Journal of Sea Research 65 (2011) 51–57
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Journal of Sea Research
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Clearance rates of ephyrae and small medusae of the common jellyfish Aurelia auritaoffered different types of prey
Hans Ulrik Riisgård ⁎, Caroline V. MadsenMarine Biological Research Centre (University of Southern Denmark), Hindsholmvej 11, 5300 Kerteminde, Denmark
⁎ Corresponding author. Tel./fax: +45 6532 1433.E-mail address: [email protected] (H.U. Riisgård).
1385-1101/$ – see front matter © 2010 Elsevier B.V. Aldoi:10.1016/j.seares.2010.07.002
a b s t r a c t
a r t i c l e i n f oArticle history:Received 9 April 2010Received in revised form 6 July 2010Accepted 9 July 2010Available online 18 July 2010
Keywords:EphyraeMedusaeClearance RateIngestion RateRetention EfficiencyAurelia aurita
Prey selection and knowledge of the amounts of water processed by the early stages of the common jellyfishAurelia aurita may at certain times of the year be crucial for understanding the plankton dynamics in marineecosystems with mass occurrences of this jellyfish. In the present study we used two different methods(“clearance method” and “ingestion-rate method”) to estimate the amount of water cleared per unit of timeof different types and sizes of prey organisms offered to A. aurita ephyrae and small medusae. The meanclearance rates of medusae, estimated with Artemia sp. nauplii as prey by both methods, agreed well, namely3.8±1.4 l h−1 by the clearance method and 3.2±1.1 l h−1 by the ingestion-rate method. Both methodsshowed that copepods (nauplii and adults) and mussel veligers are captured with considerably lowerefficiency, 22 to 37% and 14 to 30%, respectively, than Artemia salina nauplii. By contrast, the waterprocessing rates of ephyrae measured by the clearance method with A. salina nauplii as prey were 3 to5 times lower than those measured by the ingestion-rate method. This indicates that the prerequisite of fullmixing for using the clearance method may not have been fulfilled in the ephyrae experiments. The studydemonstrates that the predation impact of the young stages of A. aurita is strongly dependent on itsdevelopmental stage (ephyra versus medusa), and the types and sizes of prey organisms. The estimatedprey-digestion time of 1.3 h in a steady-state feeding experiment with constant prey concentration supportsthe reliability of the ingestion-rate method, which eliminates the negative “container effects” of theclearance method, and it seems to be useful in future jellyfish studies, especially on small species/youngerstages in which both type and number of prey can be easily and precisely assessed.
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1. Introduction
The cosmopolitan scyphomedusa Aurelia aurita is particularlyabundant during summer in North Atlantic coastal waters where it isrecognized as an important predator in plankton communities (Hayet al., 1990). High densities of this pelagic gelatinous predator canseriously affect populations of zooplankton and ichthyoplankton andmay be detrimental to fisheries through competition for food withfishes as well as direct predation on eggs and larvae of fish (Möller,1980; Purcell, 1997; Hansson et al., 2005; Purcell and Decker, 2005).
Aurelia aurita has a life cyclewith twomorphs, a pelagicmedusa anda benthic polyp (Hernroth and Gröndahl, 1985; Papathanassiou et al.,1987; Schneider and Behrends, 1994; Miyake et al., 1997; Ishii andTakagi, 2003). The medusa has sexual reproduction and larvaldevelopment, followed by disappearance of adult medusae from thewater columnand planulametamorphoses into the polyp benthic stage.The time and length of occurrence of the ephyra stage varies betweenlocalities (Miyake et al., 1997). The occurrence of ephyrae in northern
areas may be seasonally restricted, mainly occurring either in spring orboth in spring and autumn, or it may be continuous (Båmstedt et al.,1999). In the western Baltic Sea the great majority of ephyrae areproduced in April andMay (Möller, 1980). The development of A. auritaephyrae to medusae was recently followed by Riisgård et al. (2010) inthe shallowcove of KertingeNor (Denmark). Thefirst ephyrae appearedinMarch anddisappeared again inMay, and clearly, therewas producedone well-defined year group of A. aurita with a maximum of about400 ind.m−3 in May 2009, followed by a general decrease in densityduring the period May to August, probably due to flush out of the coveby water exchange. Natural populations of A. aurita are usually foodlimited (Schneider and Behrends, 1994) and in Kertinge Nor themaximum diameter of the umbrella is usually only a few centimetre(compared to about 30 cm inmost otherwaters) owing to an extremelyhigh abundance of small medusae causing shortage of prey and thusrestricting their own growth (Olesen et al., 1994; Olesen, 1995; Riisgårdet al. 1995; Nielsen et al., 1997).
The ephyra is typically smaller than 10 mm in diameter and lackstentacles (Sullivan et al., 1997).The ephyra stage in A. aurita's life cycle isseldom studied, and information on their abundance, feeding rate, prey-capture efficiency, and population predation impact is limited (Olesenet al., 1994; Hansson et al., 2005; Møller and Riisgård, 2007b,c).
52 H.U. Riisgård, C.V. Madsen / Journal of Sea Research 65 (2011) 51–57
Feeding of jellyfish predators is characterized by selectivity, whichdepends onmany factors such asprey size and swimming speed, predatortentacle length, width and spacing, predator swimming behavior andresulting bell-margin water flow, nematocyst types affecting penetrationof prey with different vulnerability to toxin and escape abilities (Costelloand Colin, 1994; Ford et al., 1997; Purcell, 1997; Sullivan et al., 1997;Suchman, 2000). The A. aurita ephyrae capture a variety of prey types(Stoecker et al., 1987; Möller 1989; Båmstedt, 1990; Olesen et al., 1994;Olesen, 1995; Sullivan et al., 1994, 1997; Hansson, 2006), but prey size,prey-escape speed, and surface properties of prey strongly influence thecapture efficiency. Thus, using video observations of free-swimmingephyrae and their prey, Sullivan et al. (1997) observed that captureefficiencies of ephyrae feeding on large prey (barnacle nauplii, brineshrimp, hydromedusae) were 4 to 12 times greater than for small preytypes (rotifers, copepod nauplii), and further, that capture efficiencies forprey of equal sizes differed, indicating that factors in addition to sizeinfluence the predator–prey interaction. Likewise, Møller and Riisgård(2007c) found that the measured clearance rates of A. aurita wereconsiderably higher on 3-day old Artemia nauplii than on 1-day oldArtemia.
In ecological studies, prey-selection mechanisms are important forunderstanding how jellyfish predationmay alter the zooplankton speciescomposition (Costello and Colin, 1994; Purcell, 1997; Ford et al., 1997),and likewise, knowledge of the actual amounts of prey eaten by thejellyfish is crucial to understand the plankton dynamics in marineecosystems with frequent mass occurrences of jellyfish (Olesen et al.,1994; Hansson et al., 2005;Møller and Riisgård, 2007a,b,c; Purcell, 2009).
In the present study, we used two fundamentally differentmethods, the “clearance method” and the “ingestion-rate method,”to determine the amount of water cleared per unit of time of differenttypes of prey organisms offered to A. aurita ephyrae and smallmedusae. This approach enabled us to evaluate the relative prey-capture efficiency of the early jellyfish stages, and to evaluate themerits of the two clearance methods.
2. Materials and methods
2.1. Prey organisms
The jellyfish used in the clearance experiments were offereddifferent types of cultivated prey organisms: brine shrimp nauplii(Artemia salina), nauplii and adult copepods (Acartia tonsa), rotifers(Brachionus plicatilis), and mussel veligers (Mytilus edulis). All preyorganisms were fed a monoculture of Rhodomonas sp. Freshly-collected barnacle cypris larvae (Semibalanus balanoides) were offeredas prey in some clearance experiments.
2.2. Clearance method
Ephyrae and small medusae of A. auritawere collected in Februaryand July of 2005, respectively, from Kertinge Nor, a shallow cove onthe east coast of the island of Fyn, Denmark. The jellyfish werebrought to the laboratory and kept in storage aquaria (15 °C; 20 psu)until experiments could be performed. If kept for longer than a fewdays, the jellyfish were fed A. salina nauplii.
A. aurita (ephyrae andmedusae) clearance rates were measured inlaboratory experiments as the volume of water cleared of preyorganisms per unit time. A known number of prey organisms wereadded to 3 to 7 experimental tanks with known volumes (V) offiltered seawater. By using a pipette, big drops of water with preyfrom the cultivating tankwere placed on the bottom of a Petri disc andthe number of prey organisms in each drop was counted so that theexact number of prey, subsequently added by washing all the dropsinto the experimental tank, was known. At time zero, jellyfish (3 to 9ephyrae or 1 medusa) were added to each experimental tank, and onetank without jellyfish served as control. For ephyrae 0.2 to 0.8 l of
filtered seawater was added to a glass beaker; for medusae, 6 l ofwater was added to an aquarium. The reduction in the number of preyorganisms as a function of timewas followed by removing the jellyfishfrom one aquarium at time intervals and filtering (80-μm mesh) allthe water (i.e. data for each aquarium represents 1 time); the retainedprey organisms were counted by use of a stereo-microscope. Theindividual clearance rate (Cl, ml h−1) was determined from theexponential reduction in prey concentration from the formula:
Cl = aV = n; ð1Þ
where a=slope of the fitted regression line in a plot of lnCt versus time,n=number of jellyfish in the experimental tank, V (ml)=volume ofseawater in tank, and Ct is prey concentration at time t. All experimentswere conducted at 15 °C and 20 psu.
2.3. Ingestion-rate method
Ephyrae and small medusae of A. auritawere collected in April andJune–July 2009, respectively, from Kertinge Nor. The jellyfish werebrought to the laboratory and kept in storage aquaria until experi-ments could be performed. If kept for longer than a few days, thejellyfish were fed A. salina nauplii.
A known number of jellyfish were carefully transferred in a beakerwith water to the experimental tank containing a known volume ofseawater (60 or 70 l) and allowed to acclimate to the ambient watersalinity and temperature (20 psu, 12.4 °C) for some hours, until theundisturbed jellyfish were swimming freely around in the water and novisible zooplankton remained in the gastric pouches of the medusae. Attime zero, 3 types of prey organisms were added in the sameconcentration (C) of 10 prey l−1. Every 10 min afterwards, one or severaljellyfish were taken out (and not later returned), and the number of eachtype of prey seen in the stomach were counted by use of a stereo-microscope. The ingestion rate (I, prey min−1) was determined from theslope of the regression line based on the number of prey in the stomach asa function of time. The clearance rate (Cl, l h−1) then was determined as:
Cl = I × 60 = C ð2Þ
A precondition for using the equation is that the prey concentra-tion remains constant throughout the experimental time. This wasapproximated by use of the large tank volume so that the preyconcentration remained approximately constant during the experi-ment; no more than 15% of the prey organisms were removed by theend of the experiment.
Because it was important to count all the prey ingested, theoptimum concentration for the experimental procedure was initiallydetermined. Jellyfish may regurgitate their stomach contents if theprey concentration is too high. Preliminary tests with differentconcentrations of A. salina nauplii showed that regurgitation did notoccur at or below 10 prey l−1. To ensure that the number of each preytype in the stomach could be identified, the experimental period was60 min. Prey organisms were classified as digested when no solidmaterial was seen in the stomach.
2.4. Steady-state experiment and digestion time
In steady state (i.e. ingestion rate of prey=digestion rate of prey), theingestion rate (I, prey h−1), clearance rate (Cl, l ind.−1 h−1), number ofprey in the gastric pouches of themedusae (G), prey concentration in theambient water (C, prey l−1), and prey-digestion time (E, h) areinterconnected and can be expressed by the following equations:
I = G= E ð3Þ
Cl = I = C ð4Þ
Fig. 2. Aurelia aurita ephyrae. (A and B) Simultaneous clearance (15 °C) of different preyorganisms due to feeding by ephyrae (5.5 mm). Regression lines and estimatedclearances (ml h−1 ind.−1) are shown.
53H.U. Riisgård, C.V. Madsen / Journal of Sea Research 65 (2011) 51–57
The number of prey organisms (A. salina nauplii) in the gut of A.aurita (34±3 mm in diameter) was monitored during a 3-h experi-ment in which 6 medusae were removed every 60 min from a 70-laquarium with 10 prey l−1.
3. Results
3.1. Clearance method
Fig. 1 shows two examples of clearance experiments with A. auritaephyrae. Clearance rates of A. aurita ephyrae were measured inexperiments in which different types of prey, i.e. copepods (naupliiand adults), barnacle cypris larvae, and hydromedusae were providedsimultaneously (Fig. 2). The clearance rate measured for ephyraefeeding on adult copepods (0.8 ml h−1 ind.−1) was very low comparedto the clearance on copepod nauplii (about 14 ml h−1 ind.−1). Ephyraeretained adult copepods and barnacle cypris larvae at very low rates ascompared with Artemia nauplii (Table 1). Furthermore, the clearancerates of Artemia and rotifers increased with increasing ephyra size. Forephyrae of same size (i.e. 5.1 to 5.2 mm diameter), the estimated meanclearance rates were 54.4±17.2 ml h−1 (n=9) for Artemia, 23.0±10.0 ml h−1 (n=3) for rotifers, and 18.9±15.0 ml h−1 (n=5) forcopepod nauplii. Thus, rotifers and copepod nauplii are cleared with 42and 35% efficiency, respectively, in relation to Artemia. Estimatedclearance rates of A. aurita medusae simultaneously provided withdifferent prey organisms showed the relative retention efficiencieswereabout 37 and 16% for nauplii and adult copepods, respectively, and 30%for mussel veligers, as compared with Artemia nauplii as the reference(Fig. 3, Table 2).
3.2. Ingestion-rate method
Examples of how the ingestion rate was determined from the slopeof the regression line based on the number of prey in the stomach as afunction of time are shown in Figs. 4 and 5. Clearance rates estimatedfor A. aurita ephyrae by the ingestion-rate method in experiments
Fig. 1. Aurelia aurita ephyrae. Examples of exponential reduction in prey concentrationdue to filtration by jellyfish in two clearance experiments (15 °C) with 0.9 mm (upper,Exp. #2) and 0.5 mm Artemia salina nauplii (lower, Exp. #3) offered as food. (♦)Regression lines and their equations are shown; (◊) control experiment withoutjellyfish. Estimated clearance rates and experimental conditions are shown in Table 1.
with 3 prey types showed that the relative retention efficiencies, ascompared to rotifers, were 83, 38 and 36% for 0.5, 0.9 mm, and newlyhatched Artemia, respectively, but only 8% for copepod nauplii(Tables 3, 4). The clearance rates of A. aurita medusae feeding ondifferent prey organisms showed that the relative retention efficien-cies, as compared with Artemia (0.7 mm),were about 60% for rotifers,35 and 22% for copepod adults and nauplii, and 14% for musselveligers (Tables 5, 6).
3.3. Steady-state experiment and digestion time
The mean (±SD) numbers of prey in the gut were 38.0±14.9(n=6), 46.5±6.8 (6), and 44.0±9.3 (6) after 1, 2, and 3 h,respectively, and the overall mean in the steady-state period wasG=42.8±4.4 (n=3). The clearance rate (Table 6) was measured tobe Cl=3.2 l h−1 so that I=Cl×C=3.2×10=32 prey h−1, and thus,the prey-digestion time is estimated at E=G/I=42.8/32=1.3 h,which is in good agreement with the actually observed digestion timefor A. salina nauplii.
4. Discussion
The clearance rates reported here compare well with the previouslimited data on the youngest stages of A. aurita (Olesen et al., 1994;Olesen, 1995; Hansson et al., 2005; Møller and Riisgård, 2007a,b,c).We demonstrated that the clearance rates for ephyrae and smallmedusae of A. aurita feeding on various prey organisms varyconsiderably, depending on size and stage of A. aurita, type and sizeof prey, and probably also on the method used to measure theclearance rates (Tables 2, 4, 6). The mean clearance rates measured onmedusae using A. salina nauplii as prey by means of the clearancemethod and the ingestion method were in good agreement, namely3.8±1.4 and 3.2±1.1 l h−1, respectively (Tables 2 and 6), and bothmethods showed that copepods nauplii and adults (22 to 37%) andmussel veligers (14 to 30%) were captured with considerably lower
Table 1Aurelia aurita ephyrae. Clearance rate (Cl) of ephyrae measured in experiments (15 °C) with only one type of prey (Exp. #1 to #9), or 2 types (Exp. #10 to #17). V=volume of waterin experimental glass beakers; n=number of ephyrae in experimental beakers; N=number of tanks used in clearance experiment; D=inter-rhopalia diameter; C0=initialconcentration of prey organisms Exp. #18 to #19 refer to experiments shown in Fig. 3A, B and C, respectively.
Exp. # V(l)
n N D(mm)
Prey Prey size(mm)
C0(prey l−1)
Cl(ml h−1)
1 0.2 4 3 5.9±0.2 Artemia 0.9 50 53.12 0.2 4 7 5.9±0.2 Artemia 0.9 50 59.13 0.2 4 5 5.2±0.2 Artemia 0.5 50 38.44 0.2 4 6 5.2±0.2 Rotifers 0.2 535 25.85 0.2 3 6 4.5±0.3 Rotifers 0.2 780 12.06 0.2 4 6 4.5±0,1 Rotifers 0.2 855 21.67 0.2 4 5 5.2±0.2 Artemia 0.5 50 41.78 0.2 7 4 4.6±0.1 Artemia 0.5 50 8.19 0.65 7 9 5.2±0.2 Artemia 0.5 50 55.910 0.64 6
74 5.2±0.1 Artemia
Copepods0.5Nauplii
5239
54.77.7
11 0.64 66
3 3.4±0.2 ArtemiaRotifers
0.50.2
78734
3.82.6
12 0.64 77
4 4.1±0.2 ArtemiaRotifers
0.50.2
78730
18.210.6
13 0.64 77
4 5.2±0.2 ArtemiaRotifers
0.50.2
78395
28.89.6
14 0.64 77
4 5.1±0.2 ArtemiaCopepods
0.5Nauplii
3897
47.03.8
15 0.8 66
4 5.1±0.2 ArtemiaArtemia
0.50.9
3535
54.085.2
16 0.8 66
4 5.1±0.1 ArtemiaCopepods
0.5Nauplii
3063
72.045.6
17 0.8 66
4 5.1±0.2 RotifersCopepods
0.2Nauplii
43865
33.624.0
18 0.64 15 7 6.2±0.9 CopepodsBarnacles
NaupliiCypris
3030
11.013.8
19 0.5 15 5 5.1±0.6 CopepodsCopepods
AdultsNauplii
3030
0.813.6
54 H.U. Riisgård, C.V. Madsen / Journal of Sea Research 65 (2011) 51–57
efficiencies than were A. salina nauplii. However, when the clearancerates for ephyrae were compared (Fig. 6, Table 4), the clearance rateson Artemia nauplii (0.9 mm) were 3–5 times higher when measuredby the ingestion-rate method than by the clearance method. Thisindicates that the important prerequisite for using the clearancemethod (Eq. (1)), namely “full mixing,” has not been fulfilled.Whereas larger medusae swimming around in a tank with a relativelysmall volume of watermay create nearly full mixing, this apparently isnot true for very small medusae and ephyrae, and some supplemen-tary mechanical mixing may be appropriate. Use of a small tank toincrease mixing, however, can introduce the “wall effect,” in whichjellyfish hit the wall of the tank; normal swimming activity isdisturbed, tentacle length may be shortening, and thus, prey-captureefficiencies and clearance rates may be reduced. This may perhapsalso explain the observation that “containers generally reduce” thefeeding rates of even small species, and that “clearance ratesgenerally” give lower feeding rate estimates than the gut-contentmethod (Purcell, 2009).
The mechanics of prey selection by A. aurita ephyrae wasstudied by Sullivan et al. (1997), who observed that A. salinanauplii and rotifers continue to swim after entrainment and arecaptured more often than copepod nauplii of equal size, whichcease normal swimming (“play dead”). Unlike the ephyrae, A.aurita medusae are able to capture adult copepods, and Sullivan etal. (1994) suggested that this may be due to the so-calledmarginal-flow mechanism of feeding used by A. aurita medusae,cf. Costello and Colin (1994).
Ephyraemay be important in reducing dense patches of zooplanktonprey. Olesen et al. (1994) reported that the maximum abundance in theshallow Kertinge Nor (Denmark) was 300 ephyrae m−3 in early spring.The clearance rate of 5 mm ephyrae (12.4 °C) was about 679 ml h−1
when rotiferswereofferedasprey (Table4). Thus, at a populationdensityof 300 ephyrae m−3, the volume specific clearance rate of the ephyrae is
estimated to be about Fpop=4.9 day−1. The half-life of zooplankton(rotifers), as calculated according toHansson et al. (2005): t1/2=ln2/Fpop,would be 0.14 days. The short half-life time indicates an importantpredation impact, although we emphasize that the impact is stronglydependent on both type and size of prey as demonstrated here.
The estimated prey-digestion time of E=1.3 h in the present studyagrees well with a digestion time of 1.4 h (9.5 °C) for A. salina in thegut of A. aurita (umbrella diameter 3.5 to 14.5 mm) reported byMartinussen and Båmstedt (1999, 2001), and thus supports thereliability of the clearance rates estimated by the ingestion-ratemethod which may prove to be useful in future jellyfish studies,especially on small species and younger stages in which the type andnumber of prey can easily and precisely assessed.
Fish larvae are often among the gut contents of field caught A.aurita (e.g. Möller, 1980; Bailey and Batty, 1983; de Lafontaineand Legett, 1987, 1988; Purcell, 1997; Elliott and Leggett, 1997;Hansson et al., 2005; Titelman and Hansson, 2006) and thereforeit is of interest to compare the present clearance rates of smallmedusae with clearance rates obtained in other studies, not onlyusing other zooplankton as prey, but also fish larvae. Theliterature on clearance rates of A. aurita medusae has previouslybeen compiled by Olesen (1995) and Titelman and Hansson(2006), and should not be repeated here. But in order to evaluatethe relative retention efficiency (or predation efficiency) ofdifferent prey, clearance rates of small medusae of comparablesize (about 40 mm diameter) offered various prey organisms havebeen placed together in Table 7. It is seen that fish larvae and A.salina nauplii are cleared with near same rate whereas “mixedzooplankton,” rotifers, copepods, and not least ciliates areretained with increasingly lower efficiency which probablyreflects the importance of both prey-escape behavior and preysize for predation efficiency (e.g. Sullivan et al., 1994; Suchmanand Sullivan, 2000).
Fig. 3. Aurelia aurita medusae. Simultaneous clearance (15 °C) of different preyorganisms by medusae (43.3±0.1 mm) in 4 experiments (A to D). Regression lines andestimated clearances (ml h−1 ind.−1) are shown.
Table 2Aurelia aurita medusae (43.3±0.1 mm). Relative retention efficiency of different preyorganisms offered as food in clearance experiments (15 °C). Mean clearance rates areobtained from experiments shown in Fig. 6.
Prey Clearance rate(l h−1 ind.−1)
Relative retention(%)
Artemia (0.6 to 0.7 mm) 3.8±1.4 (n=3) 100Copepods (nauplii, 2-day old) 1.4±1.0 (n=4) 37Mussel veligers 1.1±0.5 (n=2) 30Copepods (adult) 0.6±0.3 (n=3) 16
Fig. 4. Aurelia aurita ephyrae. Mean (±SD) number of prey organisms (Artemia salinanauplii) in the stomachs of 3 ephyrae (mean diameter: 5±1 mm) as a function offeeding time in two experiments (A and B; 12.4 °C). Linear regression lines andequations are shown.
Fig. 5. Aurelia auritamedusae. Number of prey organisms (Artemia salina nauplii) in thestomach of single medusa as a function of feeding time (12.4 °C). (A) Mean diameter ofmedusae: 33±2 mm; (B) mean diameter: 33±3 mm. Linear regression lines andequations are shown.
55H.U. Riisgård, C.V. Madsen / Journal of Sea Research 65 (2011) 51–57
Acknowledgements
Thanks are due to Jennifer E. Purcell and an anonymous reviewerfor constructive comments on the manuscript. The study wassupported by a grant from FNU, the Danish Agency for ScienceTechnology and Innovation (H.U. Riisgård, grant no. 09-073291).
Table 3Aurelia aurita ephyrae (5±1 mm). Clearance rate (Cl=I/C) for ephyrae measured iningestion-rate experiments with 3 types of prey organisms (#1 to #4), or one type (#5and #6) in experimental aquaria with 60 l seawater (12.4 °C). C=concentration of preyorganisms; I=ingestion rate of prey with [r2] for the linear regression line where slopeexpresses the ingestion rate.
Exp. # Prey Prey size (mm) C (prey l−1) I (prey min−1) Cl (ml h−1)
1 Artemia 0.5 3.3 0.021 [0.801] 377Artemia 0.9 0.006 [0.742] 101Copepods Nauplii 0.003 [0.258] 51
2 Artemia 0.5 3.3 0.024 [0.620] 432Artemia 0.9 0.007 [0.539] 123Copepods Nauplii 0.003 [0.223] 54
3 Artemia 0.5 3.3 0.045 [0.696] 816Artemia 0.9 0.023 [0.543] 405Rotifers 0.2 0.041 [0.678] 737
4 Artemia 0.5 3.3 0.035 [0.570] 629Artemia 0.9 0.023 [0.514] 405Rotifers 0.2 0.035 [0.906] 622
5 Artemia Newly hatched 10 0.043 [0.828] 2606 Artemia Newly hatched 10 0.038 [0.909] 226
Table 4Aurelia aurita ephyrae (5±1 mm). Relative retention efficiency of different preyorganisms offered as food in ingestion-rate experiments (12.4 °C). Mean clearancerates (Cl±SD) are obtained from experiments shown in Table 3.
Prey Cl(ml h−1)
Relative retention(%)
Rotifers 679±25 100Artemia (0.5 mm) 564±200 83Artemia (0.9 mm) 259±170 38Artemia (newly hatched) 243±3 36Copepods (nauplii) 52±82 8
Table 5Aurelia aurita medusae. Clearance rate (Cl=I/C) measured in ingestion-rate experi-ments with 3 types of prey organisms (#1 to #4), 2 types of prey (#5 and 6), and onetype (#7 and 8). D=inter-rhopalia diameter (±SD); V=volume of water inexperimental aquarium (12.4 °C); C=concentration of prey organisms; I=ingestionrate with [r2] for the linear regression line where slope expresses the ingestion rate.
Exp.#
D(mm)
V(l)
Prey Prey size(mm)
C(prey l−1)
I(prey min−1)
Cl(l h−1)
1 29.1±0.9 60 Copepods Adults 3.3 0.073 [0.722] 1.3Copepods Nauplii 0.050 [0.820] 0.9Artemia 0.7 0.190 [0.835] 3.4
2 28.1±2.3 60 Copepods Adults 3.3 0.067 [0.721] 1.2Copepods Nauplii 0.065 [0.798] 1.2Artemia 0.7 0.289 [0.901] 5.2
3 32.3±1.6 60 Copepods Adults 3.3 0.056 [0.345] 1.0Copepods Nauplii 0.016 [0.604] 0.3Rotifers 0.116 [0.714] 2.1
4 32.5±1.0 60 Copepods Adults 3.3 0.055 [0.742] 1.0Copepods Nauplii 0.023 [0.689] 0.4Rotifers 0.2 0.096 [0.614] 1.7
5 29.2±2.4 70 Artemia 0.7 5 0.185 [0.539] 2.2Musselveligers
0.4 0.044 [0.656] 0.5
6 29.5±1.8 70 Artemia 0.7 5 0.175 [0.836] 2.1Musselveligers
0.4 0.032 [0.463] 0.4
7 32.7±2.3 70 Artemia 0.7 10 0.479 [0.687] 2.98 32.8±3.1 70 Artemia 0.7 10 0.565 [0.849] 3.4
Table 6Aurelia aurita medusa (28.1 to 32.8 mm). Relative retention efficiency of different preyorganisms offered as food in ingestion-rate experiments (12.4 °C). Mean clearance rates(Cl±SD) are obtained from experiments shown in Table 3.
Prey Cl (l h−1) Relative retention (%)
Artemia (0.7 mm) 3.2±1.1 100Rotifers 1.9±0.3 60Copepods (adults) 1.1±0.2 35Copepods (nauplii) 0.7±0.4 22Mussel veligers 0.5±0.1 14
Fig. 6. Aurelia aurita ephyrae. Clearance rate of jellyfish as a function of inter-rhopaliadiameter measured in experiments (15 °C) in which different types of prey organisms ofdifferent size have been offered as food. Experimental conditions are shown in Table 1.
Table 7Aurelia aurita. Clearance rate (Cl) of small medusae with comparable umbrella diameter(D) on different types of prey.
D(mm)
Temp.(°C)
Prey Cl(l h−1)
Reference
40a) 15 Balanion sp.(ciliate)
0.15 Stoecker et al. (1987)
40b) 15 Acartia tonsa(copepod)
0.7 Møller and Riisgård(2007a,b,c)
40c) 15 Brachionus plicatilis(rotifer)
1.2 Olesen (1995)
47 15 Mixed zooplankton 1.4 Båmstedt (1990)30.2±0.1 15 Artemia salina
(0.7 mm)3.2±1.1 This study
(ingestion-ratemethod)
43.3±0.1 15 Artemia salina(0.6–0.7 mm)
3.8±1.4 This study(clearance ratemethod)
38 8.7 Mallotus villosus(capelin, yolksac)
3.0 de Lafontaine andLegett (1988)
40d) 8 Gadus morhua(cod, yolksac)
5.0 Titelman andHansson (2006)
a) Estimated from the equation (Stoecker et al., 1987, Fig. 1 therein): Cl=2.14+0.4 V,where V=biovolume (cm3).
b) Estimated from the equation (Møller and Riisgård, 2007a,b,c): Cl=0.0073D(mm)2.1.c) Estimated from the equation (Olesen, 1995): Cl=1.08A−73.05, where A=cross
sectional area of medusa (mm2).d) Estimated from the equation (Titelman and Hansson, 2006): Cl (l h−1)=0.476D
(cm)1.698.
56 H.U. Riisgård, C.V. Madsen / Journal of Sea Research 65 (2011) 51–57
References
Bailey, K.M., Batty, R.S., 1983. A laboratory study of predation by Aurelia aurita on larvalherring (Clupea harengus): experimental observations compared with modelpredictions. Mar. Biol. 72, 295–301.
Båmstedt, U., 1990. Trophodynamics of the scyphomedusae Aurelia aurita. Predationrate in relation to abundance, size and type of prey organism. J Plank. Res. 12,215–229.
Båmstedt, U., Lane, J., Martinussen, M.B., 1999. Bioenergetics of ephyra larvae of thescyphozoan jellyfish Aurelia aurita in relation to temperature and salinity. Mar. Biol.135, 89–98.
Costello, J.H., Colin, S.P., 1994. Morphology, fluid motion and predation by thescyphomedusa Aurelia aurita. Mar. Biol. 121, 327–334.
de Lafontaine, Y., Leggett, W.C., 1987. Effect of container size on estimates of mortalityand predation rates in experiments with macrozooplankton and larval fish. Can. J.Fish. Aquat. Sci. 44, 1534–1543.
de Lafontaine, Legett, W.C., 1988. Predation by jellyfish on larval fish: an experimentalevaluation employing in situ enclosures. Ca. J. Fish. Aquat. Sci. 45, 1173–1190.
Elliott, J.K., Leggett, W.C., 1997. Influence of temperature on size-dependent predationby fish (Gasterosteus aculeatus) and a jellyfish (Aurelia aurita) on larval capelin(Mallotus villosus). Can. J. Fish. Aquat. Sci. 54, 2759–2766.
Ford, M.D., Costello, J.H., Heidelberg, K.B., 1997. Swimming and feeding by thescyphomedusa Chrysaora quinquecirrha. Mar. Biol. 129, 355–362.
57H.U. Riisgård, C.V. Madsen / Journal of Sea Research 65 (2011) 51–57
Hansson, L.J., 2006. A method for in situ estimation of prey selectivity and predationrate in large plankton, exemplified with the jellyfish Aurelia aurita (L.). J. Exp. Mar.Biol. Ecol. 328, 113–126.
Hansson, L.J., Moeslund, O., Kiørboe, T., Riisgård, H.U., 2005. Clearance rates of jellyfishand their potential predation impact on zooplankton and fish larvae in a nereticecosystem (Limfjorden, Denmark). Mar. Ecol. Prog. Ser. 304, 117–131.
Hay, S.J., Hislop, J.R.G., Shanks, A.M., 1990. North Sea scyphomedusae: summerdistribution, estimated biomass and significance particularly for 0-group gadoidfish. Neth. J. Sea Res. 25, 113–130.
Hernroth, L., Gröndahl, F., 1985. On the biology of Aurelia aurita (L.): 2. Major factorsregulating the occurrence of ephyrae and young medusae in the Gullmar Fjord,western Sweden. Bull. Mar. Sci. 37, 567–576.
Ishii, H., Takagi, A., 2003. Development time of planula larvae on the oral arm of thescyphomedusa Aurelia aurita. J. Plank. Res. 25, 1447–1450.
Martinussen, M.B., Båmstedt, U., 1999. Nutritional ecology of gelatinous planktonicpredators. Digestion rate in relation to type and amount of prey. J. Exp. Mar. Biol.Ecol. 232, 61–84.
Martinussen, M.B., Båmstedt, U., 2001. Digestion rate in relation to temperature of twogelatinous planktonic predators. Sarsia 86, 21–35.
Miyake, H., Iwao, K., Kakinuma, Y., 1997. Life history and environment of Aurelia aurita.South Pacific Study 17, 273–285.
Möller, H., 1980. Scyphomedusae as predators and food competitors of larval fish.Meeresforsch. Rep. mar. Res. 28, 90–100.
Møller, L.F., Riisgård, H.U., 2007a. Impact of jellyfish and mussels on algal bloomscaused by seasonal oxygen depletion and nutrient release from the sediment in aDanish fjord. J. Exp. Mar. Biol. Ecol. 351, 92–105.
Møller, L.F., Riisgård, H.U., 2007b. Feeding, bioenergetics and growth in the commonjellyfish, Aurelia aurita, and two hydromedusae, Sarsia tubulosa and Aequoreavitrina. Mar. Ecol. Prog. Ser. 346, 167–177.
Møller, L.F., Riisgård, H.U., 2007c. Population dynamics, growth and predation impact ofthe common jellyfish, Aurelia aurita, and two hydromedusae, Sarsia tubulosa andAequorea vitrina in Limfjorden (Denmark). Mar. Ecol. Prog. Ser. 346, 153–165.
Nielsen, A.S., Pedersen, A.W., Riisgård, H.U., 1997. Implications of density drivencurrents for interaction between jellyfish (Aurelia aurita) and zooplankton in aDanish fjord. Sarsia 82, 297–305.
Olesen, N.J., 1995. Clearance potential of jellyfish Aurelia aurita, and predation impacton zooplankton in a shallow cove. Mar. Ecol. Prog. Ser. 124, 63–72.
Olesen, N.J., Frandsen, K., Riisgård, H.U., 1994. Population dynamics, growth andenergetics of jellyfish Aurelia aurita in a shallow fjord. Mar. Ecol. Prog. Ser. 105,9–18.
Papathanassiou, P., Panayotidis, P., Anagnostaki, K., 1987. Notes on the biology andecology of the jellyfish Aurelia aurita Lam. in Elefsis Bay (Saronikos Gulf, Greece).Mar. Ecol. 8, 49–58.
Purcell, J.E., 1997. Pelagic cnidarians and ctenophores as predators: selective predation,feeding rates, and effects on prey populations. Ann. Inst. Océanogr. 73, 125–137.
Purcell, J.E., 2009. Extension of methods for jellyfish and ctenophore trophic ecology tolarge-scale research. Hydrobiologia 616, 23–50.
Purcell, J.E., Decker, M.B., 2005. Effects of climate on relative predation byscyphomedusae and ctenophores on copepods in Chesapeake Bay during 1987–2000. Limnol. Oceanogr. 50, 376–387.
Riisgård, H.U., Barth-Jensen, C., Madsen, C.V., 2010. High abundance of the jellyfishAurelia aurita excludes the invasive ctenophore Mnemiopsis leidyi to establish in ashallow cove (Kertinge Nor, Denmark). Aquat. Inv. 5, 347–356.
Schneider, G., Behrends, G., 1994. Population dynamics and the trophic role of Aureliaaurita medusae in the Kiel Bight and western Baltic. ICES J. Mar. Sci. 51, 359–367.
Suchman, C.L., 2000. Escape behavior of Acartia hudsonica copepods during interactionswith scyphomedusae. J. Plank. Res. 22, 2307–2323.
Suchman, C.L., Sullivan, B.K., 2000. Effect of prey size on vulnerability of copepods topredation by the scyphomedusae Aurelia aurita and Cyanea sp. J. Plank. Res. 22,2289–2306.
Sullivan, B.K., Garcia, J.R., Klein-MacPhee, G., 1994. Prey selection by the scyphome-dusan predator Aurelia aurita. Mar. Biol. 121, 335–341.
Sullivan, B.K., Suchman, C.L., Costello, J.H., 1997. Mechanics of prey selection by ephyraeof the scyphomedusa Aurelia aurita. Mar. Biol. 130, 213–222.
Stoecker, D., Michaels, A.E., Davis, L.H., 1987. Grazing by the jellyfish, Aurelia aurita, onmicrozooplankton. J. Plank. Res. 9, 901–915.
Titelman, J., Hansson, L.J., 2006. Feeding rates of the jellyfish Aurelia aurita on fishlarvae. Mar. Biol. 149, 297–306.
