Purification, Toxicity and Functional Characterization of a New Proteinaceous Mussel Biotoxin from Bizerte Lagoon

The marine environment is known to be occupied by microorganisms. The potential toxicity of some of these marine microorganisms, that are capable of producing unknown biotoxins, has always been underestimated. Indeed, these biotoxins may be a threat to human health through the consumption of contaminated seafood and fish. For more than ten years, recurrent but atypical toxicity has been detected in mussels from Bizerte lagoon (North of Tunisia) during routine tests. In this study, we have isolated and characterized a new proteinaceous marine biotoxin, named Mussel Toxic Peptide (MTP). Using HPLC, electrophoresis and LC/MS studies, we showed that MTP has a protein characteristic UV-spectrum, can be visualized by protein specific reagents such as Coomassie, and has a molecular mass of 6.4 kDa. Patch-clamp experiments performed on cultured N18 neuroblastoma cells revealed that MTP (0.9–18 µM) markedly inhibited voltage-gated Na current, but was about 23 times less active in blocking voltage-gated K current at equimolar concentrations. To the best of our knowledge, this is the first time that a proteinaceous marine biotoxin with relatively high molecular mass is isolated and involved in the contamination of mussels harvested from shellfish farming areas.

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).

Inventory and new records of benthic amphipods from macrophytes and fine sand communities of the Bizerte lagoon (Tunisia, SW Mediterranean Sea)

Shallow water benthic communities from the Bizerte lagoon (northern Tunisia) were investigated at 33 stations sampled in April and July of 2016 and 2017. A total of 18 amphipod species were recorded among which two new species were recorded: one for Tunisian coasts (Jassa marmorata) and a second one for the Mediterranean Sea (Serejohyale spinidactylus). In addition, and compared to previous studies, nine amphipod species were collected for the first time in this lagoon. Amphipod assemblages were numerically dominated by the families Melitidae (28%), Caprellidae (14.5%) and Ampithoidae (11.7%). Three species: Cymadusa filosa, Dexamine spinosa and Elasmopus rapax were numerically dominant. According to their biogeography, most of the recorded amphipod species (11–18) showed an Atlantic–Mediterranean distribution, whereas four were cosmopolitan and three lessepsian Indo-Pacific migrants, but no species were Mediterranean endemic. Specimens of both Jassa marmorata and Serejohyale spinidactylus are illustrated and described.