Marine heatwaves drive recurrent mass mortalities in the Mediterranean Sea

Shifts in survival and reproduction after chronic warming enhance the potential of a marine copepod to persist under extreme heat events

The study of a species' thermal tolerance and vital rates responses provides useful metrics to characterize its vulnerability to ocean warming. Under prolonged thermal stress, plastic and adaptive processes can adjust the physiology of organisms. Yet it is uncertain whether the species can expand their upper thermal limits to cope with rapid and extreme changes in environmental temperature. In this study, we reared the marine copepod Paracartia grani at control (19°C) and warmer conditions (25°C) for >18 generations and assessed their survival and fecundity under short-term exposure to a range of temperatures (11-34°C). After multigenerational warming, the upper tolerance to acute exposure (24 h) increased by 1-1.3°C, although this enhancement decreased to 0.3-0.8°C after longer thermal stress (7 days). Warm-reared copepods were smaller and produced significantly fewer offspring at the optimum temperature. No shift in the thermal breadth of the reproductive response was observed. Yet the fecundity rates of the warm-reared copepods in the upper thermal range were up to 21-fold higher than the control. Our results show that chronic warming improved tolerance to stress temperatures and fecundity of P. grani, therefore, enhancing its chances to persist under extreme heat events.

Holobiont responses of mesophotic precious red coral Corallium rubrum to thermal anomalies

Marine heat waves (MHWs) have increased in frequency and intensity worldwide, causing mass mortality of benthic organisms and loss of biodiversity in shallow waters. The Mediterranean Sea is no exception, with shallow populations of habitat-forming octocorals facing the threat of local extinction. The mesophotic zone, which is less affected by MHWs, may be of ecological importance in conservation strategies for these species. However, our understanding of the response of mesophotic octocoral holobionts to changes in seawater temperature remains limited. To address this knowledge gap, we conducted a study on an iconic Mediterranean octocoral, the red coral Corallium rubrum sampled at 60 m depth and 15 °C. We exposed the colonies to temperatures they occasionally experience (18 °C) and temperatures that could occur at the end of the century if global warming continues (21 °C). We also tested their response to extremely cold and warm temperatures (12 °C and 24 °C). Our results show a high tolerance of C. rubrum to a two-month long exposure to temperatures ranging from 12 to 21 °C as no colony showed signs of tissue loss, reduced feeding ability, stress-induced gene expression, or disruption of host-bacterial symbioses. At 24 °C, however, we measured a sharp decrease in the relative abundance of Spirochaetaceae, which are the predominant bacterial symbionts under healthy conditions, along with a relative increase in Vibrionaceae. Tissue loss and overexpression of the tumor necrosis factor receptor 1 gene were also observed after two weeks of exposure. In light of ongoing global warming, our study helps predict the consequences of MHWs on mesophotic coralligenous reefs and the biodiversity that depends on them.

Sea cucumbers bioturbation potential outcomes on marine benthic trophic status under different temperature regimes

Eutrophication affects coastal oceans worldwide, modifies primary production and sediment biogeochemistry and, overall, is progressively compromising marine ecosystems' integrity. Because of their known bioturbation ability, sea cucumbers are supposed to be candidates for mitigating benthic eutrophication. To provide insights on this, we investigated differences in organic matter quantity and biochemical composition (as proxies of benthic trophic status) of sediments and feces of the sea cucumber Holothuria tubulosa acclimated in mesocosms at temperatures comprised between natural conditions (14-26 °C) and an extreme of 29 °C (representing the highest anomaly under heat waves in the Mediterrranean Sea). Organic matter features differed significantly between sediments characterized by different trophic statuses and the holothuroid's feces, though with some exceptions. Feces resulted almost always organically enriched when compared with the ambient sediments, though with variable differences in composition in sediments characterized by different initial trophic status. Our results point out that sea cucumbers maintain their bioreactor capacity at all experimental temperatures including the (anomalous) highest one, irrespectively of the available food, suggesting that they could be profitably utilized to mitigate benthic eutrophication also in a warmer Mediterranean Sea.

Impaired reproduction, energy reserves and dysbiosis: The overlooked consequences of heatwaves in a bivalve mollusc

Extreme events like Marine Heatwaves (MHWs) are becoming more intense, severe, and frequent, threatening benthic communities, specifically bivalves. However, the consequences of non-lethal MHWs on animals are still poorly understood. Here, we exposed the Manila clam Ruditapes philippinarum to non-lethal MHW for 30 days and provided an integrative view of its effects. Our result indicated that albeit non-lethal, MHW reduced clam's energy reserves (by reducing their hepato-somatic index), triggered antioxidant defenses (particularly in males), impaired reproduction (via the production of smaller oocytes in females), triggered dysbiosis in the digestive gland microbiota and altered animals' behaviour (by impacting their burying capacity) and filtration rate. Such effects were seen also at RNA-seq (i.e. many down-regulated genes belonged to reproduction) and metabolome level. Interestingly, negative effects were more pronounced in males than in females. Our results show that MHWs influence animal physiology at multiple levels, likely impacting its fitness and its ecosystem services.

Seafloor warm water temperature anomalies impact benthic macrofauna communities of a high-Arctic cold-water fjord

Amid the alarming atmospheric and oceanic warming rates taking place in the Arctic, western fjords around the Svalbard archipelago are experiencing an increased frequency of warm water intrusions in recent decades, causing ecological shifts in their ecosystems. However, hardly anything is known about their potential impacts on the until recently considered stable and colder northern fjords. We analyzed macrobenthic fauna from four locations in Rijpfjorden (a high-Arctic fjord in the north of Svalbard) along its axis, sampled intermittently in the years 2003, 2007, 2010, 2013 and 2017. After a strong seafloor warm water temperature anomaly (SfWWTA) in 2006, the abundance of individuals and species richness dropped significantly across the entire fjord in 2007, together with diversity declines at the outer parts (reflected in Shannon index drops) and increases in beta diversity between inner and outer parts of the fjord. After a period of three years with stable water temperatures and higher sea-ice cover, communities recovered through recolonization processes by 2010, leading to homogenization in community composition across the fjord and less beta diversity. For the last two periods (2010-2013 and 2013-2017), beta diversity between the inner and outer parts gradually increased again, and both the inner and outer sites started to re-assemble in different directions. A few taxa began to dominate the fjord from 2010 onwards at the outer parts, translating into evenness and diversity drops. The inner basin, however, although experiencing strong shifts in abundances, was partially protected by a fjordic sill from impacts of these temperature anomalies and remained comparatively more stable regarding community diversity after the disturbance event. Our results indicate that although shifts in abundances were behind important spatio-temporal community fluctuations, beta diversity variations were also driven by the occurrence-based macrofauna data, suggesting an important role of rare taxa. This is the first multidecadal time series of soft-bottom macrobenthic communities for a high-Arctic fjord, indicating that potential periodic marine heatwaves might drive shifts in community structure, either through direct effects from thermal stress on the communities or through changes in environmental regimes led by temperature fluctuations (i.e. sea ice cover and glacial runoff, which could lead to shifts in primary production and food supply to the benthos). Although high-Arctic macrobenthic communities might be resilient to some extent, sustained warm water anomalies could lead to permanent changes in cold-water fjordic benthic systems.

Functional and structural responses of plankton communities toward consecutive experimental heatwaves in Mediterranean coastal waters

The frequency of marine heatwaves (HWs) is projected to increase in the Mediterranean Sea over the next decades. An in situ mesocosm experiment was performed in a Mediterranean lagoon for 33 days. Three mesocosms were used as controls following the natural temperature of the lagoon. In three others, two HWs of + 5 °C compared to the controls were applied from experimental day (d) 1 to d5 (HW1) and from d11 to d15 (HW2). High-frequency data of oxygen, chlorophyll-a (chl-a), temperature, salinity and light from sensors immersed in all mesocosms were used to calculate gross primary production (GPP), respiration (R) and phytoplankton growth (µ) and loss (L) rates. Nutrients and phytoplankton community structure from pigments were also analyzed. HW1 significantly increased GPP, R, chl-a, µ and L by 7 to 38%. HW2 shifted the system toward heterotrophy by only enhancing R. Thus, the effects of the first HW resulted in the attenuation of those of a second HW on phytoplankton processes, but not on community respiration, which was strongly regulated by temperature. In addition, natural phytoplankton succession from diatoms to haptophytes was altered by both HWs as cyanobacteria and chlorophytes were favored at the expense of haptophytes. These results indicate that HWs have pronounced effects on Mediterranean plankton communities.

Photogrammetry as a promising tool to unveil marine caves' benthic assemblages

Traditionally, monitoring approaches to survey marine caves have been constrained by equipment limitations and strict safety protocols. Nowadays, the rise of new approaches opens new possibilities to describe these peculiar ecosystems. The current study aimed to explore the potential of Structure from Motion (SfM) photogrammetry to assess the abundance and spatial distribution of the sessile benthic assemblages inside a semi-submerged marine cave. Additionally, since impacts of recent date mussel Lithophaga lithophaga illegal fishing were recorded, a special emphasis was paid to its distribution and densities. The results of SfM were compared with a more "traditional approach", by simulating photo-quadrats deployments over the produced orthomosaics. A total of 22 sessile taxa were identified, with Porifera representing the dominant taxa within the cave, and L. lithophaga presenting a density of 88.3 holes/m². SfM and photo-quadrats obtained comparable results regarding species richness, percentage cover of identified taxa and most of the seascape metrics, while, in terms of taxa density estimations, photo-quadrats highly overestimated their values. SfM resulted in a suitable non-invasive technique to record marine cave assemblages. Seascape indexes proved to be a comprehensive way to describe the spatial pattern of distribution of benthic organisms, establishing a useful baseline to assess future community shifts.

Conservation status of upper-mesophotic octocoral habitats at Sporades Archipelago (Aegean Sea)

Octocoral forests created by the yellow sea fan Eunicella cavolini and the red sea fan Paramuricea clavata were studied at the National Marine Park of Alonissos Northern Sporades (Aegean Sea, Greece), between 30 and 45 m depth, in order to assess their conservation status and the occurrence of both natural and anthropogenic stressors. The area was characterized by rich and dense coral forests, with densities up to 55.2 colonies m^-2 for E. cavolini and 28.0 colonies m^-2 for P. clavata. The coral population showed signs of stress, although mortality was low. A combination of stressors linked to global warming and fishing impacts, including macroalgal epibiosis, tip necrosis, increasing coral feeders, and abandoned fishing gears, could impair the status of these habitats in the near future. Although the effects of climate change are global, local conservation actions may reduce direct anthropogenic impacts and enhance habitats' resilience.

Temporal and spatial variability in population traits of an intertidal fucoid reveals local-scale climatic refugia

Global change is imposing significant losses in the functional traits of marine organisms. Although areas of climatic refugia ameliorate local conditions and help them to persist, the extent to which mesoscale effects contribute for intraregional variability on population traits and conservation is uncertain. Here we assess patterns of conservation status of Fucus guiryi, the main intertidal habitat-forming seaweed in the Strait of Gibraltar (southern Spain and northern Morocco). We investigated the demography, reproductive phenology, and morphology at northern and southern side populations. Population traits were compared seasonally within populations from each side, and at spatial scale in early summer 2019. In the last decade three populations became extinct; two marginal populations had dispersed individuals with a narrower fertility season and miniaturized individuals below 3 cm; and five populations showed variable density and cover with more than 20% of reproductive individuals over the seasons. Highest density, cover, morphology, and reproductive potential was detected at one population from each side, suggesting local-scale climatic refugia in upwelling areas located inside marine protected areas. Southern recruits were more warm-tolerant but grew less at colder conditions than northern ones, revealing a mesoscale heterogeneity in thermal affinities. This study evidenced functional losses and distinct reproductive strategies experienced by F. guiryi at peripheral locations and urges to prioritize its conservation and restoration at contemporary climatic refugia.

Mediterranean Sea heatwaves jeopardize greater amberjack's (Seriola dumerili) aquaculture productivity through impacts on the fish microbiota

Climate change is dramatically increasing the frequency and severity of marine heatwaves (MHWs) in the Mediterranean basin, strongly affecting marine food production systems. However, how it will shape the ecology of aquaculture systems, and the cascading effects on productivity, is still a major knowledge gap. The present work aims to increase our understanding of future impacts, caused by raising water temperatures, on the interaction between water and fish microbiotas, and consequential effects upon fish growth. Thus, the bacterial communities present in the water tanks, and mucosal tissues (skin, gills and gut), of greater amberjack farmed in recirculatory aquaculture systems (RAS), at three different temperatures (24, 29 and 33 °C), were characterized in a longitudinal study. The greater amberjack (Seriola dumerili) is a teleost species with high potential for EU aquaculture diversification due to its fast growth, excellent flesh quality and global market. We show that higher water temperatures disrupt the greater amberjack's microbiota. Our results demonstrate the causal mediation exerted by this bacterial community shifts on the reduction of fish growth. The abundance of members of the Pseudoalteromonas is positively correlated with fish performance, whereas members of the Psychrobacter, Chryseomicrobium, Paracoccus and Enterovibrio are suggested as biomarkers for dysbiosis, at higher water temperatures. Hence, opening new evidence-based avenues for the development of targeted microbiota-based biotechnological tools, designed to increase the resilience and adaptation to climate change of the Mediterranean aquaculture industry.

Are Mediterranean marine threatened species at high risk by climate change?

Rapid anthropogenic climate change is driving threatened biodiversity one step closer to extinction. Effects on native biodiversity are determined by an interplay between species' exposure to climate change and their specific ecological and life-history characteristics that render them even more susceptible. Impacts on biodiversity have already been reported, however, a systematic risk evaluation of threatened marine populations is lacking. Here, we employ a trait-based approach to assess the risk of 90 threatened marine Mediterranean species to climate change, combining species' exposure to increased sea temperature and intrinsic vulnerability. One-quarter of the threatened marine biodiversity of the Mediterranean Sea is predicted to be under elevated levels of climate risk, with various traits identified as key vulnerability traits. High-risk taxa including sea turtles, marine mammals, Anthozoa and Chondrichthyes are highlighted. Climate risk, vulnerability and exposure hotspots are distributed along the Western Mediterranean, Alboran, Aegean, and Adriatic Seas. At each Mediterranean marine ecoregion, 21%-31% of their threatened species have high climate risk. All Mediterranean marine protected areas host threatened species with high risk to climate change, with 90% having a minimum of 4 up to 19 species of high climate risk, making the objective of a climate-smart conservation strategy a crucial task for immediate planning and action. Our findings aspire to offer new insights for systematic, spatially strategic planning and prioritization of vulnerable marine life in the face of accelerating climate change.

Tracking contemporary microbial evolution in a changing ocean

Ocean microbes are fundamental for the functioning of the Earth system. Yet, our understanding of how they are reacting to global change in terms of evolution is limited. Microbes typically grow in large populations and reproduce quickly, which may allow them to rapidly adapt to environmental stressors compared to larger organisms. However, genetic evidence of contemporary evolution in wild microbes is scarce. We must begin coordinated efforts to establish new microbial time-series and explore novel tools, experiments, and data to fill this knowledge gap. The development of coordinated microbial 'genomic' observatories will provide the unprecedented opportunity to track contemporary microbial evolution in the ocean and explore the role of evolution in enabling wild microbes to respond to global change.

Experimental thermocline deepening highlights the resilience of the seagrass Posidonia oceanica: An opportunity to investigate shoot adaptability

The deepening of the thermocline, correlated to the rising temperature, can contribute affecting seagrass performance in a changing climate scenario. Here, the effect of the thermocline deepening on the seagrass Posidonia oceanica has been investigated in Cyprus through a manipulative experiment that allowed also testing the effects of the irradiance, origin depth and translocation. P. oceanica shoots were collected from 31 m of depth and transplanted at 12 m under a shading net, simulating the 31 m light conditions. Morphology (i.e. leaf area, leaf necrosis, number of leaves) and physiology (i.e. growth rate) were evaluated. Thermocline and origin depth effects were found with an increase of leaf necrosis, while a translocation effect was highlighted by a decrease in leaf area. No differences in shoot growth rate due to treatments were found. This experiment indicated an overall wide morphological and physiological acclimation of P. oceanica cuttings in coping with future thermocline conditions and it indirectly provides information for restoration efforts.

Invading the Greek Seas: Spatiotemporal Patterns of Marine Impactful Alien and Cryptogenic Species

The Greek Seas are greatly exposed to the proliferation of marine alien species. At least 242 alien species have been reported within Greek territorial waters, three-quarters of which are considered established, while their rate of introduction is increasing. Some of these species exhibit high invasiveness, imposing severe impacts on native ecosystems and ecosystem services. The spatiotemporal proliferation of these species outside their natural boundaries depends on several parameters, including their biological characteristics, native distribution range, introduction pathway, and time of initial introduction. Knowing the current and potential alien species distribution is essential for the implementation of effective management actions. To investigate the distribution of impactful cryptogenic and alien species (ICAS) in the Greek Seas, we combined all records available until the end of 2020 from eight types of data sources: (1) scientific literature, (2) grey literature, (3) offline databases, (4) online scientific databases, (5) personal observations of independent researchers, (6) communications with divers and diving centers, (7) in situ underwater sampling, and (8) social networks. The results of 5478 georeferenced records refer to 60 marine ICAS belonging to 16 taxonomic groups. The number of records and the overall number of ICAS present an increasing trend from the northern to the southern parts of our study area, and there is a clear distinction in community composition between the northern and southern subregions. This latitudinal gradient is mainly due to the large number of thermophilous Lessepsian species of West Indo-Pacific origin, which reach the southern parts of the study area through unaided dispersal. On the other hand, transport stowaways appear to be more prevalent in areas located near large ports, which show significant differences in ICAS numbers and community composition compared to sites located far from ports. Most records (>40% of the total) were associated with rocky reefs, partly reflecting the preference of divers for this habitat type but also the presence of conspicuous, reef-associated impactful fish. The number of published records, as well as the number of reported ICAS, shows a dramatic increase with time, highlighting the urgent need for immediate proactive management actions and scientifically informed control measures.

Effects of high temperature and marine heat waves on seagrasses: Is warming affecting the nutritional value of Posidonia oceanica?

Primary producers nutritional content affects the entire food web. Here, changes in nutritional value associated with temperature rise and the occurrence of marine heat waves (MHWs) were explored in the endemic Mediterranean seagrass Posidonia oceanica. The variability of fatty acids (FAs) composition and carbon (C) and nitrogen (N) content were examined during summer 2021 from five Mediterranean sites located at the same latitude but under different thermal environments. The results highlighted a decrease in unsaturated FAs and C/N ratio and an increase of monounsaturated FA (MUFA) and N content when a MHW occurred. By contrast, the leaf biochemical composition seems to be adapted to local water temperature since only few significant changes in MUFA were found and N and C/N had an opposite pattern compared to when a MHW occurs. The projected increase in temperature and frequency of MHW suggest future changes in the nutritional value and palatability of leaves.

Marine protected areas, marine heatwaves, and the resilience of nearshore fish communities

Anthropogenic stressors from climate change can affect individual species, community structure, and ecosystem function. Marine heatwaves (MHWs) are intense thermal anomalies where water temperature is significantly elevated for five or more days. Climate projections suggest an increase in the frequency and severity of MHWs in the coming decades. While there is evidence that marine protected areas (MPAs) may be able to buffer individual species from climate impacts, there is not sufficient evidence to support the idea that MPAs can mitigate large-scale changes in marine communities in response to MHWs. California experienced an intense MHW and subsequent El Niño Southern Oscillation event from 2014 to 2016. We sought to examine changes in rocky reef fish communities at four MPAs and associated reference sites in relation to the MHW. We observed a decline in taxonomic diversity and a profound shift in trophic diversity inside and outside MPAs following the MHW. However, MPAs seemed to dampen the loss of trophic diversity and in the four years following the MHW, taxonomic diversity recovered 75% faster in the MPAs compared to reference sites. Our results suggest that MPAs may contribute to long-term resilience of nearshore fish communities through both resistance to change and recovery from warming events.

Marine heat waves drive bleaching and necrosis of temperate sponges

Marine heat waves (MHWs) are extended periods of excessively warm water¹ that are increasing in frequency, duration, intensity, and impact, and they likely represent a greater threat to marine ecosystems than the more gradual increases in sea surface temperature.^2,3,4 Sponges are major and important components of global benthic marine communities,^5,6,7 with earlier studies identifying tropical sponges as potential climate change "winners."^8,9,10,11 In contrast, cold-water sponges may be less tolerant to predicted ocean warming and concurrent MHWs. Here, we report how a series of unprecedented MHWs in New Zealand have impacted millions of sponges at a spatial scale far greater than previously reported anywhere in the world. We reported sponge tissue necrosis¹² and bleaching (symbiont loss/dysfunction),¹³ which have been previously associated with temperature stress,^6,12,14 for three common sponge species across multiple biogeographical regions, with the severity of impact being correlated with MHW intensity. Given the ecological importance of sponges,¹⁵ their loss from these rocky temperate reefs will likely have important ecosystem-level consequences.

Cardiovascular oxygen transport and peripheral oxygen extraction capacity contribute to acute heat tolerance in European seabass

This study evaluated whether different parameters describing cardiovascular function, energy metabolism, oxygen transport and oxidative stress were related to the critical thermal maximum (CT_MAX) of European seabass (Dicentrarchus labrax) and if there were differential changes in these parameters during and after heat shock in animals with different CT_MAX in order to characterize which physiological features make seabass vulnerable to heat waves. Seabass (n = 621) were tested for CT_MAX and the physiological parameters were measured in individuals with good or poor temperature tolerance before and after a heat shock (change in temperature from 15 °C to 28 °C in 1.5 h). Fish with good thermal tolerance had larger ventricles with higher maximal heart rate during the heat shock than individuals with poor tolerance. Furthermore, they initially had a high ventricular Ca²⁺-ATPase activity, which was reduced to a similar level as in fish with poor tolerance following heat shock. The activity of heart lactate dehydrogenase increased in fish with high tolerance, when they were exposed to heat shock, while the aerobic enzyme activity did not differ between groups. The tolerant individuals had smaller red muscle fibers with higher myoglobin content than the poorly tolerant ones. The poorly tolerant individuals had higher hematocrit, which increased with heat shock in both groups. The poorly tolerant individuals had also higher activity of enzymes related to oxidative stress especially after heat shock. In general, CT_MAX was not depending on merely one physiological factor but several organ and cellular parameters were related to the CT_MAX of seabass and when working in combination they might protect the highly tolerant seabass from future heat waves.

Lethal and sublethal effects of thermal stress on octocorals early life-history stages

The frequency and severity of marine heatwaves causing mass mortality events in tropical and temperate coral species increases every year, with serious consequences on the stability and resilience of coral populations. Although recovery and persistence of coral populations after stress events is closely related to adult fitness, as well as larval survival and settlement, much remains unknown about the effects of thermal stress on early life-history stages of temperate coral species. In the present study, the reproductive phenology and the effect of increased water temperature (+4°C and +6°C above ambient, 20°C) on larval survival and settlement was evaluated for two of the most representative Mediterranean octocoral species (Eunicella singularis and Corallium rubrum). Our study shows that reproductive behavior is more variable than previously reported and breeding period occurs over a longer period in both species. Thermal stress did not affect the survival of symbiotic E. singularis larvae but drastically reduced the survival of the non-symbiotic C. rubrum larvae. Results on larval biomass and caloric consumption suggest that higher mortality rates of C. rubrum exposed to increased temperature were not related to depletion of endogenous energy in larvae. The results also show that settlement rates of E. singularis did not change in response to elevated temperature after 20 days of exposure, but larvae may settle fast and close to their native population at 26°C (+6°C). Although previous experimental studies found that adult colonies of both octocoral species are mostly resistant to thermal stress, our results on early life-history stages suggest that the persistence and inter-connectivity of local populations may be severely compromised under continued trends in ocean warming.

Signals of loss: Local collapse of neglected vermetid reefs in the western Mediterranean Sea

During the summer of 2022, an extensive die-off of Dendropoma cristatum and other marine organisms associated with vermetid reefs was observed in the western Mediterranean Sea (northern coast of Sicily). Quantitative data from more than 300 km of coastal stripe indicated that the percentage of dead D. cristatum specimens, showing empty and/or transversely fractured shells, ranged from 64 to 84 % in populations having a density of 2900-4730 ind./m², suggesting that millions of organisms had recently died along the Sicilian coast. This high mortality range coincided with prolonged desiccation events during which biogenic vermetid reefs were exposed to extreme warm-air conditions for several consecutive days. This warning report about neglected shallow vermetid reefs raises concern regarding the loss of Mediterranean biodiversity, underlining the need to develop and implement monitoring and conservation efforts on a basin-wide scale.

Field thermo acclimation increases the resilience of Posidonia oceanica seedlings to marine heat waves

Acclimation is a response that results from chronic exposure of an individual to a new environment. This study aimed to investigate whether the thermal environment affects the early development of the seagrass Posidonia oceanica, and whether the effects of a field-simulated Marine Heat Wave (MHW) on seedlings change depending on acclimation. The experiment was done in the field using a crossed design of Acclimation (acclimated vs unacclimated) and MHW (present vs absent) factors. Acclimation has initially constrained the development of P. oceanica seedlings, but then it increased their resilience to the MHW, under both a morphological and biochemical (fatty acid saturation) level. This treatment could be considered in P. oceanica restoration projects in a climate change-impaired sea, by purposely inducing an increased resistance to heat before transplants.

Mediterranean Sea shelters for the gold coral Savalia savaglia (Bertoloni, 1819): An assessment of potential distribution of a rare parasitic species

Savalia savaglia is an ecosystem engineer listed as Near-Threatened by the IUCN, even though effective management and proper monitoring efforts to assess its distribution is still lacking. The record of large, long-established colonies can indicate the occurrence of areas with limited human local pressure. These areas may be considered as proxies for the creation of baselines of reference useful to design restoration strategies. The aim of this work was to update the distribution of S. savaglia Mediterranean populations to develop an Ecological Niche Model, highlighting potential areas for future monitoring programs. Occurrence data were collected and harmonized into a single dataset using the scientific literature and validated observations to feed a presence-only MaxEnt model, obtaining a basin-level potential distribution of the species. The results of our study can support decision-makers in marine spatial planning measures including the preservation of mesophotic environments and prioritizing areas for conservation.