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Reproductive strategy of the jellyfishAurelia aurita (Cnidaria Scyphomedusae)in the Suez Canal and its migrationbetween the Red Sea and MediterraneanHamed A. El-Serehy a & Khaled A. Al-Rasheid aa Department of Zoology, College of Science , King Saud University ,Riyadh , 11451 , Saudi ArabiaPublished online: 08 Sep 2011.

To cite this article: Hamed A. El-Serehy & Khaled A. Al-Rasheid (2011) Reproductive strategy ofthe jellyfish Aurelia aurita (Cnidaria Scyphomedusae) in the Suez Canal and its migration betweenthe Red Sea and Mediterranean, Aquatic Ecosystem Health & Management, 14:3, 269-275, DOI:10.1080/14634988.2010.527231

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Reproductive strategy of the jellyfish Aurelia aurita(Cnidaria Scyphomedusae) in the Suez Canal and itsmigration between the Red Sea and Mediterranean

Hamed A. El-Serehy∗ and Khaled A. Al-RasheidDepartment of Zoology, College of Science, King Saud University, Riyadh 11451, Saudi Arabia

∗Corresponding author: helserehy@ksu.edu.sa

The life history of the common jellyfish A. aurita (Linnaeus) in the Suez Canal was investigated bymonthly sampling over a 28 month period from September 2006 to December 2008. Young medusae of2–3 cm diameter appeared during February/March. Growth was rapid. Some specimens of this cohortreached 16 cm and spawned by March/May and then decreased in size or died. Others reached a maximalsize of 10 cm by September, after which spawning took place. A few mature individuals remained afterspawning in the next year but decreased in size. Release of ephyrae seems to be induced by a lowering ofambient environmental temperature to below 16◦C, with peak of release occurring in December–February.A drop in temperature may be the primary cue for strobilation in the Suez Canal. A. aurita seems to bean immigrant plankter to the Suez Canal, and much interest was focused on determining from which endof the canal these organisms were invading the opposite sea. However, the canal itself, along with itslakes, should also be considered as a substantial permanent habitat in its own right. The canal cannot beconsidered only as a funnel or corridor through which animals pass like ships from one sea to the other.

A. aurita appears to enter the Suez Canal from the south via water currents; to do so it needs to becarried over a distance of 20 km along the canal from the Gulf of Suez into the Bitter Lakes, then passacross the Bitter Lakes before being carried a further 12 km along the canal into Lake Timsah. Transport ofA. aurita southward along the canal from the Mediterranean is unlikely to take place during most seasonsof the year because it would require transport against the dominant-water flow; it is possible only duringa brief period (July–September) of reversed flow. Because the main part of the 80 km from the Red Seais canalized, passive transport of A. aurita by water currents from the north could occur within a weekduring the brief period of reversed flow even at the low speed of 0.5 km hour−1. Moreover, conditions(barriers, obstacles and/or links) along the migratory route of the Suez Canal, in either direction, are likelyto determine the success of passive transport of A. aurita.

Keywords: gelatinous plankton, life span, medusae, ephyrae

Introduction

The Suez Canal is the main link between theMediterranean Sea and the Red Sea. It is situatedbetween longitudes of 32◦20′ and 32◦ 35′ E and lat-

itudes of 29◦ 55′ & 31◦ 15′ N. On route from PortSaid on the Mediterranean Sea to the Suez Port onthe Red Sea, the Suez Canal has been largely ex-cavated. Only about 70 km of the Canal has beenexcavated on dry land, while the rest of the waterway

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Aquatic Ecosystem Health & Management, 14(3):269–275, 2011. Copyright C© 2011 AEHMS. ISSN: 1463-4988 print / 1539-4077 onlineDOI: 10.1080/14634988.2010.527231

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crosses a series of lakes and swamps (from the north:Manzalah Lake, Ballah, Timsah Lake, and the twoBitter Lakes) (Por, 1978). The 45 km through Man-zalah Lake were deepened in the shallow lake, withthe excavated earth forming two dams that containthe Canal. By this, the eastern end of Manzalah hasbeen cut off from the main lake.

In the earlier years after its opening in 1869,the canal had a navigational depth of 8 m andsurface width of 59–98 m (Luksch, 1898; Mor-cos, 1971, 1972). Later on, successive projects towiden and deepen the canal have brought its depth to10–23 m and its surface width to 135–345 m (Por,1978; El-Serehy and Sleigh, 1992).

Prominent biological characteristics of the SuezCanal include low levels of chlorophyll a (often <1µg l−1 in the surface layer; El-Serehy et al., 2000a,2000b) and high abundances of the diatom Pleu-rosigma sp., dinoflagellate Protoperidinium leo-nis, green algae Staurasstrum sp, tintinnid Favellapanamensis, foraminiferid Globigerina inflata (El-Serehy et al., 1999), cyclopoid Oithona nana,calanoid Paracalanus crassirostris and harpacticoidEuterpina accutifrons (El-Serehy et al., 2001).

A. aurita eats any meso or macro-zooplanktersavailable whenever their size is suitable, includ-ing large protozoans, cyclopid copepods, calanoidcopepods, harpactecoid copepods, gastropod lar-vae and bivalve larvae. Therefore, its predationimpact on zooplankton usually leads to changesin species composition and community structureof zooplankton in general (Omori et al., 1995).The role of jellyfish and other gelatinous plank-ton in the marine ecosystem of the Suez Canal isof interest not only biologically, but also socio-economically. Aspects requiring further researchinclude their reproductive behaviour, factors lead-ing to large standing stocks and mass occur-rences, rapid growth rate, impact of predation rate,and detrimental effects on coastal industrial ac-tivities including desalination plants; coastal ar-tisanal fisheries and tourism (Yasuda, 1988). Inthe Suez Canal, mass occurrences of Aurelia au-rita (Linnaeus, 1881) periodically cause seriousproblems for net fishing during spring and au-tumn.

The aim of the present research was to investigatethe environmental factors affecting the life strat-egy of Aurelia aurita in the Suez Canal by assess-ing its reproductive strategy and migration activityover a 28 month period which began in September,2006.

Material and Methods

Sample collection

Aurelia aurita was sampled monthly using a con-ical net with an 80-cm mouth diameter (3 mm meshaperture) from September 2006 to December 2008at six stations in the Suez Canal. The six selectedstations were Suez, Little Bitter Lake, Great BitterLake, Timsah Lake, El Qantara and Ras EL Ech(Figure 1). Multiple quantitative samples of 18 nethauls were taken monthly at almost the same timeof day between 10:00 h and 13:00 h. The net wastowed horizontally in the surface layer for 5 minat approximately 2 knots with a RGS flowmeter at-tached to the mouth of the net. The water depth atall the fixed stations was relatively shallow, rang-ing from 10 m to 23 m. Surface and bottom watertemperature were measured during sampling. Addi-tional samples of A. aurita were occasionally takenwhenever they aggregated at the surface, in order toobtain sufficient individuals for analyses of growthpatterns. Bell diameter, sex, and wet weight of A.aurita were measured and the presence of planulalarvae in the pits of the oral arms was checkedon all live material immediately after sampling.Measurements of the bell diameter, to the nearest1.0 mm, were made by placing the specimen on ascale with the dorsal side down to flatten out the bell.Sex was identified by the basal form of the oral arms(Russell, 1970). Wet weight was measured after ex-ternal water was soaked up rapidly using blottingpaper. Ephyrae and young medusae without sexualcharacteristics on the oral arms were not sexed, norwere some adult medusae that lacked oral arms af-ter reproduction. Standing stock of A. aurita wasexpressed by the number of individuals m−3 andalso by wet weight m−3. Cohort analyses of the belldiameter histograms were made according to Cassie(1954) and Taylor (1965).

Results

Figure 2 shows the monthly records of water tem-perature at the surface and bottom in the Suez Canalduring the period of the present study as average val-ues of the six fixed stations. The water of the canalis well mixed in all months except during June toSeptember, when stratification occurs. All stationsshowed more or less similar temperature patterns.Maximum surface water temperature was 31 ±1.9◦C in August and 15.0 ± 0.4◦C during January.

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Figure 1. A map of the Suez Canal showing the six samplinglocalities of Suez, Little Bitter Lake, Great Bitter Lake, TimsahLake, El-Qantara and Ras El Ech.

Monthly changes of the standing stock of A. au-rita over the 28-month period indicated that both thenumber of individuals and wet weight were highestin April 2007 (being 0.3 ± 0.06 individuals m−3 and70.0 ± 6.5 g wet wt m−3). Both the number of indi-viduals and biomass varied in each year and showed

seasonal patterns with lowest values in mid- summer(June–July) and mid- winter (December–January)(Figures 3 and 4). Monthly size-frequency distribu-tions of the bell diameter generally showed a broaddistribution with several size groups at any one time(Figure 5).

The ephyrae of 0.1–0.3 cm bell diameter ap-peared in December 2006/January 2007 and youngmedusae of 2–3 cm in February/March 2007.Growth seemed rapid. Most specimens of this co-hort reached 16 cm and spawned by March/Mayand then decreased in size or died. Others reached amaximal size of 10 cm by September, when anotherspawning event took place. A few mature individu-als remained after the spawning into the next yearof 2008 and decreased in size.

The mean sex ratio was approximately 1:1throughout the sampling period, with only minorfluctuations. The minimal bell diameter size of fe-males with planula larvae was 5–5.5 cm, and planulalarvae were observed on the oral arms throughoutcertain months (September, October and November2007) of the year.

Discussion

In the present study, ephyrae of Aurelia aurita ap-peared in December 2006/February 2007 and youngmedusae occurred during February/March 2007,which indicated that strobilation probably occuredin winter. Kakinuma (1962) showed that loweringof the temperature from 25◦C to 15◦C caused maxi-mum strobilation in specimen sampled from MutsuBay, Japan. In Gull mar Fjord, Sweden, the ephyraewere most abundant in October and November whenthe temperature at 20 m deep dropped from 15◦Cto 5◦C (Hernorth and Grondahl, 1983, 1985). Fromthis, it is inferred that strobilation of A. aurita prob-ably becomes most active after periods of fallingtemperature in winter, and that environmental con-ditions during the polyp stage may be the underly-ing causes of mass occurrences. The ephyrae growto adult medusae with a maximum bell size within2–3 months, then decrease in size or die.

Generally, the reduction in size is a commonphenomenon in A. aurita, both in the sea and inaquaria. Moller (1980) found that bell diameter re-duced by 13–18% from August to September aftersexual reproduction. Hamner and Jenssen (1974)found that starvation also led to shrinkage, whereadult medusae reduced by 70% in bell diameter

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Figure 2. Monthly records of average water temperature at the surface and bottom of the Suez Canal from September 2006 toDecember 2008.

after 100 days starvation, but markedly increasedin size again when fed.

The life history strategy of A. aurita in the SuezCanal is different from that in Tokyo Bay, Japan;Kiel Bight, Germany; Urazoko Bay, Japan andTomales Bay, California. In Tokyo Bay, ephyraeappeared in March and grew to young medusae

in April and to adults of 25 cm by July/August2007 (Omori et al., 1995). In Kiel Bight, Germany,ephyrae grow to young medusae of 1.0 cm belldiameter by late April and to adults of 25 cm inAugust, and then undergo reduction (Moller, 1980).In Urazoko Bay Japan, young medusae appearedin May and reached a maximal size of 20 cm in

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Figure 3. Monthly records of the number of individuals of Aurelia aurita per cubic meter as average values of the six fixed stations.

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Figure 4. Monthly records of wet weight per cubic meter of Aurelia aurita as average values of the six fixed stations.

April/May of the next year (Yasuda, 1971). InTomales Bay, California, there are two different lifehistory patterns. One is annual, in which the youngmedusae grow rapidly, mature in mid-summer anddie; whereas the other pattern shows continuousgrowth until winter, with spawning in the next year(Hamner and Jenssen, 1974). These differencesreflect the wide capability of A. aurita to altertheir life strategy depending on environmentalconditions.

The jellyfish A. aurita recorded in the presentstudy occurred in the canal in one or more of the sta-tions sampled, and appeared to survive the spring inthe canal in high numbers. But how did this speciesoriginally come to the canal, and is this zooplankterannually re-introduced into self-sustaining isolatedpopulations? Migration of marine fauna may takeplace by passive transport by currents (common forplanktonic organisms, adults and planktonic larvaeof benthic forms), by other animals or man; andby active migration (common for larger active ani-mals). A. aurita most likely enters the Suez Canal bywater currents. To do so from the south it needs tobe carried over a distance of 20 km along the canalfrom the Gulf of Suez into the Bitter Lakes, then passacross the Bitter Lakes before being carried a further12 km along the canal into Timsah Lake. Transport

of A. aurita southward along the canal from theMediterranean is unlikely to take place during mostseasons of the year because it would require trans-port against the dominant water flow, so it is onlypossible during a brief period (July–September) ofreversal of flow. Because the main part of the 80km from the Red Sea is canalized, passive trans-port of A. aurita by water currents from the northcould occur within a week even at the low speedof 0.5 km hour−1. Moreover, conditions (barriers,obstacles and/or links) along the migratory routeof the Suez Canal, in either direction, are likely todetermine the success of passive transport of A. au-rita. Because this species seems to thrive better inspring and autumn than in winter and summer, thisspecies is more likely to have originated from theRed Sea, migrated along with the dominant watercurrents rather than from the Mediterranean againstthe water currents. The success of A. aurita to in-habit the canal ecosystem suggests that the SuezCanal ecosystem is able to contain at least someself sustaining isolated population of zooplanktonspecies, which may reflect the fact that the SuezCanal is a habitat of its own and should not be merelyconsidered as a funnel or corridor through which jel-lyfish medusae pass like ships from one end to theother.

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Figure 5. Percentage frequency distribution of the bell diameter in cm of Aurelia aurita. Percentage of individuals in which sex wasnot determined is indicated by solid shading. Histograms are not shown for months with less than15 individuals.

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Conclusions

In conclusion, the jellyfish A. aurita is an immi-grant species to the Suez Canal. It enters the canalthrough passive transport by water current from theRed Sea. It would appear to inhabit the canal ecosys-tem successfully and survive the spring in the canalin high numbers. Temperature is the primary cueenvironmental factor controlling strobilation of Aaurita in the Suez Canal water and growth seemsrapid. Ephyrae appear in winter, followed by youngmedusa, which in turn become mature and spawnin the canal water during spring or autumn and thendie. A few mature individuals remain after spawn-ing into the next year but decrease in size. Furtherstudies are now necessary to closely examine thefull impact of this jellyfish on the Suez Canal.

Acknowledgements

The authors would like to acknowledge the sup-port of King Saud University, Deanship of ScientificResearch and College of Science Research Center,Project No. (Zoo/2010/35).

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