Plankton community composition changes in response to nutrient enrichment were examined at 2 sites in the eastern Mediterranean. Samples from bacteria up to mesozooplankton were taken upstream and ...downstream of finfish farms in the north Aegean (Lesvos, Greece) and on the southern coast of Cyprus. The pattern of change appeared to be similar, albeit of different magnitude, in both areas. In Cyprus, results showed an increase in bacteria and a decrease in diatom abundance close to the cages, response to effluents was limited, and consequent growth was controlled by microzooplankton. In Lesvos, results showed increased abundance of bacteria, nanoflagellates and mesozooplankton, a decrease in diatoms and an increase in larger dinoflagellates and ciliates downstream of the farm. A shift towards a more diverse microplankton community was observed, consistent with the intermediate disturbance hypothesis. The community consisted of larger-sized microzooplankton, and changes persisted throughout the downstream stations. Results showed that the plankton response to nutrient enrichment is more pronounced at intermediate distances from the farm. The community composition changes observed in Lesvos indicate that even in exposed sites with high current velocities there is an influence of farm cages. Changes manifest in terms of size for some groups and abundance for others. Although fish farms have been associated with degradation of the environment in which they are located, this was not apparent in the present study. Indeed, the shifts induced by farm effluents can help us identify drivers of change and assess community responses to perturbations in a dynamic environment.
► Leaf and epiphyte specific N uptake increased at impacted meadow. ► Higher leaf and epiphyte N suggests linkage between N uptake and accumulation. ► Leaf N uptake per unit area decreased at ...impacted meadow. ► Epiphyte overgrowth hindered N uptake by leaves. ► Less N was transferred daily from water column to benthos at impacted meadow.
In situ nitrogen uptake by leaves and epiphytes was studied in a Mediterranean seagrass (
Posidonia oceanica) meadow impacted from a fish farm and a pristine meadow, using
15NH
4 and
15NO
3 as tracers. In the impacted meadow both leaves and epiphytes yielded higher N concentrations and showed higher specific N uptake, suggesting a linkage between N uptake and its accumulation. Epiphytes took up N faster than leaves in relation to their corresponding biomass, but when assessed per unit area, N uptake was higher in leaves. Leaf N uptake was negatively correlated with epiphyte N uptake. With increasing epiphyte load on leaves, N leaf uptake decreased while N epiphyte uptake increased, indicating that epiphyte overgrowth hinders N uptake by
P. oceanica leaves. Epiphyte contribution to total N uptake increased, while that of leaves decreased at the impacted meadow. However, 2–3 times less N was transferred daily from the water column to the benthic compartment, through seagrass and epiphyte uptake on total, at the impacted meadow. Therefore, it is probably still the loss of the key species – the seagrass – which plays the most important role in N cycling in seagrass ecosystems.
Foraging success affects reproductive output in sea turtles, and is therefore an important factor to measure in order to understand population dynamics. During 2010 and 2011, we used satellite ...telemetry to track the at-sea behavior of 20 post-nesting loggerhead turtles Caretta caretta from Rethymno, Crete, Greece. Nineteen transmitters provided location and dive data throughout the turtles’ migration towards their foraging grounds and the transition into foraging behavior. We identified 3 foraging regions: (1) 9 turtles migrated southwest towards the North African coast, with 8 concentrated in the region of the Gulf of Gabès, Tunisia; (2) 6 turtles migrated north towards the Aegean Sea; and (3) 4 turtles did not take long-distance migrations, instead remaining resident within the waters of Crete. Two fitness proxies were associated with differences in post-nesting strategies. Turtles foraging in northern waters had significantly larger curved and straight carapace lengths and clutch sizes than turtles foraging near Crete or Africa. Those differences reflect the disparity in benthic prey abundances among the 3 regions. The Aegean had a higher abundance of macrobenthic fauna than the other 2 regions, and the Gulf of Gabès had an increased level of eutrophication. Deterioration of the aquatic resources in the Gulf of Gabès region may be a contributing factor in the observed steady decline in clutch size and total nests per season in 2 critical nesting beaches for loggerheads in Greece.
Biological and geochemical variables in the water column and sediments were monitored along a transect of a mussel farm located in a transitional environment in Maliakos Gulf, a semi-enclosed gulf in ...eastern Mediterranean. Analyses of water, sediment and macrofauna samples were used to calculate ecological status indicators in the context of the European Water Framework Directive. The water column ecological status was “Poor” or “Bad” showing little change with distance from the farm, but the ecological status of the benthic communities was found to be “Good,” although there were quantitative changes in macrofaunal indices with distance from the farm.
•Mussel farming in Maliakos Gulf, Aegean Sea induced minor changes in the surrounding environment.•It caused minor quantitative changes in biogeochemical variables of the water column and sediment.•The water column status was eutrophic (“Poor”) while the benthic status was “Good.”•Mussel farming did not to improve the water quality or deteriorate benthic quality.
The use of the term “biodiversity” in the aquatic literature has expanded rapidly during the last years. In this paper, we address the influence of the geographic, social and economic characteristics ...of a country in the published effort as it appears in the bibliography from the corresponding author of each publication. Social and geographic characteristics are expressed by coast length, population, the population living a maximum of 100 km from the coast, population density, total fish catches, and continental shelf surface. Economic characteristics are expressed by gross national product, gross national product per capita, footprint and ecological deficit. Our results showed that the majority of the published aquatic biodiversity research was in aquatic ecology journals. The number of publications referring to marine biodiversity per country of origin of the corresponding author was significantly correlated to the length of coastline, fisheries production, gross national product, population density and other economic, social and geographic characteristics of the country. Most of the highly publishing countries are developed countries with an ecologically harmful lifestyle. The research per country carried out in non-adjacent to the country sea zones remains low.
We investigated changes in sediment bacterial community structure across a spatial organic enrichment gradient associated with fish farms in two different sites in the Eastern Mediterranean (Greece). ...The observed trend was similar at both fish farms even though they are far from each other. The mean number of the most abundant operational taxonomic units (OTUs) was not significantly different, either among samples across the organic enrichment gradient or between impacted and control samples at both fish farms. Nevertheless, community structure differed both within each site (impacted vs. control samples) and between the two sites. We found that most of between-site differences in community structure could be attributed to differences in grain size, redox potential of the sediment, and, to a lesser extent, chlorophyll α, while within-site differences were attributed to the distance from the cage and the median grain size. Sequenced DGGE bands that were present only at samples directly beneath the cages, affiliated with different phylogenetic groups at each site. These results indicate that aquaculture effluents affect the structure of sediment bacterial communities, but without any apparent impact on the number of the most abundant OTUs.
Community metabolism and dissolved organic and inorganic nutrient fluxes were assessed in impacted from fish farm discharges and reference vegetated (Posidonia oceanica) and adjacent unvegetated ...communities in the Aegean Sea, Greece. Both metabolism and nutrient fluxes significantly differed between impacted and reference communities, but the effect depended on community type and time of year. Net community production (NCP) in the impacted vegetated community decreased by 60%, respiration (R) by 34%, and gross primary production (GPP) by 44%. The GPP: R ratio declined more (35%) in the impacted unvegetated than in the corresponding vegetated community (15%), implying that proximity to the fish farm has a severe impact on the unvegetated community, leading to imbalanced metabolism (GPP < R) and heterotrophic (GPP: R = 0.9) conditions. Higher release of dissolved organic and inorganic carbon, nitrogen, and phosphorous was observed in the impacted vegetated community compared to the corresponding unvegetated one, implying intensification of mineralization in the seagrass community. On an annual scale, the impacted vegetated community supported increased DOC efflux by 204%, DON by 1639%, NH₄ by 122%, and NO₃ by 26%, whereas it supported release of DOP and P0₄ compared to the reference community, which removed these dissolved nutrients from the water column. The impacted unvegetated community supported an annual increase of DOC efflux by 208% and P0₄ by 42% and it released DON, NH₄ , NO₃, and DOP, whereas the reference community took up these nutrients. Proximity to the fish farm altered the ecosystem state by lowering the productivity and by enhancing the nutrient release.
A new mesocosm setup containing both water column and sediment suitable for benthic‐pelagic coupling experiments is described. The presence of a large volume of water (>1.5 m3) with sufficient depth ...(4 m) on the top of the sediment, combined with a large volume of sediment on the bottom (30 cm height, 80 L volume) offers new opportunities for benthic‐pelagic experiments on the mesocosm scale. The experimental setup includes a mesocosm bag, a securing ring with a cap on the top, a sediment container on the bottom, sediment traps, an autonomous water sampling system at specific depths, and a newly developed sediment sampler for collecting samples without disturbing the system. The mesocosm setup was successfully deployed in the context of a benthic‐pelagic coupling eutrophication experiment in the CRETACOSMOS mesocosm facilities of the Hellenic Centre for Marine Research in Crete. A number of variables related to the technical aspects and proper ecosystem functions of the mesocosm setup were monitored throughout the duration of the experiment (58 d), which proved that the proposed setup is suitable for benthic‐pelagic coupling experiments, providing an intermediate experimental tool between small‐scale micro/benthocosm experiments and large scale in situ sea experiments.
The fish farming impact on sediment and macrofauna associated with
Posidonia oceanica meadows has been studied in three coastal areas (Spain, Italy and Greece) of the Mediterranean Sea. The stations ...were characterized by coarse sediment with a low percentage of silt/clay and oxic conditions. Chlorophyll
a and organic carbon were occasionally enhanced in the vicinity of the cages and nitrogen remained almost constant between the stations. Phosphorus consistently showed a decreasing trend towards the reference station. Macrofaunal biomass peaked at an intermediate distance from the fish cages. Diversity indices were quite high at all stations, implying that the specific sites were not under severe stress due to aquaculture. A tenuous clustering of stations with distance from the farm was encountered, which was mainly attributed to abundance shifts rather than presence/absence of typical species. It is suggested that oxic conditions induced by intense currents and supported by coarse sediments at the study sites allow the existence of diversified communities with high abundance and biomass.
Microphytobenthos is a major factor in the functioning of shallow ecosystems as it is an essential component of primary productivity in coastal areas. Organic matter enrichment is a stressor that ...affects the microphytobenthic community of the marine sediments. However, it is unclear to what extend the microphytobenthic response to organic enrichment depends on the stressor itself (i.e. the nature of organic matter enrichment) or on the origin of the community in general (i.e. the pool of photosynthetic organisms present in the sampling site). Hence, an ex-situ organic matter enrichment experiment was used to examine changes in microphytobenthic communities when incubated under the same organic matter addition stress, using sedimentary pigment content as a proxy. Specifically, sediment samples from two different locations were incubated under the same stressor in the laboratory, i.e. presence/absence of organic matter enrichment. Our results suggested that the sediment biogeochemical response to organic matter enrichment was different between the two sites, and also the microphytobenthic communities that grew in both sediments differed.
•Pigments were used as indicators of different photosynthetic groups present in the microphytobenthos from two sites.•Environmental stressor or source site plays the major role in determining microphytobenthos?•Different benthic photosynthetic communities developed from different source communities under the same stressor.
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