As a seafood delicacy, the purple sea urchin Paracentrotus lividus is the most exploited echinoid species in the Mediterranean Sea, with a significant increase in total catches being reported over the last 2 decades. This work presents: (i) the findings from two demographic monitoring campaigns, conducted on P. lividus populations in summer 2023, at shallow depths within the coastal areas of Sicily and Apulia; (ii) a meta-analysis of the P. lividus density in the Mediterranean Sea over the last 30 years. In both sampled areas, the recorded individual density was lower than ever, with an average value of 0.2 ind/m². No significant difference in P. lividus density was detected between protected and non-protected areas. The observed rarity of the edible sea urchin is corroborated by a meta-regression analysis of data from 44 published articles over the period 1990–2020, showing that the decline of P. lividus populations in the Mediterranean Sea began in 2003, coincident with the occurrence of a pan-European heat wave and with the anomalous warming of the entire Mediterranean Sea.

Quantitative studies on population dynamics and life history traits of key species are useful to predict changes in the structure and organization of biological communities. In this context, Hermodice carunculata (Pallas, 1766) is a selective scavenger/carnivore polychaete species (known as a fireworm) that, in recent years, has exhibited a northern expansion along the whole basin, including the Italian coasts, and an increasing abundance in its southern areas. Here we report ecological data and fireworm abundances from two shallow stations of the Salento peninsula in the Ionian Sea (Lecce, Italy), characterized by different hydrodynamic exposure levels and structural communities. The observed densities by visual census in the years 2019–2021 (up to 18 ind./15 m²) document a striking shift compared to the past anecdotal reports of the rare occurrence of fireworms along the studied area. Additionally, their abundance seems to be driven by the substrate coverage; in fact, a higher density of fireworms was observed where the biodiversity is richer. Results from this study will serve as a baseline reference for future investigation of the invasiveness potential of a species that can act as a biological marker of ocean warming.

Since the opening of the Suez Canal in 1869, hundreds of Indo-Pacific species have rapidly colonised the Mediterranean. Understanding the spatial and temporal patterns of this biological invasion is crucial for assessing its ecological impact. A notable example is the non-indigenous oyster Dendostrea sp., first discovered in Türkiye in 1998 and later found throughout the easternmost Mediterranean, though its identity remained uncertain. This study clarifies the taxonomic identity and the introduction pathways of Dendostrea sp. using molecular analyses. Over 100 specimens from 25 sites in the eastern Mediterranean, as well as Île d’Ambre and Rodrigues in the Mauritius Archipelago (the native range), were sequenced for mitochondrial DNA (COI) and compared to 422 sequences from GenBank. Phylogenetic and species delimitation analyses identified the Mediterranean oysters as D. cf. crenulifera, conspecific with oysters from Rodrigues. The Mediterranean populations exhibited high genetic diversity, lack of phylogeographic structure and showed no evidence of a founder effect. These findings suggest that D. cf. crenulifera entered the Mediterranean over two decades ago through multiple shipping-mediated introductions from its native range and successfully established, likely aided by the decline of native biodiversity. The observed genetic diversity pattern across the Mediterranean indicates high propagule pressure driving the species’ invasion history, which likely underpins its establishment success by reducing the deleterious consequences of population bottlenecks and overcoming the so-called genetic paradox. This study underscores the value of molecular surveys in identifying taxonomically challenging non-indigenous species and uncovering their invasion histories.

Sampling activities conducted in the Tyre Coast Nature Reserve, southern Lebanon, to study the marine annelid fauna of the area, allowed for the revision of the diversity of this group in Lebanon. We particularly focused on non-indigenous species (NIS), which were characterised from morphological and molecular points of view. A total of 116 taxa were collected; 10 species are reported here for the first time in the Mediterranean Sea, while 6 species with presumable Indo-Pacific affinity are likely new to science. Seventy-three taxa were native, while 43 taxa were NIS; among the latter, 24 species are reported for the first time in Lebanon. Molecular data were obtained for 28 NIS, representing the first data from the Mediterranean Sea for 23 of them. Non-indigenous annelids occurring along the coast of Lebanon mainly have Indo-Pacific affinity. However, molecular data highlighted inconsistencies between the sampled material and the sequences available in public repositories, suggesting the widespread occurrence of species complexes in these taxa. These results suggest that further research on Indo-Pacific annelids is needed to understand their diversity patterns and invasion pathways. Additionally, the large number of new records of annelids in Lebanese waters indicate that further studies are needed to explore their diversity in comparison with neighbouring Mediterranean regions.

This paper is part of a series of studies aimed at understanding the potential exploitation of the biomass of the polychaete worm Sabella spallanzanii (Gmelin, 1791), which is obtained as a by-product of an innovative Integrated Multi-Trophic Aquaculture (IMTA) system. IMTA systems are designed according to an ecosystem approach with the aim to reduce marine monoculture impact while further increasing production via exploitation of valuable by-products. S. spallanzanii can remove large amounts of suspended matter by filtering large volumes of water per hour and performs well as an extractive organism under IMTA; however, it currently lacks any economic value, thus hindering its sustainable large-scale implementation. However, S. spallazanii has the potential to become competitive as a newcomer in fish bait, as an ornamental organism, and in fish feed markets. Notably, sabella meal has already been successfully tested as an attractant in an innovative fish feed. Here, we refer to the use of sabella meal as the main component (60%) in the formulation of a novel aquarium fish feed. Following the biochemical analysis of farmed sabella meal, the experimental feed was formulated by adding spirulina (25%) and dry garlic (15%) in such proportion as to be isoproteic and isoenergetic to the commercial control feed. After preliminary observations of the palatability of sabella meal for several tropical fish species, the novel experimental feed was tested on ocellaris clownfish, Amphiprion ocellaris (Cuvier, 1830), by evaluating their growth response in a 70-day feeding trial. The fish seemed to enjoy the experimental feed at least as much as the control, and both the control and treatment groups showed no significant differences in weight gain (p = 0.46), specific growth rate (p = 0.76), and feed conversion ratio (p = 0.48), reinforcing the suitability of S. spallanzanii as a viable source of animal proteins to be employed in the fish feed industry in a circular economy perspective.