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Bloom and bust: why do blooms of jellyfish collapse?

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Research on jellyfish blooms has focused heavily on the factors influencing the production of blooms. Identifying the factors that cause blooms to collapse, however, is important for predicting the duration of blooms and when they are likely to disappear. We assembled studies from the literature to assess the persistence of populations of medusae, the timing of the disappearance of the populations and the potential cause of the populations’ declines. We found 76 observations that met our criteria for inclusion that were derived from 33 studies and included 47 different taxa. Most populations exhibited strongly seasonal patterns of occurrence, but the population dynamics of the same or closely related species varied greatly across small spatial and temporal scales. Duration of occurrence was negatively related to latitude, but latitude explained only 8 % of the total variability, and no relationship existed when tropical species were excluded from the analysis. Senescence after spawning, infestations of parasites, food limitation, disease, low salinity, extreme water temperatures, predation and intertidal stranding were most commonly cited as causing blooms to collapse. Improving understanding of when and why blooms collapse will benefit coastal industries that are affected by blooms and greatly improve our understanding of how jellyfish blooms impact the ecology of the systems they inhabit.
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79
K.A. Pitt and C.H. Lucas (eds.), Jellyfi sh Blooms, DOI 10.1007/978-94-007-7015-7_4,
© Springer Science+Business Media Dordrecht 2014
Abstract Research on jellyfi sh blooms has focused heavily on the factors infl uencing
the production of blooms. Identifying the factors that cause blooms to collapse,
however, is important for predicting the duration of blooms and when they are likely
to disappear. We assembled studies from the literature to assess the persistence of
populations of medusae, the timing of the disappearance of the populations and the
potential cause of the populations’ declines. We found 76 observations that met our
criteria for inclusion that were derived from 33 studies and included 47 different
taxa. Most populations exhibited strongly seasonal patterns of occurrence, but the
population dynamics of the same or closely related species varied greatly across
small spatial and temporal scales. Duration of occurrence was negatively related to
latitude, but latitude explained only 8 % of the total variability, and no relationship
existed when tropical species were excluded from the analysis. Senescence after
spawning, infestations of parasites, food limitation, disease, low salinity, extreme water
temperatures, predation and intertidal stranding were most commonly cited as causing
blooms to collapse. Improving understanding of when and why blooms collapse will
benefi t coastal industries that are affected by blooms and greatly improve our under-
standing of how jellyfi sh blooms impact the ecology of the systems they inhabit.
Keywords Jellyfi sh blooms Cnidarians Biogeochemical cycling Jelly-falls
Population dynamics Feeding ecology Parasitism Hyperiid amphipods
Digenean trematodes Physiological tolerance Catabolism
Chapter 4
Bloom and Bust: Why Do Blooms
of Jellyfi sh Collapse?
Kylie A. Pitt , Ariella Chelsky Budarf , Joanna G. Browne ,
and Robert H. Condon
K. A. Pitt (*) A. C. Budarf J. G. Browne
Australian Rivers Institute and Griffi th School of Environment , Griffi th University ,
Gold Coast Campus , QLD 4222 , Australia
e-mail: k.pitt@griffi th.edu.au; a.budarf@griffi th.edu.au; jbrowne@museum.vic.gov.au
R. H. Condon
Dauphin Island Sea Lab , 101 Bienville Blvd , Dauphin Island , AL 36528 , USA
Department of Marine Science , University of South Alabama , Mobile , AL 36688 , USA
e-mail: rcondon@disl.org
80
4.1 Introduction
Jellyfi sh (i.e. cnidarian medusae and ctenophores) are renowned for their ‘boom and
bust’ population dynamics. Prolifi c rates of production, coupled with growth
rates (based on wet weight) that are two to three times those of non-gelatinous
pelagic taxa (Pitt et al. 2013 ), can result in the seemingly sudden appearance of
conspicuous, and often spectacular, population blooms. The biomass of blooms
regularly exceeds 10 t wet weight 100 m
−3 (Lilley et al. 2011 ). Typically, however,
blooms are short-lived, sustained for periods of weeks to months, after which the
populations disappear, often abruptly (i.e. collapse).
Concern regarding the perceived global increase in jellyfi sh blooms, coupled
with their potential negative ecological and socioeconomic impacts, has, over the
past two decades, seen a surge in studies that have tried to identify the causes of
blooms (see Condon et al. 2012 ). Identifying natural and anthropogenic causes of
blooms is important for predicting bloom events, developing potential management
or eradication strategies and forecasting how jellyfi sh populations may respond to
changing ocean conditions. However, such enormous fl uctuations in biomass
(both appearance and disappearance) are likely to have major infl uences on the
ecology of marine systems. For example, the disappearance of what is often the
dominant predator of zooplankton releases predation pressure on zooplankton
and may initiate trophic cascades. Jellyfi sh also provide shelter to juvenile fi sh
and invertebrates and, therefore, may infl uence recruitment and population dynamics
of such taxa (see Doyle et al., Chap. 5 ). The sudden disappearance of jellyfi sh also
has major implications for biogeochemical cycling because jellyfi sh turn over large
quantities of assimilated material as carbon-rich dissolved organic material, which
is shunted toward rapid uptake and respiration by specifi c microbial phylotypes
(Condon et al. 2011 ). Because microbial respiration converts potential food web
energy into a form that can only be utilised by autotrophs (i.e. carbon dioxide), this
detour of carbon represents a diversion of carbon away from higher trophic levels.
Following the collapse of blooms, therefore, the transfer of carbon to higher
trophic levels may be restored. Moreover, microbial respiration associated with
decomposition of medusae can create an oxygen demand that exceeds the rate of
oxygen resupply, resulting in localised hypoxia or anoxia (Pitt et al. 2009a ).
Consequently, understanding the causes of declines, the timing and locations where
blooms collapse and the ecological and biogeochemical consequences of bloom
collapses is equally as important as understanding the production of blooms.
Senescing jellyfi sh typically exhibit increased rates of physical damage, loads of
parasites and rates of infection (Mills 1993 ). The pattern of mortality varies little
among taxa and usually involves degeneration of the tentacles, oral structures and
gonads, reduced swimming ability and, fi nally, necrosis of the epithelial tissues of the
bell (Brewer 1989 ; Kikinger 1992 ). The fate of moribund jellyfi sh is poorly known,
but their specifi c density exceeds that of seawater and also living jellyfi sh (Yamamoto
et al. 2008 ) suggesting that they are likely to sink rapidly. The observation of largely
K.A. Pitt et al.
81
intact moribund jellyfi sh on the seafl oor, so-called jelly-falls (Lebrato et al. 2012 ),
supports this argument. Rapid sinking of medusae may accelerate regional rates of
carbon export from surface waters in open ocean regions (Yamamoto et al. 2008 ;
Lebrato and Jones 2009 ) and increase transfer effi ciency of the biological pump to
the deep sea (Billett et al. 2006 ). For example, Billett et al. ( 2006 ) observed in the
Arabian Sea the massive ‘jelly-fl ux’ of Crambionella orsini carcasses at 3,000 m
following a surface bloom, which contained an order of magnitude more carbon
than the total annual carbon fl ux as measured by sediment traps. Given the dearth of
long-term time series of jellyfi sh communities and their biogeochemical infl uences
in the open ocean (Condon et al. 2012 ), it is unclear on what spatial and temporal
scales jelly-falls occur and how they are linked to ‘boom and bust’ dynamics of
jellyfi sh blooms, although recent information suggests that jelly- falls are prevalent
in coastal areas and oligotrophic gyres (Yamamoto et al. 2008 ; Lebrato et al. 2012 )
and have occurred over geological timescales (Hagadorn et al. 2002 ; Condon et al.
2012 ). Similarly, information on how jelly-falls relate to carbon export processes
are sparse (but see Lebrato et al. 2013 ) but jellyfi sh size, density and shape, physical
advection and microbial decomposition (Riemann et al. 2006 ; Tinta et al. 2012 ;
Lebrato et al. 2013 ) are likely the primary driving factors infl uencing sinking of
jellyfi sh blooms (Lebrato et al. 2011 ).
The major objective of this chapter is to analyse the literature to elucidate
temporal and spatial trends in the persistence of jellyfi sh populations and to identify
the major causes of declines in jellyfi sh populations. The major drivers identifi ed as
causing blooms to collapse are then reviewed.
4.2 Literature Analysis
We searched the literature for studies of population dynamics to assess the persistence
of the population, timing of the disappearance of the population and the potential
cause of the population’s decline. Although ctenophores are usually considered
‘jellyfi sh’, they were not included in the analysis because their populations are
typically restocked annually from overwintering populations (Costello et al. 2006 )
indicating that at least some of the population is perennial. Only studies that
sampled medusae at intervals of less than 2 months and that sampled for 1 year,
or that sampled from before the initial appearance of the population and until after
the population had disappeared, were included. A linear regression was used to
test whether the duration of the occurrence of populations was related to latitude.
The duration of the population was determined by the period when medusae were
abundant (i.e. rare occurrences were excluded; Table 4.1 ).
Our analysis found 76 observations that met our criteria and included 44 obser-
vations of hydrozoans (including four siphonophores) and 32 observations of
scyphozoans (Table 4.1 ). The observations were derived from 33 studies and included
47 different taxa. Only eight observations were derived from the southern hemisphere
4 Bloom and Bust: Why Do Blooms of Jellyfi sh Collapse?
82
Table 4.1 Patterns of occurrence of medusae (and ephyrae when reported) and potential source of mortality for the population or for individuals within the
population. Lines indicate duration of occurrence. Dashed lines indicate that medusae or ephyrae were rare (as defi ned or stated by author). Blue lines = northern
hemisphere, green lines = southern hemisphere (seasons in the table refer to the appropriate season in the respective hemisphere). A single line per entry
indicates that only 1 year was sampled; patterns were identical between years or indicate a general pattern if 2 years sampled. Two lines for a given entry
represent differences in patterns of occurrence during each year
K.A. Pitt et al.
83
(continued)
4 Bloom and Bust: Why Do Blooms of Jellyfi sh Collapse?
84
Table 4.1 (continued)
Taxon: H hydrozoa, SP siphonophore, S scyphozoa
a Data were presented for two locations: Korsfjord and the nearby Fanafjord. To avoid over- representation of this one study in the table, only data for Korsfjord
are presented because the Korsfjord was sampled more extensively than the Fanafjord. Medusae were considered to be rare when densities were <10 ind. 1,000 m
−3
b Reported as Phialidium hemisphaerica
c Reported as Phialucium carolinae
d Invasive species
e Reported as Podocoryne minima
f Sampled Kiel Bight and Eckernforde Bay from May to Sept. Only data for Eckernforde Bay are included because the occurrence of the population in Kiel
Bight exceeded the duration of the sampling programme
g Mostly represented by ephyrae
K.A. Pitt et al.
85
(seven from Australia and one from Brazil). Two studies from Norway (Hosia and
Båmstedt 2007 ) and Portugal (Primo et al. 2012 ) which sampled multiple hydro-
zoan taxa contributed 17 and 9 observations, respectively. Most populations exhib-
ited strongly seasonal patterns with the majority exhibiting greatest abundances
between mid-spring and mid-autumn in their respective hemispheres. Seventeen
taxa occurred year-round, but at least one third of those still exhibited strong
seasonal variations in abundances. Rarely was the cause of the decline in the
population reliably identifi ed; however, authors frequently speculated about the
cause of mortality, which included senescence after spawning, infestations of parasites,
food limitation, disease, low salinity, extreme water temperatures (low and high),
predation, advection and intertidal stranding.
Surprisingly, populations of the same or closely related species sometimes
exhibited different dynamics at different locations or times. For example, the
most commonly sampled species, the scyphozoan Aurelia aurita , exhibited
strong seasonal patterns of occurrence in six studies but occurred throughout the
year in seven studies (Table 4.1 ). The pattern of occurrence of A. aurita also
varied substantially among years at a single location. For example, in Tomales Bay,
California, A. aurita exhibited a seasonal occurrence during 1 year, whilst the
population persisted throughout the following year (Hamner and Jenssen 1974 ).
Patterns of occurrence can also vary greatly over spatial scales of 10s of kilometres.
In the southern UK, for example, A. aurita persists year-round in a man-made
coastal lake but occurs seasonally nearby in Southampton Water (Lucas et al. 1997 ).
However, some caution must be applied to these observations of Aurelia because
the genus contains numerous cryptic species (Dawson and Jacobs 2001 ) and
some variations (particularly among locations) could refl ect taxonomic differences.
The invasive rhizostome, Phyllorhiza punctata , occurs predominantly during summer
and autumn in subtropical and temperature locations such as southern Western
Australia (Rippingale and Kelly 1995 ), the Gulf of Mexico (Graham et al. 2003 )
and southern Brazil (Haddad and Nogueira 2006 ), but populations of medusae
persist year-round in tropical Puerto Rico, despite still exhibiting distinct seasonal
cycles of recruitment and mortality (García 1990 ). These observations suggest that
populations of medusae may rarely achieve their potential maximum longevity
and that environmental conditions are most likely the primary drivers of mortality.
This conclusion is further supported by observations that medusae can survive
much longer (sometimes several years) in captivity than they do in the fi eld
(Zahn 1981 ).
The persistence of populations was negatively correlated with latitude ( P = 0.02),
but latitude explained only a small amount of the total variability (r
2 = 0.081), and
the relationship was largely driven by the year-round persistence of three of the
four tropical species recorded (i.e. Aurelia aurita and Mastigias papua in Palau and
Phyllorhiza punctata in Puerto Rico) (Fig. 4.1 ). When tropical species were
excluded, no relationship with latitude existed (r
2 = 0.006; P > 0.05).
4 Bloom and Bust: Why Do Blooms of Jellyfi sh Collapse?
86
4.3 Common Causes of Mortality of Medusae
4.3.1 Food Limitation
Medusae can be voracious predators of zooplankton. The very high water content of
medusae enables them to attain body sizes that are much larger than other plankti-
vores of equivalent carbon content (Acuña et al. 2011 ). This trait enables medusae
to support large feeding structures that can effi ciently clear large volumes of water
and theoretically enables medusae to survive in lower concentrations of prey than
other competing planktivores, such as fi sh (Acuña et al. 2011 ). Changes in growth
(Olesen et al. 1994 ) and biomass (Möller 1980 ; Miglietta et al. 2008 ) of medusae
populations often correlate with zooplankton production after correcting for tempo-
ral lags. When prey are plentiful, medusae can grow rapidly (e.g. wet weight-
specifi c growth of 0.88 d
−1 for Cotylorhiza tuberculata ; Kikinger 1992 ), and the
biomass of the population has the potential to accumulate until rates of predation by
medusae exceed secondary production of zooplankton and the biomass of medusae
cannot be sustained (Purcell and Decker 2005 ). When prey become limited, how-
ever, growth of medusae may be inhibited, and individuals may attain smaller sizes
than when food is unlimited (e.g. Schneider and Behrends 1994 ; Lucas et al. 1997 ).
Indeed, food limitation is regularly cited as a major cause of population declines
(Table 4.1 ). However, sometimes medusae have continued to grow (Møller and
Riisgård 2007 ) and accumulate biomass (Olesen et al. 1994 ) despite the biomass of
0
2
4
6
8
10
12
0 102030405060
Duration of occurrence (months)
Latitude (degrees N or S)
Tropics
Fig. 4.1 Relationship between duration of occurrence of medusae and latitude
K.A. Pitt et al.
87
zooplankton appearing to be too low to support the population. This may be because
rates of secondary production are very high despite the low standing biomass or that
medusae effi ciently exploit patches of zooplankton or may be able to supplement
their diet by feeding on picoplankton (e.g. cyanobacteria) and microplankton
(e.g. ciliates). Alternatively, the biomass of zooplankton in these studies may have
been underestimated because neither study sampled the demersal zooplankton that
emerges from the benthos into the water column at night. Emergent zooplankton are
an important dietary source for jellyfi sh because tactile predators such as jellyfi sh
can feed continuously during the day and night (Pitt et al. 2008 ), which may also
allow them to outcompete visual predators for food resources in waters that are
dark or contain high humic content (Aksnes et al. 2004 ). Indeed, in Kertinge Nor,
Denmark, densities of epibenthic copepods in the water column can be 20 times
greater at night than during the day (Olesen et al. 1994 ) and could, therefore, provide
a signifi cant food source.
If food is limited when medusae fi rst recruit, growth appears to be inhibited, and
medusae attain only small sizes. In Horsea Lake, UK, zooplankton productivity is
much lower than in the nearby Southampton Water, and A. aurita in Horsea Lake
are, correspondingly, much smaller than those in Southampton Water (Lucas et al.
1997 ). Moreover, the bell diameter of A. aurita was negatively correlated with pop-
ulation density over 20 years of observations in Kertinge Nor, Denmark (Riisgård
et al. 2010 ) and over 9 years in Kiel Bight, Germany (Schneider and Behrends
1994 ), suggesting that competition for food may limit growth.
4.3.2 Predation
Until recently, jellyfi sh were considered a trophic dead end; however, recent studies
indicate jellyfi sh are consumed by a variety of marine predators, including turtles,
birds, fi sh and other gelatinous zooplankton (reviewed by Arai 2005 ). While a
diverse range of predators feed on jellyfi sh, predation by fi sh and other gelatinous
zooplankton has the largest potential to impact jellyfi sh populations (Arai 2005 ).
Top-down regulation of jellyfi sh populations is diffi cult to demonstrate and quan-
tify; however, several authors have speculated that intense, intra-guild predation by
other gelatinous predators can regulate some medusae (Table 4.1 ). For example, in
Nova Scotia, Canada, the hydromedusa Rathkea octopunctata comprised 34 % of
the diet of the scyphomedusa Aurelia aurita indicating that A. aurita may regulate
natural populations of R. octopunctata (Matsakis and Conover 1991 ). In Norway,
Cyanea capillata preys heavily on A. aurita (Fig. 4.2 ), and the decline in the
A. aurita population coincides with an increase in C. capillata (Båmstedt et al. 1994 ).
Overlapping temporal succession of several hydrozoans in Norway may similarly
indicate intra-guild predation (Hosia and Båmstedt 2007 ).
A wide range of fi sh consume jellyfi sh, including spiny dogfi sh, chum
salmon, ocean sunfi sh, Atlantic mackerel and Atlantic cod (Arai
1988 ; Ates 1988 ;
Link and Ford 2006 ). Although sh probably exert signifi cant predatory pressure,
4 Bloom and Bust: Why Do Blooms of Jellyfi sh Collapse?
88
the importance of jellyfi sh as a dietary component is unknown due to unquantifi ed
digestion rates (Purcell and Arai 2001 ; Cardona et al. 2012 ). Diffi culties with gut
content analysis may be circumvented by using stable and enriched isotopes
(Pitt et al. 2009b ) and molecular techniques. A recent study in the Mediterranean
Sea used
13 C and
15 N stable isotopes as a tool to estimate the relative contribution of
gelatinous zooplankton to the diets of several apex predators (Cardona et al. 2012 ).
Although this study provided evidence that loggerhead sea turtles, ocean sunfi sh
and various opportunistic feeders potentially consume large quantities of jellyfi sh,
further research is needed to quantify rates and determine whether these predators
can regulate populations of jellyfi sh.
4.3.3 Parasitism
Parasitism is likely to be an important factor in the decline of many jellyfi sh blooms
and in the regulation of medusae populations. Medusae are infected by many types
of parasites, including hyperiid amphipods (Laval
1980 ; Dittrich 1988 ); digenean
trematodes, or fl ukes (Martorelli and Cremonte 1998 ); cestodes (Vannucci-Mendes
1944 ); isopods (Barham and Pickwell 1969 ); nematodes (Svendsen 1990 );
barnacles (Pagès 2000 ); sea anemones (McDermott et al. 1982 ) and, potentially,
microbes (Doores and Cook 1976 ). Parasites that infect non-gelatinous hosts
can cause the host populations to crash (e.g. krill: Gómez-Gutiérrez et al. 2003 ;
Fig. 4.2 Cyanea capillata capturing Aurelia aurita in Kiel Fjord, Germany (Reproduced by
permission of Kylie Pitt)
K.A. Pitt et al.
89
sh: Heins et al. 2010 ), and there is strong circumstantial evidence to suggest that
hyperiid amphipods may contribute to declines in medusa populations (Mills 1993 ),
and ctenophore populations have also been adversely affected by platyhelminth
worms (Yip 1984 ) and parasitic anemones (Reitzel et al. 2007 ). Blooms of jellyfi sh
are likely to be particularly susceptible to parasitism because abundances of para-
sites are positively correlated to densities of hosts (Arneberg et al. 1998 ) and the
population size of hosts is a determinant of parasite infection (Bagge et al. 2004 ).
4.3.3.1 Hyperiid Amphipods
Hyperiid amphipods are a paraphyletic group of marine amphipods whose features
(e.g. large eyes, maxillipeds with no palps) are believed to have arisen through their
association with planktonic hosts (Lützen 2005 ). While some hyperiid amphipods
are primarily free-living, most appear to depend on gelatinous hosts for at least
some stage of their life cycle (Arai 2005 ). These hosts include medusae (Fig. 4.3a ),
siphonophores, planktonic molluscs and salps (Gasca and Haddock 2004 ). In many
hyperiid species, females brood eggs and then deposit juveniles onto the host.
The juveniles then feed on their host until they reach a more independent stage
(Laval 1980 ). Some hyperiid adults continue to feed on their host’s tissues (Towanda
and Thuesen 2006 ), while others become free-living. Parathemisto gaudichaudi is
generally regarded as free-living; however, juveniles have been found associated
with salps (Madin and Harbison 1977 ). Other hyperiids attach to the outside of their
host and feed on plankton, entrained (Condon and Norman 1999 ) or caught by
the host (Laval 1972 ).
Hyperiid amphipods can be prevalent in populations of medusae. At times,
100 % of the population may be infected (Towanda and Thuesen 2006 ), and indi-
vidual medusae may host hundreds of hyperiids (Dittrich 1988 ; Towanda and
Thuesen 2006 ). Medusae have a remarkable ability to regenerate damaged tissues
when food is abundant (Mills 1993 ), but if dense infestations of parasites occur
during times when food is scarce, mortality may occur. For example, prior to the
disappearance of the hydromedusae Aequorea victoria and Mitrocoma cellularia
from Puget Sound, USA, individuals exhibited high proportions of grazing damage
(>75 % and 67–100 %, respectively) which was attributed primarily to the hyperiid
amphipods Parathemisto pacifi ca and Hyperia medusarum . Low proportions of
hydromedusae had food in their guts (44 % and 66 %, respectively) and were seem-
ingly unable to regenerate lost tissue. The hyperiid Hyperia galba had a similar
effect on populations of the scyphomedusae Chrysaora hysoscella , Aurelia aurita ,
Rhizostoma pulmo , Cyanea capillata and C. lamarckii over two consecutive years
in waters around Helgoland in the North Sea (Dittrich 1988 ). By autumn almost all
medusae were parasitised, and the number of amphipods per medusa reached 486
on C. hysoscella . The increasing rates of infection coincided with the medusae
shrinking, as the hyperiids consumed the gonads and then the mesoglea. Regeneration
by medusae appeared unable to offset rates of tissue loss, and by the end of autumn,
all the medusae had disappeared (Dittrich
1988 ). While there have been many
4 Bloom and Bust: Why Do Blooms of Jellyfi sh Collapse?
90
studies on hyperiid amphipods and their hosts (see reviews of Harbison et al. 1977 ;
Madin and Harbison 1977 ; Laval 1980 ), only Mills ( 1993 ) and Dittrich ( 1988 )
attempted to determine their effect on medusae populations. Other species of medu-
sae for which hyperiids may have caused or contributed to the disappearance of
populations include Aurelia aurita (Möller 1980 ; Møller and Riisgård 2007 ) and
Cyanea capillata (Metz 1967 ).
4.3.3.2 Digenean Trematodes
Digenean trematodes, which are parasitic fl atworms (fl ukes), infect at least 62 species
of medusae (Browne unpubl.). Although there are approximately 18,000 species
Fig. 4.3 ( ab ) Ectoparasites
in Port Phillip Bay, Australia;
( a ) hyperiid amphipods
Hyperia gaudichaudi
(indicated with arrows ) on
the oral arms of the
scyphozoan Catostylus
mosaicus (scale bar is 2 cm)
and ( b ) anemone Peachia
hilli (indicated by arrow )
attached to the scyphozoan
Pseudorhiza haeckeli (scale
bar is 0.5 cm) (Reproduced
by permission of Joanna
Browne)
K.A. Pitt et al.
91
of digeneans, only 13 infect medusae (Browne unpubl.). Digeneans have a complex
life cycle, mostly involving three hosts. The fi rst host is normally a mollusc, the
intermediate host is normally another invertebrate and the fi nal host is almost
always a vertebrate. Different life history stages of the parasite occur in each host,
and some are capable of reproduction (e.g. sporocysts in the mollusc host and
sexual adults in the vertebrate host). Digeneans that use jellyfi sh as an intermediate
host leave their mollusc host and penetrate the jellyfi sh and develop into metacer-
cariae which is a juvenile resting stage in an intermediate host. When the jellyfi sh
are eaten by suitable fi sh hosts, the metacercariae develop into sexual adults within
the fi sh. The metacercariae are likely to feed upon the jellyfi sh tissue, and highly
parasitised medusae can have an ‘ablandamiento total’ (=overall softening) of tissue
(Girola et al. 1992 ).
The proportion of medusae infected by digeneans in a population can be very
high (Fraser 1970 ) and is often higher than that observed in other planktonic inter-
mediate hosts (Marcogliese 1995 ). Rates of infection by digeneans in studies that
sampled >1,400 individuals of one medusa species ranged from 0.1 % to 97.6 %
(Diaz Briz et al. 2012 ) and depended on the species of digenean and host and
season. The only study to have examined the direct effect of digenean parasites on
a population of gelatinous zooplankton has focused on ctenophores. Yip ( 1984 )
sampled populations of the host ctenophore Pleurobrachia pileus monthly for 3½
years and observed a sharp decline in abundance of the ctenophore following
periods of heavy infection by parasites (predominately Opechona bacillaris and
didymozoid larvae). She proposed that effects on the host could include competition
for food, consumption of body tissue and increasing body weight of the host interfering
with normal movement.
4.3.3.3 Parasitic Anemones
Larval anemones of the genera Edwardsiella and Peachia (Fig. 4.3b ) parasitise jelly-
sh and feed on their intestinal fl uids, gonads and mouth tissues (Badham 1917 ;
Spaulding 1972 ; Mills 1993 ). As adults, the anemones are benthic and free-living
(McDermott et al. 1982 ; Reitzel et al. 2006 ). While many medusae are infected by
larval anemones (Lauckner 1980 ), the only ecological studies about their effects on
host populations have been done on ctenophores. In the laboratory, larval E. lineata
decreased the growth rates of their host ctenophore M. leidyi and indirectly decreased
fecundity through their infl uence on host size (Bumann and Puls 1996 ). These par-
asite-induced effects led the anemone to be proposed as a biological control on its
invasive host M. leidyi (Bumann and Puls 1996 ). However, using the anemone as a
biological control would be risky because the anemone is linked to the skin irritation
‘sea bathers eruption’ (Freudenthal and Joseph 1993 ) and may alter benthic
communities (Bumann and Puls 1996 ). Recently, E. lineata is believed to have
followed its invasive host to the northeast Atlantic (although there is some diffi culty
in differentiating E. lineata and the similar E. carnea ) (Selander et al.
2010 ).
4 Bloom and Bust: Why Do Blooms of Jellyfi sh Collapse?
92
4.3.3.4 Importance of Medusae Parasites and Relevance to Blooms
While there have been many studies of some medusae parasites, particularly
hyperiids, those above are examples of the few that have examined the effects
of parasites on medusae populations through time. Many medusa parasites
(e.g. microbes) that have the potential to have detrimental effects on their hosts are
poorly understood (Ohtsuka et al. 2009 ), but further research will enable perspective
of their importance and relevance to medusae mortality and decline of blooms.
Recently the ability of parasites to affect entire communities has been high-
lighted (Lafferty 2008 ; Hatcher et al. 2012 ). Medusae parasites may infl uence
other organisms through predation, transference and regulation of host populations.
Parasites which use medusae as intermediate hosts may be transferred to commer-
cially important species. For example, the mackerels Scomber scombrus , S. japonicus
and S. australasicus are infected by numerous digeneans that use jellyfi sh as hosts
(Bray and Gibson 1990 ; Bartoli and Bray 2004 ). The transmission of parasites
depends on the density of the hosts (e.g. farmed salmonids and sea lice: Jansen
et al. 2012 ), and when jellyfi sh form blooms, parasites such as larval anemones and
hyperiids may spread more easily between medusae hosts (Spaulding 1972 ; Laval
1980 ). There may also be increased transfer of parasites to predators; the parasitic
anemone, Edwardsiella lineata , is transferred when its host Mnemiopsis leidyi is
eaten by Beroë ovata (Reitzel et al. 2007 ). Peaks in medusa populations offer an
increased abundance of hosts and therefore appear to be linked to peaks in parasite
abundance (Williams and Robins 1981 ; Dittrich 1988 ). Medusae parasites may
have positive effects on other animals by relieving predation pressure by the medusae
hosts, or they may be a food source. For example, hyperiid amphipods are picked
directly from their hosts by pile perch Rhacochilus vacca , the symbiont crab Cancer
gracilis (Towanda and Thuesen 2006 ) and sea birds (Harrison 1984 ).
4.3.4 Disease
While disease is often considered to be a potential cause of mortality in medusae,
few studies have confi rmed infections as a cause of death. Hydromedusae with
bacterial infections are able to recover if suffi cient food is available (Mills 1993 ).
However, at the end of the hydromedusae’s seasonal occurrence, the reduced avail-
ability of prey may render them more susceptible to these infections (Mills 1993 ).
Late in the season, for example, over 80 % of the hydromedusa Clytia gregaria had
bacterial infections on their bells, which was thought to contribute to mortality
when coupled with limited food availability (Mills 1993 ). Similarly, mortality of
Gonionemus vertens was thought to be primarily due to infection characteristically
associated with senescence (Mills 1993 ). Bacteria also infected wounds generated
by bites of argonauts in the rhizostome Phyllorhiza punctata which may have
exacerbated the physical injuries incurred (Heeger et al.
1992 ). Although pathogens
other than bacteria (e.g. viruses and fungi) probably infect medusae, no studies of
such pathogens exist.
K.A. Pitt et al.
93
4.3.5 Death Post-Spawning
Scyphozoan jellyfi sh have, on several occasions, been observed to die shortly after
spawning (Table 4.1 ). Mortality post-spawning has been examined particularly in
Aurelia aurita . In the Baltic Sea mortality rates prior to maturation were low, but
after spawning the medusae degraded and died (Möller 1980 ). Starvation and
increased parasitism were suggested to be the major cause of degradation rather
than spawning itself. However, Spangenberg ( 1965 ) observed that sexual products
and gastric fi laments of Aurelia aurita were released simultaneously during spawn-
ing. Because gastric fi laments (or gastric cirri) are necessary for digestion within
the stomach, their loss during spawning suggests starvation as the most likely
explanation for deterioration in this case (Spangenberg 1965 ; Arai 1997 ). Contrary
to these studies, however, Hamner and Jenssen ( 1974 ) found that after spawning
medusae were able to ‘ripen’ gonads within a couple of weeks. Therefore, their
observations in the laboratory did not support simultaneous deterioration of somatic
and reproductive tissue, although they did observe deterioration and mortality
post-spawning in the fi eld.
Cyanea is another genus that reportedly spawns and then deteriorates (Fancett
1986 ). However, in the Niantic River estuary, USA, Cyanea sp. lose their tentacles
prior to losing their oral folds (which contain the planulae) and gonads, and so the
major cause of death may be starvation due to loss of tentacles rather than spawning
(Brewer 1989 ).
4.3.6 Metabolic Intolerances to Physical Conditions
Patterns of occurrence of many medusae are often correlated with seasonal changes
in physical parameters such as temperature or salinity (e.g. Fancett 1986 ; Lo and
Chen 2008 ; Primo et al. 2012 ) which, in turn, are correlated with a variety of other
changes, such as decreased zooplankton production. Only in regions where seasonal
changes in the physical environment exceed the physiological tolerances of species,
however, are physical factors likely to be the main driver of mortality. To rigorously
identify physical conditions as the main cause of mortality requires experiments on
tolerance limits to be undertaken, preferably at the location of interest to account for
local adaptation, and then related to fi eld observations.
4.3.6.1 Temperature
Although populations of medusae often disappear when water temperatures decrease
during autumn, only in Chesapeake Bay is there robust evidence that death of medusae
is caused by cooling water temperatures. In laboratory experiments, the pulsation
rate of Chrysaora quinquecirrha slows with declining water temperature, and at
10 °C medusae cease to pulse and die (Gatz et al. 1973 ). These results are consistent
4 Bloom and Bust: Why Do Blooms of Jellyfi sh Collapse?
94
with observations in the fi eld and laboratory, whereby medusae sink deeper into the
water column when the temperature decreases to 15 °C and then disappear entirely
from the water column at 10 °C (Sexton et al. 2010 ), suggesting that the cold water
may have been the dominant cause of death. Warm temperatures can also invoke
mortality. For example, following an ENSO event in 1997–1998 which elevated
temperatures 1–2 °C above their long-term seasonal average, the normally perennial
population of the zooxanthellate rhizostome Mastigias papua disappeared from
Ongeim’l Tketau lake in Palau (Dawson et al. 2001 ; Martin et al. 2006 ). Concurrent
laboratory experiments showed that mortality of medusae increased greatly at
temperatures similar to those measured in the lake; therefore, warm water was
considered the major cause of mass mortality (Dawson et al. 2001 ).
4.3.6.2 Salinity
Evidence linking changes in salinity to mortality events of medusae is relatively
weak and constrained to correlative observations. For example, Aurelia aurita
disappears from the surface waters of a coastal lagoon in Taiwan following heavy
rain during summer, but it is unclear whether the population dies, is advected from
the lagoon or simply remains below the halocline (Lo and Chen 2008 ). In Western
Australia, the distribution and persistence of Phyllorhiza punctata appears to be
correlated to rainfall, with periods of heavy rain preceding the disappearance of the
population (Rippingale and Kelly 1995 ). Populations of Chrysaora quinquecirrha
in the mesohaline region of Chesapeake Bay are similarly correlated with stream-
ow and salinity (Cargo and King 1990 ; Purcell et al. 1999 ), but research has
focused mainly on the effects of salinity on production of medusae rather than as a
cause of mortality.
4.3.6.3 UV Radiation
Ultraviolet (UV) radiation damages tissues and induces vertical migration in zoo-
plankton (Rhode et al. 2001 ). Consequently UV radiation could be detrimental to
medusae. In Lake Tanganyika, the freshwater hydrozoan, Limnocnida tanganjicae ,
died within 1 h when exposed to UV radiation equivalent to that found close to the
surface waters (Salonen et al. 2012 ). However, L. tanganjicae undertakes diel verti-
cal migration, and this, presumably, prevents mortality in situ. The upside-down
jellyfi sh Cassiopea sp. is restricted to occurring in shallow waters due to its need to
photosynthesise and, therefore, may be susceptible to exposure to UV radiation.
The zooxanthellae within this species synthesise mycosporine-like amino acids
that have a photoprotective function and that can be translocated to the host to
provide protection against UV radiation (Banaszak and Trench 1995 ). Pigments
may also be formed through uptake of glycoproteins, which may serve to protect
cells in zooxanthellate medusae from UV radiation (Blanquet and Phelan
1987 ).
K.A. Pitt et al.
95
Whilst no studies have attributed large-scale mortality of medusae to UV radiation,
increasing levels of radiation could, potentially, induce mortality in shallow systems
where vertical migration is not possible.
4.3.7 Stranding
Mass strandings of jellyfi sh are common on beaches (e.g. Houghton et al. 2007 ;
Fuentes et al. 2010 ; Fig. 4.4 ) and, because of their conspicuous nature, often attract
the attention of media (Lilley et al. 2009 ; Condon et al. 2012 ). Strandings, however,
are more likely to be a consequence, rather than a cause of mortality for medusae,
and the timing of events may relate to oceanographic and weather conditions. For
example, large numbers of the rhizostome Cotylorhiza tuberculata strand on
beaches in Vlyho Bay, Greece, during autumn, associated with strengthening winds
(Kikinger
1992 ). These strandings may be facilitated by reduced swimming ability
associated with sloughing of the subumbrella muscles as the medusae senesce
(Kikinger 1992 ). Moreover, Chrysaora hysoscella that wash ashore on beaches in
the Irish Sea often lack peripheral tentacles and oral arms, indicating that these
medusae may have senesced prior to stranding (Houghton et al. 2007 ). Mass strandings
of decaying medusae on beaches may represent a substantial input of carbon to
beach environments, which are typically poorly productive and rely on allochthonous
inputs of organic matter.
Fig. 4.4 Mass stranding of Crambione mastigophora at Cable Beach, Broome, Western Australia
(Reproduced by permission of James Browne, Kimberley Marine Research Station, Cygnet Bay)
4 Bloom and Bust: Why Do Blooms of Jellyfi sh Collapse?
96
4.4 Factors That Promote Survival of Jellyfi sh
The persistence of medusae populations may relate to their variable abilities to
either withstand the drivers of mortality or to recover from them (see also Lucas and
Dawson, Chap. 2 ). The ability of medusae to catabolise their own tissues when
starving and to heal wounds and regenerate lost body parts is likely to provide
medusae with the ability to potentially survive stressors.
4.4.1 Ability to Shrink When Starved
When food is scarce, most organisms can utilise stores of lipids to sustain
themselves. Medusae, however, contain approximately half the lipid content (as %
ash- free dry weight, AFDW) of non-gelatinous pelagic taxa (Clarke et al. 1992 ;
Donnelly et al. 1994 ), and the majority of lipids are phospholipids which constitute
components of cell membranes (Arai et al. 1989 , Costello 1992 ). Due to the lack of
storage lipids, the ubiquitous responses of medusae to starvation are to catabolise
their own tissues and rapidly lose mass (Hatai 1917 ; Hamner and Jenssen 1974 ;
Arai et al. 1989 ). The degree of degrowth can be remarkable. For example, Cassiopea
can lose up to 99 % of its mass (Mayer 1914 ), and A. aurita can shrink to a quarter
of its original diameter and remain viable; however, once the diameter is less than
2 cm, the medusae usually become deformed and deteriorate (Hamner and Jenssen
1974 ). In the hydromedusa Aequorea victoria , proteins, lipids and carbohydrates
are catabolised at similar rates (Arai et al. 1989 ). However, while A. aurita and
A. victoria shrink rapidly when starved (Hamner and Jensen 1974 ; Arai et al. 1989 ),
the hydromedusa Cladonema californicum actually increases diameter and maintains
an enlarged diameter for up to 28 days following the onset of starvation, despite
losing 69–77 % of its dry mass (Costello 1998 ). Maintaining their diameter
whilst losing mass, however, compromises their ability to swim (Costello 1998 ).
The difference in response of the few taxa for which starvation has been studied
may refl ect differences in their feeding ecologies. Specifi cally, C. californicum is an
ambush ‘sit and wait’ predator that relies on maximising encounter rates to capture
prey, whereas A. aurita and A. victoria are cruising predators that use vortices
generated by active swimming to entrain their prey (Costello 1998 ). Consequently,
A. aurita and A. victoria depend much more heavily on swimming to capture prey and
regrow. Maximising bell diameter, potentially at the expense of maintaining other
structures, such as muscles, may optimise survival of ambush predators and maximise
their chance for recovery once prey become more numerous (Costello 1998 ).
Aurelia aurita and Cladonema californicum can both regrow following more
than 6 weeks of starvation (Hamner and Jenssen 1974 ; Costello 1998 ). In both species
the pattern of growth following starvation is normal, and individuals can reinstate
normal feeding and reproductive processes. However, whilst in the laboratory
medusae exhibit an extraordinary ability to degrow and regrow, we could fi nd no
examples of cohorts of medusae recovering after shrinking in the fi eld. In the fi eld,
K.A. Pitt et al.
97
degrowth is usually determined from a decrease in the average size of medusae
(Möller 1980 ); however, decreases in average size can also be explained by selec-
tive mortality or advection of the larger size classes in the population (Brewer 1989 ;
Olesen et al. 1994 ) and, therefore, need to be interpreted cautiously. Degrowth
(where it has been claimed) is usually observed during autumn (e.g. Möller 1980 ;
Ishii and Båmstedt 1998 ; Møller and Riisgård 2007 ) which coincides with cooling
water temperatures and reduced rates of zooplankton production, conditions that
typically persist for several months. Whilst medusae can sustain at least three
months starvation in the laboratory (Hamner and Jensen 1974 ), the two studies of
regrowth by medusae have been undertaken at relatively warm and constant
temperatures (16–18 °C, Hamner and Jensen 1974 ; 18 °C, Costello 1998 – both
studies done in California). Indeed, interactive effects between regrowth and
temperature are yet to be tested but may demonstrate that regrowth is not viable
when water temperatures approach the thermal minimum for a species.
4.4.2 Ability to Heal Injuries and Regenerate Lost Body Parts
Medusae have remarkable abilities to heal injuries and regrow damaged body parts
(Zeleney 1907 ; Mills 1993 ). For example, parasitic hyperiid amphipods often consume
the manubria of the hydromedusa Aequorea victoria (Mills 1993 ). However, if the
damaged individual is transferred to an aquarium and fed well, it can regenerate a new
manubrium within 6 days (Mills 1993 ). Similarly, a hole penetrating the centre of the
umbrella of Mitrocoma can heal within 7 days (Mills 1993 ). Whilst injuries can heal
under laboratory conditions, recovery from injury also appears to occur in the fi eld.
For example, it is common to see substantial scars created by the healing of injuries
derived from the blades of boat propellers in large medusae (Pitt pers. obs.). Rates
of regeneration increase with severity of the injury, up until a threshold. For example,
regeneration of the oral arms of Cassiopea xamachana increased as additional oral
arms were removed, with the maximum rate of regeneration associated with the
removal of 6 of the 8 oral arms (Zeleney 1907 ). Moreover, jellyfi sh can also regen-
erate the same body parts multiple times (Zeleney 1907 ). Mechanisms of wound
healing are, however, very poorly studied. Very small wounds (1.2 mm diameter)
in the myoepithelial cells of the swimming muscle are closed by the muscle cells
differentiating into epithelial cells and migrating to the centre of the wound before
dedifferentiating into contractile muscle cells again (Lin et al. 2000 ).
4.5 Conclusions
Rarely have the causes of mortality of medusae been reliably identifi ed. Extreme
variability in persistence of populations of the same species among locations and
between years indicates that medusae may only rarely attain their maximum
4 Bloom and Bust: Why Do Blooms of Jellyfi sh Collapse?
98
physiological longevity in the fi eld, with environmental parameters that vary both
temporally and spatially the main drivers of mortality. Mortality is likely due to
multiple stressors interacting rather than individual events. Small variations in the
timing or magnitude of the stressors may invoke changes in the rate or timing of
mortality. Mass mortality, particularly in shallow or enclosed water bodies, such as
coastal lagoons and fjords, can have major implications for the ecology and bio-
geochemical cycling of the systems. Being able to predict the duration of blooms
and when they are likely to decline could benefi t coastal industries, such as tourism,
sheries and power generation, which are often negatively impacted by jellyfi sh
(see Lucas et al., Chap. 6 ). Reliable identifi cation of the factors leading to the
collapse of blooms should, therefore, be a priority for research.
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4 Bloom and Bust: Why Do Blooms of Jellyfi sh Collapse?
... According to the World Health Organization (WHO), P. physalis is a dangerous aquatic organism for human health and suggests not to bathe in places they usually arrive (WHO, 2003). P. physalis also represent a potential hazard to coastal ecosystem food webs because they are efficient consumers of zooplankton (Pitt et al., 2014). ...
Article
The massive influxes of pelagic Sargassum and Physalia physalis have become an increasingly recurrent phenomenon on the Atlantic coasts, affecting the economy and the structure of coastal ecosystems. For the first time, a study assesses the simultaneous arrival of these pelagic organisms. This study was conducted from June/2019 through June/2021 on the littoral of La Habana, one of the circulation points of the currents that form the North Atlantic Subtropical Gyre (NASG) run. Transects of 40 m were located parallel to the shoreline, the biomass of pelagic Sargassum was weighed, and the number of colonies of P. physalis was counted at the intertidal zone. The biomass of pelagic Sargassum was estimated as dry biomass. The simultaneous arrival of pelagic Sargassum and P. physalis was reported. Simultaneous arrivals of these pelagic species were recorded in the winter seasons, with the occurrence of cold fronts, low mean temperatures (22-27 • C), and strong northerly winds. Most months with the arrival of these pelagic species coincided with a negative average magnitude of the Arctic Oscillation Index, which favors the occurrence of cold fronts and northerly winds. The mean landing dry biomass of Sargassum during the peak months was low (0.73 ± 0.54 kg/m 2) compared to the Mexican Caribbean. 145 P. physalis colonies over 100 m of coast length per year were reported during the study period. The higher visual occurrence of Sargassum natans I and the higher percentage of left-handed P. physalis colonies (56.16 ± 3.37) may indicate that the NASG area, which encloses the Sargasso Sea, could be the primary source of arrivals to La Habana littoral. As reported, the distribution of sightings of pelagic Sargassum and P. physalis coincided in several regions in the Atlantic Ocean and represents an urgent call for coordinated monitoring and development of predictive forecasting of beach landings. This work suggests that there are Atlantic coastal sites such as La Habana littoral that could host the dangerous simultaneous arrivals of pelagic Sargassum and P. physalis. Finally, the use of remote sensing techniques with in situ observations is considered important for future work, since using remote sensing techniques alone seems to miss important events such as those documented in this study.
... When conditions are favorable some jellyfish species form extensive blooms, reaching high biomass within a short period of time by efficiently grazing on phytoplankton, zooplankton and fish larvae (Acuña et al., 2011;Pitt et al., 2013). Jellyfish blooms are often shortlived and collapse abruptly due to various largely unexplored environmental factors (Pitt et al., 2014;Schnedler-Meyer et al., 2018;Goldstein and Steiner, 2020). Thus, with their "boom and bust" population dynamics, jellyfish can represent an important perturbation to the surrounding ecosystem. ...
Article
Full-text available
When jellyfish blooms decay, sinking jellyfish detrital organic matter (jelly-OM), rich in proteins and characterized by a low C:N ratio, becomes a significant source of OM for marine microorganisms. Yet, the key players and the process of microbial jelly-OM degradation and the consequences for marine ecosystems remain unclear. We simulated the scenario potentially experienced by the coastal pelagic microbiome after the decay of a bloom of the cosmopolitan Aurelia aurita s.l. We show that about half of the jelly-OM is instantly available as dissolved organic matter and thus, exclusively and readily accessible to microbes. During a typical decay of an A. aurita bloom in the northern Adriatic Sea about 100 mg of jelly-OM L–1 becomes available, about 44 μmol L–1 as dissolved organic carbon (DOC), 13 μmol L–1 as total dissolved nitrogen, 11 μmol L–1 of total hydrolyzable dissolved amino acids (THDAA) and 0.6 μmol L–1 PO43–. The labile jelly-OM was degraded within 1.5 days (>98% of proteins, ∼70% of THDAA, 97% of dissolved free amino acids and the entire jelly-DOC pool) by a consortium of Pseudoalteromonas, Alteromonas, and Vibrio. These bacteria accounted for >90% of all metabolically active jelly-OM degraders, exhibiting high bacterial growth efficiencies. This implies that a major fraction of the detrital jelly-OM is rapidly incorporated into biomass by opportunistic bacteria. Microbial processing of jelly-OM resulted in the accumulation of tryptophan, dissolved combined amino acids and inorganic nutrients, with possible implications for biogeochemical cycles.
... The giant rhizostome jellyfish, Nemopilema nomurai Kishinouye, 1922 endemic to the East Asian Marginal Seas, is an example of a bloom-forming species that was particularly reported due to its vast size and subsequent disturbance to human activities particularly fishing(Uye, 2008;Dong, Liu and Keesing, 2010). In 2005 numbers of N nomurai were as numerous as 3-5x10 8 medusae through the Tsushima Current, followed by a 'bloom and bust' (terminology coined byPitt et al., 2014) event in 2006 whereby the numbers drastically dropped back to that of previous years. Uye(2008) reports that N. nomurai is subject to such cyclic bloom and bust events which is of ecological and climatic significance as well as a nuisance to various human activities.Temporal studies on oceanic deep-sea jellyfish are limited, due to the inherent sampling difficulties and expense accrued by longer-term monitoring. ...
Thesis
Macroecology provides a framework for understanding how local- and regional-scale processes interact, allowing us to understand how the biological and ecological traits of individual species influence large-scale patterns in diversity. The majority of macroecological studies to date have been centred on the terrestrial environment where large databases on species ranges, body size and associated environmental variables are readily available. Due to the inaccessibility of the deep sea, coupled with its relatively recent exploration, deep sea macroecology is the least represented within marine macroecology as a whole. Jellyfish, a significant constituent of the zooplankton, form important and often conspicuous components of marine ecosystems. Jellyfish studies covering large spatial scales are mostly focused on the shallow-water, bloom-forming species that have more apparent anthropogenic interactions, such as Aurelia aurita. The structural simplicity of jellyfish permits the rapid adaptation to changing environments. Plasticity in traits such as feeding, physiology, reproductive output, somatic growth and size are common; and as such allow populations to persist. The coronate medusae Periphylla periphylla Péron and Lesueur, 1810 and Atolla spp. are the most recognised deep-sea jellyfish, and both have cosmopolitan distributions. Little remains known about these genera beyond the early descriptions of the species, particularly relating to their macroecology and the expression of plastic traits according to varying environments. This study presents a large volume of morphological data using museum collections genera in order to better describe morphological variation on a global scale and to examine what factors might drive such variation. P. periphylla and Atolla spp. exhibit cosmopolitan distributions across the global dataset, found at depths ranging from 0 to 5486 m and 4900 m respectively. Across the global oceanic dataset and case study areas of the Iberian Basin and Porcupine Abyssal Plain, P. periphylla demonstrate no morphological plasticity across temporal or spatial scales, with variation in tentacle number observed within a number of Atolla species, A. gigantea, A. parva, A. vanhoffeni and A. russelli. This may be indicative of the genetic distance between the two species within Coronatae. The first comprehensive comparison between fjord and oceanic P. periphylla populations is described. Contrasting patterns were observed between fjord and oceanic environments, with larger males than females within the fjord population, and larger females than males within the oceanic population. Larger fjord specimens were observed across all sample seasons. The oceanic population provides evidence of the prioritisation of reproductive output within the more variable oceanic environments. Novel methods to further the understanding of volumes of statoliths within medusae statocysts were explored, with specimens of P. periphylla of varying sizes demonstrating a range of statolith numbers, sizes and crystalline morphologies. Statoliths form part of the sensory organs and represent the only hard structures within medusae. Both the number and size of statoliths is proposed to be indicative of the individual medusa age. This thesis shows that macroecological scales are important to consider when comparing globally-distributed species, and highlights the potential of using historical collections to identify ecological patterns. By combining the morphological data with molecular analyses, it would be possible to further the understanding of ecological divergence and speciation in deep sea coronates. Rearing specimens of a known age would also further the understanding of sclerochronological processes and help to determine age in medusae which are believed to be long-lived. <br/
... Additionally, blooms can also impact power generation and manufacturing by clogging intake screens, reduce tourism, and drive additional hypoxia when they die. Consequently, understanding population and species changes over time is critical to assessing the current and future impacts of these species on food webs, nutrient cycling, fisheries, and economic development (Purcell et al. 2007, Pitt et al. 2014). ...
Article
Climate change has increased hurricane activity and intensity, leading to greater destructive forces impacting coastal communities. Barnegat Bay, New Jersey, USA, is a shallow Mid-Atlantic estuary with considerable anthropogenic development which shows vulnerability to elevated storm surges and coastal flooding. Gelatinous zooplankton were sampled monthly in the summer prior to Hurricane Sandy in October 2012, with the community dominated by 2 species, Chrysaora quinquecirrha and Mnemiopsis leidyi. These 2 species showed inverse distributions, with C. quinquecirrha dominating in the northern, lower-salinity region and M. leidyi abundant in the southern, high-salinity region of the estuary, with significant top-down control of M. leidyi by C. quinquecirrha. Following Hurricane Sandy, substantial changes in the community occurred, with a 64% increase in gelatinous zooplankton species richness. C. quinquecirrha population density significantly declined by more than 50% in 2013 (from 0.033 to 0.013 m⁻³) and remained lower in 2014 (0.012 m⁻³). Concomitantly, M. leidyi populations significantly increased from 2.4 to 5.4 m⁻³ in 2013 but dropped in 2014. The drop in 2014 was unexpected, as the C. quinquecirrha population remained low. However, the increasing density and diversity of other gelatinous species in 2013 and 2014, including Salpa sp., Turritopsis nutricula, Nemopsis bachei, Bougainvillea muscus, and Rathkea octopunctata, changed the community composition. Consequently, the destructive forces of Hurricane Sandy cascaded throughout the community by the elimination of polyp habitat for the dominant predator, thereby opening the system to community succession.
... driftwood, jellyfish, floating seaweed) can minimize early-life mortality [11,12]. Jellyfish frequently form very dense blooms, predominantly during spring and summer [13], which often coincides with the timing of the pelagic larval phase of fish species [14]. Many of the fishes that associate with jellyfish are commercially important, including pollock, jacks and trevallies [9,15]. ...
Article
Symbiotic relationships are common in nature, and are important for individual fitness and sustaining species populations. Global change is rapidly altering environmental conditions, but, with the exception of coral-microalgae interactions, we know little of how this will affect symbiotic relationships. We here test how the effects of ocean acidification, from rising anthropogenicCO2 emissions, may alter symbiotic interactions between juvenile fish and their jellyfish hosts. Fishes treated with elevated seawater CO2 concentrations, as forecast for the end of the century on a business-as-usual greenhouse gas emission scenario,were negatively affected in their behaviour. The total time that fish (yellowtail scad) spent close to their jellyfish host in a choice arena where they could see and smell their host was approximately three times shorter under future compared with ambientCO2 conditions. Likewise, the mean number of attempts to associate with jellyfishwas almost three times lower in CO2-treated compared with control fish, while only 63% (high CO2) versus 86% (control) of all individuals tested initiated an association at all. By contrast, none of three fish species tested were attracted solely to jellyfish olfactory cues under present-day CO2 conditions, suggesting that the altered fish-jellyfish association is not driven by negative effects of ocean acidification on olfaction. Because shelter is not widely available in the open water column and larvae of many (and often commercially important) pelagic species associate with jellyfish for protection against predators, modification of the fish-jellyfish symbiosis might lead to higher mortality and alter species population dynamics, and potentially have flow-on effects for their fisheries. © 2016 The Author(s) Published by the Royal Society. All rights reserved.
... A great deal of previous research has examined the conditions that favor ctenophore growth and reproductive success (Purcell et al., 2001; McNamara et al., 2014; Robinson and Graham, 2014; Gambill et al., 2015; Jaspers et al., 2015); however, significantly less attention has been given to factors that contribute to bloom demise (Rathjen et al., 2012). Both physical (low salinity, thermal stress, intertidal stranding) and biological (parasite infestation, disease, senescence following spawning, predation, food limitation) parameters have been frequently cited in jellyfish bloom demise (Pitt et al., 2014); however, no studies have directly investigated ctenophore bloom termination. While their roles in ctenophore ecology and mortality remain completely unknown, this study provides the first evidence of viruses associated with ctenophores. ...
Article
Full-text available
Gelatinous zooplankton, such as ctenophores and jellyfish, are important components of marine and brackish ecosystems and play critical roles in aquatic biogeochemistry. As voracious predators of plankton, ctenophores have key positions in aquatic food webs and are often successful invaders when introduced to new areas. Gelatinous zooplankton have strong impacts on ecosystem services, particularly in coastal environments. However, little is known about the factors responsible for regulating population dynamics of gelatinous organisms, including biological interactions that may contribute to bloom demise. Ctenophores are known to contain specific bacterial communities and a variety of invertebrate parasites and symbionts; however, no previous studies have examined the presence of viruses in these organisms. Building upon recent studies demonstrating a diversity of single-stranded DNA viruses that encode a replication initiator protein (Rep) in aquatic invertebrates, this study explored the presence of circular, Rep-encoding single-stranded DNA (CRESS-DNA) viruses in the ctenophores Mnemiopsis leidyi and Beroe ovata collected from the Skidaway River Estuary and Savannah River in Georgia, USA. Using rolling circle amplification followed by restriction enzyme digestion, this study provides the first evidence of viruses in ctenophores. Investigation of four CRESS-DNA viruses over an 8-month period using PCR demonstrated temporal trends in viral prevalence and indicated that some of the viruses may persist in ctenophore populations throughout the year. Although future work needs to examine the ecological roles of these ctenophore-associated viruses, this study indicates that viral infection may play a role in population dynamics of gelatinous zooplankton.
Article
Upside-down jellyfish (Cassiopea spp.) are predominantly tropical, but there have been recent reports of medusae in temperate environments. In 2017 they were recorded in temperate Lake Macquarie, Australia, where they have a tendency to disappear from this area through late winter (Austral, August). This raises questions about the role of temperature as a controlling factor of their abundance, and future density increases with warming oceans as a result of climate change. Here we test the degree to which temperature may drive winter die-offs of the medusa stage in temperate environments, and how this may change with altered thermal regimes. We assessed the physiological response of Cassiopea (via measurement of bell pulsation rate, bell diameter, and routine metabolic rate) under a regime mirroring Lake Macquarie's seasonal temperature drop (autumn into winter) compared to three other temperature profiles: 1) seasonal profile with predicted climate change (+ 2 °C), 2) stable temperatures equivalent to the end of autumn (20 °C) and, 3) a profile that mimicked the increasing temperatures from winter into summer (20 °C increasing to 24 °C). Overall, the results indicate that, compared to the ambient state, elevated temperatures can have positive effects on performance of Cassiopea medusae as evidenced by greater bell pulsation rate and bell diameter. The rate of bell diameter decline was lower in all elevated temperature treatments relative to the ambient profile. This highlights the capacity for elevated temperatures in the future to slow the rate of bell degradation, contributing to an increased probability of overwinter survival, thus increasing the size and duration of Cassiopea blooms in temperate waterways such as Lake Macquarie.
Article
Recurrent jellyfish blooms in the coastal zone call for understanding the impacts of jelly-falls on the functioning of benthic communities, especially in shallow enclosed ecosystems where their biomass can affect local carbon cycling and productivity. Each year, blooms of the jellyfish Aurelia coerulea appear and collapse in a semi-enclosed coastal Mediterranean lagoon (the Thau lagoon, south of France). Although the lagoon is shallow, large accumulations of dead jellyfish are never observed on its bottom, so it was hypothesized that decaying jellyfish were rapidly consumed by local macrobenthic organisms. The current work aimed to test this hypothesis, by estimating the impact of the presence of dead A. aurelia medusae on local macrobenthic community composition and assessing their biomass loss rates under different scenarios of accessibility by the macrobenthos. Unexpectedly, our results revealed a limited role of macrobenthic scavengers in the disappearance of dead medusae, although this later was particularly fast (19–78h). Only one taxon (Tritia sp., Nassariidae family) showed a significant response to the presence of dead A. coerulea medusae on the seabed. Thus, our results suggest that the fast disappearance of dead jellyfish biomass in Thau results from its rapid degradation and consumption by local microorganisms, likely due to the combined effects of high local temperatures and the small size of A. coerulea medusae. Thus, the important biomass produced during A. aurelia blooms in Thau might essentially boost its microbial food web. The potential role of jellyfish blooms in controlling biogeochemical cycles and food web functioning in shallow lagoons is discussed, underlying the need to include this process in ecosystem-based models.
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The hydrozoan Portuguese man-of-war (Physalia physalis) is distributed throughout the Havana littoral zone, which is one of the circulation points of the currents that form the North Atlantic Subtropical Gyre run. For the first time, a study was conducted monthly from May 2018 through May 2019 to better understand the temporal and spatial variation of P. physalis in this region. This study covered five beaches in Havana (Cojímar, Bacuranao, Tarará, Mégano and Santa María). Transects of 50 m were located parallel to the shoreline and the colonies that arrived at the intertidal zone were counted. The colonies of P. physalis were mostly observed in May 2018 (80), November 2018 (110), December 2018 (132), January 2019 (152) and March 2019 (126), which coincided with the dry season in Cuba. This season was related to the presence of cold fronts and a negative average magnitude of the Arctic Oscillation Index (-0.05). The beaches with a relatively linear shape had a higher number of arrivals (549 colonies) than the beaches with a horseshoe shape (109 colonies). In addition, the highest number of colonies was associated with wind velocity above 33 km.h⁻¹ (especially northerly wind), wave height above 1.5 m, and temperatures below 30 °C.
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Jellyfish often form blooms that persist for weeks to months before they collapse en masse, resulting in the sudden release of large amounts of organic matter to the environment. This study investigated the biogeochemical and ecological effects of the decomposition of jellyfish in a shallow coastal lagoon in New South Wales, Australia. Catostylus mosaicus carrion was added to the surface of shallow sub-tidal sediments and biogeochemical parameters and macrofaunal abundance immediately below the jellyfish carrion were measured over three days. Sediment plots without jellyfish served as controls. Sediment oxygen demand and carbon and nitrogen efflux increased by up to 60-fold in the jellyfish plots, compared to control plots, and dissolved organic nutrient fluxes were more sustained than in previous studies due to the use of fresh rather than frozen biomass. The decomposing jellyfish progressively altered sediment redox conditions, indicated by an increase in porewater iron (II) and sulfide concentrations measured by high-resolution in situ diffusive samplers. Abundance of some macrofaunal taxa in the jellyfish plots decreased relative to controls, however, the abundance of a carnivorous gastropod, which was presumably feeding on the carrion, increased in the jellyfish plots. While jellyfish carrion may be a food source for some macrofauna, low oxygen conditions coupled with the accumulation of toxic dissolved sulfides in the near-surface sediments may explain the overall change in the macroinfaunal community.
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During the past several decades, high numbers of gelatinous zooplankton species have been reported in many estuarine and coastal ecosystems. Coupled with media-driven public perception, a paradigm has evolved in which the global ocean ecosystems are thought to be heading toward being dominated by “nuisance” jellyfish. We question this current paradigm by presenting a broad overview of gelatinous zooplankton in a historical context to develop the hypothesis that population changes reflect the human-mediated alteration of global ocean ecosystems. To this end, we synthesize information related to the evolutionary context of contemporary gelatinous zooplankton blooms, the human frame of reference for changes in gelatinous zooplankton populations, and whether sufficient data are available to have established the paradigm. We conclude that the current paradigm in which it is believed that there has been a global increase in gelatinous zooplankton is unsubstantiated, and we develop a strategy for addressing the critical questions about long-term, human-related changes in the sea as they relate to gelatinous zooplankton blooms.
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Community ecologists generally recognize the importance of species - such as pollinators - that have clear positive effects within ecosystems. However, parasites - usually regarded in terms of their detrimental effects on the individuals they infect - can also have positive impacts on other species in the community. We now recognize that parasites influence species coexistence and extirpation by altering competition, predation, and herbivory, and that these effects can, in turn, influence ecosystem properties. Parasites and pathogens act as ecosystem engineers, alter energy budgets and nutrient cycling, and influence biodiversity. Equally, because ecosystem properties - such as biodiversity - affect parasite populations, there is the potential for feedback between parasitism and ecosystem states. Using examples from animal and plant systems, we examine this potential bidirectional interdependence and challenge the conventional wisdom that parasites have only negative or inconsequential impacts on ecological communities.
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The seasonal occurrence, population dynamics, feeding, growth, reproduction, and timing of planular deposition was determined for a semelparous annual population of Cyanea medusae in the Niantic River estuary, Connecticut, which was sampled for 14 years. The annual pattern was highly predictable. Their ephyrae appear shortly after ice-out in late February, medusae with gonads occur in late April-early May, and are reproductive (bearing planulae on their oral folds) by late May-early June. At this time (early to mid-June), the medusae deteriorate, disappearing from the plankton in late June-early July. Population size, similarly, exhibits small variation, showing only a 5-fold difference in abundance. With deterioration, the frequency of feeding medusae declines; otherwise, they are opportunistic predators on seasonally numerous zooplankton, including fish. Growth shows two phases: first, a three month period of rapid exponential growth when medusae mature; and second, a one and one half month period of decline in average size of individuals as the larger medusae die. Medusae exhibit a sequence of "organ" loss prior to death: first, the tentacles, then the oral folds, and last, the gonads. Coincident with the disappearance of these organ-deficient medusae from the water column, their planulae first appear attached to shells in the benthos. The deterioration of medusae, and in particular the loss of planulae-bearing oral folds, may be requisite for the mass release of their planulae.
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1. Peachia quinquecapitata kept in sea water tanks at the Friday Harbor Laboratories were induced to spawn. The egg is 120 µ in diameter and is covered with spines 20 µ in length.2. Cleavage leads to a hollow blastula which becomes ciliated. As the cilia appear the spines become shorter and disappear.3. Gastrulation is by invagination. The planula stage is reached when the gastrula develops an apical tuft of long cilia.4. A swimming planula can be ingested by the medusa Phialidium gregarium. After ingestion the larva begins to grow and differentiate. Planulae which did not get ingested would not develop in the laboratory.5. The larvae remained endoparasitic for an average of 11 days and probably were feeding on material in the gatrovascular cavity of the host medusa.6. After 11 days the larvae became ectoparasitic and fed on the gonads of the host medusa. After an average of 31 days of ectoparasitism anemones had acquired their adult characteristics and dropped off the host medusa to become free-living.7....