Distribution, diet and relationships of the invasive ctenophore Mnemiopsis leidyi with anchovies and zooplankton, in the northeastern Adriatic Sea

Blooms of invasive ctenophore Mnemiopsis leidyi can have massive consequences on fish stocks and marine food webs. The distribution, abundance and diet of this ctenophore were investigated in the northeastern (NE) Adriatic between 2016 and 2019. The abundance of M. leidyi was determined daily along the coast of Rovinj (Croatia), and its spatial distribution monitored by visual census from research vessels and by pelagic trawl during acoustic surveys in September of each year. Mesozooplankton samples were collected along the western coast of Istria by vertical tows from the bottom to the surface. Spatial distribution and abundance of anchovy (Engraulis encrasicolus) assemblages were determined by geo-referenced hydro-acoustic sampling using a scientific echosounder. Large swarms of M. leidyi covering several km2 were regularly reported between July and November extending up to 25 NM from the western coast of the Istrian peninsula and reaching maximum offshore densities of 270 individuals per m2. The abundance of anchovy in the areas where M. leidyi was present evidently decreased. The content of M. leidyi’s digestive tract and plankton samples consisted both mainly of cladocerans, copepods, pteropods, echinodermata and bivalvia larvae. Results indicate that M. leidyi may accumulate and increase its abundance in the stagnant and trophically rich areas of the northern Adriatic gyres, spreading to the surrounding larger areas with currents. We assume that M. leidyi presence correlates with a decrease in anchovy population due to competition for food (zooplankton). Our findings support the importance of implementing an international monitoring program throughout the Adriatic Sea and demonstrate the ability of current MEDIAS surveys to detect changes in the pelagic ecosystem throughout surveyed areas

New Mediterranean Biodiversity Records (November 2018)

In the present article, new records are given for 18 species (6 native, 9 alien and 3 cryptogenic), belonging to 5 Phyla (i.e. Chlorophyta, Cnidaria, Annelida, Mollusca and Chordata), from 8 Mediterranean countries: Spain: A large population of Polycerella emertoni reported from the Ebro Delta, the presence of pinimuricea klavereni is confirmed for the first time in the Catalan coast; Italy: the new record of Cryptonome turcica extends its distribution to the western Mediterranean Sea, the findings of Mawia benovici constitute the southernmost record of this species in the Adriatic Sea; Slovenia: second record of the alien seaslug Cuthona perca in the Mediterranean Sea; Montenegro: Styela plicata communities were recorded in Boka Kotorska Bay; Albania: the native great torpedo ray Tetronarce nobiliana recorded for the first time in Albanian waters; Greece: first record of Lagocephalus sceleratus in the Greek side of the Adriatic, the records of Cassiopea andromeda and Pterois miles are first records of these species from the Ionian Sea, the colonial ascidians Aplidium coeruleum and Didemnum protectum are recorded for the first time in the Eastern Mediterranean, an extremely abundant population of Melibe viridis is found in Messolonghi lagoon, the record of Synchiropus sechellensis is the range expansion of this species in Greek Seas, Acetabularia caliculus is recorded for the first time from Greece; Cyprus: first records of Callionymus filamentosus and Haminoea cyanomarginata from the island; Turkey: the presence of Berthellina citrina in the Mediterranean is confirmed.info:eu-repo/semantics/publishedVersio

Observation of Abrupt Changes in the Sea Surface Layer of the Adriatic Sea

We observed interannual changes in the temperature and salinity of the surface layer of the Adriatic Sea when measured during the period 2005–2020. We observed non-stationarity and a positive linear trend in the series of mixed layer depth, heat storage, and potential energy anomalies. This non-stationarity was related to the climate regime that prevailed between 2011 and 2017. We observed significant changes in the interannual variability of salinity above and below the mixed layer depth and a positive difference in the surface barrier layer. In an effort to reconstruct the cause of this phenomenon, a multi-stage investigation was conducted. The first suspected culprit was the change in wind regime over the Mediterranean and Northeast Atlantic regions in September. Using the growing neural gas algorithm, September wind fields over the past 40 years were classified into nine distinct patterns. Further analysis of the CTD data indicated an increase in heat storage, a physical property of the Adriatic Sea known to be strongly influenced by the inflow of warm water masses controlled by the bimodal oscillating system (BiOS). The observed increase in salinity confirmed the assumption that BiOS activity affects heat storage. Unexpectedly, this analysis showed that an inverse vertical salinity profile was present during the summer months of 2015, 2017, and 2020, which can only be explained by salinity changes being a dominant factor. In addition, the aforementioned wind regime caused an increase in energy loss through latent energy dissipation, contributing to an even larger increase in salinity. While changes in the depth of the mixed layer in the Adriatic are usually due to temperature changes, this phenomenon was primarily caused by abrupt changes in salinity due to a combination of BiOS and local factors. This is the first record of such an event

Observation of Abrupt Changes in the Sea Surface Layer of the Adriatic Sea

We observed interannual changes in the temperature and salinity of the surface layer of the Adriatic Sea when measured during the period 2005–2020. We observed non-stationarity and a positive linear trend in the series of mixed layer depth, heat storage, and potential energy anomalies. This non-stationarity was related to the climate regime that prevailed between 2011 and 2017. We observed significant changes in the interannual variability of salinity above and below the mixed layer depth and a positive difference in the surface barrier layer. In an effort to reconstruct the cause of this phenomenon, a multi-stage investigation was conducted. The first suspected culprit was the change in wind regime over the Mediterranean and Northeast Atlantic regions in September. Using the growing neural gas algorithm, September wind fields over the past 40 years were classified into nine distinct patterns. Further analysis of the CTD data indicated an increase in heat storage, a physical property of the Adriatic Sea known to be strongly influenced by the inflow of warm water masses controlled by the bimodal oscillating system (BiOS). The observed increase in salinity confirmed the assumption that BiOS activity affects heat storage. Unexpectedly, this analysis showed that an inverse vertical salinity profile was present during the summer months of 2015, 2017, and 2020, which can only be explained by salinity changes being a dominant factor. In addition, the aforementioned wind regime caused an increase in energy loss through latent energy dissipation, contributing to an even larger increase in salinity. While changes in the depth of the mixed layer in the Adriatic are usually due to temperature changes, this phenomenon was primarily caused by abrupt changes in salinity due to a combination of BiOS and local factors. This is the first record of such an event

First description of the shelf epipelagic plankton layers at a Mediterranean basin-scale

This research represents the first approach to the study of the shelf zooplankton community at a Mediterranean scale, using acoustic standardized data collected in June-July in 10 different geographical sub-areas (GSAs) established by the General Fisheries Commission for the Mediterranean (GFCM) within the framework of the MEDiterranean International Acoustic Survey (MEDIAS). The analysis of the zooplankton layers based on their acoustic characteristics has revealed the potential of these surveys for the study of zooplankton at a Mediterranean basin scale and, also, the need to collect biological samples to interpret the acoustic records in terms of species. The fish population’s direct assessment is established in the MEDIAS framework, but the integration of zooplankton community data would constitute a qualitative step for the understanding of the fluctuations of fish populations and therefore to achieve the objective of an ecosystem-based management. Results have revealed the ubiquity of the zooplankton layers and its ability to form layers detectable by scientific echosounders throughout the Mediterranean at the common fish assessment frequency (38 kHz). In addition, the use of two frequencies (38 and 120 kHz) has allowed to apply the dB difference method, observing changes in the difference of the Mean Volume Backscattering Strength (∆MVBS) at 38 and 120 kHz frequencies, which would be related to changes in the composition of the zooplankton community

Temperature strongly correlates with regional patterns of body size variation in Mediterranean small pelagic fish species

In this study we consider the applicability of Bergmann’s rule to the populations of small pelagic fish species in the Mediterranean Sea. Under Bergmann’s rule, body size increases with decreasing temperature and increasing latitude. Although this macroecological pattern in body sizes is well established for many taxa of endotherms and ectotherms, it does not remain universal, and the proposed mechanisms underlying it are multiple and still lack consensus. Here we explored the occurrence of geographical body size clines using measurements of average body sizes of 10 species collected in pelagic trawl hauls carried out during acoustic surveys in the Mediterranean Sea. Bergmann’s rule was evaluated by correlating body sizes with latitude and temperature for each species while accounting for potential confounding variables and sampling bias. For 5 species, namely anchovy, sardine, Atlantic chub mackerel, bogue and blue jack mackerel, we demonstrate that they follow Bergmann’s rule, with a decline in average body size by about 3.01, 3.43, 3.67, 3.82 and 3.76 % per 1°C of warming, respectively, although this did not translate with an increase in size with latitude. The adherence of these 5 pelagic fish to Bergmann’s rules strongly suggest that temperature is a major determinant of their body sizes and enables them to act as sentinel species for identifying the drivers and consequences of warming in the Mediterranean ecosystems

New Mediterranean Biodiversity Records (November 2018)

In the present article, new records are given for 18 species (6 native, 9 alien and 3 cryptogenic), belonging to 5 Phyla (i.e. Chlorophyta, Cnidaria, Annelida, Mollusca and Chordata), from 8 Mediterranean countries: Spain: A large population of Polycerellaemertoni reported from the Ebro Delta, the presence of Spinimuricea klavereni is confirmed for the first time in the Catalan coast; Italy: the new record of Cryptonome turcica extends its distribution to the western Mediterranean Sea, the findings of Mawia benovici constitute the southernmost record of this species in the Adriatic Sea; Slovenia: second record of the alien seaslug Cuthona perca in the Mediterranean Sea; Montenegro: Styela plicata communities were recorded in Boka Kotorska Bay; Albania: the native great torpedo ray Tetronarce nobiliana recorded for the first time in Albanian waters; Greece: first record of Lagocephalus sceleratus in the Greek side of the Adriatic, the records of Cassiopea andromeda and Pterois miles are first records of these species from the Ionian Sea, the colonial ascidians Aplidium coeruleum and Didemnum protectum are recorded for the first time in the Eastern Mediterranean, an extremely abundant population of Melibe viridis is found in Messolonghi lagoon, the record of Synchiropus sechellensis is the range expansion of this species in Greek Seas, Acetabularia caliculus is recorded for the first time from Greece; Cyprus: first records of Callionymus filamentosus and Haminoea cyanomarginata from the island; Turkey: the presence of Berthellina citrina in the Mediterranean is confirmed