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    Acute and subchronic effects of cellulose nanofibers on histological, antioxidant, and acetylcholine responses in the Mediterranean mussel (Mytilus galloprovincialis)
    (Pergamon-Elsevier Science Ltd, 2026) Gurkan, Mert; Gurkan, Selin Erturk; Gunes, Berkay; Saritunc, Volkan
    The utilisation of cellulose nanofibrils (CNFs) in industrial applications has seen a marked increase, giving rise to concerns regarding their potential impacts on aquatic ecosystems. The present study evaluated the acute (96 h) and sub-chronic (14 days) effects of CNFs at environmentally relevant concentrations (10, 100, and 1000 mu g/L) on the Mediterranean mussel (Mytilus galloprovincialis), a species of particular importance in marine food webs. A comprehensive analysis of the Gill and mantle tissues was conducted to ascertain any potential histopathological alterations or antioxidant responses. This analysis encompassed the measurement of superoxide dismutase (SOD), catalase (CAT), and glutathione-S-transferase (GST) activities, along with the assessment of acetylcholinesterase (AChE) activity in the mantle tissue. This approach was undertaken to evaluate the potential for neurotoxic effects. CNF exposure has been demonstrated to induce histological changes, including epithelial deformation and hemocyte infiltration, indicating oxidative damage and activation of cellular defense mechanisms. Oxidative stress parameters demonstrated a concentration-dependent increase in reactive oxygen species (ROS) under both exposure durations. AChE activity also increased, likely reflecting a compensatory response to maintain neural homeostasis. The results demonstrate that CNFs trigger coordinated antioxidant and neuroregulatory responses in M. galloprovincialis, with effects becoming more pronounced at higher concentrations and longer exposures. These findings emphasise the potential for sub-lethal effects on marine bivalves even from biodegradable nanomaterials, underscoring the necessity for comprehensive ecotoxicological assessment of nanoscale cellulose in aquatic environments and highlighting the broader implications for environmental management, regulatory policies, and safe application of nanocellulose-based products.
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    Assessment of pollution biomarker and stable isotope data in Mytilus galloprovincialis tissues
    (Springer, 2019) Yalçın Özdilek, Şükran; Demir, Neslihan; Gurkan, Selin Erturk
    Superoxide dismutase (SOD) is one of the antioxidant defense enzymes in mussels and converts the superoxide anion into hydrogen peroxide and this enzyme is used as biomarkers of oxidative damage. As well as many topics in ecology, stable isotopes are also signature for organic and heavy metal pollution in aquatic ecosystems. This study aims to compare the stable carbon and nitrogen values of different mussel tissues and the changes on the SOD values of the same tissues in order to understand the relationship between two mechanisms of bioindicator processes of physiological response of mussel to pollution. The changes in SOD activity in the gill, hepatopancreas, and mantle tissues of Mytilus galloprovincialis with C-13 and N-15 isotopes were assessed in two locations (Kepez and Guzelyal) in Canakkale. The SOD values of mussel samples were found as the gill > hepatopancreas > mantle collected from Kepez and the gill > hepatopancreas collected from Guzelyal. There were no significant differences among the mean SOD values of different tissues. There was enrichment both in nitrogen and carbon isotope values of hepatopancreas tissues both in Kepez and Guzelyal samples. There was a negative correlation between both isotope values and SOD values of samples. As well as SOD values, the isotopic composition of particularly hepatopancreas tissue is a good indicator for evaluation of pollution.
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    Health assessment of fan mussels in the southern part of the Sea of Marmara
    (Natl Centre Marine Research, 2025) Karadurmus, Ugur; Gurkan, Selin Erturk; Gurkan, Mert; Kunili, IBrahim Ender; Turgay, Emre; Sari, Mustafa
    The fan mussel (Pinna nobilis Linnaeus, 1758), a critically endangered species in the Mediterranean Sea, has experienced mass mortality events (MME) due to various pathogens, particularly the protozoan parasite Haplosporidium pinnae. Despite these challenges, the Sea of Marmara (SoM) still has significant populations of fan mussels, with no infection-related MME reported so far. This study aimed to assess the general health status of fan mussels in the SoM and understand the factors that contribute to their survival. The samples were collected on September 25, 2023, around the Kap & imath;da & gbreve; Peninsula in the southern part of the SoM, a critical area for fan mussel populations, where a total of 20 live specimens were included in advanced laboratory analysis from four stations. Findings revealed that Haplosporidium and Mycobacterium species were present in P. nobilis across all stations, with higher oxidative stress indicators in the digestive gland tissues. Results also observed different life stages of Haplosporidium in the mantle and digestive gland. Molecular analyses revealed the presence of haplosporidian parasites, Perkinsus sp., andMycobacteri-um sp. in some samples. Phylogenetic analysis showed that Haplosporidium isolates form a distinct clade separate from H. pinnae, suggesting they belong to a different species. The detected Haplosporidium species in the SoM displayed genetic differences from H. pinnae found in the Mediterranean Sea, potentially indicating a less virulent variant. This study raised the question of whether interactions between the detected Haplosporidium parasite and other pathogens or region-specific ecological characteristics were effective in the absence of a mass mortality in fan mussels in the SoM.
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    Impact of Nickel Oxide Nanoparticles (NiO) on Oxidative Stress Biomarkers and Hemocyte Counts of Mytilus galloprovincialis
    (Springernature, 2022) Gurkan, Selin Erturk
    In this study, the toxic effects of nickel oxide nanoparticles (NiO-NPs) on the model organism Mediterranean mussel (Mytilus galloprovincialis) gill, digestive gland, and hemolymph tissues for 96 h were investigated. Lipid peroxidation (MDA) determination was performed to reveal the oxidative stress generation potential of nanoparticles, and superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione-S-transferase (GST) enzyme levels were measured to determine antioxidant responses. Lysosomal membrane stability and total hemocyte counts were performed to determine cytotoxic effects. All parameters were altered in different concentrations of NiO-NPs (2, 20, and 200 mg L-1). The SOD levels increased depending on the concentration (p < 0.05), and the increases in CAT, GPx, and GST levels were lower at 20 mg L-1 concentration (p < 0.05). There was a slight difference between the exposure and the control groups in terms of GR enzyme. The MDA level increased in parallel with the concentration (p < 0.05), the stability of the cell membrane (p < 0.05), and the number of hemocyte cells decreased as a result of exposure (p < 0.05). The results emphasize that NiO-NPs may have negative effects on the aquatic environment.
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    The effects of aquaculture activities on species composition and diversity of native freshwater fish populations
    (Edp Sciences S A, 2018) Gurkan, Selin Erturk; Yalçın Özdilek, Şükran
    The rapid development of the aquaculture industry in recent years and the increase in the intensity of production has raised questions regarding potential environmental impacts. Understanding intra- and interspecific relationships between native and cultured species is important for sustainable use of natural resources. This study investigated the spatial and temporal effects of a fish farm constructed next to a river on the relative abundance and diversity of natural fish populations. Sampling was conducted at three stations, upstream and down stream from a trout farm and at a control site, on Kocabas stream in Canakkale (Turkey) monthly between August 2015 and July 2016. There was no significant difference among the three stations in fish diversity. However, a remarkable seasonal and spatial variation in the composition and relative proportion of the indigenous fish assemblage were observed among the three stations. In conclusion, the fish farm might have influenced species composition and relative abundances particularly at the downstream station.
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    The effects of trout culture on diet and food availability of native freshwater fish populations
    (Wiley, 2019) Gurkan, Selin Erturk; Yalçın Özdilek, Şükran
    Cultivation of a species or population and distribution to various regions has raised the idea of negative impacts on native species. The effect of non-native species on native species may be caused by competition for source, predation, hybridization, and parasite/disease transport. The present study aims to evaluate the possible effects of a trout farm established on the banks of Kocabas Stream (canakkale, Turkey) on feeding characteristics of some freshwater fish (Phoxinus phoxinus, Barbus oligolepis, and Squalius cii). The samples were collected monthly over a year at two stations located before and after the trout farm and at a control station on the tributary not impacted by the effects of the farm. Fish and environmental samples were gathered monthly with an electroshocker and some fishing tools between August 2015 and July 2016. The fish diet and resource incorporation into biomass were evaluated by gut content and stable isotope analyses. Changes in diet preferences when the species are exposed to source stresses and some individuals fed on farm-based feed contaminated from the farm in Kocabas Stream. In this study, it was observed that native fish populations in aquaculture regions were influenced by diet preferences. Designing enclosed systems limiting feed and waste transit in aquaculture establishments may be suitable for sustainability of these species.