The European spiny lobster, Palinurus elephas (spiny lobster or P.elephas thereafter), a highly valued species in the NW Aegean Sea, Greece, faces significant fishery pressure and population decline. This study provides novel insights into its biology, population dynamics, and fishery status in Thermaikos Gulf and the National Marine Park of Alonissos and Northern Sporades (NMPANS). Using data from 308 individuals collected in 2018–2019, we assessed morphometric relationships, age composition, growth, mortality, and exploitation rates. Carapace length-weight relationships showed negative allometry, with no significant sex differences. Eight age classes were identified, with a dominant fourth-year cohort (43.35%). Von Bertalanffy growth models estimated an asymptotic length of 234.09 mm and longevity of 24.6 years. The exploitation rate (0.85) exceeds sustainable limits (EMSY = 0.55), indicating overfishing, with fishing mortality (0.85) surpassing FMSY (0.17). Larger individuals were found in NMPANS, suggesting some protective effect, but the population remains at risk of collapse. Greek fish auction data revealed potential illegal landings, highlighting enforcement challenges. We recommend reduced landings, enhanced gear selectivity, and systematic monitoring to ensure sustainability. These findings underscore the need for ecosystem-based management to conserve P. elephas and associated threatened species.

Citizen science has become a powerful tool for generating extensive ecological data and fostering public engagement in environmental monitoring and conservation initiatives. In marine environments, where monitoring is challenging due to logistical demands and financial constraints, engagement of recreational divers in citizen science projects offers a promising avenue for expanding data collection efforts over large spatial and temporal scales. Here, we evaluate the accuracy of ecological data collected by 118 volunteer divers in three countries in the Mediterranean region by comparing their observations with those of expert scientists during 2012–2016. Using standardized monitoring protocols across multiple sites, we assessed volunteers’ abilities to identify marine species, threats and impacts, estimate abundances, and correctly report species’ absence. Our results demonstrated a notable success rate (exceeding 70

Microplastic ingestion poses a significant concern for a plethora of marine organisms due to its widespread presence in marine ecosystems. Despite growing scientific interest, the effects on marine biota are not yet well understood. This study investigates the ingestion of microplastics (MPs) by mussels from various marine environments and assesses the associated effects that can be induced by MPs and associated toxic chemicals. Biomarkers of oxidative stress (catalase, lipid peroxidation), biotransformation (glutathione S-transferase), genotoxicity (micronuclei frequency) and neurotoxicity (acetylcholinesterase) were employed. Mussels, considered reliable bioindicators of MPs pollution, were sampled by hand from diverse locations under varied anthropogenic pressures, including a highly touristic Marine Protected Area (MPA) in the Ionian Sea, a mussel farm and a fish farm in the Aegean Sea. The results revealed the highest MP ingestion in mussels from the fish farm [0.21 ± 0.04 (SE) MPs/g or 0.63 ± 0.12 (SE) MPs/Ind.], likely due to plastic aquaculture equipment use. Stereoscopic observation revealed fibers, as the predominant shape of ingested MPs across all sites, and μFTIR polymer identification revealed the presence of various types, with polyethylene (PE) and polyamide (PA) being the most abundant. Significant physiological alterations in mussels related to MP ingestion levels were observed through biomarkers indicative of oxidative stress and biotransformation, as well as the Integrated Biomarker Response (IBR index). However, laboratory experiments with mussels exposed to controlled increasing PE concentrations for four weeks, did not show significant effects triggered by the PE ingestion, possibly indicating other environmental factors, such as contaminants from aquaculture environments, may influence biomarker levels in the field. Despite the observed effects, MP ingestion rates in mussels from the field were relatively low compared to other studies. Future research should continue to investigate the interactions between MPs and marine organisms in diverse environments to better understand and mitigate their impacts.

As climate-related impacts threaten marine biodiversity globally, it is important to adjust conservation efforts to mitigate the effects of climate change. Translating scientific knowledge into practical management, however, is often complicated due to resource, economic and policy constraints, generating a knowledge-action gap. To develop potential solutions for marine turtle conservation, we explored the perceptions of key actors across 18 countries in the Mediterranean. These actors evaluated their perceived relative importance of 19 adaptation and mitigation measures that could safeguard marine turtles from climate change. Of importance, despite differences in expertise, experience and focal country, the perceptions of researchers and management practitioners largely converged with respect to prioritizing adaptation and mitigation measures. Climate change was considered to have the greatest impacts on offspring sex ratios and suitable nesting sites. The most viable adaptation/mitigation measures were considered to be reducing other pressures that act in parallel to climate change. Ecological effectiveness represented a key determinant for implementing proposed measures, followed by practical applicability, financial cost, and societal cost. This convergence in opinions across actors likely reflects long-standing initiatives in the Mediterranean region towards supporting knowledge exchange in marine turtle conservation. Our results provide important guidance on how to prioritize measures that incorporate climate change in decision-making processes related to the current and future management and protection of marine turtles at the ocean-basin scale, and could be used to guide decisions in other regions globally. Importantly, this study demonstrates a successful example of how interactive processes can be used to fill the knowledge-action gap between research and management.

In the Mediterranean Sea, the genus Pinna encompasses two large fan-shaped bivalve species, Pinna nobilis and Pinna rudis. Historically, both species coexisted in the western Mediterranean until a mass mortality event (MME) brought P. nobilis to the brink of extinction. Notably, P. rudis remained unaffected by the MME, and its recent successful recruitment and further spread have been hypothesized to be linked to the local extinction of P. nobilis. Although P. rudis has been sparsely recorded in the eastern Mediterranean Sea (with some of these records being doubtful), reports emerging in the summer of 2023 from researchers and citizens have unveiled its sudden spread in the region. This study documents the recent presence of P. rudis within Greek waters through a dedicated survey and molecularly confirmation through two distinct molecular methods. Information derived from a citizen science initiative, following photo-identification of the species was also included. Furthermore, an updated review of the distribution of P. rudis in the Mediterranean Sea, integrating data from literature and online repositories is provided. This research confirms the recent spread of P. rudis in Crete, the Greek Ionian Sea, and Cyprus (first verified records of the species in the regions), in marine areas where P. nobilis has become extinct, further strengthening the hypothesis that P. rudis has benefited from the collapse of P. nobilis populations.

Abstract Serranus hepatus is a bycatch species in the Mediterranean trawl fishery for which knowledge on biological features such as otolith morphology is generally poor in the Mediterranean Sea. In the present study, the weight–length relationship, age, growth and ten otolith morphometric variables of this species were investigated in two distant areas, the Eastern Ionian and southwestern Aegean Seas. Isometric growth in weight was defined in both areas. Growth parameters also did not differ between the two study areas. Six of the otolith variables (radius, otolith length, otolith width, otolith area, perimeter and ellipticity) showed a significant relationship with size without significant differences between the two areas. Significant differences between the two areas were only defined for five of the morphometric variables (otolith length, width and area being the most important). Further studies to discriminate between potential stocks of S. hepatus seem to be necessary, information that is needed for stock identification, stock assessment and fisheries management.

Sea turtles are highly mobile species that use oceanic, neritic, and coastal habitats as nursery, foraging, wintering, breeding and migration areas at distant locations throughout their lifetime. Due to their highly migratory nature and large-scale habitat use, they are subjected to multiple threats across marine and coastal ecosystems that can impact every stage of their life cycle and result in increased mortality rates. Here, we present new data on stranding events across the eastern Ionian Sea (central Mediterranean). Our analysis on stranding data, collected over a 6-year period, provided clear evidence of continuing and increased mortality events in the region (n = 413, Caretta caretta: 79%, Chelonia mydas: 4%, and unknown: 17%). Based on the alarming results of increased mortality, and taking into account the limitations posed by the nature of stranding data, we further identified potential risk hotspots within critical marine and coastal sea turtle habitats. To do so, we performed a spatially explicit cumulative pressure assessment at different spatial scales in an effort to identify, map, quantify, and synthesize the multiple anthropogenic pressures that are recognized to potentially impact sea turtles. Our results clearly demonstrated that the Ionian Sea is subjected to intense pressures (i.e. fisheries, marine traffic, and underwater noise). We identified three main hotspots of very high risk related to critical foraging grounds, nesting sites, and migration corridors for sea turtles regardless of the spatial scale of the analysis. We found high sea turtle mortality associated with locations characterized as high and very high risk areas. This study offers key information on mortality and spatial risk for sea turtles that can facilitate their effective conservation. Thus, our findings can be used in the light of marine spatial planning, allowing planners to more realistically assess where conservation resources should be directed to control harmful activities and to mitigate impacts on sea turtles.

Research known as Citizen Science (CS) has been recognized as an important tool for both biodiversity restoration and fisheries management projects through active involvement of citizens and therefore for public environmental awareness too. CS projects should be well designed and state clear questions, that will benefit both the research goals and the citizen scientists themselves. In January 2019, the “Red Fish Project” group was created on Facebook consisting of SCUBA divers and fishers and offering the main data source and the relevant digital material. The project’s establishment was based on previous personal experience and following specific protocols. Further information was provided by personal communications. Till October 21st, 2020 the FB group consisted of 464 members who recorded 348 European spiny lobster individuals from all sub-regions of the Aegean Sea. Based on the findings of the present study it seems that most of the citizens were unaware that the species is listed as “Vulnerable” in the IUCN Red List. Lastly, we discuss the important role of the spiny lobster in the country’s culture and that it can be listed as a charismatic, flagship species for citizens to be ocean-literate since it has been shown, that it can raise the interest of recreational divers and increase their awareness.

Meadows of Posidonia oceanica harbor rich biodiversity and ecosystem functions, yet Biological Traits Analysis on the resident benthic communities are lacking. This study aims to provide insight on the functional diversity of polychaetes communities, a dominant benthic group, between the different habitat types of P. oceanica (plain meadow, strips/patches and dead matte), as well as pilot indicators of habitat modification. The results showed how specific traits relate to the different habitat types. Plain meadow was different to strips/patches and dead matte in functional composition, diversity and thus, the ecosystem functions involved. However, an overlap was observed in functional composition between dead matte and living P. oceanica, due to the remaining matte structure. This highlights the importance of the former on ecosystem functioning and the serious consequences of its current exclusion from conservational legislation. In addition, the classification of species to ecosystem en-gineering types showed interesting potential as an indicator.

Sea level rise could result in the loss and shrinkage of coastal habitats, jeopardizing the persistence of a number of species that rely upon these highly dynamic and sensitive areas. With reproduction and population recruitment depending exclusively on low-lying sandy beaches, marine turtles are among the organisms for which sea level rise represents a major threat. Here, we provide an assessment of the potential impacts of sea level rise upon sandy beaches located at the Ionian Archipelagos, which host some of the main nesting sites of the Mediterranean population of the loggerhead marine turtle Caretta caretta. Our analyses focused on sandy beaches which host stable or sporadic nesting as well as on sites that could potentially serve as nesting grounds for the species. We demonstrated that more than 60% of the stable nesting sites (accounting for about half of the total nesting activity in the region) are likely to fail to act as nesting sites under moderate and worst case scenarios of projected sea level rise by 2100. We found that only about one fifth of the stable and the sporadic nesting beaches were characterized by high resilience to SLR, meaning that the effective zone for nesting can migrate landwards and fit in the remaining upper beach part. Potential nesting sites were subjected to even lower resilience to sea level rise, suggesting that even if marine turtles could shift to new, nearby nesting sites, the efficiency of such a response would be limited. These alarming findings call for the prioritization of conservation and restoration efforts towards sandy shores of moderate and high resilience to sea level rise which are currently used for stable or even sporadic nesting.

This paper presents the state-of-the-art research conducted as part of EN.I.R.I.S.S.T. regarding the emerging impact of shipping and transport to the environment. More specifically, it presents the digital platforms and services that are developed as part of the research infrastructure and are related to environmental sciences. The first is the “EcoMarpol Platform”, which caters for collecting and analyzing pollution-driven data as well as calculating the environmental imprint (atmospheric emissions, waste production, chemical pollution of marine waters and sediments) of maritime activities. This platform additionally includes the online monitoring of in-port emissions from shipping and pollution from ship-to-ship transfer operations or accidents and the environmental risk assessment management. The other platform is the “Passenger Sustainable Travel Platform”, as part of which a tool for calculating aircraft emissions (CO2 and air pollutants) will be developed and applied in the Greek airspace and airports.

The loss of Mediterranean macroalgal populations dominated by Cystoseira sensu lato is driven by a multitude of pressures. In the eastern Mediterranean Sea, climate change and the establishment of Lessepsian herbivore species have further intensified the ongoing decline of these canopy-forming algae. Knowledge of the reproductive phenology, embryology and growth of Cystoseira species is the first step towards successful reforestation measures. Gongolaria montagnei is one of the most common canopy-forming algal species with a wide horizontal and vertical distribution along the Greek coasts. Mature receptacles were collected from Saronikos Gulf (Aegean Sea), and germlings were cultured in mesocosms for 34 days, reaching up to 1.30 mm in length. Divisions and early developmental stages of G. montagnei are described and possible implications for future restoration efforts are discussed. A new approach to growth rate modeling, based on surface measurements of embryos and germlings is presented.

Even before the introduction of the term “Marine Heat Wave” (MHW) and its statistical definition in global-scale studies, the scientific community had studied and recorded potentially harmful impacts of persistent conditions of warm surface layers and highly stratified water columns on the marine ecosystem. The main triggers for MHWs are yet not well understood and the current knowledge is mainly based on mass mortalities linked to temperature anomalies. EM-MHeatWaves is an interdisciplinary, collaborative, DAAD/IKYDA funded research project that investigates the atmospheric forcing, oceanic circulation and ecosystem response of MHWs in the Eastern Mediterranean Sea over the past 35 years. Two universities (Justus-Liebig-University Giessen, University of the Aegean) and one research center (Hellenic Centre for Marine Research) re-examine the definition of MHWs with emphasis on the Eastern Mediterranean by applying a holistic approach that includes reverse-engineering using model data and reanalysis covering the period 1985 to 2014. We focus on the Eastern Mediterranean because of the high sensitivity of the basin’s ecosystem to atmospheric and marine warming events, the invasion of tropical alien (Lessepsian) species, the characteristic oceanic circulation with the Eastern Mediterranean Transient events, the exchange with the Black Sea through the Turkish Strait System as well as the coastal upwelling areas. In order to study the spatiotemporal characteristics of Eastern Mediterranean MHWs we work towards a better understanding of the oceanographic processes as well as of the compounding character of the atmospheric contribution. Based on the response of marine biogeochemical cycles (depletion of subsurface oxygen levels, observed changes in the mixed layer and chlorophyll maxima depths, nutrient stoichiometries, carbon uptake and sequestration rates) and their impacts on ecosystems (i.e. shifts in planktonic and benthic community regimes, mass mortality events, disease outbreaks, etc.), triggered by the rise of ocean temperatures, we study the statistical characteristics of the oceanic temperatures and assess the corresponding ocean circulation, the synchronous and lagged contribution of the large scale atmospheric circulation. We further study the signature of these extreme Mediterranean MHW events in future projections from model runs with respect to duration, severity and spatial extent and compare them to reanalysis. EM-MHeatWaves aims at strengthening the partnership between the German and Greek institutions by conducting joint research at a high scientific level.

This study investigates the trophic diversity of fishes living in a meadow of Caulerpa prolifera on a bimonthly basis between May 2006 and April 2007 in a semi-enclosed coastal marine ecosystem of the Mediterranean Sea (Elounda Bay, Crete Island). The study area is shallow and protected from waves, and it is covered by a C. prolifera bed, characterized by high organic input and a highly diverse macrobenthic community. Feeding patterns of the fish, investigated on the basis of stomach content analyses, were described in terms of numerical abundance and frequency of occurrence of prey taxa. A total of 1642 fish individuals, belonging to 17 species, were examined. In total, 45,674 prey individuals were identified belonging to 110 prey taxa, most of which were Malacostraca including their larvae and Copepoda (41,175 individuals identified to 71 taxa). Four different trophic groups were identified: herbivorous, pelagic, benthic (hyperbenthic) and piscivorous. Trophic diversity patterns of the fish species studied were also compared to the relative availability of macrobenthic and zooplanktonic taxa during the same period in the study area. The coexistence of many different, mostly benthic but also pelagic, fishes and their juveniles implies their high trophic flexibility, which is probably important for their survival in this particular habitat. Results of the present study provide basic knowledge on trophic diversity and interactions in the marine ecosystem and, therefore, some evidence as to the protection value of this particular habitat, which is essential for the implementation of a multispecies approach to decision-makers and managers of fisheries sources of the region.

Understanding the interactions among invasive species, native species and marine protected areas (MPAs), and the long-term regime shifts in MPAs is receiving increased attention, since biological invasions can alter the structure and functioning of the protected ecosystems and challenge conservation efforts. Here we found evidence of marked modifications in the rocky reef associated biota in a Mediterranean MPA from 2009 to 2019 through visual census surveys, due to the presence of invasive species altering the structure of the ecosystem and triggering complex cascading effects on the long term. Low levels of the populations of native high-level predators were accompanied by the population increase and high performance of both native and invasive fish herbivores. Subsequently the overgrazing and habitat degradation resulted in cascading effects towards the diminishing of the native and invasive invertebrate grazers and omnivorous benthic species. Our study represents a good showcase of how invasive species can coexist or exclude native biota and at the same time regulate or out-compete other established invaders and native species.

Data with high spatial resolution on the structure and diversity of marine assemblages are valuable for fisheries management and conservation planning but are seldom available. This study provides fisheries-independent, baseline information on the structure and diversity of the demersal fish assemblages of the continental shelf and upper slope off the island of Psara (Central Aegean Sea). Experimental bottom trawl hauls were conducted during 2009–2010, using identically designed trawls. All the fish in the catches were identified onboard, enumerated, and weighted to the nearest g. Species abundance and biomass were transformed to CPUE. Forty-seven taxa were identified in the catches. For 18 of the species caught no other fisheries-independent information on their abundances and distributions is available for the wider area. Among the Elasmobranchii species collected, Squalus acanthias, Dipturus oxyrinchus, and Raja clavata are species of conservation concern. Species composition was generally more similar to that reported for assemblages of the Cretan Sea and the South Aegean Sea than for assemblages of the North Aegean. The assemblages were structured with depth, a pattern that may be driven in part by the differences in benthic habitat between depth zones. No trends by depth in total numerical abundance and species diversity were identified, whereas the bathymetric change in taxonomic diversity was attributed to the depth distributions of certain species-rich orders and families. The frequency distribution of the trophic level of the species followed the broad-scale pattern that applies in the Mediterranean Sea.

Global change impacts Mediterranean fisheries and the dependent human populations. Overfishing and epizootic diseases related to extreme climatic events are currently accepted as the main threats to the production of commercial bath sponges. Believing that other factors could have impacted this insular fishery, we assembled a 150-year-long series of sponge fishing data for Greece that was analyzed in relation with variations of the pressure and of the socio-economic contexts. Sponge fishing experienced huge variations, with notably two distant short periods when the production collapsed (late nineteenth century and between 1985 and 1991). Before the 1970s, these variations are mainly attributed to socio-economic and political changes. The monitoring of the catches per unit effort indicates a clear overfishing impact only after 1977. However, after the last collapse of the overall production which followed the severe disease outbreak of the late 1980s, the catch per unit effort showed a positive trend, which tends to indicate that the stocks available bear the present fishing pressure. Fishermen have adapted towards sustainable practices, by reducing their crew and also diversifying their targets, which nevertheless calls to a more accurate monitoring of such a small-scale fishery.

The European spiny lobster Palinurus elephas is a vulnerable species that inhabits and is harvested in the Mediterranean Sea and the adjacent Atlantic waters. The fisheries associated with the spiny lobster are mainly conducted with tangle nets, trammel nets, pots, and creels. The fishing pressure has greatly reduced their numbers, changing them from a common shallow coastal species to a largely remnant population. The relative research on the species’ biology and fisheries from the eastern Mediterranean Sea is almost absent. The fishery along the Chalkidiki Peninsula, Greece, is multispecies, and fishing is conducted by a small number of artisanal fishermen mainly using trammel nets. The lobster stock—both spiny and clawed lobsters—declined significantly during the late 1980s and early 1990s, later than most cases in the Mediterranean Sea. However, data regarding the nature and status of the fishery associated with the spiny lobster in Greece are lacking. Data regarding the characteristics of the spiny regional fishery were obtained by interviews and questionnaires. Additionally, fishery surveys were conducted during the main lobster fishing season from 1 May 2017 to 31 August 2017. Sixteen species were identified (15 finfish species and one invertebrate species) as targeted. In total, 79 spiny lobsters were sampled in this study; the population’s sex ratio significantly diverts from the theoretical 1:1 (χ2 = 4.57; p < 0.05), and males were dominant. Both male and female individuals demonstrate negative allometric growth profiles. In addition, no significant differences were observed between sexes. In Greece, thus far, the knowledge and information are sporadic, limited, and/or species-specific, most of which regard finfish fisheries. Furthermore, the national legislation is rather complicated—or too generalized—thus creating great uncertainties. The in-depth knowledge and experience of fishermen should be further acknowledged and utilized, and wider collaborations among scientists, practitioners, and policy-makers should be established. The present study poses some thoughts on the effectiveness of the recent EU Landing Obligation and its contribution to the potential restoration of the species.

Marine protected areas (MPAs) socio-ecological effectiveness depends on a number of management and governance elements, among which stakeholder engagement and community support play key roles. Collaborative conservation initiatives that engage stakeholders in action research and knowledge co-production processes can enhance management and governance of MPAs. To design effective strategies aimed at reconciling biodiversity conservation and management of sustainable human uses, it is key to assess how local communities respond to such initiatives and identify the set of contextual factors, institutional, local and individual, potentially affecting these responses. This paper presents the approach and results of one such initiative, spanning 6 EU countries and 11 MPAs in the Mediterranean Sea, focusing on small-scale fishers as key MPA users. Through a collaborative project, managers and fishers agreed upon specific governance interventions (e.g. increasing stakeholder engagement, engaging fishers in monitoring activities, reducing fishing efforts) to be implemented in each MPA for one year. Structured surveys queried: MPA managers on the MPA context, governance structure, feasibility and effectiveness of the tested interventions; and small-scale fishers on their perceptions of the impact of the tested interventions on a set of 9 socio-ecological variables (e.g. amount of fish caught, level of participation in decision-making, support for the MPA). Results revealed that the interventions tested were relatively feasible, effective and cost-effective. Fishers reported positive perceptions of the interventions for the 9 variables considered, especially for level of support for the MPA and for those associated with aspects of governance. Proportional odds models highlighted perceived effects are maximized under certain institutional, local and individual circumstances (e.g. old MPAs, small fisher communities, and fishers with a high proportion of income from fisheries). Findings highlight that employing good governance processes involving stakeholders may rapidly generate improved local support for conservation and provide insights for potential leverage points upon which to act to maximize perceived effectiveness and enhance support toward MPAs.

The coralligenous habitat was studied at the large Mediterranean scale, by applying a standardized, non-destructive photo-sampling protocol, developed in the framework of the CIGESMED project. The results provided evidence to support the following statements: (a) the assemblage pattern is not homogeneously distributed across the four Mediterranean ecoregions studied (biotic gradients hypothesis); and (b) the assemblage pattern does not change significantly when the information is aggregated to higher taxonomic levels (taxonomic sufficiency hypothesis). Surrogate taxonomic categories higher than species, such as genus and family, can be used to reveal the multivariate pattern of the coralligenous assemblages. Although preliminary at the pan-Mediterranean scale, these outcomes set the scene for future comparisons as more data sets become available but also for comparisons between taxonomic and functional patterns. 1.2.3.4.