The taxonomy of Mediterranean populations of Diodora is assessed based on new molecular (COI and 28S) data. The recently described Diodora demartiniorum Buzzurro & Russo, 2005, is found to be a valid species restricted to the Gulf of Gabès (Tunisia) but possibly occurring also on the coast of Libya. However, specimens from the Aegean Sea previously identified as D. demartiniorum are molecularly (and morphologically pseudocryptically) distinct and represent a previously unrecognized species here described as D. giannispadai n. sp. It is hypothesized that the current distribution of these two species corresponds to glacial refuges during Pleistocene climate changes.

The age and growth parameters of grey triggerfish, Balistes capriscus from the Gulf of Gabès, southern Tunisia, Mediterranean Sea, were estimated from the first dorsal spine sections of 463 specimens (206 males and 257 females), whose fork length was between 139 and 427 mm and the total weight ranged from 90.04 to 1967.41 g. The monthly percentage of specimens having a terminal translucent zone has indicated that the growth zone is formed once a year, during the cold season (February). The von Bertalanffy growth equations were: FL = 420.7 [1 − e−0.233(t + 0.123)] and FL = 417.0 [1 − e−0.238(t + 0.074)], for males and females, respectively. The longevity estimated was 13 years old for both sexes. The instantaneous mortality rates were estimated to 0.23 for males and 0.24 for females. The weight–length relationships of the grey triggerfish were Wt = 21.510−3 LF3.046 and Wt = 41.010−3 LF2.835, for males and females, respectively.

The age, growth, longevity, mortality and reproductive parameters were estimated for Dipturus oxyrinchus from the Gulf of Gabès (Southern Tunisia, central Mediterranean Sea), collected monthly during 2007 from commercial fisheries. The present study provides the first data on age and growth of this species in Tunisian waters, as well as additional data on its reproduction. A total of 240 females (16.5–105 cm total length (TL)) and 280 males (15.5–95 cm TL) were examined to study the reproductive cycle. A subsample of 285 specimens (175 females and 110 males, ranging from 15.5 to 105 cm TL) were analysed to study the age and growth. The oldest female in this study was 25 yr and 105 cm TL, whereas the oldest male was 22 yr and 95 cm. The annual deposition of growth bands was verified by marginal increment and edge analysis. The von Bertalanffy growth parameters were L∞ = 123.9 ± 2.56 cm, K = 0.08 ± 0.004 yr−1 and t0 =  −1.26 ± 0.04 10−1 yr for females and L∞ = 102.1 ± 3.23 cm, K = 0.12 ± 0.007 10−3 yr−1 and t0 = −1.18 ± 0.03 10−1 yr for males. Growth was not significantly different between sexes. The maturity size was 72.05 cm for males and 82.1 cm for females. The maturity age was estimated to be 11.95 and 13.96 years, respectively, for males and females. Size and age at maturity were not significantly different between sexes. The estimated longevity was 26.18 and 38.84 yr for males and females, respectively. Based on life history parameters, natural mortality was estimated at 0.53 yr−1 for females and 0.41 yr−1 for males.

Fundamental information on the reproductive biology of the grey triggerfish Balistes capriscus from the Gulf of Gabès (south-eastern Mediterranean Sea) is based on 751 specimens, collected between June 2005 and May 2010, from commercial catches at different fishing ports at Chebba (34°14′N 11°06′E), Kerkennah (34°45′N 11°17′E) and Zarzis (33°41′N 11°48′E). The species were caught in this area using pelagic trawl nets. The calculation of the gonadosomatic index suggested that the spawning season of grey triggerfish occurred mainly between July and mid-September with a peak in July, coinciding with summer time. The first maturation occurred at 20.26 cm fork length for females and 21.3 cm fork length for males. The monthly values of hepatosomatic index and condition factor (K) indicated that the liver was the most severely stressed organ in the reproduction process of energy transfer. The absolute fecundity (F) ranged from 290,120 to 984,990 eggs per female. The fecundity of the species was determined by the size and weight of the individuals.

In Tunisia, elasmobranch landings have decreased substantially in recent years. Generally, species-specific information is largely unavailable for artisanal fisheries, but it is essential to increase knowledge and to ensure proper management of these species. This study analysed elasmobranch catches with longline fishery in the Gulf of Gabès. In total, 21 and 20 pelagic and bottom longline fishing trips were conducted, respectively, from July to September in 2007 and 2008. A total of eight elasmobranch species were caught: four batoids and four sharks. Pelagic longline captures were hooked externally while a high number of individuals captured with bottom longline were hooked internally. Discards due essentially to low commercial value and size represented 7.6% of total number of elasmobranch specimens caught. Longline landings in the Gulf of Gabès were principally composed of sandbar shark, Carcharhinus plumbeus, representing, respectively, 94.14% and 21.17% in number of pelagic and bottom longline captures. The importance of rhinobatids and Mustelus capture with bottom longline reflect their abundance in this area compared to other Mediterranean zones. Juveniles, including neonates with umbilical scars, dominated carcharhnids specimens, while smoothhound and guitarfish captures were dominated by mature individuals. Mitigation measures based on gear modifications, size limits and delineated nursery areas in the Gulf of Gabès should be developed to protect these vulnerable species.

The diet and feeding habits of the sharpsnout seabream, Diplodus puntazzo, from the Gulf of Gabès were investigated using stomach contents of 490 specimens ranging from 12.6 cm to 26.1 cm total length in size and from 29.95 g to 230.83 g in weight collected from commercial catches between April 2008 and March 2009. Of the total number of examined stomachs, 279 were empty (%VI = 56.94). This percentage varied significantly with months, attaining a maximum in spring (74.88%) and a minimum in autumn (37.38%). Eight major taxa were identified (Plantae, Spongia, Tunicata, Echinodermata, Crustacea, Annelida, Mollusca and Teleostei) in stomach contents of D. puntazzo. Plants were the most important food source, constituting 89.88% of the total Index of relative importance. The other groups, such as teleosts, molluscs, crustaceans and annelids represented accessory food. Significant differences in diet were observed in relation to season. Plants were the most important food source item in all seasons, especially during the autumn. The estimation of trophic level gave an average of 2.57 ± 0.2 for the whole population of D. puntazzo in the Gulf of Gabès. Based on the composition of its diet, this species may be considered as an omnivorous fish with a preference for vegetable material, and showing specialist feeding strategy.

Samples of common two-banded seabream Diplodus vulgaris (N = 1097), used in this study, were caught in the Gulf of Gabès (Tunisia) from March 2008 to February 2010. Total length ranged from 7 to 25 cm. Diplodus vulgaris is a protandric hermaphrodite. The overall ratio of females to males was 1:1.66. The reproductive season extended from October to February, and the peak spawning activity occurred in December–January. The total length at which 50% of the population reached maturity was 14.14 ± 0.16 cm for females and 13.57 ± 0.01 cm for males. Parameters of the length–weight relationship (TW = aTLb) for all individuals were a = 0.0185 and b = 2.9319. The youngest specimen in this study was 0+ years, whereas the oldest one was 9 years. The von Bertalanffy growth parameters for the whole sample were: L∞ = 25.4 cm, k = 0.179 and t0 = −1.631 year. The instantaneous rate of natural mortality was: M = 0.333 year−1.

The wide-eyed flounder Bothus podas podas is a small fish that belongs to the Bothidae family. This species is a demersal fish inhabiting sandy and muddy bottoms where it lives buried in the sand. In the Gulf of Gabès (Tunisia), B. podas podas is an uncommon fish caught in small quantities by trawlers, between depths of 20 and 50 m. There are very few complete studies of the biology of this fish in the Mediterranean Sea. Even in Tunisia, the biology of B. podas podas is unknown. In addition, it has been noticed that during the last few years, despite having weak commercial value, this fish has attracted the fishermen's attention of the region after the observed reduction in the flat fish stocks, particularly the Egyptian sole Solea aegyptiaca. The aim of this work was to study the reproduction of B. podas podas and determine the sex-ratio, the sexual cycle, the spawning period and the first sexual maturity. The data for this work was collected during the period of May 2004 until September 2005. In general, this study shows that the proportion of sexes is in favour of females and permits us to analyse the sex-ratio variations according to the size and age of the fish. It also seems that males grow faster than females. The monthly following of the gonad somatic index (GSI), the liver somatic index (LSI) and the condition factor (K) enabled us to determine that the period of maturation occurs from May to August, to define the spawning period from August to November and to deduce that B. podas podas uses the lipid reserves accumulated in the liver to develop its gonads. Concerning the first sexual maturity it was noted that the main size related to 25%, 50% and 75% of matured individuals were respectively for males: 19.68 cm, 21 cm and 22.34 cm and for females: 18.87 cm, 20.4 cm and 21.93 cm. The coefficients of the logistic function were for males: a = 0.827, b = 17.38 and for females: a = 0.718, b = 14.65.

The amphipod (Crustacea: Peracarida) epibionts of the sea turtles Caretta caretta and Chelonia mydas were studied in the Gulf of Gabès. A total of eight amphipod species were identified, with Hyale grimaldii and Caprella andreae by far the most common. Among these species, Ericthonius punctatus and Ampithoe riedli are recorded for the first time as epibionts of Caretta caretta and Chelonia mydas, respectively, in the Mediterranean Sea.

The summer spatial distribution of the phytoplankton community in the Gulf of Gabès (Tunisia, eastern Mediterranean Sea), together with environmental factors, were studied during a preliminary study conducted in July 2005 aboard the RV ‘Hannibal’. The phytoplankton community, which showed a decrease in concentration along a coastal–open sea gradient, was dominated by Dictyochophyceae (41%) followed by Dinophyceae (25%), Bacillariophyceae (16%), Cyanobacteriae (17%) and Euglenophyceae (1%). The phytoplankton found along the coast was dominated by opportunistic species (e.g. Dictyocha fibula) associated with high nutrient availability. In the open sea, phytoplankton development seemed influenced by Atlantic hydrodynamics. In addition, the Gulf of Gabès is characterized by an oligotrophic status with a summer stratification that impacted on species composition especially in off-shore areas. The coupling of phytoplankton dynamics to nutrients, ciliates and copepods showed the potential role played by ciliates not only as predators of phytoplankton but also as prey for filter-feeding copepods accounting for the increased fisheries productivity of the Gulf of Gabès.

We studied the summer spatial distribution of the copepod community in both the neritic and oceanic areas of the Gulf of Gabès (Tunisia, eastern Mediterranean Sea) coupled with environmental factors. Copepods were the most abundant zooplankton throughout the sampling period, contributing 78% of the total zooplankton. A total of 14 copepod families were identified in all stations, with an overwhelming abundance of Acartiidae and Oithonidae (39.05 and 39.09% of total abundance, respectively). Abundance of Acartia clausi and chlorophyll-a concentrations were negatively correlated with salinity, suggesting that this species probably escaped the high coastal salinity (38 psu). Significant correlation determined between A. clausi and tintinnids at 50 m isobaths indicates that these planktonic ciliates probably served as a substantial food link towards higher trophic levels of this area. Conversely, Oithona nana which was well adapted to high chlorophyll-a concentrations and high salinity along the coast, showed significant correlations with Dictyochophyceae, Dinophyceae, Bacillariophyceae and Euglenophyceae, suggesting that this small copepod was capable of feeding on a wide selection of phytoplankton preys.

The spatial and temporal variations of the microphytoplankton communities were examined during four oceanographic cruises conducted between July 2005 and March 2007 aboard the RV ‘Hannibal’. Water thermal stratification started in May–June, and a thermocline established at 20 m depth, but ranged between 25 m during July and more than 30 m during September. The high concentrations of chlorophyll-a were observed during the May–June semi-mixed conditions and were mainly correlated with the concentrations of phosphate, suggesting a potential limitation by this nutrient. The Bacillariophyceae were dominant in the coastal samples, whereas they declined in the offshore area, most likely due to silicate shortage. Cyanobacteriae developed over semi-mixed conditions and at the thermocline depth. Relatively constant abundance of dinoflagellates was observed during the sampling periods from the coast to the offshore area, mainly explained by the high diversity species of this group. The results suggest that some phytoplankton taxa are generally adapted to specific hydrological conditions, whereas the dinoflagellates did not seem to follow this trend. Our findings have important biogeochemical implications in relationship with the export fluxes of the particulate matter throughout the water column.

The diet of blue runner Caranx crysos (Carangidae) in the Gulf of Gabès (Tunisia, Mediterranean) is described from analysis of stomach contents (N = 1668 fish). The majority of samples were obtained from commercial purse seine and gill-net catches. The index of vacuity (%VI) was relatively high (58.7%) and differed significantly across months. Blue runner is an opportunistic predator that consumes mostly pelagic organisms, with benthic prey representing only a small proportion of the diet. The diet was quantified using the frequency of occurrence (%F), numerical abundance (%N), weight (%W) and the index of relative importance (IRI and %IRI) for each prey taxa.

The most important prey categories were teleosts (%IRI = 83.4) and crustaceans (%IRI = 16.6), with molluscs only observed occasionally (%IRI < 0.1). Fish were also the dominant food items in both terms of weight (89.60%) and frequency of occurrence (82.44%). In terms of numerical abundance, crustaceans were the most abundant prey (78.07%). Ontogenetic and seasonal differences in the diet were observed, although there was no difference between the diets of males and females.

The common guitarfish Rhinobatos rhinobatos is abundanly captured along the coast of the Gulf of Gabès (southern Tunisia). The sizes at the first sexual maturity of females and males are 790 and 700 mm total length (TL) respectively. Females are larger than males; the maximum TL for males and females is 1000 and 1200 mm respectively. The smallest gravid female observed is 750 mm TL. Rhinobatos rhinobatos is an aplacental viviparous species. The two ovaries and the two uteri are functional. Mature oocytes and foetuses are symmetrically distributed respectively in ovaries and uteri. Vitellogenesis and gestation occur simultaneously. Gestation lasts 10 to 12 months; parturition occurs from the end of summer to the beginning of autumn. Mating and ovulation take place after parturition. Ovarian fecundity is higher than uterine fecundity; means of 8.95 and 5.34 young per year are respectively calculated. There is a positive relationship between the two categories of fecundity and size of females. The size at birth ranges from 250 to 290 mm TL. The common guitarfish is purely a lecithotrophic species. The chemical balance of development is estimated at 1.02.