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Abstract

Over the last two centuries, massive outbreaks of Pelagia noctiluca were recorded on average at 12 years intervals in certain parts of the Mediterranean Sea. Population peaks of Pelagia noctiluca were sometimes accompanied by an expansion outside of its usual distribution range, and during 1977–1986 this jellyfish also populated the northern Adriatic Sea. After maintaining itself at rather high densities for several consecutive years, the Pelagia noctiluca population of the northern Adriatic collapsed rather abruptly and for no obvious reason. Environmental conditions before, during and after the invasion of Pelagia noctiluca to the northern Adriatic are described. A model using time series analysis (1984–1986) of its population size structure was utilized to simulate the abundance of this jellyfish in the northern Adriatic. Results of this modelling exercise indicate that the most important effect on Pelagia population density was maturation at an early age (thus, at smaller size). The incorporation of demographic parameters such as shrinkage (regression and recovery to sexual maturity) into the model was the second most important factor for simulating its population abundance.
... P. noctiluca individuals were each assigned to one of five size classes using measurements of bell diameter: <1.0 cm; 1.0 to < 3.5 cm (immature medusae); 3.5 to < 6.0 cm (pre mature); 6.0 to < 8.5 cm (mature); and class >8.5 cm bell diameter ( [17]). The bell diameters of P. noctiluca along the outbreak site ranged between 2 and 6.5 cm, with a marked chromatic difference observed between the immature medusae bell (< 3.5 cm diameter), which was yellowish-brown in colour, and that of premature and mature (> 3.5 cm diameter), which assumed a purple or pink colour. ...
... Physical forces such as wind, tidal effects, current direction and velocity, have been the main drivers for P. noctiluca coastal aggregations in the western Mediterranean Sea, Adriatic Sea and Maltese waters over a long period of time. It is for this reason, P. noctiluca has been considered an indicator of climate variability in the Mediterranean Sea ( [1], [16], [2], [17], [35], [6]). ...
Article
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The blooms of mauve stinger Pelagia noctiluca (Forskål, 1775) (Scyphozoa, Semaeostomeae, Pelagiidae) in the Mediterranean Sea were generally restricted to the western basin and the Adriatic Sea. The occurrence and distribution of this species in the Levantine Basin has not been investigated adequately and is still far from being satisfactory. The present study reports the first documented outbreak of P. noctiluca five years after its first appearance off the Syrian coast (the eastern Mediterranean Sea). It also provides an additional scientific knowledge of the P. noctiluca blooms in the Mediterranean Sea, and will extend the region limits of the above species blooms to the Levantine Basin.
... While the measurements showed the total length is 4.5-17 cm, the length of four oral arms that is 2.4-12.9 cm, and the length of eight tentacles is 1.8-15 cm this finding is in agreement with [20], those who found the length of eight tentacles is more than 8.5 cm. ...
Article
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The Jellyfish cnidarians are important consumers of zooplankton in the Mediterranean Sea previously known. The aim of this study is to classification this species of jellyfish and examination morphological structure. The samples were collected from the Tripoli coast of Libya in September 2018 by scoop net. The number of samples was 31 individuals, collected to study the morphological structure measurements and wet weight. The results of the morphological structure showed the diameter of medusa 2.3 - 13.4cm, while the total length was 4.5 - 17cm, and the length of four oral arms was 2.4 - 12.9cm, the length of eight tentacles was 1.8 - 15cm and wet weight was 2.0 -73g. Based on morphological features and classification, the species was identified as Pelagia noctiluca (Forskål, 1775), but the differences between individuals in medusa size and wet weight indicate refers to different ages. So, this species is considered the first appearance on the Libyan coast.
... While the measurements showed the total length is 4.5-17 cm, the length of four oral arms that is 2.4-12.9 cm, and the length of eight tentacles is 1.8-15 cm this finding is in agreement with [20], those who found the length of eight tentacles is more than 8.5 cm. ...
Article
Full-text available
The Jellyfish cnidarians are important consumers of zooplankton in the Mediterranean Sea previously known. The aim of this study is to classification this species of jellyfish and examination morphological structure. The samples were collected from the Tripoli coast of Libya in September 2018 by scoop net. The number of samples was 31 individuals, collected to study the morphological structure measurements and wet weight. The results of the morphological structure showed the diameter of medusa 2.3-13.4cm, while the total length was 4.5-17cm, and the length of four oral arms was 2.4-12.9cm, the length of eight tentacles was 1.8-15cm and wet weight was 2.0-73g. Based on morphological features and classification, the species was identified as Pelagia noctiluca (Forskål, 1775), but the differences between individuals in medusa size and wet weight indicate refers to different ages. So, this species is considered the first appearance on the Libyan coast. ‫ـ‬ ‫ل‬ ‫الظاهرية‬ ‫الخصائص‬ Pelagia noctiluca (Forskål, 1775) (Scyphozoa :Cnidaria)
... Outbreaks of P. noctiluca in the Mediterranean Sea appear to have increased in recent decades (Kogovšek et al., 2010;Bernard et al., 2011), but how it relates to climate change remains uncertain . Increasing evidence points that mild winters and productive springs favor reproductive activity and survival of early life stages (Malej et al., 2004;Milisenda et al., 2018;. However, we still struggle to understand how climate change a ects early survival during the summer months, as warm water and low food supply may drive ephyrae and metaephyrae to starve. ...
Article
Understanding processes occurring in the di erent life stages of jellyfish is key to advance knowledge on their trophic interactions and population dynamics. We describe four developmental stages of Pelagia noctiluca ephyrae and metaephyrae based on the progress of feeding structures and morphometric measurements on the central disc diameter and total body diameter. Size di ers significantly among stages, but it can overlap substantially, suggesting that it is not always coupled with development progress due to di erent somatic growth. Morphological distinction of stages is biologically important because it implies di erent levels of food specialization and capture e ciency. We further report a 25% (±13 SD) shrinkage of ephyrae and metaephyrae after storage in 4% formaldehyde solution. This metric can be used in ecological studies focusing on size-related traits of field observed individuals.
... Outbreaks of P. noctiluca in the Mediterranean Sea appear to have increased in recent decades (Kogovšek et al., 2010;Bernard et al., 2011), but how it relates to climate change remains uncertain . Increasing evidence points that mild winters and productive springs favor reproductive activity and survival of early life stages (Malej et al., 2004;Milisenda et al., 2018;. However, we still struggle to understand how climate change a ects early survival during the summer months, as warm water and low food supply may drive ephyrae and metaephyrae to starve. ...
Article
Understanding processes occurring in the different life stages of jellyfish is key to advance knowledge on their trophic interactions and population dynamics. We describe four developmental stages of Pelagia noctiluca ephyrae and metaephyrae based on the progress of feeding structures and morphometric measurements on the central disc diameter and total body diameter. Size differs significantly among stages, but it can overlap substantially, suggesting that it is not always coupled with development progress due to different somatic growth. Morphological distinction of stages is biologically important because it implies different levels of food specialization and capture efficiency. We further report a 25% (±13 SD) shrinkage of ephyrae and metaephyrae after storage in 4% formaldehyde solution. This metric can be used in ecological studies focusing on size-related traits of field observed individuals.
... Pelagia noctiluca has been classified into five size classes using measurements of bell diameter: <1.0 cm; 1.0<3.5 cm (Immature medusa); 3.5<6.0 cm (Conditionally mature); 6.0<8.5 cm (Mature);>8.5 cm (Malej & Malej, 2004). ...
Article
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Seasonal dynamics of the scyphomedusa Pelagia noctiluca were studied along with their relation to certain environmental factors between the study period that extends from January 2018 to December 2019. During 2018, stranded individuals of P. noctiluca appeared throughout this year, but their high frequency was reported in the summer. While in contrast, P. noctiluca in 2019 was reported in a very low number only during the winter season and had not been detected in the other seasons of this year. The overall results revealed that the inter-annual variations in the abundance of jellyfish were not significantly (P<0.05) correlated with water temperature, relative humidity and atmospheric pressure. Our results showed easterly winds as a significant predictor of P. noctiluca strandings. The bell diameters of examined jellyfish ranged from 30 to 130 mm, with mean of 72 mm. Stranded mature jellyfish individuals as well as young ones were recorded throughout the year 2018. The size distribution indicated that P. noctiluca can reproduce all around the year, with its more intense activityduring the spring. The continuing presence of P. noctiluca in the Moroccan Mediterranean makes it necessary to set effective strategies in order to prevent and minimize their impact on economic activities.
... Goy et al. (1989) detected for P. noctiluca, through a long-term dataset, a cyclic trend of about 12 years in the western basin of the Mediterranean. In the late 1990s, persistent blooms occurred almost annually (Malej et al., 2004;Anonymous, 2008;Mariottini et al., 2008;Anonymous, 2010a;Daly Yahia et al., 2010), and P. noctiluca records began more frequent also in areas such as the Adriatic Sea where this species was relatively rare until the last 1970s (Zavodnik, 1987). ...
Article
The rise in water temperature in the Mediterranean Sea, and associated migrations of temperate marine biota, are occurring in the context of a global warming causing an expansion of the tropical jellyfish range, exacerbating jellyfish outbreaks linked to coastal development, nutrient loading, and overfishing. The gelatinous component of plankton is considered as ‘the dark side of ecology’ capable of appearing and disappearing at unpredictable times. In the last decade an increasingly high number of gelatinous plankton blooms are occurring and this makes us wonder if ‘a Mediterranean Sea full of jellyfish is a probable future’. The reasons for rising jellyfish blooms are, probably, manifold. Current studies are aimed to highlight how climatic change is interacting with the Mediterranean ecosystem favouring entrance, abundances and success of alien species and triggering ‘regime shifts’ such as from fish to jellyfish. Jellyfish damage the economic success of power plants, fish farms, tourism, and affect fisheries consuming larvae of commercial fish species. On the other hand, several studies were also taken into account on uses for jellyfish as biofuels and foods but more experimentation is needed to improve the first encouraging results.
... Equally, the process of strobilation in Aurelia has most frequently been correlated with changing temperature, irradiance and food supply, although no variable has been singled out as the major regulator (Lucas 2001;Purcell 2007;Holst 2012). Similar results have also been demonstrated in Rhizostoma pulmo and Cotylorhiza tuberculata (two of the most common Mediterranean native jellyfish species), presenting faster planulae settlement, increasing number of produced buds and new medusae (ephyrae) at higher temperatures (Kogovšek et al. 2010;Prieto et al. 2010;Astorga et al. 2012;Purcell et al. 2012;Ruiz et al. 2012) Outbreaks of Pelagia noctiluca, the most abundant jellyfish in the Mediterranean Sea, seem to be associated with warmer winters and cold summers (Malej & Malej 2004;Rosa et al. 2013). In P. noctiluca the metabolism is directly proportional to the temperature oscillations (Rottini Sandrini & Avian 1983;Malej et al. 1986;Morand et al. 1987). ...
Article
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Water temperature directly affects life cycles, reproductive periods, and metabolism of organisms living the oceans, especially in the surface zones. Due to the ocean warming, changes in water stratification and primary productivity are affecting trophic chains in sensitive world areas, such as the Mediterranean Sea. Benthic and pelagic cnidarians exhibit complex responses to climatic conditions. For example, the structure and phenology of the Mediterranean hydrozoan community displayed marked changes in species composition, bathymetric distribution, and reproductive timing over the last decades. The regional species pool remained stable in terms of species numbers but not in terms of species identity. When the Scyphozoa group is considered, we observe that Pelagia noctiluca (among the most abundant jellyfish in the Mediterranean Sea and eastern Atlantic waters) has increasingly frequent massive outbreaks associated to warmer winters. Variations in metabolic activities, such as respiration and excretion, are strongly temperature-dependent, with direct increment of energetic costs with jellyfish size and temperature, leading to growth rate reduction. Water temperature affects sexual reproduction through changes in the energy storage and gonad development cycles. Anthozoan life cycles depend also on primary productivity and temperature: gonadal production and spawning are tightly related in shallow populations (0-30 m depth) with the spring-summer temperature trends and autumn food availability. Overall, the energy transferred from the mother colonies to the offspring may decrease, negatively affecting their potential to settle, metamorphose and feed during the first months of their lives, eventually impairing the dominance of long-living cnidarian suspension feeders in shallow benthic habitats. In this review, we describe the already ongoing effects of sea warming on several features of cnidarian reproduction, trying to elucidate how reproductive traits and potential dispersion will be affected by the cascade effects of increasing temperature in the Mediterranean Sea.
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Pelagic cnidarians have been observed stranding annually in the Tetouanise Sea, a site of intense human recreation in northwest Morocco. The abundance and size of jellyfish stranded, between January 2018 and December 2020, on the beaches of the Moroccan Mediterranean were investigated. We present data on the temporal and spatial distribution of the species in relation to environmental variables (e.g., sea surface temperature, salinity, chlorophyll and wind direction). We also examined the negative impacts of jellyfish on human activities in the Moroccan Mediterranean. Five species that represented three scyphozoans and two hydrozoans were frequently observed: Pelagia noctiluca, Velella velella, Physalia physalis, Rhizostoma pulmo and Chrysaora hysoscella. Three different models of seasonal occurrence of jellyfish were identified in this study: (1) P. noctiluca appears throughout the year but with a higher frequency during the summer, (2) P. physalis and V. velella appear in March–May and (3) the late appearing R. pulmo and C. hysoscella from July to August. The abundance of jellyfish varied from season to season, but did not differ between sampling sites. Interannual variations in the abundance of jellyfish were not significantly correlated with the environmental factors examined. However, the east wind played an important role in the stranding and formation of hotspots for jellyfish in the Moroccan coast. Continuous monitoring is needed for a more profound knowledge on the jellyfish bloom dynamics and their potential impacts on ecosystem functioning and socioeconomic activities in the Moroccan Mediterranean.
Article
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One of the obstacles to detecting regional trends in jellyfish populations is the lack of a defined baseline. In the Adriatic Sea, the jellyfish fauna (Scyphozoa and Ctenophora) is poorly studied compared to other taxa. Therefore, our goal was to collect and systematize all available data and provide a baseline for future studies. Here we present phenological data and relative abundances of jellyfish based on 2010–2019 scientific surveys and a “citizen science” sighting program along the eastern Adriatic. Inter-annual variability, seasonality and spatial distribution patterns of Scyphomedusae and Ctenophore species were described and compared with existing historical literature. Mass occurrences with a clear seasonal pattern and related to the geographical location were observed for meroplanktonic Scyphomedusae Aurelia solida, Rhizostoma pulmo, and to a lesser extent Chrysaora hysoscella, Cotylorhiza tuberculata and Discomedusa lobata. Holoplanktonic Pelagia noctiluca also formed large aggregations, which were seasonally less predictable and restricted to the central and southern Adriatic. Four species of Ctenophora produced blooms limited to a few areas: Bolinopsis vitrea, Leucothea multicornis, Cestum veneris and the non-native Mnemiopsis leidyi. However, differences between Adriatic subregions have become less pronounced since 2014. Our results suggest that gelatinous organisms are assuming an increasingly important role in the Adriatic ecosystem, which may alter the balance of the food web and lead to harmful and undesirable effects.
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Full-text available
Over the last two centuries, massive outbreaks of Pelagia noctiluca were recorded on average at 12 years intervals in certain parts of the Mediterranean Sea. Population peaks of Pelagia noctiluca were sometimes accompanied by an expansion outside its usual distribution range, and during 1977-1986 this jellyfish also populated the northern Adriatic Sea. After maintaining itself at rather high densities for several consecutive years, the Pelagia noctiluca population collapsed rather abruptly and for no obvious reason. Environmental conditions before, during and after the invasion of Pelagia noctiluca to the northern Adriatic are described. A model using time series analysis (1984-1986) of its population size structure was utilized to simulate the abundance of this jellyfish in the northern Adriatic. Results of this modelling exercise indicate that the most important effect on Pelagia population density was maturation at an early age (thus, at smaller size). The incorporation of demographic parameters such as shrinkage (regression and recovery to sexual maturity) into the model was the second most important factor for simulating its population abundance.
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The data for several parameters related to eutrophication, collected in the period 1966-1995 in open waters, were analyzed and compared with changes of the Po River flow-rate. The data were grouped in typical seasons, periods, and subareas, characterized by different dominant relevant processes. During the period 1969-1992, the flow-rate in spring was on average higher than in the previous period, and that the autumn peak shifted from November to October. Further, significant fluctuations of primary production in the open northern Adriatic have occurred since the 1970s, caused by variations of the nutrient load and oceanographic conditions.
Conference Paper
The issue of irregular massive plankton events is characterised by rather high scientific uncertainty mainly due to multiple linkages between causes and effects, but also to lack of evidence and to our inability to monitor these events at proper spatial and temporal scales. Many scales of variability that make definition of "regularity" rather difficult typify plankton dynamics. Irregular plankton events may be defined as those that show spatial and/or temporal patterns that deviate from those commonly observed. In many cases, even in marine systems where plankton have been studied for over a century like in the northern Adriatic, some important patterns are still dubious. Limited knowledge of plankton fluctuations and insufficient understanding of underlying processes make valuation of irregular and/or massive events troublesome. Irregularity of plankton events is in many cases judged from an anthropocentric point of view and public perception is that these phenomena are getting more frequent. Very often, especially in coastal marine environments, nutrient overload, i.e. eutrophication, is blamed not only for harmful algal blooms but also for other massive plankton events. Exceptional events associated with phytoplankton like discoloured waters, toxic algae or mucilage accumulations (gelatinous masses) in the northern Adriatic are a matter of great environmental concern. These problems were among priority subjects in the national marine research programmes of the Adriatic countries and in major EU funded projects (Hopkins et al., 1999). Zooplankton massive events have received limited research attention with the exception of the extraordinary abundance of stinging jellyfish Pelagia noctiluca (UNEP, 1991). Yet, massive presence of plankton organisms may have profound ecological impacts such as changes in community structure and functioning, and loss of biodiversity. Additionally, they may affect different human activities (fisheries, tourism) and pose serious health risk for humans. A survey of massive plankton events, generated by larger zooplankton in the northern Adriatic during the last 30 years, is presented. Outbreaks of red tides caused by massive presence of het-erotrophic dinoflagellate Noctiluca miliaris and mucilage accumulations were also included. The survey is based on our own observations (published and unpublished) and those reported in scientific literature. An attempt was done to relate these irregular plankton events to shifts in the trophic status of the northern Adriatic ecosystem. In their analysis of long-term changes in the northern Adriatic ecosystem related to anthropogenic eutrophication, Degobbis et al. (2000) revealed a significant increase of eutrophication that occurred during the 70's, reaching maximum in the early 80's. They also indicated that eutrophication was diminishing since the late 80's. On the basis of these findings our data on massive plankton events for the last 30 years were grouped into three periods:
Book
Because of its centrallocation in the Old World, the Adriatic Sea has long been explored and studied. Modern methods of investigation, however, have accelerated the pace of study during the last decade. These are the ADCP currentmeter, satellite imagery, drifter technology, and, last but not least, the computer with its arsenal of tools for data analysis and model simulations. As a result of this renaissance, the Adriatic Sea and its sub-basins are currently the object of intensified scrutiny by a number of scientific teams, in Europe and be­ yond. Questions concerning the mesoscale variability that dominates regional motions, the seasonal circulation of the sea, and its long-term climatic role in the broader Mediterranean, have become topics of lively discussions. The time was ripe then when an international workshop dedicated to the physical oceanography of the Adriatic Sea was convened in Trieste on 21-25 September 1998. Its objectives were to assess the current knowledge of the oceanography of the Adriatic Sea, to review the newly acquired observations, to create syn­ ergy between model simulations and observations, and to identify directions for future Adriatic oceanography. This book, however,is not the mere proceedings of the workshop. It was written as a monograph synthetizing the current knowledge of the physical oceanography of the Adriatic Sea, with the hope that it will serve as a reference to anyone interested in the Adriatic. The book also identifies topics in need of additional inquiry and proposes research directions for the next decade.
Article
Summary Laboratory tests have been performed, on the behavior of the jellyfishPelagia noctiluca as a function of the water temperature. It has been found that the usual contractions of the umbrella are almost completely missing at 6°C; they begin to appear at about 7–8°C and they reach frequencies of about 10 and 40 per min at 11 and 15°C respectively. An ambient temperature of about 11°C appears to be a threshold value below which this kind of medusa ceases to move actively and sinks, while at higher temperatures it gradually begins to shift, showing a positive thermotropism in the presence of temperature gradients greater than about 0.01 °C/cm.
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Models of population dynamics based on age-related parameters do not provide accurate predictions if within-age-class variance in those parameters is high. Often the demographic fate of an individual or population may be predicted more accurately using size rather than age classifications. A general model of size-related population dynamics is here designed to include processes, such as fragmentation and shrinkage, which are excluded from conventional age-related demographic analysis. The parameters of the model were measured in a study of a colonial, sessile coral. Differences in individual rates of growth and shrinkage resulted in huge long- term variations in calculated colony size, fecundity and mortality rates between corals of equal age. Individuals of the same age thus have widely differing probabilities of obtaining representation in subsequent generations. Population growth was simulated by adding a constant number of juvenile corals every year to the smallest size class. Although the model has no density-dependent parameters, population growth stops. The population size attained depends on the number of settling juveniles. Local populations of sessile organisms may be regulated by larval input, as well as by recurring disturbances or density-dependent interactions.-from Author