Scientific article #2

1. Read the paper.

2. Write a summary of the key points of each paper and how they relate to larger question being addressed or the course content. This summary must include at least one idea or question for discussion (see the list of discussion tips above and consider making notes about those while reading). The summary should be short (approximately ½-page single-spaced), typed, and brought to the discussion.

free plagiarism.

I need it after 13 hours

Scientific Article Discussions

It is important for scientists to be able to read, analyze, and synthesize scientific journal articles in order to answer questions and determine the current state of knowledge on a topic. We will have seven paper discussions over the course of the semester, six led by pairs of students. Each student is required to co-lead one discussion.

The discussion leaders are required to:

Examine the list of questions provided below for their assigned article discussion (#2-7) and choose a question (or come up with your own) that you would like to address with the literature discussion.

2. Find one scientific article that you think addresses that topic. (You will probably need to search through several papers to find one that actually address the question or are interesting to you).

3. Meet with me at least two weeks before the discussion day to look over your topic and journal article. Be sure you read the article before you meet with me! You need to send me the articles you propose to use at least two days in advance of our meeting.

4. On the day of discussion, give a 5-10 minute mini-lesson reiterating what the foundational question was addressed by the paper and then providing background context for the paper and summarizing the key question(s), methods, results, and conclusions. This should incorporate a PowerPoint presentation with the most pertinent (not necessarily all) information and figures…just hit the most relevant items. Try not to provide critique or opinions about the paper during the summary.

5. Facilitate discussion about the paper. Here are some tips (in no particular order) of things you might want to include in your discussion:

a. Try not to let your opinion of the paper dominate the discussion. Encourage everyone to contribute his or her thoughts.

b. Solicit people’s opinions of what they found to be the strongest or weakest parts of the paper. You can ask for everyone to respond, or specific individuals (but spread the love a little).

c. Ask for people to share what confusions they had, or what they thought was unclear.

d. Discuss whether the authors achieved what they set out to do and whether their conclusions were meaningful, reasonably “within the bounds of their data”, and/or important or generalizable to other topics.

e. You can ask people what they would have done differently for this study, or helpful follow-up studies that could be pursued.

f. Ask the group what research questions arose in their minds while reading the article(s).

g. Try to conclude with a brief summary of what ideas/conclusions were produced/shared during the article discussion you just led.

The rest of the class is required to:

1. Read the paper.

2. Write a summary of the key points of each paper and how they relate to larger question being addressed or the course content. This summary must include at least one idea or question for discussion (see the list of discussion tips above and consider making notes about those while reading). The summary should be short (approximately ½-page single-spaced), typed, and brought to the discussion.

3. Participate in the discussion during class. Active participation is essential for discussion and relies on having read the papers. (Your written summary and active participation in discussions accounts for 7.5% of your course grade.)

Article Discussion Possible Questions
: Other questions are possible, so if you have a question that is somewhat related to what we have discussed in class, then suggest that.

Article Discussion #1: (Instructor-led)

How should scientists approach the study of the natural world?

Article Discussion #2:

What environmental traits determine the geographic range of a species?

How to species respond to climate change?

Are native or invasive species better able to adapt to environmental change?

How do animals (or plants) live in the desert with such little water?

Why can some fish live in freshwater, some in salt water, and some can live in either?

How do plants maintain homeostasis of energy production under various environmental conditions?

How do organisms optimize their time when obtaining energy?

Article Discussion #3:

What are the costs and benefits of direct versus indirect development?

What environmental conditions cause variation in modes of reproduction? (between species or within one species)

Why do some organisms produce few offspring while other produce many?

What factors determine when an organism begins to reproduce?

What is better for a larvae to do, develop fast an metamorphose when small or develop more slowly and metamorphose when large?

How do different dispersal methods affect population connectivity?

What factors influence the magnitude of population dispersal?

Are (or when are) some methods of measuring abundance better/worse than others?

How does [insert some aspect of population demographics] influence change in population growth?

What ecological circumstances lead to different types of survival curves (or reproductive timing) in a species (or different species)?

What exerts more influence on populations of [insert species], density-dependent or density independent processes?

How to population outbreaks affect an ecosystem (or community)?

Can population cycles be predicted? How? (Or what factors determine population cycles?)

How impact does the allee have on a population?

More to come for the later discussions…

BIO317 Spring 2018

J E L L Y F I S H B L O O M S

Effects of climate warming on strobilation and ephyra
production of North Sea scyphozoan jellyfish

Sabine Hols

Published online: 9 March 201

� Springer Science+Business Media B.V. 20

Abstract Recent studies have correlated fluctua-

tions in jellyfish abundances with climatic changes,

leading to speculation that the warming trend in th

North Sea will affect the strobilation activity of

Scyphozoa. The present study provides long-term

data (10–22 months) on temperature effects on the

species Aurelia aurita, Cyanea capillata, Cyanea

lamarckii and Chrysaora hysoscella. Strobilation at

current winter temperature (5�C) in the German Bight
was compared to strobilation at warmer winter tem-

peratures. Simulated winter temperature of 10�C had
several positive effects on strobilation, as compared to

5�C: 1. A longer strobilation period or higher ephyra
production per polyp in A. aurita, C. lamarckii and Ch.

hysoscella; 2. Higher percentages of polyps strobilat-

ing in A. aurita and Ch. hysoscella; 3. More ephyrae

per strobila in C. capillata and C. lamarckii; 4. A

shorter strobilation duration in C. capillata and

C. lamarckii. Cold winter temperatures of 5�C
promoted strobilation in C. capillata, but inhibited

strobilation in A. aurita and reduced ephyra produc-

tion in C. lamarckii and Ch. hysoscella. These results

suggest that climate warming will benefit A. aurita,

but not cold-water C. capillata. The distributions of

C. lamarckii and Ch. hysoscella probably could

expand to the north.

Keywords Aurelia � Cyanea � Chrysaora � Polyp �
Temperature � Reproduction

Introduction

Reports of mass occurrences of large jellyfish (Scy-

phozoa) in many marine ecosystems worldwide have

increased in recent decades (Purcell et al., 2007;

Richardson et al., 2009). Negative impacts of such

medusa blooms on ecosystems, fisheries, industries

and tourism are obvious: medusae are food compet-

itors of fish and feed on fish larvae and small fish (Barz

& Hirche, 2007; Sabatés et al., 2010), the gelatinous

bodies clog fishing nets and cooling systems of coastal

industries, and jellyfish stinging swimmers have

negative effects on the tourism industry (CIESM,

2001; Purcell et al., 2007). It is possible that conse-

quences of anthropogenic activities, including overf-

ishing, eutrophication, species invasions and

especially climate change, have contributed to

increased jellyfish abundances (Purcell et al., 2007;

Richardson et al., 2009; Purcell, 2011).

Recent analyses of temperature data show a clear

warming trend in global average air and ocean

temperature (IPCC, 2007). A pronounced winter

Guest editors: J. E. Purcell, H. Mianzan & J. R. Frost / Jellyfish

Blooms: Interactions with Humans and Fisheries

S. Holst (&)
Senckenberg am Meer, German Center for Marine

Biodiversity Research, c/o Biozentrum Grindel und

Zoologisches Museum, Martin-Luther-King-Platz 3,

20146 Hamburg, Germany

e-mail: sabine.holst@senckenberg.de

123

Hydrobiologia (2012) 690:127–14

DOI 10.1007/s10750-012-1043-y

warming trend has been observed in the North and

Baltic seas, which is predicted to continue in the future

(HELCOM, 2007; Belkin, 2009). Recent rapid climate

change has changed the abundances, population

structures and biographical ranges of benthic and

planktonic North Sea species (Mieszkowska et al.,

2006; Wiltshire et al., 2010). Climate regime shifts

also affect jellyfish populations. Changes in temper-

ature, salinity, currents, predator–prey interactions

and competition have measurable effects on jellyfish

abundance and distribution (Purcell, 2005, 2009;

Molinero et al., 2008; Lynam et al., 2010). These

environmental changes will affect both the pelagic and

the benthic stages of metagenetic medusae; however,

the role of the polyps has been neglected in most

analyses and models because of the lack of data on

polyp ecology (Lynam et al., 2010).

The medusae of four semaeostome scyphozoans,

Aurelia aurita (Linneaus, 1758), Cyanea capillata

(Linneaus, 1758), Cyanea lamarckii Péron and Lesu-

eur, 1809 and Chrysaora hysoscella (Linneaus, 1766),

occur in the German Bight during the summer months,

and mass occurrences have been documented in some

years (Russell, 1970; Möller, 1980a; Hay et al., 1990;

Barz & Hirche, 2007). Like most scyphozoans, the life

cycle of these species includes planktonic medusa and

benthic polyp generations. After settlement and

metamorphosis of the planula larvae, the polyp

populations increase by asexual reproduction. Each

polyp seasonally produces one to several young

medusae (ephyrae) in a process of transversal fission

called strobilation. This process contributes to the

development of jellyfish blooms because polydisc

strobilation allows single polyps to produce many

ephyrae (Boero et al., 2008).

Information on the environmental factors and

stressors that determine the induction, timing and

magnitude of the strobilation process is limited to a few

species (e.g. Aurelia spp., reviewed in Purcell et al.,

2012). Moreover, the benthic stage is completely

undiscovered or undescribed for most scyphozoans

(Tronolone et al., 2002; Jarms, 2010). Although many

laboratory investigations on scyphopolyps have shown

that temperature significantly affects the asexual polyp

reproduction and strobilation (e.g. Holst et al., 2007;

Purcell, 2007; Willcox et al., 2007; You et al., 2008;

Liu et al., 2009), most of these studies were restricted to

short periods of a few weeks and polyps were often

exposed to extreme, abrupt changes, whereas changes

in situ would be less severe (Purcell, 2005). Long-time

investigations on the effects of natural seasonal

temperature cycles on polyp ecology are unavailable

for most species (but see Gröndahl, 1988; Brewer &

Feingold, 1991; Miyake et al., 2002; Purcell et al.,

2009; Di Camillo et al., 2010; Ishii & Katsukoshi,

2010). In the present study, I compare the long-term

(10–22 months) effects of different temperature con-

ditions on strobilation and ephyra production of four

semaeostome jellyfish species from the North Sea to

show the possible effects of increasing winter temper-

atures on the strobilation activity of Scyphozoa in the

North Sea. Strobilation at temperature conditions

similar to the current temperatures in the German

Bight was compared to that at warmer winter temper-

atures. Additional experiments without a temperature

change were conducted to determine the importance of

temperature changes as inducers of strobilation in

scyphozoan polyps. I tested the null hypotheses to

ascertain whether the percentages of polyps strobilat-

ing and the numbers of ephyrae produced per strobila

were independent of temperature; second, whether the

percentages of strobilating polyps and the number of

ephyrae produced per strobila were independent of

polyp age; and third, whether the duration of strobi-

lation was independent of the number of ephyrae per

strobila and of temperature.

Materials and methods

Polyps of the species A. aurita, C. capillata, C. lama-

rckii and Ch. hysoscella were reared from planulae

collected from female medusae in the summer periods

of 2003 and 2004 around the island of Helgoland

(details in Holst & Jarms, 2007, 2010). Watch glasses

or polyethylene plates (for C. lamarckii) colonized by

polyps in the laboratories of the Biologische Anstalt

Helgoland were transported to the Zoological Institute

of the University of Hamburg (Biocenter Grindel)

1–2 weeks after planula settlement. The substrates

were transferred into 150-ml glass bowls filled with

filtered North Sea water (salinity 35 ± 2). The bowls

were kept in incubators at 15�C in darkness before
the experiments. Only well-developed polyps with

extended tentacles were used for the experiments,

whereas small or contracted polyps were carefully

removed from the substrates with a needle. Polyps

were fed nauplii of Artemia salina for 1–2 h every

128 Hydrobiologia (2012) 690:127–1

123

7–10 days, after which the seawater in the bowls was

replaced with fresh filtered seawater of the same

temperature. During strobilation, only half of the water

was changed carefully, and uneaten food was removed

from the bowls with a pipette to avoid disturbing the

strobilation process. Polyps of each species were

cultured in three different temperature groups

(Table 1). In the 15�C group, the temperature was
constant 15�C throughout the year. In the groups
15–10–15�C and 15–05–15�C, the temperature was
15�C until mid-October and lowered to 10�C in autumn
and 5�C in winter, respectively. The temperatures were
decreased in steps of 2.5�C per month (Fig. 1), and all
cultures were kept in incubators in darkness. Polyps

were monitored for 12 months (A. aurita from 15

September, and C. capillata from 15 October) or

10 months (C. lamarckii and Ch. hysoscella from 15

October) in the first year after settlement. Additional

10-month-long experiments (from 15 October) were

conducted in the second year after settlement with

A. aurita and C. capillata polyps. The polyps were

counted monthly in all replicates, and all cultures were

checked weekly to detect beginning strobilations.

When strobilation appeared in the cultures, each

strobila was monitored individually. The developing

ephyrae in each strobila and the released ephyrae in the

cultures were counted at least twice per week.

Calculations and statistics

The numbers of ephyrae produced monthly in each

temperature group were summed and divided by the

number of polyps to calculate ephyra production for

each month. To account for production and mortality of

polyps, the mean numbers of polyps (counted monthly)

were calculated over the duration of the experiment

(Table 1) and used in calculations and statistics. The

total numbers of ephyrae produced per mean polyp

numbers were calculated for each temperature group.

The percentages of strobilating polyps in the first year

were calculated for each replicate from the total

numbers of strobilae divided by the mean numbers of

polyps in each replicate. Percentages were arcsine

square root transformed before statistical analysis to

test the first null hypothesis, H01: the percentages of

polyps strobilating were independent of the tempera-

ture treatments. In C. lamarckii, all polyps strobilated

once in all temperature groups, therefore the percent-

ages of polyps that strobilated twice were compared to

test H01. Individually monitored strobilations in the

first year were used to calculate the mean numbers of

ephyrae per strobila to test H02: the numbers of ephyrae

produced per strobila were independent of the temper-

ature treatments. Strobilations from replicates 1–3

were used for analysis in all species and temperature

groups; additional strobilations were included

from replicates 4–6 in A. aurita 15�C,

C. capillata

15–10–15�C, C. capillata 15–05–15�C and Ch. hysos-
cella 15–05–15�C. For H01 and H02, data with normal
distributions were tested by one-way analysis of

variance (ANOVA) followed by a Fisher’s least

significance difference (LSD) post-hoc test. Data not

normally distributed were tested by a Kruskal–Wallis

ANOVA on ranks and a Student–Newman–Keuls post-

hoc test. Two experimental groups were compared

with a Mann–Whitney Rank Sum Test.

Table 1 Replicates (n) in temperature groups used for analyses of strobilation in first year (1y) and second year (2y) after planula
settlement in four species of scyphozoans

Species Year n 15�C 15–10–15�C 15–05–15�C

Start Mean Start Mean Start Mean

A. aurita 1y 6 79 87.3 ± 4.9 78 102.6 ± 19.9 81 114.7 ± 32.5

1y 3 29 37.1 ± 4.8 32 46.3 ± 11.9 36 54.0 ± 16.3

2y 3 33 46.3 ± 15.2 32 47.2 ± 21.8 35 49.7 ± 22.0

C. capillata 1y 6 71 73.7 ± 4.0 75 86.3 ± 11.2 81 96.6 ± 17.3

1y 3 25 26.0 ± 2.9 25 26.0 ± 2.9 26 28.0 ± 6.

2y 3 11 18.2 ± 8.3 20 28.9 ± 10.1 24 39.1 ± 13.2

C. lamarckii 1y 6 86 76.3 ± 7.4 86 64.5 ± 14.1 85 60.5 ± 17.0

Ch. hysoscella 1y 7 108 85.0 ± 22.3 108 92.9 ± 15.7 113 81.9 ± 28.

The total polyp numbers at the beginning of the experiments (Start) and numbers of polyps in monthly counts (mean ± standard

deviation) in different temperature groups (see Fig. 1) are listed

Hydrobiologia (2012) 690:127–140 129

123

A. aurita

1st year

1 5 °C

1 5 – 1 0 – 1 5 °C

1 5 – 0 5 – 1 5 °C T
e

m
p

e
ra

tu
re

c
o

n
d

it
io

n
s

(
°C

) 15Oct-
15Nov

15Nov-
15Dec

15Dec-
15Jan

15Jan-
15Fe

15Feb-
15Mar

15Mar-
15Apr

15Apr-
15May

15May-
15Jun

15Jun-
15Jul

15Jul-
15Aug

Temperature
groups

1 5 – 0 5 – 1 5 °C
1 .0

1 5 – 1 0 – 1 5 °C
2 .1

1 5 °C

0 .2

1 5 – 0 5 – 1 5 °C
1 .7 1 5 – 1 0 – 1 5 °C

2 .7

1 5 °C
0 .3

0
1

A. aurita

2nd year

0
1

2 C. capillata
1st year

E
p

h
y

ra
e

p
e

r
p

o
ly

p
1 5 – 1 0 – 1 5 °C
0 .9

1 5 – 0 5 – 1 5 °C
1 .4

0
1

2 C. capillata
2nd year

0
1

C. lamarckii

1st year

1 5 – 1 0 – 1 5 °C
3 .2

1 5 – 0 5 – 1 5 °C
3 .0

1 5 – 0 5 – 1 5 °C
3 .7

1 5 – 1 0 – 1 5 °C
5 .4

1 5 °C

7.9

0
1

Ch. hysoscella

1st year

15 15 15 15 15 15 15

12.5 10 10 10 10 10 12.5 15

12.5

1 5 15 15

10 7.5 5 5 5 7.5 1 0 12.5 15

1 5 – 0 5 – 1 5 °C
0 .1

1 5 – 1 0 – 1 5 °C
0 .8

1 5 °C

0 .4

Ephyrae per polyp in 10 monthsEphyrae per polyp monthly

130 Hydrobiologia (2012) 690:127–140

123

For comparisons among strobilations 1 and 2 years

after settlement, the same three replicates of each

temperature group of A. aurita and C. capillata polyps

were used in both years (Table 1). The same 10-month

period (15 October–15 August) were analysed in both

years. The percentages of strobilating polyps and the

numbers of ephyrae produced per strobila were calcu-

lated for both years, as described above, and compared

by a Mann–Whitney Rank Sum Test. Two null

hypotheses were tested, H03: The percentages of

strobilating polyps were independent of polyp age

and H04: The number of ephyrae produced per strobila

was independent of the polyp age.

The durations of strobilations (days) were deter-

mined from the number of days between the start of the

strobilation, when first constrictions of the polyp body

appeared, until the end the strobilation, when the last

ephyra detached from the strobila. Only strobilations

that began and ended at the same temperature were used

in the analysis. Strobilae in the first year after polyp

settlement were analysed in C. lamarckii and Ch.

hysoscella, and in the first and second years combined in

A. aurita and C. capillata. Strobilations were analysed at

15, 10 and 5�C culture temperatures. Two null hypoth-
eses were tested by analysis of covariance (ANCOVA),

H05: The duration of strobilation was independent of the

number of ephyrae per strobila and H06: The duration of

strobilation was independent of the temperature treat-

ments. ANCOVA-tests were conducted separately for

each species. In all tests, duration was the dependent

variable; the number of ephyrae per strobila and the

culture temperature were covariates.

Results

Ephyra production and strobilation rates

A. aurita

The first A. aurita strobilations occurred in autumn in

all temperature groups in the first and second years

after polyp settlement. Ephyra were produced until

next May in both years in the 15–10–15�C group,
whereas ephyra production stopped after a tempera-

ture decrease to 5�C in January in the 15–05–15�C
groups (Fig. 1, left side). Few ephyrae per polyp were

produced in the temperature group with constant 15�C
and the most ephyrae per polyp were produced in the

15–10–15�C group in the first and in the second year
after settlement (Fig. 1, right side). Significantly

higher percentages of A. aurita polyps strobilated

after a temperature decrease in autumn than at

constant 15�C, and H01 was rejected for both years
(Figs. 2, 3; Table 2). The numbers of ephyrae pro-

duced per strobila did not differ significantly among

the temperature groups in the first year or in the second

year and H02 was not rejected (Fig. 2; Table 2). The

percentages of strobilating polyps were higher in the

second than in the first year, but the differences were

not significant, and H03 was not rejected (Fig. 3;

Table 3). Although the maximum numbers of ephyrae

per strobila were higher in the second year than in the

first, the means differed only slightly among groups,

and H04 was not rejected (Fig. 3; Table 3).

C. capillata

C. capillata polyps never strobilated in constant 15�C
during 22 months of observation. The first ephyra

appeared in February–March at the cold winter

temperature (5�C) in both years, whereas the first
ephyra appeared at least 1 month later at the 10�C
winter temperature (Fig. 1, left side). Ephyra produc-

tion continued until the beginning (second year) or end

of May (first year). In the first year, production of

ephyrae per polyp was higher in 5�C winter temper-
ature, whereas it was slightly higher in 10�C winter
temperature in the second year (Fig. 1, right side). In

the first year, the percentages of polyps strobilating

were significantly higher in the 15–05–15�C group
than in the 15–10–15�C and 15�C groups and H01 was
rejected (Fig. 2; Table 2). Although the percentages of

polyps strobilating differed only slightly for the

15–10–15�C and the 15–05–15�C groups, no strobi-
lation occurred at 15�C and H01 was rejected in the
second year as well (Fig. 3; Table 2). The numbers of

ephyrae per strobila were lower in groups with 5�C
than in those with 10�C winter temperature, but
differences were only significant in the first year (H02

Fig. 1 Numbers of ephyrae per polyp produced monthly (left
side) and total numbers of ephyrae produced per mean numbers of
polyps counted monthly during 10 months of observation (15

Oct–15 Aug, right side) in different temperature groups of A.
aurita, C. capillata, C. lamarckii and Ch. hysoscella polyps. The
culture temperature was constant 15�C from 15th July to 15th
October in all temperature groups (not shown in the figure). Polyp

numbers in different temperature groups are shown in Table 1

Hydrobiologia (2012) 690:127–140 1

123

rejected, Fig. 2; Table 2). The percentages of strobi-

lating polyps did not differ significantly in polyps of

different ages and H03 was not rejected (Fig. 3;

Table 3); however, the mean numbers of ephyrae per

strobila were significantly higher in the second year in

the 15–10–15�C group and the 15–05–15�C group
(H04 rejected, Fig. 3; Table 3).

C. lamarckii

In C. lamarckii cultures, the first ephyra appeared after

a temperature decrease to 10�C in groups 15–10–15�C
and 15–05–15�C; however, the most ephyrae per polyp
were produced in the constant 15�C group, whereas the
fewest were in the coldest winter temperature (5�C;

C. lamarckii
0
2
4

8
10
12
A. aurita
0

100

C. capillata
0
20
40
60
80
100

S
tr

o
b

il
a

n
g

p
o

ly
p

s
(

%
)

0
20
40
60
80
100
Ch. hysoscella
0
20
40
60
80
100

15°C 15-10-15°C 15-05-1

5°C

Temperature group

C. lamarckii

1 5 °C 1 5 – 1 0 – 1 5 °C 1 5 – 0 5 – 1 5 °C

Temperature group

n = 6

n = 6
n = 6

n = 7

0
2
4
6
8
10
12
E
p

h
y
ra

e
p

e
r

s
tr

o
b
il
a

14184

A. aurita
C. capillata
0
2
4
6
8
10
12

28 79

0545 51

Ch. hysoscella
0
2
4
6
8
10
12

17 29 7

Fig. 2 Strobilating polyps (mean % ± SD) (left side) and
ephyrae produced per strobila (mean number ± SD) (right side)
in the first year after polyp settlement in different temperature

groups of A. aurita, C. capillata, C. lamarckii and Ch.
hysoscella polyps; n number of replicates (numbers of polyps
as shown in Table 1). The numbers of analysed strobilae appear

inside the bars. Diamond maximal number of ephyrae produced
by one strobila. The observation time was 12 months for A.
aurita (15 Sep–15 Sep) and C. capillata (15 Oct–15 Oct) and
10 months for C. lamarckii and Ch. hysoscella (15 Oct–15
Aug). Test statistics are shown in Table 2

132 Hydrobiologia (2012) 690:127–140

123

Fig. 1). All C. lamarckii polyps strobilated at least

once in all temperature groups ([100%). The percent-
ages of polyps strobilating twice were the highest in the

15–10–15�C groups, but the differences were not
significant, and H01 was not

rejected (Fig. 2; Table 2).

The number of ephyrae produced per strobila, how-

ever, was significantly higher at constant 15�C than in
treatments with temperature decreases, and H02 was

rejected (Fig. 2; Table 2).
Ch. hysoscella

The monthly ephyra production per polyp was rela-

tively low in Ch. hysoscella (Fig. 1, left side). The

most ephyrae per polyp were in the 15–10–15�C
group, and the fewest ephyrae per polyp were

produced in the 15–05–15�C group (Fig. 1, right
side). The percentages of strobilating polyps were

significantly higher in the 15–10–15�C group than in
the other groups, and H01 was rejected (Fig. 2;

Table 2). In the 15�C and 15–05–15�C groups,
maxima of three ephyrae were produced per strobila,

whereas as many as six ephyrae per strobila were

produced in the 15–10–15�C group (Fig. 2); however,
the production of more then three ephyrae occurred

only in 7% of analysed strobilae. Consequently,

differences in ephyra production per strobila were

not significant among temperature groups and H02 was

not rejected (Fig. 2; Table 2).

Temperature change as a strobilation inducer

or inhibitor

Small percentages of polyps strobilated at constant

15�C in A. aurita, demonstrating that temperature
decrease was an important strobilation inducer; how-

ever, ephyra production stopped after temperature

decreased further to 5�C in winter. This result
demonstrated that a low winter temperature of 5�C
inhibited strobilation activity from February on

whereas a higher winter temperature of 10�C lead to
a longer strobilation period until spring (Fig. 1).

Temperature increases from 5 to 10�C in spring and
then to 15�C in summer did not induce strobilation in
A. aurita (Fig. 1).

Strobilation never occurred at constant 15�C in
C. capillata and ephyra production was lower when

temperature rose in spring and summer following

strobilation at 5 or 10�C winter temperatures (Fig. 1).
No ephyra was produced at temperatures exceeding

A. aurita
0
20
40
60
80
100
S
tr
o
b

il
a
ti

n
g
p
o
ly
p
s
(

%
)

1st year
2nd year
0
20
40
60
80
100
Temperature group
C. capillata
0
2
4
6
8
10
12
E
p
h
y
ra
e
p
e
r
s
tr
o
b
il
a
C. capillata

15°C 15-10-15°C 15-05-15°C 15°C 15-10-15°C 15-05-15°C

Temperature group
A. aurita
0
2
4
6
8
10
12

18 2815 19

18 26 1914

n = 3

n = 3
31
1st year
2nd year

Fig. 3 Strobilating polyps (mean % ± SD) (left side) and
ephyrae produced per strobila (mean number ± SD) (right side)
in the first year and in the second year after polyp settlement

in different temperature groups of A. aurita, C. capillata,
C. lamarckii and Ch. hysoscella polyps, n number of replicates

(numbers of polyps are shown in Table 1). The numbers of

analysed strobilae appear inside the bars. Diamond maximal
number of ephyrae produced by one strobila. In both analyses,

the observation time was 10 months (15 Oct–15 Aug) in both

years. Test statistics are shown in Table 3

Hydrobiologia (2012) 690:127–140 133

123

10�C in summer, suggesting strobilation inhibition at
warmer temperatures in C. capillata. In C. lamarckii,

ephyra production started earlier after a temperature

decrease to 10�C than at constant 15�C (Fig. 1),
showing a positive effect of temperature decrease on

strobilation induction, although the total ephyra pro-

duction was the highest at constant 15�C. In Ch.
hysoscella, strobilation activity was low in all tem-

perature treatments without clear responses to tem-

perature changes (Fig. 1).

Temperature effects on strobilation duration

and ephyrae per strobila

A significant effect of the number of ephyrae per

strobila on the strobilation duration was shown by

ANCOVA for all tested species (Fig. 4), and H05 was

rejected. Correlations among temperature treatments

and strobilation duration were not possible for A.

aurita because strobilation occurred mostly at 10�C;
thus, data at other temperatures were insufficient. In all

other tested species, the ANCOVA confirmed a

significant effect of temperature treatment on the

strobilation duration (Fig. 4), and H06 was rejected.

Discussion

Scyphopolyps are difficult to find and investigate in

the field because of their small sizes and their

preferences of colonizing the undersides of substrates

and concealed habitats (Pierce, 2009; Di Camillo

Table 2 Test statistics on the effects of temperature treatments on the percentages of strobilating polyps (H01) and ephyrae produced
per strobila (H02) in four species of scyphozoans

Species Null hypothesis Polyp age Test statistic P

A. aurita H01 1y F2,15 = 16.936 0.001

2y F2,6 = 14.779 0.005

H02 1y H2 = 0.573 0.751

2y H2 = 0.315 0.854

C. capillata H01 1y H2 = 13.940 \0.001
2y H2 = 6.161 0.025

H02 1y T28,79 = 1936.000 0.003

2y T18,28 = 482.000 0.182

C. lamarckii H01 1y F2,15 = 1.224 0.322

H02 1y H2 = 40.367 \0.001
Ch. hysoscella H01 1y F2,18 = 9.486 0.002

H02 1y H2 = 0.477 0.788

The temperature groups, numbers of replicates, mean values and observation times are shown in Figs. 2 and 3. Strobilations in the

first year after polyp settlement (1y) were analysed in all species. Strobilations in the second year (2y) were analysed in A. aurita and
C. capillata

Table 3 Test statistics of comparisons on strobilations in the first and second year after polyp settlement in two scyphozoan species

Species Null hypothesis 15�C 15-10-15�C 15-5-15�C

Test statistics P Test statistics P Test statistics P

A. aurita H03 T3,3 = 9.0 0.700 T3,3 = 7.0 0.200 T3,3 = 7.0 0.200

H04 No test, n \ 3 T18,26 = 424.5 0.645 T14,19 = 259.5 0.439
C. capillata H03 No strobilae T3,3 = 8.0 0.400 T3,3 = 8.5 0.400

H04 No strobilae T15,18 = 169.0 0.002 T19,28 = 292.5 \0.001

Percentages of strobilating polyps (H03) and ephyrae produced per strobila (H04) in different temperature treatments were analysed.

Replicates, mean values and observation times are shown in Fig. 3

134 Hydrobiologia (2012) 690:127–140

123

et al., 2010). Laboratory investigations allow quanti-

fication of polyp survival and reproduction and are

therefore an important source of data (e.g. Purcell,

2007; Willcox et al., 2007; Liu et al., 2009; Sötje &

Jarms, 2009; Holst & Jarms, 2010). Although the

results from field observations may differ form

laboratory experiments (Purcell et al., 2009), the

results of this study demonstrated that simulation of

natural temperature cycles in the laboratory can be

used to test the effects of seasonal temperature

changes on strobilation. The strobilation activity

documented in two consecutive years in two species

(A. aurita and C. capillata) showed that repeated

temperature cycles in the laboratory experiments

caused very similar responses of the polyps. The

temperature cycles in the present experiments with

15�C maximum summer temperature and 5�C mini-
mum winter temperature differed from the natural

annual temperature cycles because of 2.5�C temper-
ature changes per month. Nevertheless, the laboratory

temperature conditions were similar to temperatures

found recently in the German Bight (Wiltshire &

Manly, 2004; www.bsh.de/en/Marine_data). The par-

allel experiments with warmer winter temperatures

(10�C) indicated how warmer winter temperatures, as

observed and predicted to progress in the North Sea

(Belkin, 2009), could affect the strobilation activity of

scyphopolyps in situ. In these experiments, warmer

winter temperature (10�C in comparison to 5�C) pos-
itively affected strobilation in several ways: 1. A

longer strobilation period or higher ephyra production

per polyp (in A. aurita, C. lamarckii and Ch. hysos-

cella; Fig. 1); 2. Higher percentages of polyp strobi-

lation (in A. aurita and Ch. hysoscella; Fig. 2); 3.

More ephyrae per strobila (in C. capillata, C. lama-

rckii, see Fig. 2); 4. A shorter strobilation duration (in

C. capillata and C. lamarcki, see Fig. 4). Many of the

changes in species abundances, population structure

and biogeographical ranges occur as a result of

increased reproductive output and juvenile survival in

response to increased warming (Mieszkowska et al.,

2006). The results of this study suggest that this could

also be true for the North Sea scyphozoans

investigated.

In A. aurita, the experiments showed significantly

higher percentages of strobilations after a temperature

decrease in autumn compared to constant 15�C dem-
onstrating the importance of a temperature decrease for

strobilation induction in this species. Spring strobila-

tion only occurred in experiments with 10�C winter

C. lamarckii
0
10
20

0 2 4 6 8 10 12

S
tr
o
b
il
a

ti
o

n
d

u
ra

ti
o

n
(

d
)

15°C

10°C

Ephyrae per strobila

A. aurita
0
10
20

30
10°C

C. capillata
0
10
20
30
40

0 2 4 6 8 10 12 0 2 4 6 8 10 12

10°C
Ch. hysoscella
0
10
20
30
0 2 4 6 8 10 12

15°C5°C

t
e

F =12.492, p = 0 .00 1e e
F =72.285, p <0 .00 1 F =76.459, p <0 .00 1

e
t
e
t

F =10.567, p = 0 .00 2
F =6.735 , p = 0 .0 13

e
t
e
t

n=141 n=126

n=46

F =41 .720 , p <0 .00 1 F =24 .735 , p <0 .00 1

n=127 10°C

5°C

Fig. 4 Strobilation
durations (mean

days ± SD) in individually-

monitored strobilae at

different constant

temperatures in relation to

ephyrae numbers produced

in the strobilae of A. aurita,
C. capillata, C. lamarckii
and Ch. hysoscella. The
effect of ephyra numbers

produced per strobila (e) on

the strobilation duration and

the effect of the temperature

treatment (t) on the

strobilation duration were

tested by ANCOVA.

n number of analysed
strobilae. df = 1 for all

performed tests. F and
P values are shown in the
figures

Hydrobiologia (2012) 690:127–140 135

123

http://www.bsh.de/en/Marine_data

temperature, but did not occur with rising temperature

in spring after a cold winter period of 5�C. Perhaps
under natural conditions, autumn strobilation in A.

aurita polyps can happen only if the temperature

decreases slowly and the period of moderate temper-

ature of about 10�C lasts for several weeks, whereas a
rapid temperature decrease may lead to inhibition of

strobilation in autumn. In agreement with this idea, in

situ autumn strobilations of A. aurita were observed in

areas with moderate winter temperatures, such as in

Sylt, German Bight (Thiel, 1938), Osterschelde,

Netherlands (Korringa, 1953), and Gullmarfjord,

western Sweden (Hernroth & Gröndahl, 1985, Grön-

dahl, 1988); however, in areas with a rapid temperature

decrease in autumn, such as in several Baltic Sea areas,

a later start of the strobilation activity in A. aurita was

documented, and strobilation occurred mainly in

winter and spring (Palmén, 1954; Kändler, 1961;

Thiel, 1962; Rasmussen, 1973; Möller, 1980b). The

ephyrae may survive the cold winter periods in deep

water layers without further development, which could

explain the main time of ephyra abundance in the

plankton in autumn and spring (Rasmussen, 1973;

Hernroth & Gröndahl, 1985; Gröndahl, 1988). In

Southampton Water and Horsea Lake in southern

England, ephyra production begins in December and

lasts 7 months (Lucas, 1996; Lucas et al., 1997),

confirming the results of this study of an extended

strobilation phase in A. aurita at warmer winter

temperatures (Fig. 1). Recent molecular genetic study

detected that A. aurita is not a single species, but

includes members of several molecular species (Daw-

son, 2003). A. aurita populations occurring in the

North Atlantic and adjacent seas are probably adapted

to the temperature regime in these areas (Dawson,

2003), and therefore, our results reflect the strobilation

behaviour of polyps from this temperature regime only.

The tests of this study showed shorter strobilation

duration and higher ephyra production per strobila of

C. capillata polyps at warmer temperatures. On the

other hand, cold winter temperatures had positive

effects on strobilation in C. capillata polyps; strobi-

lation started earlier at colder temperatures, and unlike

A. aurita, ephyra production was not inhibited by the

cold winter temperature (5�C). In these experiments,
C. capillata was the only species without any strobi-

lation during 22 months at the warm temperature of

15�C. Strobilation induction of C. capillata may
strictly depend on a temperature decrease, which

may explain why the distribution of the species is

limited to northern boreal areas (Russell, 1970),

whereas Cyanea medusae from the warmer U.S.

Atlantic, the Gulf of Mexico and Australian waters

may represent other species of Cyanea (Bayha, 2005;

Dawson, 2005). In the North Sea, C. capillata

medusae are rare in the southern part and do not

appear in the English Channel. In the Irish Sea, their

occurrence also is limited to the northern part (Russell,

1970; Hay et al., 1990; Doyle et al., 2007). The

simulated annual seasons in present experiments

induced ephyra production from February until June,

which matched field observations on C. capillata

strobilation and occurence of the ephyrae in areas with

a similar temperature regime (Hartlaub, 1894; Ver-

wey, 1942; Gröndahl, 1988). Although the polyps are

obviously adapted to cold temperature conditions,

they have not been reported from the southern or

eastern Baltic Sea, where the C. capillata medusae

appear each summer (Möller, 1980a; Barz et al. 2006).

Recent studies demonstrated that C. capillata polyps

are able to strobilate at a low salinity of 12 and may be

more widespread in the Baltic Sea than previously

thought (Holst & Jarms, 2010). In accordance with

previous studies (Gröndahl, 1988), the results of this

study confirm that C. capillata polyps are tolerant of

cold temperatures, indicating that the low Baltic Sea

winter temperatures probably do not limit their

distribution. I therefore believe that the only reason

why the polyps have not been found in this area to date

is that there were too few efforts undertaken to find

them.

The medusae of C. lamarckii have a more southern

distribution in the North and Irish seas than do C.

capillata medusae (Russell, 1970; Hay et al., 1990;

Doyle et al., 2007). In the Baltic Sea, C. lamarckii

medusae appear rarely in Danish waters (Rasmussen,

1973), whereas they occur periodically from March

until June off the Swedish west coast (Gröndahl, 1988).

C. lamarckii ephyrae were not found in 4 years of

plankton sampling on the Swedish west coast and no

strobilation was observed on settling plates in the field,

leading to the conclusion that C. lamarckii polyps do

not strobilate there (Gröndahl, 1988). C. lamarckii

polyps have not yet been described in their natural

habitat, but present laboratory studies indicate positive

effects of warm temperature on strobilation: higher

production of ephyrae per strobila and shorter strobi-

lation duration. This may enable their distribution to

136 Hydrobiologia (2012) 690:127–140

123

expand to the northern North Sea with rising winter

temperatures due to climate changes. From there, the

polyps may also extend into the Baltic Sea because of

their high tolerance of low salinity (Holst & Jarms,

2010). The present experiments demonstrated a long

strobilation phase of C. lamarckii polyps from winter

until the next summer in agreement with observations

of abundant C. lamarckii medusae of various sizes and

different developmental stages from spring until late

summer in the German Bight and off the Dutch coast

(Verwey, 1942; Künne, 1952).

Ch. hysoscella medusae also are distributed mainly

in the southern North and Irish seas (Russell, 1970;

Hay et al., 1990; Doyle et al., 2007). Verwey (1942),

suggested strobilation of Ch. hysoscella with increas-

ing temperature in spring and summer, but the polyps

have not yet been found in their natural habitat in the

North Sea. A mild winter in 1988 in the German Bight

was followed by early appearance and high abundance

of Ch. hysoscella medusae in the summer, leading to

the conclusion that polyp’s survival during the winter

was higher at warm temperatures (Merck, 1990).

These observations agree with experimental results of

this study showing very low ephyra production at cold

winter temperatures and shorter strobilation duration

at warmer temperatures. Ch. hysoscella planulae are

able to settle at salinities at least as low as 20 (Holst &

Jarms, 2010), and thus Ch. hysoscella medusae and

polyps may be able to spread from the North Sea into

the Baltic Sea with continued climate warming.

The number of ephyrae produced by each strobila is

affected by temperature, other abiotic factors, food

supply and polyp size (Russell, 1970; Purcell et al.,

1999). The results of this study agree with those of

previous laboratory experiments on polyp cultures

demonstrating that warm temperatures increase the

strobilation rates of polyps and ephyra production,

except at very high temperatures (Purcell et al., 1999,

2012; Purcell, 2007; Liu et al., 2009). The number of

ephyrae in the strobila increases with polyp’s size

(Russell, 1970). This may explain why the C. capillata

polyps in the present experiments were able to produce

more ephyrae by the second year when they grew to a

larger size. Salinity also is known to affect strobilation

rates of North Sea Scyphozoa (Holst & Jarms, 2010)

and other species (reviewed in Purcell et al., 2009).

Purcell et al. (2009) concluded that the combined

effects of temperature, salinity, light and food deter-

mined the amount and time of strobilation in situ.

Only a few recent studies have monitored polyps in

situ (see Purcell et al., 2009; Di Camillo et al., 2010;

Ishii & Katsukoshi, 2010). Climatic changes in the

North Sea related to the North Atlantic Oscillation

(NAO) affect jellyfish abundances and may also affect

the strobilation of the benthic polyps in this area

(Lynam et al., 2010); however, the effects of the NAO

depends on the depth that macrozoobenthos animals

occur, and therefore, the estimation of the NAO’s

effect on strobilation is not possible without knowing

the locations and depths of polyp habitats (Lynam

et al., 2005). The effect of the NAO on North Sea

polyps is likely to be high because strobilation occurs

mainly in winter and spring when the NAO’s influence

is the greatest in the North Sea (Lynam et al., 2010).

The results of the present study support the idea that

variable winter temperatures affect the strobilation

activity of North Sea Scyphozoa.

Increasing winter temperature probably will affect

the abundances and distributions of scyphozoan

jellyfish species in the North Sea. The more southerly

species, C. lamarckii and Ch. hysoscella could expand

to the northern parts of the North Sea and possibly into

the Baltic Sea. The adaptable species A. aurita

presumably will benefit from warmer temperatures,

having longer strobilation periods (present study),

faster growth due to higher feeding rates (Hansson,

1997; Widmer, 2005) and higher reproduction rates of

medusae (Ishii & Takagi, 2003). The cold water C.

capillata might be the only North Sea scyphozoan that

could suffer from warmer temperatures; however, C.

capillata ephyra production also occurred at the warm

winter temperature of 10�C (Fig. 1). In general, I
assume that the abundances of scyphozoan jellyfish in

the North and Baltic seas will increase in future years

if the water temperatures continue to increase as

predicted (Belkin, 2009). This assessment agrees with

the opinion of other authors suggesting an increase of

gelatinous predators (scyphomedusae, hydromedusae,

siphonophores and ctenophores) in the North Sea due

to climate changes, including increasing temperatures,

the reduction of the ocean pH and probably, the

increasing Atlantic inflow into the North Sea (Attrill

et al., 2007; Boersma et al., 2007; Doyle et al., 2008;

Lilley et al., 2009; Licandro et al., 2010). The results

of this study and previous studies clearly show the

linkage between physical environmental factors and

ephyra production and thus forecasts of the abundance

and distribution of scyphomedusae might be possible

Hydrobiologia (2012) 690:127–140 137

123

by circulation models in future (Johnson et al., 2001,

2005; Barz et al., 2006). More knowledge on the

locations of polyp habitats and on the reproduction

cycles of the benthic polyp stage in the field is

necessary for successful monitoring and understand-

ing the population dynamics in scyphozoan jellyfish.

Acknowledgments I thank PD Dr. Gerhard Jarms for his
support, for imparting his knowledge on polyp culturing and for

providing the research facilities. I am grateful to the Biologische

Anstalt Helgoland (Alfred Wegener Institute) for providing the

guest laboratory and I am thankful for the assistance of students

and technicians of the Biocenter Grindel. I thank Drs. Ilka Sötje,

Jennifer Purcell, and the reviewers for their helpful comments

on the manuscript, and Dr. Caroline Stolter for her help in

the statistics. This study is part of a Ph. D. thesis conducted at

the Biocenter Grindel and Zoological Museum in Hamburg

supported by EUROGEL (EUROpean GELatinous Zoo-

plankton, European Commission Contract no. EVK-CT-2002-

00074).

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