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     

The common jellyfish Aurelia aurita: standing stock,excretion and nutrient regeneration in the Kiel Bight,Western Baltic

The population dynamics, ammonia and inorganic phosphate excretion, and nutrient regeneration of the common jellyfish Aurelia aurita was investigated from 1982 to 1984 in the Kiel Bight, western Baltic Sea. During summer 1982, medusae abundance ranged between 14 and 23 individuals 100 m^-3, biomass was estimated at about 5 g C 100 m^-3 and the mean final diameter of individuals was 22 cm. Abundance, based on numbers, in 1983 and 1984 was an order of magnitude lower; biomass was less than 2 g C 100 m^-3 and jellyfish grew to 30 cm. During the summers of 1983 and 1984, A. aurita biomass constituted roughly 40% of that of the total zooplankton>200 m. In 1982, for which zooplankton data were lacking, it was assumed that medusae biomass was greater than that of all other zooplankton groups. Total ammonia excretion ranged between 6.5 and 36 mol h^-1 individual^-1, whereas inorganic phosphate release was 1.4 to 5.7 mol h^-1 individual^-1. Allometric equations were calculated and exponents of 0.93 for NH₄–N release and 0.87 for PO₄–P excretion were determined. Nitrogen and phosphorus turnover rates were 5.4 and 14.6% d^-1, respectively. In 1982, the medusae population released 1 100 mol NH₄–N m^-2 d^-1, about 11% of the nitrogen requirements of the phytoplankton. The inorganic phosphate excretion (150 mol m^-2 d^-1) sustained 23% of the nutrient demands of the primary producers. In the other two years the nutrient cycling of the medusae was much less important, and satisfied only 3 to 6% of the nutrient demands. It is suggested that in some years A. aurita is the second most important source of regenerated nutrients in Kiel Bight, next to sediment.     

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.     

Laboratory study of predation by Aurelia aurita on larvae of cod,flounder, plaice and herring: development and vulnerability to capture

Capture success of the medusa Aurelia aurita preying on various developmental stages of fish larvae was measured together with larval reactivity and escape speed after being stung. These experiments were conducted in the spring of 1983 with A. aurita medusae collected from Loch Etive, Scotland and laboratory-reared larvae of Gadus morhua L., Platichthys flesus L., Pleuronectes platessa L. and Clupea harengus L. Capture success of the medusae increased with medusa size, but decreased with advancing larval development. Smaller species of larvae were more vulnerable to capture. Larval reactivity to encounters with medusae increased with advancing development, and larger species of larvae were more reactive to encounters. Larval escape swimming speeds also increased with advancing larval development and size. These results indicate that earlier stages of larvae within a species and smaller species of larvae at a given stage are more vulnerable to predation by medusae since they are less reactive to encounters. Apparently they are more susceptible to the effects of neurotoxins. Predation rates on different developmental stages of herring larvae are documented and compared with rates predicted by a predation model. Predictions fell within the range of observed predation rates, but tended to overestimate rates by larger medusae feeding on larger herring larvae. This indicates the possibility of predator satiation and/or behavioural avoidance.     

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.     

A laboratory study of predation by Aurelia aurita on larval herring (Clupea harengus): Experimental observations compared with model predictions

Predation by the medusa Aurelia aurita L. on early first-feeding stage larvae of the herring clupea harengus L. was studied in the laboratory. The medusae were captured in Loch Etive, Scotland. Herring larvae were reared from the extificially fertilized eggs of spawning Clyde herring caught in March, 1982. Swimming speeds, volume searched”, capture efficiency and predation rates increased as medusa size increased. Predation rates on fish larvae increased with prey density, but appeared to approach a maximum at high prey densities; in 1 h experiments, a maximum rate of predation of 6.64 larvae h^-1 was estimated by fitting an Ivlev function. A model to predict predation rates was constructed from swimming speeds, sizes and densities of medusae and larvae, and capture efficiency. The rates of predation predicted from the model fell within the range of experimental data, but tended to underestimate rates and did not account for saturation of medusae. Swimming patterns of medusae changed after prey capture: (a) before capture, encounter rates were low and medusae were relatively less active; (b) after capture of 1 larva, encounter rates doubled, with the stimulated medusae exhibiting increased activity and an aftered “searching” path; and (c) after capture of many larvae, swimming speeds and encounter rates of medusae decreased.     

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     

Abundance,distribution and prey composition of scyphomedusae in the southern North Sea

The annual cycle of abundance and distribution of the scyphozoan medusae Aurelia aurita, Cyanea lamarckii, C. capillata and Chrysaora hysoscella were studied in the southern North Sea in 2004 and 2005. Three different patterns of seasonal occurrence of medusae were distinguished: (1) the early occurring C. lamarckii (February–August), (2) C. capillata and A. aurita (April–August) and (3) the late appearing C. hysoscella (July/August–September). Cyanea lamarckii was the most frequently encountered species in this study; its highest mean abundance was 1.8 ± 2.7 ind. 100 m⁻³. The prey spectra of C. lamarckii, C. capillata and C. hysoscella contained several copepod and other crustacean species and thus make them potential competitors with fish larvae. Medusae in this study also consumed fish eggs and larvae, including clupeids, in all months analysed. Although peak spawning of sprat (Sprattus sprattus) coincides with the maximum abundance of medusae (May–June) the relative low abundance of all medusae species in this study makes jellyfish predation unlikely to be a factor controlling sprat recruitment in the time frame investigated.     

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.Communicated by J. Grassle, New Brunswick     

Release of dissolved organic carbon from the estuarine intertidal macroalga Enteromorpha prolifera

The estuarine macroalga Enteromorpha prolifera was collected from Coos Bay, Oregon, USA during 1981, and its release of photosynthate as dissolved organic carbon (DOC) was studied using ¹⁴C as a tracer. During photosynthesis in 30 S sea water, with a fixation rate averaging 7.37 mg C g^-1 dry wt h^-1, release ranged from 0.13 to 0.57 mg C g^-1 dry wt h^-1 and from 1.65 to 6.23% of total fixed carbon. Release of DOC appears to be linear with time over 3 h. As exposed algae become increasingly desiccated, their photosynthetic rates decline dramatically, but upon reimmersion the highly desiccated algae lose a larger fraction of their fixed carbon than the slightly desiccated algae. This loss comes in a pulse release of DOC over the initial 15 min, followed by declining release rates. The pulse loss due to rainfall is 5 times greater than that due to tidal resubmergence, and may briefly exceed the prior photosynthetic rate. Although lowering the salinity from 30 to 5 does not substantially alter photosynthetic rates, it does increase the DOC release range up to 1.02 mg C g^-1 dry wt h^-1 and 16.10% of fixed carbon. Heterotrophic microbes from the algal habitat readily use the available DOC at about 15% h^-1.     

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.     

Rate-temperature responses in scyphozoan medusae and polyps

The effects of temperature on oxygen consumption and spontaneous rhythmic activity have been investigated in various stages of the life histories of 3 species of jellyfish from the Chesapeake Bay, USA. All 3 species clearly show the ability to acclimate positively to temperature change. Thermal sensitivity of metabolism in the winter medusa Cyanea capillata fulva is fairly low at temperature intervals which are experienced in nature. Polyps of the two summer medusae, Chrysaora quinquecirrha and Aurelia aurita, show reduced metabolic sensitivity at temperatures normally accompanying high developmental activity and the onset of strobilation.     

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.     

Phytoplankton exudate release as an energy source for the growth of pelagic bacteria

The release of dissolved organic carbon (DOC) from phytolankton during photosynthesis, and the utilization of this carbon by planktonic bacteria, was studied using ¹⁴CO₂ and selective filtration. Natural sea water samples from a coastal area of the Northern Baltic Sea were incubated in the laboratory for detailed studies, and in situ for estimation of annual dynamics. In a laboratory incubation (at +1°C) the concentration of ¹⁴C-labelled dissolved organic carbon increased for about 2 h and then reached a steady state, representing about 0. 1% of the total DOC. Labelled organic carbon in the phytoplankton and bacterial fractions continued to increase almost linearly. The continuous increase in the bacterial fraction is thought to represent almost instantaneous utilization of the DOC released from the phytoplankton during photosynthesis. As an annual average, in 4 h in situ incubations, about 65% of the labelled organic carbon was found in the phytoplankton fraction (>3 m), about 27% in the bacterial fraction (0.2 to 3 m) and the remaining 8% as DOC (<0.2 m). Large variations in these percentages were recorded. The measured annual primary production was 93 g C m^-2 (March to December), and the estimated bacterial production due to phytoplankton exudates 29 g C m^-2. This represents a release of DOC of about 45% of the corrected annual primary production of 110 g C m^-2 (assuming a bacterial growth efficiency of 0.6).     

Life cycle ofRhopilema nomadica: a new immigrant scyphomedusan in the Mediterranean

Rhopilema nomadica is an Indopacific scyphomedusan, which has migrated into the eastern Mediterranean in recent years. Large aggregations of the medusae were recorded in Haifa Bay, Israel, reaching 5.5×10⁵ medusae per square nautical mile during summer 1989. The life cycle ofR. nomadica from planula to young medusa is described. Fertilization is external and planulae are formed within a few hours at 20°C. After settlement, polyps were fed withArtemia sp. nauplii and developed into polydisc strobilae within 45 d. The strobilation process was completed within 7 d, and the liberated ephyrae developed into young medusae within 2 mo. Asexual reproduction occurred mainly via podocyst formation. The population explosion ofR. nomadica could be attributed to its high reproductive potential.     

A commensal relationship between the scyphozoan medusae<Emphasis Type="Italic"> Catostylus mosaicus</Emphasis> and the copepod<Emphasis Type="Italic"> Paramacrochiron maximum</Emphasis>

The copepod Paramacrochiron maximum was found in high numbers (up to 5,675 copepods/medusa) on the oral arms of the scyphozoan Catostylus mosaicus. This association was considered to be commensalism for the following reasons: P. maximum (Lichomolgidae) was abundant on the medusae (approximately 805 copepods/kg of medusae) and very rare in the water column (approximately 5.99×10^-4 copepods/kg of water); copepodites and adults of the symbiont were present on the host; the copepods were on the medusae both day and night, at different times (nine occasions between March 1999 and May 2000) and different locations (Botany Bay and Lake Illawarra, NSW, Australia). Over 40 taxa of plankton were found on the oral arms of C. mosaicus (including protists, cnidarians, polychaetes, molluscs, a wide range of holoplanktonic and meroplanktonic crustaceans, chaetognaths and fish eggs). These taxa were abundant in the water column and we concluded that they were prey. Symbiotic amphipods and carangid fishes were found with medusae. We conclude that there is a symbiotic association between P. maximum and C. mosaicus and care should be taken not to confound these copepods with the prey of C. mosaicus. Poecilostomid copepods are well known for consuming mucus and feeding is likely to be a major reason for the association.Communicated by G.F. Humphrey, Sydney     

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.     

Polyp and medusa of Dipurena bicircella n. sp. (Hydrozoa: Corynidae) from Northern California

The polyp and medusa of Dipurena bicircella n. sp., a metagenic hydrozoan from Northern California, USA, is described. The arrangement of capitate tentacles of the polyp, in two alternating cycles or circlets, is unique to the genus Dipurena as well as to the family Corynidae. Medusae released in the laboratory attained sexual maturity in 2 weeks. The adult medusa can be distinguished from other medusae of the genus by means of 2 gonad rings, a slight terminal nematocyst cluster on each tentacle, and a relatively small size (about 2 mm in bell height). The polyp was not found in association with sponges, as is the case with some of the other polyps of the genus Dipurena. The medusa is not yet known from the plankton.     

Prey, feeding rates, and asexual reproduction rates of the introduced oligohaline hydrozoan Moerisia lyonsi

Moerisia lyonsi Boulenger (Hydrozoa) medusae and benthic polyps were found at 0 to 5‰ salinity in the Choptank River subestuary of Chesapeake Bay, USA. This species was introduced to the bay at least 30 years before 1996. Medusae and polyps of M. lyonsi are very small and inconspicuous, and may occur widely, but unnoticed, in oligohaline waters of the Chesapeake Bay system and in other estuaries. Medusae consumed copepod nauplii and adults, but not barnacle nauplii, polychaete and ctenophore larvae or tintinnids, in laboratory experiments. Predation rates on copepods by medusae increased with increasing medusa diameter and prey densities. Feeding rates on copepod nauplii were higher than on adults and showed no saturation over the range of prey densities tested (1 to 64 prey l⁻¹). By contrast, predation on copepod adults was maximum (1 copepod medusa⁻¹ h⁻¹) at 32 and 64 copepods l⁻¹. Unexpectedly, M. lyonsi colonized mesocosms at the Horn Point Laboratory during the spring and summer in 4 years (1994 to 1997), and reached extremely high densities (up to 13.6 medusae l⁻¹). Densities of copepod adults and nauplii were low when medusa densities were high, and estimated predation effects suggested that M. lyonsi predation limited copepod populations in the mesocosms. Polyps of M. lyonsi asexually produced both polyp buds and medusae. Rates of asexual reproduction increased with increasing prey availability, from an average total during a 38 d experiment of 9.5 buds polyp⁻¹ when each polyp was fed 1 copepod d⁻¹, to an average total of 146.7 buds polyp⁻¹ when fed 8 copepods d⁻¹. The maximum daily production measured was 8 polyp buds and 22 medusae polyp⁻¹. The colonizing potential of this hydrozoan is great, given the high rates of asexual reproduction, fairly wide salinity tolerance, and existence of a cyst stage. Received: 29 October 1998 / Accepted: 3 March 1999     

Derivation of the reduced life cycle of <Emphasis Type="Italic">Thecoscyphus zibrowii</Emphasis> Werner, 1984 (Cnidaria,Scyphozoa)

The species Thecoscyphus zibrowii Werner, 1984 has an exceptional life cycle, which lacks a medusa stage but develops an extraordinary structure (egg sac) for reproduction. Investigation of the life cycle, as well as anatomical and histological studies of the different developmental stages of T. zibrowii were performed to provide evidence for a possible homology of the egg sac with the medusa stage and to determine whether the reduced metagenesis of T. zibrowii is derived from strobilation. The egg sac showed several characteristics, which were compared to those of coronate medusae. The ectodermis of the egg sac had a plate-like appearance and was completely ciliated as is typical for coronate medusae. The number and the location of the gonads were similar to those of coronate medusae. The cnidocysts were significantly larger in the egg sac than in the polyp. A size difference of cnidocysts in the medusa and the polyp stage is known for several Coronatae. Characteristics of egg sac formation were compared to characteristics of strobilation. The formation of the early operculum was similar in T. zibrowii and N. eumedusoides. The constriction of egg sac and strobila occurred in the same mode and the gastric cavities of two egg sacs stayed in contact in a similar fashion to the gastric cavities of the strobila discs. The developmental zones of cnidoblasts of the egg sac and polyp were separated during the formation of the egg sac which showed a similar developmental gradient to a strobila. The existence of all of these consistent characteristics makes it very likely that the egg sac structure was homologous to a medusa. The species T. zibrowii would therefore be derived from a metagenetic ancestor. This species has reduced the medusa generation to the greatest extent within the Nausithoidae and has demonstrated thus far the endpoint of a regressive evolution of the medusa generation.