Life cycle of the jellyWsh Lychnorhiza lucerna ... - Springer Link

Mar Biol (2008) 156:1–12 DOI 10.1007/s00227-008-1050-8

ORIGINAL PAPER

Life cycle of the jellyWsh Lychnorhiza lucerna (Scyphozoa: Rhizostomeae) A. Schiariti · M. Kawahara · S. Uye · H. W. Mianzan

Received: 22 June 2008 / Accepted: 20 August 2008 / Published online: 10 October 2008 © Springer-Verlag 2008

Abstract The life cycle of Lychnorhiza lucerna (Scyphozoa: Rhizostomeae) and the settlement preferences of its larvae were studied using laboratory-based rearing experiments. Mature medusae of L. lucerna were collected from the beach of the Río de la Plata estuary, Argentina. This species displayed the typical metagenetic, (i.e. medusoid and polypoid), life cycle reported for other rhizostomes. The fertilized eggs developed into motile and short lived planulae. The majority of planulae settled on the air-water interface (p < 0.001). Of those that settled on the settlement plates provided, no signiWcant diVerences were observed between styrene slides, glass slides and shells of the bivalve Mactra isabelleana (p > 0.05). No planulae settled on stones. Several hours after planulae settled, they metamorphosed into sessile four-tentacled scyphistomae. Most scyphistomae attached onto the air-water interface. At 19–22°C, the scyphistomae grew up to 22 tentacles and reached 1,500
m height. The scyphistomae increased their numbers by means of formation of podocysts from which new polyps emerged and strobilated. Strobilation occurred 46 days after settlement. Only polydisk strobilation was

Communicated by S.A. Poulet. A. Schiariti (&) · H. W. Mianzan Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), Paseo V. Ocampo No 1, B7602HSA Mar del Plata, Argentina e-mail: [email protected] A. Schiariti · H. W. Mianzan Concejo Nacional de Investigaciones CientíWcas y Técnicas (CONICET), Rivadavia 1906, Buenos Aires 1033, Argentina M. Kawahara · S. Uye Graduate School of Biosphere Science, Hiroshima University, Hiroshima, Japan

observed and each strobila always produced three ephyrae. After releasing ephyrae, strobilae returned to normal scyphistomae and were capable of repeating strobilation. A single founder polyp was estimated to produce up to 60 ephyrae over 4 months. Ephyrae developed into metephyrae 15 days after release at 19–22°C. In this paper we describe the morphological and some behavioural features of L. lucerna in the polypoid and early medusoid stages.

Introduction It is widely suggested that jellyWsh have increased in numbers during the last 20 years, possibly as a consequence of global warming, overWshing, and eutrophication (e.g. Brodeur et al. 1999; Mills 2001). Their large swarms can have great ecological and societal impacts (Mianzan and Cornelius 1999). While some populations of jellyWsh exhibit a regular annual pattern of occurrence, the actual sizes of the populations can Xuctuate enormously among years (Mills 2001; Graham et al. 2001). The study of scyphozoan life cycles can provide clues for understanding interannual Xuctuations. Metagenesis is observed in all scyphozoans life cycles with few exceptions (Arai 1997). The general pattern includes a fertilized egg that develops into a planula and hence into a polyp (scyphistoma). The polyp (benthic) produces one or more medusae (planktonic) asexually via strobilation, which then reproduce sexually. Either planulae or polyps may also reproduce asexually by budding, or may form cysts (Arai 1997). As the growth rate of the scyphistomae and their ability to multiply asexually have an important eVect on the demography of jellyWsh population (Keen 1987), both planktonic and benthic phases of the jellyWsh life histories must be considered to understand the changes in jellyWsh

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population sizes. However, in most cases we have information only about the planktonic phase of their life cycles (Mills 2001). The study of jellyWsh life cycles will permit a better understanding about changes in jellyWsh populations and will aid identiWcation of polyps in the Weld. Unfortunately, few complete scyphozoan life cycles have been documented. For example, the life cycles of only 14 of the 90 species of Rhizostomeae (Kramp 1970) have been described (Table 1). Lychnorhiza lucerna Haeckel 1880 (Fig. 1) is the most abundant rhizostome in the southern Atlantic coasts of South America (Mianzan 1986; A. C. Morandini personal communication). It is distributed from French Guyana (5°N) (Kramp 1961; 1970) to Buenos Aires Province in Argentina (38°S) (Mianzan 1986). While there has been no monitoring of populations of L. lucerna, there are several accounts of large numbers of this species in the Río de la Plata estuary (35–37°S) and the adjacent marine area (Álvarez Colombo et al. 2003; M. Marchi personal communication; Schiariti unpublished data). While Morandini (2003) reported the presence of this species in Brazil (Cananéia Region, 23°S) throughout the year, in Argentinean waters the presence of this medusa is restricted to the warmer months (late December to early May) (Schiariti unpublished data.) At present, aggregations of this species are often nuisances for local Wshermen because they reduce total Wsh captures and catch quality, damage nets and even prevent Wshermen from operating. However, it is unknown if the Argentinean population complete their entire life cycle locally, or whether the population is sustained by a northern population of polyps, with the medusae being advected southwards by the summer net current circulation. The morphology of adult L. lucerna was described in detail by Vannucci (1951) and some re-descriptions have been made by Kramp (1961) and Mianzan (1986). Few studies about the biology or ecology of the species have been done. Álvarez Colombo et al. (2003) reported large abundances of L. lucerna detected by acoustic methods in the Río de la Plata estuary, and Vannucci-Mendes (1944), Zamponi (2002), Morandini (2003) and Nogueira Jr. and Haddad (2005) reported associations between this jellyWsh and species such as cestodes (Dibothriorhynchus dinoi), crustaceans (Periclimenes sp. and Libinia ferreirae and Libinia spinosa) and Wsh (Chloroscombrus chrysurus and Hemicaranx amblyrhynchus). Finally, Morandini (2003) described temporal variations in abundances and size-frequency distributions in the Cananéia region (25°S) as well as some aspects of the gametogenesis. However, the life cycle of L. lucerna has not been previously described. In the present study, we described the life cycle of the rhizostome L. lucerna based on experiments conducted in the laboratory as a Wrst step in studying its population

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dynamics, geographic origins and transportation routes. Emphasis was placed on the benthic stages, namely the settlement preferences of planulae, the asexual reproduction of scyphistomae, the process of strobilation, and the development of the ephyra.

Materials and methods Twenty-eight stranded L. lucerna were collected in March 2006 from beaches along the Argentinean coast of the Rio de la Plata estuary. JellyWsh were transferred to the laboratory within 2 h in a 20-liter container with seawater. JellyWsh were measured, weighed and their sex and gonadal maturity state were determined using a microscope. Mature females (n = 5) were examined microscopically for the presence of fertilized eggs or planulae. Gonadal tissue (ca. 10 g) from 10–15 specimens, including both males and females, was removed and incubated with weak aeration in 500 ml plastic buckets containing 25
m mesh Wltered seawater. Gonadal tissue was incubated at a salinity of 17 psu which was the approximate salinity at locations where the medusae were collected. After 24 h, planulae were removed using a Pasteur pipette under a dissecting microscope and 100 planulae were transferred to each of 13 buckets containing 250 ml Wltered seawater (17 psu). These procedures were undertaken at ambient temperature (19–22°C). A manipulative experiment was used to identify the settlement preferences of planulae. One each of four diVerent types of substrata (styrene and glass slides, empty bivalve shells (Mactra isabelleana d`Orbigny 1846 and stones) were randomly placed in each of the 13 buckets. Empty M. isabelleana shells and small stones were selected from a range of possible substrata common in the study area. Styrene and glass slides were used as artiWcial controls. Styrene and glass slides were cut into identical dimensions of 25 £ 25 £ 1 mm. Shells (ca. 20 mm shell length) and stones (rounded shape, ca. 20 mm diameter) of similar sizes were selected. Shells were placed with either the concave or the convex side facing upwards. All plates were placed Xat on the bottom of the buckets as described by Pitt (2000). The number of scyphistomae that settled on each plate was counted 72 h after the planulae were transferred to the buckets. Counts were converted to densities to overcome diVerences between the areas of each substratum. Given the heteroscedasticity of the data set (Bartlett test, p < 0.001), a Kruskal–Wallis test was performed to examine variation in scyphistomae density among types of substrata (Sokal and Rohlf 1999). Multiple comparisons were made using a Dunn test (Sokal and Rohlf 1999).

Cone-shapedc, stalk length moderate, oral disk width moderate, prominent dome-shaped proboscis

Goblet-shaped, stalk long, oral disk width moderate

Goblet-shaped, stalk length moderate, oral disk with prominent dome-shaped and clavate proboscis

Not described

Cone-shaped, stalk length moderate, oral disk wide

Cup shaped, stalk length short

Cone-shaped, proboscis clavate

Lychnorhiza lucerna

Mastigias papua

Nemopilema nomurai

Phyllorhiza punctata

Rhizostoma pulmo

Rhizostoma octopus

Rhopilema esculentum

Cone-shaped, stalk length moderate, oral disk width moderate, proboscis clavate

1.5

Goblet-shaped, stalk long, oral disk width moderate

Cotylorhiza tuberculata

Rhopilema verrilli

5

Goblet-shaped, stalk long, oral disk width moderate

Cephea cephea

2.5

3.5

Up to 20

16

Up to 24

32

12b

2.3

16

16

Usually 16, up to 18

18–22

16

16

12–20

32

32

c.a. 4

2.6

2.3

2.9

Not described

Not described

Not described

Goblet-shaped, stalk length moderate, dome-shaped proboscis

c.a. 2

Cassiopea xamachana

Goblet-shaped, stalk long, oral disk wide

Cassiopea andromeda

Scyphistoma No. of max. height (mm)a tentacles

Catostylus mosaicus

Scyphistoma shape

Species

Podocyst

Podocyst

Podocyst, polyp buds (rare)

Motile buds, polyp buds, stolon buds, podocyst, strobila buds

Motile buds

Podocyst

Motile buds

Podocyst

Motile buds

Motile buds

Podocyst, polyp buds, partial Wssion

Motile buds

Motile buds

Asexual reproduction

Monodisk, occasionally polydisk

Polydisk

Monodisk and polydisk

Polydisk

Monodisk

Polydisk

Monodisk

Polydisk

Monodisk

Monodisk

Monodisk and polydisk

Monodisk

Monodisk, occasionally polydisk

Type of strobilation

Up to 3

Up to 17

1–5

12–18 segments without ephyrae development

1

3–7

1

3

1

1

Up to 5

1

Usually 1, up to 2

No. of ephyrae per strobila

Cargo (1971); Calder (1973)

Ding and Cheng, (1981); Cheng and Ding (1983); Cheng et al. (1984); Guo (1990)

Holst et al. (2007)

PaspaleV (1938)

Rippingale and Kelly (1995); Lange and Kaiser (1995)

Kawahara et al. (2006); Kawahara personal observation

Uchida (1926); Sugiura (1963)

Present work

Claus (1890, 1893); Kikinger (1992)

Sugiura (1966)

Pitt (2000)

Bigelow (1900)

Bigelow (1900); Gohar and Eisawy (1960); Ludwig (1969); Neumann (1977); Rahat and Adar (1980); Hofmann and Honegger (1990)

References

Table 1 List of rhizostome species with described life cycles and morphological features of the known scyphistoma and strobila. ModiWed and updated from Calder (1982), Pitt (2000) and Holst et al. (2007)

Mar Biol (2008) 156:1–12 3

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123

c

b

a

From pedal disk to mouth Is not clear from the source if tentacles are included Shape usually changes after feeding or in response to external stimuli. Thus, we considered the shape of the scyphistoma when it is in steady state

Calder (1982) 1–3, usually 2 Polydisk, occasionally monodisk Cone-shaped, stalk length moderate, oral disk width moderate, proboscis dome- or knob-shaped Stomolophus meleagris

2

16

Podocyst

5–6 Polydisk Goblet-shaped, stalk length moderate, proboscis extraordinary clavate Rhopilema nomadica

2

16

Podocyst, buds (rare)

No. of ephyrae per strobila Type of strobilation Asexual reproduction No. of Scyphistoma max. height (mm)a tentacles Scyphistoma shape Species

Table 1 continued

Lotan et al. (1992)

Mar Biol (2008) 156:1–12

References

4

Fig. 1 Lychnorhiza lucerna. a Range of spatial distribution of the medusae reported by Kramp (1970) and Mianzan and Cornelius (1999); b Two diVerent phenotypes of L. lucerna with whitish or purplish-blue marginal lobs. Sampling area is indicated by a circle. Scale bar = 5 cm

Scyphistomae were cultured in darkness under constant conditions of temperature (22 § 1°C) and salinity (17 § 0.5 psu). Young scyphistomae (4–6 tentacles) were fed at 2–3 days intervals with rotifers (Brachionus sp., ca. 240
m body length) that had been previously fed the green alga Nannochloropsis oculata (Müller et al. 2003). When approximately 50% of the scyphistomae had more than 6 tentacles, a mixed diet of rotifers and newly hatched Artemia franciscana nauplii was provided at 2–3 day intervals. Dead Artemia and sedimented debris were removed with a pipette from the buckets daily, and ca. 20% of the water was replaced by fresh seawater at 2 day intervals. We observed ephyrae production in four buckets without any induced thermal shock. From the remaining nine buckets, four buckets were randomly selected and kept at 16 § 1°C for 30 days. Then, those buckets were returned to 22°C to induce strobilation. Ephyrae liberated from strobilae were transferred to a modiWed planktonkreisel (ca. 4 l) (RaskoV et al. 2003) and reared to metephyrae under the same conditions as the polyps. DiVerent developmental stages of scyphistomae, ephyrae and metephyrae were examined and photographed under a binocular microscope.

Mar Biol (2008) 156:1–12

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Results Lychnorhiza lucerna possesses a metagenetic life cycle with medusoid and polypoid generations (Fig. 2). The fertilized eggs developed into motile, short-lived planulae which settled onto hard substrates and metamorphosed into fourtentacled scyphistomae. The scyphistomae increased their numbers by the formation of podocysts. Polydisk strobilae always produced three ephyrae. The strobilae were able to produce podocysts during strobilation. Moreover, after releasing ephyrae, the strobilae returned to normal scyphistomae and repeated the strobilation up to Wve times during the 4 month experiment. A single scyphistoma, therefore, produced between 50 and 60 ephyrae over this period. It took ca. 120 days for a fertilized egg to develop to a metephyra. Gonad All collected jellyWsh were mature and had colored gonads (testis: greenish, ovary: light to dark brown). Of 28 medusae sampled for artiWcial fertilization (14.8 § 1.3 cm mean bell diameter; 634 § 50 g mean wet weight), 16 were males and 12 females. All males had sperm follicles containing mobile spermatozoa, indicating that they were fully mature (Fig. 3b). The ovaries contained oocytes ranging from 30 to 120
m in diameter (Fig. 3a). The oocytes of 60–120
m diameter had a germinal vesicle, indicating that oogenesis stopped at the

Fig. 3 Lychnorhiza lucerna. a Oocytes in the ovary; b sperm follicles in the testis; c a fertilized egg with polar bodies. pb Polar bodies. Scale bars = 140
m (a, b); 60
m (c)

Prophase I stage of meiosis. Neither fertilized eggs nor planulae were found in or on the ovary or the oral arms of females. Fertilization and planula Fertilized eggs were collected 1–3 days after the start of the incubation. They were approximately the same size as the largest oocytes and had two polar bodies in the transparent perivitelline space, which was about 4
m thick (Fig. 3c).

Fig. 2 Schematic representation of Lychnorhiza lucerna life cycle. Inter-stage durations are also shown (stippling indicates shadows, not pigmentation)

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Mar Biol (2008) 156:1–12

density of planulae attached to the underside of the water surface was signiWcantly greater (p < 0.001) than on the other types of substrata (Fig. 4). No signiWcant diVerences were found between the density of planulae attached on the styrene and glass slides and shells (Fig. 4). Scyphistoma

Fig. 4 Lychnorhiza lucerna. Mean density of scyphistomae (§SD) on diVerent substrata. AWI air-water interface, SS styrene slides, GS Glass slides, BS Bivalve shells, ST stones (no settlement observed). Equal letters indicate no signiWcant diVerences at
= 0.05

Actively swimming planulae were found 24 h after fertilization at 19–22°C. The larvae were elongated with a rounded anterior end, which was broader than the somewhat laterally compressed posterior end. No mouth structures were apparent suggesting that planulae were lecithotrophic. They swam by ciliary action rotating around their longitudinal axis. Planulae varied in size from 95 to 207
m in length and 39–54
m in width. Planulae settled ca. 3 h after formation on all types of substrata except on the stones (Fig. 4). Strangely, the

Fig. 5 Scyphistomae stages of Lychnorhiza lucerna. a Newly metamorphosed, 4-tentacled scyphistoma; b intermediate 8–10 tentacled scyphistoma, t6 days post-settlement; c fully developed, 18–22-tentacled scyphistoma, t25 days post-settlement, producing podocyst by stolon formation; d a scyphistoma with a branched tentacle indicated by a circle, e a common “tentacle cleaning” behavior observed in all

123

Scyphistomae appeared 24 h after the planulae had settled. They were translucent-white, cone-shaped, and typically had four Wliform tentacles bearing nematocyst batteries (Fig. 5a). Newly metamorphosed scyphistomae were ca. 220
m height (from the pedal disk to the mouth) with a calyx width of ca. 90
m. These initial tentacles arose from the distal end of the calyx as four perradial angles in the margin of the peristome and developed almost simultaneously. Four additional tentacles subsequently appeared one by one. After eight perradial and interradial tentacles formed, new tentacles appeared in between to form a fully developed scyphistoma with up to 22 tentacles. The base of the scyphistoma was attached to the substratum by a stalk enclosed within a transparent cuticle. If scyphistomae were dislodged, they were capable of reattachment within a few days by their pedal disk or by the formation of a new pedal stolon. The oral disk was largely occupied by a prominent dome-shaped proboscis. The mouth was capable of extensive expansion and could ingest prey of similar sizes to the scyphistomae themselves; a one-day-old scyphistoma ingested rotifers of ca. 240
m body length.

scyphistoma stages, f–g simultaneous production of three podocysts, indicating the order of formation by 1, 2 and 3. The Wrst formed podocyst (4) which has been liberated from the stolon and left behind. See text for details. n Nematocyst batteries, p podocysts; Scale bars = 200
m (a, e, f); 400
m (b, d); 650
m (c)

Mar Biol (2008) 156:1–12

Intermediate 8–10-tentacled scyphistomae were formed about 6 days after settlement (Fig. 5b). They were 700– 1,000
m high with a calyx width of 300–600
m. The Xexible knob-shaped mouth (proboscis) occupied most of the oral disk. They were capable of ingesting Artemia nauplii of 500
m length and 160
m width. Fully developed scyphistomae were observed 20– 25 days after settlement. They reached up to 1,500
m height with calyx diameter between 550 and 800
m and bore 18–22 tentacles (Fig. 5c). The stalk was somewhat variable in length and width depending on stolon formation and/or the shape and size of ingested prey. When fully expanded, the tentacles (some were bifurcated, Fig. 5d) exceeded the body length by about 2.5 times. Scyphistomae were voracious, catching and eating several prey within a few minutes. For example, a fully developed scyphistoma captured seven Artemia and two rotifers in less than 30 s and ingested them all within 3.2 min. As soon as a tentacle made contact with a prey, it was drawn to the mouth. At the same instant, the mouth bent toward the tentacle, opened widely and the prey was transferred to the gastrovascular cavity within a few seconds. When a second prey was captured before the Wrst prey was ingested, the tentacle with the second prey remained contracted until the Wrst prey was ingested. Then, the mouth bent towards and ingested the second prey. A sort of tentacle “cleaning” behaviour, i.e. drawing the tentacles to the mouth (Fig. 5e), was repeatedly observed in most scyphistomae while not feeding. A yellowish, crater-shaped podocyst was formed at the base of the stalk by means of stolon formation. The stolon emerged from the stalk and attached to the substratum 0.23– 0.85 mm away from the scyphistoma. The scyphistoma then

7

moved to the new attachment site leaving a podocyst behind (Fig. 5 c, f, g). In several cases, simultaneous formation of 2–3 podocysts was observed (Fig. 5f, g). Podocyst diameter ranged between 200 and 444
m (n = 50; mean = 319
m; SD = 77
m). A single scyphistoma formed up to 17 podocysts which extended ca. 3.4 mm in row length. From those 17 podocysts, three new scyphistomae were formed, and they in turn produced new podocysts. Strobila Polydisk strobilation was observed in four buckets, (30%) 46 days after settlement at constant temperature (22°C). Strobilation was also observed in all of the four buckets that were chilled for 30 days and returned to 22°C. No ephyrae were produced in the remaining Wve buckets kept under constant temperature. Segmentation of the calyx occurred in the early strobila (Fig. 6a). A weak circular incision was formed at the base of the tentacles ca.5 days after the Wrst noticeable sign of strobilation (Fig. 6b), and the incision became progressively deeper and more pronounced within the following 30 h. The second incision occurred proximal to the Wrst one, each forming a segment representing an incipient ephyra (Fig. 6c, d). Rhopalia and marginal lappets developed and conspicuous, shiny statocysts appeared 1 day after the second incision. At this time, the ephyrae started to pulsate by contracting their marginal lappets. Strobilae fed and produced podocysts throughout strobilation. The entire process of strobilation, from the appearance of the Wrst segmentation to the liberation of the last (the third) ephyra, occurred within 8 days. Well-fed founder scyphistomae were able to strobilate Wve times over 4 months.

Fig. 6 a–e Stages of strobilation in Lychnorhiza lucerna. Arrows show calyx incisions that indicate the incipient ephyra formation; three strobilae (1, 2, and 3) with diVerent degrees of development. All scale bars = 300
m

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8

Ephyra and metephyra Newly liberated ephyrae were approximately 1.4–1.9 mm wide from lappet tip to lappet tip when extended. Ephyrae usually possessed eight marginal lobes. Each lobe contained a pair of lappets and a rhopalium (Fig. 7a), but aberrant specimens had as few as four and as many as 12 marginal lobes. Each lappet presented a variable number of tips ranging between two and nine. Rhopalar clefts were Ushaped and their length was ca. twice their width (Fig. 7d). Radial canals had somewhat square-shaped ends with slight lateral horns which extended into the lappet on both sides (Fig. 7d). The mesoglea was thin. Gastric cirri were observed in the gastrovascular cavity (one or two per quadrant). The manubrium was circular or irregularly shaped (Fig. 7f), but as the ephyra developed, it elongated and began to constrict longitudinally in four places (Fig. 7b). As the constriction deepened, the manubrium divided into four oral arms and papillae started to develop. Nematocysts batteries were observed on the exumbrella and formed a deWned pattern. They were arranged in two concentric whorls. The inner whorl surrounded the manubrium and the larger outer whorl surrounded the marginal lobes (Fig. 7a). Ephyrae were translucent but after ingestion of Artemia nauplii the endoderm acquired a light-orange colour (Fig. 7e). When ephyrae reached 3–4 mm diameter, secondary lappets emerged at the adradial planes and the nematocyst batteries spread out peripherally around the bell and

Fig. 7 Lychnorhiza lucerna. a–c Developmental sequence of ephyrae. a Oral view of newly released ephyra with its typical arrangement of nematocyst batteries (nb), b advanced ephyra 4–5 days old with primary (1) and secondary (2) lappets, and nb reduced in size and spread out peripherally around the bell, c 12 days old metephyra with ring (rc) and radial canals (rac) still in formation, d Detail of rhopalar clefts and radial canals in a newly released ephyra. Arrows indicate lateral horns

123

Mar Biol (2008) 156:1–12

reduced in size (Fig. 7b). After catching the prey with its nematocyst batteries, young ephyrae extended their manubriums toward the prey and ingested it. Once within the body, the prey was retained in the gastric cirri until digestion was completed. Advanced ephyrae ate up to nine Artemia nauplii simultaneously. Ephyrae reached the metephyra stage 7–12 days post-liberation. Metephyra were 6–8 mm from lappet tip to lappet tip. The secondary lappets reached the length of the primary lappets making the bell margin polygonal (Fig. 7c, g). The mesoglea thickened and the four oral arms bifurcated into eight. The tips of each arm then branched into two wings bearing papillae (Fig. 7g). A ring canal appeared along the bell margin. Advanced metephyra reached up to 14 mm width ca. 20 day post-liberation.

Discussion and conclusions Scyphistoma and asexual reproduction As was reported for other rhizostome species (e.g. Pitt 2000; Kawahara et al. 2006), L. lucerna planulae settled on a variety of natural and artiWcial substrata indicating that they do not have a preferred type of substratum for settlement. The attachment of large number of scyphistomae to the water’s surface could be due to the experimental conditions (i.e. the small volume of still water in the buckets) and

extending into the lappet on both sides, e Colored ectoderm after Artemia ingestion. Arrow indicates the radial canals in formation, f Irregular shaped manubrium in newly liberated ephyra, g oral arms in the young metephyra bifurcated into 8. Each arm branched into two wings at the tip bearing papillae. gc Gastric cirri. Scale bars = 300
m (a, b, e, f); 100
m (d); 1 mm (g); 2 mm (c)

Mar Biol (2008) 156:1–12

this probably does not occur in nature. The Río de la Plata estuary is characterized by the predominance of sandy, clayey, and silty bottoms (Urien 1972). As it is presumed that hard substrates are indispensable for the attachment of polyps, settlement of L. lucerna planulae in Buenos Aires coast could be limited by the availability of suitable substrates. So far, the morphological features of scyphistomae have been described for 15 rhizostome species including L. lucerna in the present study (Table 1 and references herein). Their basic form is goblet- or cone-shaped; they attach aborally to the substratum by a pedal disk and bear an oral whorl of tentacles. Among them, L. lucerna scyphistomae most resemble Rhopilema verrilli Fewkes 1887 and Stomolophus meleagris Agassiz 1,862 (Calder 1973; 1982) particularly in their cone-shaped calyx and prominent proboscis. Rhizostome scyphistomae may reproduce asexually by three diVerent means, i.e. budding, Wssion, and podocyst production (Arai 1997). Regarding podocyst production, there have been some discrepancies in the literature and the terms podocyst and pedal cyst have been used with diVerent meanings, or even as synonyms (see Cargo and Rabenold 1980; Magnusen 1980; Arai 1997; Pitt 2000). To avoid confusion, we followed in this paper the meaning proposed by Blanquet (1972), where podocysts are deWned as small bits of tissue containing epidermal and mesenchymal cells separated from the pedal disc and covered by a thin chitinous cuticle. The podocysts are usually formed either beneath the pedal disc of the scyphistomae or at the tip of extended stolons. In L. lucerna, as well as Rhopilema nomadica Galil et al. 1990 (Lotan et al. 1992), podocysts formed at the base of the pedal disk. Conversely, in Catostylus mosaicus Quoy and Gaimard 1824, podocysts formed at the point where the stolon attached to the substratum (Pitt 2000). In contrast, scyphistomae of Rhopilema verrilli produce podocysts both at the base of pedal disk and at the tip of stolon (Calder 1973). Podocysts are considered to be a dormant stage that is produced when exposed to stressful conditions such as extreme temperature, salinity, oxygen depletion, starvation or bacterial fouling (Cargo and Schultz 1966; Blanquet 1972; Arai 1997; Pitt 2000). Once podocyst production is initiated, its production rate is dependent on the nutritional state of the scyphistomae (see Arai 1997). The podocyst production rate of L. lucerna was among the highest values reported for rhizostomes (i.e. ten podocysts per scyphistoma per month). Substantial bacterial fouling occurred during the experiment and killed some scyphistomae. Therefore, bacterial fouling may have triggered podocyst formation. In some rhizostomes (e.g. Mastigias papua Lesson 1830, Rhopilema esculentum Kishinouye 1891, Rhizostoma pulmo Macri 1778), strobilation is initiated by a speciWc

9

trigger, such as a sudden temperature increase, prolonged chilling (4–6 weeks) followed by return to normal temperatures, a decrease in food supply, a change in pH, increases in salinity, and treatment with iodine, thyroxine and iodinated compounds such as the neck-inducing factor (NIF) or potassium iodide (e.g. Spangenberg 1971; Loeb 1973; 1974; Olmon and Webb 1974). We observed that L. lucerna strobilated repeatedly under constant temperature (22°C). In addition, strobilation was also induced by chilling the scyphistomae for 30 days and returning them to original temperature. Hence, strobilation in L. lucerna could occur at a constant temperature (22°C), and pre-cooling was not necessarily required. Repeated strobilation by a single scyphistoma has been documented for many rhizostomes such as Cassiopea andromeda Forskål 1775 (Gohar and Eisawy 1960), M. papua (Sugiura 1963), Cephea cephea Forskål 1775 (Sugiura 1966) and R. nomadica (Lotan et al. 1992). In species that undergo polydisk strobilation, the number of ephyrae liberated per strobilation event usually varies among scyphistomae of the same species under the same conditions (e.g. Lotan et al. 1992; Pitt 2000; Kawahara et al. 2006). Conversely, we observed that the well-fed scyphistomae of L. lucerna, which underwent strobilation up to Wve times during the experiment, always produced three discs. Ephyra and metephyra The eight marginal lobes formed in L. lucerna ephyrae were typical of the number usually observed for Scyphozoa. It has been suggested that the top (Wrst) one or two disks that form in the strobila are usually larger than the remainder, and may contain as many as 12 lappets or rhopalial lobes (Berrill 1949). In contrast, the lowest disks are usually the smallest and have as few as four lappets (Berrill 1949). Contrary to Berrill’s hypothesis, we did not Wnd any correlation between the number of marginal lobes and the position of the ephyrae in the strobila. We observed, for example, the release of a typical ephyra having eight lappets followed by other two ephyrae possessing 11 and 12 lappets, respectively. Berrill (1949) also found that the number of rhopalia that formed during strobilation persisted throughout development of the pelagic stages of the life cycle and determined the structural pattern of the adult medusa. Berrill’s Wndings could not be conWrmed in the current study, however, because all ephyrae that did not have exactly eight marginal lobes exhibited swimming disabilities and died a few days after being released. The ephyral stage is the most diYcult stage to identify in the development of scyphozoan medusae because of the similar morphologies that diVerent species share. Even among the studies of scyphozoan life cycles, only a few included descriptions of ephyrae (see Tronolone et al.

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10

2002). There are, however, some structural characters present in the newly liberated ephyra which can be used as distinguishing features (Russell 1970). Only eight other species of scyphomedusae have been reported within the distributional range of L. lucerna (Mianzan and Cornelius 1999) and among them, there are descriptions of ephyrae for only Wve species: Chrysaora lactea Eschscholtz 1829 (Mianzan 1986; Morandini et al. 2004), Pelagia noctiluca Forskål 1775 (Russell 1970; Rottini Sandrini and Avian 1983), A. aurita Linné 1758 (Spangenberg 1965), P. punctata von Lendenfeld 1884 (Tronolone et al. 2002) and S. meleagris (Calder 1982). Of those already described, none have marginal lappets with branching tips similar to those of L. lucerna (Fig. 7a, d, e). The arrangement of the nematocysts batteries on the exumbrella also appears to be diVerent to the other co-occurring species and could also be useful to identify newly liberated ephyrae (H. W. Mianzan unpublished data). The life cycle of L. lucerna was similar to that described for other rhizostome species, and consisted of medusoid and polypoid generations. The spatial and temporal distribution of medusae may be regulated by the occurrence and reproduction of the benthic polyps (Brewer and Feingold 1991). The polyp generation may have, therefore, an important role in the formation of jellyWsh blooms (Jarms 2007). In the present study, we found that that one founder L. lucerna scyphistoma could produce up to 60 ephyrae during 4 months. Although these results are preliminary and experiments estimating the potential asexual reproduction of this species should be performed, they highlight the key role scyphistomae may have in determining abundances, and Xuctuations in abundances, of L. lucerna medusae. Besides, knowledge of survival rates of ephyrae is also required to fully understand the factors inXuencing medusae population dynamics. Medusae of L. lucerna are common in coastal waters from southern Brazil (22–23°S) to the Buenos Aires province in Argentina (38°S). However, while this species occurs throughout the year in Brazil (23°S) (Morandini 2003), in Argentinean waters the presence of this medusa is restricted to the warmer month (late December to early May) (Schiariti et al. in preparation). The natural locations of the scyphistomae and the factors that induce their strobilation remain unresolved. Our results indicate that L. lucerna may be capable of reproducing asexually as well as sexually all along its known range of distribution. However, in the Rio de la Plata estuary, we expect that this species could be limited by availability of suitable (hard) substrates. Acknowledgments We thank Mundo Marino, Mundo Marino Foundation and Miguel Marchi for providing support and facilities in jellyWsh collection. We also thank Dr. Jack Costello and two anonymous

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Mar Biol (2008) 156:1–12 reviewers for improving this manuscript and Dr. M. D. Viñas for allowing us the use of temperature-controlled chamber. Finally we are grateful to the Aquaculture Project (INIDEP) and especially to Federico Bianca who provided us sea water, rotifers and Artemia eggs. This work was supported by Fundación Antorchas 13900–13, CONICET PIP 5009, FONCyT PICT 1553, the Inter-American Institute for Global Change Research CRN-2076, which is supported by the US National Science Foundation (Grant GEO-0452325), and Japan Science Promotion Society (No 16405001). This is INIDEP contribution No 1488.

References Álvarez Colombo G, Mianzan HW, Madirolas A (2003) Acoustic characterization of gelatinous-plankton aggregations: four case studies from the Argentinean continental shelf. ICES J Mar Sci 60:650–657. doi:10.1016/S1054-3139(03)00051-1 Arai MN (1997) A functional biology of Scyphozoa. Chapman & Hall, London Berrill N (1949) Developmental analysis of Scyphomedusae. Biol Rev Camb Philos Soc 24:393–410. doi:10.1111/j.1469-185X.1949. tb00581.x Bigelow RP (1900) The anatomy and development of Cassiopea xamachana. Mem Boston Soc Nat Hist 5:191–236 Blanquet RS (1972) Structural and chemical aspects of the podocyst cuticle of the scyphozoan medusa, Chrysaora quinquecirrha. Biol Bull 142:1–10. doi:10.2307/1540241 Brewer RH, Feingold JS (1991) The eVect of temperature on the benthic stages of Cyanea (Cnidaria: Scyphozoa), and their seasonal distribution in the Niantic River estuary, Connecticut. J Exp Mar Biol Ecol 152:49–60. doi:10.1016/0022-0981(91)90134-I Brodeur RD, Mills CE, Overland JE, Walters GE, Schumacher JD (1999) Evidence for a substantial increase in gelatinous zooplankton in the Bering Sea, with possible links to climate change. Fish Oceanogr 8:296–306. doi:10.1046/j.1365-2419.1999.00115.x Calder DR (1973) Laboratory observations on the life history of Rhopilema verrilli (Scyphozoa: Rhizostomeae). Mar Biol (Berl) 21:109–114. doi:10.1007/BF00354606 Calder DR (1982) Life history of the Cannonball jellyWsh, Stomolophus meleagris L. Agassiz, 1860 (Scyphozoa, Rhizostomida). Biol Bull 162:149–162. doi:10.2307/1540810 Cargo DG (1971) The sessile stages of a Scyphozoan identiWed as Rhopilema verrilli. Tulane Stud Zool Bot 17:31–34 Cargo DG, Rabenold GE (1980) Observations on the asexual reproductive activities of the sessile stages of the sea nettle Chrysaora quinquecirrha (Scyphozoa). Estuaries 3:20–27. doi:10.2307/ 1351931 Cargo DG, Schultz LP (1966) Notes on the biology of the Sea Nettle, Chrysaora quinquecirrha, in Chesapeake Bay. Chesap Sci 7:95– 100. doi:10.2307/1351129 Chen J, Ding G (1983) EVect of temperature on strobilation of jellyWsh (Rhopilema esculenta Kishinouye—Scyphozoa, Rhizostomeae). Acta Zoologica Sin 29:195–206 Chen J, Ding G (1984) EVect of light on the strobilation of edible medusa, Rhopilema esculenta Kishinouye (Cnidaria, Scyphozoa). Oceanologia Limnol sin 15:310–316 Claus C (1890) Über die Entwicklung des Scyphostoma von Cotylorhiza, Aurelia und Chrysaora, sowie ueber die systematische Stellung der Scyphomedusen. I. Arbeiten Zoologischen Inst Univ Wien Zoologischen Stn Triest 9:85–128 Claus C (1893) Über die Entwicklung des Scyphostoma von Cotylorhiza, Aurelia, und Chrysaora, sowie ueber die systematische Stellung der Scyphomedusen. II. Arbeiten Zoologischen Inst Univ Wien Zoologischen Stn Triest 10:1–70

Mar Biol (2008) 156:1–12 Ding G, Chen J (1981) The life history of Rhopilema esculenta Kishinouye. J Fish China 5:93–104 Suichan Xuebao Gohar HAF, Eisawy AM (1960) The development of Cassiopea andromeda (Scyphomedusae). Publ Mar Biol Sta Ghardaqa Red Sea 11:147–190 Graham WM, Pagès F, Hammer WM (2001) A physical context for gelatinous zooplankton aggregations: a review. Hydrobiologia 451:199–212. doi:10.1023/A:1011876004427 Guo P (1990) EVect of nutritional condition on the formation and germination of the podocyst of scyphistomae of Rhopilema esculenta Kishinouye. J Fish China 14:206–211 Suichan Xuebao Haeckel E (1880) Das System der Medusen. I, 2: system der Acraspeden. Gustav Fischer, Jena, pp 361–672 Hofmann DK, Honegger TG (1990) Bud formation and metamorphosis in Cassiopea andromeda (Cnidaria: Scyphozoa): a developmental and ultraestructural study. Mar Biol (Berl) 105:509–518. doi:10.1007/BF01316322 Holst S, Sötje I, Tiemann H, Jarms G (2007) Life cycle of the rhizostome jellyWsh Rhizostoma octopus (L.) (Scyphozoa, Rhizostomeae), with studies on cnidocysts and statoliths. Mar Biol (Berl) 151:1695–1710. doi:10.1007/s00227-006-0594-8 Jarms G (2007) The polyps of the Scyphozoa and their impact on jellyWsh blooms. Second International JellyWsh Blooms, 24–27 June, Gold Coast, Australia Kawahara M, Uye S-i, Ohtsu K, Iizumi H (2006) Unusual population explosion of the giant jellyWsh Nemopilema nomurai (Scyphozoa: Rhizostomeae) in East Asian waters. Mar Ecol Prog Ser 307:161– 173. doi:10.3354/meps307161 Keen SL (1987) Recruitment of Aurelia aurita (Cnidaria: Scyophozoa) larvae is position-dependent, and independent of conespeciWc density, within a settling surface. Mar Ecol Prog Ser 38:151–160. doi:10.3354/meps038151 Kikinger R (1992) Cotylorhiza tuberculata (Cnidaria: Scyphozoa) Life history of a stationary population. Mar Ecol (Berl) 13:333– 362. doi:10.1111/j.1439-0485.1992.tb00359.x Kramp PL (1961) Synopsis of the medusae of the world. J Mar Biol Assoc UK 40:7–469 Kramp PL (1970) Zoogeographical studies on Rhizostomeae (Scyphozoa). Vidensk Meddr dansk naturh Foren 133:7–30 Lange J, Kaiser R (1995) The mantenance of pelagic jellyWsh in the Zoo-Aquarium Berlin. Int Zoo Yb 34:59–64. doi:10.1111/j.17481090.1995.tb00658.x Loeb MJ (1973) The eVect of light on strobilation in the Chesapeake Bay sea nettle Chrysaora quinquecirrha. Mar Biol (Berlin) 20:144–147. doi:10.1007/BF00351452 Loeb MJ (1974) Strobilation in the Chesapeake Bay sea nettle Chrysaora quinquecirrha II. Partial characterization of the neck-inducing factor from strobilating polyps. Comp Biochem Physiol 47:291–301. doi:10.1016/0300-9629(74)90073-5 Lotan A, Ben-Hillel R, Loya Y (1992) Life cycle of Rhopilema nomadica: a new immigrant scyphomedusan in the Mediterranean. Mar Biol (Berl) 112:237–242. doi:10.1007/BF00702467 Ludwig FD (1969) Die Zooxanthellen bei Cassiopea andromeda Eschscholtz 1829 (Polyp-Stadium) und ihre Bedeutung für die Strobilation. Zool Jb 86:238–277 Abt Anat Ontog Tiere Magnusen JE (1980) Epidermal cell movement during podocyst formation in Chrysaora quinquecirrha. In: Tardent O, Tardent R (eds) Developmental and cellular biology of coelenterates. Elsevier/North Holland Biomedical Press, Amsterdam, pp 435– 440 Mianzan HW (1986) Estudio sistemático y bioecológico de algunas medusas Scyphozoa de la región subantártica. PhD, La Plata Mianzan HW, Cornelius PFS (1999) Cubomedusae and Scyphomedusae. In: Boltovskoy D (ed) South Atlantic Zooplankton. Blackuys Publishers, pp 513–559

11 Mills CE (2001) JellyWsh Blooms: are populations increasing globally in response to changing ocean conditions? Hydrobiologia 451:55–68. doi:10.1023/A:1011888006302 Morandini AC (2003) Estrutura populacional de Chrysaora lactea e Lychnorhiza lucerna (Cnidaria, Scyphozoa) em amostras de plâncton, com a redescrição das espécies. PhD. Instituto de Biociências da Universidade de São Paulo, São Paulo Morandini AC, Lang da Silveira F, Jarms G (2004) The life cycle of Chrysaora lactea Eschscholtz, 1829 (Cnidaria, Scyphozoa) with notes on the scyphistoma stage of three other species. Hydrobiologia 530/531:347–354. doi:10.1007/s10750-004-2694-0 Müller MI, Cadaveira ML, Masakazu O (2003) Cultivo de rotíferos en Argentina - Primer alimento para larvas de peces marinos VIII Jornadas Nacionales de Ciencias del Mar. Mar del Plata, Argentina Neumann R (1977) Polyp morphogenesis in a scyphozoan: evidence for a head inhibitor from the presumptive foot end in vegetative buds of Cassiopea andromeda. Wilhelm Roux⬘s Archs devl Biol 183:79–83 Nogueira M Jr, Haddad MA (2005) Lychnorhiza lucerna Haeckel (Scyphozoa, Rhizostomeae) and Libinia ferreirae Brito Capello (Decapoda, Majidae) association in southern Brazil. Rev Bras Zoologia 22:908–912 Olmon JE, Webb KL (1974) Metabolism of 131I in relation to strobilation of Aurelia aurita L. (Scyphozoa). J Exp Mar Biol Ecol 16:113–122. doi:10.1016/0022-0981(74)90014-8 PaspaleV BW (1938) Über die Entwicklung von Rhizostoma pulmo Agass. Trud chernomorsk biol Sta Varna 7:1–25 Pitt KA (2000) Life history and settlement preferences of the edible jellyWsh Catostylus mosaicus (Scyphozoa: Rhizostomeae). Mar Biol (Berl) 136:269–279. doi:10.1007/s002270050685 Rahat M, Adar O (1980) EVect of symbiotic zooxanthellae and temperature on budding and strobilation in Cassiopeia andromeda (Eschscholz). Biol Bull 159:394–401. doi:10.2307/1541102 RaskoV KA, Sommer FA, Hamner WM, Cross KM (2003) Collection and culture techniques for gelatinous zooplancton. Biol Bull 204:68–80. doi:10.2307/1543497 Rippingale RJ, Kelly SJ (1995) Reproduction and survival of Phyllorhiza punctata (Cnidaria: Rhizostomeae) in a seasonally Xuctuating regime in western Australia. Mar Freshw Res 46:1145–1151. doi:10.1071/MF9951145 Rottini Sandrini L, Avian M (1983) Biological cycle of Pelagia noctiluca: morphological aspects of the development from planula to ephyra. Mar Biol (Berl) 74:169–174. doi:10.1007/BF00413920 Russell FRS (1970) II Pelagic Scyphozoa with a supplement to the Wrst volume on hydromedusae The medusae of the British isles. Cambridge University Press, New York Sokal RR, Rohlf FJ (1999) Introducción a la Bioestadística. Editorial Reverté, Barcelona Spangenberg DB (1965) Cultivation of the life stages of Aurelia aurita under controlled conditions. J Exp Zool 159:303–318. doi:10.1002/jez.1401590303 Spangenberg DB (1971) Thyroxine induced metamorphosis in Aurelia. J Exp Zool 178:183–194. doi:10.1002/jez.1401780205 Sugiura Y (1963) On the life history of rhizostome medusa I. Mastigias papua L. Agassiz. Annot Zool Jpn 36:194–202 Sugiura Y (1966) On the life-history of Rhizostome medusae IV. Cephea cephea. Embryologia (Nagoya) 9:105–122 Tronolone VB, Morandini AC, Migotto AE (2002) On the occurrence of scyphozoan ephyrae (Cnidaria, Scyphozoa, Semaeostomeae and Rhizostomeae) in the Southeastern Brazilian coast. Biota Neotropica 2:1–18 Uchida T (1926) The anatomy and development of a rhizostome medusa, Mastigias papua L. Agassiz, with observations on the phylogeny of Rhizostomeae. J Fac Sci imp Univ Tokyo (IV: Zool) 1:45–95

123

12 Urien CM (1972) Río de la Plata estuarine environment. Geol Soc Am Memoir 133:213–233 Vannucci M (1951) Hydrozoa e Scyphozoa existentes no Instituto Paulista de OceanograWa I. Bol Inst Paul OceanograWa 2:69–104 Vannucci-Mendes M (1944) Sôbre a larva de Dibothriorhynchus dinoi, sp. n. parasita dos Rhizostomata. (Cestoda, Tetrarhynchidea). Arq Museu Paranaense 4:47–82

123

Mar Biol (2008) 156:1–12 Zamponi MO (2002) The association between medusa Lychnorhiza lucerna (Scyphomedusae, Rhizostomeae) and Decapod Libinia spinosa (Brachyura, Majidae) recorded for the Wrst time in neritic waters of Argentina. Russ J Mar Biol 28:267–269. doi:10.1023/ A:1020229328660