Mesozooplankton production and respiration across a trophic gradient in a coastal Eastern Mediterranean ecosystem

The Inner Saronikos Gulf has served as an area of continuous environmental monitoring for many decades, primarily due to the operation of primary and secondary sewage treatment facilities of the Psyttalia Waste Water Treatment Plant (WWTP). In this groundbreaking study within the region, we conducted measurements of biochemical indices related to respiration (referred to as spETS) and growth (referred to as spAARS) of mesozooplankton. These measurements were then correlated with both biological and environmental data. The ecological quality of the inner Saronikos Gulf was ameliorated moving away from the sewage outfall and thus mesozooplankton sampling encompassed various sites located across a trophic gradient from the WWTP during different seasons (May, September, November 2017, and January 2018). Our observations revealed seasonal variations in both zooplankton abundance and composition, alongside spatial disparities in environmental data. In terms of biochemical data, we observed significant seasonal fluctuations in spETS and R respiration values. Notably, the lowest respiration R value (0.22 mg C m⁻³ d⁻1) was recorded in May, while the highest (4.74 mg C m⁻³ d⁻1) was observed in September. Nevertheless, the variations in spETS and spAARS values among different sites did not demonstrate statistically significant differences. Furthermore, the values of these indices (spETS and spAARS) exhibit a positive correlation with temperature and mesozooplankton biomass at a significance level of 0.01. Lastly, it is noteworthy that phytoplankton production, measured in terms of carbon content (mg C m⁻2), appeared to adequately meet the carbon requirements of the zooplankton throughout all the examined months.

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.

Impacts of dredged-material disposal on the coastal soft-bottom macrofauna, Saronikos Gulf, Greece

Dredged sediments derived by the low course and estuary of the metropolitan river of Athens (Kifissos River) were dumped every day for 21 months to an open-sea site in the Saronikos Gulf. The spoil-ground and surrounding area was monitored prior, during and post to dumping for 24 months, over 6-month intervals. Dumping significantly changed the granulometry of the pre-existing superficial sediments to finer-grained only in the spoil ground and increased the sediment contamination load (aliphatic, polycyclic aromatic hydrocarbons and heavy metals) throughout the study area. Microtox® SPT showed that sediment toxicity levels were high at almost all sampling stations. During dumping, burial of natural soft-bottom habitats degraded severely the communities of the spoil-ground resulting in an almost azoic state, as well as significantly declined the species number and abundance of benthic communities in locations up to 3.2 km away from the spoil-ground, due to dispersion of the spoil and smothering. Benthic indices on the surrounding sites were significantly correlated with hydrocarbon concentrations and sediment toxicity levels. Post to dumping, the macrofauna communities of the spoil-ground were still significantly degraded, but the surrounding areas showed patterns of recovery. However, the high concentrations of aliphatic, polycyclic aromatic hydrocarbons and levels of toxicity persisted in the sediments after the ceasing of dumping operations in the study area, implying the ecological hazard imposed on the area.

A screening procedure for selecting the most suitable dredged material placement site at the sea. The case of the South Euboean Gulf, Greece

The selection of the best site for the placement of dredged sedimentary material (∼7,000 m(3)) from the Aliveri coastal area in the adjacent South Euboean Gulf (Greece) was accomplished through a screening procedure. The initial stage comprised the determination of physical, chemical, and biological characteristics of the dredged sediment before the commencement of any dredging operation. Grain size measurements, geochemical analyses together with the use of pollution/toxicity indices and empirical sediment quality guidelines, and the conduct of an acute toxicity test showed that the dredged material consisted of "unpolluted to slightly polluted" silty sands and sandy silts. However, the local authorities planned to place this sediment in the neighboring open sea area, i.e., the South Euboean Gulf, due to the absence of any beneficial use or alternative dumping option (i.e., dumping on public lands). Therefore, the next stage of the screening procedure, based on criteria such as the national legislation, seabed and seawater column characteristics, influence of the water mass circulation pattern on the post-placement migration of dredged sediment, impact on living resources and human activities (i.e., aquaculture and fishing), effect on significant marine sites (i.e., sites of scientific, ecological, and historical importance, navigation routes, military zones), and seafloor engineering uses, led to the evaluation of the suitability of the South Euboean Gulf as a potential dumping area. Then, the identification of the appropriate dredged material placement sites in the South Euboean Gulf was based on a cluster analysis, which tested the physicochemical resemblance of the dredged material and the surface sediments of 19 potential placement locations in the gulf. After the statistical process, only four sites situated near the north shoreline of the South Euboean Gulf were qualified as the best dredged material placement locations.

Genotoxicity and oxidative stress biomarkers in Carassius gibelio as endpoints for toxicity testing of Ukrainian polluted river waters

This study aimed to assess oxidative stress and genotoxicity biomarkers in Prussian carp Carassius gibelio laboratory-exposed to water from polluted Ukrainian rivers in order to evaluate their usefulness as endpoints in a short-term bioassay for toxicity testing of freshwaters. The micronucleus (MN) test and the frequency of cells with double nuclei (DN) in erythrocytes and gill cells were used as indicators of chromosome aberrations and abnormalities in cell divisions, respectively. Cellular antioxidant defenses i.e. antioxidant enzyme activities (catalase, Se-dependent glutathione peroxidase, total glutathione peroxidase and glutathione-S-transferase) and oxidative damage, i.e. lipid peroxidation (measured as thiobarbituric acid reactive substances) in the fish liver were used as biomarkers of oxidative stress. Exposure to the polluted river water samples for 96 h resulted in significantly increased MN and DN frequencies, limited increases in antioxidant enzyme activities and no changes in lipid peroxidation. Results suggest that MN and DN frequencies in C gibelio are useful endpoints in a short-term bioassay for genotoxicity testing of environmental water samples in contrast to the oxidative stress biomarkers applied that showed low potential for assessing sublethal effects after a 96 h exposure.

Cellular responses in the skin of the gilthead sea bream Sparus aurata L. and the sea bass Dicentrarchus labrax (L.) exposed to high ammonia

Adult gilthead sea bream Sparus aurata and sea bass Dicentrarchus labrax were exposed for 24 and 48 h, respectively, to two concentrations of ammonia each (mean values of 3·34 and 13·10 mg l(-1) TA-N in S. aurata; 2·99 and 11·90 mg l(-1) TA-N in D. labrax). Light microscopy and computerized morphometry were used to evaluate ammonia-induced alterations in skin structure during exposure and following recovery in normal water. In S. aurata, ammonia exposure induced a concentration-dependent increase in the number (hyperplasia) of neutral mucous cells (mc), with peak values at 24 h recovery after exposure. An increase in the dispersion of melanosomes in skin melanocytes was also observed in the dermis and occasionally in the epidermis of S. aurata, with peak values at 24 h of ammonia exposure. Exposure of D. labrax to ammonia had, likewise, concentration-dependent effects on mucous secretion. Of the two types of mc in this species, there was an increase in the number of the neutral mc and a reduction in the much more numerous acid mc, with peak values at 24 and 48 h, respectively, of ammonia exposure. The more intense mucous secretion in D. labrax compared to S. aurata could be related to the lower tolerance to ammonia in D. labrax, as reported elsewhere. Finally, the increase in melanosome dispersion was less evident in D. labrax, due to highly variable control values. These morphological alterations to the skin could be useful indicators of non-specific stress in cultured fishes.