Feeding habits of the invasive spider crab Libinia dubia from the Mediterranean Sea were studied in the Gulf of Gabès (Tunisia) using the frequency of occurrence and points methods. The population was sampled at least monthly between November 2015 and October 2016. Stomach contents of 384 specimens were analysed. Results indicate that L. dubia is an herbivorous species exhibiting clear preferences for algae (ALG) and Magnoliophyta (MAG) (62.03%, 7.13 points and 59.36%, 5.3 points respectively) although Echinodermata (ECH), Porifera (POR), Cnidaria (CNI), Mollusca (MOL), Polychaeta (POL), Crustacea (CRU) and fish (FIS) were accidentally consumed along with Bryozoa (BRY), sediment (SED), and unidentifiable materials (UNM). The diversity of ALG ingested was studied in detail: Chlorophyceae were found in 87.93% of stomachs containing ALG and contributed most of points to the stomach contents (4.18 points) followed respectively by Phaeophyceae (81.03%, 2.27 points) and Rhodophyceae (40.95%, 0.68 points).Very low Vacuity Index was recorded (VI = 2.6%). Ingested items varied significantly with regard to the season (Chi-square test, χ2calculated = 87.86 > χ2theoretical = 7.81, df = 3, p < 0.05) and crab size (χ2calculated = 14.25 > χ2theoretical = 5.99, df = 2, p = 0.026). Insignificant differences were registered by studying Carapace Width-Stomach Weight (CW-SW) relationships (T-test, tcalculated < ttheoretical, p > 0.05). Kruskal-Wallis test was applied so that the composition of crab diet among groups could be compared (H = 1.1, df = 3, p = 0.77).
On 14th October 2021, a single specimen of Sargocentron caudimaculatum was captured in the locality of Cape Bon, Eastern Tunisia, by a local fisher using gillnets at 60 m depth, on rocky bottom. This observation represents the first record of this species in the Mediterranean Sea. General information on the squirrelfishes and the importance of molecular tools for the proper identification of morphologically challenging non-indigenous organisms were raised and discussed.
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