Croatian Adriatic Sea Research Articles

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.

Seascape Context as a Driver of the Fish Community Structure of Posidonia oceanica Meadows in the Adriatic Sea

Abstract Marine underwater habitats dominated by seagrass Posidonia oceanica play an essential role in fish community assembly, affecting taxonomic and functional diversity, abundance and fish behavior. The value of seagrasses as habitat depends on the spatial arrangement of the seascape elements and the availability of alternative habitats. Little is known about the effect of the seascape context of P. oceanica meadows on fish assemblages in the Mediterranean Sea. To identify P. oceanica meadows’ relative importance as a habitat for fishes, fish communities in the Croatian Adriatic Sea were investigated, using SCUBA lure-assisted visual census. The results show a significant effect of different arrangements of P. oceanica meadows’ seascape elements and surrounding habitats on fish community structure. Fragmented mosaic meadows with P. oceanica growing directly on and between rocky-algal reefs/boulders had significantly higher fish abundances compared to both types of continuous meadows (bordering rock and bordering sand). Continuous meadows bordering sand harbored the highest number of unique species. Evidence that alternative structured habitats within proximity to seagrass beds may affect the community structure of associated fish assemblages is provided, highlighting the need to consider P. oceanica meadows’ seascape context in conservation management and experimental design for fish community structure.

Monitoring and analysis of marine litter in Vodenjak cove on Iž Island, central Croatian Adriatic Sea

Marine litter is recognized as a global marine environmental problem. Beach litter surveys are used to monitor litter pollution and can be used to determine the origins of litter which can be used for the improvement of waste management. This research studied abundance, composition and sources of marine litter on the beach during one year period in four seasons in Vodenjak cove, central Croatian Adriatic. The results showed that this part of the coast was very dirty according to Clean Coast Index (48.4) and the litter density was 2.55 items/m2. The highest density was recorded during winter (4.24 items/m2). The largest part of the collected litter belonged to the category of artificial polymer materials and accounts for 94.88%. Litter sources have not been identified for 43.77% of the total waste collected, while 34.38% of waste has been identified as originating from land-based sources such as poor waste management, tourism and recreational activities. Single-use plastic items accounted for 31.35% of all items collected.

Posidonia oceanica lower depth limits along a latitudinal gradient in the eastern Adriatic Sea

AbstractAlthough extensive studies have been made on Posidonia oceanica ecosystems, in terms of their phenological characteristics, shoot density, biomass, and associated faunal assemblages, little attention has been given to the depth distribution of this species in the Adriatic Sea. The depth limits of the Mediterranean endemic seagrass P. oceanica growing along the eastern coast of the Croatian Adriatic Sea were examined by the use of SCUBA diving. Fifty-two independent measurements show that the lower depth limit of P. oceanica in the Croatian Adriatic Sea ranges from 24 m in the north to 36 m in the south, with a strong latitudinal gradient. The information on maximum depth distribution is an important asset when the increased human pressure and rapid environmental changes pose a threat to the survival of this slow-growing marine species.

Sea turtle strandings, sightings and accidental catch along the Croatian Adriatic coast

The northern Adriatic Sea has long been known as the foraging and developmental habitat of loggerhead sea turtles. Previous literature on stranded, floating, sighted, and accidentally caught sea turtles is fragmentary and mainly obtained from this shallower northern part. This work presents data on 272 records of stranded, floating, sighted and accidentally captured turtles within the entire Croatian Adriatic. The data was collected through the national stranding network for strictly protected marine species run by the Croatian Agency for the Environment and Nature during a six-year period (2010-2015). We focused on analysing spatial and temporal observations, age structure, and reporting sources. The collected morphometric data revealed that most measured C. caretta (85%) were immature individuals found stranded and floating at sea. These observations were location-dependent with a tendency towards the shallow northern areas (≤200 m). Most of the stranded individuals were severely decomposed preventing the determination of possible mortality causes. Most non-decomposed individuals had fishery- or boat-inflicted mechanical injuries confirming fishing activities and boat collisions as threats to young C. caretta individuals in the Croatian Adriatic Sea. Results also revealed an important contribution of local people in reporting the C. caretta strandings and sightings whereas most accidentally caught individuals were reported by unknown sources. Altogether, the data presented in this paper indicate possibilities for improving the ongoing sea turtle monitoring and conservation activities along the entire Croatian Adriatic coast.

Is central Croatian Adriatic Sea under plastic attack? Preliminary results of composition, abundance and sources of marine litter on three beaches

Marine litter is a worldwide problem. It impacts negatively marine environment, organisms, human health and coastal communities. In this research, abundance, composition and sources of marine litter (macro-debris > 2.5 cm) and beach cleanliness were assessed for three beaches in the central Croatian Adriatic Sea. Mean abundance for the studied region was 3.35 items/m2 and the highest recorded CCI value was 150. Most of the collected litter was made of artificial polymer material (93.86%), and main sources of litter were shoreline activities representing (31.68% of the total sample) and fishing and aquaculture representing (12.66% of the total sample). Land-based and sea-based sources accounted for 32.76% and 15.16%, respectively. Results from the present study provide another evidence of marine litter problem and high presence of plastic items in the marine environment of the Adriatic Sea. Presence of litter from different countries shows the internationality of marine litter problem which can only be solved by international collaborations and partnerships as well as by taking individual responsibility of all. Presence of the short-life single-use plastic items and the problems associated with them have been recognized in this study as most of the items collected were single-use items. High abundance of these items indicates not only their large use in everyday life, but also the lack of awareness of the general public about the environmental problem they cause. Moreover, the results obtained in this research imply the need for better waste management systems.

Social structure and spatial distribution of bottlenose dolphins (Tursiops truncatus) along the Croatian Adriatic coast

Abstract Previous studies suggest that the common bottlenose dolphin population in the Croatian Adriatic Sea is structured into distinct local communities. However, their home ranges and levels of interaction remain unknown. Dedicated boat‐based surveys were conducted seasonally, in three adjacent study sites from 2013 to 2017. Photo‐identification data were used to identify distinct local communities by relating the social structure descriptors to the home ranges of individual animals, and to determine the community home ranges and identify the levels of interactions between them. The overlaps between the home ranges of individuals (50 and 95% kernel density estimators [KDE]) were positively correlated to association strengths between them. Three distinct communities were identified by the hierarchical cluster analysis. The individuals' 95% KDE home range overlaps and association strengths were significantly higher within the three communities than between them, indicating both social and spatial segregation. The 95% KDE home ranges of the communities showed very low to no overlap. The individuals ranged mainly centrally within the home range of their respective community. The probabilities of movement, expressed as lagged identification rates, were significantly higher within than between community home ranges. However, 37 out of 1024 identified individuals were observed in more than one community home range, indicating that the communities are not isolated. Four out of the six Sites of Community Importance currently in place within the Croatian Adriatic Sea lie within the home ranges of the three local bottlenose dolphin communities. Once these sites are declared as Special Areas of Conservation, the management scheme will need to accommodate for differences in the spatial and social ecology of these communities, and environmental and anthropogenic factors acting upon them. The results of this work provide baseline information for such tailored management.

Comparison of amnesic, paralytic and lipophilic toxins profiles in cockle (Acanthocardia tuberculata) and smooth clam (Callista chione) from the central Adriatic Sea (Croatia)

Searching for Amnesic (ASP), Paralytic (PSP) and Lipophilic (LT) toxins in seafood is of great importance for consumer protection. Studies are usually focused on the most aquacultured species, the mussel. But, there are a number of potentially commercially important shellfish species as rough cockle Acanthocardia tuberculata (Linnaeus, 1758) and smooth clam Callista chione (Linnaeus, 1758) which are common in the Croatian Adriatic Sea. Investigation of marine biotoxins accumulation in these two species of shellfish from the Adriatic Sea has not been conducted up to now. In order to detect the potential marine biotoxin profile of A. tuberculata and C. chione wild populations, samples were taken monthly during one-year survey from the estuarine area in the central Adriatic Sea. HPLC-FLD with pre-column oxidation and HPLC-UV-DAD methods were employed for PSP and ASP toxins determination, respectively, while LTs were determined by LC-MS/MS. This research had revealed the differences in the accumulation of ASP, PSP and LT toxins between the two studied species, as Acanthocardia tuberculata showed more diverse profile with higher concentrations of analysed toxins. Both investigated shellfish species had shown levels of these biotoxins under the legal limits set by the European Commission.

Contribution of Wind and Waves in Exchange of Seawater through Flushing Culverts in Marinas

In this work contribution of wind and waves on the water exchange through flushing culverts between the marina and surrounding water body have been investigated. The hybrid modelling technique was used. Results of culvert discharge, produced by waves on physical model, were implemented in 3D circulation model. Using circulation model, the optimum flushing culverts position in body of breakwater was defined for marinas with hypothetical geometry, characteristic for Croatian Adriatic Sea. The model was forced by wind from 8 directions and velocities 1-5 Bf. Furthermore, numerical simulations were also done for a real - world marina – the Icici marina. The real breakwater geometry and hydrographic conditions (depths, tides, sea temperatures and salinity) were included. The analysis results show that the flushing culverts may have important contribution to seawater exchange in marina, even in summertime situations with significant wave heights of 0.5 m and duration of 6 hours.

New data on the occurrence of the critically endangered common angelshark, Squatina squatina, in the Croatian Adriatic Sea

New data on the occurrence of the critically endangered common angelshark, Squatina squatina, in the Croatian Adriatic Sea

Održivi turizam kao razvojna mogućnost na primjeru Dugog otoka

In this paper authors have tried to elaborate some aspects of socioeconomic approach which would eventually unveil the future of economic and cultural development of the island of Dugi otok. It can be argued that the development of tourism as well as other economic activities on the island of Dugi otok can be attested as a paradigm for all bigger islands on the Croatian Adriatic sea. Sustainable tourism development on Dugi otok can only be durable if all other production and land axploitation activities adopt the paradigm of sustainable development. The island of Dugi otok is probably the best model of what can be called an unpolished diamonds of the Croatian Adriatic with so many resources that wait to be properly activated in order to preserve the authentic life experience on the island. This research paper has tried to prove that along with sustainable amount of mass tourism, there should develop appropriate quantity of specific niche tourism products with aim to enhance the value of authentic sustainable development of island tourism.

Natural causes of changes in marine environment: Mercury speciation and distribution in anchialine caves

Mercury speciation and distribution were assessed, for the first time, from the water, sediment, rock, soil and air of anchialine caves. We evaluated the origin and distribution of four mercury species (total (THg), reactive (RHg), dissolved gaseous mercury (DGM) and monomethylmercury (MeHg)) in water from Bjejajka cave (Bjejajka) and Lenga Pit (Lenga) in the Croatian Adriatic Sea from 2006 to 2011.Concentrations of all mercury species were elevated at both sites compared to adjacent seawater, which had concentration range of 0.5–2.4 ng L−1 for THg, 0.06–0.2 ng L−1 for RHg, 0.02–0.07 ng L−1 for DGM, and 0.01–0.02 ng L−1 for MeHg. In Bjejajka, the maximum THg concentration (350 ng L−1) in the middle layer (3–7 m) of the 12 m deep stratified water column was up to 3 orders of magnitude greater than in adjacent seawater. During and after the rainy sampling periods in January 2009 and 2010, mixing of Bjejajka water column resulted in elevated concentrations, up to 3700 ng L−1 of THg (4 orders of magnitude higher compared to values in nearby seawater) in the bottom water layer. MeHg concentrations in the Bjejajka water column were also considerably elevated (0.7–6.3 ng L−1) compared to the surrounding seawater (0.01–0.02 ng L−1). The vertical distribution of MeHg concentrations followed that of THg, however the ratio of MeHg/THg above the Bjejajka halocline was drastically higher (up to 57%) compared to MeHg proportion (1–2 %) below the halocline, which was similar to that of surface seawater. In sediment of Bjejajka, THg concentrations were up to 3.3 mg kg−1, considerably above concentrations in unpolluted Adriatic marine sediment (0.1–0.3 mg kg−1). The highest THg amounts found in soil and air were inside and in close proximity to Bjejajka, while THg in rock (≤0.01 mg kg−1) were below reported values for unaltered carbonates.Laboratory experiments indicate that bat guano was the major source of elevated mercury concentrations in the water column and sediment of Bjejajka. Concentrations of THg in bat guano were up to 0.45 mg kg−1, above the range of THg concentrations found in unpolluted marine sediment. Seventy-two days after the addition of bat guano in solution, a 100-fold higher Hg concentration was observed, from 2.5 up to 252 ng L−1. In Lenga bat guano was not spotted and THg water and sediment concentrations were drastically lower, mostly below 7 ng L−1 and 0.8 mg kg−1, respectively.

Description of a new marine diatom, Cocconeis caulerpacola sp. nov. (Bacillariophyceae), epiphytic on invasive Caulerpa species

A new species of Cocconeis has been found growing on thalli of the invasive green alga Caulerpa taxifolia collected from the Croatian Adriatic Sea (Bay of Stari Grad, the Island of Hvar, Central Adriatic, Croatia), the coasts of the Mediterranean (Saint Raphaël, west of Cannes, France) and the eastern coast of Australia (Moreton Bay, southeast Queensland). Additionally, it was observed on samples of Caulerpa racemosa, another invasive alga in the Mediterranean. Preserved thalli of Caulerpa and cleaned material of the new diatom were studied by light and electron microscopy (SEM and TEM). The morphology and fine structure of the new marine epiphytic diatom, for which we propose the name Cocconeis caulerpacola Witkowski, Car & Dobosz, was determined, including the internal and external structure of the raphe and sternum valve, and the cingulum. Comparison between the new species and three closely related species, C. borbonica, C. diruptoides and C. pseudodiruptoides, was made using material from our samples, as well as material from Vis (Adriatic Sea) obtained from the Hustedt collection. Surprisingly, C. caulerpacola is able to colonize Caulerpa taxifolia in very high abundance, but its occurrence seems to be strongly patchy. Indeed, it seems that C. taxifolia is a suitable host for epiphytic diatoms, in particular this tiny Cocconeis, despite its reputation as a ‘killer seaweed’. Cocconeis caulerpacola was observed on Caulerpa species in varying abundance over a wide geographical range.

Morphometric characteristics and nuclear marker Me 15/16 analyses of mussel Mytilus galloprovincialis populations along the eastern Adriatic coast

Mussels Mytilus spp. belong to a group of key species in marine, coastal ecosystems. This work demonstrated the dominant presence and morphological variations (shell shape) of Mediterranean mussel M. galloprovincialis along eastern Adriatic coast (22 sites), from Limski kanal to Dubrovnik. Morphometric characteristics of sampled mussel specimens were inside normal values for M. galloprovincials: height/length 55.89±5.08 % and width/length 38.76±3.42 %. Different alleles coding an adhesive protein of the byssus were observed in the population of mussels in Croatian Adriatic Sea. Only 2 specimens among the 110 analysed were found that showed a heterozygote genotype: one with an E (edulis) allele and one with a T (trossulus) allele, all others were identified as homozygotes for the G (galloprovincialis) allele . The presence of the E allele at low frequency in M. galloprovincialis mussels can simply be explained by introgression, as M. edulis and M. galloprovincialis are known to hybridise and exchange genes in the European contact zone. The presence of the T allele is very surprising. According to the current distribution of the three species, a T allele would first need to introgress the edulis genetic background before to have the opportunity to introgress the galloprovincialis background, while this is not observed –the T allele has never been sampled in M. edulis to date. Shell height/length values of heterozygote mussels: GE (h/l 46.90 %, w/l 38.45 %) and MT (h/l 48.91 %, w/l 39.11 %) were closer to M. edulis (h/l 44.50±2.26 %, w/l 35.38±2.00 %), while the width/length values were typical for M. galloprovincialis. Further analyses using different genetic markers and detailed shell morphometric measurements on larger numbers of specimens are needed to clarify the processes underlying introgression in Mediterranean mussels.