Effects of global warming on Mediterranean coral forests

Signals of loss, part two: A phytal community collapsing under extreme-climate conditions on a Mediterranean vermetid reef

Climate change is increasing the frequency and intensity of transient extreme climate events that can be catastrophic for ecological communities. We studied the 2014-2022 period along the northern coasts of Sicily (Western Mediterranean Sea), evaluating the ecological impacts on three macroalgae (Ericaria amentacea, Jania rubens, and Padina pavonica) and one complex of species (Laurencia complex) inhabiting the vermetid bioconstructions. All climatological metrics indicate that desiccation conditions occurred in the intertidal zones for many consecutive days during 2022, compared to previous years. These extreme conditions have led to a drastic algal biomass reduction, especially for E. amentacea, P. pavonica, and Laurencia complex species. Consistently, the analysis of mollusc communities associated with macroalgae highlighted a sharp collapse, with a general inverse relationship between community composition and structure versus air temperature values. This worrying evidence indicates that anomalous desiccation conditions could have serious short-term impacts on the fragile and neglected vermetid ecosystem.

Assessing the economic value of Posidonia oceanica (L.) at Tremiti Islands (Mediterranean Sea): An ecosystem condition-based approach

In the context of limiting global warming, the seagrass Posidonia oceanica (L.) gained the centrality of several international climate change mitigation projects being the most effective carbon storage sink among Mediterranean seagrasses. To assess and monitor the change of environmental conditions and economic values of natural resources, the present study moves from the insights of the System of Environmental-Economic Accounting - Ecosystem Accounting to assess the economic value of the carbon sequestration and storage capacity of the Mediterranean-endemic seagrass P. oceanica at the Tremiti Islands Marine Protected Area. The economic value is compared across: i. the reference study by Pergent-Martini et al.; ii. the ecological condition-based approach; and iii. the unit value transfer. Based on the obtained outcomes, an ecosystem-based approach would prevent biases in the accounting of the ecosystem-service provision capacity of P. oceanica and help the policy maker to implement adequate public investment policies to mitigate its overall degradation.

Effects of aquaculture effluents on the slender sea pen Virgularia mirabilis

This study aims to assess in situ the impact of effluents originating from an Atlantic salmon (Salmo salar) farm on a nearby slender sea pen (Virgularia mirabilis) field. We evidenced (1) the presence and persistence of emamectin residues (i.e. a common chemotherapeutants used for treating ectoparasites in salmons) in V. mirabilis tissue 56 days after treatment and (2) lethal and sublethal responses of V. mirabilis to effluents discharged by the salmon farm. Particularly, sea pens near the fish farm exhibited significant overproduction of mucus, contraction of polyps' tentacles, and disappearance of associated fauna. Furthermore, sea pens located directly underneath the farm showed substantial tissue necrosis and, in the most severe case, complete tissue loss and mortality. Our results suggest that lethal damages on sea pens occur directly below the farm, and that sublethal effects are visible up to 500 m from the farm. However, the presence of V. mirabilis below the studied farm, which has been active for more than twenty years, suggests that V. mirabilis population possesses the capacity to recover from the impacts of the farm, thereby preventing the complete disappearance from the area. In this context, it would be particularly interesting to run a temporal survey following the health state of V. mirabilis during an entire production cycle to have a more precise overview of fish farm impacts on this species, including during and after the post-production fallowing period.

Culture dependent analysis of bacterial activity, biofilm-formation and oxidative stress of seawater with the contamination of microplastics under climate change consideration

Temperature changes due to climate change and microplastic contamination are worldwide concerns, creating various problems in the marine environment. Therefore, this study was carried out to discover the impact of different temperatures of seawater exposed to different types of plastic materials on culture dependent bacterial responses and oxidative characteristics. Seawater was exposed to microplastics obtained from various plastic materials at different temperature (-18, +4, +20, and +35 °C) for seven days. Then microplastics were removed from the suspension and microplastic-exposed seawater samples were analyzed for bacterial activity, biofilm formation and oxidative characteristics (antioxidant, catalase, glutathione, and superoxide dismutase) using Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus. The results showed that the activity and biofilm formation of Pseudomonas aeruginosa and Staphylococcus aureus were affected through oxidative stress by catalase, glutathione, and superoxide dismutase due to the microplastic deformation by temperature changes. This study confirms that temperature changes as a result of climate change might influence microplastic degradation and their contamination impact in seawater in terms of bacterial metabolic and oxidation reactions.

Impacts of Climate Change on Marine Foundation Species

Marine foundation species are the biotic basis for many of the world's coastal ecosystems, providing structural habitat, food, and protection for myriad plants and animals as well as many ecosystem services. However, climate change poses a significant threat to foundation species and the ecosystems they support. We review the impacts of climate change on common marine foundation species, including corals, kelps, seagrasses, salt marsh plants, mangroves, and bivalves. It is evident that marine foundation species have already been severely impacted by several climate change drivers, often through interactive effects with other human stressors, such as pollution, overfishing, and coastal development. Despite considerable variation in geographical, environmental, and ecological contexts, direct and indirect effects of gradual warming and subsequent heatwaves have emerged as the most pervasive drivers of observed impact and potent threat across all marine foundation species, but effects from sea level rise, ocean acidification, and increased storminess are expected to increase. Documented impacts include changes in the genetic structures, physiology, abundance, and distribution of the foundation species themselves and changes to their interactions with other species, with flow-on effects to associated communities, biodiversity, and ecosystem functioning. We discuss strategies to support marine foundation species into the Anthropocene, in order to increase their resilience and ensure the persistence of the ecosystem services they provide.

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.

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.

Seasonal methane emission from municipal solid waste disposal sites in Lagos, Nigeria

The Municipal Solid Waste (MSW) Sector is a major source of Methane (CH₄) emission, a Greenhouse Gas (GHG) that contributes to Climate Change. However, governments of developing countries have not been able to address the challenges posed by this sector due to inadequate funding and technical requirement. The objective of this study was to determine how seasonal variation influences the CH₄ gas emission. The First Order Decay (FOD) Tier 1 Model was used to estimate CH₄ emission from four Solid Waste Disposal Sites (SWDS) in Lagos namely: Ewu-Elepe (Ewu), Abule-Egba (A/E), Soluos (Sol), and Olushosun (Olu) covering the dry and wet seasons, respectively for the inventory year 2020. A known weight of the wet waste deposited was characterized. The study revealed that the Degradable Organic Carbon (DOC) for the dry season was 12.897 GgC/kgWaste while that of the wet season was 12.547 GgC/kgWaste. But, the methane gas generated during the wet season was 0.331 Gg higher than that of the dry season which was 0.134 Gg for the study period. This is an appreciable quantity of methane that can contribute to the global Climate Change impact if not addressed. Therefore, these waste types should be segregated from other recyclables and processed into compost or energy resource.

Marine heatwaves drive recurrent mass mortalities in the Mediterranean Sea

Climate change is causing an increase in the frequency and intensity of marine heatwaves (MHWs) and mass mortality events (MMEs) of marine organisms are one of their main ecological impacts. Here, we show that during the 2015-2019 period, the Mediterranean Sea has experienced exceptional thermal conditions resulting in the onset of five consecutive years of widespread MMEs across the basin. These MMEs affected thousands of kilometers of coastline from the surface to 45 m, across a range of marine habitats and taxa (50 taxa across 8 phyla). Significant relationships were found between the incidence of MMEs and the heat exposure associated with MHWs observed both at the surface and across depths. Our findings reveal that the Mediterranean Sea is experiencing an acceleration of the ecological impacts of MHWs which poses an unprecedented threat to its ecosystems' health and functioning. Overall, we show that increasing the resolution of empirical observation is critical to enhancing our ability to more effectively understand and manage the consequences of climate change.

The Status of Posidonia oceanica at Tremiti Islands Marine Protected Area (Adriatic Sea)

Simple Summary

The seagrass Posidonia oceanica is the most important marine phanerogam of the Mediterranean Sea due to its meadows’ complexity, persistence, and extension. These habitats provide a suite of ecosystem goods and services, being of primary importance in marine conservation. Despite their central role in the coastal ecology, P. oceanica meadows are undergoing overall deterioration and fragmentation in the basin mostly due to anthropogenic impacts at local to global scales. In the last decades, several management measures have been proposed aiming to improve the meadow health conditions, while the periodic monitoring of P. oceanica meadows allows for verifying their effectiveness. Here, we report the results of the monitoring of P. oceanica at Tremiti Islands Marine Protected Area (Adriatic Sea, Italy) carried out in 2003, 2015, and 2020. A general worsening was observed, particularly enhanced by direct anthropogenic impacts mostly related to anchoring practices, as well as by a certain level of sedimentation possibly deriving from coastal development. However, the identification of these impacts and the correct management of human activities to mitigate them produced positive results in a relatively short time span.

Abstract

Posidonia oceanica meadows are Mediterranean coastal habitats of great conservation importance. This study is focused on a meadow located at Tremiti Islands Marine Protected Area (Adriatic Sea, Italy), which was monitored in 2003, 2015, and 2020 to evaluate its health state over time in relation to coastal human activities, which have been highly affecting this MPA for the last 20 years. To assess any change in the physiognomy of the meadow, rhizome density, percentage coverage, and lower limit progressions and/or regression over time were evaluated by scuba diving, while the distribution and extension of the meadow were assessed through habitat mapping using a side-scan sonar. Moreover, phenological and lepidochronological analyses were performed on the collected rhizomes to assess the leaf area index (LAI, m²m⁻²) and the rhizome age (lepidochronological years). Our study showed a general deterioration of P. oceanica meadow from 2003 to 2020, with a significant reduction of its absolute and relative rhizome density and LAI at almost all sampling stations, absence of renovation of the meadow, and lower limit regression and overall worsening of the main conservation status indicators. However, appropriate management actions, such as the establishment of mooring buoy fields, supported the improvement of the P. oceanica status at the local scale with a significant increase in density and LAI and the presence of active stolonization processes, suggesting that mitigation actions can play a crucial role in the conservation of this habitat. On the contrary, local anthropogenic impacts, especially anchoring and coastal development, markedly affect the resilience of P. oceanica meadows to global stressors, such as climate change.

Food from the Depths of the Mediterranean: The Role of Habitats, Changes in the Sea-Bottom Temperature and Fishing Pressure

As part of the “Innovations in the Food System: Exploring the Future of Food” Special Issue, this paper briefly reviews studies that highlight a link between deep-sea fishery resources (deep-sea food resources) and vulnerable marine ecosystems (VME), species, and habitats in the Mediterranean Sea, providing new insights into changes in commercial and experimental catches of the deep-sea fishery resources in the central Mediterranean over the last 30 years. About 40% of the total landing of Mediterranean deep-water species is caught in the central basin. Significant changes in the abundance of some of these resources with time, sea-bottom temperature (SBT), and fishing effort (FE) have been detected, as well as an effect of the Santa Maria di Leuca cold-water coral province on the abundance of the deep-sea commercial crustaceans and fishes. The implications of these findings and the presence of several geomorphological features, sensitive habitats, and VMEs in the central Mediterranean are discussed with respect to the objectives of biodiversity conservation combined with those of management of fishery resources.

Drawing the borders of the mesophotic zone of the Mediterranean Sea using satellite data

The 30–150 m bathymetric range is commonly adopted in the literature to constrain the mesophotic zone. However, such depth interval varies depending on sunlight penetration, which is primarily a function of solar radiation incidence and water clarity. This is especially obvious in the Mediterranean Sea with its peculiar biophysical properties. Integrating information on light regime in the estimation of the bathymetric range of the mesophotic zone would provide a more robust definition, orienting conservation actions targeting its ecosystems. We present a first assessment of the spatial and vertical extension of the mesophotic zone in the Mediterranean Sea based upon light penetration, comparing our prediction with literature data. Our study also represents a baseline to monitor future variations in the bathymetric interval associated with the mesophotic zone in the Mediterranean Sea in relation to global changes.

A Newly Discovered Forest of the Whip Coral Viminella flagellum (Anthozoa, Alcyonacea) in the Mediterranean Sea: A Non-Invasive Method to Assess Its Population Structure

Simple Summary

Some corals belonging to the orders Alcyonacea and Antipatharia have elongated, unbranched shapes, and are generally addressed as sea whips. The octocorals Viminella flagellum are the main sea whip species inhabiting the Mediterranean Sea, where they can form large colony aggregations known as coral forests. These habitats are of great conservation importance; they provide a suite of ecosystem goods and services, and their monitoring is essential to plan appropriate conservation strategies. One of the most important indicators on the status of a coral forest is its population structure, such as the frequency of different size classes within the coral population. This is very difficult to assess in sea whips because of the length and high flexibility. Here, we report on the findings of a newly discovered, monospecific forest of V. flagellum in Aeolian Archipelago (Mediterranean Sea), and we present a new method to study its population structure using video analysis. The results of the survey indicate that the Aeolian coral population was in good condition, without significant anthropogenic impacts. The new method presented here proved to be an effective and promising tool for the monitoring of this vulnerable marine ecosystem. It can be applied to every known population of V. flagellum as well as adapted to other sea-whip species.

Abstract

Coral forests are vulnerable marine ecosystems formed by arborescent corals (e.g., Anthozoa of the orders Alcyonacea and Antipatharia). The population structure of the habitat-forming corals can inform on the status of the habitat, representing an essential aspect to monitor. Most Mediterranean corals live in the mesophotic and aphotic zones, and their population structures can be assessed by analyzing images collected by underwater vehicles. This is still not possible in whip-like corals, whose colony lengths and flexibilities impede the taking of direct length measurements from images. This study reports on the occurrence of a monospecific forest, of the whip coral Viminella flagellum in the Aeolian Archipelago (Southern Tyrrhenian Sea; 149 m depth), and the assessment of its population structure through an ad-hoc, non-invasive method to estimate a colony height based on its width. The forest of V. flagellum showed a mean density of 19.4 ± 0.2 colonies m⁻² (up to 44.8 colonies m⁻²) and no signs of anthropogenic impacts. The population was dominated by young colonies, with the presence of large adults and active recruitment. The new model proved to be effective for non-invasive monitoring of this near threatened species, representing a needed step towards appropriate conservation actions.