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Coastal lagoons and brackish ponds are extremely dynamic and temporary ecosystems that follow natural changes throughout their geological history. The correct management of the lagoons ensures their integrity and proper functioning. For this reason, their ecological status should be surveyed for assessing the most appropriate strategies of use. In the present study, historical datasets collected in 2003–2004 are used to investigate the spatiotemporal variation in the species composition and community structure of the macrobenthos of the Tortolì Lagoon (Sardinia, Italy) and to assess their relationship with key environmental variables. Owing to the presence of a riverine runoff at a site and confined areas at some distance from the sea inlet, we hypothesize the marked spatiotemporal changes of the macrobenthic community consistent with the high environmental variability typical of coastal lagoons. The results show a surprisingly high benthic biodiversity for a medium-sized lagoon (250 ha), with 101 species unevenly distributed across the lagoon. The environmental variables did not explain the zonation of the macrobenthic community as that typically found along a lagoonal gradient, due to a marked marine influence. The sampling sites were in fact discriminated by the species distribution according to their ecological affinity; in particular, the most distinctive characteristics of the Tortolì Lagoon emerged from the strictly marine species that represented the most abundant group, consistently with the high marinization of the lagoon. Our results show that the Tortolì Lagoon constitutes a peculiar ecosystem within Mediterranean lagoons, departing from the classic confinement theory.

Mesophotic habitats in the Mediterranean Sea host rich and diverse benthic assemblages, dominated by invertebrates alongside sciaphilous algae. Recent findings suggest that certain mesophotic bioconstructions built by invertebrates, while classified under the coralligenous definition, differ significantly in their taxonomic composition. This study investigates diversity patterns in megabenthic assemblages associated with algal and invertebrate bioconstructions along the Apulian coast, using α- and β-diversity metrics derived from an image analysis approach. Across 360 analyzed frames, 81 taxa were identified, revealing distinct coverage patterns that separate mesophotic algal assemblages from both coral and oyster bioconstructions. Morphological seabed features and primary bioconstructors played a key role in shaping the associated communities. These findings highlight the substantial differences between upper and deeper megabenthic assemblages and emphasize the ecological importance of mesophotic bioconstructions as biodiversity hotspots, underscoring their role in supporting Mediterranean marine ecosystems and the need for targeted conservation strategies.

Having a reliable ecological reference baseline is pivotal to understanding the current status of benthic assemblages. Ecological awareness of our perception of environmental changes could be better described based on historical data. Otherwise, we meet with the shifting baseline syndrome (SBS). Facing SBS harmful consequences on environmental and cultural heritage, as well as on conservation strategies, requires combining historical data with contemporary biomonitoring. In the present “era of biodiversity”, we advocate for (1) the crucial role of taxonomy as a study of life diversity and (2) the robust, informative value of museum collections as memories of past ecosystem conditions. This scenario requires taxonomist skills to understand community composition and diversity, as well as to determine ecosystem change trends and rates. In this paper, we focus on six Mediterranean benthic habitats to track biological and structural changes that have occurred in the last few decades. We highlight the perception of biological changes when historical records make possible effective comparisons between past reference situations and current data. We conclude that the better we know the past, the more we understand present (and will understand future) ecosystem functioning. Achieving this goal is intrinsically linked to investing in training new taxonomists who are able to assure intergeneration connectivity to transmit cultural and environmental heritage, a key aspect to understanding and managing our changing ecosystems.

Bryozoan assemblages of three mesophotic habitats, recently found in the Adriatic and Ionian Seas, were investigated in terms of species composition and diversity, colonial growth forms, and species ecological affinity, with the purposes to analyze variations and similarities between the different bioconstructions and to compare the mesophotic assemblages with those of other benthic habitats. Bryozoans came from three sites off the Apulian coast: Monopoli, 30–55-m depth, where scleractinians are dominant; Otranto, 45–64-m depth; and Santa Maria di Leuca, 45–70-m depth, where the bivalve Neopycnodonte cochlear is the main bioconstructor. A total number of 50 species of bryozoans were recorded, accounting for about 10% of the total number of Mediterranean species. Only few species were shared between the three sites, whereas a considerable pool of species was characteristic of each site. The β-diversity and Sörensen similarity analyses highlighted the highest similarity between the two southern sites, Otranto and Santa Maria di Leuca, with respect to the northern site of Monopoli, in agreement with the hydrological pattern of the area. The encrusting zoarial type was the most abundant in each site, and few species with erect, celleporiform and petraliform colonies were found. The Sörensen similarity, based on data of zoarial forms composition, revealed values considerably higher than those based on species composition, thus highlighting the similar ecological role played by the bryozoans in all the sites. Moreover, significant differences between the mesophotic bryozoan assemblages and those of other benthic Mediterranean habitats were highlighted, showing higher affinity with the coralligenous and detritic sciaphilic habitats. The relevant ecological role of bryozoans as binders in the bioconstructions of the Mediterranean mesophotic zone has been exhibited.

Marine bioconstructions are complex habitats that represent a hotspot of biodiversity. Among Mediterranean bioconstructions, those thriving on mesophotic bottoms on southeastern Italian coasts are of particular interest due to their horizontal and vertical extension. In general, the communities that develop in the Mediterranean twilight zone encompassed within the first 30 m of depth are better known, while relatively few data are available on those at greater depths. By further investigating the diversity and structure of mesophotic bioconstructions in the southern Adriatic, we can improve our understanding of Mediterranean biodiversity while developing effective conservation strategies to preserve these habitats of particular interest. The dataset reported here comprises records of benthic marine taxa from algae and invertebrate mesophotic bioconstructions investigated at six sites along the southern Adriatic coast of Italy, at depths between approximately 25 and 65 m. The dataset contains a total of 1718 records, covering 11 phyla and 648 benthic taxa, of which 580 were recognized at the species level. These data could provide a reference point for further investigations with descriptive or management purposes, including the possible assessment of mesophotic bioconstructions as refuges for shallow-water species.

Historical traces of organisms on the seafloor, such as shells and tubes, constitute the ecological memory of ancient benthic assemblages and serve as an important resource for understanding the assembly of modern communities. Archeological shipwrecks are particularly interesting submerged substrata for both their archeological and biological implications. For the first time, we studied the species composition and life-history traits of dominant organisms in the benthic assemblage on a bronze Carthaginian naval ram, which sank more than two thousand years ago in the Southern Tyrrhenian Sea. By comparing the species composition of the ram assemblage with those of the surrounding habitats, we inferred possible colonization patterns for the ram and discussed the informative role of the shipwreck as a proxy of marine biodiversity. The ram assemblage was rich in species, including both sessile (bryozoans, serpulid polychaetes, and few bivalves) and motile (gastropods) species. Sexual reproduction with free-spawning fertilization and long-duration larvae characterized most species. The long submersion time of the ram, together with the reproductive strategies, growth forms, and motility of the dominant species were key factors shaping the community of the ram. The ram itself offers an archeological artifact of inestimable value, but our analysis revealed it to be an effective collector of fauna from the surrounding seabed. The ram community hosted species from a range of nearby natural habitats (mostly coralligenous, detritic bottoms, and zoosteracean meadows) and thus served as a proxy for marine biodiversity on the surrounding seabed. We conclude that the presence of many species on the ram that commonly occur in adjacent habitats of great environmental value was informative and highlight the important marine biodiversity in the area of the Aegadian archipelago.

A comprehensive overview of the benthic assemblages associated with bioconstructions in the mesophotic zone of the southern Adriatic Sea is provided through a comparison of algal- and invertebrate-based bioconstructions. To characterize these bioconstructions, sampling was conducted at six sites along the Apulian coast (Italy). Algal-based bioconstructions were found in shallower areas and corresponded to coralligenous sensu stricto, while two distinct invertebrate-based bioconstructions, built by scleractinians and bivalves, were observed at greater depths. A multi-taxa approach, which recorded 511 benthic taxa, revealed significant differences in the taxonomic composition of their associated benthic assemblages, although similar species richness values were observed across all types of bioconstructions. Given the marked difference in terms of primary constructor species between the coralligenous sensu stricto and invertebrate bioconstructions, we propose referring to the latter as Mesophotic Coral Bioconstructions (MCB) and Mesophotic Oyster Bioconstructions (MOB). β-diversity analysis identified a turnover in benthic fauna along the North–South gradient, with higher β-diversity values between distant sites and lower values between nearby sites, likely driven by North–South circulation dynamics in the region. Additionally, the distinctions observed along the depth gradient are consistent with the decrease in irradiance, which causes a shift from photoautotrophic to heterotrophic builder species. These findings underscore the role of mesophotic bioconstructions along the Apulian coast as biodiversity hotspots and confirm their importance in understanding mesophotic ecosystem dynamics in the Mediterranean Sea.