Eastern Adriatic Sea Research Articles

Multi-Criteria Analysis of Coast Guard Resource Deployment for Improvement of Maritime Safety and Environmental Protection: Case Study of Eastern Adriatic Sea

Multi-Criteria Analysis of Coast Guard Resource Deployment for Improvement of Maritime Safety and Environmental Protection: Case Study of Eastern Adriatic Sea

Phytoplankton Assemblage over a 14-Year Period in the Adriatic Sea: Patterns and Trends.

Considering the role of phytoplankton in the functioning and health of marine systems, it is important to characterize its responses to a changing environment. The central Adriatic Sea, as a generally oligotrophic area, is a suitable environment to distinguish between regular fluctuations in phytoplankton and those caused by anthropogenic or climatic influences. This study provides a long-term perspective of phytoplankton assemblage in the central eastern Adriatic Sea, with 14 years of continuous time series data collected at two coastal and two offshore stations. The predominant phytoplankton groups were diatoms and phytoflagellates, but their proportion varied depending on the vicinity of the coast, as evidenced also by the distribution of chlorophyll a. In the coastal environment, the phytoplankton biomass was substantially higher, with a higher proportion of microphytoplankton, while small phytoplankton accounted for the majority of biomass in the offshore area. In addition, a decreasing trend in diatom abundance was observed in the coastal waters, while such trend was not so evident in the offshore area. Using a neural gas algorithm, five clusters were defined based on the contribution of the major groups. The observed increase in diversity, especially in dinoflagellates, which outnumber diatom taxa, could be a possible adaptation of dinoflagellates to the increased natural solar radiation in summer and the increased sea surface temperature.

A Climatology of Convective Precipitation over Europe

Abstract The annual, seasonal, and diurnal spatiotemporal heavy convective precipitation patterns over a pan-European domain are analyzed in this study using a combination of datasets, including the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (GPM) (IMERG) precipitation rate product, E-OBS ground-based precipitation gauge data, European climatological gauge-adjusted radar precipitation dataset (EURADCLIM), Operational Programme for the Exchange of Weather Radar Information (OPERA) ground-based radar-derived precipitation rates, and fifth major global reanalysis produced by ECMWF (ERA5) total and convective precipitation products. Arrival Time Difference Network (ATDnet) lightning data are used in conjunction with IMERG and EURADCLIM precipitation rates, with an imposed threshold of 10 mm h−1 to classify precipitation as convective. Annually, the largest convective precipitation accumulations are over the European seas and coastlines. In summer, convective precipitation is more common over the European continent, though relatively large accumulations exist over the northern coastal waters and the southern seas, with a seasonal localized maximum over the northern Adriatic Sea. Activity shifts southward to the Mediterranean and its coastlines in autumn and winter, with maxima over the Ionian Sea, the eastern Adriatic Sea, and the adjacent coastline. Over the continent, 1%–10% of the total precipitation accumulated is classified as convective, increasing to 10%–40% over the surrounding seas. In contrast, 30%–50% of ERA5 precipitation accumulations over land is produced by the convective parameterization scheme and 40%–60% over the seas; however, only 1% of ERA5 convective precipitation accumulations are from rain rates exceeding 10 mm h−1. Regional analyses indicate that convective precipitation rates over the inland mountains follow diurnal heating, though little to no diurnal pattern exists in convective precipitation rates over the seas and coastal mountains.

Microbial communities as indicators of marine ecosystem health: Insights from coastal sediments in the eastern Adriatic Sea

Considering the adaptability and responsiveness of microorganisms to environmental changes, their indicator potential is still not acknowledged in European directives. This comprehensive study examined the changes of microbial communities in sediments and a range of geochemical parameters from pristine and anthropogenically impacted coastal areas in the eastern Adriatic Sea. Various analytical methods found evidence of sediment contamination (high toxicity level, enrichments of metals, tributyltin) in certain areas, leading to the categorization of sediments based on the level of anthropogenic disturbance. Prokaryotes were identified as the most promising group of microbes for further research, with specific bacterial families (Rhodobacteraceae, Ectothiorhodospiraceae, Cyclobacteriaceae) and genera (Boseongicola, B2M28, Subgroup 23, Sva0485, Thiogranum) proposed as potential indicators of environmental status. Finally, predictive models were developed to identify key indicator variables for assessing anthropogenic impact in sediments. This research represents an essential step toward incorporating microbial communities into assessments of benthic environmental health.

Some biological and morphological aspects of Eriphia verrucosa (Forskål, 1775) in the eastern Adriatic Sea

Aim: To investigate and describe the length-weight relationship and sex ratio of the species Eriphia verrucosa in the eastern Adriatic and to determine whether there is external dimorphism by morphometric analysis of the body. Methods: All samples were collected in the coastal area in the intertidal zone of Kaštela Bay (Split-Dalmatia County, Croatia). The sample catching was done at night after 10 p.m. with a hand net and an LED headlamp; afterwards, each specimen was weighed, prepared for further processing and frozen. The processing of each specimen included sex determination and detailed morphometric measurements. In females, a total of eight morphometric measures were measured and additionally the length of the gonopods in males. For each morphometric measure except gonopod length (GL), the average value and the corresponding 95% confidence interval were determined. Results: A total of 73 individual specimens of E. verrucose were sampled, of which 35 were males and 38 were females. The gender ratio was 0.92:1 in favor of females (P = 0.726). The largest body weight measured during this research was a male with a mass of 263.6 g, and the smallest was also a male with a weight of 7.3 g. The largest number of individuals belonged to the length class of 45–50 mm. Sexual dimorphism between males and females was recorded for all morphometric measures. According to the b coefficient of length-weight yield, the growth of E. verrucosa can be characterized as negatively allometric. Conclusions: In this research, the biological characteristics of the species E. verrucosa in the eastern Adriatic were analyzed. The length-weight ratio (CL-W) for the total sample was W = 0.0076 × CL2.5086, for males W = 0.0078 × CL2.5116 and for females W = 0.0169 × CL2.2911. Based on the length-weight ratio, sex ratio and the morphometric analysis of the body, sexual dimorphism is documented, which was not previously found for the warty crab in that area.

Polychlorinated biphenyls in mussels, small pelagic fish, tuna, turtles, and dolphins from the Croatian Adriatic Sea waters: an overview of the last two decades of monitoring.

This review summarises our two decades of polychlorinated biphenyl (PCB) monitoring in different marine organisms along the eastern Adriatic Sea. The aim was to gain an insight into the trends of PCB distribution in order to evaluate the effectiveness of past and current legislation and suggest further action. Here we mainly focus on PCB levels in wild and farmed Mediterranean mussels, wild and farmed bluefin tuna, loggerhead sea turtles, common bottlenose dolphins, and small pelagic fish. The use of artificial intelligence and advanced statistics enabled an insight into the influence of various variables on the uptake of PCBs in the investigated organisms as well as into their mutual dependence. Our findings suggest that PCBs in small pelagic fish and mussels reflect global pollution and that high levels in dolphins and wild tuna tissues raise particular concern, as they confirm their biomagnification up the food chain. Therefore, the ongoing PCB monitoring should focus on predatory species in particular to help us better understand PCB contamination in marine ecosystems in our efforts to protect the environment and human health.

New records of hard-bottom polychaete species in the central Adriatic Sea

Adriatic Sea is a diverse marine ecosystem that supports a rich biodiversity of polychaete species on soft and hard-bottoms, with 764 recorded species in the latest inventory list. Benthic surveys conducted in 2018 in the hard-bottom infralittoral zone on the east coast of the central Adriatic Sea revealed one previously unreported species for the Adriatic Sea, Syllis kabilica Ben-Eliahu, 1977 (Syllidae), as well as two species reported for the first time in the eastern Adriatic Sea, Syllis tyrrhena (Licher and Kuper, 1998) (Syllidae), and Streblosoma nogueirai Lezzi and Giangrande, 2019 (Terebellidae). Furthermore, one alien species was identified, Lysidice collaris Grube, 1868 (Eunicidae). These findings provide new insights into the distribution and diversity of polychaete fauna in the Adriatic Sea.

Biometrijske osobine rumenca okana, Pagellus bogaraveo (Brunnich, 1769) (Osteichthyes: Sparidae) u istočnom dijelu Jadrana

A biometric analysis was performed on a sample of 420 specimens of the blackspot seabream, Pagellus bogaraveo (Brunnich, 1769), from the eastern Adriatic Sea. The total length of all specimens ranged from 9.2 to 47.8 cm (23.70 ± 7.63 cm). Eighteen morphometric and eight meristic characteristics were determined. There were no statistically significant differences between the sexes in the morphometric and meristic characteristics of the blackspot seabream in the Adriatic Sea. Regarding meristic characteristics, there are no significant morphological differences between the blackspot seabream population in the Adriatic Sea and that in other areas of the Mediterranean Sea and the eastern Atlantic Ocean. Relative growth was studied by comparing changes in morphological characteristics with growth in total length and head length. The results indicate the presence of a single population of P. bogaraveo in the Adriatic Sea.

Global warming scenarios for the Eastern Adriatic Sea indicate a higher risk of invasiveness of non-native marine organisms relative to current climate conditions.

The online version contains supplementary material available at 10.1007/s42995-023-00196-9.

Barcoding (COI) Sea Cucumber Holothuria mammata Distribution Analysis: Adriatic Rare or Common Species?

The overexploitation of the western Pacific Ocean has expanded the sea cucumber fishery into new regions to supply the Asian market. In 2013, sea cucumbers were removed from the Croatian marine protected species list, and commercial fishery took place for a short period (2017-2018) in the Eastern Adriatic Sea. However, holothuroid species are difficult to distinguish. Holothuria mammata is a species that has rarely been reported in this region and strongly resembles the common species Holothuria tubulosa. This is the first study to assess the genetic diversity of sea cucumbers in the Adriatic Sea using genetic barcoding of the mitochondrial gene cytochrome c oxidase subunit 1 (COI). Specimens for barcoding were collected from the northern and central Adriatic, along with a specimen that had been previously identified as H. sp. cf. mammata based on its morphological characteristics. While genetic analyses showed identified this specimen as H. tubulosa, 30% of the collected specimens were genetically identified as H. mammata. These results call into question the historically accepted sea cucumber assemblage in the Adriatic Sea, which regarded H. mammata as a rare species and generally disregarded its presence in large census studies. Such species distribution data are extremely important in developing and monitoring a sustainable fishery.

Estimation of Water Quality Parameters in Oligotrophic Coastal Waters Using Uncrewed-Aerial-Vehicle-Obtained Hyperspectral Data

Water quality monitoring in coastal areas and estuaries poses significant challenges due to the intricate interplay of hydrodynamic, chemical, and biological processes, regardless of the chosen monitoring methods. In this study, we analyzed the applicability of different monitoring sources using in situ data, uncrewed-aerial-vehicle (UAV)-mounted hyperspectral sensing, and Sentinel-2-based multispectral imagery. In the first part of the study, we evaluated the applicability of existing empirical algorithms for water quality (WQ) parameter retrieval using hyperspectral, simulated multispectral, and satellite multispectral datasets and in situ measurements. In particular, we focused on three optically active WQ parameters: chlorophyll a (Chl,a), turbidity (TUR), and colored dissolved organic matter (CDOM) in oligotrophic coastal waters. We observed that most existing algorithms performed poorly when applied to different reflectance datasets, similar to previous findings in small and optically complex water bodies. Hence, we proposed a novel set of locally based empirical algorithms tailored for determining water quality parameters, which constituted the second part of our study. The newly developed regression-based algorithms utilized all possible combinations of spectral bands derived from UAV-generated hyperspectral data and exhibited coefficients of determination exceeding 0.9 for the three considered WQ parameters. The presented two-part approach was demonstrated in the semi-enclosed area of Kaštela Bay and the Jadro River estuary in the Central Eastern Adriatic Sea. This study introduces a promising and efficient screening method for UAV-based water quality monitoring in coastal areas worldwide. Such an approach may support decision-making processes related to coastal management and ultimately contribute to the conservation of coastal water ecosystems.

(Re-)Examining age and growth increments of the clam Venus verrucosa

Warty venus Venus verrucosa is a commercially important bivalve species that is widely distributed in the Mediterranean Sea. Understanding the main biological characteristics of exploited species, including their age and growth dynamics, are crucial for fisheries assessment, monitoring programmes and sustainable resource management. In this study, we analysed the age of the largest V. verrucosa specimens collected in Pag Bay, eastern Adriatic Sea, to investigate the maximal lifespan of this species. We used images of acetate peel replicas of the shell hinge region to visualize and count the growth increments. Radiocarbon content (14C) of selected shell material was analysed to corroborate the long lifespan derived from counting the growth lines in acetate peel replicas of etched shell sections. The maximum estimated lifespan of the analysed V. verrucosa specimens was 29 years, which is more than a decade longer than previously known. Pronounced variations in growth rates were noted among specimens of similar size, clearly indicating that shell size is not a reliable indicator of age for this species. Therefore, caution is advised when using the size-frequency distribution of the population to interpret the age structure of V. verrucosa.

Analysis of the eastern Adriatic sea level extremes

Aim: To examine the frequency, strength, and driving mech-anisms of the eastern Adriatic sea level extremes.Methods: In 2017, a tide-gauge station, and a meteorological station have been installed at Stari Grad (Hvar Island, east-ern middle Adriatic Sea). Three years of sea level and at-mospheric measurements were analysed. Ten strongest ep-isodes of the following extreme types were extracted from sea level data: positive long-period (T >210 min) extremes; negative long-period (T >210 min) extremes; short-period (T < 210) extremes. Long-period extremes were defined as situations when sea level surpasses (is lower than) 99.7 (i.e., 2) percentile of residual long-period sea level height, and short-period extremes as situations when 2.5-h variance of short-period sea level oscillations is higher than 99.4 per-centile of total variance of short-period series. Types of sea level extremes were subsequently associated to characteris-tic atmospheric situations.Results: Positive long-period extremes commonly appeared during the presence of low-pressure atmospheric systems over the Adriatic – such system were accompanied with strong SE winds. Negative long-period extremes were as-sociated with presence of high atmospheric pressure fields over the Adriatic Sea, either with strong NE winds, or calm weather. Appearance of short-period sea level extremes corresponded to either low atmospheric pressure fields and strong SE wind, or normal/high pressure fields and calm weather/no winds over the Adriatic. A strong seasonal sig-nal was detected, with the positive long-period extremes occurring mostly during November to February, and the negative long-period extremes occurring during January to February. The short-period extremes appeared throughout the year, but strongest events appeared during May to July.Conclusion: Results show that Stari Grad is a flood-prone lo-cation, both when it comes to positive long-period extremes and to short-period extremes. Furthermore, long-period and short-period extremes occasionally occur simultane-ously in Stari Grad, pointing to a previously unknown added hazard level

Sustainable Management of High-Impact Non-Native Molluscs and Their Potential Commercial Importance in the Eastern Adriatic Sea

Molluscs, especially bivalves, play an important role in food production and are the dominant group in mariculture worldwide. They are also an important component of the marine ecosystem, influencing the food web and nutrient cycling, as well as creating and modifying habitats. In the Mediterranean Sea, about 578 non-native species have been reported, including 230 taxa of non-native mollusc species. In most regional European seas, including the Mediterranean, the socioeconomic impacts of high-impact mollusc species have generally been poorly studied, and only a few well-documented cases have been reported. The present study collects scientific information on non-native molluscs in Croatian waters that are classified as high impact according to the European Alien Species Information Network EASIN: one Gastropoda—Rapana venosa—and seven Bivalvia species—Anadara kagoshimensis, Anadara transversa, Arcuatula senhousia, Brachidontes pharaonis, Magallana gigas, Pinctada radiata, and Ruditapes philippinarum. This study aims to fill the gap in the literature on high-impact non-native molluscs in the eastern Adriatic Sea through reviewing the literature on examples from other European seas, focusing on the possibility of commercialization and sustainable management of high-impact non-native molluscs. The invasion of non-native molluscs must be managed appropriately, especially if commercialisation is chosen as a management strategy. Additional management measures must be selected and objectively evaluated, taking into account the specificities, location and feasibility of the proposed measures. The study could help researchers, decision-makers, and the public to address the problems with high-impact species in the Adriatic countries, but also in other regions where the monitoring of high-impact non-native species is still inadequate. In addition to Croatia, the monitoring and management of these species is also important for other countries in the eastern Adriatic: Slovenia, Montenegro and Albania.

Struktura populacije atlantskog plavog raka, Callinectes sapidus na istočnoj obali Jadrana (Hrvatska, Crna Gora)

The Atlantic blue crab, Callinectes sapidus, is a highly invasive species that poses a significant threat to Mediterranean ecosystems. In the last two decades, it has become established in several marine and estuarine areas of the eastern Adriatic Sea, resulting in a decline in commercial catches and damage to fishing gear. This article reviews the current status of blue crab invasion in Montenegro and Croatia and analyses its abundance and population structure. Overall 619 crabs were sampled (male:female ratio, 1:1.91). Both carapace width and weight differed significantly between males and females, with males having a wider carapace and more weight. There was a significant difference in carapace width and weight among sites. For the total population, the mean male and female carapace width was 130.3 ± 30.8 and 108.8 ± 41.4 mm, respectively. In addition, the mean male and female weight was 187.2 ± 85.6 and 132.5 ± 39.1 g, respectively. Coefficient b between the weight and carapace width of blue crabs was significant at all locations, although it varied between males and females. This work will also document the impacts of the blue crab invasion on local ecosystems and provide comprehensive overview of populations structures and shed light on this important aspect of blue crab ecology.

Morphological Characteristics and DNA Barcoding of the Rare Blanket Octopus Tremoctopus violaceus (Cephalopoda: Tremoctopodidae) in the Adriatic Sea

Tremoctopods are epipelagic argonautoid octopods characterized by their expanded dorsal webs and strong sexual size dimorphism, with dwarfed males. The scarcity of taxonomic features attributed to this genus presents a challenge, and there is growing evidence of species misidentification in Tremoctopus genus on a molecular level. In this study, we investigated four female specimens of blanket octopus Tremoctopus violaceus caught by purse seine fishing in the Central Eastern Adriatic Sea in 2019. Individuals had smooth, firm and muscular bodies, dark bluish purple on the dorsal and iridescent silvery on the ventral side, with dorsal mantle lengths of 113, 82, 80 and 78 mm. The constructed phylogenetic trees based on the 16S ribosomal RNA and cytochrome c oxidase subunit I sequences of investigated Adriatic specimens and publicly available sequences showed strong support for the T. violaceus clade, consisting of individuals collected from the Adriatic Sea, Mediterranean Sea and Atlantic Ocean, with the exclusion of Indo-Pacific clade most probably corresponding to T. gracilis. To fully understand the life-history traits of Tremoctopus species, future research should focus on DNA-based methods for correct species identification combined with morphological characters, geographic distribution and ecological information.

Age, Growth, and Validation of Otolith Morphometrics as Predictors of Age in the Blackspot Seabream, Pagellus bogaraveo, (Brunnich, 1768) from the Eastern Adriatic Sea

The age and growth of the blackspot seabream, Pagellus bogaraveo, were determined by examining sagittal otoliths from fish sampled in the eastern Adriatic Sea. A total of 674 specimens (181 males, 90 hermaphrodites, 108 females, and 295 immatures) ranging from 8.80 to 47.27 cm (21.93 ± 9.00 cm) in total length were analyzed. The maximum observed age for the whole sample was 13 years. The sample was dominated by 1-year-old specimens as a consequence of an abundance of juvenile specimens collected by beach seines. Growth was described by the von Bertalanffy growth curve (L∞ = 52.3 cm, K = 0.15 year−1, t0 = 0.49 year, R2 = 0.97), and the growth performance index (Φ’) was 2.61. The length, width, thickness, and mass of the otoliths were compared with the total length and age of P. bogaraveo from the eastern Adriatic. The analysis showed that the measures were adequate predictors of age. These results can be of value for more effective management measures aimed at the conservation of this species.

Six species of sea slugs (Gastropoda: Heterobranchia) new for the marine fauna of Bosnia and Herzegovina

Abstract In this paper six heterobranch mollusc species are reported for the first time for Bosnia and Herzegovina: Berthellina edwardsi (Vayssiere, 1896), Felimida luteorosea (Rapp, 1827), Thuridilla hopei (Verany, 1853), Dendrodoris grandiflora (Rapp, 1827), Camachoaglaja africana (Pruvot-Fol, 1953) and Felimare villafranca (Risso, 1818). The study was conducted in October 2021 on Klek Peninsula and in Neum Bay (eastern Adriatic Sea, Bosnia and Herzegovina). This paper significantly extends the knowledge of the national marine heterobranch molluscs fauna, almost doubling the number of species known for the country, as only seven heterobranch species were reported for Bosnia and Herzegovina until now.

Fecundity, Length at First Sexual Maturity and Gonadal Development of Lepidorhombus boscii in the Eastern Adriatic Sea.

This study presents data on the seasonal changes in population structure, maturation, fecundity and reproduction of the Lepidorhombus boscii from the central-eastern Adriatic Sea. This species is a commercially valuable fish in the Adriatic Sea; still, knowledge about its reproductive biology is very scarce. The analyses are based on the data collected between July 2020 and June 2021 by bottom trawls. In total, 963 individuals were collected out of which 508 were females (47.24%) and 455 were males (52.75%). Throughout the year, oocytes in the previtellogenic and vitellogenic stages were present in the ovaries, and the development of the ovaries followed the values of the gonadosomatic index. L. boscii has asynchronous ovarian development and a prolonged spawning season in the Adriatic Sea with the main spawning season between November and March. The oocyte diameter ranged from 34.01 to 562.72 μm (178.49 ± 129.83 μm). This study presents the first information on the reproductive cycle of L. boscii in the eastern Adriatic Sea and contributes to the understanding of the biology of this species necessary for its sustainable management.

First documented record of neonate angular roughshark Oxynotus centrina from the eastern Adriatic Sea

Many biological aspects of deep-water sharks are poorly known due to their rarity and difficulties in conducting detailed research on them. The angular roughshark (Oxynotus centrina) is a rare species, critically endangered in the Mediterranean Sea, of which records are scarce across this region. Here we present a record of a female neonate O. centrina from the south-eastern Adriatic Sea, caught by a Montenegrin commercial trawler. Scientific observers were present on-board and collected the specimen, which was subsequently analysed in the laboratory. The specimen was 225 mm long (TL), weighed 59.6 g and had an unhealed umbilical scar. To date, records of this species in the Adriatic Sea have comprised of both adult and older juvenile individuals, but no records of neonates were found in the published literature. In this work, the basic biological observations of the specimen are reported.