Preliminary assessment of methanogenic microbial communities in marine caves of Zakynthos Island (Ionian Sea, Greece)

Mediterranean marine caves remain largely unexplored, while particularly limited information is available about the microbial life existing in these unique environments. The present study is a preliminary assessment of the composition of the active anaerobic microbial community colonizing the walls of newly explored systems of underwater caves and small cavities in Zakynthos Island. The interior of these caves is densely coated with egg-shaped, foam-shaped and filamentous biological structures that are characterised by a strong odor of hydrogen sulfide gas. A total of twelve structures scrapped from cave rocks were subjected to anaerobic cultivation for up to 208 days. Strong to moderate methanogenesis was observed in two different types of egg-shaped structures and one foam-like structure. Interestingly, this was observed in experiments that were performed at room temperature (i.e. 25oC) which is substantially lower than those typically considered optimum for methane production (e.g. 35oC). Analysis of the 16S rRNA genes revealed a clear dominance of archaea and bacteria closely related to known methane producers and sulfate reducers, including members of the families Methanomicrobiaceae, Desulfobulbaceae, Desulfobacteraceae, Desulfuromonaceae, Campylobacteraceae, Marinifilaceae, Clostridiaceae, Incertae Sedis – Family I & II. These results show that Mediterranean marine caves can host members of archaea and bacteria with potential biotechnological interest that deserve further investigation

Assessing the regional conservation status of sponges (Porifera): the case of the Aegean ecoregion

Sponges are among the less-studied benthic invertebrates as regards their extinction risk and conservation status. Herein, we evaluate the regional conservation status of sponges in the Aegean ecoregion (Eastern Mediterranean Sea), using the IUCN Red List criteria. We examined 20 sponge taxa falling into three categories: i) threatened species listed in Annex II of the Barcelona Convention, ii) bath sponge species (Annex III of the Barcelona Convention), and iii) Aegean endemics. The regional geographic range of the examined taxa was depicted on detailed distribution maps, based mostly on recent observations by the authors and literature data. When possible, population trends were estimated based on historical data, and threats were identified. The suggested regional conservation status of the examined sponge species is as follows: i) nine species were characterised as ‘Data Deficient (DD)’ due to limited available information; ii) seven species were assigned to the ‘Least Concern (LC)’ category; iii) the four harvested bath sponge species were assigned to the Endangered (EN) category, based on their population decline in the Aegean region during the past decades. The present evaluation, besides providing scientific data for the regional protection and management of sponge populations, can form a basis for wider assessment and consequent conservation of Porifera

Polytraits : a database on biological traits of marine polychaetes

The study of ecosystem functioning – the role which organisms play in an ecosystem – is becoming increasingly important in marine ecological research. The functional structure of a community can be represented by a set of functional traits assigned to behavioural, reproductive and morphological characteristics. The collection of these traits from the literature is however a laborious and time-consuming process, and gaps of knowledge and restricted availability of literature are a common problem. Trait data are not yet readily being shared by research communities, and even if they are, a lack of trait data repositories and standards for data formats leads to the publication of trait information in forms which cannot be processed by computers. This paper describes Polytraits (http://polytraits.lifewatchgreece.eu), a database on biological traits of marine polychaetes (bristle worms, Polychaeta: Annelida). At present, the database contains almost 20,000 records on morphological, behavioural and reproductive characteristics of more than 1,000 marine polychaete species, all referenced by literature sources. All data can be freely accessed through the project website in different ways and formats, both human-readable and machine-readable, and have been submitted to the Encyclopedia of Life for archival and integration with trait information from other sources

An acoustic Odyssey: Characterisation of the vocal fish community inhabiting Neptune seagrass meadows across the Mediterranean Sea.

Passive acoustic monitoring (PAM) uses hydrophones to record all components of underwater soundscapes, including fish calls. Several studies have used PAM to investigate different aspects of vocal fish species, such as presence, distribution, relative abundance, diel, lunar and seasonal cycle of activity as well as for delimitating spawning areas and for studying wild fish spawning behaviour. A recent study conducted in Mediterranean rocky reefs has proved that the analysis of vocal fish communities provides high discrimination potential of species assemblages. Aside from this study, most investigations to date have considered fish species in isolation, and there is a general paucity of data addressing acoustic communication of fishes living in natural communities. We present a preliminary characterisation of vocal fish communities over a geographical and environmental gradient in Mediterranean Posidonia oceanica meadows and adjacent areas. We compared abundance and diversity of fish sounds recorded during the peak of fish vocal season in Posidonia oceanica meadows (-20 m) along a longitudinal axis (Mallorca, Corsica and Crete). These results are discussed in a framework that highlights the investment of different vocal fish species in partitioning their active acoustic space (in terms of both frequency and time) over small- and large-scale gradients. Our study supports the potential of PAM to provide high resolution information on fish population dynamics

Isotopic Niche and Trophic Position of the Invasive Portunid Portunus segnis Forskål, (1775) in Elounda Bay (Crete Island, Eastern Mediterranean)

There is a growing recognition that an advanced understanding of the trophic characteristics of an invasive consumer can provide important information on its ecological impact. In recent years, the blue swimming crab Portunus segnis, one of the earliest Lessepsian invaders, has considerably expanded its distribution range in the Mediterranean Sea, yet, its trophic habits in invaded areas remain scarcely investigated. In this study, we used carbon and nitrogen stable isotopes analysis (SIA) to determine the trophic position and isotopic niche of the crab compared with other representatives of the flora and fauna occurring in Elounda Bay (Crete). P. segnis showed a trophic position of 3.9, higher than the values determined by SIA or conventional gut content analysis in other areas of the Mediterranean Sea or in the native range. Crab specimens showed a high inter-individual variability in both delta C-13 and delta N-15 values; further analysis indicated negligible differences in the isotopic niche of adult males and females. Conversely, delta N-15 values were significantly related to the size of the specimens, ultimately suggesting an ontogenetic dietary shift. This study represents the first attempt to characterize the trophic habits of the blue swimming crab in the context of an invaded food web and may contribute to the implementation of long-term management strategies of control and mitigation of its ecological impact

Early Succession Patterns of Benthic Assemblages on Artificial Reefs in the Oligotrophic Eastern Mediterranean Basin

The colonization of artificial structures by benthic organisms in the marine realm is known to be affected by the general trophic patterns of the biogeographical zone and the prevailing environmental traits at the local scale. The present work aims to present quantitative data on the early settlement progress of macrofaunal benthic assemblages developing on artificial reefs (ARs) deployed at the Underwater Biotechnological Park of Crete (UBPC) in the oligotrophic Eastern Mediterranean. Visual census and subsequent image analysis combined with scraped quadrats were used to describe the establishment of the communities and their development over three consecutive campaigns, span-ning 5 years post-deployment. Macroalgae consistently dominated in terms of coverage, while sessile invertebrates displayed different patterns over the years. Polychaeta and Bryozoa were gradually replaced by Cnidaria, while Porifera and Mollusca displayed an increasing trend over the years. Motile benthos was mainly represented by Mollusca, while the abundance of Polychaeta increased in contrast to that of Crustacea. For both sessile and motile assemblages, significant differences were observed among the years. The results of this study indicate that ecological succession is still ongoing, and further improvement in the monitoring methodology can assist towards a more accurate assessment of the community composition in complex AR structures.European Union MIS 5002670, MIS 502740

Pinna nobilis in the Greek seas (NE Mediterranean): on the brink of extinction?

The Mediterranean endemic fan mussel Pinna nobilis is suffering an ongoing basin-scale mass mortality event (MME) since 2016. As most Mediterranean populations have collapsed, the species has been declared as Critically Endangered in the IUCN Red List of threatened species. In an effort to track the progress of the MME and provide updated information on the status of the species in the Greek seas, data collected through dedicated surveys and opportunistic assessments during 2019 and 2020 have been compiled. During surveys conducted at 258 sites, a total of 14,589 fan mussels were recorded, of which 81.1% were dead. Of the remaining 2,762 live individuals, 256 were juveniles. Two marine areas that still sustain living populations were identified, namely Kalloni Gulf (Lesvos Island), and Laganas Bay (Zakynthos Island). The inner part of Kalloni Gulf appears to maintain the largest surviving population of the species in the eastern Mediterranean, with an abundance estimate of 684,000 individuals (95% confidence interval: 322,000-1,453,000). Solitary, potentially resistant, scattered individuals were recorded at several sites. Other previously abundant populations that had been assessed in the past, specifically those of Lake Vouliagmeni (Korinthiakos Gulf), Souda Bay (Crete) and Gera Gulf (Lesvos Island) with a total of ~350,000 individuals, have now been wiped out. Our results document the collapse of most P. nobilis populations throughout the Greek seas. The MME has progressed substantially between early 2019 and mid-2020, as indicated by the increase in mortality at sites consecutively monitored multiple times. This work highlights the urgent need for continuous monitoring of surviving populations and calls for immediate implementation of an effective protection and management strategy that will ensure the persistence of surviving individuals and the production of resistant offspring

State of the knowledge on European marine habitat mapping and degraded habitats

During the last decades, several EU Directives and other international legislations have generated a large number of national initiatives (e.g. marine atlases) and EU programmes on habitat mapping. Nevertheless, the outcomes of these initiatives are fragmented and, to our best knowledge, to date there is no systematic assessment regarding the nature, quality and availability of information across the European seas. One of the main goals of the MERCES project (www.merces-project.eu) is to produce a census of available maps of European key marine habitats, along with their degradation status and restoration potential in the European Seas, providing a potential basis for future discussion on restoration activities. MERCES is producing a census of European marine key habitat maps, degraded habitat maps and investigating key habitat restoration potential. To do this MERCES has i. reviewed known existing habitat maps of European regional seas and provided source citations for all of the information ii. reviewed degraded habitat map resources by regional sea and habitat type (e.g. seagrass, macroalgae, coral gardens, sponge aggregations, seamounts, vents), associated habitat deterioration (e.g. extent of decline), the most common human activities and pressures reported, and the recovery and restoration potential of these habitats iii. reviewed 6 key habitats (including kelp and macroalgal forests, seagrass meadows, coralligenous assemblages, coral gardens and deep-sea bottom communities) and linked 6 major habitat features, such as dynamics, connectivity, structural complexity and vulnerability, to consequences for restoration and the likelihood of restoration succes

Where Is More Important Than How in Coastal and Marine Ecosystems Restoration

Restoration is considered an effective strategy to accelerate the recovery of biological communities at local scale. However, the effects of restoration actions in the marine ecosystems are still unpredictable.We performed a global analysis of published literature to identify the factors increasing the probability of restoration success in coastal and marine systems. Our results confirm that the majority of active restoration initiatives are still concentrated in the northern hemisphere and that most of information gathered from restoration efforts derives from a relatively small subset of species. The analysis also indicates that many studies are still experimental in nature, covering small spatial and temporal scales. Despite the limits of assessing restoration effectiveness in absence of a standardized definition of success, the context (degree of human impact, ecosystem type, habitat) of where the restoration activity is undertaken is of greater relevance to a successful outcome than how (method) the restoration is carried out. Contrary to expectations, we found that restoration is not necessarily more successful closer to protected areas (PA) and in areas of moderate human impact. This result can be motivated by the limits in assessing the success of interventions and by the tendency of selecting areas in more obvious need of restoration, where the potential of actively restoring a degraded site is more evident. Restoration sites prioritization considering human uses and conservation status present in the region is of vital importance to obtain the intended outcomes and galvanize further actions