Fish assemblages along the coasts of Tunisia: a baseline study to assess the effectiveness of future Marine Protected Areas

The present study investigated coastal fish assemblages, using Underwater Visual Census (UVC) transects, in Tunisia (south Mediterranean basin). The rationale behind this work is to get i) a suggestive evidence about the status of fish assemblages, and ii) baseline data at 3 locations in Tunisia where 3 MPAs will be established, before the implementation of protection measures. At each location, we used a sampling design where fish censuses were performed in two types of zone: zones that will be inside MPAs, and zones that will remain outside. On the whole, 49 taxa belonging to 19 families were censused. Data reveal clear symptoms of overfishing, especially in terms of dominance of small- and medium-sized individuals of commercially relevant species. Our analyses, moreover, did not show any significant difference in whole fish assemblage structures (considering both density and biomass), patterns of average species richness, total fish density and biomass, density and biomass of different trophic categories of fishes, size distribution of commercially relevant species, between future-protected and unprotected zones. Overall, results suggest that 1) current fish assemblages at the three studied locations are likely to be seriously impacted by fishing activities, and 2) these data could be used as reliable baselines to assess the effectiveness of protection measures within the MPAs that will be established in the future. Our study is the first in Tunisia, and in North African coasts, that assessed distribution patterns of coastal fish assemblages by means of UVC, using a formal spatially replicated sampling design for resource management

Tunisian reservoirs : diagnosis and biological potentialities

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Using a three-isotope Bayesian mixing model to assess the contribution of refuse dumps in the diet of the yellow-legged gull Larus michahellis

SUMMARY.¿ The yellow-legged gull Larus michahellis is usually considered as an opportunistic species that depends on food derived from anthropogenic activity, such as garbage and fishery discards. However, although it has become a problematic species in many Mediterranean countries, there is stillno information about its status in Tunisia. The aim of this work was to assess the differential use of marine and terrestrial resources by the yellow-legged gulls breeding in an urban area on Chikly Island. Dietary reconstructions were performed through the analysis of regurgitates and δ13C, δ34S and δ15N of feathers of fledglings. Contrary to most Mediterranean breeding colonies, and to our expectations, the mixing model showed that yellow-legged gulls from Chikly are above all marine foragers. Whereas the Lake of Tunis was the principal source of food in 2005 and 2007, chicks from 2006 were fed mainly with prey from the Gulf of Tunis. Although the Gulf is located further from the breeding colony and has less fishing activity than the Lake, our study demonstrated that it is used as an alternative foraging habitat. The Bayesian mixing model approach proved to be a useful tool for evaluating temporal variations in the feeding ecology of the colony, which is relevant information in the management of a wild species. This study also demonstrated the importance of isotopic variability among years for inferring diet diversity and food availability for the colony, thereby allowing demographic forecasts when trophic resources vary in abundance or the foraging habitat is disturbed

Distribución y abundancia de los primeros estadios de desarrollo de Sardina pilchardus en el golfo de Túnez (Mediterráneo central) en relación con los factores ambientales

Four seasonal surveys were carried out in the Gulf of Tunis between summer 2002 and spring 2003 to study the abundance and distribution of Sardina pilchardus eggs and larvae in relation to environmental parameters. In the Gulf of Tunis, Sardina pilchardus begins spawning in autumn (23 eggs/10 m²) and attains its peak in winter (257 eggs/10 m²) when the mean SST is lowest (13.4°C). Sardine reproduction seems to be triggered by the decrease in the SST. In winter, the main spawning areas were located to the south of Zembra Island and the north of Cape Bon. Larvae were more abundant in winter (38 larvae/10 m²), while lower densities were collected in autumn and spring (1 larva/10 m²). The highest abundance of larvae (288 larvae/10 m²) was recorded southwest of Zembra Island. Eggs and larvae were mainly concentrated in the relatively warmer and saltier waters with high zooplankton abundance and, inversely, with a low concentration of nitrate and chlorophyll a and a low diatom abundance.Se llevaron a cabo cuatro campañas en el golfo de Túnez, entre verano del 2002 y primavera del 2003, con el objetivo de estudiar la abundancia y distribución de los huevos y larvas de Sardina pilchardus en relación con parámetros ambientales. En el golfo de Túnez Sardina pilchardus inicia la freza en otoño (23 huevos/10 m²), alcanzando el pico de puesta en invierno (257 huevos/10 m²), cuando la temperatura superficial media (SST) es mínima (13.4°C). La reproducción de la sardina se dispara al parecer por el descenso de la SST. En invierno, las principales áreas de puesta se localizaron al sur de la isla de Zembra y en el norte del Cabo Bon. Las larvas fueron más abundantes en invierno (38 larvas/10 m²); mientras que se recogieron menores densidades en otoño y primavera (1 larva/10 m²). La mayor abundancia larvaria (288 larvas/10 m²) fue observada en el suroeste de la isla de Zembra. Los huevos y larvas se concentraron principalmente en las aguas relativamente más cálidas y salinas, con altas abundancias de zooplancton, e inversamente bajas concentraciones de nitrato, clorofila a y abundancia de diatomeas

Combining ecosystem indicators and life cycle assessment for environmental assessment of demersal trawling in Tunisia

The approach consisted of conducting LCA and calculating ecosystem indicators to provide a complete assessment of trawling’s environmental impacts and the ecosystem characteristics associated with seafood production. The functional unit for the LCA was set to 1 t of landed seafood, and system boundaries included several operational stages related to demersal trawling. Several ecosystem indicators from EwE were calculated. Demersal trawling in the exploited ecosystem of the Gulf of Gabes (southern Tunisia) was used as a case study to illustrate the applicability of the approach. Several management plans were simulated and their influence on environmental performance was assessed. Ecospace, the spatial module of EwE, was used to simulate management scenarios: establishment of marine protected areas, extension of the biological rest period, and decrease in the number of demersal trawlers

Variabilité du phytoplancton en relation avec les facteurs environnementaux dans un lac salé temporaire

To establish a relationship between environmental variables and phytoplankton dynamics, physicochemical characteristics and phytoplankton sampling were performed in Sabkhet El Adhibet (Southeastern Tunisia) monthly from November 2005 to April 2006 and from November 2006 to April 2007 (the site dries annually between May and late October). All measured water quality variables showed considerable seasonal variation, and quantitative and qualitative differences in phytoplankton communities were recorded. The maximum phytoplankton density was recorded in January 2006, whereas lowest values occurred in November 2006. Sixteen species belonging to 6 orders were recorded, among which diatoms (52.1 %) and chlorophytes (39.8 %) were the most abundant. The correlation analysis between phytoplankton (density and composition) and abiotic variables revealed that orthophosphate is the major factor affecting the phytoplankton dynamics, and there were no correlation between phytoplankton and all the other environmental parameters. The PCA analysis of the phytoplankton composition and density revealed two main PCA axis explaining 82.99 % of the variance. The first axis was associated with diatoms, cryptophytes, euglenophytes, dinophytes and total phytoplankton, with a contribution of 21.8, 21.6, 21.3, 17.4 and 17.4 %, respectively. The second axis was correlated with chlorophytes (55.3 %) and cyanobacterias (26.3 %)Dans ce travail, afin de déterminer l'impact des différentes variables environnementales sur le phytoplancton dans un milieu hypersalé, un suivi des paramètres abiotiques et biotiques a été réalisé au niveau de Sabkhet El Adhibet (sud-est Tunisien), durant les périodes allant de novembre 2005 à avril 2006 et de novembre 2006 à avril 2007 (le site étant sec entre le début du mois de mai et la fin du mois d'octobre). Les résultats obtenus ont permis l'identification de 16 espèces de phytoplancton, appartenant aux groupes des diatomées, chlorophycées, dinophycées, euglénophycées, cryptophycées et cyanobactéries. La plus grande densité microalgale a été observée en décembre 2005 et janvier 2006 avec respectivement 8,6 et 14,6 106 cellules.L-1, alors que la plus petite densité a été enregistrée en novembre 2006 avec 0,19 106 cellules.L-1. L'analyse de la composition en phytoplancton révèle que ce sont les diatomées et les chlorophycées qui présentent la fraction la plus importante du phytoplancton, avec respectivement un maximum de 97,8 % (novembre 2006) et 95,7 % (janvier 2007). Le pourcentage moyen décroissant, relatif à chaque groupe de phytoplancton, de toute la période d'investigation est comme suit: diatomées (52,1 %), chlorophycées (39,8 %), dinophycées (3,2 %), euglénophycées (3 %), cryptophycées (1,1 %) et cyanobactéries (0,8 %). Toutefois, nous remarquons une grande variation mensuelle de la composition phytoplanctonique avec les diatomées et les chlorophycées présentes au niveau de tous les échantillons, tandis que les dinophycées, les euglenophycées et les cryptophycées sont absentes au niveau de nos échantillons durant certaines périodes de l'année. L'étude de la corrélation, entre la composition et la densité des phytoplanctons avec les différents paramètres abiotiques, montre que c'est l'orthophosphate qui affecte le plus la dynamique et la variation phytoplanctonique dans le milieu. Par ailleurs, aucune corrélation n'a été observée entre le phytoplancton et les autres paramètres environnementaux

Áreas de puesta y distribución larvaria de anchoa Engraulis encrasicolus en relación con las condiciones ambientales en el Golfo de Túnez (Mediterráneo Central)

Early life stages of anchovy were investigated in the Gulf of Tunis by means of four seasonal surveys carried out from summer 2002 to spring 2003. Anchovy eggs and larvae were found all year round, but they were much more abundant in spring and summer. In spring, the main spawning area was located in the north of the Gulf, to the west and southwest of Zembra Island. In summer, higher egg and larva abundances were also observed to the southwest of Zembra Island, but secondary spawning grounds were detected in the vicinity of the mouths of the Rivers Majreda and Meliane. No direct correlations between sea surface temperature (SST), salinity (SSS) and chlorophyll a and the horizontal distribution of eggs and larvae were observed. However, egg distributions in all seasons and larval distributions in summer and autumn were significantly related to depth. The temporal variation of temperature seems to control the spawning intensity and the beginning of spawning seems to be triggered by the increase in SST.Se estudiaron los huevos y larvas de anchoa en el Golfo de Túnez por medio de cuatro campañas estacionales llevadas a cabo entre verano del 2002 y primavera del 2003. Los huevos y larvas de anchoa se encontraron a lo largo de todo el año; pero fueron mucho más abundantes en primavera y verano. En primavera, la principal área de puesta se localizó en el norte del Golfo, al oeste y suroeste de la isla de Zembra. En verano, las mayores concentraciones de huevos y larvas también se encontraron en el suroeste de la isla de Zembra; pero se detectaron áreas de puesta secundarias cerca de las desembocaduras de los ríos Majreda y Meliane. No se encontraron correlaciones directas entre la temperatura superficial (SST), la salinidad (SSS) y la clorofila a y la distribución horizontal de huevos y larvas de anchoa. Sin embargo, la distribución de huevos, durante todo el año, y las distribuciones larvarias, en verano y otoño, se relacionaron de forma significativa con la profundidad. La variación temporal de la temperatura parece controlar la intensidad de la puesta y el inicio de la freza parece dispararse por el incremento de la SST

Tunisian reservoirs: diagnosis and biological potentialities

Due to scarcity, irregular rainfall and increasing water demand, several reservoirs have been built in recent decades in Tunisia to meet water needs for essential uses, which is generally done without analysis of their capacity to maintain a high quality of aquatic life and equitable distribution of water resources. Currently, 90% of available water resources are already mobilized and climate change exacerbates the country's aridity which makes it difficult to monitor water needs. With a view to contributing to their effective management and setting future directions for controlling and improving inland fish productivity, a comparative limnological study was carried out on 8 artificial reservoirs that were stocked with mullet fry. This study, based on a review of existing data, provides information on the availability and quality of inland water resources in relation to international standards and the biological potential (plankton, fish and other organisms) of these reservoirs. The satisfactory water quality for aquatic life, as well as the significant growth and production of introduced species associated with the rearing of mullet fry, clearly show that, despite several problems, Tunisian reservoirs represent an important potential that still needs to be developed. To this end, we recommend to improve the fishing techniques and the stocking of mullet fry. In addition, the strengthening of fishermen's groups, the encouragement of private initiative and the quality control of water and fish meat are highly requested

Mugilids fisheries of Tunisian coasts and lagoons

With its 1300 km coastline and 110 000 ha of coastal lagoons, Tunisia offers important resources to demersal and pelagic fisheries. Among all the exploited fish species in Tunisia, mugilids are the most widespread. They are known in temperate, subtropical and tropical regions, and occur both in coastal areas, lagoon ecosystems and inland waters. Six mugilids species have been inventoried in Tunisia. Their migratory behavior consists of moving back and forth between brackish and saline environment where they spend a large part of their life cycles. This behavior results in a peculiar high vulnerability to human pressure. Consequently, they require special attention from fisheries managers for sustainable catches. This study was based on the data from the national fishing and aquaculture directorate (DGPA) statistics, and comprised time series from 1995 to 2015. We looked for clear tendencies and correlations between harvest from the coastal sea and lagoons of the different coastal regions, in relation to recruitment in coastal marine waters. We focused on two species, i.e. Mugil cephalus and Liza aurata, which are best appreciated for local consumption and, therefore, most targeted by the fishery in Tunisia. The Tunisian lagoons show a decreasing trend in mugilids landings. This may be explained by the disturbance of migratory ways and the degradation of the coastal habitats, by the harvest of fry used for the inland water-stocking program, and by the multiplication of droughts. Particularly the latter strongly limits the migration of juveniles. The harvest in the coastal zones is relatively stable, follows perfectly the total national landings, with although a clear increase since 2011 as a result of uncontrolled illegal fishing. The negative correlation between the total harvests of mugilids in the coastal sea and coastal lagoon was highly significant (Pearson coefficient r = −0.702, p < 0.001)

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century