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

A MSFD complementary approach for the assessment of pressures, knowledge and data gaps in Southern European Seas : the PERSEUS experience

PERSEUS project aims to identify the most relevant pressures exerted on the ecosystems of the Southern European Seas (SES), highlighting knowledge and data gaps that endanger the achievement of SES Good Environmental Status (GES) as mandated by the Marine Strategy Framework Directive (MSFD). A complementary approach has been adopted, by a meta-analysis of existing literature on pressure/impact/knowledge gaps summarized in tables related to the MSFD descriptors, discriminating open waters from coastal areas. A comparative assessment of the Initial Assessments (IAs) for five SES countries has been also independently performed. The comparison between meta-analysis results and IAs shows similarities for coastal areas only. Major knowledge gaps have been detected for the biodiversity, marine food web, marine litter and underwater noise descriptors. The meta-analysis also allowed the identification of additional research themes targeting research topics that are requested to the achievement of GES. 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license.peer-reviewe

Environmental drivers explain regional variation of changes in fish and invertebrate functional groups across the Mediterranean Sea from 1994 to 2012

Functional groups are sets of species that play a similar role in a food web. We defined functional groups of fish species based on their morphological characteristics, while using expert knowledge for invertebrates. We measured 9 morphological traits of 72 fish species, and carried out multivariate analyses to assign fish species to functional groups. The analysis identified 9 trait-based fish functional groups to which were added 3 expert-based invertebrate functional groups. The habitat (position in the water column) and potential diet of each group were identified from the literature. Using the MEDITS bottom trawl survey data collected at 10 to 800 m depth, we calculated relative change in the 12 fish and invertebrate functional group biomasses for 12 Mediterranean areas over the period 1994 to 2012. Multiple regression trees identified 4 regions with similar changes: (1) the Adriatic and the Ionian Sea; (2) the Tyrrhenian Sea and the Strait of Sicily; (3) the Balearic Islands and other enclosed areas such as the Gulf of Lions and Aegean Sea; and (4) the Ligurian Sea and Sardinia. The biomass of all functional groups increased or remained stable in the first 2 regions, while around half the functional group biomasses decreased in the other 2 regions. These regional differences in functional group biomass changes were mainly associated with regional variations in the time trends of bottom water temperature (37%), bottom water dissolved oxygen (23%) and mean catch levels (9%). This study contributes to the EU Marine Strategy Framework Directive by proposing food web indicators based on morphologically and habitat defined functional groups

Spatial distribution pattern of European hake, Merluccius merluccius (Pisces: Merlucciidae), in the Mediterranean Sea

The present study provides updated information on the occurrence, abundance and biomass distribution patterns and length frequencies of Merluccius merluccius in the Mediterranean Sea, by analysing a time series of data from the Mediterranean International Trawl Surveys (MEDITS) from 1994 to 2015. The highest values of abundance and biomass were observed in the Sardinian Seas. The use of a generalized additive model, in which standardized biomass indices (kg km–2) were analysed as a function of environmental variables, explained how ecological factors could affect the spatio-temporal distribution of European hake biomass in the basin. High biomass levels predicted by the model were observed especially at 200 m depth and between 14°C and 18°C, highlighting the preference of the species for colder waters. A strong reduction of biomass was observed since the year 2009, probably due to the strengthening of the seasonal thermocline that had greatly reduced the availability of food. The general decrease in biomass of several stocks of anchovy and sardine, preys of European hake, might be indirectly connected to the decreasing biomass detected in the present study. The length analysis shows median values lower than 200 mm total length of most of the investigated areas.El presente estudio proporciona información sobre los patrones de ocurrencia, abundancia y distribución de biomasa, y las longitudes de Merluccius merluccius en el mar Mediterráneo, considerando el análisis de una serie temporal proveniente de las campañas internacionales de pesca de arrastre en el Mediterráneo (MEDITS) de 1994 a 2015. Los valores más altos de abundancia y biomasa se observaron en los mares de Cerdeña. El uso del modelo GAM, en el que se analizaron los índices estandarizados de biomasa (BI, kg km–2) en función de las variables ambientales, permitió explicar cómo los factores ecológicos podrían afectar la distribución espacio-temporal de la biomasa de merluza europea en la cuenca. Los niveles altos de biomasa pronosticados por el modelo se observaron especialmente a 200 m de profundidad y entre 14 y 18°C, destacando la preferencia de la especie por aguas más frías. Se observó una fuerte reducción de la biomasa desde el año 2009, probablemente debido al fortalecimiento de la termoclina estacional que había reducido en gran medida la disponibilidad de alimentos. Otros procesos como la disminución general de la biomasa de varias poblaciones de anchoa y sardina, las presas de merluza europea, podrían estar indirectamente relacionadas con la disminución de la biomasa detectada en el presente estudio. El análisis de longitud muestra valores medios inferiores a 200 mm TL de la mayoría de las áreas investigadas

Temporal patterns of the Shannon diversity H’ at six different Mediterranean bioregions using the MEDITS sampling carried out during 1994–2012.

<p>Temporal patterns of the Shannon diversity H’ at six different Mediterranean bioregions using the MEDITS sampling carried out during 1994–2012.</p

Environmentally driven synchronies of Mediterranean cephalopod populations

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.Versión del edito

Boxplots of Shannon diversity (A) and Species richness (B) per haul, obtained using all MEDITS samples taken during 1994–2012.

<p>Boxplots of Shannon diversity (A) and Species richness (B) per haul, obtained using all MEDITS samples taken during 1994–2012.</p

GAM outputs for partial effects for factor “year” (mean ± S.E.) on Shannon diversity (A) and species richness (B) of Mediterranean cephalopods collected during MEDITS sampling (2003–2008).

<p>GAM outputs for partial effects for factor “year” (mean ± S.E.) on Shannon diversity (A) and species richness (B) of Mediterranean cephalopods collected during MEDITS sampling (2003–2008).</p

Shannon diversity (A) and Species richness (B) per haul from MEDITS sampling (1994–2012), calculated for the following bioregions: Iberian-Lions (IL), Tyrrhenian Sea (TY), Strait of Sicily (SS), Adriatic Sea (AD), Ionian Sea (IO) and Southern Aegean Sea (AG).

<p>Shannon diversity (A) and Species richness (B) per haul from MEDITS sampling (1994–2012), calculated for the following bioregions: Iberian-Lions (IL), Tyrrhenian Sea (TY), Strait of Sicily (SS), Adriatic Sea (AD), Ionian Sea (IO) and Southern Aegean Sea (AG).</p

Species accumulation curves of MEDITS sampling at different Mediterranean bioregions.

<p>Species accumulation curves of MEDITS sampling at different Mediterranean bioregions.</p