with gene bodies. Phylogenetic analysis showed that ctenophores have distinct forms of DNA methyltransferase 1 (DNMT1); the zf-CXXC domain type, which localized DNMT1 to CpG sites, and is a metazoan specific innovation. We also show that ctenophores encode the full repertoire of putative enzymes for 6-mA DNA methylation, and these genes are expressed in the aboral organ of Mnemiopsis. Using an ELISA-based colorimetric assay, we experimentally confirmed the presence of 6-mA methylation in the genomes of three different species of ctenophores, M. leidyi, Beroe abyssicola, and Pleurobrachia bachei. The functional role of this novel epigenomic mark is currently unknown. In summary, despite their compact genomes, there is a wide variety of epigenomic mechanisms employed by basal metazoans that provide novel insights into the evolutionary origins of biological novelties.

Rapid evolution of the compact and unusual mitochondrial genome in the ctenophore, Pleurobrachia bachei

Ctenophores are one of the most basally branching lineages of metazoans with the largest mitochondrial organelles in the animal kingdom. We sequenced the mitochondrial (mtDNA) genome from the Pacific cidipid ctenophore, Pleurobrachia bachei. The circular mitochondrial genome is 11,016nts, with only 12 genes, and one of the smallest metazoan mtDNA genomes recorded. The protein coding genes are intronless cox1–3, cob, nad1, 3, 4, 4L and 5. The nad2 and 6 genes are represented as short fragments whereas the atp6 gene was found in the nuclear genome. Only the large ribosomal RNA subunit and two tRNAs were present with possibly the small subunit unidentifiable due to extensive fragmentation. The observed unique features of this mitochondrial genome suggest that nuclear and mitochondrial genomes have evolved at very different rates. This reduced mtDNA genome sharply contrasts with the very large sizes of mtDNA found in other basal metazoans including Porifera (sponges), and Placozoa (Trichoplax).

Distribution of carnivorous gelatinous zooplankton in the upwelling zone off central Chile (austral spring 2001)

) nearshore,characteristics of upwelling conditions in eastern boundary regions, occurredthroughout the cruise. Two groups of gelatinous carnivorous zooplankton wereidentified associated with the density front structure: one located coastward fromthe front (Sphaeronectes gracilis, Euphysa aurata and Beroe cucumis) and another locatedseaward from the front (Liriope tetraphylla, Pleurobrachia bachei, Abylopsis tetragona andThalassocalyce inconstans). The most abundant species occurred more frequently inwell-oxygenated waters; however, high abundances (10–100 ind. 100 m

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

To estimate the predation effect of the predominant ctenophore Pleurobrachia bachei on the small-copepod community in the upwelling area off Mejillones (23° S), northern Chile, a series of oceanographic cruises and predation experiments were conducted in the austral springs 2000, 2001 and 2002. The daily consumption rates and predatory effect of P. bachei on the small copepods (in terms of % of standing stock and biomass removed daily) were determined at three stations located in relation to the shelf-break (coastal, shelf-break and oceanic) reaching values up to 4.5% per day of the <1500 μm copepod standing stock. Our results indicate that the ctenophores were most abundant at the coastal station, that small copepods dominated the copepod community (being more abundant nearshore), and that the relative frequency of ctenophores with copepods in their guts was also higher near the coast. The predatory effect of P. bachei on the small-copepod community was also higher in the coastal zone. However, the effect of this predation on the copepod biomass in terms of carbon did not decrease steadily seawards, which may be due to the larger sized copepods consumed at the offshore stations. Determinations of predatory effect on the secondary production of the more abundant small-copepod populations (i.e 26% daily in 2000) suggest that this single species of Pleurobrachia is modulating the population growth rate of the small copepods, the copepod community size structure, and maybe even the alternance of key species in the Mejillones coastal upwelling zone.

The role of aerobic metabolism and intragel oxygen in hypoxia tolerance of three ctenophores: Pleurobrachia bachei, Bolinopsis infundibulum and Mnemiopsis leidyi

Ctenophores are important members of planktonic communities that are often abundant in dysaerobic environments. Previous studies have shown that ctenophores are not adversely affected by extended periods of hypoxia. The three species used in this study, Pleurobrachia bachei, Bolinopsis infundibulum, and Mnemiopsis leidyi, were all able to oxyregulate to very low partial pressures of oxygen (PO2s). These species were found to have mean critical oxygen tensions of 7.7, 10.6, and 7.2 hPa respectively. In general, ctenophores are better oxyregulators than medusae and many species of shrimps, fish and squid. Intragel oxygen was measured using a fibre optic oxygen optode. All these ctenophores have intragel subsurface [O2]s of 5–10% below that of the surrounding seawater. Intragel oxygen measurements of P. bachei showed a gradient of decreasing PO2 from surface tissues to the gut. Specimens of P. bachei over 14 mm in diameter had anaerobic guts. Survival times in anoxia ranged from 0 h for M. leidyi to up to 6 h for P. bachei. Ctenophores rely on aerobic metabolism to tolerate hypoxia.

Macrozooplankton and micronekton of the lower San Francisco estuary: Seasonal, interannual, and regional variation in relation to environmental conditions

Macrozooplankton and micronekton are intermediaries linking lower trophic levels (e.g., phytoplankton and mesozooplankton) to higher ones (e.g., fishes and birds). These organisms have not been extensively studied in the San Francisco Estuary (SFE), California. The objective of this study was to determine the distribution and abundance of macrozooplankton and micronekton in the SFE and to describe how these vary seasonally, interannually, and regionally in relation to environmental variables. Water column macrozooplankton and micronekton were sampled monthly from September 1997 to December 2000 at 6 stations spanning North, Central, and South Bays using a Methot Trawl. The macrozooplankton and micronekton in the lower SFE were dominated by 4 fishes and 7 invertebrates that comprised 98% of the total catch. Correspondence analyses revealed 4 groups of species that exhibited similar patterns of distri- bution and abundance. The assemblages changed between the wet and dry seasons and with distance from the coastal ocean. Based on abundance patterns, the dominant taxa in the lower SFE can be classified as: organisms spawned from common members of neritic assemblages that use mostly North Bay and that are abundant during the dry season (Clupea pallasi, Spirinchus thaleichthys, Porichthys notatus); estuarine-dependent organisms with broad distributions in the estuary year-round (Crangon franciscorum, Crangon nigricauda, Engraulis mordax); resident species remaining within the estuary but occurring mostly in South Bay during the wet season (Palaemon macrodactlyus, Synidotea laticauda, Neomysis kadi- akensis); and gelatinous species (Pleurobrachia bachei, Polyorchis spp.) occurring in all three bays with a single peak in abundance in December and January in North and South Bays. The variation in distribution, abundance, and composition of macrozooplankton and micronekton was related to life history strategies, distance from the coastal ocean, and season.

Abundancia estacional y distribución vertical del zooplancton gelatinoso carnívoro en una área de surgencia en el norte del Sistema de la Corriente de Humboldt

Seasonal abundance and vertical distribution of the carnivorous gelatinous zooplankton in an upwelling area of the northern Humboldt Current System ABSTRACT. The seasonal abundance and vertical distribution of gelatinous zooplankton collected during four cruises off Mejillones bay were analyzed. In this area we identified 44 species of macroplankton distributed in 23 siphonophores, 17 hydromedusae, and 4 ctenophores. Eight species, Sphaeronectes irregularis, Rhizophysa eysenhardti, Amphogona apicata, Proboscidactyla stellata, Sarsia coccometra, Pleurobrachia bachei, Thalassocalyce inconstans and Velamen parallelum, are the first records in the Humboldt Current System. The seasonal distribution showed an increase in abundance in spring and summer, with the highest aggregations (> 2600 ind·100 m -3 ) of Aglaura hemistoma, Solmundella bitentaculata, Muggiaea atlantica and Pleurobrachia bachei in October and Obelia spp. in February. The highest densities were observed in the coastal station and in the oceanic front, while the oceanic station was characterized by a strong decrease in abundance. The vertical distribution showed that the most dominant species were founded in the first 100 m of the water column, with a higher concentration of organisms in the first 25 or 50 m of depth. This vertical distribution could be limited by presence of a minimum dissolved oxygen layer (< 1 ml·L -1 ) in shallow waters (30-50

Impact of formalin preservation on Pleurobrachia bachei (Ctenophora)

Here, we report on the impact of formalin preservation on the physical dimensions of the tentaculate ctenophore Pleurobrachia bachei A. Agassiz collected in the North East Pacific Ocean. Contrary to previously published papers [Oorthuyzen, W., Sadée, C., 1982. Voorkomen en groei van Pleurobrachia pileus en Aurelia aurita in de westelijke Wadddenzee en hun mogelijke rol als predator van platvislarven. Netherlands Institute of Sea Research, Texel; Yip, 1982. A note on the effect of preserving ctenophores in formaldehyde–seawater. Ir. Nat. J. 20 416–419] where a standard 20% shrinkage was applied to whole populations, we found that shrinkage rates are not constant and vary widely with the size of the specimen. A size reduction of 5–80% was observed in individuals ranging from 23 to 5 mm in boreal diameter when alive. The relationship between dry weight (DW) and length is also affected by the preservation process. Previously published biomass data and physiological rates based on preserved samples should therefore be re-examined when population was largely dominated by small size individuals.

Digestion of pelagic Ctenophora and Cnidaria by fish

The diet of chum salmon (Oncorhynchus keta) can range from a primarily arthropod to a primarily gelatinous composition. Because no data exist for the digestion rates of gelatinous prey in any fish, it has not been possible to convert data on stomach contents to feeding rates. We measured rates of digestion to address this issue. In freely feeding age-0 chum salmon, the ctenophore Pleurobrachia bachei was digested almost completely within 1 h, whereas 70% of shrimp sections of similar mass remained after 5 h at 13°C. To examine the fast progress of digestion at smaller intervals, age-0 and age-1 fish were also force-fed with whole P. bachei or sections of the hydromedusa Aequorea victoria. These data emphasize the necessity of examining fish stomachs very quickly after capture. Although gelatinous organisms have high water and salt content relative to their organic content, given the rapid rates of digestion observed, coelenterates might rival arthropods as energy sources.

Prey selection and dietary overlap among zooplanktivorous jellyfish and juvenile fishes in Prince William Sound, Alaska

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 210:67-83 (2001) - doi:10.3354/meps210067 Prey selection and dietary overlap among zooplanktivorous jellyfish and juvenile fishes in Prince William Sound, Alaska Jennifer E. Purcell1,*, Molly V. Sturdevant2 1University of Maryland Center for Environmental Science, Horn Point Laboratory, PO Box 775, Cambridge, Maryland 21613, USA 2NOAA/NMFS, Alaska Fisheries Science Center, Auke Bay Laboratory, 11305 Glacier Highway, Juneau, Alaska 99801, USA *Present address: Shannan Point Marine Center, 1900 Shannon Point Rd., Anacortes, Washington 98221, USA. E-mail: purcell@hpl.umces.edu ABSTRACT: The potential for competition for food among zooplanktivorous species of gelatinous zooplankton and fishes has been the subject of much speculation. Here, we evaluate the dietary overlaps among 2 scyphomedusan species, Aurelia labiata and Cyanea capillata, 1 ctenophore species, Pleurobrachia bachei, 1 hydromedusan species, Aequorea aequorea var. albida, and juveniles (Age 0) of 4 forage fish species, walleye pollock Theragra chalcogramma, Pacific sandlance Ammodytes hexapterus, Pacific herring Clupea pallasi, and pink salmon Oncorhynchus gorbuscha. Zooplankton samples collected in July-August 1995 to 1998 showed great similarity among years (86 to 96%), which allowed valid dietary comparisons between pelagic coelenterates and fishes collected in different years during that period. The predators fell into 2 groups, one that ate primarily crustacean prey (A. labiata, P. bachei, juvenile walleye pollock, sandlance, and herring), and another that ate mostly larvaceans (C. capillata, A. aequorea, and juvenile pink salmon). Species within the first group showed significant positive selection for crustacean prey and significant negative selection for larvaceans. The opposite trends were observed in the second group. Dietary overlaps were higher among crustacean-eating species (63 ± 13%) and larvacean-eating species (66 ± 10%) than when comparing crustacean- with larvacean-eating species (24 ± 14%). Dietary overlaps among pelagic coelenterate species (41 ± 21%) and among fish species (42 ± 25%) were similar, while overlaps between pelagic coelenterate and fish species averaged 50 ± 21%. These pelagic coelenterate and fish species were collected together in 45 purse seine sets taken in Prince William Sound in July 1999. We conclude that the diets of pelagic coelenterate and forage fish species overlap substantially, and that the species co-occur spatially and temporally. Therefore, the potential for competition for prey exists for these zooplanktivores in Prince William Sound. KEY WORDS: Aurelia · Competition · Ctenophore · Cyanea · Herring · Pollock · Salmon · Sandlance · Zooplankton Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 210. Online publication date: January 26, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Estimating the predatory impact of gelatinous zooplankton

We propose a new approach to assess the predatory impact of gelatinous zooplankton on their prey, in which information from field samples and laboratory experiments allows us to estimate predator ingestion rates from analyses of predator gut contents. The feasibility of this approach was tested in laboratory experiments with the ctenophore Pleurobrachia bachei feeding on adult stages of the copepods Pseudocalanus newmani and Acartia longiremis. We developed a simple model of predator ingestion-egestion dynamics. The model assumes that predator clearance rates, F, and instantaneous egestion rates, c, are constant over the range of prey concentrations appropriate to the field study. A series of experiments was designed to test the validity of these assumptions and to estimate values of the parameters F and E for Pleurobrachia feeding on Pseudocalanus and Acartia. Results from these experiments indicate that the above assumptions are reasonable for these predator-prey pairs until prey concentrations exceed 60,000 prey m- 3. Ingestion rates are shown to be proportional to predator gut contents, with the slope of the relationship providing an estimate of the instantaneous egestion rate. Provided that the model assumptions are met, this approach can be used to estimate the predatory impact of other planktivorous predators on more complex prey assemblages.

Ectoparasitism by a dinoflagellate (Dinoflagellata: Oodinidae) on 5 ctenophores (Ctenophora) and a hydromedusa (Cnidaria)

Oodiniurn sp., an ectoparasitic oodinid dinoflagellate that closely resembles Oodinium jordani McLean & Nielsen, 1989 described from Sagitta elegans Verrill, 1873 (Phylum Chaetognatha), has been seen to parasitize Beroe abyssjcola Mortensen, 1927, Bolinopsis ?infundibulum (0. F . Miiller, 1776), Euplokamis dunlapae Mills, 1987, Dryodora glandiformis (Mertens, 1833), and Pleurobrachia bachei A. Agassiz, 1860, which represent 3 orders of the phylum Ctenophora, and the hydromedusa Euphysa sp. (phylum Cnidaria) in marine waters of the San Juan Archipelago, Washington State, USA. Up to several hundred trophozoites may be found on a single ctenophore, although most ctenophore hosts carry less than 50; the hydromedusa never carried more than 4. The parasites occurred on their ctenophore and medusan hosts from late October through early April, and not in the warmer months. These are the first reported instances of parasitism by a dinoflagellate on the Ctenophora, and by an Oodinium on the Cnidaria.

Daily ration and predation by medusae and ctenophores in Saanich Inlet, B.C., Canada

The daily ration and predation impact of medusae and ctenophores in the upper 25 m of Saanich Inlet were determined using data from gut contents analyses, digestion times, and predator/prey densities. The weight-specific daily rations of the 3 major gelatinous predators ( Pleurobrachia bachei, Phialidium gregarium, and Phialidium lomae) were a negative power function of their biomass. Small predators obtained a ration much in excess of maintenance needs, while the largest specimens had little excess carbon growth or reproduction. In the upper 25 m predation impact was small on the total mesozooplankton, (mostly <1%·d −1 of biomass cropped), but it was higher in the upper 5 m (5 to 10%·d −1 of biomass removed). Specific predation on Euphausia pacifica eggs and nauplii was much greater, with 10 to 40% of stocks consumed by gelatinous predators per day. In Saanich Inlet, medusae and ctenophores were significant consumers of commercially important euphausiids (eggs and larvae), and are probably competitors of juvenile salmon for these same prey.

Foraging Behavior and Prey Selection by the Ambush Entangling Predator Pleurobrachia Bachei

Ctenophores and other gelatinous predators in the ocean are ephemeral in their spatial and temporal distributions, but often have a dramatic impact on the dynamics of their prey populations. Considerable information is currently available on the functional and numerical responses of several nearshore ctenophore species; however, an understanding of their potential for shaping the structure of natural zooplankton assemblages requires further information on the selective nature of their predation. Prey selection by the tentaculate ctenophore Pleurobrachia bachei was examined in the laboratory with predation experiments and videotaped observations of predator and prey behavior. Prey types offered to the ctenophore included each of the developmental stages of Calanus pacificus, adult Acartia clausii, and adult Pseudocalanus sp. Pleurobrachia exhibited an unusual, bimodal pattern of prey selection on the different developmental stages of Calanus. Calanus' vulnerability increased through the naupliar stages, dropped at the first copepodid stage, and then rose again throughout the subsequent copepodid stages prior to another decline at the adult stage. Adult Acartia and Pseudocalanus were found to be among the most vulnerable of the prey types offered to Pleurobrachia. We conclude that Pleurobrachia's diet is determined by the relative availability and vulnerability of prey, and that vulnerability to the ctenophore can be predicted from prey swimming speeds and the susceptibility of prey after encounter.

Seasonal changes in the standing stocks, growth rates, and production rates of gelatinous predators in Saanich Inlet, British Columbia

Thirty-three species of gelatinous predators (medusae and ctenophores) were collected in the uppermost 25 m of Saanich Inlet over 3 spring seasons. Of these, 6 species (5 hydromedusae: Aequorea victoria, Aglantha digitale, Mitrocoma cellularia, Phialidium gregarium, and Phialidium lomae; and 1 ctenophore: Pleurobrachia bachei) cornpnsed more than 90 O/O of the total gelatinous predator biomass. P. bachei comprised 40 % of the total dry weight of gelatinous predators, with peak standlng stocks reaching 100 mg DW m-3 (-5 mg C m-3). Phialidium spp, formed 20 % of the total dry weight, with P. gregarium reaching a maxlmum value at 1 station of about 200 mg DW m-3 (-20 mg C m-3). Total gelatinous predator bionlass, at a single stabon, reached nearly 400 mg DW m-3 (-30 mg C m-3) in late May. A conservative estimate of net yearly production in the upper 25 m is 6 to 10 mg C m-J. Standing stocks of individual species had doubling times of 5 to 17 d . Food supply (mainly the abundance of euphausiid eggs), coupled with temperature, were probably the pnmary factors regulating growth and production.

MORPHOLOGICAL AND BEHAVIORAL DEFENSES OF TROCHOPHORE LARVAE OFSABELLARIA CEMENTARIUM(POLYCHAETA) AGAINST FOUR PLANKTONIC PREDATORS

Controlled experiments were conducted by offering eggs, pre-setal trochophores, and setose trochophores of the polychaete Sabellaria cementarium to four planktonic predators, Pleurobrachia bachei (Ctenophora), Aequorea victoria (Hydrozoa), brach-yuran megalopa (Crustacea), and juvenile Sebastes spp. (Pisces). Each predator species captures prey with different mechanisms and the prey, while similar in size, differ in motility and presence or absence of setae.Consumption of non-motile eggs was greater by megalopa but less by A. victoria than consumption of pre-setal trochophores; it is suggested that differences in predator feeding mechanisms account for these differences. Setose trochophores were always consumed at lower rates than the younger stages. The evidence suggests that setae can function in larval defense against an array of predators with different feeding mechanisms, but that swimming may increase, decrease, or have no effect upon rate of predation, depending upon predator species.

EVIDENCE THAT ION REGULATION IN HYDROMEDUSAE AND CTENOPHORES DOES NOT FACILITATE VERTICAL MIGRATION

Medusae and ctenophores, like many types of gelatinous zooplankton, actively exclude sulphate ion from their mesogloeal body fluid and thus gain lift(buoyancy). It is hypothesized that vertically migrating species might show day/night variations in the rate of sulphate elimination to regulate buoyancy dynamically and that such changes are a major factor in vertical migration. To test this hypothesis, a series of laboratory experiments were conducted using medusae and ctenophores. Concentrations of radioactive sulphate were measured in equilibrium (uptake) experiments and concentrations of sodium, magnesium, potassium, and calcium ions were measured using atomic absorption spectrophotometry. No evidence of day/night (light/dark) changes in ion concentrations were found for the hydromedusae Aequorea victoria, Aglantha digitale, Gonionemus vertens, Mitrocoma cellularia, Phiaildium gregarium, Polyorchis penicillatus, Sarsia tubulosa, and Stomotoca atra or for the ctenophore Pleurobrachia bachei. It is concluded that changes in ionic regulation are not a major factor in diel vertical migration. It is thus hypothesized that for these animals vertical migration is accomplished solely by swimming.