Predatory behavior ofPhacellophora camtschatica and size-selective predation uponAurelia aurita (Scyphozoa: Cnidaria) in Saanich Inlet,British Columbia

Predation uponAurelia aurita byPhacellophora camtschatica was studied by SCUBA divers in a fjord in British Columbia between July and September 1986. The behavior and size ofP. camtschatica affected their foraging success. Larger predators captured more and larger prey. The size and behavior of the prey also affected the probability of capture. Predators were found at densities which can affect both the size composition and the overall numbers of the prey population.     

Morphology,fluid motion and predation by the scyphomedusa Aurelia aurita

Although medusan predators play demonstrably important roles in a variety of marine ecosystems, the mechanics of prey capture and, hence, prey selection, have remained poorly defined. A review of the literature describing the commonly studied medusa Aurelia aurita (Linnaeus 1758) reveals no distinct patterns of prey selectivity and suggests that A. aurita is a generalist and feeds unselectively upon available zooplankton. We examined the mechanics of prey capture by A. aurita using video methods to record body and fluid motions. Medusae were collected between February and June in 1990 and 1991 from Woods Hole, Massachusetts and Narragansett Bay, Rhode Island, USA. Tentaculate A. aurita create fluid motions during swimming which entrain prey and bring them into contact with tentacles. We suggest that this mechanism dominates prey selection by A. aurita. In this case, we predict that medusae of a specific diameter will positively select prey with escape speeds slower than the flow velocities at their bell margins. Negatively selected prey escape faster than the medusan flow velocity draws them to capture surfaces. Faster prey will be captured by larger medusac because flow field velocity is a function of bell diameter. On the basis of prey escape velocities and flow field velocities of A. aurita with diameters of 0.8 to 7.1 cm, we predict that A. aurita will select zooplankton such as barnacle nauplii and some slow swimming hydromedusae, while faster copepods will be negatively selected.     

Potential dietary effects on the fatty acid composition of the common jellyfish Aurelia aurita

Fatty acid composition of the natural and aquarium-reared common jellyfish Aurelia aurita was investigated. Fatty acid composition of the aquarium-reared A. aurita clearly reflected that of the diet, brine shrimp (Artemia). In the same way, fatty acid composition of the natural A. aurita was assumed to reflect those of natural diets. Samples of natural A. aurita were collected from April 1995 to September 1995 in the Seto Inland Sea, Japan, and their fatty acids were analyzed by gas chromatography and mass spectrometry. Variation of fatty acid compositions was seasonal rather than dependent on body size. Two major seasonal groups were divided by the cluster analysis of the A. aurita fatty acid composition: the April–June and the August–September clusters. The April–June cluster was characterized by high contents of the (n − 3)-fatty acids of diatom origin, accumulated via the grazing food chain. By contrast, the August–September cluster was characterized by an increase in (n − 6)-fatty acids of macroalgal origin, probably transferred via the detritus food chain. These results suggest that the diet of natural A. aurita may shift between the diatom-based food chain and the detritus-based food chain. Received: 12 April 2000 / Accepted: 1 December 2000     

A comparative ecological study on the scyphozoans Aurelia aurita,Cyanea capillata and C. lamarckii in the Gullmar Fjord,western Sweden, 1982 to 1986

During the years 1982 to 1986, the life cycles and population dynamics of three scyphozoans, Aurelia aurita (L.), Cyanea capillata (L.) and C. lamarckii (Person and Lesueur), were studied in the Gullmar Fjord on the Swedish west coast. The settling of planulae, strobilation of scyphistomae and release of ephyrae were followed on ceramic settling plates in the laboratory and in the field. Weekly to bi-weekly hauls with Bongo nets were used to study the abundance of ephyrae and medusae. The results show great differences in the life cycles and ecology of the three species. A. aurita utilizes the best season for scyphistoma growth (August to September) and strobilates during the highest zooplankton abundance in October. C. capillata strobilates during the spring (March to May), and the abundance of C. capillata medusae is more dependent on immigration from the North Sea than A. aurita. C. lamarckii does not reproduce at all in the Gullmar Fjord and is totally dependent on immigration from the North Sea. The possibility of interspecific competition between A. aurita and C. capillata is discussed. A preliminary experiment showed that scyphistomae of A. aurita eat planula larvae of C. capillata during the autumn.     

Feeding rates of the jellyfish Aurelia aurita on fish larvae

We quantified feeding rates of field caught Aurelia aurita feeding on yolk sac cod (Gadus morhua) larvae in a series of incubation experiments. A short-time (~1 h) functional response experiment with a wide range of prey concentrations (0.5–16 prey l⁻¹, initial concentration) revealed that ingestion rates increased linearly over this range, such that clearance rates were similar between the different prey concentrations. This suggests that A. aurita is capable of efficiently utilizing dense prey patches. This indication was further supported by a linear increase of prey captured by A. aurita during 2.5 h of feeding at extremely high prey concentration (>200 prey l⁻¹). Clearance rate in darkness scaled with jellyfish diameter to a power of ~1.7 for jellyfish 3.9–9.5 cm in diameter. The jellyfish did not alter their umbrella pulse frequency in response to presence of fish larvae. There were no significant differences between A. aurita feeding rates in light and darkness for yolk sac prey ages 0–7 days (at 7.5°C). Although prey vision and escape abilities of fish may develop rapidly during early larval ontogeny, these factors apparently have little impact on interactions with predators such as A. aurita during the yolk sac stage.     

Nucleic acid and protein levels in strobilating polyps of Chrysaora quinquecirrha and Aurelia aurita

Levels of DNA, RNA, and protein were measured in scyphistomae of the scyphozoans Aurelia aurita and Chrysaora quinquecirrha during strobilation. In synchronously developing populations of A. aurita, the amount of DNA per polyp increases 41 to 260% during strobilation, whereas RNA and protein remain relatively constant. The RNA/DNA ratio drops by about 50% during strobilation in both C. quinquecirrha and A. aurita, and protein/DNA decreases by 50% in A. aurita. Specific RNA reserves are probably not accumulated in advance of strobilation, since strobilation is blocked immediately in both species by 1 to 3 g/ml actinomycin D. The size and DNA content of polyps are usually increased by prolonged incubation at temperatures of 12° to 15°C, which facilitates strobilation; however, the RNA/DNA and protein/DNA ratios of such polyps are not significantly increased by the cold conditioning.Contribution No. 472 from the Virginia Institute of Marine Science.     

Allozyme and morphological evidence for a newly introduced species of Aurelia in San Francisco Bay,California

The jellyfish Aurelia aurita (Linnaeus, 1758) is usually considered to be a cosmopolitan species. Aurelia sp. medusae observed at Foster City, San Francisco Bay, California, USA, since 1988 are morphologically distinct from Aurelia sp. collected 200 km away in Monterey Bay, but are morphologically similar to aquarium-cultured Aurelia sp. from Japan. They differ consistently in radial canal morphology. In allozyme electrophoresis, significant differences at 12 of 14 polymorphic loci strongly suggest that Aurelia sp. from Foster City and Tokyo Bay belong to one species, while Aurelia sp. from Monterey Bay and Vancouver Island belong to a second species. We propose that Aurelia sp. at Foster City is a recent introduction, possibly from Japan via ships' ballast water. The identities and taxonomic affinities of the two Aurelia defined in this study, and their relationships with the Linnaen A. aurita described from the North Atlantic, will require genetic and morphological study of the currently recognized species A. aurita and A. limbata (Brandt, 1838) from several zoogeographical provinces.     

Sexual reproduction of the scyphomedusa Aurelia aurita in relation to temperature and variable food supply

The effects of food availability and temperature on sexual maturation and female reproductive output of the scyphomedusa Aurelia aurita was examined in two populations from the contrasting environments of Southampton Water and Horsea Lake, England. Trends in oogenesis and subsequent reproductive output differed markedly between the two populations. In Southampton Water, the onset of sexual maturation occurred earliest in the larger medusae, but eventually all females became ripe, the smallest being 45 mm bell diameter (BD). The decrease in minimum size at maturity was correlated with increasing temperature. In A. aurita from Horsea Lake, size at maturity varied on a seasonal basis, with the smallest ripe female being only 19 to 20 mm BD. There were spring and autumn periods of sexual maturation in this population. During the autumn period, it is likely that food limitation was playing a more critical role in determining medusa size, with decreasing temperature indirectly affecting A. aurita by limiting primary and secondary production. In similar-sized ripe medusae, fecundity was greater in Southampton Water, but the planula larvae produced were significantly smaller than those in Horsea Lake. It is suggested that in Horsea Lake, the quality of the larvae are greater in terms of biochemical content to ensure survival of the few gametes produced (i.e. K-strategy). Comparison of the reproductive effort of the two A. aurita populations revealed that medusae from Southampton Water, which experience greater food availability, are able to direct more energy to reproduction than Horsea Lake medusae. In the latter, A. aurita medusae appear to partition the available food resources into either somatic growth (and therefore increased future fecundity) when food is abundant, or reproductive growth when food is scarce. Received: 24 June 1997 / Accepted: 23 March 1998     

Invading <Emphasis Type="Italic">Aurelia aurita</Emphasis> has established scyphistoma populations in the Caspian Sea

The Caspian Sea has no endemic Scyphozoa. In 1999, a mass accumulation of Aurelia medusae was recorded, indicating that sometime earlier, jellyfish had invaded the basin, but since then no scyphozoans have been reported in the Caspian. In the fall of 2008, we found scyphistomae (scyphoid polyps) during a cruise to the eastern Middle Caspian. The scyphistomae were numerous (100–10,000 ind. m⁻²) and occupied a depth range of 30–73 m. Genetic data (18S rDNA, ITS-1 and COI) showed that the scyphistomae belonged to the species A. aurita. The current genetic data set is insufficient to determine the source region(s) of the invasive A. aurita. It remains unclear why no moon jellies have been recorded in the Caspian in the last 10 years. Because swarming scyphomedusae are often pests, the presence of scyphistomae should be considered as a warning of a possible outbreak of A. aurita medusae in the Caspian.     

Distribution and abundance of moon jellyfish (Aurelia aurita) and its zooplankton food in the Black Sea

The distribution of moon jellyfish (Aurelia aurita Linnaeus, 1758) in the Black Sea was determined from plankton samples collected above the anoxic zone (maximum depth 200 m) in the summer, winter and spring during 1991–1995. Distribution was patchy. Average biomass ranged from 98 to 380 g m⁻², and abundance varied from 2 to 14 individuals m⁻². Biomass and abundance peaked in late spring and summer. The distribution was correlated with hydrographic features in the Black Sea, with higher concentrations occurring at the peripheries of anticyclonic eddies. Centers of the two main cyclonic gyres generally had a low biomass of A. aurita. From July 1992 to March 1995, the populations were largely concentrated in offshore regions. A. aurita were confined to the upper part of the mixed layer. Smaller A. aurita (≤1 cm) were present in early spring (March), and individuals reached maximum size in the summer. Release of the epyhrae occurred in spring on the northwestern shelf of the sea when the seawater temperature was 11–12 °C. Microscopic analysis of stomach contents showed that copepods and mollusks form their main diet. Received: 3 September 2000 / Accepted: 29 September 2000     

Macrobenthic species assemblages in Ellis Fjord,Vestfold Hills,Antarctica

A study was made of the sub-littoral benthic environment of Ellis Fjord, a 10 km-long fjord located near Davis Station, in the Vestfold Hills, Antarctica, over a 15 mo period (November 1984 to February 1986). Data were collected by SCUBA diving and underwater photography and were inhitially analysed by ordination techniques (non-metric multidimensional scaling). Ordinations showed substratum type to be the factor most strongly associated with changes in the distribution and abundance of macrobenthic species within the fjord. Other factors shown to be associated with changes in macrobenthic species assemblages were depth, distance from the fjord mouth, bottom slope, shoreline characteristics, current speed, and the presence of low-salinity water at shallow depths during the summer melt. The four major substratum types in Ellis Fjord were sand, rock, Serpula narconensis colonies and Phyllophora antarctica thalli. S. narconensis colonies supported the most species and sand substrate supported the least. P. antarctica is the only macrophyte species which occurred in the fjord. S. narconensis colonies in Ellis Fjord from one of the largest known tubeworm reefs in the world. The assemblages of benthic species in Ellis Fjord were different from those seen at other sub-littoral benthic sites off the Vestfold Hills, and at other Antarctic sites. There was a far greater proportion of filter-feeding species in the fjord than at other sub-littoral benthic sites off the Vestfold Hills. Factors which are thought to have caused these differences are the high level of organic but low level of inorganic input into the benthic system of the fjord, and the absence of anchor ice from the fjord.     

Release of dissolved organic carbon (DOC) by the scyphozoan jellyfish Aurelia aurita and its potential influence on the production of planktic bacteria

A series of incubation experiments were made to measure the rate of release of dissolved organic carbon (DOC) by the jellyfish Aurelia aurita (L.) (collected in 1991–1992 in Gullmarsfjorden, Sweden). Release of DOC by medusae (9.5 to 18 cm in diameter) from the Skagerrak ranged from 0.70 to 1.6 mg C ind^-1 d^-1 with a mean of 1.2 mg C ind^-1 d^-1 (SD=0.29 mg C ind^-1 d^-1, n=10). Based on data from the literature for two medusa populations, this can be equivalent to 2.5 and 7.1% of the carbon assimilated in one season (June to September). This was similar to the amount of carbon allocated to reproduction. Bacterial abundance was monitored to evaluate the possible stimulating effect of the DOC released. Bacterial growth was stimulated by the presence of A. aurita. The importance of A. aurita as a source of DOC on a large scale is small compared to exudate from primary producers. The volume surrounding each medusa, wherein the DOC released may be enough to sustain a bacterial production such as the one reported from the Swedish west coast, is equivalent to a sphere with a diameter of 0.5 m. Thus, considering the patchy distribution of medusae, the local influence of their DOC release could be important.     

Results of the UNDP (SF)/FAO regional fisheries survey in West Africa. Report No. 1. Deep-scattering Sardinella aurita off Mauritania

Scattering layers beyond the Continental Shelf, in deep water, were often observed during cruises with the charter vessel of the Regional Fisheries Survey in West Africa. The layers were located at depths of 100 to 350 m during daytime; at night, they generally ascended to the surface. They consisted mainly of myctophids and small squids. In this report, results of first observations on deep-scattering layers of Sardinella aurita (Cuv. et Val.) are given. The layers occurred off Mauritania during the months of hydrological transition, characterized by low water-temperatures. In these months, S. aurita were rarely caught over the shelf. Apparently, they migrate north and south in deep water, and were not detected by commercial vessels. The environmental conditions and the difficulties for the industrial fishery during this transitional period are briefly described. the temporal and spatial occurrence of deep-scattering S. aurita is given, and diurnal vertical migrations are shown, together with examples of echo records. Results of fishing operations made in the layer, and some biological observations on S. aurita are presented.     

Seasonal development of scyphozoan medusae and the predatory impact of Aurelia aurita on the zooplankton community in the Bornholm Basin (central Baltic Sea)

The annual cycle of abundance and distribution of the scyphozoan medusae Aurelia aurita and Cyanea capillata was studied in the Bornholm Basin (central Baltic Sea) in 2002. Seasonal changes in prey composition and predatory impact were investigated by analyzing stomach contents. A. aurita occurred from July to November, with a maximum mean abundance of 2.3 ind. per 100 m³ in August, whereas C. capillata was caught in much smaller numbers from July to September. No ephyrae of either species were found; therefore, advection of medusae from the western Baltic Sea is assumed. From July to October, ~80% of A. aurita medusae was distributed in the upper 20 m above the thermocline, whereas C. capillata occurred only in the halocline below 45 m. A. aurita did not migrate vertically and fed mainly on the most abundant cladoceran species Bosmina coregoni maritima. Further prey organisms were the cladocerans Evadne nordmanni and Podon spp., mollusk larvae and copepods. Copepod nauplii and copepodite stages I–III were not eaten by the medusae, neither were fish eggs and larvae used as prey. Based on mean medusa and zooplankton abundance from the upper 20 m, the predatory impact was very low. In August, when mean abundance of A. aurita was highest, only 0.1% of the copepod and 0.5% of the cladoceran standing stock were eaten per day. However, in regions with higher medusa or lower zooplankton abundance, up to 7.9% of the cladoceran standing stock was consumed per day. Hence, A. aurita did not regulate the zooplankton community in the Bornholm Basin, and fish larvae did not suffer from competition with and predation by the medusae.Communicated by O. Kinne, Oldendorf/Luhe     

Prey selection by the scyphomedusan predator Aurelia aurita

We describe feeding behavior of Aurelia aurita (Linnaeus) using gut content analyses of field-collected specimens and a mesocosm experiment. The field studies were conducted in Narragansett Bay, Rhode Island, USA from March to April 1988, and the mesocosm studies were done at the Marine Ecosystems Research Laboratory at the University of Rhode Island. Patterns of prey selection changed with medusa diameter. Smaller medusae (12 mm diameter) consumed mostly hydromedusan prey whereas larger medusae (up to 30 mm diameter) ingested greater numbers of copepod prey. While larger medusae did feed on copepods, their diet also contained more barnacle nauplii and hydromedusae than expected from the relative abundances of these prey types in plankton samples. A marginal flow mechanism of feeding by A. aurita provided an explanation for the patterns of prey selection we observed in medusae of different sizes and among widely divergent prey types. Our data indicated that large prey, with escape speeds slower than the marginal flow velocities around the bell margins of A. aurita, made up a substantial fraction of the daily ration when they were available. Such prey species may be more important to nutrition than the more abundant copepods and microzooplankton. Successful development of young medusae may depend upon an adequate supply of slowly escaping prey.     

Ultrastructural observations on prey capture and digestion in the scyphomedusa Aurelia aurita

Aurelia aurita medusae are able to catch their prey with their entire body surface. Catch efficiency in medusae caught in Kiel harbour in May 1985 was found to be highest at the tentacles and lowest at the subumbrella. Surface structures of the medusa as well as the cnidom are described by SEM observations. Microbasic heterotrichous euryteles and atrichous isorhizas were found. Discharged nematocysts on the prey's skin indicate different functions of the two types. The villi in the gastral cavity show a characteristic morphological differentiation that consists of a ciliated distal and a basal area covered by vesicles. Four types of glandular cells were identified by TEM observations. Mucous cell types preferably occur in densely ciliated areas. The presence of serous cells is restricted to the basal region of the gastral villi and gastral cavity where the extracellular predigestion takes place. The time of food passage in young medusae of A. aurita decreases from 19 h at 4°C to 4 h at 22°C.     

Energetic costs of swarming behavior for the copepod Dioithona oculata

The cyclopoid copepod Dioithona oculata forms dense swarms within shafts of sunlight that penetrate the mangrove prop-root habitat of islands off the coast of Belize. Previous studies, based on in situ video recordings and laboratory studies, have shown that D. oculata is capable of maintaining fixed-position swarms in spite of currents of up to 2 cm s⁻¹. The purpose of this study was to examine the energetic costs of maintaining these swarms, in terms of increased metabolic costs of maintaining position in currents and in terms of reduced feeding rates in densely packed swarms during the day. Using a sealed, variable-speed flow-through chamber, the respiration rates of D. oculata were measured while swarms maintained position in different current speeds. The results indicate that active metabolism (swimming at maximum speed to maintain the swarm in a current) is approximately three times greater than routine metabolism (normal swimming speeds in the absence of currents), indicating a significant metabolic cost of maintaining swarms in the presence of currents. In addition, gut-pigment analysis indicated that feeding rates of these copepods were often reduced in swarms during the day compared to when the copepods were dispersed at night. Given the high “cost” of swarming, the adaptive value of swarming in terms of reduced predation, increased opportunities for mating, and reduced dispersal, must be substantial. Received: 4 June 1997 / Accepted: 18 September 1997     

Nest site selection in the open-nesting honeybee Apis florea

We studied nest site selection by swarms of the red dwarf honeybee, Apis florea. By video recording and decoding all dances of four swarms, we were able to determine the direction and distances indicated by 1,239 dances performed by the bees. The bees also performed a total of 715 nondirectional dances; dances that were so brief that no directional information could be extracted. Even though dances converged over time to a smaller number of areas, in none of the swarms did dances converge to one site. As a result, even prior to lift off, bees performed dances indicating nest sites in several different directions. Two of four swarms traveled directly in what seemed to be the general direction indicated by the majority of dances in the half hour prior to swarm lift off. The other two traveled along circuitous routes in the general direction indicated by the dances. We suggest that nest site selection in A. florea has similar elements to nest site selection in the better-studied Apis mellifera. However, the observation that many more locations are indicated by dances prior to lift off also shows that there are fundamental differences between the two species.     

Comparison of laboratory rates of predation of five species of marine fish larvae by three planktonic invertebrates: effects of larval size on vulnerability

Rates of predation by the invertebrates Aurelia aurita, Thysanoessa raschi and Euchaeta norvegica on larval stages of cod (Gadus morhua L.), flunder (Platichthys flesus L.), plaice (Pleuronectes platessa L.), herring (Clupea harengus L.), and turbot (Scophthalmus maximus L.) were determined. Experiments were conducted in late winter and early spring 1982 with predators collected in Loch Etive, Scotland and prey obtained from several locations in Great Britain. Early stages of the smallest species, cod, flounder and turbot, tended to be most vulnerable to all three predators, while the early stages of the larger species, plaice and herring, and older stages of all species, were less vulnerable. For all stages and species of larvae, predation rates by the three predators were most closely related to larval length and escape swimming speed. Larval length itself was closely correlated to indices of larval escape ability. Low predation rates on large larvae by E. norvegica could be due to handling difficulties, whereas for A. aurita and T. raschi these low rates were due to escape abilities of the larger larvae. Prey movement is an important stimulus eliciting predation in E. norvegica but not in A. aurita or T. raschi.     

Ovarian morphology and oogenesis in Aurelia aurita (Scyphozoa: Semaeostomae): ultrastructural evidence of heterosynthetic yolk formation in a primitive metazoan

In Aurelia aurita, the ovaries arise as horseshoe-shaped evaginations of the gastrodermis in the floor of four interradial gastric pouches. Germ-cell islands arise within endodermally-derived gastrodermal cells. Oocytes grow and gradually bulge into the mesoglea while maintaining physical contact throughout vitellogenesis with specialized cells called trophocytes. Ultrastructural changes suggest that these cells transport yolk precursors from the coelenteron to the oocytes in a manner similar to that reported for the trophonema cells of anthozoan ovaries. Vitellogenesis involves both the autosynthetic activity of the oocyte organelles (Golgi complex and rough endoplasmic reticulum) and the heterosynthetic incorporation of precursors through endocytotic processes involving both coated pits and vesicles and smooth-surfaced tubules. Ultrastructural data suggest that different types or classes of yolk precursors enter the oocyte through the trophocytes and via the surrounding mesoglea. To our knowledge, this is the most primitive animal in which this type of yolk synthesis has been described. The trophocyte-oocyte relationship in oocytes of A. aurita is reminiscent of the trophonema-oocyte relationship in anthozoans and supports the belief that the Anthozoa and Scyphozoa share a close phylogenetic relationship.