Sponge assemblages play a significant role in the functioning of the Mediterranean benthic ecosystem. The main goal of this study was to investigate the diversity and distribution of poorly known sponge communities in the mesophotic and deep-sea substrates of the eastern Mediterranean Sea. More than 1500 sponge specimens belonging to 87 taxa were collected from 156 stations during experimental and commercial bottom trawling in the Aegean Sea and the eastern part of the Ionian ecoregion, at depths of between 10 and 800 m. A total of 79 sponge species were found in the Aegean and 40 species in the Ionian Sea. Eight of these species are included in lists of endangered and threatened species, two were newly recorded in the Aegean and six were first recorded in the east Ionian Sea. Both community structure and diversity differed between the two ecoregions. Species richness, biomass, abundance and diversity decreased with increasing depth, while different species dominated, in terms of biomass, abundance and frequency of appearance, in the two ecoregions and the separate depth zones. In contrast with previous investigations, which mostly examined shallow-water sponges, no clear resemblance patterns were observed among the north and south Aegean subareas, probably due to the homogeneity of the deep-sea habitats under investigation. This study, using sampling material from fish stock monitoring programs for the first time, contributed to our knowledge of the largely unknown eastern Mediterranean mesophotic and deep-sea sponge populations, which are subjected to intensive trawling activities.

Mediterranean bottom trawling is generally characterised by a highly diversified mixed catch, composed of fish, cephalopods,crustaceans, and other megabenthic invertebrates. Although management of Mediterranean trawling requires a multispecies approach on a community basis, this does not seem to be the case in the relevant literature. Herein, we present an extensive review ofthe existing knowledge on megabenthic invertebrate communities, focusing on the trawlable bottoms. A total of 207 publicationsfrom 1930 to the early 2021 was collected and classified into seven research areas. Research effort on soft bottom megabenthicinvertebrates of trawlable grounds was higher for the Western Mediterranean and the depth zone of 50-200 m. Overall, 1,797 taxawere reported belonging to different taxonomic groups, the most diverse of which were Mollusca, Crustacea, Polychaeta, andPorifera. Among the reported taxa, 43 species are alien to the Mediterranean Sea, and 42 are included in the lists of threatened/ endangered and protected species under the Barcelona and Bern Conventions. The Western Mediterranean and the Aegean Sea werethe ecoregions with the highest number of megabenthic invertebrate species reported from trawlable grounds. All Mediterraneanecoregions were grouped according to their megabenthic fauna at a similarity level of 27%. The present work compiles the knownscattered information, highlights knowledge gaps, and underlines the need for time series data on the megabenthic communitiesof the Mediterranean fishing grounds.

European hake, Merluccius merluccius L. 1758, is a highly valuable demersal fish species exploited in both the east Atlantic and the Mediterranean Sea. Changes in the size-at-maturity of this species have been reported in various geographic areas. Size-at-maturity is a key parameter in fishery management. Our main goal was to study the trend of the size-at-maturity of European hake in the eastern Ionian Sea (Central Mediterranean) over the last five decades. Utilizing a multi-decadal series of data for various environmental variables, we employed multivariate analyses and non-additive modeling in an attempt to identify shifts in the climatic environment of the eastern Ionian Sea and whether the maturation of the hake population could be affected by these changes. The analyses used suggest a plausible environmental regime shift in the study area in the late 1990s/early 2000s. The decrease in size-at-maturity that was detected in the last two decades may, thus, be associated with environmental changes. However, as many fish stocks already experience fishery-induced evolution, further investigation is necessary to determine whether this environmental effect is an additional stressor on a possibly already fishery-impacted population. The outcomes of this study highlight the importance of investigating the relationship between fish reproductive traits and altered environmental conditions, as the latter are generally ignored during assessments, affecting the robustness of fishery management.

Gyaros Island (Aegean Sea) is a recently (2019) established MPA in the Mediterranean Sea, allowing spatiotemporal small-scale fishing (SSF) activities with specific access rules. However, due to the inability of the state authorities to establish any fishing permit process, Gyaros MPA initially functioned as a No-Take Zone (NTZ), offering a rare opportunity for scientific monitoring. Significant political pressure by fisher organizations led to the opening of the MPA in June 2022 without any fishing permit restriction. The unprecedented ‘race for fish’ that followed led to a significant deterioration of the MPA status, as confirmed by scientific monitoring before and after the opening. Outcry from national media, based on concerns raised by the scientific community and NGOs, resulted in lifting access to fishing in September 2022, upgrading Gyaros MPA to a full NTZ. This study aimed to assess if and how the MPA functioning was impacted based on a series of experimental fishing trials and questionnaire surveys conducted with local fishers. Although a substantial part of the fishing community’s mindset is embracing MPAs, our results also suggest that the self-interests of a fishers’ minority, along with non-science-based policy by the national authorities, have led to overfishing and deterioration of MPA status.

This study aims to investigate the ecological role of sponges as habitat formers on soft-bottom habitats of the mesophotic zone. As habitat formers, sponges significantly enhance benthic habitat complexity and establish associations with a plethora of organisms consequently augmenting local biodiversity. This role becomes particularly critical in areas subjected to intensive bottom trawling, where sponges often comprise a substantial portion of the discarded material. The examination of 114 massive sponge specimens, belonging to 10 sponge species, which were collected as bycatch from bottom trawls in the Aegean and Ionian ecoregions, revealed a total of over 4600 associated individuals of 78 invertebrate taxa, with crustaceans, mollusks, and polychaetes being the dominant groups. The composition of sponge-associated communities showed strong similarities to previously reported cases from shallow water hard substrates of the eastern Mediterranean, while displaying host-specific differences likely influenced by sponge morphology. Although depth did not significantly affect species richness, Shannon diversity, or evenness, a decrease in abundance of associated invertebrates was observed in deeper samples, suggesting a depth-related pattern that deserves further investigation. By forming stable substrate “islands” in otherwise unstable soft substrate environments, sponges play a vital role in structuring benthic communities. Their removal through bottom trawling not only results in the loss of the sponges themselves, but also disrupts the diverse communities they support. We suggest that sponge-associated fauna should be recognized as part of the discarded bycatch and emphasize the need for broader assessments of sponge-mediated biodiversity across similar Mediterranean habitats to support effective management and conservation strategies.