Trophic Interactions of European Hake Merluccius merluccius (Linnaeus, 1758) in Benthic Communities off the Moroccan Mediterranean Coastline: Seasonal and Ontogenetic Shifts

The European hake, Merluccius merluccius (Linnaeus, 1758), is one of the most important resources for Mediterranean fisheries. Due to its pivotal role in energy transfer from lower to higher trophic levels, this species is a crucial component of the ecosystem’s functioning. The ecological role of Merluccius merluccius, off the Moroccan Mediterranean Sea (southern Alboran Sea), was investigated, exploring seasonal and ontogenetic shifts, geographical variations in prey composition, and feeding strategy. Between November 2020 and July 2022, a total of 402 hake specimens were collected by oceanographic bottom trawl surveys (MEDITS) that were carried out during warm and cold seasons to assess their diet and feeding habits. The sample was analyzed according to fish sizes and seasons, and qualitative/quantitative feeding indices were calculated. The trophic spectrum of Merluccius merluccius included 24 prey items in total, mainly belonging to Osteichthyes (12), Crustacea (10), Cephalopoda (1), and Polychaeta (1), suggesting a generalist behavior of this predator as in numerous regions of the Mediterranean Sea, with several species that occasionally occurs in its diet. In the Moroccan Mediterranean Sea, Osteichthyes proved to be the most important prey item (%IRI = 78.56) among the different zoological groups, followed by Crustacea (%IRI = 16.22). The other food items were occasionally and randomly consumed, and cannibalism was low (0.8%). Hierarchical cluster analysis and nonmetric multidimensional scaling (nMDS) showed different feeding habits of two main groups separated at 60% similarity: small specimens 0.05). A trophic level (TROPH) of 4.1 was calculated, indicating that the species is a top predator (quaternary consumers). The TROPH values ranged between 2.58 and 4.38 from juveniles to adults, increasing asymptotically with the size of specimens. In contrast to what has previously been found in other Mediterranean regions, where ichthyophagous hake feed mostly on pelagic Osteichthyes, such as Engraulis encrasicolus, Sardina pilchardus, and Micromesistius poutassou, the study points up the vital role played by Atlantic horse mackerel Trachurus trachurus for hake diet in the Moroccan Mediterranean Sea. Information on the feeding ecology of fish species as provided in this study is essential to improve ecosystem conservation in accordance with multispecies approach to fishery management, leading to a better understanding of the role of hake in the Moroccan Mediterranean Sea demersal communities

Heavy Metals Concentration in Sardina pilchardus (Walbaum, 1792) from the Moroccan Mediterranean Coast and Potential Human Health Risk Assessment

Due to their toxicity, long persistence, bioaccumulative nature, and biomagnification in the food chain, heavy metals pose a serious hazard. The aim of this study was to evaluate the health risks associated with the consumption of Sardina pilchardus (Walbaum, 1792) and to study the spatiotemporal dynamics of four potentially toxic metallic elements. Three hundred and sixty specimens of sardine were collected between December 2020 and October 2021 at three Mediterranean coast sites, Beni-Ensar, Ras el Ma, and El-Houceima, in the northeast region of Morocco. The toxic metallic elements were evaluated by assessing the contamination level of cadmium (Cd), mercury (Hg), lead (Pb), and arsenic (As) in the muscle, liver, and gills of sardine from the Mediterranean Moroccan coast. The results showed a significant effect of the study area, organ, and season (p>0.05) on Moroccan Mediterranean sardine heavy metal contamination levels. Regardless the location and season, the liver presents the higher concentration of the studied metals (p<0.05). The highest heavy metal concentrations of Cd (0.408 μg·g−1 wet weight (ww)), Hg (0.044 μg·g−1 ww), and As (6.74 μg·g−1 ww) were found in winter while the concentration of Pb was the highest in autumn (0.056 μg·g−1 ww). Furthermore, the lowest contamination of metal levels was found in the spring. El-Houceima region contains the highest values for Hg (0.093 μg·g−1 ww), Pb (0.018 μg·g−1 ww), and As (7.73 μg·g−1 ww). However, the highest values for Cd (0.172 μg·g−1 ww) were recorded in Beni-Ensar. Regarding the assessment of possible risks to human health, the results showed that the indices are below the established safety values in the case of estimated weekly intake, and target hazard quotient (THQ). In contrast, the carcinogenic risk index and total THQ were above the threshold limits and thus represented a potential carcinogenic risk to human health