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Highlights The density of Parastichopus regalis increased from 50 to 107 m depth and subsequently decreased. No seasonal evisceration was observed.  The organic matter content in the foregut was double the content in the sediment.  Organic matter absorption efficiency during feeding was 16.64%. The P. regalis population may transit up to 13,855 kg wet weight of sediment y −1 km −2 . Graphical abstract Holothurians provide important ecosystem services by enhancing sediment health through bioturbation. The sea cucumber Parastichopus regalis has a wide distribution in the Mediterranean Sea. Even though it is a commercially exploited species, little is known about its ecological traits and there is no information on the bioturbation potential resulting from its feeding activity. To address these knowledge gaps, the population density, demographic structure, musculature and evisceration of P. regalis were investigated on Arenys de Mar, NW Mediterranean. Food assimilation efficiency, and feeding and bioturbation rates were assessed through field and laboratory experiments. The exploited population exhibited a healthy distribution of sizes/ages, and the density values were similar to or greater than those described in other Mediterranean areas. This species did not show seasonal evisceration, and seasonal patterns in muscle weight depended on year and body size. The field results indicated that P. regalis selected organic matter from the sediment as food. The average individual feeding rate was 8.6 g wet sediment d −1 . The bioturbation role of the P. regalis population in the studied area was especially important at depths between 81 m and 124 m, where it consumed between 7.6 and 13.8 t of wet sediment y −1 km −2 . These results highlight the important role that this species play in deep habitats as sediment bioturbator, controlling the accumulation of dead organic matter.

Coastal lagoons are among the marine habitats with the highest biological productivity, and supports a great variety of human activities and pressures that makes them especially vulnerable to trophic imbalances. While dystrophic crises are common in many lagoons, others like the Mar Menor show homeostatic mechanisms, high resilience and clear waters. This paper analyses the water column descriptors dynamic during the last 22 years in this lagoon, in the context of a eutrophication process produced by an increase in nutrient inputs, mainly derived from agriculture. Despite the increase in nitrate loads, the lagoon maintained two decades of homeostatic regulation, keeping the water transparency and relatively low levels of nutrients and chlorophyll a (Prebreak phase), followed by a sudden change of state in 2016 with an abrupt increase in nutrients and chlorophyll a concentration and loss of water transparency (Break phase), and a relatively rapid recovery after the reduction of nutrient discharges (Recovery phase). The activation of the regulation mechanisms is manifested by an ammonium production, as a consequence of the trophic web activity. The low relationship between chlorophyll and nutrients, mainly at small spatio-temporal scales, disagrees with the eutrophication traditional models, suggesting a rapid response of primary producers to nutrient inputs and a zooplankton control in the short-term, which in turn is controlled by the rest of the trophic web components. Homeostatic properties that provide resistance to the Mar Menor lagoon to deal with eutrophication are based on several mechanisms: channelling its production towards the benthic system (maintaining high biomasses of primary producers, filter feeders and detritivores), a top-down control of the pelagic trophic web exerted by ichthyoplankton and jellyfish, and exporting surplus production outside the system. Resilience of the system would be based on the high turnover in the species composition related to the restricted connectivity with the sea, the spatio-temporal variability of the environmental conditions, and the multiplicity of spatial-temporal scales involved in lagoon processes. TRIX index was sensitive to the water quality changes. However, in our study, its current score does not allow to anticipate or alert the eutrophication risk and the trophic breakpoint of the system.

The study of jellyfish blooms has gained attention in the recent decades because of the importance of forecasting and anticipating them and avoiding their interference with human activities. However, after thirty years of scientific effort (monitoring systems, empirical laboratory and field studies, modeling, etc.), the occurrence of blooms remains unpredictable, and their consequences unavoidable. Climate change, eutrophication, overfishing, coastal construction, and species translocation have been suggested as stressors that increase them, but robust evidence to support these claims is limited. The widespread belief that jellyfish blooms are “increasing in number” has been challenged in recent years. Among the gelatinous zooplankton, the bloom forming species are concentrated in the class Scyphozoa, and the number of species with at least one recorded bloom has increased during the last decade. The analyses of long-term time series show seasonality in the dynamic of each blooming jellyfish species population, but the blooms vary in intensity and there are years of an unexplained absence of jellyfish. In this review, we focus on the current state of knowledge, uncertainties and gaps in the critical points that can strongly influence the intensity of the bloom or even lead to the absence of the medusa population. These points include ephyrae, planulae and scyphistoma natural, predatory or fishing mortality, the molecular pathway of strobilation, benthic population dynamics, planula settlement and ephyra to medusa transition success. Some of these points account for certain empirical laboratory evidence under controlled conditions, and are difficult to be studied on the field, but the different sources of non-typically recorded variability need to be addressed to improve our understanding of jellyfish population dynamics.

The genus Aurelia is one of the most extensively studied within the class Scyphozoa. However, much of the research was historically attributed to the species Aurelia aurita (Linnaeus, 1758) before the recognition of its taxonomic complexity. Initially considered cosmopolitan and globally distributed, recent phylogenetic analysis has challenged this assumption. Consequently, the current distribution of species within the genus Aurelia and the processes that led to this distribution remain largely unexplored. After genetically confirming that the species traditionally present in the Mar Menor coastal lagoon in the southwestern Mediterranean corresponds to A. solida, we compiled data on the locations where moon jellyfish species have been genetically identified and mapped these coordinates to the geological period when the genus Aurelia diverged from other scyphozoan genera. We propose two hypotheses to explain the disjunct distribution of certain species. The first one assumes recent human-mediated introductions, while the second posits an absence of introductions. Both hypotheses, supported by fossil and historical records, suggest a Paleo-Tethys origin of the genus Aurelia. Migration from this area explains most of the genus’s current distribution without human intervention, being the Mediterranean Sea, where A. solida should be considered autochthonous, part of their natural distribution range.

The temporal variation and the spatial structure of marine populations strongly depend on the early life stages of the individuals and on their interaction with the environment. The physical dispersion of propagules (eggs and larvae) is a fundamental aspect, conditioning the successful recruitment of juveniles in the adult population. Coastal transitional ecosystems such as lagoons plays a role of nursery for species with economic relevance, such as demersal fishes, mollusks and crustaceans. Those environments promote the recruitment of the early stages for several organisms because they act as area of retention for propagules and concentration for resources. We applied in three different European coastal lagoon a lagrangian particle tracking model coupled with a hydrodynamic model, and developed a method to evaluate the connectivity inside a lagoon and between a lagoon and the sea. Each particle represents a generic passive pelagic larva with a duration of one month. The average connectivity has been estimated after two years of simulation under realistic tide and wind forcings. Our results allow to characterize the lagoons behavior considering different spatial scales and to compare the dynamics of different systems. This study is a first step toward a better knowledge of the factors influencing the ecological role of coastal lagoons.

Marine protected areas (MPAs) are globally important environmental management tools that provide protection from the effects of human exploitation and activities, supporting the conservation of marine biological diversity, habitats, ecosystems and the processes they host, as well as resources in a broad sense. Consequently, they are also expected to manage and enhance marine ecosystem services and material, non-material, consumptive and non-consumptive goods, and benefits for humans. There is however certain confusion on what constitutes an ecosystem service, and it is not always easy to distinguish between them and societal benefits. The main nuance is that an ecosystem service is the aptitude an ecosystem has or develops naturally or as consequence of a management action, and that manifests through its own properties (productivity, diversity, stability, quality of its key parameters, etc.), while a societal benefit is the economic or other profitability (emotional, educational, scientific, etc.) that humans obtain from said service or quality. In this work, 268 publications, together with our own experiences in the different investigations carried out in the MPAs that are part of the BiodivERsA3-2015-21 RESERVEBENEFIT European project, have been selected, reviewed and discussed to analyze the knowledge status of the expected ecosystem services of MPAs and the societal benefits derived from them, sometimes providing information on their evidence, when they exist. We define and classify the effects of protection, ecosystem services and societal benefits and elaborate a conceptual model of the cause-effect relationships between them.

Mediterranean coastal lagoons are among the most productive of marine ecosystems but, at the same time, they are strongly affected by anthropogenic pressures that could alter their fisheries. This work looks at how the Mar Menor coastal lagoon fishery evolved from the eighteenth century to 2012, and provides data about landings, effort and gears. The relationships between fishing yields and the environmental consequences of the most important human activities in the lagoon (including the dredging and widening of inlets in the last two centuries and eutrophication episodes in the 1990s) are examined using uni- and multi-variate analysis. While mean total yield tended to remain constant, significant changes in the specific composition of the catch and in the dominance of the main target species have occurred. The lagoon seems to have the ability to support a wide range of pressures and environmental changes, since it has been seen to recover each time from specific human impacts, maintaining the fishery yields close to the total maximum sustainable yield. However, other factors, like climate change or the spread of aquaculture exploitations, may have overlapping effects, introducing long term trends in the fisheries concerned.

Tunisia occupies a strategic biogeographic position in the Mediterranean Sea and the Strait of Sicily is considered a biogeographical boundary that separates the eastern and western basins. Despite the importance of marine biodiversity in Tunisia, the few studies of Echinodermata fauna in this region data from long ago. In order to update and produce a validated checklist of the echinoderms that occur in northern Tunisia, a study of this phylum was carried out between 2012 and 2016. Forty-five species were inventoried and distributed into the five living Echinodermata classes (Crinoidea, Asteroidea, Ophiuroidea, Echinoidea and Holothuroidea). New occurrences of four species from Tunisian marine waters [Asterina pancerii (Gasco, 1876), Luidia atlantidea (Madsen, 1950), Ophiactis virens (Sars, 1859) and Leptopentacta tergestina (Sars, 1857)], are cited and discussed here for the first time.

Storms and tsunamis, which may seriously endanger human society, are amongst the most devastating marine catastrophes that can occur in coastal areas. Many such events are known and have been reported for the Mediterranean, a region where high-frequency occurrences of these extreme events coincides with some of the most densely populated coastal areas in the world. In a sediment core from the Mar Menor (SE Spain), we discovered eight coarse-grained layers which document marine incursions during periods of intense storm activity or tsunami events. Based on radiocarbon dating, these extreme events occurred around 5250, 4000, 3600, 3010, 2300, 1350, 650, and 80 years cal BP. No comparable events have been observed during the 20th and 21st centuries. The results indicate little likelihood of a tsunami origin for these coarse-grained layers, although historical tsunami events are recorded in this region. These periods of surge events seem to coincide with the coldest periods in Europe during the late Holocene, suggesting a control by a climatic mechanism for periods of increased storm activity. Spectral analyses performed on the sand percentage revealed four major periodicities of 1228 ± 327, 732 ± 80, 562 ± 58, and 319 ± 16 years. Amongst the well-known proxies that have revealed a millennial-scale climate variability during the Holocene, the ice-rafted debris (IRD) indices in the North Atlantic developed by Bond et al. (1997, 2001) present a cyclicity of 1470 ± 500 years, which matches the 1228 ± 327-year periodicity evidenced in the Mar Menor, considering the respective uncertainties in the periodicities. Thus, an in-phase storm activity in the western Mediterranean is found with the coldest periods in Europe and with the North Atlantic thermohaline circulation. However, further investigations, such as additional coring and high-resolution coastal imagery, are needed to better constrain the main cause of these multiple events.