Mucilage Events Research Articles

The last fortress fell: mass mortality of Pinna nobilis in the Sea of Marmara

A spring 2021 cruise to the south Marmara Islands revealed a mass mortality event of Pinna nobilis, which were reported to be healthy just seven months ago. The cause of death might be associated with the epidemic infection or a catastrophic mucilage event seen after November 2020 in the Sea of Marmara. A total of 191 Pinna nobilis individuals were found at seven stations out of 10, of which 88% were dead. In the present study, the population density (dead and alive individuals) of P. nobilis was found to be between 0.3 ind.100 m-2 and 12 ind.100 m-2 in the area. A total of three live and four dead juvenile individuals were observed in the area, indicating low recent recruitment. The highest number of dead Pinna nobilis individuals (92 specimens) was encountered in shallow-waters (0-4 m depth). A total of 34 species belonging to six taxonomic groups (Sipuncula, Oligochaeta, Polychaeta, Crustacea, Mollusca, and Pisces) were found within the dead shells of four P. nobilis individuals. The mass mortality of Pinna nobilis in the Sea of Marmara, the last remaining disease-free sea, indicates the necessity of establishing and implementing emergency action plans for this species, including ex-situ conservation.

Metagenomic characterization of planktonic communities during a mucilage event in the Çanakkale Strait (Dardanelles), Turkey

Bu çalışma da Çanakkale Boğazı'ında (Dardanel) müsilaj oluşumu sırasında planktonik toplulukların kompozisyonları metagenomik yaklaşımla araştırılmıştır. Müsilaj örnekleri, Çanakkale Boğazı'nın üç farklı istasyonunda (İstasyon 1: 40°15'22.53"K, 26°40'43.58"D; İstasyon 2: 40°10'59.21"K 26°37'81.17"D; İstasyon 3: 40°11'15.67"K, 26°39'90.81"D) yoğun müsilaj oluşumu gözlemlenen Mayıs 2021'de toplanmıştır. Filum düzeyinde toplam sekans sayısının 86.68% ini kapsayan baskın planktonik ökaryotlar, Dinoflagellata (%38.57), Protalveolata (%15.03), Diatomea (%12.41), Nematozoa (%8.44), Apicomplexa (%6.79) ve Chlorophyta (%5.43) olarak belirlenmiştir. En baskın OTU'ler (>%10), Alexandrium ve Syndiniales_Group_II olup, diğer baskın OTU'lar (>%2) ise Viscosia sp., Lankesteria, Arcocellulus, Thalassiosira ve Nannochloris olmuştur.
 Bu çalışma, Türkiye'de meydana gelen bir müsilaj olayı sırasında Çanakkale Boğazı'nda planktonik toplulukların durumunu netleştirmiştir. Sonuç olarak, en baskın cinsin müsilaj üretme kabiliyeti olduğu bilinen Alexandrium olduğu belirlenmiştir. Bazı Alexandrium türleri toksin üretebilir, insan sağlığı üzerinde ciddi etkilere neden olabilir ve çift kabuklu, karides ve balık ölümlerine yol açabilir. Bu nedenle müsilaj yapısındaki Alexandrium toksinlerinin belirlenmesi için daha detaylı bir çalışmaya ihtiyaç vardır. Ayrıca elde edilen müsilajın ağır metal içeriği araştırılmıştır. Müsilajın yapısındaki As ve Cr konsantrasyonları atıklar için belirlenen düzenli depolama sahalarına bertaraf etme sınırlarının üzerindedir. Bu nedenle deniz yüzeyinden toplanan müsilajın düzenli depolama sahalarına gönderilmeden önce ağır metal içeriği kontrol edilmelidir.

Temporal variations in phytoplankton composition in the northeastern Sea of Marmara: potentially toxic species and mucilage event

Temporal variations in phytoplankton composition in the northeastern Sea of Marmara was investigated associated with physico-chemical variables from January 2004 to December 2007. The occurrence of potentially toxic species and a mucilage event was also evaluated during this study period. The confined upper layer of the Sea of Marmara is mesotrophic to eutrophic and has higher productivity when compared to the neighbouring Black Sea and Aegean Sea. 132 taxa in the micro-phytoplankton community were identified, 11 of which are known to be potentially toxic. The most abundant species were Pseudo-nitzschia species from diatoms and Prorocentrum micans from dinoflagellates. Potentially toxic species were more common at the coastal stations. The onset of a mucilage formation was observed in October 2007, and well-known mucilage producers such as Gonyaulax hyalina (reported as G. fragilis) and Thalassiosira gravida (reported as T. rotula) dominated the phytoplankton community during this event. A marked decrease in the number of species and diversity index following June 2007 and reported shifts in the zooplankton community during the same period points to probable cascading effects in the pelagic ecosystem of the Sea of Marmara.

Temporal variations in the abundance of picoplanktonic Synechococcus (Cyanobacteria) during a mucilage event in the Gulfs of Bandırma and Erdek

The marine cyanobacterium Synechococcus plays an important role in microbial food webs and is a significant contributor to primary production in the world's oceans. The abundance distribution of picoplanktonic Synechococcus was investigated in the Gulfs of Bandırma and Erdek (in the Sea of Marmara), in which water samples were taken seasonally between August 2007 and August 2008 during an intense period of mucilage formation. The mucilage phenomenon occurred in the Sea of Marmara between October 2007 and February 2008. In both sites, Synechococcus abundance was highest in November 2007, at 32.68 × 104 cells ml−1 in the Gulf of Bandırma and 34.83 × 104 cells ml−1 in the Gulf of Erdek, with the high values in November 2007 coinciding with mucilage formation. In contrast, the lowest Synechococcus abundance was 0.85 × 104 cells ml−1 in February 2008 in the Gulf of Bandırma and 3.27 × 104 cells ml−1 in May 2007 in the Gulf of Erdek. The two-layered structure of the Sea of Marmara affected the vertical distribution of Synechococcus, in which the maximum abundance of Synechococcus occurred in the upper layers and the minimum abundance values at the deeper layers of both gulfs. This layered structure also strongly affected the relationship between Synechococcus and environmental parameters. In this sense, Synechococcus abundance was negatively correlated with salinity and nitrate but was positively correlated with chlorophyll-a in the Gulfs of Bandırma and Erdek but was not correlated with temperature or phosphate in either gulf. Despite the fact that Synechococcus is temperature dependent, the abundance distribution was influenced more by other environmental factors than by temperature.

Dynamics of microbial communities across the three domains of life over an annual cycle with emphasis on marine mucilage in the Southern Bay of Biscay resolved by microbial fingerprinting

Marine mucilage has been described as worldwide phenomena occurring sporadically, or frequently in certain coastal areas. They are transitory phenomena that can remain in the photic zone for several days or weeks. Their occurrence has been more frequent and persistent, and their magnitude has increased during the last decades. Their formation typically reflects an imbalance in the marine microbial communities, and has frequently be linked to global changes. Recurrent marine mucilage events have been observed in recent years in the Southern Bay of Biscay near the French coast, mainly south of the Adour estuary. In this study, we used a fingerprinting method (T-RFLP) targeting 16S and 18S rRNA genes to investigate marine microbial community composition and dynamics over an annual cycle across the three domains of life in coastal water at three depths, in the Adour River upstream of the mouth and in the marine mucilage. In line with studies conducted in marine environments we highlighted that the dynamics of marine microbial communities in the Bay of Biscay coincided with two environmental contexts: winter and spring on one hand and summer and autumn on the other hand. More interestingly, this dynamics affects also the marine pelagic mucilage that was observed during the sampling campaigns. Thus, the composition of the marine mucilage that appears in winter/spring context diverges from the composition of the marine mucilage that occurred during the summer/autumn context. We highlighted also that marine microbial communities were partly different from marine mucilage communities with an enrichment of some microorganisms suggesting that marine mucilage behaves as a microhabitat in seawater and possesses distinct microbial assemblages from the surrounding communities.

Gonyaulax hyalina and Gonyaulax fragilis (Dinoflagellata), two names associated with ‘mare sporco’, indicate the same species

:Aggregates of mucilaginous material have been at times observed in coastal and oceanic sea waters. In the Adriatic Sea (Mediterranean Sea), these events have been known since the 18th century as ‘mare sporco’ (= dirty sea), and in recent years, they have been associated with the dinoflagellate Gonyaulax fragilis; whereas, in New Zealand mucilage events were linked to Gonyaulax hyalina. In summer 2012, during a ‘mare sporco’ event in the Gulf of Naples (Mediterranean Sea), numerous cells of a species tentatively identified as Gonyaulax hyalina were detected in the mucilaginous aggregates. Since the boundary between G. fragilis and G. hyalina was not clear, we compared a strain isolated from the Gulf of Naples in 2012 with two strains from the Adriatic Sea and New Zealand waters, the latter two identified as G. fragilis and G. hyalina, respectively. Detailed light microscopy and scanning electron microscopy observations of the three strains showed that all shared the same thecal plate pattern and morphological features. Partial small subunit and large subunit rDNA regions of the three strains were identical. Based on these results and on a revision of the taxonomic history of the two taxa, we propose that G. fragilis and G. hyalina are the same species. Gonyaulax fragilis was described as Steiniella fragilis by Schütt in 1895 and transferred to G. fragilis by Kofoid in 1911. Gonyaulax hyalina was described a few years later by Ostenfeld and Schmidt in 1901. Thus, the name G. fragilis has priority, while G. hyalina is to be considered a synonym.

Benthic mucilage blooms threaten coralligenous reefs

Mucilaginous aggregates produced by planktonic or benthic algae are considered ecological threats to marine systems. The study evaluated the effects of the spread of benthic mucilaginous aggregates on the structure of coralligenous assemblages. The assemblage and the quality of a site subjected to a benthic mucilage bloom were compared to those of two reference sites using a Before/After-Control/Impact (BACI) design. Results showed the α and β-diversity, ESCA and COARSE quality ecological indices and the cover of encrusting algae and bryozoans were lower at the impact site after the mucilage event than at the control sites and at the impact site before the mucilage event. An opposite pattern was observed for the necrosis of gorgonians and the cover of algal turf. This study describes for the first time the impacts of ephemeral mucilage blooms on the whole coralligenous assemblage, identifying a further threat of this habitat and the need of adequate monitoring programs.

Structural and functional response of phytoplankton to reduced river inputs and anomalous physical-chemical conditions in the Gulf of Trieste (northern Adriatic Sea)

We studied the influence of anomalous meteorological and hydrological conditions that occurred in the Gulf of Trieste from March 2006 to February 2007 on phytoplankton structure and function. We computed monthly mean (or median) air temperature, total precipitation, wind speed, river discharge, seawater temperature, salinity, photosynthetic available radiation (PAR), cyanobacteria, nano- and microphytoplankton abundances during the study year and compared them to climatological (1999–2014 for PAR; 1999–2007 for nanophytoplankton; 1998–2015 for the other variables) mean/median data. We then related the cyanobacteria (0.2–2 μm), nano- (2–20 μm) and microphytoplankton (20–200 μm) of the study year to inorganic nutrient concentrations. Median river inputs in October and November were 9- and 15-fold lower, respectively, than the time series medians, with consequent high salinity from May to November (up to +1.26 compared to the climatological data). Monthly mean seawater temperatures were lower than the climatological values (−2.95 °C at the surface) from March to August 2006 and higher (+2.15 °C at the surface) from September to February 2007. Reductions in freshwater input and nutrient depletion were likely responsible for a decrease in microphytoplankton (median annual abundance over 60% lower than the climatologic median) and cyanobacteria (up to 47% lower than the climatology). Significant seasonal differences in cyanobacteria and microphytoplankton abundances (RANOSIM = 0.52; p < 0.05), as well as in seawater temperature and salinity (RANOSIM = 0.73; p < 0.05) between the study period and the climatology were highlighted. The late spring diatom bloom was not reflected in high photosynthetic rates whereas an unusually high primary production was estimated in November (7.11 ± 1.01 μgC L−1 h−1), when a mucilage event occurred due to very stable atmospheric and oceanographic conditions. The typical seasonal succession of pelagic phototrophs (micro-, nanophytoplankton and cyanobacteria) was altered since an exceptional cyanobacteria bloom first developed in April, followed by a delayed diatom bloom in May.

Microfouling communities from pelagic and benthic marine plastic debris sampled across Mediterranean coastal waters

The present study used scanning electron microscopy to characterize the organisms colonizing marine plastic debris collected from pelagic and benthic habitats across Mediterranean coastal waters of Greece, Italy and Spain. A total of 42 fragments of plastic were collected during the COMSOM experimental cruise, 16 from the seafloor and 26 from surface waters. The results showed that diatoms were the most abundant organisms on both pelagic and benthic plastics. The diatom Ceratoneis closterium , frequently observed on surface plastics (73%), is a harmful microalgae associated with mucilage events in the Mediterranean. The abundance of marine plastic in coastal and oceanic waters may provide new habitats that offer an easy substrate for these invasive organisms. Furthermore, the colonization of these new environments might reduce the success of life strategies, or drive the organisms out of their essential habitat by dispersion and rafting phenomena. The results of the present work highlight the need to increase our knowledge of the consequences of colonization of plastics introduced into the marine environment, and the need to raise awareness of the potential impacts of debris accumulation on biodiversity of marine ecosystems.

Sea dynamics impacts on the macroaggregates: A case study of the 1997 mucilage event in the northern Adriatic

We analysed the 1997 summer mucilage event in the northern Adriatic and showed that macroaggregates were formed in the upper layers of the water column in central parts of large gyres and were dispersed by currents which seem to be of geostrophic origin. Beside Cylindrotheca closterium, an already established regular opportunistic species of the mucilage phenomenon, originating from the sediment, we detected another benthic species, Thalassionema nitzschioides, of sporadic character. Both were present in scarce amounts in the water column at the time of sampling first macroaggregates, but reached high abundances after/close to the mucilage event ending. The first, and the most intense surface heat loss episode, on 18 July (heat loss of around 240Wm−2, during episode of NW wind), in time of first macroaggregates formation, introduced C. closterium from sediment into the water column and enabled dispersion of T. nitzschioides, present in central region both in water and in first macroaggregate samples, eastwards and westwards. The later, less intense surface heat loss episodes, between end of July and mid of August (30–160Wm−2, induced mostly by NE winds) were efficient (1) in tearing already formed macroaggregates, enabling in that way release of opportunistic species from a macroaggregate into the surrounding water column, and (2) in transporting lower salinity waters of specific species populations with macroaggregates form west to east, extending the event to large area. We hypothesise, first, that summer surface heat loss episodes play a role in sustaining mucilage events by introduction of C. closterium from the sediment and/or decaying macroaggregates in the water column. Second, that geostrophic currents are important in spreading of various types of aggregates, including marine snow, over the wider marine areas.

Changes in abundance and community structure of the zooplankton population during the 2008 mucilage event in the northeastern Marmara Sea

The composition and abundance of zooplankton and the corresponding environmental conditions were investigated during the 2008 mucilage event (April-December 2008) in the Marmara Sea. As a result, 46 zooplanktonic taxa were identified. Copepods and cladocerans were generally the most abundant groups. Mnemiopsis leidyi had a significant seasonality, and abundance was related to fluctuations in temperature and salinity. The most important species were Acartia clausi and Penilia avirostris, but these species did not reach their usual autumn maximum. As a result, the mucilage event in 2008 caused significant shifts in zooplankton abundance and community structure in the Marmara Sea.

Relevant scales of variability of the benthic allochthonous microalga Chrysophaeum taylorii

Chrysophaeum taylorii (Pelagophyceae) is an allochthonous benthic microalga recently recorded in the Mediterranean Sea. During summer, the occurrence of C. taylorii is usually visible to the naked eye due to the large amount of mucilage this species produces. Information on the spatio-temporal variability of this species and on the predictability of massive mucilage events is still scarce and requires to define ad hoc managing strategies of major bloom events. The aim of this work was to identify the relevant scales of variation in the abundance of C. taylorii abundance and to estimate the relative recurrence of its blooms, testing the hypothesis that mucilage was depend- ent on the cell density. The first approach was the identi- fication of the most appropriate sampling procedure to estimate benthic cell abundance of C. taylorii. The second one was the estimation of the magnitude of variation in C. taylorii cell abundance attributable to each of several spa- tial (areas, sites, zones and replicates) and temporal scales (fortnights and years) in the Marine Protected area of Tavolara Punta Coda Cavallo (Western Mediterranean Sea). The results indicate fortnight and year as the most relevant scales of variability in the cell abundance of C. taylorii and

Collapse of zooplankton stocks during Liriope tetraphylla (Hydromedusa) blooms and dense mucilaginous aggregations in a thermohaline stratified basin

AbstractA growing number of studies report an increase in jellyfish populations worldwide that may have consequences for marine planktonic food web dynamics. The principal objective of this study was to understand the changes in a zooplankton community during blooms of Liriope tetraphylla and subsequent mucilage events in the Sea of Marmara, a small highly stratified transitional basin between the Black and Aegean Seas. Liriope blooms observed in 2006 and 2007 reached a maximum abundance of 2978 ind.·m−3, following the species' first observation in 2005. Jellyfish species are known to play a key guild role by restructuring plankton communities and in the Sea of Marmara Liriope caused a temporal regime shift from a crustacean‐ to a jellyfish‐controlled system. A rapid decline in abundance of most important zooplankton species followed the Liriope increase, together with a drastic shift in community structure. The dominant summer–autumn species Penilia avirostris (Cladocera) vanished in the autumn of 2006 and was diminished ~30‐fold in 2007 when compared with years without Liriope. The decline in zooplankton and the devastating effects of mucilage on pelagic ecosystem and socio‐economics through restricting commercial fisheries implied sensitivity of the already perturbed Marmara ecosystem to changes in predator densities and environmental stability.

Potential environmental factors influencing mucilage formation in the northern Adriatic Sea

In the northern Adriatic Sea, Mediterranean Sea, the mucilage phenomenon is usually related to the aggregation of extracellular organic matter of phytoplanktonic origin under special seasonal and trophic conditions. Environmental factors, such as temperature, salinity, nitrogen, phosphorus and N/P ratio as well as polysaccharide and monosaccharide levels in the presence and absence of mucilage were investigated in the northern Adriatic Sea. Variations in temperature and salinity during spring in years characterised by mucilage events have been recognised having an important role in preparing a favourable physical environment where mucilage formation could take place. Since the DIN/TP ratio increased markedly during the spring months (March–April) in 2002, 2003 and 2004, preceding the early summer mucilage outbreaks, it appeared that the DIN/TP ratio may be a more robust predictor than the DIN/DIP ratio, which, although more commonly used, exhibited a discontinuous trend. The contents of total carbohydrates, including monosaccharides and polysaccharides, in seawater also varied according to the presence or absence of mucilage, with an increase of polysaccharide levels during the late spring or early summer in the period of the mucilage appearance. The role of carbohydrates in the macro-aggregate formation was also investigated.

Benthic diatom response to changing environmental conditions

In the Gulf of Trieste (northern Adriatic Sea, Italy) the benthic diatom community dynamics has been studied for seven years (1999–2005) at two sublittoral stations and related to variations of temperature, salinity, nutrient concentrations, freshwater inflow and mucilage. Bin-averaged temperature versus abundance of the main genera revealed that Nitzschia and Navicula presented a positive stepped trend with increasing temperature. An increase of ca. 860 ± 150 cells per cm3 per °C was calculated for Navicula and up to 590 ± 170 cells per cm3 per °C for Nitzschia. The genus Pleurosigma revealed a negative trend with increasing temperature, with a calculated decrease of ca. 140 ± 60 cells per cm3 per °C. A negative relation between Diploneis and temperature was found only in the shallower site. A peak of the tychopelagic genus Cylindrotheca was observed in correspondence with high salinity, but no significant results between bin-averaged salinity and benthic diatom abundance were found. Significant negative relations were obtained between bin-averaged abundance of Pleurosigma and H4SiO4 and NO3− at the deeper station and between the bin-averaged abundance of Gyrosigma and NH4+ at the coastal station. In this site the abundance of Gyrosigma showed a significant increasing trend over the study period. Navicula and Nitzschia seemed to suffer from the presence of mucilage events occurred in summer 2000 and 2004 whereas Diploneis occupied the ecological niche which remained temporarily uncovered by Navicula and Nitzschia. An exceptional freshwater plume with extremely high terrigenous input in November 2000 completely covered the benthic diatom community, causing a remarkable decrease in its total abundance in late autumn and winter 2000–01. The Gulf of Trieste may be considered a natural megacosm due to its geomorphologic characteristics and therefore the benthic diatom response to changing environmental conditions observed in this site could be extended beyond the geographical limits of this particular ecosystem.

Organic matter recycling during a mucilage event and its influence on the surrounding environment (Ligurian Sea, NW Mediterranean)

The development of benthic mucilage in the Marine Protected Area of Portofino (Ligurian Sea) during the summer of 2009 was studied to verify the influence of this event on the surrounding environment (seawater and soft-bottom). The calm meteorological and sea conditions at the beginning of the time frame under consideration caused the thermal stratification of the water column. This stratification was one of the driving factors influencing the development of the mucilage, which developed on a large boulder surface above the pycnocline. Mucilage was progressively detached from the boulder surface by hydrodynamism, together with macroalgae, and sank onto the sediment below the thermocline. Increased surface-water movements, caused by meteorological forcing during the study period, influenced the aggregation–disaggregation of mucilage flocks above the thermocline, leading to increased dissolved oxygen concentrations and enhanced production and turnover of the organic matter (OM). Mixing with the adjacent seawater led to the fertilisation of the surrounding environment with potentially labile OM and inorganic phosphorus, which caused increases in the hydrolytic enzymatic activity. Conversely, below the thermocline, the sunken mucilage and algae aggregates supported a heterotrophic consumption system. Dissolved oxygen concentrations were lower than those recorded in the mucilage lying above the thermocline, making more carbohydrates than proteins and labile phosphorus available. Despite the slow oxygenation of this mucilage, it contributed to the food supply for the soft-bottom macrofauna, which showed an increase in density, diversity and biomass during the study. These results suggest that the development and fate of the mucilage, as well as its interactions with the surrounding environment, were principally regulated by physical features. In the oligotrophic coastal area of the Ligurian Sea, certain compartments of the ecosystem were able to promptly respond and take advantage of the mucilage event of the summer of 2009, although the persistence of mucilage on hard substrates is known to cause suffocation and macroalgae biomass depletion. It is proposed that, at least in oligotrophic conditions and as long as mucilage persistence doesn't cause severe oxygen depletion, its appearance might have an enhancing rather than a detrimental effect on the seawater and soft-bottom biogeochemical processes.

High downward flux of mucilaginous aggregates in the Ligurian Sea during summer 2002: similarities with the mucilage phenomenon in the Adriatic Sea

AbstractThe DYFAMED sediment trap station in the Ligurian Sea (NW Mediterranean) has been active since 1986 and today comprises the longest time‐series of downward particle flux in the Mediterranean Sea. As such, it provides valuable information on the interannual variability of the particle flux, and also documents possible recent changes in the NW Mediterranean pelagic ecosystems. We report an unprecedented episode of downward flux of mucilaginous material at the DYFAMED station during summer 2002 in association with singular hydrometeorological conditions. The rain of mucilaginous aggregates clogged a PPS5 sediment trap at 260 m depth and was also clearly detected at 1080 m depth. The possible factors governing the development and sinking of the mucilaginous material are discussed. A very sharp increase of sea surface temperature during June and the presence of freshened waters in the surface the following month resulted in a stronger than usual stratification of the upper water column throughout the summer season. We suggest that the steepness of the vertical density gradient was responsible for the unusual accumulation of mucous aggregates. Additionally, a diatom bloom took place during the nutrient‐depleted conditions typical of summer, a factor which may have contributed to feed the pycnocline with transparent exopolymer substances. A storm occurring in the beginning of August relaxed the stratification and promoted the deposition of the mucilaginous aggregates accumulated in the upper water column during the preceding months. Important similarities of ambient conditions preceding the apparition of mucilaginous material in our open‐sea site and those reported in the Adriatic Sea during major mucilage events, suggest that general climatic conditions, rather than local factors, drive the occurrence of major accumulations of mucilaginous material in the water column at both sub‐basins of the Mediterranean Sea. In this regard, the strength of the air temperature increase during the onset of the stratified season is proposed as a major controlling factor.

Significance of Bacterial Activity for the Distribution and Dynamics of Transparent Exopolymer Particles in the Mediterranean Sea

The study of transparent exopolymer particles (TEP) in the Mediterranean Sea is particularly relevant as they can be promoters of mucilage events, a frequent phenomenon there. We assessed the influence of bacterioplankton on TEP distribution and dynamics across the west-east axis of the Mediterranean Sea. We performed an extensive study of TEP, dissolved carbohydrates, and their relationships with bacterial abundance and bacterial production (BP). A significant and positive relationship was observed between BP and TEP in the study region (r (2) = 0.51, p < 0.001). The direct release of TEP by bacteria was experimentally corroborated using regrowth cultures where increases in TEP tracked bacterial growth in abundance and production. These TEP increases were positively related to the increases in BP (r (2) = 0.78, p < 0.05). The consistency (similar slopes) of the regression lines between BP and TEP in natural conditions and between the increases of BP and TEP in the experiments underlines the relevant role of bacteria in the formation of TEP in this area.

Viral production in the Gulf of Trieste (Northern Adriatic Sea): Preliminary results using different methodological approaches

Although the temporal and spatial variability of virioplankton in the northernmost part of the Adriatic Sea has been repeatedly explored suggesting that viruses constitute an extremely dynamic component of the plankton community and hypothesizing their importance in marine food webs and mucilage events, there is still no information about viral replication rates. Hence, the contribution of viruses to bacterial mortality and the cycling of organic matter in this part of the Adriatic basin are still not fully comprehended. Assessment of the role of viral lysis requires a robust means of estimating viral production. Since, up to now, none of the available methods evolved to a state of a standard yet, in this preliminary study 3 different experimental approaches were simultaneously assayed (viral production estimated by radiotracer incorporation method [TdR], dilution technique for the estimate of viral production in already infected bacteria [DIL] and serial dilution method in manipulated phage-host assemblage [SER]). The present study provided the first evidence of viral production rates in this study area, that resulted in comprising between ∼ 3.5–15 × 10 8 viruses L − 1 h − 1 and critically faced up the results obtained by different techniques with the consideration that they suffer from different biases. Based on TdR and DIL viral proliferation estimates, viral lysis was responsible for the loss of 54 to 95% of the bacterial standing stock, while the viral-induced mortality by SER (325% d − 1 ) was likely consistently overestimated. These results indicate that viral lysis is a significant factor for prokaryotic mortality suggesting its implication as an important pathway for the cycling of dissolved organic matter in the Gulf of Trieste.

Phytoplankton Composition and Environmental Conditions of the Mucilage Event in the Sea of Marmara

The composition and abundance of phytoplankton and the corresponding environmental conditions were investigated during a mucilage event (October 2007-February 2008) in the Sea of Marmara. The mucilage producers Gonyaulax fragilis, Skeletonema costatum, and Cylindrotheca closterium were identified as abundant species. Thallassiosira rotula was also identified in large numbers. The maximum number of G. fragilis was observed at 83,600 cells L^{-1} in November 2007 during the first sampling occasion on the surface layer of İzmit Bay, and T. rotula was the most abundant diatom species, with 131,040 cells L^{-1} in the same period. G. fragilis was recorded at 96,250 cells L^{-1} in the dense mucilage-containing water samples collected from Değirmendere (İzmit Bay) in January 2008, and C. closterium was the dominant (161,250 cells L^{-1}) diatom species in the same sample. Species diversity values (H'_{log2}) increased from November to February, displaying maximum values of 2.5-3.5 in February at almost all stations (depths of 0.5 and 10 m), caused by the balanced increase of diatom species and their individual numbers in the total phytoplankton abundance. The surface layer waters of İzmit Bay exhibited severely low nitrogen to phosphorus ratio (N:P) values (0.1-14.4) compared to the Redfield ratio (16), which could be supported by the fact that the limiting nutrient for the Sea of Marmara is nitrogen. Even though there is a lack of data from before the mucilage period, the data obtained during the lifespan of the event indicated that a mixture of several phytoplankton species might have played a key role in the mucilage formation. The high organic carbon content of the mucilage (24% org-C) and the surrounding waters support the possibility that the event could have been related to organically rich cellular exudates of phytoplankton.