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The authors thank all the people involved in collecting/providing material or organising sampling campaigns: Peter Schuchert (MHNG, Switzerland), Tullia Isotta Terraneo (KAUST, Saudi Arabia), Malek Amr Gusti (KAUST, Saudi Arabia), Timothy Ravasi (OIST, Japan), the captain and crew of the MV Dream-Master (Saudi Arabia), the KAUST Coastal and Marine Resources Core Lab, Inga Dehnert (UNIMIB, Italy), Nicholas WL Yap (NUS, Singapore), Sudhanshi S Jain (NUS, Singapore), Stephen Keable (Australian Museum), Penny Berents (Australian Museum), Anne Hoggett (Australian Museum), Lyle Vail (Australian Museum). Additionally, we wish to thank Leen P. van Ofwegen (Naturalis, The Netherlands) for his valuable help in identifying the octocoral Paralemnalia sp., Peter Schuchert for his comments on an earlier version of the manuscript, and two anonymous referees for their thorough revision of this work. Permissions relevant to undertake the research have been obtained from the applicable governmental agencies. Fieldwork at St. Eustatius was funded through a Martin Fellowship from Naturalis Biodiversity Center to SM, while logistic support was supplied by St. Eustatius Marine Parks (STENAPA), the Caribbean Netherlands Science Institute (CNSI) and Scubaqua Dive Centre. Samples from Eilat (Israel) were collected during the HyDRa Project funded by the EU FP7 Research Infrastructure Initiative ‘ASSEMBLE’ (Grant #227799) to DP. Financial support to DP for collecting samples at Lizard Island (Australia) was provided by the 2018 John and Laurine Proud Fellowship and the Australian Museum’s Lizard Island Research Station. Fieldwork in Mozambique was conducted during the Green Bubbles financed by EU’s H2020 research and innovation programme to DP, under the Marie Sklodowska-Curie grant agreement no 643712 (Permit n° 09/2018 ANAC). Fieldwork in Singapore was partially funded by the National Research Foundation, Prime Minister’s Office, Singapore under its Marine Science R&D Programme (MSRDP-P03) to DH.

Population dynamics in lower metazoans are strongly regulated by environmental factors. The running climate crisis could affect regularity of life strategies; therefore, studying life cycles and reproductive patterns of benthic species may provide key information on effects of environmental changes in temperate seas. The North Adriatic Sea is a peculiar basin due to high food availability and high fluctuations of physical parameters. Here, cnidarians are one of the most abundant taxa and sea anemones are the largest representatives. Aim of this study is to assess the life history and the reproductive biology of two potential species models: the sea anemones: Anemonia viridis and Exaiptasia diaphana. The present research is the first quantitative study on the variations in abundance and reproductive biology of the two species. We reported new insights about abundance fluctuations throughout the year and about the gametogenesis of the two sea anemones. In particular, data on spermatogenesis of A. viridis from the Mediterranean Sea were supplied for the first time.

Mesophotic habitats, hosting benthic assemblages totally unknown and unexpected in the early 2000s, are attracting an increasing interest from scientists. Realizing that many long living and habitat forming species are playing a unique pocket of biodiversity in the frame of climate crisis, it is important to recognize the potential of the mesophotic zone in conservation strategies. The mesophotic zone is characterized by environmental factors generally more stable than the shallow counterpart; therefore, it represents a refuge habitat to preserve species that, in shallow waters, may be involved in bleaching events, massive mortalities or other pathologies generally triggered by thermal anomalies. The definition of the mesophotic zone in the temperate seas is confused, creating possible misunderstandings and problems not only from a scientific point of view but also in communication and outreach strategies. Here, we review the scientific literature to build the best definition possible based on the maximum consensus coming from papers analysis. Moreover, the key roles of mesophotic habitats, including ecosystem engineers as animal forests, have been schematized to enhance the perception of the potential risks we are running in case of damage or loss of these habitats.

This paper investigated the long-term changes (from 1973 to 2013) of the seagrass meadows of Zostera marina, Zostera noltei and Cymodocea nodosa in the Adriatic Sea subjected to multiple pressures. We examined the changes of the meadows by means of field data collection, observations and analysis of aerial photography to identify the most important drivers of habitat loss. The major decline of seagrass extension observed from 1973 to 1989, was primarily driven by urban development, and by the increase of the blue tourism. From 1989 to 2007 seagrass habitats progressively recovered due to the decrease of urbanization, but from 2007 to 2013 a further significant loss of seagrass meadows was apparently driven by thermal anomalies coupled with an increasing anthropogenic pressure. Our long-term analysis provides evidence that the rates of seagrass loss are faster than the recovery rates (i.e., -4.5 loss rate vs +2.5% recovery rate per year).

4th World Conference on Marine Biodiversity (WCMB 2018), 13-16 May 2018, Montreal, The temperate coralligenous bioconcretions are mainly built by the accumulation of encrusting coralline algae growing at low irradiance levels. They harbour approximately 10% of marine Mediterranean species (about 1600 species), including long-lived algae and invertebrates. Enhanced by climate change, several pressures affect coralligenous assemblages, leading to increased frequency of mass mortalities and dramatic loss of habitat complexity and biodiversity. The EU-funded project MERCES is developing innovative methodologies to restore macroinvertebrate habitat-forming species from three key taxonomic groups: Cnidaria/Anthozoa, Porifera/Demospongiae and Bryozoa. Restoration protocols are based on fragments/transplants from donor organisms and recruitment-enhancing devices. Collaboration with volunteers (divers and diving operators) in several phases of field activities proved crucial both to minimize underwater working time and to increase the sense of stewardship in a major users’ segment. Additionally, the MERCES project explores how to enhance restoration success by identifying the mechanisms conferring resistance to thermal stress in gorgonians. This is pursued by coupling thermotolerance experiments with next generation sequencing tools and facilitation processes (by comparing the outcomes of mono-specific vs. multi-specific transplanted assemblages). Results will be included in the strategic planning of restoration efforts in the Mediterranean in the context of global change

Lytocarpia myriophyllum, the biggest hydroid of the Mediterranean, lives at soft bottoms. It is severely threatened by bottom trawling activities. To assess its possible influence on trophodynamics and biodiversity of surrounding sediments, we compared the organic matter content and biochemical composition, and meiofaunal biodiversity in sediments below L. myriophyllum colonies and in surrounding bare sediments. Below L. myriophyllum sediments, the protein to carbohydrate ratio, the lipid contents and meiofaunal abundance showed values higher than in bare sediments, suggesting that L. myriophyllum may influence the availability of resources for benthic consumers. The richness of meiofaunal taxa and nematode species generally decreased from below the colonies to bare sediments suggesting that the presence of L. myriophyllum colonies can have a certain influence also on benthic biodiversity. The possible influence of L. myriophyllum on trophodynamics and biodiversity of neighbouring soft bottoms claims for ...

In the Mediterranean Sea, as well as in other parts of the word, intense bottom trawling threatens deep and mesophotic assemblages, compromising mainly the survivorship of erect organisms and of the habitat complexity they shape. Protection of species able to affect their habitats, by increasing spatial complexity and enhancing interspecific interactions, is crucial for biodiversity conservation. It is urgent to highlight the occurrence of those species which act as ecosystem engineers and/or habitat former to enhance awareness on their ecological role and to develop focused conservation strategies. Lytocarpia myriophyllum is the largest Leptomedusan hydroid of the Mediterranean Sea, with colonies up to 1 m high, and the most abundant Aglaopheniid in the eastern part of the North Atlantic Ocean. This species creates wide forests on soft bottoms stabilizing sediments, providing refuge and food for several other associated organisms and could be defined both a habitat former and an ecosystem engineer. Thanks to trimix diving here we report on new insights on the morphological, biological and ecological features of L. myriophyllum meadows from the Mediterranean Sea furnishing a baseline for protection plans focused on these facies. This work demonstrates that direct studies of mesophotic habitats allow to collect far more detailed information than grabs, ROVs, or towed camera arrays and highlights the urgent need to redefine the vertical extension of several marine protected areas.