The Gulf of Sirte is a largely unexplored area in the southernmost Mediterranean Sea.We are presenting here 2008 summer data on the distribution pattern of living coccolithophores, a main phytoplankton calcifying group, in 105 samples from 20 stations. The survey includes coastal and offshore stations, enabling us to provide indications on the dynamics of phytoplankton productivity in relation to oceanographic processes. The total coccosphere concentrations show higher values in the offshore stations and lower ones for coastal sites. Umbellosphaera tenuis, Emiliania huxleyi, Florisphaera profunda, Syracosphaera pulchra HOL (Calyptrosphaera oblonga) and Rhabdosphaera spp. dominate the assemblages. The coccolithophore community shows the typical vertical zonation, with K-strategist taxa (among others U. tenuis, Rhabdosphaera spp. and Discosphaera tubifera) in the upper 75 meters depth and Lower Photic Zone taxa, dominated by F. profunda, below. The latter species shows its maximum development in the Deep Chlorophyll Maximum layer, which occurs in the upper part of the Levantine Intermediate Water, where the nutrient content is higher than in the overlying layers. The mesoscale oceanographic circulation significantly affects the spatial and vertical distribution of coccolithophores, with the thermocline and halocline depth shaping the vertical zonation of coccolithophore taxa and resulting in a strong lateral gradient within the gulf: in the eastern sector, under the influence of the Gulf of Sirte anticyclone, the DCM is deeper and so is the occurrence of K-strategist taxa and F. profunda.

In this study, we consider the applicability of Bergmann’s rule to the populations of small pelagic fish species in the Mediterranean Sea. Under Bergmann’s rule, body size increases with decreasing temperature and increasing latitude. Although this macroecological pattern in body sizes is well established for many taxa of endotherms and ectotherms, it remains not universal and the proposed mechanisms underlying it are multiple and still lack consensus. We explored here the occurrence of geographical body size clines using measurements of average body sizes of 10 species collected in pelagic trawl hauls carried out during acoustic surveys in the Mediterranean Sea. Bergmann’s rule was evaluated by correlating body sizes with latitude and temperature for each species while accounting for potential confounding variables and sampling bias. For 5 species, namely anchovy, sardine, Atlantic chub mackerel, bogue, and blue jack mackerel, we demonstrate that they follow a Bergmann’s rule, with a decline in average body size by about 3.01, 3.43, 3.67, 3.82, and 3.76 % per 1°C of warming respectively, although this did not translate with an increase in size with latitude. The adherence of these 5 pelagic fish to Bergmann’s rules strongly suggests that temperature is a major determinant of their body sizes and enables them to act as sentinel species for identifying the drivers and consequences of warming in the Mediterranean ecosystems.

Merluccius merluccius is an economically and ecologically important demersal species inhabiting the Atlantic Ocean and the Mediterranean Sea; however, reproductive knowledge about this species, along the North African coast is still missing. Monthly samples were collected from November 2010 to October 2011 along the North Tunisian coast. Morphometric parameters were measured, and histological preparations of gonadic tissues provided detailed information on the reproductive biology. Ovary maturity data showed a protracted spawning season throughout the year, with peaks in January, April and August. In females of M. merluccius, seasonal variability in weight and length were noticed, with higher values in the first part of the study period (November–April) than from May to October. Analysing separately these two periods, significant relationships were observed between gonadic maturation indices and the somatic and gonadic indices, suggesting a seasonal differential use of energy intake. From November to May the fish alternate the use of their energy for body growth and reserves for later uses (i.e fat, muscle and liver mass) or for gonadic growth. From June to October the energy is converted mainly into gonad weight and less to somatic growth. The maturity ogives obtained by macroscopic and histological maturity staging methods showed significant differences; however, in both cases the length at first maturity estimates were around 29 cm. Nonetheless, when selecting the main spawning period, the L50 estimation was heavily reduced to 24 cm, suggesting careful attention in the selection of the samples to be used specially for fishery management purposes.

Understanding the drivers of fish growth is essential for predicting productivity, stability, and resilience of exploited populations. For the European sardine (Sardina pilchardus) in the Strait of Sicily (Central Mediterranean Sea, GSA16), growth parameters or length at age estimates have never been published before. To fill this data gap, the length and age as well as the von Bertalanffy parameters (the most widely used growth model) were estimated. Data from landing samples during the period 2009–2019 were collected by two methods (purse seine and mid-water pelagic trawl). Temporal trends in average length at age, as well as an overall age-length key were obtained and compared with other areas across the geographical distribution range of sardine in the Mediterranean Sea. The observed age range was 0–3 years with most of the individuals belonging to Age 1 (52%) and Age 2 (43%). The mean length at age, for the entire study period, was 11.7 (±0.08) cm for Age 0; 13.4 (±0.09) cm for Age 1; 15 (±0.1) cm for Age 2; and 16.6 (±0.11) cm for Age 3. Furthermore, during the considered period, a reduction in the length at age was observed in the older classes (Age 2 and Age 3). The estimated parameters of the von Bertalanffy growth model were L_inf = 18 (±1.15) cm, K= 0.459 (±0.018), and t₀ = −1.99 (±0.008) and, accordingly, the mortality vector was obtained according to Gislason’s model, for each age class, these values were 0.99 (0.98–1.02) C at Age 0; 0.71 (0.7–0.73) y⁻¹ at Age 1; 0.6 (0.59–0.62) y⁻¹ at Age 2; 0.54 (0.53–0.56) y⁻¹ at Age 3; and 0.51 (0.49–0.53) y⁻¹ at Age 4. Results appeared in agreement with literature from other areas of the Mediterranean Sea and suggested a poor condition status of the sardine stock in the GSA16.