Sea Coastal Zone Research Articles

Eukaryotic Sequences in the 16SrRNA Metagenomic Dataset of Algal-bacterial Consortia of the White Sea Coastal Zone.

The libraries of bacterial 16SrRNA gene fragment from algal-bacterial consortia of the White Sea coastal zone are analyzed. Up to 3% of the reads have revealed to correspond to eukaryotic rRNA. They related to following main eukaryotic clades: Discoba, Stramenopiles, Ciliata, Amoebozoa, and Nucletmycea. Amoebae, especially Vermamoeba, were present in all samples. In one sample, heterolobose amoeba Paravahlkampfia was detected. These microorganisms are parasites of microalgae, which can induce significant damage to industrial cultures. However, the data on their physiology and distribution are scarce. This study provides new evidence about the diversity of herbivorous eukaryotic microorganisms in natural algal-containing consortia.

Rapid Changes in Land‐Sea Thermal Contrast Across China's Coastal Zone in a Warming Climate

AbstractCoastal areas are important sites of environmental and socioeconomic activities and are significantly influenced by climate change. Here we analyzed the current and future responses of spatiotemporal characteristics of land‐sea thermal contrast (LSTC) along China's coastal zone to global warming. Using the European Centre for Medium‐Range Weather Forecasts Re‐Analysis (ERA)‐Interim and 18 Coupled Model Intercomparison Project 5 models, we find that the rate of global warming significantly influenced the LSTC in summer. The LSTC first decreased and then increased during the warming and hiatus periods, respectively. In winter, the LSTC decreased in the Bohai Sea coastal zone, Yellow Sea‐East China Sea coastal zone, and South China Sea coastal zone at rates of 0.46 (p < 0.01), 0.18 (p < 0.01), and 0.19 °C/decade, respectively. Spatially, the LSTC decreased in summer and winter with the decrease in latitude and increased in summer and winter with the decrease in longitude. These changes were caused by urbanization, land use changes, and topography. The spatial distribution was more strongly controlled by land than by sea. Meanwhile, the land/sea warming ratio was concentrated within the range of 0–1 and 1–2, and land/sea temperature variation trends commonly followed the same direction. Overall, land/sea surface temperature variations had similar amplitudes. Under three Representative Concentration Pathways (RCPs), the warming rate difference between land and sea in summer is small, but the land warms faster than the sea in winter, resulting in the LSTC decreasing fast in winter. Under RCP4.5 and RCP8.5, the linear trends in LSTC in Bohai Sea coastal zone, Yellow Sea‐East China Sea coastal zone, and South China Sea coastal zone ranged from 0.05 to 0.08 (p < 0.01) and 0.13 to 0.15 °C/decade (p < 0.01), respectively.

Migration patterns and survival of stocked Atlantic sturgeon (Acipenser oxyrinchusMitchill, 1815) in Nemunas Basin, Baltic Sea

The restoration of the Atlantic sturgeon Acipenser oxyrinchus in Lithuania started in 2011. Two rivers (Neris and Šventoji) were chosen for reintroduction in the Nemunas river basin based on historical data and ecological conditions. Since 2011, more than 116 thousand of sturgeon juveniles have been stocked in Lithuania. In order to achieve successful population restoration, it is vital to evaluate the efficiency of performed artificial stocking. Analysis of post-stocking survival, migration patterns, predation pressure, fisheries-related mortality and possible aggregation zones are all important to understand the main threats and prepare possible mitigation measures necessary for population establishment during the initial phase of restoration. Therefore, conventional and radio tagging studies were performed during the initial restoration phase in Lithuania. Atlantic sturgeon downstream migration was divergent in summer and appeared to have no significant associations with fish size, river quality or hydrophysical parameters, but in autumn migration speed and even survival in small rivers seemed to depend on flow velocity and water discharge. The distribution of recaptured tagged juveniles coincided with dominant currents in the Curonian Lagoon and Baltic Sea. Some tagged specimens migrated long distances, with two sturgeons from Lithuania being caught in Estonian and Finnish territorial waters at up to 800 km from their release site. Tag recapture analysis and mortality rate of tagged fish clearly indicate that annual fisheries-related mortality exceeds the required threshold of 5% for population establishment. High survival in rivers indicates that the main threat for a successful sturgeon reintroduction program is commercial fishing in the Curonian Lagoon and Baltic Sea coastal zone.

Aspects on the History of Observations and Measurements in the Black Sea Coastal Zone, Rehabilitation Projects and Marine Modeling Issues

Abstract Over time, the content, scope and objectives of hydrological research in the Romanian Black Sea coastal area varied according to the state of society development, technology development and financial resources. Along with the activities of capitalizing on natural resources, water use, river and sea navigation, there have been demands for knowledge of the water regime and the interaction between the resource potential and the characteristics of the hydrological regime. As a result, hydrographic and hydrological research was started and developed in the Black Sea coastal zone. These researches developed in the first half of the nineteenth century, and then continued throughout this century and later in the twentieth century, with interruptions caused by the two world wars. Among the important activities that have taken place over time, there have been hydro-technical works. The design and elaboration of the projects of these works were based on the knowledge of the hydrographic and hydrological characteristics of the Black Sea coastal zone. This knowledge has evolved over time so that there is currently an important pool of data and information related to the hydrological, morphological, hydrochemical, hydrobiological characteristics of the water bodies mentioned. The paper presents briefly the most important moments of the history of the monitoring activity carried out over time in the Black Sea coastal zone, the types of coastal and transitional waters in Romania, coastal rehabilitation projects of the Black Sea, hydrological features, the structure of the marine complex model pom / ersem III) BREG / BSHELF.

Ecological model of the Bay of Biscay and English Channel shelf for environmental status assessment part 1: Nutrients, phytoplankton and oxygen

European directives (Water Framework Directive - WFD and Marine Strategy Framework Directive - MSFD) require a regular survey of several descriptors of the Environmental Status of coastal waters of the North-east Atlantic Ocean. Especially for the MSFD, which may concern large continental shelf areas where measurements are scarce, realistic ecological models can help assessing the Environmental Status. The ECO-MARS3D model of the pelagic ecosystem of the Bay of Biscay and English Channel continental shelf (NE Atlantic) has been developed for these applied purposes and validated against various types of historic data. This first paper deals with the basic biogeochemical version, which contains inorganic nutrients (NH4, NO3, PO4, Si(OH)4), three phytoplankton bulk types (diatoms, nanoflagellates and dinoflagellates), two zooplankton bulk types, particulate detrital forms and dissolved oxygen. A second paper presents a version of this model including 3 harmful phytoplanktonic groups. A simulation covering the 2000–2010 decade is compared to satellite sea surface data for temperature and surface chlorophyll, to the Southampton-Bilbao and Ouistreham-Portsmouth ferrybox surface data for temperature, salinity, chlorophyll and nutrients, to point samples provided by the French network of phytoplankton monitoring (REPHY) for inorganic nutrients and chlorophyll, and to high frequency time series of dissolved oxygen measured by a moored automatic buoy. From a spatial point of view, the model provides realistic fields of annual means of surface temperature (but with a systematic bias of about + 1.0 °C) and phytoplanktonic biomass. From a seasonal point of view, the temperature and salinity follow correctly the observed variations. For nutrient and total chlorophyll, the model succeeds in reproducing the difference amounting to one order of magnitude between the North Sea coastal zones and the oligotrophic oceanic zone above the abyssal plain of the bay of Biscay. It also reproduces the spring-neap tide oscillation visible in satellite observations of surface chlorophyll. Simulated seasonal cycles are realistic in the coastal stations, but the French Atlantic coast seems slightly too nutrient-rich. In coastal eutrophicated areas, the model does not produce chlorophyll peaks as high as measured. In the Vilaine bay (France), the summer hypoxic conditions (down to 4 mg/L O2 or less) are correctly reproduced. This ecological model has been used off-line to map some classical eutrophication descriptors (winter DIN and DIP, March-October 90th percentile of chlorophyll) used by the WFD and MSFD European directives. It has also been turned into an operational real-time mode, as part of the French Previmer project (now: http://marc.ifremer.fr/resultats/production_primaire).

Trophic Characteristics of Mnemiopsis leidyi and Its Impact on the Plankton Community in Black Sea Coastal Waters

The quantitative development of Mnemiopsis leidyi, the species structure of mesoplankton, and the food spectrum of ctenophores were studied in the shelf zone off the Crimean coast of the Black Sea during the summer seasons of 2013 and 2014. The feeding rate of the M. leidyi population and its predation pressure on the entire zooplankton community and certain species populations have been estimated from data on the diet composition, digestion time, and abundance of ctenophores. The volume of water cleared by M. leidyi varies by more than an order of magnitude depending on the systematic affiliation of the organisms consumed: it is maximum in the case of preying on Cladocera and Bivalvia veligers (up to 12 L ind.–1 h–1) and significantly lower for Copepoda (0.4–2.0 L ind.–1 h–1). The relationship between the value of the specific daily ration and carbon content in a M. leidyi body in the summer months of 2013 and 2014 is described by a parabolic equation with an exponent of –0.346 to –0.852. In 2014, the highest predation pressure, compared to other groups, was exerted on Copepoda and veligers of Bivalvia (on average 2.9 ± 1.5 and 2.2 ± 0.7% of biomass per day). The mean daily rate of predation on zooplankton in the Black Sea coastal zone was lower in 2014 (1.54 ± 0.58%) than in 2013 (3.94 ± 1.2% of zooplankton biomass) due to the low abundance of ctenophores. A comparative analysis of long-term data on the trophic role of the ctenophore in the plankton community has shown that the food spectrum, as well as the rate of predation on certain groups, varies from year to year. The low rate of predation on forage zooplankton by the M. leidyi population in recent years (2–5% of biomass per day) does not influence the interannual zooplankton dynamics in Black Sea coastal waters.

Ecological-Economic Model of Managing Recreational Potential of the Sea Coastal Zone

Ecological-Economic Model of Managing Recreational Potential of the Sea Coastal Zone

Main Development Problems of Vulnerability Mapping of Sea-Coastal Zones to Oil Spills

Vulnerability mapping of sea-coastal zones is an important element of oil spill response plans, environmental support for offshore projects, and the integrated management of the marine environment. The creation of such maps is a complex scientific problem. In their development, it is necessary to take into account differences in the nature of biotic and abiotic components existing in the cartographic area, dissimilarities in their relative vulnerability and significance, the seasonal variability of ecosystem components, and other factors. The purpose of this paper is to briefly review the main elements of international and Russian methods of mapping the vulnerability of sea-coastal zones to oil spills, and the development problems of such maps, including problems of using rank (ordinal) values, and to note possible solutions. Based on the analysis of key existing international and Russian approaches to vulnerability mapping, it was concluded that almost all methods of map calculations use rank (ordinal) values. However, arithmetic operations cannot be performed with them, as they lead to incorrect results. The paper shortly describes the main problems of mapping the vulnerability of sea-coastal zones to oil (the choice of the map scales and season limits for them, differences in the units of biota abundance, the calculation of relative vulnerability coefficients for the considered biotic components, the summation of the vulnerability of objects of different types, etc.). For some problems, possible solutions are outlined.

Ekologo-ekonomicheskaya model' upravleniya rekreatsionnym potentsialom pribrezhnoy zony morya

Ekologo-ekonomicheskaya model' upravleniya rekreatsionnym potentsialom pribrezhnoy zony morya

Carbonate formation mechanism in paleosol sediments of the Bohai Sea coastal zone, China

The Bohai Sea coastal zone of China consists of the Pacific Ocean to the east and Eurasia to the west; hence, this region is influenced by both the ocean and continental landmasses. The carbonate formation mechanism of eolian sediment within this area is poorly understood. The loess-paleosol sediments of the Miaodao stratigraphical section (MDS) contain a record of carbonate changes in this region during the last interglacial period. New insights into regional carbonate formation mechanisms since the last interglacial period were obtained by analyzing the ages of various sedimentary facies in combination with proxy paleoclimatic indices (including average grain size, standard deviation, CaCO3 content, and clay minerals), as well as via foraminiferal analysis. The results led to three principal findings: (1) The carbonate content change in the MDS was neither controlled by grain size nor affected by minerals. The carbonate change controlled by precipitate leaching in the Loess Plateau region cannot explain the eolian sediments within the Bohai Sea coastal zone. (2) Various subsections contain obvious carbonate content changes caused by foraminiferal deposits atop the eolian sediments, which were deposited by storm surges during a high sea-level period. This increased the carbonate content in the eolian sediments and restricted the carbonate content in the Bohai Sea coastal zone. (3) Newly detected foraminifera of the last interglacial period on the eolian sediment of the MDS were the main source of carbonate content, providing a new understanding of the carbonate formation mechanism in eolian sediments different from that of the Loess Plateau.

The temporal and spatial variability of coastal dune erosion in the Polish Baltic coastal zone

The study looked at the temporal and spatial variability of dune erosion in the Polish Baltic coastal zone in the period 1972–2008. The dynamics of coastal dune erosion in the area are presented in relationship to the main hydro-meteorological factors: storm surges and types of atmospheric circulation. The greatest destruction of the coastal dunes in Poland was observed on sandbar sections, where the erosion was over 100,000 m3 per 1 km, causing dune baseline retreat by several tens of meters. The main causes of this considerable coastal erosion are the sudden rise of the sea level and the waves during extreme storm surges, when the loss of dune sediment across the entire Polish Baltic Sea coastal zone can reach about 400,000 m3. These extremely erosive storm surges are particularly generated by cyclonic atmospheric circulation, which accounts for more than 52% of such surges from the north-west, north, and west. It was also found that sea level increases of more than 1 meter (about 602 cm) above the mean sea level (about 500 cm) can result in significant erosion of coastal dunes in Poland (>100,000 m3). However, there is a relationship between the intensity of the dune erosion and sea level. The results of the present study could be applied to studies of Baltic coastal dunes functioning in the lagoon-spit coastline, especially in the stretch from Estonia to Germany.

Building digital topography model of the intertidal zone between Caofeidian Nanpu town and Tanggu district using multi-period remote sensing data

The intertidal zone, a change zone of land and sea interaction, has abundant land reserves, tourism and other resources, which has a location advantage of great engineering construction in China’s coastal areas and thus is very important to investigate and monitor the topography of the tidal zone and also keep track of its topographic changes. In this study, the new section of the Bohai sea coastal zone from Nanpu to Tianjin Bohai sea area has been chosen as an example. Based on the terrain feature of the information expressed by the multi-period remote sensing image information and the tidal water level information as well as the tidal data acquisition time in the remote sensing image data, we have been calculated the water line (or edge point) digital elevation topography inversion analysis, and also constructed the digital terrain elevation model, and most importantly have provided a kind of quantitative method to get tidal zone (tide beach) terrain information.

Anthropogenic and climatic impacts on a coastal environment in the Baltic Sea over the last 1000 years

Coastal environments have experienced large ecological changes as a result of human activities over the last 100–200 years. To understand the severity and potential consequences of such changes, paleoenvironmental records provide important contextual information. The Baltic Sea coastal zone is naturally a vulnerable system and subject to significant human-induced impacts. To put the recent environmental degradation in the Baltic coastal zone into a long-term perspective, and to assess the natural and anthropogenic drivers of environmental change, we present sedimentary records covering the last 1000 years obtained from a coastal inlet (Gasfjarden) and a nearby lake (Lake Storsjon) in Sweden. We investigate the links between a pollen-based land cover reconstruction from Lake Storsjon and paleoenvironmental variables from Gasfjarden itself, including diatom assemblages, organic carbon (C) and nitrogen (N) contents, stable C and N isotopic ratios, and biogenic silica contents. The Lake Storsjon record shows that regional land use was characterized by small-scale agricultural activity between 900 and 1400 CE, which slightly intensified between 1400 and 1800 CE. Substantial expansion of cropland was observed between 1800 and 1950 CE, before afforestation between 1950 and 2010 CE. From the Gasfjarden record, prior to 1800 CE, relatively minor changes in the diatom and geochemical proxies were found. The onset of cultural eutrophication in Gasfjarden can be traced to the 1800s and intensified land use is identified as the main driver. Anthropogenic activities in the 20th century have caused unprecedented ecosystem changes in the coastal inlet, as reflected in the diatom composition and geochemical proxies.

Three-dimensional distribution of anthropogenic microparticles in the body of sandy beaches

External oceanographic conditions rather than anthropogenic influence are shown to cause the 3-dimensional distribution of anthropogenic microparticles (MP, 0.5–5mm) within the body of sandy beaches of a non-tidal sea with strong wind/wave climate and seasonal sea level variations (the Baltic Sea). A patchy structure is confirmed in all three dimensions, with background concentrations of several tens of MP items per kg of dry sample weight versus peaking spots with several hundreds of items per kg dry weight. The background MP concentrations are of the same order of magnitude for the beach surface, beach body, and sands of underwater coastal slopes, highlighting that the contaminated by MPs sand cover of the entire sea coastal zone is one single entity, repeatedly re-distributed between its underwater and beach parts by every next storm. Peaking concentrations are related to stormy events and places with stronger water dynamics, and are associated with locations of coarser sands within the beach body and wracklines at the beach surface. This suggests that marine waters are the source of anthropogenic microparticles for the beach, and not vice versa. The prevalence of wave-driven over wind-driven beaching mechanism for MPs extracted from the beach samples is confirmed by the flotation tests. Size distribution of the extracted MPs is found to be similar to that obtained for plastics floating at the ocean surface. Such a coherency for different oceanic environments speaks in favor of independence of general fragmentation processes on the particular external conditions, shifting the attention to the fragmentation process and material properties of synthetic particles in marine environment. CapsuleStormy winds, surface waves, and sea level variations rather than anthropogenic load define 3-d variability of pollution by synthetic microparticles within the sand body of beaches.

New insight into defining the lakes of the southern Baltic coastal zone.

There exist many classification systems of hydrographic entities such as lakes found along the coastlines of seas and oceans. Each system has its advantages and can be used with some success in the area of protection and management. This paper aims to evaluate whether the studied lakes are only coastal lakes or rather bodies of water of a completely different hydrological and hydrochemical nature. The attempt to create a new classification system of Polish coastal lakes is related to the incompleteness of lake information in existing classifications. Thus far, the most frequently used are classifications based solely on lake basin morphogenesis or hydrochemical properties. The classifications in this paper are based not only on the magnitude of lake water salinity or hydrochemical analysis but also on isolation from the Baltic Sea and other sources of water. The key element of the new classification system for coastal bodies of water is a departure from the existing system used to classify lakes in Poland and the introduction of ion-"tracking" methods designed to identify anion and cation distributions in each body of water of interest. As a result of the work, a new classification of lakes of the southern Baltic Sea coastal zone was created. Featured objects such as permanently brackish lakes, brackish lakes that may turn into freshwater lakes from time to time, freshwater lakes that may turn into brackish lakes from time to time, freshwater lakes that experience low levels of salinity due to specific incidents, and permanently freshwater lakes. The authors have adopted 200mg Cl-dm-3 as a maximum value of lake water salinity. There are many conditions that determine the membership of a lake to a particular group, but the most important is the isolation lakes from the Baltic Sea. Changing a condition may change the classification of a lake.

Examples of complex measures to improve water exchange in marina

The modeling of the marina and coastal structures near the Anapa city on Black sea coast of Russia have been carried out. The optimal configuration of the protected breakwaters and other hydrotechnical struc- tures are chosen for protecting of the marina area in the Anapa region. This configuration protect the marina from incoming waves impact and guaran- tee the need water exchange. A flow, induced by breaking wave, is consid- ered as a main factor of the water exchange. Represented results of re- searches and the variant of engineering decision in sea coastal zone is pos- sible to consider as attempt of management by coastal processes on rather complex sites of the coast with the joint decision about engineering re- quirements of an object, management of the water quality in the coastal zone of the sea and choice of optimum variants with the least of influence on an environment.

Radioactivity of the lower sector of Danube River and the Black Sea coastal zone in relation to some hydrological characteristics

Abstract On ecosystems, the radioactive material can have several consequences: the mechanisms of self-regulation of biocoenosis are affected; the interactions and composition of flora and fauna in biocoenosis are modified etc., and on humans, radioactive material presents a major risk through external exposure and internal exposure to radiation. On the other hand, floods and droughts, among others, can have the effect that they can act as a support for radionuclides. The existence of risks of radioactive and chemical pollution on the lower course of the Danube, in the Black Sea Danube spill area as well as in the Black Sea coastal area, where a number of complex processes occur, determined the study of the radiochemical processes taking place in these areas. The paper addresses the following issues: radiation risk and nuclear risk, general hydrological characteristics, radioactivity of the Lower Danube water and coastal zone of the Black Sea, radioactivity of the Lower Danube sediments and coastal zone of the Black Sea, modeling of radiochemical processes.

Efficiency of the coastal filter: Nitrogen and phosphorus removal in the Baltic Sea

AbstractAn important function of coastal ecosystems is the reduction of the nutrient flux from land to the open sea, the coastal filter. In this study, we focused on the two most important coastal biogeochemical processes that remove nitrogen and phosphorus permanently: denitrification and phosphorus burial. We compiled removal rates from coastal systems around the Baltic Sea and analyzed their spatial variation and regulating environmental factors. These analyses were used to scale up denitrification and phosphorus burial rates for the entire Baltic Sea coastal zone. Denitrification rates ranged from non‐detectable to 12 mmol N m−2 d−1, and correlated positively with both bottom water nitrate concentration and sediment organic carbon content. The rates exhibited a strong decreasing gradient from land to the open coast, which was likely driven by the availability of nitrate and labile organic carbon, but a high proportion of non‐cohesive sediments in the coastal zone decreased the denitrification efficiency relative to the open sea. Phosphorus burial rates varied from 0.21 g P m−2 yr−1 in open coastal systems to 2.28 g P m−2 yr−1 in estuaries. Our analysis suggests that archipelagos are important phosphorus traps and account for 45% of the coastal P removal, while covering only 17% of the coastal areas. High burial rates could partly be sustained by phosphorus import from the open Baltic Sea. We estimate that the coastal filter in the Baltic Sea removes 16% of nitrogen and 53% of phosphorus inputs from land.

Modeling of the meso- and submesoscale dynamic processes in the Black sea coastal zones

The article presents an analysis of simulation results for the Black Sea circulation. The calculations were carried out with a horizontal resolution of 1.6~km and taking into account the real atmospheric forcing for 2006 and 2011. Eddies with characteristic mesoscale and submesoscale spatio-temporal parameters were reconstructed in the velocity fields. It is shown that the simulated hydrophysical fields correspond to observed data. The most intensive generation of eddies with the scale of less than 10~km and orbital velocities of 20 -- 30~cm/s was observed in the neighborhood of the Crimean Peninsula, in the north-eastern and south-eastern parts of the sea. Vortex structures in the shelf zones were formed in all seasons with weak winds of directions. Their size depended on the depth and length of the shelf, as well as on the dimensions of coastal capes. The analysis of spatial and temporal variability of salinity fields and the longshore velocity component in the vertical cross-section passing through eddy centers showed that two main mechanisms of coastal eddies formation dominated in the Black Sea. The first mechanism is baroclinic instability, which arises with increasing horizontal density gradient in the periphery of large eddies or currents due to water rising/lowering. The second mechanism is the streamlining of shore inhomogeneities by the coastal current with a velocity higher than 40~cm/s.

Distribution, Community Composition, and Potential Metabolic Activity of Bacterioplankton in an Urbanized Mediterranean Sea Coastal Zone.

Bacterioplankton are fundamental components of marine ecosystems and influence the entire biosphere by contributing to the global biogeochemical cycles of key elements. Yet, there is a significant gap in knowledge about their diversity and specific activities, as well as environmental factors that shape their community composition and function. Here, the distribution and diversity of surface bacterioplankton along the coastline of the Gulf of Naples (GON; Italy) were investigated using flow cytometry coupled with high-throughput sequencing of the 16S rRNA gene. Heterotrophic bacteria numerically dominated the bacterioplankton and comprised mainly Alphaproteobacteria, Gammaproteobacteria, and Bacteroidetes Distinct communities occupied river-influenced, coastal, and offshore sites, as indicated by Bray-Curtis dissimilarity, distance metric (UniFrac), linear discriminant analysis effect size (LEfSe), and multivariate analyses. The heterogeneity in diversity and community composition was mainly due to salinity and changes in environmental conditions across sites, as defined by nutrient and chlorophyll a concentrations. Bacterioplankton communities were composed of a few dominant taxa and a large proportion (92%) of rare taxa (here defined as operational taxonomic units [OTUs] accounting for <0.1% of the total sequence abundance), the majority of which were unique to each site. The relationship between 16S rRNA and the 16S rRNA gene, i.e., between potential metabolic activity and abundance, was positive for the whole community. However, analysis of individual OTUs revealed high rRNA-to-rRNA gene ratios for most (71.6% ± 16.7%) of the rare taxa, suggesting that these low-abundance organisms were potentially active and hence might be playing an important role in ecosystem diversity and functioning in the GON.IMPORTANCE The study of bacterioplankton in coastal zones is of critical importance, considering that these areas are highly productive and anthropogenically impacted. Their richness and evenness, as well as their potential activity, are very important to assess ecosystem health and functioning. Here, we investigated bacterial distribution, community composition, and potential metabolic activity in the GON, which is an ideal test site due to its heterogeneous environment characterized by a complex hydrodynamics and terrestrial inputs of varied quantities and quality. Our study demonstrates that bacterioplankton communities in this region are highly diverse and strongly regulated by a combination of different environmental factors leading to their heterogeneous distribution, with the rare taxa contributing to a major proportion of diversity and shifts in community composition and potentially holding a key role in ecosystem functioning.