Mapping diversity indices: not a trivial issue

Mapping diversity indices, that is estimating values in all locations of a given area from some sampled locations, is central to numerous research and applied fields in ecology. Two approaches are used to map diversity indices without including abiotic or biotic variables: (i) the indirect approach, which consists in estimating each individual species distribution over the area, then stacking the distributions of all species to estimate and map a posteriori the diversity index, (ii) the direct approach, which relies on computing a diversity index in each sampled locations and then to interpolate these values to all locations of the studied area for mapping. For both approaches, we document drawbacks from theoretical and practical viewpoints and argue about the need for adequate interpolation methods. First, we point out that the indirect approach is problematic because of the high proportion of rare species in natural communities. This leads to zero-inflated distributions, which cannot be interpolated using standard statistical approaches. Secondly, the direct approach is inaccurate because diversity indices are not spatially additive, that is the diversity of a studied area (e.g. region) is not the sum of the local diversities. Therefore, the arithmetic variance and some of its derivatives, such as the variogram, are not appropriate to ecologically measure variation in diversity indices. For the direct approach, we propose to consider the -diversity, which quantifies diversity variations between locations, by the mean of a -gram within the interpolation procedure. We applied this method, as well as the traditional interpolation methods for comparison purposes on different faunistic and floristic data sets collected from scientific surveys. We considered two common diversity indices, the species richness and the Rao\u27s quadratic entropy, knowing that the above issues are true for complementary species diversity indices as well as those dealing with other biodiversity levels such as genetic diversity. We conclude that none of the approaches provided an accurate mapping of diversity indices and that further methodological developments are still needed. We finally discuss lines of research that may resolve this key issue, dealing with conditional simulations and models taking into account biotic and abiotic explanatory variables

Otolith microchemistry reveals contrasting intra-stock structuring in two demersal species off the Iberian Peninsula

Trabajo presentado en el 7th International Otolith Symposium, celebrado en Viña del Mar (Chile), entre el 9 y el 13 de octubre de 2023.Peer reviewe

Accounting for ocean connectivity and hydroclimate in fish recruitment fluctuations within transboundary metapopulations

International audienceMarine resources stewardships are progressively becoming more receptive to an effective incorporation of both ecosystem and environmental complexities into the analytical frameworks of fisheries assessment. Understanding and predicting marine fish production for spatially and demographically complex populations in changing environmental conditions is however still a difficult task. Indeed, fisheries assessment is mostly based on deterministic models that lack realistic parameterizations of the intricate biological and physical processes shaping recruitment, a cornerstone in population dynamics. We use here a large metapopulation of a harvested fish, the European hake (Merluccius merluccius), managed across transnational boundaries in the northwestern Mediterranean, to model fish recruitment dynamics in terms of physics-dependent drivers related to dispersal and survival. The connectivity among nearby subpopulations is evaluated by simulating multi-annual Lagrangian indices of larval retention, imports, and self-recruitment. Along with a proxy of the regional hydroclimate influencing early life stages survival, we then statistically determine the relative contribution of dispersal and hydroclimate for recruitment across contiguous management units. We show that inter-annual variability of recruitment is well reproduced by hydroclimatic influences and synthetic connectivity estimates. Self-recruitment (i.e., the ratio of retained locally produced larvae to the total number of incoming larvae) is the most powerful metric as it integrates the roles of retained local recruits and immigrants from surrounding subpopulations and is able to capture circulation patterns affecting recruitment at the scale of management units. We also reveal that the climatic impact on recruitment is spatially structured at regional scale due to contrasting biophysical processes not related to dispersal. Self-recruitment calculated for each management unit explains between 19% and 32.9% of the variance of recruitment variability, that is much larger than the one explained by spawning stock biomass alone, supporting an increase of consideration of connectivity processes into stocks assessment. By acknowledging the structural and ecological complexity of marine populations, this study provides the scientific basis to link spatial management and temporal assessment within large marine metapopulations. Our results suggest that fisheries management could be improved by combining information of physical oceanography (from observing systems and operational models), opening new opportunities such as the development of short-term projections and dynamic spatial management

Patrones de distribución espacio temporal de las especies de macrúridos en el Mediterráneo norte

The present study describes for the first time the spatial distribution of five macrourid species throughout the Mediterranean Sea and analyses depth, geographical and time-related trends regarding their abundance, biomass and mean fish weight. The data were collected as part of the MEDITS annual bottom trawl survey carried out by several European Mediterranean countries from 1994 to 2015, using the same standardized gear and sampling protocol. The most represented species in terms of abundance and biomass was Coelorinchus caelorhincus. The bathymetric trend was different for each species. The shallowest occurring species was C. caelorhincus, followed by Hymenocephalus italicus and Nezumia sclerorhynchus, while Nezumia aequalis and Trachyrincus scabrus were the deepest. Overall, the mean weight of all the species increased with depth. C. caelorhincus and H. italicus occurred in the entire study area: the first species showed relatively high catches in most areas, while the second was more abundant in the central and easternmost areas. N. aequalis and T. scabrus were mainly reported in the western basin, and N. sclerorhynchus in the central-eastern areas of the Mediterranean. An increasing inter-annual trend in abundance was only detected for C. caelorhincus and N. sclerorhynchus, while variable fluctuations were observed in the other species.El presente estudio describe por primera vez la distribución espacial de cinco especies de macrúridos a lo largo del Mediterráneo en su vertiente europea, analizando las tendencias batimétricas, geográficas y temporales de la abundancia, la biomasa y el peso medio de las especies. Los datos utilizados provienen de las campañas de arrastre de fondo anuales, MEDITS, desde 1994 a 2015, llevadas a cabo por los países mediterráneos europeos utilizando un arte de arrastre y un protocolo de muestreo estandarizado. La especie más representativa en términos de abundancia y biomasa fue Coelorinchus caelorhincus. Las tendencias batimétricas fueron variables según la especie. La más costera fue C. caelorhincus seguida de Hymenocephalus italicus y Nezumia sclerorhynchus mientras que Nezumia aequalis y Trachyrincus scabrus son las que se localizaron a mayor profundidad. En general, el peso medio de las especies se incrementó con la profundidad. Geográficamente, C. caelorhincus e H. italicus se encontraron distribuidas a lo largo de toda el área de estudio: la primera mostró capturas relativamente elevadas en la mayoría de las áreas mientras que la segunda fue más abundante en las zonas central y oriental. N. aequalis y T. scabrus se capturaron fundamentalmente en la cuenca occidental mientras que N. sclerorhychus en las áreas centro-este del Mediterráneo. Únicamente se detectó incremento interanual en C. caelorhincus y N. sclerorhynchus, mientras que en el resto de las especies no se registó incremento ni descenso sino fluctuaciones interanuales

Patrón de abundancia espacio-temporal de la gamba de altura, Parapenaeus longirostris, y de la cigala, Nephrops norvegicus, en las aguas mediterráneas europeas

The main characteristics concerning the distribution of two of the most important decapod crustaceans of commercial interest in the Mediterranean Sea, the deep-water rose shrimp, Parapenaeus longirostris, and the Norway lobster, Nephrops norvegicus, are studied in the European Mediterranean waters. The study is based on data collected under the MEDITS trawl surveys from 1994 to 2015 from the Gibraltar Straits to the northeastern Levantine Basin (Cyprus waters). The observed differences can be interpreted as different responses to environmental drivers related to the differing life history traits of the two species. In fact, N. norvegicus is a long-living, benthic burrowing species with low growth and mortality rates, while P. longirostris is an epibenthic, short-living species characterized by higher rates of growth and mortality.Se investigaron las características de la distribución de dos de los crustáceos decápodos más importantes a nivel comercial del mar Mediterráneo, la gamba de altura, Parapenaeus longirostris y la cigala, Nephrops norvegicus, en aguas mediterráneas europeas. El presente estudio se basa en datos recopilados en las campañas de pesca experimental de arrastre MEDITS, relizadas de 1994 a 2015 desde el estrecho de Gibraltar hasta la cuenca levantina nororiental (aguas de Chipre). Las diferencias observadas en el patrón de distribución se pueden interpretar como distintas respuestas a factores ambientales relacionados con los diferentes rasgos del ciclo vital de las dos especies. De hecho, N. norvegicus es una especie bentónica de vida larga, con bajas tasas de crecimiento y mortalidad, mientras que P. longirostris es una especie epibentónica de vida corta, caracterizada por tasas más altas de crecimiento y de mortalidad

Large-Scale Spatio-Temporal Patterns of Mediterranean Cephalopod Diversity

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 diversityVersión del editor4,411

Guide du chef de mission de la campagne MEDITS (série Française) (MEDiterranean International Trawl Survey)

Ce document détaille la succession des actions à conduire lors des campagnes MEDITS. Il vient en complément du manuel des protocoles officiel

Stock Assessment Form Demersal species. Hake GSA7. Reference year: 1998-2015. Reporting year 2016.

Hake is one of the most important demersal target species for the commercial fisheries in the Gulf of Lions (GSA 7). In this area, hake is exploited by French trawlers, French gillnetters, Spanish trawlers and Spanish longliners. Since 1998, an average of 243 boats are involved in this fishery and, according to official statistics, the total annual catches for the period 1998-2015 have oscillated around an average value of 1961 tons (1139 tons in 2015). In 2009, because of the large decline of small pelagic fish species in the area, the trawlers fishing small pelagic have diverted their effort on demersal species. Between 1998 and 2015, the number of French trawlers operating in the GSA 07 has decreased by 50%. The French trawler fleet is the largest considering catches realized, the proportion of boats and catches are respectively (27% and 73%). The length of hake in the trawler catches ranges between 3 and 92 cm total length (TL), with an average size of 21 cm TL. The second largest fleet is the French gillnetters (41 and 16% respectively, range 13-86 cm TL and average size 39 cm TL), followed by the Spanish trawlers (9 and 10%, respectively, range 5-88 cm TL, and average size 24 cm TL), and the Spanish longliners (4 and 1%, respectively, range 22-96 cm TL and average size 52 cm TL). The hake trawlers exploit a highly diversified species assemblage: Striped red mullet (Mullus surmuletus), red mullet (M. barbatus), angler fish (L. piscatorius), blackbellied angler fish (L. budegassa), european conger (Conger conger), poor-cod (Trisopterus minutus capelanus), fourspotted megrim (Lepidorhombus boscii), soles (Solea spp.), horned octopus (Eledone cirrhosa), squids (Illex coindetii), gilthead seabream (Sparus aurata), European seabass (Dicentrarchus labrax), seabreams (Pagellus spp.), blue whiting (Micromesistius poutassou), tub gurnard (Chelidonichtys lucerna). The stock is in an overexploitation status with a relative low biomass with periodically higher recruitments (1998, 2001-2002 and 2007). Since 2007, the recruitment follows a decreasing trend and is currently at a low level. The recruitment estimated for 2015 is 38152 thousands individuals, which is below the series average (54906 thousands). The spawning stock biomass (SSB) displays a decreasing trend over the analysed period, especially in the very recent year. The exploitation level is currently above the level estimated to be sustainable. The reference point F0.1 (0.15), chosen as proxy of FMSY and as the exploitation reference point consistent with high long term yields is highly lower than current fishing mortality (Fcur=1,92). The exploitation is mainly concentrated on young individuals

MARBEC-Obs : towards a virtual observatory of marine and coastal ecosystems, mainly in Mediterranean and tropical areas

International audienceMARBEC is the largest French research unit in marine biodiversity (IRD IFREMER CNRS and University of Montpellier) with many international partnerships.MARBEC-Obs is in charge of 20 durable observatories, contributing to research and expertise on the state of coastal and marine ecosystems, biodiversity and the impact of human activities exploiting this biodiversity. The services and functionalities offered by the information systems combine modeling, statistical analysis, data management and data visualisation.MARBEC-Obs can evolve towards a virtual observatory of marine and coastal ecosystems, mainly in Mediterranean and tropical areas