Seasonal changes in the population dynamics of Aurelia aurita in Thau lagoon

Seasonal dynamics of the scyphomedusae, Aurelia aurita, was investigated twice a month from January 2010 to June 2011 and related to environmental conditions in Thau lagoon, southwestern Mediterranean Sea. Strobilation, indicated by the presence of 1 mm ephyrae, occurred from November to the middle of April. Maximum abundances up to 330 ind.100 m-3 were reached in May 2011, few weeks after the last ephyrae release. The population declines afterwards steadily until disappearing from the water column. Concurrent with increased water temperature and mesozooplankton predation during May, growth rates increased from 0.04 mm.day-1 to a peak of 4.5 mm.day-1, with a maximum bell diameter of 11.3 cm reached on the 7th May. During the study period, there was no advection of A. aurita between Thau lagoon and the coastal waters

Centropages Kroyeri egg production rate as a function of lagoon summer conditions

EnDaily egg production of the neritic calanoid copepod Centropages kroyeri was measured from 4 to 23 August 2003 at a site in North lagoon of Tunis and related to summer environmental variables and food availability. Food availability was evaluated by assuming a direct correlation with concentrations of the Chlorophyll a (Chl a), the particulate organic carbon (POC), and some easily extractable macromolecular compounds such as proteins, carbohydrates and lipids, from the seston. The egg production Rate (EPR) was estimated by incubating mature females with natural filtered seawater. The EPR of Centropages kroyeri ranged from 4.2 (± 2.5) to 8.4 (± 6.2) eggs female–1 day–1. This value was positively affected by salinity (r = 0.501, P<0.01). Among indices of food availability, only seston proteins were positively correlated (r = 0.840, P<0.0001) with the daily EPR of the species

Jellyfish Stings Trigger Gill Disorders and Increased Mortality in Farmed Sparus aurata (Linnaeus, 1758) in the Mediterranean Sea

none8siJellyfish are of particular concern for marine finfish aquaculture. In recent years repeated mass mortality episodes of farmed fish were caused by blooms of gelatinous cnidarian stingers, as a consequence of a wide range of hemolytic, cytotoxic, and neurotoxic properties of associated cnidocytes venoms. The mauve stinger jellyfish Pelagia noctiluca (Scyphozoa) has been identified as direct causative agent for several documented fish mortality events both in Northern Europe and the Mediterranean Sea aquaculture farms. We investigated the effects of P. noctiluca envenomations on the gilthead sea bream Sparus aurata by in vivo laboratory assays. Fish were incubated for 8 hours with jellyfish at 3 different densities in 300 l experimental tanks. Gill disorders were assessed by histological analyses and histopathological scoring of samples collected at time intervals from 3 hours to 4 weeks after initial exposure. Fish gills showed different extent and severity of gill lesions according to jellyfish density and incubation time, and long after the removal of jellyfish from tanks. Jellyfish envenomation elicits local and systemic inflammation reactions, histopathology and gill cell toxicity, with severe impacts on fish health. Altogether, these results shows P. noctiluca swarms may represent a high risk for Mediterranean finfish aquaculture farms, generating significant gill damage after only a few hours of contact with farmed S. aurata. Due to the growth of the aquaculture sector and the increased frequency of jellyfish blooms in the coastal waters, negative interactions between stinging jellyfish and farmed fish are likely to increase with the potential for significant economic losses.Bosch-Belmar, Mar; M'Rabet, Charaf; Dhaouadi, Raouf; Chalghaf, Mohamed; Daly Yahia, Mohamed Néjib; Fuentes, Verónica; Piraino, Stefano; Kéfi-Daly Yahia, OnsBosch Belmar, Mar; M'Rabet, Charaf; Dhaouadi, Raouf; Chalghaf, Mohamed; Daly Yahia, Mohamed Néjib; Fuentes, Verónica; Piraino, Stefano; Kéfi Daly Yahia, On

Jellyfish diversity, trends and patterns in Southwestern Mediterranean Sea: a citizen science and field monitoring alliance

Jellyfish (Cnidaria and Ctenophora) are an essential component of marine ecosystems and represent a potential effect, positive or negative, for several economic activities. Jellyfish blooms and non-indigenous species (NIS) introduction can shift ecological community structure and energy transfer. Despite their importance in ecosystem function and services, knowledge of jellyfish fauna diversity and phenology are largely lacking for the southern Mediterranean Sea. Here, we present an overview of the current state of jellyfish biodiversity in Tunisia. Based on a comprehensive literature survey, historical records and unpublished data, 66 jellyfish species, including 11 non-indigenous species, have been recorded in Tunisia between 1994 and 2020. Additionally, based on field surveys and a citizen science sighting program between 2004 and 2020, we present data on the spatial distribution of 13 conspicuous jellyfish taxa and the phenology of the eight most frequently detected species (Aurelia solida, Cotylorhiza tuberculata, Pelagia noctiluca, Phyllorhiza punctata, Rhizostoma pulmo, Rhopilema nomadica, Olindias muelleri and Velella velella) in Tunisian two ecoregions, the Western Mediterranean and the Tunisian Plateau. The 17 year survey showed a shift in R. pulmo, A. solida and P. noctiluca phenology. Additionally, citizen science revealed an increase in the spatial range of P. punctata (NIS) and the distinct phenologies of populations in the two ecoregions

Population dynamics and predatory impact of the alien jellyfish Aurelia solida (Cnidaria, Scyphozoa) in the Bizerte Lagoon (southwestern Mediterranean Sea)

Understanding the life cycle strategies and predatory impact of alien jellyfish species is critical to mitigate the impact these organisms may have on local populations, biodiversity, and ultimately on the functioning of food webs. In the Mediterranean Sea, little is known about the dynamics of alien jellyfish, although this area is a biodiversity hotspot and one of the most threatened by an increasing number of alien jellyfish. Here, we investigated the population dynamics and predatory impact of a non-indigenous scyphomedusa, Aurelia solida Browne 1905, in the Bizerte Lagoon, Tunisia. The study was based on a bimonthly survey performed over two consecutive years, from November 2012 to August 2014. Field observations showed that the planktonic phase of A. solida occurs from winter to early summer. Prey composition was investigated by means of gut content and field zooplankton analyses. Calanoid copepods, mollusc larvae and larvaceans represented the main food items of A. solida. To determine the jellyfish feeding rate and their predatory impact on zooplankton populations, the digestion time for zooplankton prey was assessed at three different temperatures: 13, 18 and 23 °C in laboratory conditions, corresponding to the average range of temperatures encountered by A. solida in the Bizerte Lagoon. We found that A. solida consumed 0.5–22.5% and 0.02–37.3% of the daily zooplankton standing stock in 2013 and 2014, respectively. These results indicate a non-negligible but restricted seasonal grazing impact on some mesozooplankton groups, explained by the relatively short lifespan of the medusa stage (5–6 months)

The invasive tropical scyphozoan Rhopilema nomadica Galil, 1990 reaches the Tunisian coast of the Mediterranean Sea

The alien Erythraean jellyfish Rhopilema nomadica was first recorded in Tunisia waters (Gulf of Gabes) in 2008. Subsequently it was sighted in the Bizerte Channel and Gulf of Tunis where it has been regularly observed since 2010 during summer and autumn months.peer-reviewe

Distribution of resting cysts of the potentially toxic dinoflagellate Alexandrium pseudogonyaulax in recently-deposited sediment within Bizerte Lagoon (Mediterranean coast, Tunisia)

This study investigated the spatial distribution of Alexandrium pseudogonyaulax resting cysts in recently deposited sediment of Bizerte lagoon (South-Western Mediterranean, Tunisia). This lagoon is the subject of many anthropogenic impacts, such as holding important fishing and aquaculture activities. A. pseudogonyaulax has been shown to produce Goniodomin A, which is a biologically-active compound. We showed that this dinoflagellate produces two types of resting cysts, which could be distinguished by the presence or the absence of a paratabulate wall. The average cyst density across the whole lagoon was rather high, reaching 639 cysts g1 of dry sediment (DS). Cyst densities varied widely among the sampled stations, with the highest density of 1685 cyst g1 DS being recorded at station 51 near a mussel farm. With respect to sediment characteristics, the highest cyst densities were found within silty sediments with high water content values. The distribution of A. pseudongoyaulax cysts in Bizerte lagoon appears to be related to hydrodynamic factors.peer-reviewe

Do the levels of industrial pollutants influence the distribution and abundance of dinoflagellate cysts in the recently-deposited sediment of a Mediterranean coastal ecosystem?

We studied the relationships between sediment industrial pollutants concentrations, sediment characteristics and the dinoflagellate cyst abundance within a coastal lagoon by investigating a total of 55 sampling stations within the Bizerte lagoon, a highly anthropized Mediterranean ecosystem. The sediment of Bizerte lagoon is char- acterized by a high dinocyst abundance, reaching a maximum value of 2742 cysts·g−1 of dry sediment. The investigated cyst diversity was characterized by the presence of 22 dominant dinocyst morphotypes belonging to 11 genera. Two dinoflagellate species dominated the assemblage: Alexandrium pseudogonyaulax and Protoperidinium claudicans, representing 29 to 89% and 5 to 38% of the total cyst abundance, respectively, depending on the station. Seven morphotypes belonging to potentially toxic species were detected, including Alexandrium minutum, A. pseudogonyaulax, Alexandrium catenella/tamarense species complex, Lingulodinium polyedrum, Gonyaulax cf. spinifera complex, Prorocentrum micans and Protoceratium reticulatum. Pearson correlation values showed a positive correlation (α = 0.05) between cyst abundance and both water content and fine silt sediment content. Clustering revealed that the highest abundance of cysts corresponds to stations presenting the higher amounts of heavy metals. The simultaneous autoregressive model (SAM) highlighted a significant correlation (α = 0.05) between cyst accumulation and two main factors: sediment water content and sediment content for several heavy metals, including Hg, Cd, Cu, Ni and Cr. These results suggest that the degree of heavy metal pollution could influence cyst accumulation patterns.peer-reviewe