life cycle of phacellophora camtschatica (cnidaria: scyphozoa)

Life Cycle of Phacellophora camtschatica (Cnidaria: Scyphozoa)Author(s): Chad L. WidmerSource: Invertebrate Biology, Vol. 125, No. 2 (2006), pp. 83-90Published by: Wiley on behalf of American Microscopical SocietyStable URL: http://www.jstor.org/stable/3701507 .

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Invertebrate Biology 125(2): 83-90.

? 2006, The Authors Journal compilation C 2006, The American Microscopical Society, Inc. DOI: 10.1111/j.1744-7410.2006.00043.x

Life cycle of Phacellophora camtschatica (Cnidaria: Scyphozoa)

Chad L. Widmera

Husbandry Division, Monterey Bay Aquarium, 886 Cannery Row, Monterey, California 93940, USA

Abstract. Gelatinous zooplankton play important roles in marine ecosystems and at times can have significant impacts on human activities. Many scyphozoans have enigmatic life cycles and the specific habitat for benthic life history stages is unknown. This is especially true for many of the large surface-cruising scyphomedusae of the northeast Pacific Ocean. Phacellophora camtschatica belongs to the family Ulmaridae and is known to have scyphistomae in the life history. However, the life cycle of P. camtschatica has not been formally described. Here the life cycle of members of P. camtschatica is described based on laboratory observations and compared with early life history stages in the scyphomedusa Aurelia labiata.

Additional key words. Cnidaria, Scyphomedusa, Scyphistoma, Ephyra, Ulmaridae

Jellyfishes play important roles in marine ecosystems and when abundant can form blooms that may have significant impacts on human activities (Mills 2001). Medusae prey upon zooplankton (Schneider & Behrends 1998; Robison 2004) and may directly compete with commercially important fish for food (Purcell & Sturdevant 2001). Jellyfishes can have significant impacts on commercial fishing efforts by clogging nets and fouling catches. In addition, jellyfishes sting swimmers at beaches and sometimes clog the seawater intakes of power plants (Mills 2001) and large public aquaria (C.L. Widmer, unpubl. data).

Species in the family Ulmaridae are found in both nearshore surface waters and the deep sea. The family is characterized by having simple or branched ra- dial canals and a ring canal, and may or may not have subgenital pits (Kramp 1961; Mianzan & Corn- elius 1999). Members of the genus Aurelia LAMARCK 1816 have scyphistomae in their life history and are generally thought to be a nearshore species (Gersh- win 2001). The mesopelagic jellyfish Stygiomedusa gigantea BROWNE 1910 is viviparous (Russell & Rees 1960) and two recently described species in the family, Tiburonia granrojo MATSUMOTO, RASKOFF, & LINDSAY 2003 (Matsumoto et al. 2003) and Stel- lamedusa ventana RASKOFF & MATSUMOTO 2004 (Raskoff & Matsumoto 2004), are mesopelagic, with life cycles that are unknown.

Phacellophora camtschatica BRANDT 1835 is the only valid species of the genus and also belongs to the family Ulmaridae (Kramp 1961). It has a polyp in its life history (Wrobel & Mills 1998; Jarms 2003), but the full life cycle has not been formally described. Relatively little is known about this large, graceful medusa, except that it is a medusivore (Strand & Hamner 1988) and plays host to several symbiotic organisms including juveniles of the crab Cancer gracilis DANA 1852, hyperiid amphipods LAVAL 1980, the barnacle Alepas pacifica PILSBRY 1907, and juvenile fishes (Wrobel & Mills 1998; C.L. Widmer, unpubl. data). The purpose of this study is to describe the life cycle in Phacellophora camtschatica, based on laboratory observations, and compare it with the early life history stages of the sympatric scyphomedusa Aurelia labiata CHAMISSO & EYSEN- HARDT 1821.

Methods

Eight mature medusae of Phacellophora camtschatica (Fig. 1), ranging 30-55 cm in bell diameter, were collected with wide-mouthed buckets from the surface waters of Monterey Bay, CA, USA in June 2004, aboard the R V Plankton Boat. Medusae were trans- ported to the jelly culture laboratory at the Monterey Bay Aquarium (Monterey, CA, USA) within 2 h. Medusae were placed in stretch kreisels (Raskoff et al. 2003) at 14'C until in vitro techniques were completed (usually <2 d).

Forceps were used to remove small samples of gonad from mature male and female medusae. The

a Author for correspondence. E-mail: [email protected]



84 Widmer

Fig. 1. Mature medusa of Phacellophora camtschatica. Scale bar = 10 cm.

gonads were then placed together inside 20-cm-diameter glass culture dishes filled with 1 L of 0.05 ?tm filtered seawater. Culture dishes were partially submerged in chilled baths on seawater tables in order to maintain the temperature at 14'C. Gonads and gametes were given daily water changes with a pipette until embryos began to form. When planulae developed, daily water changes ceased and gonads were re- moved from the dishes in order to prevent degradation by ciliate fouling. During the whole in vitro fertilization procedure, culture dishes were exposed to ambient laboratory overhead lighting (3500 K, 32 W, Sylvania Oct- ron, Danvers, MA) for - 9 hd-1 followed by darkness.

Developing polyps were fed rotifers, Brachionus plicatilis MULLER 1786, each day until the polyps

reached the 16-tentacled stage of development. At this stage they were large enough to eat nauplii of Artemiafranciscana KELLOG 1906, so the dishes with polyps were placed in flow-through tanks (Raskoff et al. 2003) with 0.05 ?tm filtered seawater. Develop- ing medusae were fed nauplii and appropriately sized (Strand & Hamner 1988), small, cultured moon jel- lies, Aurelia labiata, daily.

Observations were made at the Monterey Bay Aquarium jelly laboratory using a dissecting stereo- microscope (Leica Wild M8, Leica, Bannockburn, IL) and a compound light microscope (Olympus BX40, Olympus, Melville, NY). Specimens were photo- graphed using a digital camera (Nikon Coolpix 950, Nikon, Melville, NY) mounted on the microscopes.

Results

Life cycle summary

Fertilized eggs developed into ciliated planulae that swam, settled, and metamorphosed into scyphistomae (polyps). Polyps underwent 2-, 4-, 8-, and 16-tentacled stages of development before reaching the mature complement of 3044 tentacles. The polyps repro- duced asexually by side budding, and strobilated, releasing ephyrae that grew into mature medusae. It took - 9 months for an ephyra to become a sexually mature medusa under laboratory conditions.

Gametes

Eggs were - 180-195 jam

in diameter (Fig. 2A). Sperm were produced in follicles (Fig. 2B); the sperm follicles were irregularly shaped and densely packed

A

Fig. 2. A. Egg. B. Sperm follicles. Scale bars = 100 ?tm.

Invertebrate Biology vol. 125, no. 2, spring 2006



Life cycle of Phacellophora camtschatica 85

on the gonad. The follicles were generally 120-160 tm long and 70-110 ?im wide.

Planulae

Planulae were -360 ?tm long and 170 [tm wide. They were completely covered with cilia. They swam for --3-5 d before they selected a site, attached to the bottom, and metamorphosed into scyphistomae. About 90% of the planulae attached to the under- side of the surface tension of the water.

Developing scyphistoma

The early two-tentacled-stage scyphistoma (Fig. 3A) had two rudimentary perradial tentacle bulbs. The polyps were conical in shape and the height ranged 0.2-0.45 mm. The oral disc width ranged

0.15-0.25 mm (n = 10). The manubrium appeared as a small, elevated central portion of the oral disc. The base of the scyphistoma had a thin stalk surrounded by a thin periderm sheath. The polyps ranged from yellow to white in color.

Polyps at the four-tentacled stage (Fig. 3B) had two primary and two secondary slender, filiform, perradial tentacles. The polyp calyx was conical and became more distinct from the slender periderm sheath. The height of polyps ranged 0.3-0.8 mm and the mean oral disc width ranged 0.25-0.4mm (n = 10). The mouth lips were visible and form a cruciform figure. Coloration was the same as the two-tentacled polyps.

At the eight-tentacled stage, polyps developed four additional interradial tentacles and increased in overall length (Fig. 3C). Polyps ranged 0.7-0.9 mm high and 0.4-0.6 mm wide (n = 10). A small, thin,

:~? ,~?,sr ?ra~-~

Fig. 3. Developing early scyphistomae at the 2-, 4-, 8-, and 16- tentacled stages of development. A. Rudimentary two-tentacled- stage polyp (scale bar = 0.3 mm). B. Four-tentacled-stage polyp (scale bar = 0.5mm). C. Late eight-tentacled-stage polyp wrest- ling a nauplius of Artemia (scale bar=0.5mm). D. Sixteen-tentacled-stage polyp (scale bar = 1.0 mm).




86 Widmer

A

Fig. 4. A. Mature scyphistomae of Phacellophora camtschatica. B. Mature scyphistoma with new polyp budding from base of calyx. Scale bars = 2 mm.

periderm-sheathed stalk formed at the base of the calyx, significantly increasing the overall length of polyps at this stage compared with earlier stages. Gastric septa became visible. Polyps at this stage were capable of feeding upon rotifers (Brachionus plicatilis), but had trouble managing the larger nauplii of Artemia (Fig. 3C).

Polyps at the 16-tentacled stage (Fig. 3D) had four perradial, four interradial, and eight adradial filiform tentacles. The height of polyps ranged 1.2-1.8 mm and the oral disc diameters ranged 0.7-1.1 mm (n = 10). The polyps had a conical-to-goblet-shaped calyx perched upon a stalk of medium thickness con- nected to a thinner stalk. The point at which the stalk attached to the substrate was markedly thinner than where it attached to the base of the polyp, and was surrounded by a funnel-shaped periderm. The polyps had a cruciform mouth and the septal funnels were clearly visible from above. The polyps were easily capable of feeding upon nauplii of Artemiafranciscana. At this stage, polyps ranged from orange to yellow- white in color.

Mature scyphistoma

Mature scyphistomae of Phacellophora camntscha- tica (Fig. 4) had a mean height of 7.95 mm and a mean oral disc width of 2.65 mm (Table 1). The tentacles were amphicoronate, with retracted tentacles nearly as long as the scyphistomae were tall. When the tentacles were relaxed and extended, they had a mean length of 17.8 mm. In mature scyphistomae, tentacle number varied 30-44. The tentacles were ar- ranged in a single whorl around a thin, raised cruciform mouth. There were three kinds of nematocysts

on the tentacles of the scyphistomae: --5% of the nematocysts were holotrichous isorhizas 4-5 m long x 3.5-4 im wide; nearly 900% of the nematocysts were medium-sized heterotrichous microbasic euryteles 8-9 m long x 5-6.5 im wide; the remaining 5% of nematocyts were large heterotrichous microbasic euryteles 12-17 ?tm long x 8-14 ?Im wide. The septal funnels were conspicuous.

Polyps were yellowish white to pale orange in col- or. The scyphistomae had a goblet-shaped calyx perched upon a stalk with two distinct regions. Where the stalk was attached to the base of the polyp it was thicker than where the stalk attached to the substrate (Fig. 4). The thinner basal portion of the stalk was surrounded by a transparent funnel-shaped periderm and had a broadened basal attachment disc. The point at which the polyp attached to the substrate was comprised of several micro-stolons inter- nal to the periderm sheath. Asexual proliferation

Table 1. Summary of morphological characters of mature scyphistomae of Phacellophora camtschatica and Aurelia labiata. All measurements were in mm. Data are from cultures maintained at the Monterey Bay Aquarium, CA, n = 30.

Species Height Oral disc Number of Tentacle Podocyst width tentacles length diameter

P. camtschatica Mean 7.95 2.65 37.5 17.8 None Range 7-11 2.2-3.5 30-44 13-20

A. labiata Mean 2.2 1.4 18.7 7.2 0.46 Range 1.7-2.9 0.9-2.2 16-21 6-9 0.35-0.6





i;-.-?:I U~Yr~T

JF" , b ,c~ r?(zt ql gi~z 7 Irl f5(

-~i-?:?

~ ~ar? '~s~? 1 B

?i?~ ?a~ pp'

a 1- " ~J;ab ~ i:

~dlp rbr B ,1 ~4~?

Fig. 5. Strobilae of Phacellophora camtschatica in various stages of development. A. Early-stage strobila, pinching and thinning phase. B. Middle-stage strobila, elongating and transverse fission. C. Mature strobila ready to begin releasing ephyrae. Scale bars = 3 mm.

occurred by side budding, typically one bud per polyp at a time (Fig. 4B). The budding occurred at the junction of the bottom of the calyx and the top of the medium thickness stalk. Scyphistomae also repro- duced asexually, although less frequently, by fission. No podocysts were observed. Mature scyphistomae were easily capable of capturing nauplii of Artemia with their tentacles.

Polyp locomotion

Scyphistomae did not creep about on pedal discs. Rather, a single stolon was produced at the junction of the top of the medium thickness stalk and the bottom of the calyx. A typical stolon found a new attachment site, reattached, and a new thin periderm was produced. The vacated periderm did not regen- erate polyps. Asexual proliferation and locomotion were often concurrent processes.

Strobila

At the first stage of strobilation the calyx became. thinner just below the oral disc and segmentation of the calyx was observed with several discs appearing at the thinned place on the polyp (Fig. 5A). The tentacles of the polyp shortened and thickened, and

gradually the entire polyp lengthened and thinned to an even diameter and became segmented except for the basal polyp (Fig. 5B). Maturation of the ephyrae was successive; distal ephyrae matured and were released first while developing ephyrae proximal to the basal polyp formed (Fig. 5C). Fully developed ephyrae pulsed in rhythmic waves by contracting their lappets until their release. The waves started at the basal polyp and moved distally. Early scyphistomae were pale yellow in color. As ephyrae matured, the scyphistomae took on the color of the developing ephyrae (darker orange-yellow) except for the basal polyp, which remained pale yellow-white in color. Strobilae produced 8-15 ephyrae. Before the last ephyra was released, the tentacles on the basal polyp regenerated. After the last ephyra was released, the basal polyp soon also regenerated a mouth. It is important to note that for - 2-3 weeks the basal polyp, with newly regenerated tentacles and mouth, is much smaller than mature, pre-strobila-phase polyps.

Ephyra

Newly liberated ephyrae (Fig. 6) had a mean diameter, from lappet tip to lappet tip, of 5.34 mm (Table 2). Typical ephyrae had 16 marginal arms, although the number ranged 13-18. Ephyrae had




88 Widmer

Fig. 6. Newly liberated ephyra of Phacellophora camtschatica. Scale bar = 2 mm. Note that this specimen has 17 arms (lobes).

pointed lappets and a single rhopalium per arm, sit- uated between the two lappets. The mouth was cruciform, with two gastric filaments per quadrant. Nematocyst batteries were scattered evenly over the exumbrellar surface and an additional, much smaller and single, nematocyst battery was also present at the subumbrellar base of each marginal arm. The rudi- ments of four single primary tentacles (interradial) budded from the subumbrella at the base of the cleft between the marginal arms. Ephyrae were yellow to pale orange in color.

Medusa development

As the ephyrae matured, the four rudimentary interradial tentacles continued to elongate and became filiform. Evenly scattered exumbrellar nematocyst

Table 2. Summary of morphological characters of newly liberated ephyrae of Phacellophora camtschatica and Au- relia labiata. Data are from cultures maintained at the Monterey Bay Aquarium, CA, n = 30.

Species Diameter Arms per Ephyra color (mm) ephyra

P. camtschatica Mean 5.3 16 Orange-yellow Range 3.5-6.2

A. labiata Mean 3.9 8 Blonde/reddish

brown Range 2-5

batteries persisted throughout development from ephyrae through maturity. When the medusae reached -2.5cm in bell diameter, additional single tentacles formed in the remaining vacant basal subumbrellar clefts between the marginal arms. There were a total of four perradial tentacles, four interradial tentacles, and eight adradial subumbrellar tentacles (a total of 16 tentacles). The oral arms began to elongate at this stage as well. When medusae reached a bell diameter of -3 cm, they had two tentacles per subumbrellar marginal cleft. At 4.5-5 cm in bell diameter, medusae had a single row of six tentacles per cleft. Cultured individuals of P. camtschatica reached sexual maturity after -9 months, were -12 cm in bell diameter, and had a single row of -15-17 tentacles per subumbrellar marginal cleft.

Discussion

Of the described species in the family Ulmaridae that occur in the northeast Pacific, only Aurelia aurita LINNAEUS 1785 (Yasuda 1979; Lucas 2001), Au- relia labiata GERSHWIN 2001, Aurelia limbata BRANDT 1838 (Uchida & Nagao 1963), and Phacellophora camtschatica (Wrobel & Mills 1998; Jarms 2003; this study) are known to have polyps in their life history. In general, P. camtschatica has larger individuals than A. labiata, having larger scyphistomae (this study), ephyrae (this study), and medusae (Wrobel & Mills 1998; Gershwin 2001). Members of P. camtschatica had a mean of 37.5 tentacles per mature scyphistoma, whereas A. labiata had a mean of 18.7 tentacles per mature polyp. Scyphistomae of P. camtschatica maintained by the author at the Monterey Bay Aquarium for >4 years did not produce podocysts in that time, but A. labiata did, making podocysts irregular in shape and greenish yellow in color.

The size and health of scyphistomae varies, de- pending on culture conditions. Scyphistomae may be affected by temperature, salinity, dissolved oxygen, and nutritive condition (Arai 1997; Purcell et al. 1999; Condon et al. 2001). Therefore, the size of morphological structures alone should not be used as a method for distinguishing species at the scyphistoma level. Rather, careful examination of polyp morphol- ogy should be employed. Polyps of P. camtschatica had a very thin basal attachment stalk surrounded by a transparent funnel-shaped cuticle. Polyps of A. labiata in culture at the Monterey Bay Aquarium did not have a distinct stalk, and similarly Gershwin (2001) reported no stalks for polyps of A. labiata. However, members of other species of Aurelia do have small basal stalks (Chapman 1968), but not as





large or conspicuous as the stalks found in P. camtschatica. Furthermore, the transparent stalks reported here for P. camtschatica are much smaller and far less distinct than the readily visible tubes reported for polyps belonging to the order Coronatae (Jarms et al. 2002).

Polyps of P. camtschatica are most readily distin- guishable from polyps of Aurelia spp. in the predictable nature of the polyp body form and the predominant asexual reproductive method in P. camtschatica. These polyps typically had a single thin basal stalk which led to a thicker stalk, attached to a goblet-shaped calyx (Fig. 4). When asexual reproduction by side budding took place, only a single bud per polyp developed at the base of the polyp calyx. Polyps of A. labiata, on the other hand, were far less predictable in the reproductive method and location of new polyp bud formation. Polyps of A. labiata produced two or more side buds per polyp or possi- bly none at all. They also facultatively generated stolons that were longer than the polyps were tall, and could produce additional polyp buds along the length as well (Gershwin 2001; C.L. Widmer, unpubl. data). When polyps of P. camtschatica developed stolons, there was only one produced at a time, whereas polyps of A. labiata produced two or more as conditions dictated.

Medusae of P. camtschatica appear to be near or at the top of the food chain for surface-cruising scyphomedusae of the northeast Pacific and as such could be very important in regulating related planktonic marine communities (Strand & Hamner 1988; Robi- son 2004). Medusae of P. camtschatica actively feed on most gelatinous zooplankton they are able to physically manipulate (Strand & Hamner 1988). It is possible that preying upon gelatinous zooplankton may begin as soon as ephyrae of P. camtschatica are released from the strobila; these ephyrae were larger than those of other studied scyphomedusae, and the newly liberated ephyrae of P. camtschatica were also able to eat newly liberated ephyrae of A. labiata (C.L. Widmer, unpubl. data). The medusivorous properties of P. camtschatica may be beneficial for some human activities by keeping the populations of potentially bothersome species of jellyfish at bay. Should healthy populations of P. camtschatica disappear, it is possible that there could be an increase in the overall abundance of their gelatinous prey.

The habitats for scyphistomae of P. camtschatica and similarly most other species of scyphomedusae native to the northeast Pacific are presently unknown, making assessment of human activities on habitat and in situ ecological studies for this stage in their developmental life histories impossible. One ex-

ception to this rule seems to be that members of A. labiata, having polyps with some known habitats and locations, tend toward living attached to the under- sides of nearshore man-made floating objects (Gersh- win 2001). Finding the scyphistoma stage for species of the northeast Pacific, perhaps by using ROV technology, is in this author's opinion the "Holy Grail" of jellyfish science; it would allow in situ studies to be conducted toward a better understanding of bloom ecology. This may be especially important for species that are likely to feel the effects of El Niflo events and increasing sea surface temperature trends (Lau & Weng 1999).

Acknowledgments. I thank G. Jarms, A. Morandini, and P. Reynolds for their helpful comments when reviewing the manuscript. I also thank M. Murray, C.J. Slager, J. Hoech, K. Raskoff, G. Matsuomoto, L. Zeideberg, M. Faulkner, R. Hamilton, M. Ezcurra, C. Widmer family, A. Pereyra, J. Welch, G. Peterson, E. Francis, T. Davies, T. Knowles, J. Mariottini, B. Upton, H. Davidson, M. Badger, Monterey Bay Aquarium, J. DeMartini, G. Brusca, Humboldt State University, E. Kneivel, and the U.S. Army College Fund. This life cycle work is dedicated to the memory of my father Clyde D. Widmer; keep the shiny side up.

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