Environmental Control of Phase Transition and Polyp Survival of a Massive-Outbreaker Jellyfish

A number of causes have been proposed to account for the occurrence of gelatinous zooplankton (both jellyfish and ctenophore) blooms. Jellyfish species have a complex life history involving a benthic asexual phase (polyp) and a pelagic sexual phase (medusa). Strong environmental control of jellyfish life cycles is suspected, but not fully understood. This study presents a comprehensive analysis on the physicochemical conditions that control the survival and phase transition of Cotylorhiza tuberculata; a scyphozoan that generates large outbreaks in the Mediterranean Sea. Laboratory experiments indicated that the influence of temperature on strobilation and polyp survival was the critical factor controlling the capacity of this species to proliferate. Early life stages were less sensitive to other factors such as salinity variations or the competitive advantage provided by zooxanthellae in a context of coastal eutrophication. Coherently with laboratory results, the presence/absence of outbreaks of this jellyfish in a particular year seems to be driven by temperature. This is the first time the environmental forcing of the mechanism driving the life cycle of a jellyfish has been disentangled via laboratory experimentation. Projecting this understanding to a field population under climatological variability results in a pattern coherent with in situ records

Mediterranean Jellyfish Venoms: A Review on Scyphomedusae

The production of natural toxins is an interesting aspect, which characterizes the physiology and the ecology of a number of marine species that use them for defence/offence purposes. Cnidarians are of particular concern from this point of view; their venoms are contained in specialized structures–the nematocysts–which, after mechanical or chemical stimulation, inject the venom in the prey or in the attacker. Cnidarian stinging is a serious health problem for humans in the zones where extremely venomous jellyfish or anemones are common, such as in temperate and tropical oceanic waters and particularly along several Pacific coasts, and severe cases of envenomation, including also lethal cases mainly induced by cubomedusae, were reported. On the contrary, in the Mediterranean region the problem of jellyfish stings is quite modest, even though they can have anyhow an impact on public health and be of importance from the ecological and economic point of view owing to the implications on ecosystems and on some human activities such as tourism, bathing and fishing. This paper reviews the knowledge about the various aspects related to the occurrence and the stinging of the Mediterranean scyphozoan jellyfish as well as the activity of their venoms

Effects of the tsunami of 26 December 2004 on Rasdhoo and northern Ari atolls, Maldives

Volume: 544Start Page: 93End Page: 10

Episodio di mortalit\ue0\ua0 in pesci delle isole Maldive

Scopo della ricerca \ue8 stato individuare l\u201feziologia di due episodi di elevata mortalit\ue0 verificatisi nell\u201festate e nel mese di dicembre 2007 in pesci di alcuni atolli delle isole Maldive. Sui campioni ittici pervenuti in laboratorio sono stati condotti esami necroscopici, parassitologici, batteriologici ed istopatologici. Sono stati esaminati 1 Scarus ghobban (Scaridae), 1 Aphareus sp. (Lutjanidae), 11 Odonus niger (Balistidae) spiaggiati e 2 esemplari moribondi di quest\u201fultima specie. Sono state inoltre condotte indagini tossicologiche per la ricerca di arsenico, cadmio, cromo, mercurio e piombo. Al verificarsi della mortalit\ue0 sono stati rilevati i parametri ambientali: temperatura, ossigeno disciolto, pH e conducibilit\ue0 elettrica. L\u201fesame parassitologico ha evidenziato la presenza di metacercarie di Trematodi Digenei nel cristallino e di un nematode a livello intestinale in Aphareus sp., e di crostacei Copepodi a livello branchiale e Microsporidi a livello renale in O. niger. L\u201fesame batteriologico ha permesso l\u201fisolamento di Streptococcus iniae in S. ghobban e in Aphareus sp. All\u201fesame virologico, condotto mediante RT-PCR, solo S. ghobban \ue8 risultato positivo per Betanodavirus. All\u201fesame istopatologico, sebbene fossero presenti fenomeni degenerativi post-mortali, sono state osservate alla colorazione di Gram, in S. ghobban e in un soggetto di O. niger, piccole colonie batteriche Gram positive di forma ovoidale o sferica disposte a catenella, riferibili a streptococchi. L\u201fesame tossicologico ha evidenziato livelli di metalli pesanti nella norma. I parametri ambientali rientravano anch\u201fessi nella norma: temperatura 27,2-29,0\ub0C, pH 8,2, conduttivit\ue0 49,66-50,9 mS/cm, ossigeno disciolto 5,3-5,9 mg/l. La presenza dei parassiti nei pesci esaminati a bassi livelli d\u201finfestazione, cos\uec come il riscontro di Betanodavirus in un unico soggetto, non sarebbero responsabili dell\u201fepisodio morboso osservato. L\u201fisolamento di Streptococcus iniae appare invece interessante in quanto rappresenterebbe uno dei patogeni di pi\uf9 importante riscontro nelle specie ittiche sia dulciacquicole che marine. Dai risultati ottenuti si pu\uf2 evincere quindi che l\u201fagente eziologico responsabile del grave episodio di mortalit\ue0 descritto possa essere S. iniae in associazione con altri fattori biotici e abiotici; inoltre essendo agente di zoonosi si rendono necessarie ulteriori indagini sulla presenza di questo patogeno nelle acque delle isole Maldive alla luce dell\u201festrema importanza delle attivit\ue0 turistiche di queste aree geografiche