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Background Mediterranean marine coastal habitats have been and continue to be threatened by human-related pressures, such as resource over-exploitation, pollution, habitat loss and fragmentation, and the invasion of non-native species (Airoldi and Beck, 2007; Micheli et al., 2013). Since 2001, volunteer certified trained snorkelers, freedivers, and scuba divers (hereafter EcoDivers) have collected data for selected key marine species, recording their occurrence, distribution, abundance, and bathymetric range along the Mediterranean Sea coasts, using the Reef Check Mediterranean Underwater Coastal Environment Monitoring (RCMed U-CEM) protocol (Turicchia et al., 2021b). For this protocol, 43 taxa were selected based on two or more criteria, including ease of identification, being included in the international lists of protected species, being sensitive to human impacts, and being key indicators of the shift that Mediterranean coastal habitats can undergo under local pressures and climate change. Biotic and abiotic measurements are reported using the controlled thesaurus from the Natural Environment Research Council (NERC; http://vocab.nerc.ac.uk) Vocabulary Server maintained by the British Oceanographic Data Center (BODC), and the Darwin Core Archive (DwC-A), an internationally recognized biodiversity informatics standardized data system intended to facilitate information sharing on biological diversity.

Since 2001, trained snorkelers, freedivers, and scuba diver volunteers (collectively called EcoDivers) have been recording data on the distribution, abundance, and bathymetric range of 43 selected key marine species along the Mediterranean Sea coasts using the Reef Check Mediterranean Underwater Coastal Environment Monitoring (RCMed U-CEM) protocol. The taxa, including algae, invertebrates, and fishes, were selected by a combination of criteria, including ease of identification and being a key indicator of shifts in the Mediterranean subtidal habitats due to local pressures and climate change. The dataset collected using the RCMed U-CEM protocol is openly accessible across different platforms and allows for various uses. It has proven to be useful for several purposes, such as monitoring the ecological status of Mediterranean coastal environments, assessing the effects of human impacts and management interventions, as well as complementing scientific papers on species distribution and abundance, distribution modeling, and historical series. Also, the commitment of volunteers promotes marine stewardship and environmental awareness in marine conservation. Here, we describe the RCMed U-CEM protocol from training volunteers to recording, delivering, and sharing data, including the quality assurance and control (QA/QC) procedures.

Sandy beaches and the nearshore environment are dynamic coastal systems characterized by sediment mobilization driven by alternating stormy and mild wave conditions. However, this natural behavior of beaches can be altered by coastal defense structures. Repeated surveys carried out with autonomous surface vehicles (ASVs) may represent an interesting tool for studying nearshore dynamics and testing the effects of mitigation strategies against erosion. We present a one-year experiment involving repeated stratigraphic and morpho-bathymetric surveys of a nearshore environment prone to coastal erosion along the Emilia-Romagna coast (NE Italy), the Lido di Dante beach, carried out between October 2020 and December 2021 using an ASV. Seafloor and subseafloor “snapshots” collected at different time intervals enabled us to delineate the seasonal variability and shed light on key controlling variables, which could be used to integrate and calibrate remote-sensing observations and modeling. The results demonstrated that repeated surveys could be successfully employed for monitoring coastal areas and represent a promising tool for studying coastal dynamics on a medium/short (years/months) timescale.

The northern Adriatic continental shelf hosts several coralligenous reefs rising from the sedimentary bottom and characterized by three main benthic assemblages, respectively, dominated by algal turfs, encrusting calcareous rhodophyte (ECRs) or erect sponges. Bioconstruction and bioerosion processes have been investigated using recruitment travertine limestone tiles deployed in a random site for each main benthic assemblages off Chioggia, 6.1–14.4 km offshore and 20.2–25.4 m depth. Tiles were retrieved after 3 and 12 years and analyzed by X-ray computed tomography (CT), allowing for non-destructively identifying and quantifying deposited and eroded limestone. The main builders were ECRs, serpulids, bryozoans, barnacles, and the bivalves Anomia ephippium , while the most effective borers were sponges from the genus Cliona and the bivalve Rocellaria dubia . The deposition of limestone after 12 years was greater at the site MR08 dominated by ECRs (12.52 ± 2.22 kg m –2 ), intermediate at the site P213 dominated by erect sponges (4.20 ± 1.24 kg m –2 ), and lower in the site P204 dominated by algal turfs (2.20 ± 0.72 kg m –2 ). At MR08, the deposition rate did not vary much over time (from 1.295 ± 0.270 to 1.080 ± 0.198 kg m –2 a –1 ), while in the other two sites, it significantly slowed down after the first survey period: from 0.952 ± 0.199 to 0.350 ± 0.103 kg m –2 a –1 at P213, and from 1.470 ± 0.462 to 0.203 ± 0.058 kg m –2 a –1 at P204. The amount of eroded limestone increased with the exposure time, with no significant differences among sites, from 1.13 ± 0.29 to 10.39 ± 1.14 kg m –2 on average at 3 and 12 years, respectively. The bioerosion rate also increased with the exposure time and was slightly higher at MR08 (from 0.682 ± 0.208 to 1.105 ± 0.088 kg m –2 a –1 ), mostly eroded by Cliona rhodensis in addition to C. viridis , compared to P204 (from 0.267 ± 0.078 to 0.676 ± 0.172 kg m –2 a –1 ) and P213 (from 0.179 ± 0.065 to 0.816 ± 0.171 kg m –2 a –1 ). Overall, bioconstruction has overcome the bioerosion processes in 3 years. In 12 years, the estimated net balance was essentially nil at all sites. Combining field experiment and CT analysis, this study provides the first quantification of the bioerosion and bioconstruction processes in the northern Adriatic coralligenous reefs, a fundamental step toward their conservation.

Marine animal forests are benthic communities dominated by sessile suspension feeders (such as sponges, corals, and bivalves) able to generate three-dimensional (3D) frameworks with high structural complexity. The biodiversity and functioning of marine animal forests are strictly related to their 3D complexity. The present paper aims at providing new perspectives in underwater optical surveys. Starting from the current gaps in data collection and analysis that critically limit the study and conservation of marine animal forests, we discuss the main technological and methodological needs for the investigation of their 3D structural complexity at different spatial and temporal scales. Despite recent technological advances, it seems that several issues in data acquisition and processing need to be solved, to properly map the different benthic habitats in which marine animal forests are present, their health status and to measure structural complexity. Proper precision and accuracy should be chosen and assured in relation to the biological and ecological processes investigated. Besides, standardized methods and protocols are strictly necessary to meet the FAIR (findability, accessibility, interoperability, and reusability) data principles for the stewardship of habitat mapping and biodiversity, biomass, and growth data.

A sediment bypassing plant based on innovative jet pump, ejectors, has been tested in the first-of-a-kind demo application at the harbor of Cervia (Italy, Northern Adriatic Sea). The ejector is a jet pump aimed to reduce sediment accumulation in navigation channels and coastal areas. Herein we present results of the first study assessing the potential ecological effects of the ejectors plant. Sediment characteristics, benthic, and fish assemblages before and after the plant activation have been analyzed in the putatively impacted (the sediment removal and discharge) areas and four control locations, one time before and two times after plant activation. Ejectors plant operation resulted in a reduction of the mud and organic matter content in the sediment, as well as in changes in shell debris amount in the impacted areas. Abundance and species richness of benthic macroinvertebrates, initially reduced in the impacted areas, probably due to the previous repeated dredging, returned to higher values during demo plant continuous operation. Higher diversity of fish fauna was observed in the study area during plant operation period. Observed dynamics of the ecological status of the marine habitat suggest that an ejectors plant could represent an eco-friendly solution alternative to dredging operations to solve harbor siltation problems.

Artisanal and small-scale gold mines (ASGMs) have been accompanied by widespread usage of mercury amalgamation to extract gold from ores, putting Indonesia among the top three global emitters of this pollutant and posing potential risks to the marine ecosystem and human health. Although the use of mercury has been largely eliminated following the signature of the Minamata Convention on Mercury, the practice of mercury amalgamation in ASGM has persisted in several regions, including the North Sulawesi. This study assesses how on the contamination of mercury and other trace elements coming from both industrial mines and ASGMs affects marine sediments and their bioaccumulation in two tissues (body wall and guts) of the edible holothurian Holothuria ( Halodeima ) atra , by comparing samples collected downstream of four mining areas to four control sites in the North Sulawesi province, Indonesia. In sediments, mean concentrations of arsenic, gold, cobalt, chromium, copper, mercury, nickel, lead, antimony, and zinc were significantly higher at sites receiving mine discharges than at control sites. Downstream to gold mines, compared to control sites, significant higher concentrations of As, Au, Cr, Hg, and Ni in holothurians body walls and of As, Au, Co, Cr, Cu, Hg, Pb, Sb, Sn, and Zn in holothurians guts were found. In general, higher contaminations in sediments and tissues were found at the site near the oldest artisanal mine. Trace element levels in H. atra specimens in North Sulawesi were generally higher than those reported in other regions. In the study area, these holothurians significantly bioaccumulate Hg, As, Zn, Cd, Cu, Sn, and biota-sediment accumulation factors were higher in guts than in body walls. From an environmental and human health perspective, Hg is resulted the most concerning element in surface sediment and H. atra specimens. Based on this evidence, further studies are urgently needed to understand better the effect of mercury and other potentially toxic trace elements in marine ecosystems and food webs in mining areas both in North Sulawesi and in many still poorly investigated southeast Pacific areas.

The northern Adriatic Sea (NAS) hosts numerous biogenic subtidal reefs that are considered biodiversity hotspots. Several studies have already investigated the origin and biodiversity of these reefs. However, many of them are still unexplored and further knowledge is needed for their conservation. Here, the spatial variability, epibenthic community structure, and environmental features that characterize these habitats were investigated. Fifteen randomly selected reefs were sampled between 2013 and 2017, including some remote sites that have never been studied before. A fuzzy k-means clustering method and redundancy analysis were used to find similarities among sites in terms of epibenthic assemblages and to model relationships with abiotic variables. The results showed that these reefs are highly heterogeneous in terms of species composition and geomorphological features. The results were also consistent with previous studies and highlighted three main types of benthic assemblages defined by the dominance of different organisms, mainly reflecting the coastal-offshore gradient: nearshore reefs, generally dominated by stress-tolerant species; reefs at a middle distance from the coast, characterized by sponges, non-calcareous encrusting algae and ascidians; offshore reefs, dominated by reef builders. However, distance from the coast was not the only factor affecting species distribution, as other local factors and environmental characteristics also played a role. This kind of biogenic reefs in temperate seas are still poorly known. The present work contributed to shed further light on these habitats, by complementing the results of previous studies on their natural diversity, highlighting the specificity of the epibenthic communities of NAS reefs and the need to improve current, still inadequate, conservation measures.

The zoanthid Parazoanthus axinellae (Schmidt, 1862) is a widespread coral species in the Mediterranean coralligenous assemblages where two morphotypes are found: Slender and Stocky, differing in size, color, and preferred substrate. Due to these marked differences, Slender and Stocky morphotypes were hypothesized to be two species. Here, we used 2bRAD to obtain genome‐wide genotyped single nucleotide polymorphisms (SNPs) to investigate the genetic differentiation between Slender and Stocky morphs, as well as their population structure. A total of 101 specimens of P. axinellae were sampled and genotyped from eight locations along the Italian coastline. In four locations, samples of the two morphotypes were collected in sympatry. 2bRAD genome-wide SNPs were used to assess the genetic divergence between the two morphotypes (1319 SNPs), and population connectivity patterns within Slender (1926 SNPs) and Stocky (1871 SNPs) morphotypes. Marked and consistent differentiation was detected between Slender and Stocky morphotypes. The widely distributed Slender morphotype showed higher population mixing patterns, while populations of the Stocky morphotype exhibited a stronger genetic structure at a regional scale. The strong genetic differentiation observed between P. axinellae Slender and Stocky morphotypes provides additional evidence that these morphs could be attributed to different species, although further morphological and ecological studies are required to validate this hypothesis. Our study highlights the importance of resolving phylogenetic and taxonomic disparities within taxonomically problematic groups, such as the P. axinellae species complex, when performing genetic connectivity studies for management and conservation purposes. Graphical Abstract Schematic overview of the main genetic structuring patterns observed in this study. Coral polyps were colored to intuitively associate the reader to Parazoanthus axinellae morphotypes, with orange tones being attributed to the Stocky morphotype, and yellow tones to the Slender morphotype. Bidirectional arrows represent gene flow between coral individuals, with the number and thickness of arrows corresponding to the intensity of gene flow rates. The red dashed line represents the potential reproductive isolation between Slender and Stocky morphs