Nemopsis Bachei Research Articles

Bacterial associations with the hydromedusa Nemopsis bachei and scyphomedusa Aurelia aurita from the North Atlantic Ocean

ABSTRACTRecent studies suggest that jellyfish influence the community composition of marine microorganisms, but few studies have been conducted contrasting communities among different jellyfish taxa. In this study microbial communities were compared between two cnidarians found in North Atlantic Ocean coastal waters during the spring–summer months. Microbial communities associated with the invasive hydrozoan Nemopsis bachei and the cosmopolitan scyphozoan Aurelia aurita (Cnidaria) were characterized based on the 16S rRNA gene sequence. The bacterial communities associated with the jellyfish were significantly different from the communities in seawater, and N. bachei and A. aurita hosted taxon-specific bacterial groups. Gammaproteobacteria, Bacteroidetes and Alphaproteobacteria dominated bacterial sequences on N. bachei, the dominant orders including Vibrionales, Flavobacteriales, Rhizobiales and Rickettsiales. Vibrio spp. and Photobacterium spp. were abundant in N. bachei, and Tenacibaculum sp. (Bacteroidetes) had a host-specific association with N. bachei. Mycoplasmatales was a prominent, unique, and potentially host-promoted association in A. aurita, and overall Cyanobacteria, Tenericutes and unclassified bacteria dominated the sequences in A. aurita. This is the first description of the microbial community composition in N. bachei, which has been reported as an invasive species in eastern North Atlantic waters. Overall these results suggest that different cnidarians in North Atlantic coastal waters promote growth of distinct microbial communities. Jellyfish could thus differentially influence microbially mediated biogeochemical cycles and food webs in regions where they proliferate.

Spatial and temporal patterns of occurrence of three alien hydromedusae, Blackfordia virginica (Mayer, 1910), Nemopsis bachei (Agassiz, 1849) and Maeotias marginata (Modeer, 1791), in the Gironde Estuary (France)

Spatial and temporal patterns of occurrence of three alien hydromedusae, Blackfordia virginica (Mayer, 1910), Nemopsis bachei (Agassiz, 1849) and Maeotias marginata (Modeer, 1791), in the Gironde Estuary (France)

Gelatinous zooplankton in the Belgian part of the North Sea and the adjacent Schelde estuary: Spatio-temporal distribution patterns and population dynamics

Many ocean ecosystems are thought to be heading towards a dominance of gelatinous organisms. However, gelatinous zooplankton has been largely understudied and the absence of quantitative long-term data for the studied area impedes drawing conclusions on potential increasing densities. This study gives a comprehensive overview of the spatio-temporal distribution patterns of gelatinous zooplankton in terms of diversity and density in the Belgian part of the North Sea and the adjacent Schelde estuary, based on monthly and seasonal samples between March 2011 and February 2012. Three Scyphozoa, three Ctenophora and 27 Hydrozoa taxa were identified, including three non-indigenous species: Mnemiopsis leidyi, Nemopsis bachei and Lovenella assimilis. In general, one gelatinous zooplankton assemblage was found across locations and seasons. Average gelatinous zooplankton densities reached up to 18ind·m−3 near the coast, gradually declining towards the open sea. In the brackish Schelde estuary, average densities remained below 3ind·m−3. Highest gelatinous zooplankton densities were recorded in summer and autumn. Overall, hydromedusae were the most important group both in terms of diversity and density. The ctenophore Pleurobrachia pileus and the hydromedusa Clytia sp. were present in every season and at every location. Gelatinous zooplankton densities never outnumbered the non-gelatinous zooplankton densities recorded from the WP3 samples. The spatial and temporal distribution patterns seemed to be mainly driven by temperature (season) and salinity (location). Other environmental parameters including (larger) non-gelatinous zooplankton densities (as an important food source) were not retained in the most parsimonious DistLM model.In terms of population dynamics, Beroe sp. seemed to follow the three reproductive cycles of its prey P. pileus and the presence of M. leidyi, which were abundant in a broad size spectrum in summer and autumn. In general, gelatinous zooplankton diversity was higher, but densities were in the same order of magnitude compared to adjacent areas in the North Sea. This study provides a baseline against which a potential increase in gelatinous zooplankton in the Belgian part of the North Sea and the Schelde estuary can be measured.

The conserved mitochondrial gene distribution in relatives of Turritopsis nutricula, an immortal jellyfish.

Turritopsis nutricula (T. nutricula) is the one of the known reported organisms that can revert its life cycle to the polyp stage even after becoming sexually mature, defining itself as the only immortal organism in the animal kingdom. Therefore, the animal is having prime importance in basic biological, aging, and biomedical researches. However, till date, the genome of this organism has not been sequenced and even there is no molecular phylogenetic study to reveal its close relatives. Here, using phylogenetic analysis based on available 16s rRNA gene and protein sequences of Cytochrome oxidase subunit-I (COI or COX1) of T. nutricula, we have predicted the closest relatives of the organism. While we found Nemopsis bachei could be closest organism based on COX1 gene sequence; T. dohrnii may be designated as the closest taxon to T. nutricula based on rRNA. Moreover, we have figured out four species that showed similar root distance based on COX1 protein sequence.

Reynolds number limits for jet propulsion: A numerical study of simplified jellyfish

The Scallop theorem states that reciprocal methods of locomotion, such as jet propulsion or paddling, will not work in Stokes flow (Reynolds number=0). In nature the effective limit of jet propulsion is still in the range where inertial forces are significant. It appears that almost all animals that use jet propulsion swim at Reynolds numbers ( Re) of about 5 or more. Juvenile squid and octopods hatch from the egg already swimming in this inertial regime. Juvenile jellyfish, or ephyrae, break off from polyps swimming at Re greater than 5. Many other organisms, such as scallops, rarely swim at Re less than 100. The limitations of jet propulsion at intermediate Re is explored here using the immersed boundary method to solve the 2D Navier–Stokes equations coupled to the motion of a simplified jellyfish. The contraction and expansion kinematics are prescribed, but the forward and backward swimming motions of the idealized jellyfish are emergent properties determined by the resulting fluid dynamics. Simulations are performed for both an oblate bell shape using a paddling mode of swimming and a prolate bell shape using jet propulsion. Average forward velocities and work put into the system are calculated for Re between 1 and 320. The results show that forward velocities rapidly decay with decreasing Re for all bell shapes when Re < 10 . Similarly, the work required to generate the pulsing motion increases significantly for Re < 10 . When compared to actual organisms, the swimming velocities and vortex separation patterns for the model prolate agree with those observed in Nemopsis bachei. The forward swimming velocities of the model oblate jellyfish after two pulse cycles are comparable to those reported for Aurelia aurita, but discrepancies are observed in the vortex dynamics between when the 2D model oblate jellyfish and the organism. This discrepancy is likely due to a combination of the differences between the 3D reality of the jellyfish and the 2D simplification, as well as the rigidity of the time varying geometry imposed by the idealized model.

Behavior of Nemopsis bachei L. Agassiz, 1849 medusae in the presence of physical gradients and biological thin layers

In pelagic systems, thin layers (discontinuities with narrow vertical extents and high concentrations of organisms) create patches of food, and aggregations of gelatinous zooplankton can exploit such resources. The establishment, maintenance, and trophic effects of these functional relationships depend on behavioral responses to thin layers by individuals, which remain largely unexplored. In this study, we used laboratory experiments to test the hypothesis that a common and abundant hydromedusa predator, Nemopsis bachei L. Agassiz, 1849, would respond similarly to salinity gradients with and without thin layers of algae and copepods. Approximately 75% of the hydromedusae remained in both types of discontinuities. These distributions were not created solely by passive responses related to osmoconformation or an inability to swim through salinity gradients because approximately 25% of hydromedusae swam through or away from salinity gradients or biological thin layers. Biological thin layers stimulated feeding. Feeding success was related directly to encounter rates and it was independent of swimming, as expected for an ambush predator. Feeding increased at higher prey densities, and capture, handling time, and ingestion were not saturated even at 150–200 copepods l−1. The proportion of N. bachei that ceased feeding and began swimming increased when encounters with prey decreased to approximately 2 encounters hydromedusa−1 10 min−1. Thus, hydromedusae may seek new patches of prey once encounter rates and subsequent feeding success fall below a threshold. Exposing N. bachei to salinity gradients with and without biological thin layers indicated that these hydromedusae will remain in discontinuities and exert predation pressure that should be considered when assessing trophic webs and estimating carbon flux.

Grazing and assimilation rate estimates of hydromedusae from a temperate tidal creek system

Previous research implicates gelatinous zooplankton grazing for reducing microzooplankton populations and influencing pelagic carbon fluxes. The principal objective of this study was to determine in situ ingestion rates and assimilation efficiencies for seasonal hydromedusae populations in North Inlet, SC, USA. Hydromedusae collected during July 2005, 2006 and January 2006 were exposed to natural plankton communities that were previously radiolabeled with 14C. Ingestion rates and assimilation efficiencies were calculated from measurements of hydromedusae tissue radioactivity after ingestion and egestion, respectively. Net tows determined that the numerically dominant gelatinous predators in this system were Bougainvillia muscus (July 2005, 2006) and Nemopsis bachei (January 2006). Summer ingestion rates for B. muscus significantly increased with increased temperature, but there was no effect of temperature on winter ingestion rates for N. bachei, suggesting temperature responses are species specific. Moreover, there was a significant species effect on ingestion rates for July 2006. Hydromedusae assimilation efficiencies are relatively constant throughout the year and are not significantly affected by temperature, species, or season. Seasonal differences in grazing are likely a function of the pelagic community and temperature-dependent metabolism. These results coupled with seasonal hydromedusae abundance data imply summer populations of hydromedusae graze more heavily on prey than winter populations, while also assimilating more carbon into predator tissue. Effects of hydromedusae predation may include modification of trophic structure, shifts in algal community composition, and decline in ecosystem stability, leading to impacts on sustainable commercial fisheries.

Enclosure Experiments on Survival and Growth of Black Drum Eggs and Larvae in Lower Chesapeake Bay

Experiments in 2.2 m3, in situ mesocosm enclosures indicate that black drum, Pogonias cromis, eggs and larvae potentially can survive in the lower Chesapeake Bay at ambient microzooplankton prey levels (≈200 prey 1−1) in the absence of predators. In growth experiments, larva mean growth rates to 10 d posthatch were similar (0.17 mm d−1 and 0.18 mm d−1) when fed at prey levels of 50 prey 1−1 and 200 prey 1−1. Individual growth rates, however, were more variable at 50 prey 1−1. Mortality rates also were comparable in 50 (27% d−1) and 200 (23% d−1) prey 1−1 enclosures. In a second experiment, the predation potentials of the hydromedusa Nemopsis bachei and the lobate ctenophore Mnemiopsis leidyi were estimated in relation to initial black drum egg prey density, presence of alternative <1 mm zooplankton prey, and estimated daily abundance of the jellyfish on the black drum spawning grounds. Mortality rates per medusa and ctenophore were similar (0.02–0.03 d−1), were not affected by presence of alternative prey, and were directly related to initial egg density. Results suggest that the gelatinous predators, especially the hydromedusa, could have cleared a high (≈38%) but variable fraction of the water column daily of fish eggs and yolk-sac larvae during the black drum spawning season. We hypothesize that the poor or episodic recruitment success of black drum in Chesapeake Bay results from a short spawning season that often coincides with abundance peaks of gelatinous predators and that predation on eggs and yolk-sac larvae may control recruitment.

Quantitative feeding ecology of the hydromedusan Nemopsis bachei in Chesapeake Bay

We determined feeding rates of the hydromedusan Nemopsis bachei L. Agassiz in the mesohaline region of Chesapeake Bay, USA during the spring of 1989 and 1990 from gut contents, digestion rates and abundances of medusae and zooplankton. The medusae consumed primarily copepodites of Acartia tonsa, selecting against naupliar stages. The peak abundance of N. bachei medusae was in April to May, when densities averaged more than 10 m-3. Medusa densities were similar in both years, but were greatest (maximum of 132 medusae m-3) along a southern transect sampled only in 1990. At peak densities, N. bachei medusae consumed 30% d-1 of the copepodite standing stocks, but they consumed <1% d-1 at the lower densities typical of late May or early June. The predation effects were generally greater than those reported for other hydromedusan species. But even at peak predation, N. bachei medusae could not have controlled or reduced A. tonsa copepod populations, which had a production rate of 85% d-1 at that time. Medusa feeding rates were highest at nighttime, and were correlated with prey density in the field, but not in the laboratory.