Role of Bacteria in the Carbon and Nitrogen Flow between Water-Column and Sediment in a Shallow Marine Bay (Bay of Piran, Northern Adriatic Sea)

Abstract. The interdependences between phytoplankton standing crop, bacterial biomass and the dissolved organic matter (DOM) pool in the water column were investigated and related to sediment parameters in a shallow marine bay (Bay of Piran, Northern Adriatic Sea) over an annual cycle. Bacterioplankton density varied between 1–10 × 10⁵ cells ml^-1, with lowest density observed in March corresponding to the low Chi a concentrations during this period. Generation times as determined by dialysis incubations ranged between 4h (June) and 82 h (March). Mean bacterial secondary production rates during summer were about 40 mg C m^-1 d^-1 and 5mg C m^-3.d^-1 during winter. With a short time lag, DOM concentrations followed the fluctuation in Chi a.
Sediment oxygen demand measurements revealed a mean mineralization rate of about 260 mg C m^-2 d^-1 during summer and 100–200 mg C m^-2 d^-1 in winter. Sediment bacterial density varied between 10⁸ - 10⁹ cells g (sediment dry wt)^-1 in the top 5 cm sediment layer or, in terms of biomass, 4.3 g C m^-l during summer and 0.6 g C m^-2 during winter. Highest concentrations of DOM in pore waters were measured in September, coinciding with high rates of sediment oxygen demand.     

Microbial Biomass Dynamics Along a Trophic Gradient at the Atlantic Barrier Reef off Belize (Central America)

Abstract. Recent findings indicate that heterotrophic bacteria and not phytoplankton are the most numerous biomass components even in the euphotic zone of oligotrophic, open oceans. In this study it was hypothesized that the microbial biomass components change within a few hundred meters as oligotrophic water flows across the reef and becomes enriched with nutrients. Along a trophic gradient, four stations at the Atlantic Barrier Reef off Belize (Central America) were sampled for microbial biomass components. Phytoplankton biomass (measured as chlorophyll a) ranged from the most oligotrophic station (St. 1) to the most eutrophic station (St. 4) from 6.9–415.5 μg CI"' (assuming a C:chl a ratio of 30): heterotrophic bacterial biomass increased 4-fold (from 10.1–46.4μg C 1^-1), heterotrophic nanoflagellate (HNAN) biomass increased from 4.6-19ug C 1^-1, and cyanobacteria from 0.9-4.5 μg C-1^-1. Production estimates derived from seawater cultures revealed a 5-fold increase in bacterial production from the oligotrophic station (3.7 ug C 1^-1 d^-1) to the eutrophic St. 4 (17.8ug C-1-d1^-1)- Cyanobacterial production rose from 1.1–3.5ug C-1–d^-1 and HNAN production from 0.65-1.13 μg C-1^-1 -d^-1. While cyanobacteria contributed between 13 and 20% to the autotrophic plankton component in the oligotrophic waters, their contribution dropped to about 1 % at the eutrophic stations.     

The Ecology of Amorphous Aggregations (Marine Snow) in the Northern Adriatic Sea:

Abstract. In the water-column of the Gulf of Trieste (Northern Adriatic Sea) flocculent, amorphous aggregates known as marine snow reach maximum density and dimensions up to 20cm in diameter during summer months. Sampling of these fragile macro-aggregates was carried out by SCUBA-divers.
A large detrital component was found to be embedded in an organic matrix together with a large array of intact phytoplankton species. Heterotrophic bacterial density ranged from 2–65 × 10⁸ cells-g^-1 (marine snow dry wt) and is therefore of the same order of magnitude as in the surface layer of the sediments of the Gulf. In terms of biomass, bacteria reached only 30–95% of heterotrophic microflagellates.
A mean abundance of marine snow of 5g (marine snow dry wt) m^-3 was obtained for the water-column above the pyenolinc. At this boundary layer, however, a mean abundance of about 10g (marine snow dry wt) m^-3 led to the formation of a distinct, 10-50cm thick layer. Based on these data and sedimentation rates of marine snow to the pyenoclinc (38 g [marine snow dry wt] m^-2 d^-1) the potential ecological significance of these macro-aggregates for the pelagic system of the Gulf of Trieste is discussed.     

Contribution of the Bacterial and Microphytobenthic Microflora in the Energetic Demand of the Meiobenthos in an Intertidal Muddy Sediment (Kerguelen Archipelago)

Abstract. An intertidal mud sediment in the Kerguelen Archipelago was sampled weekly from January 1982 to March 1983. Measurements were taken for organic matter (carbon and nitrogen) and biological (bacteria, microphytobenthos, and mciofauna) parameters. The sediment is rich in organic matter, with a mean organic carbon content of 130gC- m-². Benthic living components yield low mean biomasscs in relation to the total organic pool. Besides some marine inputs, the main allochthonous source was identified as terrestrial inputs. Benthic activities seemed strongly governed by food availability and not by temperature. Obvious seasonal changes in bacterial abundances (direct counts), primary production, and mciofauna distributions were observed. Photosynthctic production reached high values (up to 2275 mg C-m^-2-d^-1), reflecting the presence of a dense microphytobenthos. Preliminary energy budgets for two seasons (spring and winter) have been constructed. In both periods, the measured primary production can support the high mciofauna production.     

Response of Summer Phytoplankton to Episodic Meteorological Events (Gulf of Trieste, Adriatic Sea)

Abstract. Despite increasing evidence that atmospheric deposition may contribute considerably to new production in coastal seas, the role of this nutrient source in the shallow northern Adriatic ecosystem has remained largely unassessed. This study demonstrates that locally collected rain water significantly stimulates primary production and phytoplankton biomass accumulation in microcosm experiments. The concentration of nutrients in rain water collected during summer storms (11.38–77.19 μmol·1^-1 nitrate. 4.45–36.38 μmol.1·1 ammonium, 0.93–4.75 μmol·1^-1 phosphate) indicated that the precipitation is influenced by anthropogenic emissions from urbanised and industrialised regions of the European continent. Rainfall events delivered relatively large (127 tons nitrogen, 9.5 tons phosphorus in the period 10 June to 10 September, 1993). though episodic, nutrient input into the area. Field measurements showed that storm events were followed by an increase of phytoplankton standing crop and a shift of community structure.     

Temporal Variations of Benthic Bacterial Microflora on the Northwestern Mediterranean Continental Shelf and Slope

Abstract. Bacterial (direct and heterotrophic counts, heterotrophic potentials) and organic matter (org C, org N) parameters were studied over 2 years in the surface sediments of 3 stations located on the continental shelf (station A: 15m; station B: 35m) and slope (station C: 910m) in the northwestern Mediterranean Basin.
Although logistic constraints did not allow a satisfactory sampling periodicity in the offshore survey, some seasonal trends were still observable at the deepest station. Variations were quantitatively more important in the two shallow sediments (from 3×10² heterotrophic bacteria – ml^-1 in December 1984 to 10⁷ heterotrophic bacteria-ml^-1 in March 1986). Epifluorcsccncc direct counts were relatively constant (5×10⁸ cells-ml^-1), while heterotrophic potentials (with ¹⁴C labelled glucose and glutamic acid) showed a succession of very short pulses over the year. Different concentrations of organic matter (from 0.2% orgC at 15m to 0.8% orgC at 35m) appeared to sustain very similar bacterial numbers. Nevertheless, a certain relation between the seasonal evolution of bacterial and organic matter parameters was discernable. Although depth apparently had no measurable effect on maximal spring bacterial densities, it seemed to lessen the summer and winter decreases in the two shallow stations.     

Vertical Patterns of Suspended Matter Characteristics Along a Coastal-basin Transect in the Western Baltic Sea

Suspended particulate matter samples were collected from the water column, the bottom nepheloid layer and the ‘ fluffy layer ’ from four stations along a coastal-basin transect in the Pomeranian Bight, western Baltic Sea. Sampling was performed nine times between October 1996 and December 1998 for various analyses, including electron probe x-ray micro analysis for detailed mineralogical investigations.Specific vertical patterns of clay mineral distributions were found. Suspended particulate matter (SPM) in the bottom nepheloid layer and the ‘ fluffy layer ’ overlying sediments was enriched in organic carbon and hydrated three layer clay minerals, whereas the non-aggregated SPM was dominated by quartz and biogenic opal. It appears that separation effects operate during aggregation of mineral particles and organic matter in repeated cycles of resuspension and settling. No clear seasonal variations in the composition of the SPM were found, in spite of high spatial and temporal variability of biological and physical variables. The results suggest that preferential incorporation, possibly aided by microbiological colonization, of hydrated three layer silicates into the organic flocs is a process that occurs under a wide range of conditions. Because aggregates sink faster than individual particles, aggregate formation led to a relative enrichment of illite and smectite in the near-bottom layers. Considering the affinity of organic contaminants and heavy metals to organic matter, the selective removal of aggregated organic matter and hydrated three-layer clay minerals from the water column and enhanced transport in the near-bottom fluffy layer may be a natural cleansing mechanism operating in the shallow waters of the bight.     

Benthic Fluxes of Dissolved Inorganic Nitrogen in a Coastal Lagoon of the Northern Adriatic Sea: an Interpretation of Spatial Variability Based on Sediment Features and Infauna Activity

Abstract. Dark respiration rates, dissolved inorganic nitrogen (DIN) fluxes and nitrification rates were measured at two sites in the microtidal Sacca di Goro lagoon in September 2000. DIN fluxes correlated with the biomass of the dominant macrofauna species (the amphipod Corophium spp. at station Giralda and the polychaete Neanthes spp. at station Faro). Respiration (> 6 mmol O₂ m⁻²h⁻¹) and ammonium fluxes (> 80μmol N m⁻²h⁻¹) were higher at station Giralda despite the lower organic matter content (4.5 %) and lower macrofauna biomass (4 g AFDW m⁻²). At both sites ammonium fluxes were significantly correlated with the biomass of the benthic infauna, but Corophium stimulated ammonium NH₄⁺ fluxes 3-fold compared to Neanthes. The amphipod also enhanced nitrification rates (> 300 μmol N m⁻²h⁻¹) due to the high density of its burrows, the higher NH₄⁺ regeneration rates and the enhanced oxygen supply to the bacteria.     

Nutrients, Chlorophyll a and Phytoplankton in the İskenderun Bay (Northeastern Mediterranean)

Abstract. The monthly changes in chlorophyll a , phytoplankton abundance and nutrient concentrations at two stations, one at the inshore and the other at the deep waters of the northern part of İskenderun Bay, were investigated between 1994 – 1995. The vertical distribution of nutrients and phytoplankton biomass were also studied at the deep station. The concentrations of NO₃+NO₂-N, PO₄-P and SiO₄-Si of surface water at both stations were 0.31 – 1.63 µg-at · l^-1, 0.08 – 0.60 µg-at · l^-1 and 0.50 – 2.7 µg-at · l^-1, respectively. The highest concentrations were measured at the inshore station and clear differences were found between the inshore and deep-water stations. Chlorophyll a concentrations ranged from 0.17 to 2.78 µg · l^-1 and the highest value was measured in March. At the inshore station, which was affected by land run-off, phytoplankton abundance reached the highest value (21,308 cells · l^-1) in October 1995, with a marked dominance of Pseudonitzschia pungens (20,200 cells · l^-1). The nutrient and chlorophyll a concentrations at the inshore station were higher than those at the deep station. One reason for this is the land-based nutrient input into the coastal area here. In spite of these effects, the bay is not eutrophicated because of circulation events in the northeastern Mediterranean.     

Nitrogen Assimilation and Partitioning in the Mediterranean Seagrass Posidonia oceanica

Abstract. The supply of nitrogen (N) often limits the productivity of marine macrophytes. In vitro and in vivo assays of glutamine synthetase (GS) activity were employed to investigate patterns of N assimilation by the Mediterranean seagrass Posidonia oceanica (L.) DELILE. Biomass-specific GS activity wa measured in root tissue, in leaves within a shoot, in shoots collected at two sites during two season and over a depth range of 5–33 m. Root tissue was less important than shoot tissue in assimilating inorganic N in P. oceanica , due both to the small roots' biomass (ca. 3% of total plant biomass and greatly lower (10- to 50-fold) GS activities. While the GS activity and N assimilatory potentia (biomass × GS activity; μmol N-h-^-1) were greatest in leaf 2, leaves 1 and 3–5 assimilated N a significant rates. Shoots from a site characterized by elevated N availability in the winter water column and no significant sediment N reservoir exhibited GS activities that were 9-times higher than shoot from a more oligotrophic site. Shoot GS activities in July increased linearly from 5 to 33 m and wer correlated with light availability as defined by H^sat, (daily period during which photosynthetic reaction are light-saturated). This may represent metabolic compensation by P. oceanica to maintain N influx. Factors contributing to the ecological success of P. oceanica include the ability to assimilate N under conditions of severe light limitation (< 35 μmol photons. m^-2. s^-1), and metabolic plasticity to ensur the de novo generation of N-containing organic compounds.     

Chlorophyll in Copepod Faecal Pellets: Changes in Pellet Numbers and Pigment Content during a Declining Baltic Spring Bloom

Abstract. Zooplankton stock as well as faecal pellet numbers were monitored over 2 weeks during May in the central Baltic. Considerable changes in concentrations of chlorophyll and its derivates in copepod faecal pellets as well as in surface sediments were found during this period. The maximum concentration of 1.05 ngchl. a faecal pellet^-1, measured on 12 May, decreased by the end of the month to 0.08 ngchl. a faecal pellet^-1. This decrease was positively correlated with the disappearance of intact diatoms inside faeces. A flux of 1.53mgchl. a -m^-2-day^-1 via faecal pellets was calculated for the deep water layer (60–80 m) in mid May. This decreased to 0.005mgchl. a m^-2 day^-1 by the end of May. Chi. a accounted for up to 10 % of total pigments in samples from the top centimetre of the sediment surface. The means of transportation of faecal pellets as well as their function as a food supply to deeper ecosystems are discussed.     

Detritus Rolling Down a Vertical Cliff of the Ligurian Sea (Italy): The Écological Role in Hard Bottom Communities

Abstract. The detritus rolling down a vertical cliff was studied at Portofino Promontory (Ligurian Sea, Italy) at 16 m depth (January 1988- January 1989). The large amount of collected sediment is mainly due to the position of the traps; they collected not only the sedimenting material, but also the detritus rolling down along the cliff. The amount of sediment matter is 7 times greater in winter than in summer, showing a good correlation with rough seas and rain that cause a "mechanical cleaning" of animal and plant debris (Sérpulid tubes, shells, exuvias. leaves) along the cliff.
The Total Suspended Matter (TSM) in the water column shows maximum values in March and September. The organic fraction has an average concentration of 0.81 mg 1^-l. The phytoplanktonic biomass, measured as Chi a , shows an annual cycle with a peak in spring (1–2.7μg·l^-1). while in other periods of the year the value is about 0.3-0.5 μg·1^-1. A significant relationship was found between organic detritus in the collected sédiments and the Chi a in the water column. The great influence of the rocky wall detritus on the normal trend of the TSM in the coastal water column is pointed out.     

Primary Production and Growth Dynamics in Posidonia oceanica

Abstract. Studies on leaf growth and production were performed in two stands, at depths of 5 m and 22m, in the Posidonia oceanica (L.) D elile bed off Lacco Ameno, Ischia (Gulf of Naples). Experiments were carried out in situ from May 1988 to August 1989 at monthly intervals.
Leaf growth and production profiles differed in the two stands investigated. Growth rates were higher at 5 m, with a peak in autumn (5.8 mg · shoot^-1· d^-1) and another in March (3.8 mg · shoot^-1· d^-1). At 22 m the maximum rate occurred in May (3.9 mg · shoot^-1· d^-1). These differential growth rates resulted in a delayed maximum leaf surface and biomass at the deep stand, where lower irradiance values and different temperature patterns were also found. The biomass of epiphytic algae showed trends similar to those of leaves; however, there were remarkable differences in the values between the two stations and for the two investigated years.
The production data of the present study are compared with those of other reports, and it is shown that growth processes are greatly influenced by physical factors.     

Population Structure and Secondary Production of the Mediterranean Octocoral Lophogorgia ceratophyta (L. 1758)

Abstract. The gorgonian Lophogorgia ceratophyta thrives in turbid water at Tinetto Rock, La Spezia Gulf, Ligurian Sea. Its age structure suggests that the population is in a steady state; nevertheless, it is difficult to discern whether the main factors controlling this population are biological or event-related. Secondary production was estimated by means of an increment-summation method and yielded 0.54 g ash-free dry weight (AFDW)*m^-1 a^-1. This estimate does not take into account biomass losses due to reproductive output and non-lethal predation. Standing stock biomass was 5.44 g AFDW e m^-2. The annual P/B ratio was 0.10 and turnover time about 10a     

The Diatom Nitzschia sicula (Castr.) Hust. and Naupliar Faecal Minipellets in the Adriatic sea

Abstract. Nitzschia sicula (C astr .) H ust ., a planktonic pennate diatom, dominated the microphytoplankton (10⁴-5 times 10⁴ cells. 1^-1) in the central, oligotrophic Southern Adriatic Pit waters (20-50m layer) in May 1990. Nauplii dominated the microzooplankton (3 indiv. 1^-1in the 0-50m layer, 130 μm mean body length) and produced a considerable amount of faecal (mini)pellets (1900. 1^-1 at 50m, mean diameter 47μm), which were compactly filled with N. sicula frustules. The subsurface accumulation of diatoms and nauplii was probably the result of both productive activity under specific hydrographic conditions and the convergence in a relatively strong southern Adriatic cyclonic gyre; the advective transport of populations along the shear zone, at the boundary between water masses of different thermo-haline characteristics may also have played a role. The amount of minipellets was high if compared with the data available from other seas. This was probably due to high production of minipellets, their slow sinking rate, and/or an absence of manipulation of the faecal material by zooplankton.     

Species composition,abundance and biomass of microphytoplankton in the KwaZulu-Natal Bight on the east coast of South Africa

Nearshore marine environments are influenced by an array of variables that can either be land-derived or of marine origin, and nearshore phytoplankton communities may differ in their taxonomic composition and biomass in response to such variables. The KwaZulu-Natal Bight (hereafter referred to as ‘the bight’) is an oligo-mesotrophic, nearshore oceanic environment, that is influenced by both terrestrial run-off and upwelling. A microphytoplankton survey of the bight conducted over several stations and depths and two seasons was conducted in order to ascertain species composition, abundance and biomass. Microphytoplankton abundance was generally low (a maximum of 180 000 cells l–1 was recorded) but differed considerably between sites and seasons. A total of 99 taxa of mainly Bacillariophyceae and some Dinophyceae, Prymnesiophyceae and Cyanophyceae were identified in the present study. In the central bight, higher abundance and biomass were measured in February (wet season), which may be a possible consequence of terrestrial nutrient inputs. In the northern and southern bight we measured higher abundance and biomass in August (dry season). Upwelling was not detected during the study, but an influence of terrestrial nutrient sources was detected at the coastal stations. Turbid conditions were specific to the site near the Thukela River mouth and possibly influenced abundance, biomass and species composition at this site. Historic data on microphytoplankton composition are scarce, but comparisons with surveys from the 1960s reveal that around 60% of the common diatoms recorded then also occurred in the present study. Small taxa [20–200 µm] dominated the microphytoplankton community. Community composition was fairly uniform throughout the bight in both seasons, dominated in general by Chaetoceros species, and on occasion co-dominated by Thalassionema nitzschioides and Dactyliosolen fragilissimus.     

Variations of Hydrochemical Features in the Coastal Waters of Monte Conero: 1982–1990

Abstract. This paper briefly summarises research carried out in 1982–1990 in the coastal area off Monte Conero, SW northern Adriatic Sea. Oceanographic data on temperature, salinity, oxygen saturation, nutrients (nitrates, silicates and orthophosphates), and chlorophylls were collected to characterise this coastal ecosystem in view of the setting up of the "Costa del Monte Conero" protected marine area.
Towards the coast the physical and chemical parameters exhibited a seasonal periodicity.
Temperature showed a clear annual periodicity with a certain interannual variability; this also holds true for oxygen saturation, with peaks in March and minima in September, though without hypoxic events.
Nutrient concentrations peaked at the surface layer at the coastal station from December to March (nitrates: 35–50 μmol 1⁻¹; silicates: 22–70 μmol 1⁻¹; orthophosphates: 0.37–0.54 μmol 1⁻¹) and minima in summer (Jul-Aug) on surface and bottom (0–12μmol 1⁻¹, 0–18.5 μmol 1⁻¹, and 0–0.15 μmol 1⁻¹, respectively). From 1988 to 1990 nutrient peaks were lower and coastal salinity exceed 33, with nitrates below 16 μmol 1⁻¹, silicates below 8 μmol 1⁻¹, and orthophosphates less than 0.2 μmol 1⁻¹.
In the coastal area of Senigallia, 40 km to the north, where the influence of the coastal current that carries the river inflows to the south is stronger, the seasonal cycle was similar, albeit with higher values for nutrients and chlorophylls.     

The Deep-Water Peyssonnelia Beds from the Balearic Islands (Western Mediterranean)

Abstract. Peyssonnelia bed distribution on continental shelf bottoms of the Balearic Islands (Western Mediterranean) ranges from 40 to 90 m depth. Different species of Peyssonnelia dominate these bottoms and, according to multivariate techniques, two main assemblages have been distinguished: the Peyssonnelia rosa-marina beds and the Peyssonnelia sp. beds, together with some transition samples between Peyssonnelia and maërl beds. Erect red algae are always abundant. Although average yearly irradiance reaching these beds is only 6.4-0.3% of subsurface irradiance, the species richness averages 45 species per sample (1600 cm²) and mean biomass is 2835 g dw. m^-2. The high carbonate content of the living algae of these bottoms suggests that they are important contributors to the production of sediments in the Balearic continental shelf.     

Description of the Phytoplanktonic Community of the Oligotrophic Waters of the SE Aegean Sea (Mediterranean)

Abstract. A seasonal sampling program of five stations off the Island of Rhodes (SE Aegean Sea) was carried out in 1983–1984. Temperature, salinity, Secchi disk transparency, P-PO₄, N-NO₃, N-NO₂, N-NH₃, Si-SiO₂, and chl a were measured and phytoplankton species recorded. Cell concentrations and chl a varied seasonally. with the highest values in summer (l.2 times 10⁴ -1^--¹ total mean cells; 0.13 mgam^-3 total mean chl a ) and the lowest in winter (2.3 times 10³, 1^--¹ total mean cells; 0.06 mg^.m-^- total mean chl a ). A variation in cell abundance among stations was also noted. Quantitative relationships among the recorded taxa showed that diatoms and dinoflagellates were richer in species composition (88 and 58 total species, respectively) than coccolithophores (8 species) and other flagellates (8 species). Comparison of phytoplankton samples from different depths and stations by cluster analysis showed an irregularity or discontinuity in species associations. The SE Aegean Sea was characterized as oligotrophic on the basis of the estimated nutrient and phytoplankton concentration levels.     

Respiratory Rate and Assessment of Secondary Production in the Holothuroid Holothuria tubulosa (Echinodermata) from Mediterranean Seagrass Beds

Abstract. Respiration in Holothuria tubulosa was investigated in individuals from the Posidonia oceanica meadow off Lacco Ameno (Ischia Island, Italy). Respiratory rates increase with increasing body weight and increasing sea water temperature. Oxygen consumption of an average individual (7g dw body wall) ranges from 0.409 (14 °C) to 1.300 (26 °C) mg O₂· h^-1. Data on population density, mean size of individuals, and annual sea water temperature variations allow an assessment of holothuroid production. Values of 45.65 and 13.75 kJ · m^-2· y^-1 were calculated for shallow (3 to 10 m) and deep (25 to 33 m) areas of the Posidonia meadow, respectively. Holothuroid production shows a bathymetric pattern similar to primary production of the Posidonia -epiphytes complex and the production of Posidonia litter.