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Maturity is one of the most important biological parameters used in stock assessment programmes. Indeed, the macroscopic stage of gonadal development is an essential feature in estimating the maturity ogive and spawning stock biomass. It is also useful for determining the spawning season of a species and for monitoring long-term changes in the spawning cycle as well as for many other research needs related to the biology of fish. Despite the efforts made during the last few decades to standardize maturity stage data among all the researchers, marine biologists continue without a manageable and unique maturity scale to describe the reproductive development of fish gonads. For these reasons, the objectives of this article are 1) to investigate the biological parameters of five selected key species (Mullus barbatus, Galeus melastomus, Etmopterus spinax, Aristeus antennatus, Loligo vulgaris) with different reproductive strategies following the macroscopic maturity scales based on the same univocal criteria adopted in the MEDITS programme and described in this work; and 2) to compare them among some Mediterranean geographical sub-areas (GSAs) involved in the programme. Neither spawning periods nor size at first maturity (SFM50) for the studied species showed particular differences in the investigated GSAs. La madurez es uno de los parámetros biológicos más relevantes utilizados en los programas de evaluación de stock. De hecho, la etapa macroscópica del desarrollo gonadal es una característica esencial en la estimación de la madurez de la biomasa de la ojiva y del desove. También es útil para determinar la temporada de desove de una especie y para monitorear los cambios a largo plazo en el ciclo de desove, así como para muchas otras necesidades de investigación relacionadas con la biología de los peces. A pesar de los esfuerzos realizados durante las últimas décadas para estandarizar los datos de las etapas de madurez entre todos los investigadores, los biólogos marinos continúan sin una escala de madurez única y manejable para describir el desarrollo reproductivo de las gónadas de peces. Por estas razones, el objetivo de este artículo es 1) investigar los parámetros biológicos de 5 especies clave seleccionadas (Mullus barbatus, Galeus melastomus, Etmopterus spinax, Aristeus antennatus, Loligo vulgaris) con diferentes estrategias reproductivas siguiendo las escalas de madurez macroscópica basadas en criterios iguales y unívocos adoptados en el programa MEDITS y descritos en este trabajo y 2) para compararlos entre algunas sub-áreas geográficas del Mediterráneo (GSAs) involucradas en el programa. Tanto los períodos de desove como el tamaño en la primera madurez (SFM50) para las especies estudiadas no han mostrado diferencias particulares en las GSA investigadas.

Despite being commonly recognized by the general public, knowledge about the biology and life-history of electric rays is still scarce. Globally, according to the International Union for Conservation of Nature, more of the 80% of the species belonging to the Torpedinidae family are, indeed, classified as Data Deficient, so as, in most of the cases, no proper management measures are available for the conservation of these species. For this reason, the main goal of this study is to provide new information on life-history traits of three species inhabiting the Mediterranean Sea. Age and growth were estimated through direct annuli count of 146 vertebral centra sections of Torpedo marmorata. Females’ growth pattern was found to be better described by a S-shaped function (Gompertz L∞ = 622 mm TL; k = 0.15; IP = 2.75 years), while males’ by a logarithmic one (von Bertalanffy L∞ = 485 mm TL; k = 0.14; t0 = -2.28). The oldest female and male were aged 17 (560 mm TL) and 11 (432 mm TL), respectively. Females (L50 = 379 mm TL and A50 = 5.5 years) appeared to mature later than males (L50 = 272 mm TL and A50 = 3.8 years), also attaining bigger sizes. Despite the observation of late-pregnant females being found only in autumn and regressing ones in autumn and winter, the presence of juveniles during the whole year may indicate a longer reproductive period. The stomach content analysis identified T. marmorata as a top predator (TROPH = 4.38) with a very narrow trophic niche (Bi = 0.22), extremely specialized in feeding on bony fishes. In addition, this work provides new and updated information on T. torpedo and the rare Tetronarce nobiliana growth, reproductive features and diet. Therefore, offering new essential data to assess the population conditions of all Torpedinidae species that inhabit the Mediterranean Sea, will lead to effective conservation plans.

The aim of the present study was to evaluate, through a Collaborative Fisheries Research (CFR) project, the efficacy of artificial dens as a possible integrative action for the management of O. vulgaris in the wild. Artificial dens, anchored on rocky substrates at a depth of 38–42 m in a temporary Fully Protected Area (FPA) off the western coast of Sardinia (central western Mediterranean Sea), showed their effectiveness as a temporary and/or safe site for Octopus vulgaris spawning. The suitability of these artificial dens was demonstrated by the presence of egg strings and females in parental care, and by the fact that all of the brooding-phases until the hatching had taken place inside. The presence of abundant cobbles, appeared to be a key factor in the building of a solid barrier for protection at the entrance of the spawning artificial dens, similar to those seen in natural dens. In addition, our results demonstrate the potential coexistence of artificial dens with natural ones, suggesting their potential use as integrative tool for the management of O. vulgaris. Close collaboration with fishermen in the framework of a CFR project within FPA may increase the success of this management action, through the enforcement of the area. Brooding details and laid egg features revealed by the monitoring are reported and discussed.

Marine litter is an ever-increasing problem that demands immediate reduction plans and mitigation actions that should act synergically to efficiently meet ambitious goals. Since the seafloor has been recognized as the major sink for marine debris, the study of litter accumulation dynamics represent a fundamental tool to evaluate possible removal actions. We analysed a 7 years (2013–2019) standardized data series collected along Sardinian fishing grounds through MEDiterranean International Trawl Survey, for which estimates of density and weight of seafloor macro-litter were calculated for over 707 hauls. Results show the absence of any temporal trend in seafloor macro-litter density and weight, but rather indicate a spatial and bathymetric segregation of different litter categories. Our data showed how different sources and physical features of macro-litter items (i.e., plastic and fishing gear, rubber, glass, metals, and cloth) led to spatially segregated accumulation hotspots. We also point out here how the identification of seafloor macro-litter hotspots using aggregated data that include plastic items could obscure the identification of other segregated but yet relevant hotspots of other macro-litter categories accumulated in the marine environment. These hotspots often occurred at shallower depths and closer to coastlines, thus representing potential spots where eventual future litter removal action could be prioritized.

Eye lens of 196 Loligo vulgaris and 205 Loligo forbesii collected by trawl surveys from 2013 to 2015 in Sardinian waters (Mediterranean Sea) were analysed for age determination. In an alternative to the technique previously used in Sepia officinalis and Enteroctopus megalocyatus, in this study, we proposed the elimination of decalcification and dehydration steps to reduce the time of lens processing. In addition, lenses were included in epoxy resin, which was then subject to lapping, to ensure clear reading and counting of the increments. The number of increments counted in L. vulgaris (59–520) and in L. forbesii (51–543) was strongly related to mantle length and weight of the animals, with no statistical differences between the sexes. Assuming daily growth increments, L. vulgaris was estimated to have a life span of 17 months for males and 14 months for females, while L. forbesii males had an estimated life span of 18 and 16.5 months for females. The exponential model was the best fit for growth data for both species and sexes, showing higher growth for males in comparison with females. These results preliminarily indicate that the eye lens is a valid tool for age determination of the two Loliginidae species, but it would benefit from validation by additional studies.

Genetic information is crucial for the proper exploitation of Octopus vulgaris, the most commercially valuable octopus species worldwide. The main aim of the present study was to investigate genetic structure, with the intent to inform effective management of the common octopus in Sardinia (western Mediterranean Sea), one of the most productive areas within Italian waters. Patterns of population structure were assessed in 246 specimens from seven population samples. Variation in five nuclear-encoded microsatellites and sequences of two mitochondrial genes (COI and COIII) highlighted high variability and low but significant genetic differentiation among populations, which clustered into four groups corresponding to the north, northwest, south, and east coasts of Sardinia. Secondarily, the sequence data from Sardinia were compared with GenBank data from other areas. AMOVA and Bayesian analyses supported the occurrence of significant differences within the Mediterranean Sea, and between Eastern Atlantic and Mediterranean samples. The described genetic differentiation at a regional geographical scale could be determined by a combination of historical and/or current events restricting gene flow. The occurrence of significant genetic structuring at different spatial scales is an important piece of information to define the most appropriate conservation strategies in the area, both at the local and regional level.

The movements of Octopus vulgaris were investigated by a mark–recapture study (1604 specimens tagged), carried out during a commercial octopus traps fishery, at a depth of 20–50 m, over a rocky substrate area of the Sardinian Sea (central western Mediterranean Sea). Overall 87 specimens (56 males and 31 females) were recaptured after 4 and 63 days from the tagging. The difference between the depth at release and recapture varied up to 5.0 m but in 100% of males and in 80% of females the variation was less than 3.0 m. Theoretical straight distances travelled by recaptures ranged from 9 to 5800 m in males and from 9 to 1700 m in females, regardless of the days of freedom. There was no correlation between distances and sex or body size and no marked orientation was found except for medium males that move preferentially in the south western direction. The movements of O. vulgaris , generally linked to the availability of food, partners and/or shelters, in this study were limited within 1 km in most of the recaptures (84–86%). This high site fidelity, within the rocky area investigated, could represent useful information for management plans of this species like the creation of small no-take areas.

International audience; Cephalopod assemblages at the scale of the entire Mediterranean Sea were analysed using information from 2 decades of standardized scientific bottom trawl surveys. Western and eastern assemblages (6 yr of data) were compared using a combined approach of multivariate ordination techniques and non-linear regressions. These methods enabled us to distinguish assemblages and simultaneously analyse the influence of geographic, bathymetric and environmental (sea surface temperature and chlorophyll a concentration) gradients on observed community patterns. Despite few differences in species composition between sub-basins, the relative contribution of species differed. Bathymetry was the primary structural driver for the cephalopod communities of both basins, and contributed to 3 assemblages (shallow water, upper slope and middle slope). Winter temperature influenced community assemblages more strongly in the western than in the eastern basin, in contrast to a small but consistent winter productivity influence on community assemblages in both basins. Thus, the environmental parameters analysed did not cause an immediate change in cephalopod assemblages, but rather an effect lagged by several months. Differences in the relative importance of environmental drivers show that different processes operate in the 2 basins. These results demonstrate similarities and differences between Mediterranean basins regarding important cephalopod functional groups. This information should help integrative ecosystem management approaches currently used in fisheries and conservation management.

T-bar anchor tags and Petersen discs were used during a preliminary mark–recapture experiment in the wild on 268Octopus vulgaris.Discs, despite causing some injuries, were characterized by a quicker healing (within 5 days) and a higher retention rate than T-bar tags (about 97% versus 22%, respectively), therefore they were considered the best technique for tagging the animals in the subsequent growth studies. From 2010 to 2013, a total of 1604O. vulgaris(74.4% with a total weight −1) and higher mean daily growth rates in females (3.07–3.65 g day−1) than in males (2.08–2.98 g day−1) were recorded, but this difference was not statistically significant. Using tag–recapture data, the first exponential growth curves for both sexes ofOctopus vulgarisof small–medium size from the Mediterranean Sea were obtained, and compared with those available in the literature for the species.

A specimen of the rare squid genus Octopoteuthis (Cephalopoda: Octopoteuthidae) from 1600 m in the Sardinian Channel (central western Mediterranean) is described. Meristic and morphological data are provided. The specimen was a spent female and details of the reproductive system and implanted spermatangia are reported. Genetic analysis of this specimen and comparison with those available for species in this genus were carried out. Due to issues associated with the taxonomy of the genus Octopoteuthis, it was not possible to identify the specimen to the species level. The taxonomy of the genus is discussed.

The Mediterranean Sea is characterized by large scale gradients of temperature, productivity and salinity, in addition to pronounced mesoscale differences. Such a heterogeneous system is expected to shape the population dynamics of marine species. On the other hand, prevailing environmental and climatic conditions at whole basin scale may force spatially distant populations to fluctuate in synchrony. Cephalopods are excellent case studies to test these hypotheses owing to their high sensitivity to environmental conditions. Data of two cephalopod species with contrasting life histories (benthic octopus vs nectobenthic squid), obtained from scientific surveys carried out throughout the Mediterranean during the last 20 years were analyzed. The objectives of this study and the methods used to achieve them (in parentheses) were: (i) to investigate synchronies in spatially separated populations (decorrelation analysis); (ii) detect underlying common abundance trends over distant regions (dynamic factor analysis, DFA); and (iii) analyse putative influences of key environmental drivers such as productivity and sea surface temperature on the population dynamics at regional scale (general linear models, GLM). In accordance with their contrasting spatial mobility, the distance from where synchrony could no longer be detected (decorrelation scale) was higher in squid than in octopus (349 vs 217 km); for comparison, the maximum distance between locations was 2620 km. The DFA revealed a general increasing trend in the abundance of both species in most areas, which agrees with the already reported worldwide proliferation of cephalopods. DFA results also showed that population dynamics are more similar in the eastern than in the western Mediterranean basin. According to the GLM models, cephalopod populations were negatively affected by productivity, which would be explained by an increase of competition and predation by fishes. While warmer years coincided with declining octopus numbers, areas of high sea surface temperature showed higher densities of squid. Our results are relevant for regional fisheries management and demonstrate that the regionalisation objectives envisaged under the new Common Fishery Policy may not be adequate for Mediterranean cephalopod stocks., SI

The Mediterranean red coral, Corallium rubrum, is one of the most precious corals worldwide. Below 50 m depth, C. rubrum populations are generally characterised by large and sparse colonies, whereas shallow populations (above 50 m depth) show high densities of small colonies. We show here instead that populations dwelling between 80 and 170 m depth exhibited a continuous range of population density (from 2 to 75 colonies per 0.25 m2), with less than 1% of variance explained by water depth. An inverse relationship between maximum population density and mean colony height was found, suggesting that self-thinning processes may shape population structure. Moreover, demographically young populations composed of small and dense colonies dominated along rocky vertical walls, whereas mature populations characterised by large and sparsely distributed colonies were found only in horizontal beds not covered by sediment. We hypothesise that, in the long term, shallow protected populations should resemble to present deep populations, with sparsely distributed large colonies. Since the density of red coral colonies can decay as a result of self-thinning mechanisms, we advise that future protection strategies should be based also on a measure of red coral spatial coverage instead of population density.

First investigation on the relationship between reproductive development and estimated age/size in a wild population ofOctopus vulgariswas performed in the Sardinian waters (central western Mediterranean Sea) in order to have a useful tool for integral fishing management in the area. Full sexual maturity was registered from April to August for females with a peak in summer whereas for males it was observed all year round. Size at maturity was 320 g for males (70 mm dorsal mantle length (ML)) and 520 g for females (120 mm ML). From 61 to 465 and from 80 to 390 daily growth increments were counted on the lateral wall of the upper beak, respectively in males and females, obtaining a positive relationship between estimated age and size of the specimens. The sexual maturation was primarily size-dependent with a secondary role played by the age especially in males. The estimated age of 390 and 465 days respectively of the largest female (4661 g) and male (5344 g) as well as that of two males at the end of their lives (‘spent’) of 310 and 420 days old, have suggested a lifecycle of about 1 year for both genders.

The male reproductive system of the bobtail squid Neorossia caroli (Cephalopoda: Sepiolidae) is described in detail, based on observations of 90 mature males caught from 500 to 1600 m depth in Sardinian waters (western Mediterranean Sea). Reproductive organs in mature specimens accounted for up to 6% of total body weight. Of this, 70% was represented by the spermatophoric complex. Up to 83 spermatophores were found inside the Needham's sac. Mean spermatophore length was 16.7 mm. Sperm mass, cement body, and ejaculatory apparatus represented 63.2%, 13.1%, and 23.7% of the total spermatophore length, respectively. Inverted spermatophores, empty spermatophore sheaths, and spermatangia were also found in the sac, and their presence is discussed. Spermatangia implanted in several parts of the bodies of males (e.g., head, funnel, and eyes) were recorded and their occurrence is discussed. The spermatophoric reaction was induced in the laboratory by submerging spermatophores in seawater, and it is described briefly.

A sample of 360 Bathypolypus sponsalis from the central western Mediterranean Sea (the Sardinian Channel and the Tyrrhenian Sea) was analysed in order to describe size, depth distribution and reproductive data. The first record of the species in the Tyrrhenian Sea and of a spent female are reported in this paper. The size-structure of the sample was in between values of documented data from the western and eastern Mediterranean basins and the minimum mature sizes in both sexes and spermatophore length were similar to previous data from the eastern Mediterranean Sea. Low values of gonadosomatic index and fecundity, the asynchronous ovulation, in addition to an extended reproductive period, have been associated with an intermittent spawning strategy.

Several aspects of the biology of Opisthoteuthis calypso were studied based on 38 individuals (23 males, 14 females and 1 indeterminate) retrieved from bottom trawls fished at 871 to 1420 m depth in the Sardinian Channel (central western Mediterranean). Data on full maturity of females are presented for the first time for this species. Information on the distribution, size, structure and fecundity for both sexes is provided, and the biological characteristics of the Sardinian samples are compared to those of other Mediterranean and Atlantic samples. Morphological variability and the peculiar structure of the shell and beak are reported and discussed. Molecular DNA sequences were obtained and compared with sequences available for the genus Opisthoteuthis.

The contribution that a small restocking area (central western Mediterranean) has made to the Palinurus elephas (Fabr., 1787) population was examined by comparing the abundances recorded inside and outside the area before (1997) and after the establishment of the reserve (1998–2005). From 1998 to 2002 a progressive percentage increase of P. elephas biomass values was recorded both inside the area and in the surrounding zones. The total mean abundance within the reserve (CPUE=0.23±0.10 kg/50 m/boat) was 7.5 times greater than that for the neighbouring zone (CPUE=0.03±0.07 kg/50 m/boat). The inter-annual analysis of lobster size inside the area also showed a progressive increase of adults and juveniles. The results high-lighted the effectiveness of fishing restrictions in rebuilding the lobsters population and suggest that small MPAs should be set up.

WOS: 000382753200012, The genus Octopoteuthis includes squids inhabiting meso-and bathypelagic waters worldwide. Of the seven presently named species distributed in the world's oceans, only Octopoteuthis sicula has been reported for certain in the Mediterranean Sea to date. However, mixed and confusing descriptions of the systematic characters useful for identifying the species occur in the literature. Similarly, molecular analysis results available for the genus are contradictory and inconsistent. The research herein was undertaken firstly to clarify the systematic status of the genus in the Mediterranean Sea and confirm the presence of a single species, namely O. sicula. Additional goals were the assessment of the validity of systematic characters to identify the species and the analysis of beak morphology to provide useful tools in prey-predator relationship studies. Octopoteuthis specimens from various areas of the Mediterranean Sea and the Atlantic and Pacific oceans were compared, and the analysis of traditional morphological characters was combined with molecular genetics and the study of beaks. Molecular genetics and beak morphology results support the existence of a single species in the Mediterranean Sea. Additional evidence would suggest that this species is also distributed in the north-eastern Atlantic. The morphological characters reported in the literature to identify O. sicula did not identify Mediterranean specimens, with the exception of the two tail photophores. All information collected supports the need for a reconsideration of morphological characters used to identify Octopoteuthis species., David and Lucile Packard FoundationThe David & Lucile Packard Foundation, We heartily thank Jonathan Ablett for his kind assistance in loaning the holotype of Octopoteuthis sicula and providing photographs and related information. We also want to thank the David and Lucile Packard Foundation for the support given to part of the research at the base of this work. Angel Guerra provided positive criticism and constructive suggestions which greatly improved the quality of this document, for which we are deeply grateful. We also wish to thank our friend and colleague Louise Allcock for her critical reading of the manuscript and helpful suggestions. Last but not least, we feel grateful to the reviewers for their suggestions and their much appreciated supportive attitude and useful comments.

Growth of spiny lobsters Palinurus elephas was investigated using tagging data. A total of 4044 lobsters were tagged and released between 1997 and 2004 in an area off central‐western Sardinia, Italy, where fishing is banned. The growth increments of 248 lobsters, recaptured inside the no‐take area and in the surrounding zones, were recorded and analysed with two different procedures, and von Bertalanffy growth parameters were estimated for each sex. Males showed a higher asymptotic carapace length than females (167.9 versus 120.2mm). Growth increments recorded inside and outside the no‐take area did not reveal any density‐dependent effects on females. Small but non‐significant differences were evident for males, showing faster growth in lobsters caught outside the no‐take area.

First observations on reproduction of Neorossia caroli from the southern Sardinian sea are reported, based on the analyses of an egg clutch and specimens collected by bottom trawl on sandy and muddy grounds. The egg clutch, consisting of 13 white eggs of 9 mm length with embryos at an advanced developmental stage, was found at 1200 m depth, attached to a piece of hard substrate. Adult specimens were collected in a depth range between 400 and 1600 metres. DNA sequences indicated that embryos, spermatangia and adults belonged to the same species, the carol bobtail squid, N. caroli. Fecundity analysis made on 40 females showed a variable number of eggs (20–611) in the ovaries, with the combined presence of advanced and developing oocytes, and few smooth eggs ready to be spawned in the oviducts of mature females. Several sperm reservoirs (spermatangia) were embedded in the mantle of some of the females, in the anterior ventral area overlying the oviduct.

The presence of spawning and nursery grounds of Aristeids in the central western Mediterranean Sea were investigated using fishery-independent data (trawl surveys, 1994–2012). Spatial distributions were generated for mature animals and recruits, for both spring/summer and autumn data, using an inverse distance weighted deterministic interpolation. The persistence index was used to identify stable spawning and nursery grounds in the Sardinian slope region for Aristaeomorpha foliacea and Aristeus antennatus. Areas of aggregation for recruits and mature females appear connected with important physical habitat features. The analysis also suggests a seasonal bathymetric distribution for nursery areas. The recruits of A. foliacea are located in the upper part of the continental slope (377-450 m) in spring-summer and reach greater depths (468-628 m) in autumn. For A. antennatus, for which nursery areas only emerge in autumn, there is presumably an opposite ontogenic migration, from deep sea to upper slope, during the summer (575-681 m). Results indicate also a partial overlap between the nursery and spawning grounds of both species. In this particular areas, local environmental conditions such as upwelling events or the presence of canyons and seamounts seem to play an important role in their distribution. This study generated also relevant information on the spatial and temporal distribution of seasonal or persistent aggregations of spawners and recruits, providing scientific elements to suggest the feasibility of protecting these important resources.

In this paper we report information about the sexual maturity process of 245 Octopus vulgaris specimens (75 females and 170 males) from the Mediterranean Sea. For both sexes, six stages of sexual maturity (immature, developing, maturing, mature, spawning, and spent) are identified on the basis of macroscopic and microscopic observations of the reproductive system and linked with some reproductive indices. A good correspondence between gonad appearance and its histological structure is observed, highlighting, in females, how oviducal gland morphology plays a crucial role in the macroscopic evaluation of maturity. The Gonadosomatic and Hayashi indices, in the two genders, and the Oviducal Gland index in females alone do not allow distinguishing all the stages in an irrefutable way. Data on the potential fecundity, oocyte and spermatophore size are reported and compared with literature. In addition, spermatophore components are also computed. The results reported in this paper lead to easy identification of the different phases of sexual maturation of O. vulgaris and could constitute an important tool for defining assessment models in view of sound management of this species.

Abundance indexes and frequency of positive hauls data obtained for Illex coindetii and Eledone moschata from eight Mediterranean experimental trawl surveys carried out in the Sardinia Seas were analysed with an explorative methodology. Two sets of yearly surveys (homogeneous among them but different when considering the two groups) were thereby identified and the relative species density (N/km2) GIS distribution maps computed. A trawl survey, "anomalous" if compared to the others of the considered historical series, was put in evidence, the anomaly resulting in a very high recruitment pulse for Illex coindetii. Given the role of environmental factors (e.g., water temperature, currents regimes, up-welling events, etc.) on cephalopods life cycles, Sea Surface Temperature (SST) images for each month of a historical series of years, i.e. 1993-2001, including those of the trawl surveys considered, were gathered and qualitatively analysed to investigate SST relationship with the observed abundance/frequency fluctuations. Basic information available on the currents systems characterizing Sardinia waters was also collected and analysed. Results did not show a clear qualitative relationship between SST and the observed general variability, but evidenced a good correspondence between both species distribution and the analysed hydrological patterns. Very interestingly, however, the unusually high pulse of recruitment observed for I. coindetii during 1997, corresponded to unusually high SST values recorded during the period November 1996-April 1997, indicating a hydrological situation different from the usual pattern. These anomalous values could reflect the shifting toward north of the Algerian current and, consequently, of the frontal zone off the western Sardinian coasts, occurred from 1996 to 1998. This, in turn, could have generated/determined optimal conditions for the eggs development and hatching (e.g., salinity, nutrients and temperature favourable conditions), thus the recruitment pulse observed.

Species diversity is widely recognized as an important trait of ecosystems’ functioning and resilience. Understanding the causes of diversity patterns and their interaction with the environmental conditions is essential in order to effectively assess and preserve existing diversity. While diversity patterns of most recurrent groups such as fish are commonly studied, other important taxa such as cephalopods have received less attention. In this work we present spatio-temporal trends of cephalopod diversity across the entire Mediterranean Sea during the last 19 years, analysing data from the annual bottom trawl survey MEDITS conducted by 5 different Mediterranean countries using standardized gears and sampling protocols. The influence of local and regional environmental variability in different Mediterranean regions is analysed applying generalized additive models, using species richness and the Shannon Wiener index as diversity descriptors. While the western basin showed a high diversity, our analyses do not support a steady eastward decrease of diversity as proposed in some previous studies. Instead, high Shannon diversity was also found in the Adriatic and Aegean Seas, and high species richness in the eastern Ionian Sea. Overall diversity did not show any consistent trend over the last two decades. Except in the Adriatic Sea, diversity showed a hump-shaped trend with depth in all regions, being highest between 200–400 m depth. Our results indicate that high Chlorophyll a concentrations and warmer temperatures seem to enhance species diversity, and the influence of these parameters is stronger for richness than for Shannon diversity, SI