SEVENTH FRAMEWORK PROGRAMME Area 6.4.1.2. Cross-cutting research activities relevant to GEO ENV.2008.4.1.2.1. Monitoring and observing oxygen depletion throughout the different Earth system components
Deliverable D 4.2 “Report on assessment of changes in oxygen availability using organic and inorganic proxies, benthic communities structure, and hypoxia indicator species”, month 30 Editor: Namik Çagatay (ITU-EMCOL) with all partners of WP4
Project acronym: HYPOX Project full title: In situ monitoring of oxygen depletion in hypoxic ecosystems of coastal and open seas, and land-locked water bodies Grant agreement no.: 226213
Date of preparation: 03 October 2011, revisions: 09 & 19 January 2012
TABLE OF CONTENTS
1.INTRODUCTION...... 3
2.INORGANIC AND ORGANIC GEOCHEMICAL PROXIES...... 4
2.1.Inorganic geochemical studies in the Istanbul Strait (Bosphorus) Outlet Area of Black Sea (ITU-EMCOL)...... 4
2.2.Inorganic Geochemical Studies Lake Rotsee and Lake Zurich(EAWAG)...... 13
2.3.Porewater Phosphorus-Iron Dynamics in the Eckernförde Bay (SW Baltic Sea) (IFM-GEOMAR)...... 17
2.4.Inorganic and Organic Studies in Baltic Sea, Black Sea and meromictic lake Alat (Fuessen Bavaria) (MfN)...... 20
2.5.Natural radionuclides and Cesium studies in the Greek Lagoons (Amvrakikos Gulf)...... 21
2.6.Noble Gases in the Black Sea (EAWAG)...... 27
2.7.Biomarkers studies in the Lake Rotsee and Lake Zurich (both Switzerland), Amvrakikos Gulf (Greece) and the Black Sea(EAWAG)...... 29
3.BENTHIC COMMUNITIES AND HYPOXIA INDICATOR SPECIES...... 34
3.1.Benthic communities structure and hypoxia indicator species in the Crimean shelf and Istanbul Strait‟s (Bosporus) outlet area of Black Sea (IBSS)...... 34
3.2.Macrobenthos studies on the Romanian Shelf (GeoEcoMar)...... 58
3.3.Benthic foraminifera studies in the Amvrakikos Gulf (UPAT)...... 109
2 1. INTRODUCTION
This report summarizes the changes in oxygen availability using organic and inorganic proxies, benthic communities‟ structure, and hypoxia indicator species in the Black Sea shelf areas (Istanbul Strait outlet area, Crimean shelf and Sevastopol area, and the Romanian shelf), Amvrakikos Gulf (Greek Lagoons) in the Ionian Sea, Swiss Lakes (Lake Zurich and Lake Rotsee), and Eckernförde Bay (Germany) in the Baltic Sea. The main objectives are to reconstruct the recent and past changes in the redox conditions using geochemical proxies and to give brief information about structures of the benthic communities and species that indicate hypoxia in the various basins.
In the Bosphorus outlet area (Turkey) of the Black Sea, geochemical analyses of cores were carried out by the ITU team to study the hypoxia history and the effects of Mediterranean water in the ventilation of the area, using XRF core scanning and TOC/TIC analysis. Benthic community and indicator species studies were carried out by the IBSS, together with the CTD casting by MPI in the area.
Lipid biomarkers were studied in Lake Rotsee and Lake Zurich by Eawag. For the latter study site, trace metals were additionally analyzed. Eawag project members focused on lipid biomarkers in the Amvrakikos Gulf, and UPAT determined the age model of the obtained cores and foraminiferal assemblages. In the Black Sea, Eawag project members are still analyzing the sediment pore-water samples for noble gas concentrations, and results are not available at this point. In addition, UPAT studied natural radionuclides and Cs distributions in sediment cores in the Amvrakikos Gulf.
Pore water geochemistry was analysed for phosphorus-iron dynamics in the Eckernförde Bay (Germany) in the Baltic Sea by the IFM-GEOMAR. Nitrogen and carbon isotopes were studied by MfN in sediment cores in northern Baltic Sea (Bottenwiek). MfN further studied purple sulphur bacteria in Lake Alat (Bavaria, Germany). These studies by MfN were carried out in the frame of an MSc and a BSc theses.
Benthic population structure and hypoxia indicator species in the Black Sea shelf areas (Istanbul Strait outlet area, Crimean shelf and Sevastopol area, and the Romanian shelf) were studied by IBSS and GeoEcoMar.
3 2. INORGANIC AND ORGANIC GEOCHEMICAL PROXIES 2.1. Inorganic geochemical studies in the Istanbul Strait (Bosphorus) Outlet Area of Black Sea (ITU-EMCOL)
Site description: İstanbul Strait (Bosphorus) is the only connection of Black Sea to the world ocean via Sea of Marmara and Çanakkale (Dardannelles) Strait. The İstanbul Strait outlet area of the Black Sea (ISBS) includes the shelf and upper slope areas north of the Strait (Fig. 1.1; Hypox D4.3, 2010). This area is characterized by the Mediterranean inflow that is responsible for the ventilation and sluggish deep circulation of the anoxic Black Sea basin (Oğuz et al., 1993; Özsoy and Ünlüata, 1997). The anoxic/oxic boundary is located at a depth of 100-150 m with a ~30 m thick suboxic zone (Murray et al., 1989; 1993; Codispoti et al., 1991; Baştürk et al., 1994). Presently, a two-way current system occurs in the Bosphorus channel, with the Black Sea water forming the upper current and the warm and saline Mediterranean Water (MW) the undercurrent (Özsoy and Ünlüata, 1997; De Iorio et al., 1999; Özsoy et al., 2001).
The MW enters the ISBS shelf through the submarine extension of the Istanbul Strait‟s channel, and then spreads as a uniform 2-3 m thick saline sheet over the shelf. At depths of 50-75 m, it mixes with the Cold Intermediate Water (CIW) and sinks along the continental slope forming a series of lateral intrusions to depths of 500 m.
The ISBS outlet area is also characterized by a fan-delta complex on the mid and outer shelf areas with an anastomosing distributary channels, 5-8 m high levées, in-channel stream-lined bars, crevasse splays, and NW-SE oriented linear to wavy sedimentary structures in between the channel-levée complexes (Fig.2.1) (De Iorio and Yüce, 1998; Flood et al., 2009, Hypox D.4.3, 2010; Okay et al., 2011). Shallow sill depth of the Istanbul Strait together with the oxygen consumption by organic matter mineralization is responsible for the establishment of a permanent oxic-anoxic boundary (chemocline) in the area. The oxic-anoxic boundary is presently at 100-150 m depth, but may have varied in the past as result of the changes in the amounts of the MW, of riverine water input and global sea level.
4
Fig.2.1. Multibeam bathymetric map of the Istanbul Strait (Bosphorus) outlet area. Bathymetry data is compiled by Okay, et al., (2011) from NATO expedition of Di Iorio and Yüce (1999) and BLaSOn2 expedition (2002) carried out with Le Suroit and Dokuz Eylül University, Turkey. The shelf edge is marked by 110 m bathymetric contour that markes a change from green to blue colour.
Cores and Core analysis: Geophysical subbottom profiling and sediment coring along depth transects from -75 m to -307 m on the shelf and upper slope areas onboard RVs Arar and MS Merian were carried out within the framework of the EC FP7 Hypox project (Fig.2.2). A total of 81 cores and 4 long cores were analyzed for physical properties using Geotek Multi-Sensor Core Logger (MSCL;), 42 cores for elemental analysis by Itrax XRF Core Scanner, and 22 cores for total organic (TOC) and inorganic (TIC) contents by Shimadzu TOC analyser. 17 core samples were dated by AMS C-14 analysis. The core data produced by Hypox project in the ISBS outlet area can be found in data portal PANGAEA Archive /http://www.pangaea. de/search?count=10&q=arar_2009+geochemistry&minlat=&minlon=&maxlat=&maxlon=& mandate=&maxdate=&env=All&offset=20 and http:// www.pangaea.de/ search?count =10&q =MSM15%2F1+geochemistry&minlat=&minlon=&maxlat=&maxlon=&mindate=&maxdate =&env=All&offset=0), and the discussion in Erdem (2011, MSc Thesis).
Holocene Basin Evolution: High resolution seismic profiles and sedimentary cores show the evidence of two low stand shelf crossing unconformities: a post-Younger Dryas transgression
5 unconformity (α) and a younger unconformity (α1) that form the base of the channel-levée complex dated at ca. 7 14C kyr BP (Fig.2.3, Fig.2.4) (Aksu at al., 2002; Ryan et al, 2003;
Major et al., 2006; Flood et al., 2009; this Hypox study). The α1 unconformity was formed by the subaqueous erosion by the latest saline Mediterranean inflow and subsequent deposition of the fan-delta complex under mainly submarine conditions.
Fig.2.2. Bathymetric map of the Istanbul Strait‟s outlet area in the Black Sea, showing the location of the seismic lines and cores.
Results of Inorganic Geochemical Studies: The anoxia development started after the latest connection with Mediterranean. The oxic/anoxic boundary and changes in the bottom water conditions in the slope area are detectable by changes in the lithological properties and Mn anomalies associated with the Fe-C-S system in the cores located between -120 m and -150 m, which show the rise of the oxic/anoxic boundary to depths between -120 m and -150 m around 6.8 ka BP (Fig.2.5 and Fig.2.6).
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Fig.2.3. A part of the seismic profile SL-1 representing water depths of 90-95 m on mid shelf area. The sedimentary units on top belong to the channel-levée complex that is sampled by Core MSM015- 291 whose digital colour image is shown on the right with the AMS C-14 ages. The unconformity α1 is a flat surface at -98 m. The sediments below the unconformity is dated at ca. 10 ka BP (post Younger Dryas). Vertical exaggeration = 8.1. See inset map for location of the line shown with red rectangle on Line SL-1.
Mediterranean inflow initially used the NW trending main channel transporting oxygenated waters to the western side of the area. This NW transport stopped at 5.3 ka BP. Anoxic bottom water conditions started to prevail in the western area at that time as a result of this change in the direction of the inflow. The ventilation effect of MW on the seafloor can be observed in the eastern part of the outlet area down to at least -307 m (depth limit of the transects) as indicated by high Mn counts on the XRF scanner profiles (Fig.2.7). Such Mn anomalies in upper slope cores, not associated with Fe and S anomalies are probably formed by deposition of Mn (II) from the water column. In the western part of the area Mn profiles do not show high counts on XRF scanner profiles (Fig.2.8) (Erdem, 2011). In addition to Mn anomalies, the transition from oxic to anoxic conditions are shown by changes in mud colour from gray green through gray and dark gray to black, and by the disappearance of the euryhaline bivalves and benthic foraminifera. Lithological differences and benthic fauna are visible in optical and radiographic images obtained by XRF core scanner and given in Figs 2.5 to 2.9. In these figures the optical digital colour image is shown on the left and gray scale
7 digital radiographic image and the right as columnar sections. In the radiographic images, the increased intensity of grey scale indicates increased intensity of the sediment.
A recent rise in the oxic/anoxic interface is determined in a sedimentary core collected at -83 m. This rise is indicated by increased values of Mn-Fe-S at 7-13 cm interval and higher TOC values above 13 cm core depth, corresponding to intersection of the oxic/anoxic interface with the shelf area (Fig.2.9) (Erdem, 2011). A recent age of 505 14C years (uncalibrated) was obtained from 21-23 cm of this core. This age is too recent to calibrate, but suggest that the event at 7-13 cm depth interval is recent and possibly correlates with an event dated around 250-300 a BP by Lyons et al. (1993) at 10 cm core depth in the same area, using radionuclide techniques.
Fig.2.4. A part of the seismic profile SL-4 water at depths of 85-90m on mid shelf area, showing the levée deposits of a distributary channel. The sedimentary units on top belong to the channel-levée complex that is sampled by Core MSM015-235 whose digital colour image is shown on the right with the AMS C-14 ages. The unconformity α1 overlain by sediments dated ca. 7 ka BP. Vertical exaggeration = 8.2. See inset map for location of the line shown with red rectangle on Line SL-4.
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Fig.2.5. XRF and TOC/TIC results of sediment core G17B collected from -120 m depth in the western part (SL8) of the area above the present oxic/anoxic interface. The wide column on the right is digital colour image and the narrow column is the grey digital radiographic image. Grey shaded area indicates a lower unit with abundant benthic shells showing oxygenated bottom water conditions. Yellow shaded area on top represents a redox front developed in the sediment under oxic water conditions (see text for details). Elemental concentrations are in cps. See Fig.2.2 for core location.
Fig.2.6. XRF and TOC/TIC results of sediment core 245 collected from -152 m depth in the eastern part (SL1) of the area below the present oxic/anoxic interface. Grey shaded area indicates oxygenated bottom water conditions by high values of Mn, Ca, TIC, changes in Fe and S values, as well as shell abundance and colour changes observed in the optical and radiographic images. Above the boundary, minor Mn fluctuations not associated with Fe and S show the MW ventilation effect. Elemental concentrations are in cps. See Fig.2.2 for core location.
9
Fig.2.7. XRF and TOC/TIC results of sediment core 192 collected from -307 m depth in the eastern part (SL1) of the area below the present oxic/anoxic interface. MW ventilation effect is indicated by Mn fluctuations not associated with Fe and S throughout the core length. Elemental concentrations are in cps. See Fig.2.2 for core location.
In the Istanbul Strait‟s (Bosphorus) outlet area, the redox changes and anoxia history have been unravelled using Mn and Fe-C-S system. Oxic/ anoxic boundary and changes in the bottom water conditions in the slope area are detectable by Mn, S and Fe anomalies in the cores, which show the rise of the redox boundary to depths between -120 m and -150 m by ca. 6.8 ka BP. As a result of this study, the change in the direction (eastward shift) at 5.3 ka BP and ventilation effect of Mediterranean inflow can be observed. In the eastern part of the outlet area down to at least -307 m, ventilation effect of MW is indicated by high Mn counts on the XRF scanner profiles until today; these Mn anomalies are unassociated with Fe-S counts. A recent (250-300 a BP) shoaling event is recorded by Mn anomalies associated with Fe and S anomalies in a core collected from western side of the study area where MW ventilation effect is not observed today.
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Fig.2.8. XRF and TOC/TIC results of sediment core 311 collected from -307 m depth in the western part (SL8) of the area below the present oxic/anoxic interface. Grey shaded area indicates past oxygenated bottom water conditions before 5.3 ka BP also indicated by changes in the colours in optical and radiographic image. Lighter grey area shows the transition zone from oxic to anoxic bottom water conditions. There is no evidence of MW ventilation effect above the transition zone as shown by the uniformly low Mn counts. Elemental concentrations are in cps. See Fig. 1.2 for core location.
Fig.2.9. Ti normalized Mn-Fe-S element profiles and TOC/TIC results of sediment core G18 collected from -83 m depth in the western part (SL8) of the area above the present oxic/anoxic interface. Yellow shaded area with enrichment of Mn-Fe-S record suggests oxic/anoxic shoaling. Elemental concentrations are in cps. See Fig.2.2 for core location.
11 References Aksu, A.E., Hiscott, R.N., Kaminski, M.A., Mudie, P.J., Gillespie, H., Abrojano, T., Yaşar, D., 2002. Last glacial-Holocene paleoceanography of the Black Sea and Marmara Sea: stable isotopic, foraminiferal and coccolith evidence. Marine Geology 190, 119-149. Baştürk, Ö., Saydam, C. Salihoğlu, I., Eremeeva, L.V., Konovalov, S.K., Stoyanov, A., Dimitrov, A., Cociasu, A., Dorogan, L. and Altabet, M., 1994. Vertical variation in the principle chemical properties of the Black Sea in the autumn of 1991, Marine Chemistry, 45: 149-165. Codispoti, L.A. Friederich, G.E., Murray, J.W., and Sakamato, C.M., 1991. Vertical variability in the Black Sea: Implications of continuous vertical profiles that penetrated the oxic/anoxic interface, Deep-Sea Res., 38(2A): 691-710. Di Iorio, D., Akal, T., Guerrini, P., Yüce, H., Gezgin, E. And Özsoy, E., 1999. Oceanographic Measurements of the West Black Sea: June 15 to July 5, 1996. Report SR- 305, SACLANTCEN; NATO, La Spezia Di Iorio, D., and Yüce, H., 1998. Observations of Mediterranean flow into the Black Sea: Journal of Geophysical Research v. 104, no. C2, p. 3091-3108. Erdem, Z., 2011.Sedimentary Record of Mediterranean Inflow Effect on Redox Conditions of Istanbul Strait Outlet Area of Black Sea.MSc thesis, Eurasian Institute of Earth Sciences.79 pages. Flood, R. D., Hiscott, R. N., and Aksu, A. E., 2009. Morphology and evolution of an anastomosed channel network where saline underflow enters the Black Sea: Sedimentology, 56: 807-839. Hypox Report D4.3., 2010. Report on coring, marine geological and geophysical surveys, 71 pages. Lyons, T.W., Berner, R.A., Anderson, R.F., 1993.Evidence for large pre-industrial perturbations of the Black Sea chemocline, Nature 365, 538-540. Major, C.O., Goldstein, S.L., Ryan, W.B.F., Lericolais, G., Piotrowski, A.M. and Hajdas, I., 2006.The co-evolution of Black Sea level and composition through the last deglaciation and its paleoclimatic significance,Quaternary Science ReviewsVolume 25, Issues 17-18, Pages 2031-2047. Murray, J.W., Jannasch, H.W., Honjo, S., Anderson; S., Reeburgh, W.S., Top, Z., Friederich, G.E.,Codispoti, L.A. and Izdar, E., 1989.Unexpected changes in the oxic/unoxic interface in the Black Sea, Nature, 338: 411-413. Murray, J.W., Friederich, G.E., Codispoti, L.A., 1993.The suboxic zone in the Black Sea, in C.P. Huang, C.R. O‟Melia and J.J. Morgan (eds.), Aquatic Chemistry, Advances in Chemical Series No. 244, Am. Chem. Soc.,Washington DC. Oğuz, T.,Latun, V.S., Latif, M.A., Vladimirov, V.V., Sur, H.I., Markov, A.A., Özsoy, E., Kotovshchikov, B.B., Eremeev, V.V., Ünlüata, Ü.,1993.Circulation in thesurfaceandintermediate layers of the Black Sea, Deep-Sea Res. Part I 40, pp. 1597-1612.
12 Okay, S., Jupinet, B., Lericolais, G., Cifci, G., and Morigi, C., 2011. Morphological and Stratigraphic Investigation of a Holocene Subaqueous Shelf Fan, North of the Istanbul Strait in the Black Sea. Turkish Journal of Earth Sciences 20, 287-305. Özsoy, E., Di Iorio, D., Gregg, M. C., and Backhaus, J. O., 2001. Mixing in the Bosphorus Strait and the Black Sea continental shelf: observations and a model of the dense water outflow: Journal of Marine Systems, 31: 99-135. Özsoy, E., and Ünlüata, Ü., 1997. Oceanography of the Black Sea: a review of some recent results, Earth-Science Reviews, 42, 231-272. Ryan, W.B.F., Major., C., Lericolais, G. and Goldstein., S.L., 2003.Catastrophic Flooding Of the Black Sea.Annu.Rev. Earth Planet. Sci. 31, 525-554.
2.2. Inorganic Geochemical Studies Lake Rotsee and Lake Zurich(EAWAG)
Site descriptions of Lake Rotsee and Lake Zurich (Switzerland): Lake Rotsee (Fig. 2.10 and 2.11) is a small (0.46 km2) prealpine, monomictic and eutrophic lake with a maximum depth of 16 m. The lake has a stable stratified water column with a strong chemocline between about 6 and 10 m depth and an anoxic hypolimnion throughout most of the year (Schubert et al., 2010). Eutrophication caused by the input of untreated sewage supply began to impact the lake about 150 years ago (Stadelmann, 1980). In short, the high sewage input into the lake led to high nutrient contents and an elevated productivity (Bloesch, 1974). The sedimentation rate was 0.375 cm/yr, obtained from 137Cs and 210Pb dating (Fig. 2.12). The mesotrophic Lake of Zurich (65 km2) has a maximal depth of 136 meters (Livingstone, 2003). Long-term monitoring data (1936-today) including oxygen concentrations exist. This lake is highly sensitive to changes in climate, namely temperature changes, showing simultaneous climate- driven deep water warming and cooling episodes with a tendency towards oligomixis (Livingstone, 1997). The sediments of Zürichsee were varved with intercalations of turbidites. The correlation of the cores and the age model was based on varve counting. The sedimentation rates were about 0.28 cm/yr for all cores, based on varve counting (Fig. 2.15).
Sampling stations Lake Rotsee and Lake Zurich (Switzerland): Lake Rotsee (Fig. 2.10 and 2.11): 50-60cm long sediment cores were obtained from a water depth of 16 m (maximum lake depth)in October 2009 (GPS position N 47° 4.251 E 8° 18.955, WGS84).
13
N
Lake Zurich
Lake Rotsee
Fig. 2.10. and Fig. 2.11. Map with the location of the studied Swiss lakes and aerial image of Lake Rotsee with the location of the sampling station.
Fig. 2.12. Both age models of Lake Rotsee. The first age model was based on 137Cs activity, with the peaks of the Chernobyl nuclear reactor accident (1986, at 8-9 cm) and the nuclear bomb test (1967/1968, at 18-19 cm). The second age model was based on the 224Ra-210Pb system. Both age models show very similar sedimentation rates, averaging 0.4 cm/yr.
14 Lake Zurich (Fig. 2.13, 2.14, 2.15): Sediment cores were taken at 3 locations in water depths of 45 m (51 cm long core), 109 m (94cm long core) and 139 m (110 cm long core, maximum lake depth).
Fig. 2.13.and 2.14. Map of Lake Zurich (Strasser et al., 2008), the red box is enlarged in Fig. 2.14, which also shows the sampling stations.
Fig. 2.15. Photograph of core ZH-5 (136 m water depth) with the age model obtained from varve counting. The laminated sediment is intercalated with turbidites (grey coloured).
15 Inorganic markers, i.e. trace metals, were analyzed in the sediment cores of Lake Zurich using the high-resolution XRF core scanner at ETH Zurich. Iron and manganese distributions showed a seasonal pattern in Lake Zurich (Fig. 2.16). Due to half-year lamination patterns and calcium abundance changes within the year, we could establish a very precise age model that allowed us to observe this seasonality of trace metals (Fig. 2.16). Our results suggest that the higher abundance of iron during fall/winter could depend on when the first traces of oxygen reach the sediments, on the dilution of calcium, or on an increased supply of iron during winter. However, we also observed higher abundances of manganese during spring, which correlated well with higher bottom water oxygen concentrations. Therefore, manganese traces oxygenation of the bottom water during spring when the lake mixes completely.
Fig. 2.16.Fullsediment core profile and the section spanning 1980-1990 for iron (Fe), manganese (Mn), calcium (Ca, together with lamination used for age model determination), XRF counts and oxygen concentration data.
References Livingstone, D.M., 1997. An example of the simultaneous occurrence of climate-driven "sawtooth" deep-water warming/cooling episodes in several Swiss lakes. International Association of Theoretical and Applied Limnology, Vol 26, Pt 2, 26: 822-828. Livingstone, D.M., 2003. Impact of secular climate change on the thermal structure of a large temperate central European lake. Climatic Change, 57(1-2): 205-225.
16 Schubert, C.J. et al., 2010. Oxidation and emission of methane in a monomictic lake (Rotsee, Switzerland). Aquatic Sciences - Research Across Boundaries, 72(4): 455-466. Stadelmann, P., 1980. Der Zustand des Rotsees bei Luzern. In: Quartierverein-Maihof (Ed.), Geschichte und Eigenart eines Quartiers. Quartierverein Maihof, Luzern, pp. 54-61.
2.3. Porewater Phosphorus-Iron Dynamics in the Eckernförde Bay (SW Baltic Sea) (IFM-GEOMAR)
Site description: Boknis Eck is a small channel located at the northern entrance of Eckernförde Bay (54 31‟N, 10‟20 E) and has a water depth of about 28 m (Fig.2.17). From mid-March until mid-September, vertical mixing is restricted by density stratification of the water column, which leads to pronounced periods of hypoxia during late summer due to microbial respiration of organic material in the deep layer and sediment (Fig.2.18). Autumn storms and a decrease in surface water temperature cause a mixing of the water column and ventilation of the deeper water layers with increased nutrient concentrations.
Fig.2.17. Location (black square) of the time series station Boknis Eck in the Eckernförde Bay (SW Baltic Sea).
The sediments at the study site in Boknis Eck are classified as fine grained muds (< 40 µm) with a carbon content of 3 to 5 wt % (Balzer et al., 1986). With no significant terrestrial runoff, the bulk of organic matter within Eckernförde Bay sediments originates from marine plankton and macroalgal sources. The dominant fauna in the sediments in winter/spring are the polychaetes Pectinariakoreni and Nephtys ciliate with recorded abundances of 201-476
17 and 63-122 individuals m-2, respectively (Graf et al., 1982). Specimens up to 10 cm long were present during winter sampling. Bacterial mats were absent on the surface of Boknis Eck sediments at the time of sampling, but Beggiatoa are present below the sediment surface at the redox interface at the top of the sulfide layer (Preisler et al., 2007). In late summer 2010 when the bottom waters became almost anoxic, a blackening of the surface sediments and colonization by Beggiatoa filaments was observed.
Sampling time and resolution: Monthly multi-core samples with core length of ca. 30 cm were obtained from Eckernförde Bay (SW Baltic Sea) from February 2010 until January 2011.
Phosphorus-Iron dynamics: During 2010, the sediments at a 28 m deep site in the Boknis Eck channel (Fig.2.17) were sampled monthly and analyzed for their major nutrients and geochemical constituents. The data were used to constrain a benthic model to study the benthic cycling of redox sensitive elements and investigate how the pathways of organic matter degradation and biogeochemical fluxes across the sediment-water interface respond to changing O2 concentrations. The model includes organic matter degradation by aerobic and anaerobic respiration pathways and can be used to quantify the total rate of O2 depletion in the sediment. An example of the model application to data from winter 2010 can be found in Dale et al. (2011) when oxygen levels in the bottom waters were high (Fig.2.18b).
Bottom water oxygen levels are well known to affect the dynamic of phosphorus and iron, which are often highly coupled (Krom and Berner, 1981). Oxygen levels decreased through spring into summer and by autumn the bottom water became anoxic. Selected porewater 2+ 3- profiles, including ferrous iron (Fe ) and phosphate (PO4 ), are shown in Fig.2.18a. The data show how the concentrations of both species increase rapidly from September to October following the onset of anoxia. Reductive dissolution of iron oxide minerals and release of 3- iron-adsorbed PO4 very likely explains these observations. To interpret these findings 3- quantitatively, the numbers at the top of the figure panels denote the diffusive fluxes of PO4 out of the sediment in mmol m-2 d-1. The flux increased by a factor 10 from 0.4 mmol m-2 d- 1in September and 4.2 mmol m-2 d-1 in October, remained fairly high in November and then returns to background levels in December when fully oxic conditions are restored in the bottom water.
18 0.4 4.2 1.4 0.5 (a) Sep Oct Nov Dec
(b) S O N
Fig.2.18. (a) Measured porewater concentrations of phosphate and ferrous iron in the upper 30 cm of Boknis Eck sediments during autumn 2010. The red lines approximate the concentration gradients in the surface layers, and the diffusive fluxes calculated from these slopes are shown above the panels. (b) Measured bottom water (28 m) oxygen concentrations during 2010 at Boknis Eck (September, October and November samplings are indicated).
The results demonstrate the dynamicity of the sediments over the short autumn anoxic period and the potential importance of the benthos in supplying nutrients to the water column for the 3- 3+ following spring. Ongoing work will address whether the PO4 and Fe fluxes out of the sediments are determined directly by the onset of anoxia or indirectly by animal mortality and hiatus in bio-irrigation.
19 References Balzer, W., Pollehne, F., Erlenkeuser, H., 1986.Cycling of organic carbon in a coastal marine system. In: P.G. Sly, Editor, Sediments and Water Interactions, Springer Verlag, New York pp. 325–330. Dale, A. W., Sommer, S., Bohlen, L., Treude, T., Bertics, V. J., Bange, H. W., Pfannkuche, O., Schorp, T., Mattsdotter, M., Wallmann, K.(in press.,2011). Rates and regulation of nitrogen cycling in seasonally hypoxic sediments during winter (Boknis Eck, SW Baltic Sea): sensitivity to environmental variables. Estuarine, Coastal and Shelf Science. Dale, A.W., Sommer, S., Pfannkuche, O., Wallmann, K. Changes in Fe and P redox dynamics in marine sediment during the onset and recovery of seasonal bottom water hypoxia. Planned submission 2012. Graf, G., Bengtsson, W., Diesner, U., Schulz, R., Theede, H.,1982. Benthic response to sedimentation of a spring phytoplankton bloom: Process and budget. Marine Biology 245, 201-208. Krom, M. D. Berner, R. A., 1981. The diagenesis of phosphorus in a nearshore marine sediment. Geochimica et CosmochimicaActa 45, 207-216. Preisler, A., de Beer, D., Lichtschlag, A., Lavik, G., Boetius, A., Jørgensen, B. B., 2007.Biological and chemical sulfide oxidation in a Beggiatoa inhabited marine sediment. The ISME Journal 1, 341-353.
2.4. Inorganic and Organic Studies in Baltic Sea, Black Sea and meromictic lake Alat (Fuessen Bavaria) (MfN)
In the frame of a master thesis in geosciences at the Freie University Berlin three short (Jacob 2011) sediment cores were studied for the impact of eutrophication in the northern most Baltic Sea (Bottenwiek). Results indicate that during the past hundred years the area of the Bottenwiek was eutrophied only to a small extent. However, sedimentary d15N and d13C(TOC) show clear trends towards higher values in more recent sediments (the last 2 decades) indicating the increasing bioproductivity and more nutrients in that area (Jacob, 2011).
In the frame of a BSc thesis in geosciences at the Freie Universität Berlin the physico- chemical stratification and stability of the meromictic and anoxic Lake Alat was studied with respect to influence of the dense population of purple sulphur bacteria on the nitrogen cycle. Green or purple sulphur bacteria had probably a significant impact in the nitrogen cycle during phases of strong anoxia in earth history (Falk, 2011).
20 Water samples and surface sediments obtained from the short cores are used for the analysis with a sub-decadal resolution. Ages are obtained by the 210Pb-dating method.
Planned publications are; 1)Fritz G.B., Pfannkuchen M., Struck U., Hengherr S., Strohmeier S. & Brümmer F. (in press) Characterizing an anoxic habitat: sulphur bacteria in a meromitic alpine lake. In: J., Seckbach (Ed.) /Anoxia: Fossils, Anaerobic and Microaerophiles./ Cellular Origin, Life in Extreme Habitats and Astrobiology, Springer Verlag. 2) Struck U. (in press).On the use of stable nitrogen isotopes in present and past anoxic environments. -In: J., Seckbach (Ed.) /Anoxia: Fossils,Anaerobic and Microaerophiles./ Cellular Origin, Life in Extreme Habitats and Astrobiology, Springer Verlag.
References
Falk, M., 2011.Physico-chemical stratification and stability of the meromictic lake Alat. - BSc thesis Geosciences, Freie Universität, Berlin, Supervisor: M. Schneider, 27pp.
Jacob, J., 2011.Ablagerungsgeschichte des anthropogenen Einflusses in der nördlichen Ostsee während der letzten 100 Jahre. - MSc-Thesis, Geoscience, Freie Universität Berlin, Supervisor: U. Struck, 84pp.
2.5. Natural radionuclides and Cesium studies in the Greek Lagoons (Amvrakikos Gulf)
Site description: Amvrakikos Gulf is a shallow (< 65m) marine semi-enclosed embayment lying on the west coast of Greece and having a surface of some 405 km2 and a coastline length of 256 km. It is separated from the open Ionian Sea by a beach barrier complex and is connected to the open sea through a narrow channel, 600 m wide and less than 8 m deep. On the basis of the bathymetry, the Gulf can be divided into the western part which is formed by a number of small basins (water depth less than 40 m) and the eastern part that is characterised by a deep basin (water depths up to 65 m) (Kapsimalis et al., 2005) (Fig. 2.19). The northern margin of the Gulf is dominated by the extensive deltas of Arachthos and Louros rivers and associated lagoons.
The Gulf receives freshwater inputs of 2202 x106 m 3 yr -1 and 609 x106 m3 yr -1, by Arachthos and Louros rivers, respectively. As a result, the Gulf is characterised by a well-stratified two
21 layer structure in the water column made up of a surface layer and a bottom layer that are separated by a strong pycnocline.
Fig. 2.19. Bathymetric map of Amvrakikos Gulf showing sediment sampling locations.
At the entrance over the sill, there is a brackish water outflow in the surface water and a saline water inflow in the near-bed region (Ferentinos et al., 2010, Papatheodorou et al., in preparation) (Fig. 2.20). This morphology and water circulation pattern makes the Amvrakikos Gulf the only Mediterranean Sea fjord (Ferentinos et al., 2010). The surface layer is well oxygenated, whereas just below the pycnocline the dissolved oxygen (DO) declines sharplyand finally attains a value of zero, thus dividing the water column into oxic, dysoxic and anoxic environments (Ferentinos et al., 2010, Papatheodorou et al., in preparation) (Fig. 2.21). During the winter oxygenation of the western shallow basin was observed while the eastern deep basin remained under hypoxia (Ferentinos et al., 2010, Papatheodorou et al., in preparation) (Fig. 2.21). At the dysoxic/anoxic interface, at a depth of approximately 35 m, a sharp redoxycline develops with Eh values between 0 and 120 mV occurring above and values between 0 and -250 mV occurring below, where oxic and anoxic biochemical processes prevail, respectively (Ferentinos et al., 2010). Measured current speeds in the central part of the Gulf demonstrate mean values ranging from 0.03 up to 0.19 m s−1 (in winter). Fast currents have been reported in the Preveza Straits ranging from 0.12 to 0.15 m s−1 with some bursts reaching 1 m s−1.
22
Fig. 2.20. Seasonal profiles of salinity in the Amvrakikos Gulf
Fig. 2.21. Seasonal profiles of dissolved oxygen in the Amvrakikos Gulf
23 Low-grade phosphate ores are located in Epirus area at the northern part of the drainage basins of Louros and Arachthos rivers (Varti-Mataraga et al., 1988). Mineralogical analyses showed that the phosphates ores in Epirus are synsedimentary calcareous phosphate deposits consisting of francolite (carbonate fluorapatite) and calcite as the main minerals and having low vulnerability to erosion (Economou et al., 2002).
Natural radionuclides and Cesium distributions in the sediment cores: Activity concentration of natural radionuclides (238U, 232Th, 226Ra, 40K) and man-made 137Cs were determined in sediment cores collected from 5 different sampling sites from the Amvrakikos Gulf (Fig. 2.19). The total concentrations of Fe and Mn were also determined and compared to total U concentration. To obtain information on the distribution of metals and radionuclides in various chemical fractions of the sediments, sequential extraction procedures (BCR) were used.
The enhanced uranium activity levels found in the sediment samples and the disequilibrium between 238U and 232Th are mainly associated with the phosphate fertilizer inputs in the Gulf via the rivers (Athanassopoulos et al., 2012)(Fig. 2.22 and 2.23). The highest 238U activities and the highest values of U/Th ratio were observed at the uppermost part of the sediment cores (Athanassopoulos et al., 2012) (Fig. 2.22 and 2.23). Moreover, the sequential extraction results further support the above interpretation (Athanassopoulos et al., 2012) (Fig. 2.24). A significant percentage of uranium was found in the mobile fractions, which might be attributed to an input of phosphate fertilizers that hold radioactive materials, especially uranium, in the Gulf, and to a lesser extent to the transport of weathering products of the phosphate rocks by surface and ground waters. Cesium (137Cs) was found in measurable concentrations (5.2 – 20.2 Bq kg-1) in all surface sediments (0-8 cm), while higher activity concentrations of 137Cs were found in the deeper sediment layers than in the surface one, suggesting a high sedimentation rate for the Amvrakikos Gulf (Athanassopoulos et al., 2012).
Preliminary results of excess 210Pb activity concentrations for the collected sediment cores showed sedimentation rates ranging from 0.3 to 0.6 cm/yr. These sedimentation rates suggest that the Cs peak due to 1986 Chernobyl accident is expected to be at a depth of about 7.2-14.4 cm and that of the 1963 nuclear weapon testing fallout peak at a depth between 14.4-28.2 cm below the present day seabed. Due to the fact that the collected surface sediment samples had a thickness of 0-6 to 0-10 cm, the Chernobyl peak could not clearly be recorded. The higher Cs activity concentration found at the depth of 20 cm in sediment core St2 could be
24 presumably attributed to the 1963 fallout peak (Fig. 2.25). On the other hand, the elevated Cs activity concentration found in the sediment core St9 at 12cm downcore depth indicates either the Chernobyl accident or the 1963 nuclear weapon testing fallout. Higher resolution Cs data and the final 210Pb data will provide the chronological framework upon which the sea bottom conditions will be examined based on microfauna (foraminifera) (see 3.2 paragraph).
Fig. 2.22. Downcore distribution of 238U activities in the sediment cores collected from Amvrakikos Gulf.
Fig. 2.23. Downcore distribution of 238U/232Thin the sediment cores collected from Amvrakikos Gulf.
25 Core 2 Core 9 Core 13 Core 16 100%
80%
60% Residual BCR C Step BCR B Step 40% BCR A Step
20%
0% U U U U U U U U U U U U 2/1 2/5 2/7 9/1 9/3 9/5 13/1 13/4 13/6 16/1 16/3 16/4
Fig. 2.24. Diagram showing the results of Sequential extraction results (BCR) for 238U in sediment samples collected from Amvrakikos Gulf.
Fig. 2.25. Downcore distribution of 137Cs in the sediment cores collected from Amvrakikos Gulf.
References
Athanassopoulos D., H., Papaefthymiou, G., Papatheodorou, M., Iatrou, M., Geraga, D., Christodoulou, E., Fakiris, 2012. Physical and chemical associations of natural radionuclides and 137Cs in the sediments of a Mediterranean fjord-like embayment, Amvrakikos Gulf (Ionian Sea), Greece. (Submitted for publication). Economou, E. D., Vaimakis, T. C., and Papamichael, E. M., 2002. The kinetics of dissolution of the carbonate minerals of phosphate ores using dilute acetic acid solutions: The case of pH range from 3.96 to 6.40. J. Colloid Interface Sci. 245, 133-141. Ferentinos, G., Papatheodorou, G., Geraga, M., Iatrou, M., Fakiris, E., Christodoulou, D., Dimitriou, E., Koutsikopoulos, C., 2010. Fjord water circulation patterns and dysoxic/anoxic conditions in a Mediterranean semi-enclosed embayment in the Amvrakikos Gulf, Greece. Estuarine, Coastal and Shelf Science 88 (4), pp. 473-481.
26 Kapsimalis, V., Pavlakis, P., Poulos, S.E., Alexandri, S., Tziavos, C., Sioulas, A., Filippas, D., Lykousis, V., 2005. Internal structure and evolution of the Late Quaternary sequence in a shallow embayment: The Amvrakikos Gulf, NW Greece. Marine Geology, 222- 223 (1-4), pp. 399-418. Varti-Mataraga, M., Papastaurou, S., Perdikatsis, V., Petridou-Nazou, V., Pitsikas, L., Pomoni-Papaioannou, F., and Skourti-Koronaiou, V., 1988. Bull. Geol. Soc. Greece 20, 343 [in Greek].
2.6. Noble Gases in the Black Sea (EAWAG)
Black Sea cores studied consisted of multi-corer cores between 30-50 cm long, noble gas cores up to 2.5m long, and reference cores up to 2.5m long. All cores are from the Crimean and the Romanian Shelf and from sampling stations offshore of the Bosporus Strait outlet area (Fig.2.26).
Fig. 2.26. Map of the Black Sea and the general location of sampling stations.
In the Black Sea we aim to reconstruct hypoxia through determination of atmospheric noble gases (He, Ne, Ar, Kr and Xe) in the pore-waters of unconsolidated sediments (Brennwald, 2004; Tomonaga, 2011a) at different water depths using sediment cores taken from three different locations. Pore-water samples were collected from sediment cores collected in three regions (Fig. 2.26): near the outlet of the Bosphorus Strait (3 cores), the Crimean Shelf (3 cores) and the Romanian shelf (3 cores). The Bosphorus core sites were chosen to represent
27 oxic (96.4 m), hypoxic (159 m) and anoxic (300 m) zones, as well as attempting to obtain samples above and below past anoxic boundaries, and hypothesized freshwater shorelines. The noble gas content could give insight into salinity and oxygen conditions before and after the Mediterranean-Bosporus connection. The three Crimean core sites were also chosen for oxic (103.9 m), hypoxic (156.4 m), and anoxic (205.9 m) conditions. Additionally, these measurements showed a large temporal variation in oxygen concentration at the hypoxic site. The 3 Romanian cores were taken in two locations on the Romanian shelf, in a seasonally oxic to anoxic (110 m) and a permanently anoxic water depth (210 m). The latter core has undergone preliminary dating and likely reaches as far back as 10-11.5 ka. It is anticipated that through the diversity of the three sites, the noble gas measurements could provide very interesting insight into past variations in oxygen and salinity along the Black Sea shelf.
Our hypothesis is based on the relationship between salinity changes and water column stability (salinity induced stratification), which, during times of stronger stratification, suppresses mixing and results in the depletion of oxygen in bottom waters. In order to evaluate the potential of noble gases as a record of oxygen abundance, we will focus on the transitions of unit 1, 2 and 3, which represent the evolution of the Black Sea from a rather oxic, limnic basin into a brackish, hypoxic, anoxic and euxinic state. Furthermore, depletion of noble gases in sediment cores can potentially trace methane ebullition. The noble gases are stripped from the pore water by the methane bubbles that form in the sediment, eventually releasing into the water column and the atmosphere as observed previously in the sediments of Lake Soppensee in Switzerland (Brennwald et al., 2005). Therefore, noble gases could be a tracer for methane production in the sediment. Analysis of the collected sediment samples is ongoing and results should become available in the coming months.
References Brennwald, M. S., 2004. The use of noble gases in lake sediment pore water as environmental tracers. Diss. ETH Nr. 15629, ETH Zurich. Brennwald, M. S., Imboden, D. M., and Kipfer, R., 2005.Release of gas bubbles from lake sediment traced by noble gas isotopes in the sediment pore water. Earth Planet. Sci. Lett., 235(1-2):31–44, doi:10.1016/j.epsl.2005.03.004. Tomonaga, Y., Brennwald M. S., and Kipfer, R., 2011a. An improved method for the analysis of dissolved noble gases in the pore water of unconsolidated sediments. Limnol. Oceanogr. Methods, 9:42-49, doi:10:4319/lom.2011.9.42.
28 2.7. Biomarkers studies in the Lake Rotsee and Lake Zurich (both Switzerland), Amvrakikos Gulf (Greece) and the Black Sea(EAWAG)
The high-resolution Lake Rotsee biomarker study revealed a complete eutrophication history dating back to the 1850s. We observed times of higher primary productivity especially around 1920 and in the 1960s, as indicated by the TOC and TOC accumulation rates (Fig. 2.27) and as previously described by Lotter (1989). This high productivity can be explained by high nutrient input from the catchment through agriculture and untreated sewage (Lotter, 1989; Stadelmann, 1980).
Periods of higher productivity resulted in enhanced stratification, as indicated by higher Tetrahymanol concentrations (Sinninghe Damsté et al., 1995) beginning in the 1920s (Fig. 2.28). The coincidence of high TOC values with higher concentrations of C16:1ω7 fatty acid (Fig. 2.28), an indicator for higher biomass of iron-, manganese and sulphate-reducing bacteria (Wakeham et al., 2007), suggest times of more intense or longer hypoxia in the lake as a result of the higher productivity, probably due to higher OM remineralisation rates.
Furthermore, the higher productivity resulted in an enhanced supply of organic matter (OM) to the sediments, which increased the overall hypolimnetic oxygen demand. Higher abundances of methanogens in the sediment were evidenced due to δ13C depleted (average of about δ13C=-30 to -40‰ VPDB) GDGT-0 (glycerol dialkyl glycerol tetraether) concentrations, indicating increased emissions of methane into the water column. The coincidence of higher TOC values with higher GDGT-0 abundance in the 1920s (Fig. 2.29) suggest higher methane production rates due to higher OM supply to the sediments, a relationship found previously by Bastviken et al. (2004). The onset of higher methane production resulted first in a radiation of aerobic methane oxidisers, traced by strongly δ13C depleted (<-50‰ VPDB) 17β-21β-bishomohopanoic acid and diploptene (Peckmann and Thiel, 2004; Spooner et al., 1994). With delay, anaerobic methanotrophic Archaea increased in abundance, which was traced by higher Archaeol, sn2- and sn3-hydroxyarchaeol concentrations (Fig. 2.29) (Hinrichs et al., 2000). The source of these markers could be shown due to their very negative δ13C signatures below -50‰ VPDB. Since the construction of a sewage treatment plant in 1974, the lake is slowly recovering, as indicated by a slight TOC decrease.
The Chromatiaceae derived pigment okenone and the pigment isorenierantene which is derived from Chlorobiaceae could be detected in Lake Rotsee, but the concentrations were too
29 low to be quantified. Both markers are indicators for photic zone euxinia, suggesting at least temporally established anoxic conditions penetrating into the photic zone (Brocks et al., 2005; Brocks and Schaeffer, 2008; Pfennig and Trüper, 1981).
Fig. 2.27. Profiles of TOC and TIC accumulation rates in Lake Rotsee.
Fig. 2.28. Profiles of C16:1ω7 FA and Tetrahymanol concentrations in Lake Rotsee.
30
Fig. 2.29. Concentration profiles of biomarkers related to the methane cycle in Lake Rotsee.
In Lake Zurich lipid biomarker degradation is probably dependent upon oxygen abundance in the water column. Such a relationship would explain why lower concentrations of biomarkers were found at shallow water depths (core ZH-6 at 109 m, in contrast to core ZH-5 at 136 m, Fig. 2.14) along with higher oxygen concentrations, resulting in larger degradation rates for the shallow core ZH-6 (Fig. 2.30). The shorter-chained saturated fatty acids (FA) are degraded more rapidly compared to longer-chained FA (Fig. 2.30).
Fig. 2.30. Degradation rate coefficients k for saturated fatty acids in Lake Zurich (exponential fit of biomarker depth profiles in the cores with Excel Solver, according to Niggemann and Schubert (2006).
31 Amvrakikos Gulf Site: Amvrakikos Gulf (Fig.2.31): 30cm long cores were obtained from 2 locations in water depths of 29 and 39 m, labelled as cores (Amv) 15 and 13, respectively.
Fig. 2.31. Map of Amvrakikos Gulf with the two sampling stations.
Results: All results for the Amvrakikos Gulf and the Black Sea are preliminary. For the Amvrakikos Gulf, we found higher terrestrial contributions at the sampling station near the Preveza strait. Two biomarkers, isorenieratene and chlorobactene, which indicate at least seasonal photic zone anoxia (Brocks et al., 2005), could be identified in the Amvrakikos Gulf, but not quantified due to their low abundance. We plan to combine biomarkers and benthic faunal data, supported by other geochemical parameters, to reconstruct hypoxia in this embayment. Additionally, we will comparethe development of hypoxia in the Amvrakikos Gulf and the Black Sea, showing similarities and differences between these two sites.
Sediment cores age models: According to the radionuclide core analysis (Fig. 2.12), the sediment cores from Lake Rotsee extend back about 150 yrs; for Lake Zurich, the longest record is from a 139 m water depth and covers at least the last 110 yrs (Fig. 2.15). Precise dating of the lower limit was not possible due to high amounts of turbidites and lack of distinct lamination. The cores from the Amvrakikos Gulf still need to be dated while the longest Black Sea core dates back about 10-11.5 kyrs.
Biomarker analyses of Lake Rotsee cores have a resolution of about 3 years in the upper 30 cm, but the resolution increases below this depth. For Lake Zurich, the sediment core resolution is up to 5 years in the upper part of the core. Radiometric age determination is still ongoing for cores from the Amvrakikos Gulf and the Black Sea.
32 References
Bastviken, D., Cole, J., Pace, M., Tranvik, L., 2004. Methane emissions from lakes: Dependence of lake characteristics, two regional assessments, and a global estimate. Global Biogeochemical Cycles, 18(4). Brocks, J.J., Love, G.D., Summons, R.E., Knoll, A.H., Logan, G.A., Bowden, S.A., 2005. Biomarker evidence for green and purple sulphur bacteria in a stratified Palaeoproterozoic sea. Nature, 437(7060), 866-870. Brocks, J.J., Schaeffer, P., 2008. Okenane, a biomarker for purple sulfur bacteria (Chromatiaceae), and other new carotenoid derivatives from the 1640 Ma Barney Creek Formation. Geochimica Et Cosmochimica Acta, 72(5): 1396-1414. Hinrichs, K.U., Summons, R.E., Orphan, V., Sylva, S.P., Hayes, J.M., 2000. Molecular and isotopic analysis of anaerobic methane-oxidizing communities in marine sediments. Organic Geochemistry, 31(12): 1685-1701. Lotter, A.F., 1989. Subfossil and Modern Diatom Plankton and the Paleolimnology of Rotsee (Switzerland) since 1850. Aquatic Sciences, 51(4): 338-350. Niggemann, J., Schubert, C.J., 2006. Fatty acid biogeochemistry of sediments from the Chilean coastal upwelling region: Sources and diagenetic changes. Organic Geochemistry, 37(5): 626-647. Peckmann, J., Thiel, V., 2004. Carbon cycling at ancient methane–seeps. Chemical Geology, 205(3-4): 443-467. Pfennig, N., Trüper, H.G., 1981. Isolation of members of the families Chromatiaceae and Chlorobiaceae. In: Starr, M.P., Trüper, H.G., Balows, A., Schlegel, H.G. (Eds.), The prokaryotes. Springer, pp. 279–289. Sinninghe Damsté, J.S. et al., 1995. Evidence for Gammacerane as an Indicator of Water Column Stratification. Geochimica Et Cosmochimica Acta, 59(9): 1895-1900. Spooner, N. et al., 1994. Stable carbon isotopic correlation of individual biolipids in aquatic organisms and a lake bottom sediment. Organic Geochemistry, 21(6-7): 823-827. Stadelmann, P., 1980. Der Zustand des Rotsees bei Luzern. In: Quartierverein-Maihof (Ed.), Geschichte und Eigenart eines Quartiers. Quartierverein Maihof, Luzern, pp. 54-61. Wakeham, S.G. et al., 2007. Microbial ecology of the stratified water column of the Black Sea as revealed by a comprehensive biomarker study. Organic Geochemistry, 38(12): 2070- 2097.
33 3. BENTHIC COMMUNITIES AND HYPOXIA INDICATOR SPECIES 3.1. Benthic communities structure and hypoxia indicator species in the Crimean shelf and Istanbul Strait’s (Bosporus) outlet area of Black Sea (IBSS)
In line with Task 4.4 and D 4.1, an extensive study of the benthic community structure and hypoxia indicator species was carried out by IBSS in the Crimean shelf and Istanbul Strait‟s (Bosporus) outlet area of the Black Sea. The samples for the studies and the data on oceanographic and benthic environmental conditions were collected during the Hypox cruises on board RVs Arar and M. S. Merian during November 2009 and April/May, 2010. In the coastal zone of the Crimea, sampling was made every 45 days throughout the year. The analyses in the water column involved CTD and dissolved O2, and in sediment pore waters dissolved O2 and H2S concentrations.
Sediment sampling for the biological studies were carried out using multi-corer (TVMUC), push-corer and box corers. At each station, the sediment cores were sampled in 0-1, 1-2, 2-3, 3-5 cm below sea floor (cmbsf) intervals.
Crimean shelf: Five selected areas for the HYPOX project were studied: 1) Dnepr Canyon (Paleo-Delta), 2) Tarkhankut seeps, 3) Sevastopol areas: Omega (Kruglaya) Bay, 4) Sevastopol Bay: inner part (Yuzhnaya bay), 5) Sevastopol Bay: outer part (reference site).
IBSS focused its studies on the changes in taxonomic structure, quantity and biomass of modern meiobenthos in response to seasonal hypoxia in the environment in the above target coastal sites of the Crimea. The structure and distribution of meiobenthic fauna was analyzed from the seafloor to 5-7 cm sediment depth. Oceanographic and O2 and H2S (by voltametric profiling) concentrations in the sediment pore waters were carried out at a sub-millimeter vertical resolution to a depth of 100 - 400 mm below seafloor.
Sampling interval in coastal zone of the Crimea was every 45 days. An additional sampling cruise was carried out in the Paleo Dnepr region during the April-May 2010.
Tarkhankut seeps: The cape Tarkhankut is the most western part of Crimea (Fig.3.1), where there are no anthropogenic and industrial sources of pollutants. The most prominent natural feature of this region is the presence of shallow methane seeps. Seeps are distributed along an axis of the Kalamit Ridge.
34 The flow of methane from the sediments to the water column at this site ranges from 17 µl·dm-2·day-1 for well-aerated sites with strong oxidizing conditions to 81700 µl·dm-2·day- 1 (58,000 mkg·dm-2·day-1) for sediment with active processes of methane genesis (Fig.3.2).
Fig.3.1. Study area at the Tarkhankut Cape
Fig.3.2. The flow of methane from the sediments to the water column at Tarkhankut Cape (July 2010)
Results of voltametric profiling of all sediment cores retrieved on different seasons reveal the presence of sulphide inside the bacterial mat, when the mat existed. The usual vertical profile of sulphide in porewater demonstrates an increase of the concentration of sulphide from zero or minimal values at the surface of sediments to the highest values at a depth of 40 to 70 mm.
35 An interesting feature is the decline in the vertical distribution of sulphide concentrations with depth below 10 cm. Though the source of methane is located deeper in sediments, methane consuming bacteria need also an oxidizer (oxygen, oxidized forms of nitrogen, manganese, iron, or sulphate) and nutrients to make oxidation of methane possible and to build up bacterial biomass. As sources of methane, oxidizers, and nutrients are located in different layers, there is a depth of the optimal ratio of their fluxes.
The only time of sulphide absence in the bottom sediments is the period of winter storms, when bacterial mats are completely disintegrated and sandy material is well washed to reveal any presence of bacterial biomass. As soon as sediments are undisturbed for several weeks, a new bacterial mat is formed resulting in suboxic and anoxic/sulfidic conditions. Thus, an average annual cycle of redox conditions consists of two seasonal periods - minimal or no sulphide period of winter storms and the sulphide maximum at the end of summer. The minimal concentrations of sulphide were about 50 µM at the depth of 25 to 60 mm with no or extremely low concentration of sulphide in the upper 15 mm of sediments and the concentration of oxygen as high as 250 µM in waters located 2 to 3 mm above the surface of sediments. On the time of maximum concentrations of sulphide at the end of summer, the sulphide concentrations can easily reach 1500 µM and it was almost 3000 µM in September of 2009. The concentration of sulphide reached 1000 µM at the surface of sediments that revealed extremely high vertical gradients of sulphide and oxygen. In September of 2009, waters were oxygenated at the distance of 10 cm above the mat, but oxygen disappeared at the distance of 2 mm above the mat. Sulphide appeared and its concentration sharply increased with depth. In December of 2009, the vertical distribution of oxygen and sulphide was different. There was oxygen at the surface of the mat, but its concentration decreased with depth and oxygen disappeared at the depth of 4 mm. Sulphide was detected within the mat, but its maximum concentration had decreased by two orders of magnitude (Fig.3.3 and Fig.3.4).
The meiobenthos density in the upper 5 cm layer of sediments varies widely depending on redox conditions. The population density varies during the day for each of the sites. Meiobenthos communities were provided with plenty of bacterial organic matter, but a limited flux of oxygen at the redox habitat. The abundance of meiobenthos is higher and it ranged from 97·103 to 632·103ind/m2 and from 243·103 to 800·103ind/m2 at two reference sites during the day.
36 05.09.2009 12-00 05.09.2009 19.00 06.09.2009 7-00
November 2009 June 2010
Fig.3.3.The vertical distribution of oxygen and sulphide in the sediments of the Tarkhankut region
Fig.3.4. Seasonal variations in the distribution of oxygen and sulphide in porewaters of methane fed microbial mat.
An expected (classical) distribution of the abundance and diversity of meiofauna has been observed at the reference site, where these characteristics are the highest in the upper layer. Contrary to this, the meiofauna abundance in the sulfidic sediments is higher in the lower
37 sediment layers where the hydrogen sulphide concentration reaches its maximum. At the same time, taxonomic richness is similar in all layers (see also D4.3report the taxonomic richness and number of main meiobenthos taxa in horizons of the bottom sediment column under high H2S concentration and under normoxia (reference site).
Indicator species: Harpacticoida relating only to one species of Darcythompsonia fairlensis (Scott, 1899) have been found at a depth of 3.5 cm of the anoxic/sulfidic bacterial mat in September 2009. Interestingly, these species have never been reported for the Black Sea. Analysis of the vertical distribution of D. fairlensis in the sediments from the surface to a depth of 7 cm with an interval of 1 cm showed the highest concentration of species in a layer of 4-5cm, where oxygen is absent, and high concentrations of hydrogen sulphide is present. In this layer of sediments, adult females, males, and copepodites at different stages have been found.
Data for July 2010, when „alive‟ samples were analyzed, very the same data were obtained. We found alive and actively moving individuals of D. fairlensis, which proved their tolerance to these environmental conditions. At the reference site, in normoxia, Harpacticoida species composition was more diverse, but these species were absent.
D. fairlensis is one of the few species of the order Harpacticoida, which is known to inhabit anoxic and hypoxic environments in other seas (Cristoni et al, 2004). This is endobenthic species, as it usually exists in shallow waters on decaying plant material. Following its distribution, "the ancestral stock of Darcythompsonia could have originated in the equatorial Tethys Sea at during the Late Triasic - Early Jurassic periods" (Gomez, 2000).
Thus, rich well-developed populations of the harpacticoids species D. fairlensis have been found in anoxic sediments and they may used as an indicator of hypoxic conditions.
Our studies of the response of main taxa and the depth of penetration of fauna in anoxic / sulfidic sediments demonstrate that some benthic fauna is adaptive to toxic H2S environment.
Sevastopol areas: Seasonal changes oxygen concentrations were studied in water column. Attendant factors in near-bottom layer water column and hydrogen sulphide in bottom sediments were studied in target sites. Different sources of organic carbon (urban in the Omega Bay and industrial in the Sevastopol Bay) may effectively support hypoxia or anoxia of bottom sediments from different regions.
38 The method of voltametric profiling including application of a glass Au-Hg microelectrode is used to collect pioneer data on high resolution vertical profiles of oxygen, dissolved sulphide, oxidized and reduced iron, reduced manganese, and iron mono sulphide in pore waters and to study regional variations in chemistry of sediments in the bays near Sevastopol. It is shown that vertical distribution of red-ox species is governed by a combination of three major factors – content of organic carbon, content of reactive iron, and the particles‟ size of sediments.
O2 and H2S concentrations in the pore water in bottom sediments column in target sites were measured in 2009-2010. On the target station were detected: temperature, salinity, O2, PO4,
Silicates, NO3, NO2, NH4 BOD5 (D3.4Tabel. 2 and Tabel. 3).
Parallel to this we analyzed distribution of meiobenthic fauna from surface of sediment to 5-7 cm depth. Some meiobenthos species as indicators of hypoxia in coastal area are revealed.
Sevastopol Bay: The inner part of the Bay has regular hypoxic events as result the effects of anthropogenic/industrial pollution last decades and restricted water exchange and low freshwater input (Fig.3.5). Biogeochemical conditions of sediments in the bay's environment are so extreme that hypoxia had become a regular feature of the inner part of the bay on summer time. To make matter worse, sediments are sulfidic and serve as a source of hydrogen sulphide for the bottom layer of water and make influence on the benthic communities.
Nutrients are released to the bay with the Black river waters and with urban and industrial waste waters providing intensive eutrophication of the bay. Besides, artificial piers at the bay's entrance dramatically limited the intensity of water exchange between the bay and the open part of the sea (Romanov et al., 2007). As the result, the sediments in bay are reached in organic carbon, which is on average 4%, but may locally reach 7%. Such sediments support intensive consumption of oxygen both in sediments and from the near-bottom layer of water and this result in anoxic and hypoxic conditions (Orekhova and Konovalov, 2009).
39
Fig.3.5.Study sited of Sevastopol Bay (Inner and Outer parts)
Sediments in the inner part of the Sevastopol Bay are always anoxic / sulphidic, but the concentration of sulphide does not increase dramatically. We observed temporal variations of hydrogen sulphate concentrations in the bottom sediment column, whereas O2 is observed only on the sediment‟s surface. H2S appeared in 2 - 20mm of depth depending on the season.
Concentration of H2S is low during all the period of investigations (Fig.3.6).
We have demonstrated that oxygen does not penetrate to sediments deeper than 2 mm. Sulphide is traced in the upper 10 mm layer of sediments. Sometimes, sulphide presents at the surface of sediments supporting the flux of sulphide from sediments to water.
The outer part of the bay is still rather clean (see Fig. 2.5). This part is actually a paleo river bed of the same river that currently releases its waters in the head of Bay. Intensive alongshore currents effectively mix and transport pollutants off the coastal sources and the bay. Hypoxic events have never been reported for the waters of the outer part of the Sevastopol Bay and the oxygen content is under influence of natural seasonal changes in T-S properties and biological activities.
Outer part of Sevastopol Bay was chosen as a reference site. Similar to other sites, the oxygen concentrations increase from summer to winter due to the increase in oxygen solubility (Fig.3.7). As compared to the other sites, BOD remains rather constant and at the minimum level due to a less heavy load of OM and more intensive ventilation in all seasons.
The Kruglaya (Omega) Bay is located at the shoreline of Sevastopol city, but no industrial objects are located around the bay (Fig.3.8). Instead, there are resorts, parks and apartment buildings at its coast. The water exchange is restricted due to the shape of the bay with a
40 broader inner part and a narrower outlet. There are several beaches at the coast of the bay, but no technological objectives are located in its vicinity. Thus, anthropogenic pressure is presented by urban waste waters.
Small depths, rather weak ventilation on summer time, discharge of municipal waste waters results in hypoxic conditions at the bottom. Concentrations of oxygen in water column typically increase from summer to winter due to more intensive ventilation. Yet, biochemical oxygen demand (BOD) also increases from summer to winter suggesting that the load of OM remains constant, but the rate of OM respiration decreases with the drop of temperature. Inorganic nitrogen does not expose a straight forward pattern, but the highest concentration of NH4 corresponds to the maximum of BOD, while nitrate increases in line with oxygen.
July 2009 September 2009 October 2009
O2, µM O2, µM O2, µM 0 50 100 150 200 250 0 50 100 150 200 250 0 50 100 150 200 250 bottom layer of water bottom layer of water 0 0 bottom layer of water 0
20 20 20
40 40 40
60 60 60
m
m
m
m m
80 m 80 80
,
,
,
h
h
h
t t
100 t 100 100
p
p
p
e e
120 e 120 120
D
D D 140 140 140 160 160 160 180 180 180 200 200 200 0 0.5 1 1.5 2 0 0.5 1 1.5 2 0 0.5 1 1.5 2 H2S, µÌ H2S, µM H2S, µM
December 2009 January 2010
O , µM 2 O2, µM 0 50 100 150 200 250 0 50 100 150 200 250 bottom layer of water bottom layer of water 0 0
20 20
40 40
60 60
m m
m 80
m 80
,
,
h h t 100
t 100
p
p e
120 e D D 120
140 140
160 160
180 180
200 200 0 50 100 150 200 250 0 0.5 1 1.5 2 H2S, µM H2S, µM Fig.3.6. The vertical distribution of oxygen and sulphide in the sediment core from the Sevastopol Bay (inner part)
41 July 2009 October 2009 January 2010
O2, µM O2, uM 0 50 100 150 200 250 300 350 400 450 0 50 100 150 200 250 300 350 400 450 O2, µM 0 50 100 150 200 250 300 350 400 450 bottom layer of water 0 0 bottom layer of water 10 0 20 20
30 20
m
m m
m 40
40 m
,
,
h
h
m t
t 50
p 40
,
p
e
e
h t
D 60
D 60 p 70 e
D 60 80 80
90 80 100 100 0 10 20 30 40 0 2 4 6 8 H2S, µM H2S, uM 100 Fig.3.7.The vertical distribution of oxygen and sulphide in the sediments from the Sevastopol Bay (outer part)
Fig.3.8. Study site at (Kruglaya) Omega Bay
We traced extremely low concentrations of oxygen in the near-bottom layer of water and in the upper layer of sediments in July of 2009.Sulfide was detected in the near-bottom layer of water and it increases in sediments reaching its maximum of 818.1 µM at the depth of 19 mm, and it decreased with depth, but remained above 140 µM within the profiled core. Yet, this situation is highly dynamic. It varies inter-annually. Thus, the situation was different in September of 2009 both in terms of the concentrations and vertical distribution of oxygen and sulphide. Those changes were rather expected because the water column stratification had decreased and the intensity of vertical exchange, thus the downward flux of oxygen, had increased from summer to fall. Yet, the bottom sediments remained anoxic / sulfidic below 40 mm, though the concentration of sulphide had decreased (Fig.3.9).
42 July 2009 September 2009 December 2009
O2, H2S, µM O2, µM O2, µM 0 200 400 600 800 1000 0 50 100 150 200 250 300 350 0 50 100 150 200 250 300 350 bootom layer of water bottom layer of water bottom layer of water 0 0 0 10 10 10 20 20 20
30 30 m 30 40 m
m 40
m
m
, ,
40 h
m 50 h
t 50
t
,
p
p e h 50 60
e 60
t
D p 70 D
e 60 70
D 70 80 80 90 80 90 100 90 100 110 110 100 0 5 10 15 20 25 30 0 5 10 15 20 25 30 110 H2S, µM H2S, µM Fig.3. 9.The vertical distribution of oxygen and sulphide in the sediment cores in the Omega Bay
Unlike in the Omega Bay, the redox conditions in the Sevastopol Bay are more stable and hypoxia is a quasi-permanent feature of this system. Local and seasonal hypoxia on bottom of the Sevastopol bays and its impact on benthos were studied. Abundance of every macro – and meiobenthos size groups were shown different dependence on the changes of depth of hydrogen sulphide appearance in the bottom floor in all three points in the Sevastopol region. Such varied benthos densities could indicate to an influence of hypoxia on benthos. In general, abundance of the benthic animals usually decreases nearing of the hydrogen sulphide boundary to the bottom surface. Such reaction is more visible for high abundant taxa.
Total macrobenthos abundance decreases with hydrogen sulphide boundary coming closer to the bottom ground surface (Fig.3.10). Among the taxonomic groups the same fact was revealed in Annelida and Bivalvia. At the same time Gastropoda reaction differed in separate points, and Crustacea abundance increased with H2S approaching to the bottom ground surface. (Zaikaet all, 2011).
The series of data, ranged according to the depth of the hydrogen sulphide appearance has been created. This series was considered to be an indicator of a degree of hypoxia. When the data were ranged in accordance with hydrogen sulphide appearance in the core, then three distinctive groups of locality were revealed: (1) H2S is observed in the surface of bottom sediments and even in near-bottom water, (2) H2S is appeared at the depth 2 - 4 mm in the core, (3) H2S is registered at the depths 12 – 36 mm in the core.
43 60 000
50 000
40 000 2
30 000 Ind.m 20 000
10 000
0 VII. 09 VIII. 09 X. 09 XII. 09 I. 10 III. 10 V. 10 VII. 10
Yuzhnaya Bay Reference site Omega Bay
Fig.3.10.Total macrobenthos quantity in three points: Yuzhnaya bay, Omega bay and reference site.
At the same time all the samples from Yuzhnaya bay are fallen within third group, the samples from reference site – within the second and third groups, and the site in Omega bay shows the most variable results. H2S boundary reached the seafloor in Omega Bay in July and December, but in October it was at the sediment depth of 36 mm. That is why benthos response is more distinctive just in Omega Bay. It was compared with general benthos quantity, with its main taxa group‟s abundance (Fig.3.11).
Fig.3.11.Dependence of total macrobenthos abundance on the depth of hydrogen sulphide appearance in sediment cores (continuous line – Omega bay, dash line – united data for two other points).
Note that the macrobenthos abundance decreases as the sulphide boundary approaches the seafloor, and that higher the abundance (as in Omega Bay), the more significant is the dependence.
44 The local and seasonal differences are shown up in the dynamics of meiobenthos abundance in the studied sites (Fig.3.12). Abundance of meiobenthos in the Sevastopol Bay and reference site in contrast to abundance in the Omega Bay reached its maximum by July 2009. In Omega maximum of abundance in May 2010 was observed (Fig.3.12). Taxonomic structure and the dominant groups were changing during study period. In gastropodes, crustacea (in macrobenthos) and nematodes (in meiobenthos), we revealed a contrary tendency: the closer to surface is the hydrogen sulphide boundary, the more is their abundance. This is clearly observed in nematodes, among which quite a lot of species prefer hypoxic habitats.
2000
1750
1500
1250
1000
750
500 thousand ind./m2 thousand 250
0 July Sept Oct Dec Jan March May July
Sevastopol Bay Reference site Omega
Fig.3.12. Dynamics of general quantity of meiobenthos is in three sites
Indicator species: It was recorded 15 species of Harpacticoida in the inner part of Sevastopol Bay. Herewith Haloschizophera pontarchis was dominated the community under strong hypoxic conditions.
At the Kruglaya Bay the seasonal dynamics of Harpacticoida species was observed. At the moment when oxygen concentration drops significantly in the bottom sediment, the Harpacticoida species composition changes were registered. Thus, it was found 12 species with dominating of Darcythompsonia fairliensis in July 2009 when in October 2009 under normoxic conditions interstitial species Scotopssyllus sp. (gen. Scotopssyllus) was dominated and D. fairliensis was found absent.
45 It is noted that D. fairliensis from Kruglaya Bay had appeared and attained maximum densities only under reduced conditions at the sediments. As be marked higher, rich well- developed populations of the harpacticoids species D. fairlensis have been found in anoxic sediments in the Tarkhankut Cape region.
It is thus; two species H. pontarchis and D. fairlensis (Copepoda, Harpacticoida) may be as an indicator of hypoxic conditions in bottom sediments at coastal zone of Crimean shelf. The analysis of species composition of other main groups of the meiobenthos is proceeding.
The İstanbul Strait (Bosporus) outlet area: The transition between hypoxic, but non-sulfidic bottom water and the anoxic/sulfidic zone in the Black Sea is the ideal area to search for animals thriving under hypoxic conditions. We investigated the response of the benthic fauna on oxygen depletion in this zone at the Bosporus Strait region and in the Crimean Shelf area along a water depth transect between 100 and 300m.
Benthic fauna analyses suggest that the oxic/anoxic transition zone supports a high abundance and rich protozoan and metazoan life. In this study, we identified „live‟ protists and other organisms based on Rose-Bengal staining. At the same time we have done direct observations of “alive” bottom fauna using microscopy on board the research vessel. We registered in situ active indigenous fauna of some forms of benthic ciliates, hydroids and nematodes in the hypoxic and anoxic/hydrogen sulphide conditions of the depths region 150- 300 m.
Altogether, these results confirm our earlier conclusion about a possible adaptation of some benthos forms to hypoxia/anoxia and the hydrogen sulphide environment. Our data suggest that some of the organisms (gromiids, allogromiids, hydrozoa, nematodes, and polychaetes) have indeed adapted to live under hypoxic/anoxic and sulfidic conditions in the Black Sea. This fauna is indigenous, rather than having been transported from adjacent oxygenated areas.
IBSS studied sediment cores in the Near-Bosporus region with the depth range 75 – 300 m depths during cruise RV Arar (November 2009) and RV Maria S. Merian (April-May 2010) (Fig.3.13).
Main groups of macrobenthos taken from multiple-corer samples at the Bosporus Strait were crustaceans, annelids, bivalves and echinodermates in November of 2009 (Fig.3.14). Macrobenthos is represented till 250m depth. Low boundary of habitat of Crustacea was at 103m, Bivalves and Echinodermates was 123m. Annelides and Gastropoda were found to 250m depth. Polychaete Vigtorniella zaikai forms accumulates the depth of 250 m in the
46 Near-Bosporus region, thought, its peaks are at the depths of 150 – 170 m, in the belt of oxygen to the hydrogen sulphide zone transition, in the sea northern half. The data obtained showed, that the main macrobenthos groups change in the Bosporus region, depending on the bathymetric gradients (Fig.3.15).
A B
Fig.3.13. Station data at Istanbul Strait‟s (Bosporus) outlet area of the Black Sea (A- cruse R/V Arar, November 2009, B-cruise R/V M.S. Merian, April-May 2010)
100000 90000 80000 70000
60000 2
50000 ind/m 40000 30000 20000 10000 0 Crustacea Annelida Bivalvia Echinodermata
Fig.3.14. Main macrobenthos groups abundance correlation at the depth of 75 min the Bosporus region (November 2009)
Taxonomical structure of meiobenthos is very diverse and was presented by 6–21 higher taxons depending on depth gradient (Fig.3.16). The main share of the total quantity falls on nematode group, and harpacticoids are the following.
47
Fig.3.15. Main macrobenthos groups quantity according to the depths in the Bosporus region (November 2009) 18
17
16
15
14
13
12 Taxa richness Taxa
11
10
9
8 75 82 88 103 122 160 190 250 300 depth (m) Fig.3.16. Taxa richness of meiobenthos along depth gradient at the Bosporus Strait (November 2009).
The meiobenthos abundance changes ranges from 9 - 1.900 (103 *indiv*m-2) along observed depths in the Bosporus Strait. Total quantity is the highest at the depth of 75 m (1861.6 thous. smpl/m2). It becomes lower, with the depth increase, forming the smaller peaks at the depths of 88 m (1011 thous. indiv. m-2), 162 m (468.5 thous. indiv. m-2) and 250 m (603.2 thous. indiv. m-2). The lowest abundance peak is at the depth of 250 m and meiobenthos quantity decreases considerably at the depth of 300 m.
Peaks of meiobenthos abundances were located at 75, 88, 103, 160, 250 m water depth, decreasing with increasing water depth from 75 to 300 m (Fig.3.17). The abundance of meiobenthos ranged from 9 - 1.900 (103 *indiv*m-2) and the meiobenthos structure is dominated by eumeiobenthos. Pseudomeiobenthos (temporary meiofauna) abundance was elevated at 103 mwater depths with the highest abundances of Turbellaria and Bivalvia taxa and at 250 m water depth, where Oligochaeta, Polychaeta and Turbellaria taxa dominated.
48
Fig.3.17. Distribution of meiobenthos abundance (N) along the water depth gradient.
The changes of abundance of benthic organisms depend on the oxygen content of the bottom sediments. The distribution of different taxonomic groups of meiobenthos along different water depths between 75 and 300 m were shown in Fig.3.18 and Fig.3.19. Such distribution provides the evidence of the existence of meiofauna with different adaptation to the oxygen depletion and anoxia.
A B
Fig.3.18. Changes in the Protozoa abundance along depth gradient of the Istanbul Strait‟s (Bosporus) outlet area of the Black Sea: A- Gromiida, B – Ciliophora.
Thus, meiobenthos had distributed of the Istanbul Strait‟s (Bosporus) outlet area of the Black Sea at depths range from 75 to 300m. The maximum of meiobenthos density is located in at a depth of 75 m, other peaks occur on the 88, 103, 160, 250 m. At a depth of 300 m amount of the meiobenthos was significantly reduced, while the importance of such groups as the Ciliophora and Nematoda increased relatively. Species identification of meiofauna is still in progress.
49 A B C
Fig.3.19. Changes in the Metazoa abundance along depth gradient of the Istanbul Strait‟s (Bosporus)outlet area of the Black Sea: A- Nematoda, B - Harpacticoida, C – Polychaeta
During RV Maria S. Merian‟ scientific cruise the data of taxonomic composition and meiobenthos abundance from Bosporus Strait area were obtained. Comparative analysis of meiofauna densities had shown the patchiness of meiobenthos distribution along the depth transects (Fig.3.20 and Fig.3.21).
Fig.3.20.Meiobenthos abundance (N) along depth gradient of the Bosporus Strait area of the Black Sea. Data from two cruises RV Arar (blue points) (November, 2009), RV Maria S. Merian (red points) (April,2010)
50
Fig.3.21. Meiobenthos taxa richness along depth gradient of the Bosporus Strait area of the Black Sea RV Maria S. Merian (April, 2010)
Indicator species: Twenty-nine Harpacticoida species belonging to 20 genera and 7 families were registered at the depth range 75-250 m in November 2009. Species distribution was varied with depth. Maximum number of species was registered at the 85 m depth. Two species – Ectinosoma melaniceps and Haloschizophera pontarchis were dominating Harpacticoida taxocen by their abundances. The first one is eurybathic, epibenthic species burrowing through the sediment up to 4 cm depth while the second one typically occurs in muddy-sandy sediments. Before Haloschizophera pontarchis was found as dominant species at the depth range 40 – 125 m near the Crimea cost of Black Sea.
At the 1 -2 cm sediment layer three typical deep-water species – Bulbamphiascus imus, Typhlamhiascus confuses, Proameira simplex were found as dominant at the 75 and 85 m depth. Two muddy-sandy species – Enhydrosoma gariensis and Normanella mucronata also were formed the high abundant assemblages. Common species for biocenosis of phaseolina mud at Crimea shelf - the Cletodes tenuipes was represented by high density at the 103 m depth.
Polychaete Vigtorniella zaikai was formed well-developed assemblages at the depth of 250 m in the Near-Bosporus region, thought, its maximum peaks are at the depths of 150 – 170 m, in the belt of oxygen to the hydrogen sulphide zone transition, in the northern sea part.
Dnepr Canyon (Paleo-Delta): During cruise RV M.S. Merian meiobenthic samples were collected at two water areas (I & II) (Fig.3.22).
51
Fig.3.22. Meiobenthos samples stations in the Crimea area, the Back Sea (RV Merian, May 2010).
The analysis of the benthos distribution is still in progress. Here we are presenting the results about change of taxonomic structure and abundance benthos in north-western part of Black Sea. These are marked the high abundance and taxa richness distinctions of benthos communities along the depth gradient. Taxonomical structure of meiobenthos is very diverse and was presented by 6–21 higher level taxons (type, class, order) depending on depth gradient. The stations of two sampling areas (I, II) were grouped by total meiofauna densities into three divisions of depth ranges in 75-85, 95-145 and 145-375 m. The benthic fauna (macro- and meiofauna) densities were calculated by number of all organisms founding in the sediment corers taken by multicorers and pushcorers (Fig.3.23). Benthos was registered at all depth range from 75 to 375m. Benthos densities were found higher at the 95-145m depth. Eumeiobenthos was dominant at two areas, contributing high share of the total meiobenthos abundance.
Maximum total zoobenthos densities of 2489704 ind./m2 were registered at the 95-105 m, minimum density of 13475 ind./m2 at the 205-215m depth, respectively. Dominant group at all depth was Nematoda. Harpacticoida, Foraminifera, Bivalvia were found as subdominant groups depends on depth range (Fig.3.24 and Fig.3.25).
52 Total zoobenthos density
2,50E+06 2 2,00E+06
1,50E+06
1,00E+06
5,00E+05 Density, ind./m Density,
0,00E+00
375
75-85
95-105
115-125 125-135 135-145 145-155 155-165 165-175 195-205 205-215 Depth range, m
Fig. 3.23.Distribution of total zoobenthos (macro- and meiofauna) at Crimea shelf along depth gradient
Fig.3.24. Rank of high meiobenthic taxa from different depth ranges.
Indicator species: Polychaete Vigtorniella zaikai was formed assemblages at the depth of 124- 175m in Crimea shelf, thought, its maximum peaks are at the depths of 135 – 163 m, in the belt of oxygen to the hydrogen sulphide zone transition, in the north-western sea part. This species was suggested to be an indicator hypoxia in water column and bottom sediments at all regions of the Black Sea.
53 100% 80% 60% 40% 20% 0% 75-85 95-145 145-375 Depth , m
Nematoda Harpacticoida Bivalvia Foraminifera Other
Fig.3.25.Contribution of meibenthos main taxa at the different depth ranges
Concluding remarks: The data from different sites of the Crimean shelf and Istanbul Strait‟s outlet area of the Black Sea show that the dependence of the zoobenthos of hypoxia appears in a change the overall abundance and a change in the share of different groups. Detailed analyses of the species composition indicate that some species increase their abundance in hypoxic conditions. For example, some the Black sea benthic species such as polychaete Vigtorniella zaikai is always present near deep oxic/anoxic boundary and can be used as indicators of hypoxia. Our data shows that meiobenthos is a very promising group as indicator species. In addition to the study of the reaction of benthic animals to the degree of hypoxia, the new data on the distribution of hypoxia in both shallow and deep waters in the Black Sea were presented . The depths limits of hydrogen sulphide zone and fluctuation of the oxic/anoxic boundary in the northern and southern parts of the sea were shown, using benthic data.
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Zaika, V.E., Konovalov, S.K., Sergeeva, N.G. (2011).The local and seasonal hypoxia occurrences at the bottom of the Sevastopol bays and their influence on macrobenthos. Mar. Ecol. J. 10(3):15-25. (in Russian).
57 3.2. Macrobenthos studies on the Romanian Shelf (GeoEcoMar)
Site description: The Romanian shelf in the NW Black Sea is characterized by the Danube inflow and delta (Panin et al.,1983; Panin and Strechie, 2006; Fig. 3.26). There have been mass mortalities of some marine organisms such as fish, molluscs, crustaceans and other animals in the Romanian littoral zone during summer months due to hypoxia development below 10 m water depth. The research covered all the Romanian continental shelf between the northern deltaic sector of Sf. Gheorghe and the southern sector of Mangalia, and from 11 m to 200 m isobaths Fig. 3.26). The Danube largely influences the ecological parameters of the continental shelf in terms of salinity, organic load and sediment grain-size. The dominant biocoenoses in the coastal zone belong to Mya arenaria, Lentidium mediterraneum and Melinna palmata. Between 50-60 m and 100 m depth there extends the biocoenosis of Modiolus phaseolinus, a unique case of species adaptation to the alluvial mud biotope. Salinity can vary between 9-22 PSU at the bottom area. In the southern area, there is a greater variety of biocoenoses, dominated by Mytilus galloprovincialis community and the associations covering the hard rocky and shelly bottoms. The substrata consisting of medium sand and broken shells deposits are predominant. Salinity usually has higher values, without sudden changes. O2 concentration in the sediment plays an essential role for benthic fauna distribution.
Macrobenthos populations: In the frame of EU FP7 Hypox Project four cruises were performed with the R/V “Mare Nigrum” in the Romanian Black Sea shelf zone along a period of three years (2009 - 2011). A south-eastward oriented transect in front of the Danube Delta, namely Sf. Gheorghe transect, as well as a sheltered area at Portita were chosen to monitor the oxygen regime, the occurrence of hypoxic events, implicitly the mechanisms controlling these phenomena. Additionally, during each year of study, supplementary researches were conducted on Constanta and Mangalia profiles for comparing the status of the northern ecosystem with the southern one.
During the program, in situ measurements and sampling were carried out in 109 stations (Fig. 3.26, Table 3.1), the water column being investigated and water samples and sediment samples collected for hydrochemical, sedimentological and biological analyses. In 2010, in addition to investigating the profiles of St. George, Portita, Constanta and Mangalia, an observatory was specially installed for the Hypox Project in Portita area, in order to monitor in-situ the oxygen, temperature, salinity, turbidity, water velocity and direction of currents in
58 the near bottom waters (depth ~ 28 m). The measurements, recorded and logged every 10 minutes, covered the period 22 May 2010 – 29 August 2010.
Some remarks concerning the results obtained by the Portita Black Sea Hypox Observatory on oxygen and some proxy parameters: Continuous in situ measurements of dissolved oxygen (DO), seawater temperature, salinity, turbidity, currents velocity and direction in the bottom waters (~28 m depth) were conducted by HYPOX observatory deployed in the Portita zone (south of the Danube Delta - 44.577770 N; 29.242567 E) during May 22, 2010 – August 29, 2010 at 10 minutes interval. In late spring, the data provided by the observatory showed well- oxygenated bottom waters, DO hourly means exceeded 200 μM (Fig. 3.27). Moreover, in early June there was a slight increase in DO level in the lower layers (up to ~250 μM), which, correlated with higher turbidity (~25 FTU), indicated, most likely, more intense photosynthetic processes throughout the water column.
Fig. 3.26. Location of sampling stations performed on the Romanian Black Sea continental shelf in May 2009, May and September 2010 and April 2011.
59 DO concentrations in the first half of July were normal; the hourly means ranged between 180 and 200 μM. In the second half of this month a significant decrease of DO in the bottom layers to concentrations below 100 μM (minimum of 78.8 μM) is not worthy. Higher values of turbidity measured during this period (Fig. 3.28) suggest an increase in the amount of sinking organic matter (dead cells of phytoplankton, detritus, etc.) subjected to oxidative decomposition processes.
Organic matter mineralization in the bottom layers led to an increased stock of nutrients throughout the water column, thus favouring intense development of phytoplankton (Fig. 3.29). The favourable light regime (shallow waters in the studied area), along with reduced velocities of bottom currents, might have led to intense photosynthetic processes in the lower layers suggested by higher values of DO and turbidity (Fig. 3.27 and 3.28). Very high seawater temperatures measured in August resulted in the lowering of the upper limit of thermocline, thus causing abnormally high values of temperatures in the lower layers (Fig. 3.27). The very high thermal regime favoured oxidative decomposition of newly formed organic matter,
Fig.3.27. Temporal distribution of DO and seawater temperatures (hourly means) in the bottom waters, in the Portita area (22 May – 29 August, 2010). Unpublished dataset, http://doi.pangaea.de/10.1594/PANGAEA.746272 (Friedrich, 2010) .
60
Fig. 3.28. Temporal distribution of turbidity and salinity (hourly means) in the bottom waters, in the Portita area (22 May – 2 9 August, 2010). leading to significantly lower DO concentrations, down to 30 – 40 μM, thus suggesting severe hypoxia in the studied area. At the same time a high input of Danubian freshwater determined a strong stratification of the water column, hindering the ventilation of the bottom water. Thus, low DO level in the bottom layers was maintained for a relatively long period (at least until the end of August) mainly favoured by the high seawater temperatures in the bottom waters (Fig. 3.27).
a)12 July 2010 b)24 July 2010 Fig. 3.29.Air photos of the Portita area.
61 c) 6 August 2010 d) 23 August 2010 Fig. 3.29. (continued).
Table 3.1: Coordinates of the sampling stations performed in 2009 – 2011 No. Stations Data Latitude Longitude Depth Degrees Minutes Degrees Minutes (m) 1 09SG01 19.05.2009 44 49.797 29 38.990 17.0 2 09SG02 20.05.2009 44 49.639 29 39.786 28.0 3 09SG03 20.05.2009 44 49.432 29 40.662 37.3 4 09SG04 20.05.2009 44 40.175 29 49.072 53.4 5 09SG05 20.05.2009 44 35.227 30 06.231 64.5 6 09SG06 21.05.2009 44 20.229 30 31.412 91.9 7 09SG07 21.05.2009 44 16.958 30 36.372 102.2 8 09SG08 21.05.2009 44 15.251 30 37.178 117.0 9 09SG09 21.05.2009 44 08.446 30 46.775 149.0 10 09SG13 21.05.2009 44 07.204 30 48.087 200.0 11 09CT01 27.05.2009 44 09.088 28 41.696 18.2 12 09CT02 27.05.2009 44 09.090 28 42.780 26.0 13 09CT03 27.05.2009 44 07.830 28 46.230 34.0 14 09CT04 27.05.2009 44 05.070 29 02.010 46.0 15 09CT05 23.05.2009 43 58.461 29 30.439 62.0 16 09CT06 23.05.2009 43 47.570 29 59.860 87.45 17 09 CT07 22.05.2009 43 45.858 30 03.977 111.0 18 09CT08 22.05.2009 43 45.210 30 07.563 122.6 19 09MA05 24.05.2009 43 46.455 29 36.338 15.4 20 09MA06 24.05.2009 43 46.161 29 38.381 27.0 21 09MA07 24.05.2009 43 46.446 29 39.651 35.5 22 09MA04 23.05.2009 43 45.577 29 24.062 66.2 23 09MA03 23.05.2009 43 44.814 29 58.015 91.3 24 09MA02 22.05.2009 43 44.541 30 01.150 110.0 25 09MA01 22.05.2009 43 44.889 30 07.656 135.0
62 No. Stations Data Latitude Longitude Depth Degrees Minutes Degrees Minutes (m) 26 09MA09 22.05.2009 43 44.066 30 09.389 150.5 27 09MA10 22.05.2009 43 44.173 30 11.208 188.9 28 10SG01 20. 05. 2010 44 49.783 29 39.106 16.0 29 10SG02 19. 05. 2010 44 49.672 29 39.748 24.0 30 10SG03 19. 05. 2010 44 49.501 29 40.595 33.0 31 10SG04 19. 05. 2010 44 40.205 29 48.980 50.0 32 10SG05 19. 05. 2010 44 35.354 30 06.142 60.0 33 10SG14 19. 05. 2010 44 27.904 30 18.754 76.0 34 10SG06 18. 05. 2010 44 20.202 30 31.432 87.0 35 10SG07 18. 05. 2010 44 16.928 30 36.485 98.0 36 10SG08 18. 05. 2010 44 15.000 30 37.493 114.0 37 10SG09 18. 05. 2010 44 08.768 30 46.875 143.0 38 10SG13 18. 05. 2010 44 08.179 30 48.135 162.0 39 10PO01 23. 05. 2010 44 39.749 29 01.634 40 10PO02 23. 05. 2010 44 37.239 29 07.818 21.0 41 10PO03 21. 05. 2010 44 35.347 29 13.375 25.0 42 10PO04 21. 05. 2010 44 30.491 29 22.512 42.3 43 10PO05 22. 05. 2010 44 34.681 29 14.620 30.5 44 10PO06 23. 05. 2010 44 35.354 29 15.510 30.0 45 10PO07 23. 05. 2010 44 33.989 29 13.548 30.0 46 10CT01 24. 05. 2010 44 09.099 28 41.716 18.0 47 10CT02 24. 05. 2010 44 09.147 28 42.956 26.7 48 10CT03 20. 05. 2010 44 07.734 28 46.448 31.0 49 10CT04 20. 05. 2010 44 04.970 29 02.055 42.0 50 10CT05 20. 05. 2010 43 58.484 29 30.706 60.0 51 10CT06 17. 05. 2010 43 48.131 29 59.928 86.0 52 10MA05 15. 05. 2010 43 46.512 28 36.215 14.5 53 10MA06 14. 05. 2010 43 46.205 28 38.391 23.0 54 10MA07 15. 05. 2010 43 46.469 28 39.316 31.5 55 10MA08 15. 05. 2010 43 46.523 28 44.092 41.6 56 10MA04 16. 05. 2010 43 45.738 29 24.231 63.0 57 10MA03 16. 05. 2010 43 44.882 29 57.788 88.0 58 10MA02 17. 05. 2010 43 44.464 30 02.396 110.0 59 10MA09 17. 05. 2010 43 44.043 30 10.047 150.0 60 10MA10 17. 05. 2010 43 44.249 30 11.499 200.0 61 MN86/CT01 22. 07. 2010 44 09.012 28 41.487 17.8 62 MN86/CT03 22. 07. 2010 44 07.626 28 46.427 31.0 63 MN86/CT04 22. 07. 2010 44 04.960 29 02.109 42.0 64 MN87/PO04 05. 09. 2010 44 30.431 29 22.497 45.2 65 MN87/PO06 06. 09. 2010 44 35.428 29 15.373 30.0 66 MN87/PO07 07. 09. 2010 44 34.058 29 13.609 30.0 67 MN87/PO03 07. 09. 2010 44 35.384 29 13.335 30.4 68 MN87/SG01 08. 09. 2010 44 49.665 29 39.026 19.0 69 MN87/SG02 08. 09. 2010 44 49.602 29 39.687 27.0
63 No. Stations Data Latitude Longitude Depth Degrees Minutes Degrees Minutes (m) 70 MN87/SG03 08. 09. 2010 44 49.454 29 40.697 36.7 71 MN87/SG04 09. 09. 2010 44 40.108 29 48.924 54.6 72 MN87/SG05 09. 09. 2010 44 35.224 30 06.124 64.0 73 MN87/SG14 09. 09. 2010 44 27.788 30 18.695 77.0 74 MN87/SG06 09. 09. 2010 44 20.095 30 31.293 92.5 75 MN90/SU01 04. 04. 2011 45 04.164 29 43.925 14.3 76 MN90/SU03 04. 04. 2011 45 02.404 30 03.733 36.5 77 MN90/R01 04. 04. 2011 44 51.491 29 42.229 37.0 78 MN90/R02 04. 04. 2011 44 51.403 29 44.536 41.2 79 MN90/R04 04. 04. 2011 44 51.816 29 45.093 39.0 80 MN90/SG01 02. 04. 2011 44 49.708 29 38.993 19.0 81 MN90/SG03 04. 04. 2011 44 49.249 29 40.377 36.0 82 MN90/SG04 05. 04. 2011 44 40.287 29 49.095 58.0 83 MN90/SG05 05. 04. 2011 44 35.401 30 06.183 64.0 84 MN90/SG14 05. 04. 2011 44 27.763 30 18.804 78.4 85 MN90/SG06 05. 04. 2011 44 20.125 30 31.344 93.0 86 MN90/SG07 05. 04. 2011 44 16.478 30 36.103 107.0 87 MN90/SG08 06. 04. 2011 44 14.676 30 36.996 119.0 88 MN90/SG09 06. 04. 2011 44 08.340 30 46.326 148.0 89 MN90/SG13 06. 04. 2011 44 08.196 30 48.058 168.0 90 MN90/PO01 01. 04. 2011 44 39.268 29 01.656 12.5 91 MN90/PO02 02. 04. 2011 44 37.276 29 06.149 20.0 92 MN90/PO03 02. 04. 2011 44 35.116 29 13.131 28.0 93 MN90/PO05 02. 04. 2011 44 34.306 29 14.355 32.0 94 MN90/PO04 02. 04. 2011 44 30.302 29 21.369 45.5 95 MN90/CT01 09. 04. 2011 44 09.088 28 41.646 27.1 96 MN90/CT02 10. 04. 2011 44 09.212 28 42.920 18.5 97 MN90/CT03 09. 04. 2011 44 07.716 28 46.376 34.6 98 MN90/CT04 09. 04. 2011 44 04.997 29 02.224 47.0 99 MN90/CT05 07. 04. 2011 43 58.576 29 30.732 65.4 100 MN90/CT06 07. 04. 2011 43 48.230 30 00.114 93.0 101 MN90/MA05 08. 04. 2011 43 46.472 28 36.183 17.0 102 MN90/MA06 08. 04. 2011 43 46.148 28 38.303 26.0 103 MN90/MA07 08. 04. 2011 43 46.480 28 39.378 34.0 104 MN90/MA08 08. 04. 2011 43 46.507 28 44.225 47.0 105 MN90/MA04 07. 04. 2011 43 45.677 29 24.311 68.0 106 MN90/MA03 07. 04. 2011 43 44.871 29 57.737 92.0 107 MN90/MA02 07. 04. 2011 43 44.515 30 02.364 116.0 108 MN90/MA09 07. 04. 2011 43 44.035 30 10.081 184.0 109 MN90/MA10 06. 04. 2011 43 43.241 30 11.108 195.0
64 Macro-benthos sampling design: Macro-benthos samples were collected by using van Veen grabs (0.135 m2, 20-25 cm penetration depths). The depth of the sampling stations varied from 10 m to 200 m. The sediment samples for macro-benthos were washed on board using a 0.5 mm sieve-mesh, and all organisms remaining on the sieve were collected and preserved in 4% neutralized formalin seawater solution (Birkett and McIntyre, 1971). In the laboratory, the animals in the samples were sorted, transferred into 70% ethanol and identified to species or a higher taxon under a dissecting microscope. The data were represented as density per square meter (indvs.m-2). The biomass, expressed as formalin wet-weight after removing excess water on blotting paper, was measured by weighing organisms with scales (accuracy 0.01 g) after three month storage at least. Bivalves were weighed without shells. The nomenclature was checked following the World Register of Marine Species (Appeltans et al., 2010).
Present ecological state of benthic ecosystem under the Danube River influence: In Sf. Gheorghe and Portita, in front of the Danube Delta, the total number of recorded taxa is 93 (Table 3.2). These include 33 Vermes, 27 Mollusca, 17 Crustacea , and 16 other groups. The mean numerical abundance and biomass are 4357 ind.m-2 and 141g.m-2, respectively.
Table 3.2: Ecological parameters for macrobenthic populations on the Romanian Continental Shelf. Numerical abundance was analyzed using multivariate techniques for whole region Taxa F% Davg DD% WD RkD Bavg DB% WB RkB Haliclona aquaeductus (Schmidt, 1862) 6,45 0,48 0,011 0,2659 71 0,0036 0,0025 0,12815 63 Halisarca dujardini Johnston, 1842 3,23 0,48 0,011 0,1880 77 0,0019 0,0014 0,06618 73 Mycale syrinx (Schmidt, 1862) 3,23 0,24 0,006 0,1329 80 0,0024 0,0017 0,07399 72 Suberites carnosus (Johnston, 1842) 9,68 1,19 0,027 0,5149 63 0,0158 0,0112 0,32923 53 Amphinema dinema (Péron & Lesueur, 1810) 6,45 0,48 0,011 0,2659 72 0,0004 0,0003 0,04185 78 Clytia hemisphaerica (Linnaeus, 1767) 3,23 0,24 0,006 0,1329 81 0,0002 0,0001 0,02093 88 Obelia longissima (Pallas, 1766) 22,58 10,26 0,236 2,3063 33 0,0076 0,0054 0,35018 51 Actinithoe clavata 35,48 9,31 0,214 2,7534 25 0,4827 0,3431 3,48943 14 Pachycerianthus solitarius (Rapp, 1829) 9,68 2,15 0,049 0,6908 54 0,4142 0,2944 1,68802 26 Stylochus tauricus Jacubowa, 1909 9,68 1,91 0,044 0,6512 55 0,0164 0,0117 0,33639 52 Amphiporus bioculatus McIntosh, 1874 3,23 0,24 0,006 0,1329 82 0,0005 0,0003 0,03309 82 Cephalotrix sp. 12,90 3,58 0,082 1,0297 48 0,0072 0,0051 0,25631 57 Leucocephalonemertes aurantiaca (Grube, 1855) 12,90 0,95 0,0219 0,5317 61 0,0045 0,0032 0,20397 59 Lineus bilineatus (Renier, 1804) 35,48 6,68 0,1534 2,3330 32 0,1795 0,1276 2,12801 22 Micrura fasciolata Ehrenberg, 1828 16,13 2,86 0,0657 1,0297 47 0,0055 0,0039 0,25091 58 Nemerini indet. 38,71 9,55 0,2191 2,9125 24 0,0191 0,0136 0,72494 41 Alitta succinea (Frey & Leuckart, 1847) 25,81 122,94 2,8213 8,5327 8 3,1949 2,2713 7,65606 6 Aonides paucibranchiata Southern, 1914 22,58 7,16 0,1643 1,9264 38 0,0487 0,0346 0,88416 36 Capitella capitata (Fabricius, 1780) 25,81 7,40 0,1698 2,0935 36 0,0011 0,0008 0,14270 61 Clymenura clypeata (Saint-Joseph, 1894) 3,23 0,24 0,0055 0,1329 83 0,0026 0,001 0,0776 71 Dipolydora quadrilobata (Jacobi, 1883) 32,26 279,77 6,4205 14,391 5 0,3657 0,260 2,8959 18 Eumida sanguinea (Örsted, 1843) 16,13 4,30 0,0986 1,2611 44 0,0150 0,0107 0,41526 49 Exogone naidina Örsted, 1845 22,58 18,14 0,4163 3,0662 23 0,0018 0,0013 0,17066 60
65 Taxa F% Davg DD% WD RkD Bavg DB% WB RkB Harmothoe imbricata (Linnaeus, 1767) 12,90 2,86 0,0657 0,9210 49 0,0223 0,0159 0,45273 48 Harmothoe impar (Johnston, 1839) 45,16 7,16 0,1643 2,7244 26 0,0088 0,0063 0,53252 46 Heteromastus filiformis (Claparède, 1864) 87,10 396,97 9,1103 28,1688 3 0,4826 0,3431 5,46629 7 Lagis koreni Malmgren, 1866 9,68 1,43 0,0329 0,5640 59 0,0122 0,0087 0,28941 56 Melinna palmata Grube, 1870 80,65 1712,26 39,295 56,2938 1 26,017 18,496 38,6222 2 Micronephthys stammeri (Augener, 1932) 61,29 19,34 0,4437 5,2151 16 0,0217 0,0154 0,97289 33 Nephtys hombergii Savigny in Lamarck, 1818 80,65 127,23 2,9199 15,3452 4 4,4925 3,1939 16,0489 4 Oriopsis armandi (Claparède, 1864) 64,52 22,44 0,5150 5,7639 15 0,0099 0,0070 0,67293 43 Phyllodoce mucosa Örsted, 1843 29,03 6,92 0,1589 2,1476 34 0,0370 0,0263 0,87389 38 Polycirrus jubatus Bobretzky, 1869 22,58 32,70 0,7505 4,1167 20 0,1255 0,0892 1,41920 29 Polydora cornuta Bosc, 1802 38,71 50,37 1,1559 6,6892 11 0,0327 0,0232 0,94868 35 Prionospio cirrifera Wirén, 1883 48,39 49,17 1,1285 7,3896 9 0,1850 0,1315 2,52269 20 Protodrilus flavocapitatus (Uljanin, 1877) 3,23 1,19 0,0274 0,2973 69 0,0001 0,0001 0,01654 89 Pygospio elegans Claparède, 1863 3,23 0,72 0,0164 0,2303 75 0,0001 0,0001 0,01282 91 Sphaerosyllis bulbosa Southern, 1914 6,45 2,15 0,0493 0,5640 60 0,0002 0,0002 0,03139 85 Spio decoratus Bobretzky, 1870 3,23 34,61 0,7943 1,6008 43 0,0430 0,0305 0,31391 54 Syllides longocirratus (Örsted, 1845) 6,45 1,91 0,0438 0,5317 62 0,0017 0,0012 0,08879 68 Terebellides stroemii Sars, 1835 25,81 25,78 0,5917 3,9075 22 1,5320 1,0892 5,30167 8 Oligochaeta indet. 96,77 717,08 16,456 39,9072 2 0,1247 0,0887 2,92907 16 Chrysallida incerta (Milaschewitch, 1916) 6,45 0,95 0,0219 0,3760 66 0,0019 0,0014 0,09359 67 Chrysallida interstincta (Adams J., 1797) 3,23 0,72 0,0164 0,2303 76 0,0014 0,0010 0,05731 74 Cylichnina umbilicata (Montagu, 1803) 9,68 0,95 0,0219 0,4605 64 0,0019 0,0014 0,11462 64 Ebala pointeli (de Folin, 1868) 3,23 0,24 0,0055 0,1329 84 0,0005 0,0003 0,03309 83 Hydrobia acuta (Draparnaud, 1805) 3,23 0,24 0,0055 0,1329 85 0,0012 0,0008 0,05232 76 Odostomia scalaris MacGillivray, 1843 3,23 0,24 0,0055 0,1329 86 0,0005 0,0003 0,03309 84 Pusillina lineolata (Michaud, 1832) 54,84 30,79 0,7067 6,2253 14 0,1151 0,0818 2,11795 23 Rapana venosa (Valenciennes, 1846) 3,23 0,24 0,0055 0,1329 87 4,5952 3,2668 3,24626 15 Retusa truncatula (Bruguière, 1792) 38,71 5,01 0,1150 2,1103 35 0,0222 0,0158 0,78163 40 Trophonopsis breviata (Jeffreys, 1882) 3,23 0,24 0,0055 0,1329 88 0,0048 0,0034 0,10464 66 Ventrosia ventrosa (Montagu, 1803) 3,23 0,95 0,0219 0,2659 73 0,0048 0,0034 0,10464 65 Abra alba (W. Wood, 1802) 48,39 6,45 0,1479 2,6753 28 0,0975 0,0693 1,83182 24 Abra prismatica (Montagu, 1808) 61,29 101,93 2,3392 11,9738 7 1,9504 1,3866 9,21873 5 Acanthocardia paucicostata (G.B. Sowerby II, 29,03 5,01 0,1150 1,8276 39 0,5962 0,4238 3,50778 13 1834) Anadara inaequivalvis (Bruguière, 1789) 12,90 1,67 0,0383 0,7034 53 2,5995 1,8481 4,88328 10 Anadara transversa (Say, 1822) 16,13 71,14 1,6325 5,1314 17 1,1630 0,8268 3,65179 11 Cerastoderma glaucum (Bruguière, 1789) 12,90 2,63 0,0603 0,8818 50 0,1022 0,0726 0,96810 34 Chamelea gallina (Linnaeus, 1758) 3,23 0,24 0,0055 0,1329 89 0,0006 0,0004 0,03699 80 Lentidium mediterraneum (O. G. Costa, 1829) 3,23 37,95 0,8710 1,6762 41 0,3366 0,2393 0,87857 37 Modiolula phaseolina (Philippi, 1844) 29,03 76,86 1,7640 7,1563 10 1,2564 0,8932 5,09244 9 Mya arenaria Linnaeus, 1758 58,06 31,75 0,7286 6,5043 13 78,119 55,537 56,7870 1 Mytilaster lineatus (Gmelin, 1791) 3,23 0,48 0,0110 0,1880 78 0,0012 0,0008 0,05232 77 Mytilus galloprovincialis Lamarck, 1819 51,61 35,81 0,8217 6,5125 12 8,2506 5,8656 17,3994 3 Parvicardium exiguum (Gmelin, 1791) 16,13 1,67 0,0383 0,7865 52 0,0263 0,0187 0,54872 45 Parvicardium simile (Milaschewisch, 1909) 9,68 1,91 0,0438 0,6512 56 0,0208 0,0148 0,37821 50 Pitar rudis (Poli, 1795) 22,58 2,15 0,0493 1,0551 46 0,8004 0,5690 3,58449 12 Spisula subtruncata (da Costa, 1778) 22,58 7,40 0,1698 1,9583 37 0,5299 0,3767 2,91671 17 Phoronis euxinicola Selys-Longchamps, 1907 64,52 109,81 2,5200 12,7507 6 0,0681 0,0484 1,76770 25 Callipallene phantoma (Dohrn, 1881) 12,90 2,15 0,0493 0,7976 51 0,0007 0,0005 0,08186 69
66 Taxa F% Davg DD% WD RkD Bavg DB% WB RkB Balanus improvisus Darwin, 1854 45,16 15,04 0,3451 3,9480 21 0,1466 0,1042 2,16928 21 Ampelisca sarsi Chevreux, 1888 38,71 6,68 0,1534 2,4367 31 0,0399 0,0283 1,04741 32 Apherusa bispinosa (Bate, 1857) 6,45 0,72 0,0164 0,3256 67 0,0004 0,0003 0,04053 79 Medicorophium runcicorne (Della Valle, 1893) 48,39 17,90 0,4109 4,4588 19 0,0072 0,0051 0,49633 47 Megamphopus cornutus Norman, 1869 3,23 1,19 0,0274 0,2973 70 0,0004 0,0003 0,02866 86 Microdeutopus damnoniensis (Bate, 1856) 3,23 0,24 0,0055 0,1329 90 0,0001 0,0000 0,01122 93 Microdeutopus versiculatus (Bate, 1856) 3,23 0,24 0,0055 0,1329 91 0,0003 0,0002 0,02563 87 Orchomene humilis (Costa, 1853) 3,23 0,24 0,0055 0,1329 92 0,0001 0,0001 0,01654 90 Perioculodes longimanus (Bate & Westwood, 32,26 3,82 0,0877 1,6815 40 0,0008 0,0005 0,13236 62 1868) Phtisica marina Slabber, 1769 35,48 8,59 0,1972 2,6454 29 0,0193 0,0137 0,69840 42 Synchelidium maculatum Stebbing, 1906 9,68 0,95 0,0219 0,4605 65 0,0002 0,0001 0,03625 81 Apseudopsis ostroumovi Bacescu & Carausu, 6,45 0,72 0,0164 0,3256 68 0,0014 0,0010 0,08105 70 1947 Cumella limicola Sars, 1879 3,23 0,48 0,0110 0,1880 79 0,0001 0,0001 0,01282 92 Eudorella truncatula (Bate, 1856) 9,68 1,91 0,0438 0,6512 57 0,0004 0,0003 0,05497 75 Iphinoe elisae Băcescu, 1950 61,29 17,19 0,3944 4,9168 18 0,0084 0,0060 0,60577 44 Liocarcinus holsatus (Fabricius, 1798) 3,23 0,24 0,0055 0,1329 93 0,7448 0,5295 1,30691 30 Upogebia pusilla (Petagna, 1792) 12,90 1,19 0,0274 0,5945 58 0,1373 0,0976 1,12210 31 Amphiura stepanovi Djakonov, 1954 19,35 16,71 0,3835 2,7244 27 0,1743 0,1239 1,54848 28 Leptosynapta inhaerens (O.F. Müller, 1776) 12,90 4,54 0,1041 1,1589 45 0,0680 0,0484 0,78999 39 Ciona intestinalis (Linnaeus, 1767) 19,35 5,97 0,1370 1,6281 42 0,5056 0,3594 2,6375 19 Eugyra adriatica Drasche, 1884 6,45 0,48 0,0110 0,2659 74 0,0215 0,0153 0,3139 55 Molgula appendiculata Heller, 1877 22,58 11,94 0,2739 2,4870 30 0,1735 0,1234 1,6691 27 TOTAL 4357,41 100 140,66 Group N.sp. Davg DD% Bavg DB% Spongia 4 2,39 0,05 0,024 0,017 Coelenterata 5 22,44 0,51 0,905 0,643 Nemertini 6 23,87 0,55 0,216 0,154 Polychaeta 25 2935,17 67,36 36,655 26,059 Oligochaeta 1 717,08 16,46 0,125 0,089 Mollusca 27 425,62 9,77 100,60 71,520 1 Crustacea 17 77,34 1,77 1,107 0,787 Echinodermata 2 21,25 0,49 0,242 0,172 Tunicata 3 18,38 0,42 0,701 0,498 Other group 3 113,86 2,61 0,085 0,061 TOTAL 93 4357,41 100 140,66 100
Analyses of the qualitative distribution of macrobenthos populations show that the greatest specific biodiversity is found in the southern areas of the Romanian platform, in the deeper zones of mussel - Mytilus and Modiolus biocoenosis, as a result of higher stability of environmental state parameters; in the northern zones, in front of the Danube Delta, specific diversity is more homogeneous (Fig. 3.30). The distribution of macrobenthic population is uneven on sedimentary bottoms; few species are widespread, most of them being found only in 4-5 stations, so they have a reduced frequency. The highest frequency in samples is given
67 by 6 opportunistic forms (Oligochaeta, then Heteromastus filiformis, Nephtys hombergii, Melinna palmata, Oriopsis armandi and Prionospio cirrifera among polichaeta) characteristic of areas subject both to anthropogenic impact and natural disturbances. (The study sector on the Romanian continental shelf of the Black Sea is known as an area predominantly covered by muddy/oozy fine sediments where there occurred periodic hypoxic events. Literature data mention that Oligochaets are detritus feeders, being found in great densities on this type of substrata and some species could be indicators of organic pollution. Unfortunately we didn‟t identified Oligochaeta to the species level; for the moment we considered Oligochaeta a generic group of opportunistic species, their identification to the species level being a difficult task requiring a specialist . The presence of Oligochaeta population in great number of individuals in the bottom sediments influenced by the Danube River, as well as in the harbor environments determined us to consider them as opportunistic forms. Non-mentioning of this aspect is a trap leading us to a misinterpretation of AZTI program which, as of matter of fact, places the Oligochaeta among the opportunistic forms.)
The ecological characteristics of the above-mentioned polychaeta species, which have well- defined preferences to environmental conditions and thus can be used as bioindicators of eutrophication and organic pollution, are as follows:
Heteromastus filiformis – opportunistic, euritopic species, indicates natural or human induced disturbances by their rich abundance; Nephtys hombergii - tolerant species to organic pollution and the diminishing of dissolved oxygen concentration in water, inhabits sandy-muddy and oozy-sandy sediments; Melinna palmata is the most common species, not only at the Romanian coast but also throughout the whole Black Sea basin; this polychaete worm prefers the soft detrital sediments (mud, muddy-sand, sometimes broken shells), in which it can dig, burying itself up to 20 cm depth. This species is an indicator of natural or anthropogenic disturbance only if it reaches high abundance, especially high biomasses; Prionospio cirrifera is a species resistant to pollution with organic substances or petroleum products, being more abundant in areas with moderate pollution. The increase in the species abundance is also indicative of increased eutrophication.
The benthic populations in the Romanian Black Sea continental shelf developed some specific features under the influence of predeltaic and estuarine habitat in the coastal area close to the Danube River mouths and in the offshore periazoic zone. According to the results obtained in
68 2009-2010, the most numerically abundant populations are found in the biocoenoses of hard- bottom mussels and muddy-shelly bottom mussels in the deeper areas of Sf. Gheorghe and Mangalia transects (Fig.3.31). The diversity of substrata in these areas is one of the ecological factors that influence the specific and numerical distribution of macrobenthic population. In Sf. Gheorghe area the high densities are given by two species of polychaeta - Melinna palmata and Dipolydora quadrilobata, the latter being a new species at the Romanian coast. Here, the detritic accumulation in the sediments in the 1970s allowed the massive development of the populations of polychaeta worm Melinna palmata. Thus, a new benthic community dominated by this muddy polychaeta worm appeared at the Romanian coast, forming a true sub-coenosis in the areas occupied before by the typical Mytilus community.
Fig. 3.30. Distribution of the benthic species number in the study area in 2009-2010
The average population density of Melinna palmata in the 1970s-1980s was around 2,330 indvs.m-2, the maximum values exceeding 17,000 indvs.m-2. In our studies this polychaeta had a frequency of 80% and the total number of individuals was 5,651 indvs.m-2 in the area influenced by the Danube River (Sf. Gheorghe and Portita transects). The polychaeta worm density ranged from 15 indvs.m-2 (St. 10PO01 - May) to 8,200 indvs.m-2 (St.10SG02 - May), with an average of 2,323.2 indvs.m-2. The biomass ranged from 0.1g.m-2 to 205 g.m-2, the average being 42.2 g.m-2. Therefore, the high values recorded for this opportunistic species
69 indicate that the state of the benthic ecosystem in the area influenced by the Danube River is still fragile.
The analysis of the mean biomass values distribution of the macrobenthic populations show that the highest biomass values can be found in the area influenced by the Danube River (Sf. Gheorghe), due to the conditions favouring the development of opportunistic organisms (e.g. large-sized bivalves Mya arenaria and Anadara inaequivalvis, the polychaeta worm Melinna palma). These species, having at their disposal abundant trophic resources available as particulate organic matter and competition with other species being absent, can have a mass development, reaching very high biomasses (Fig.3.32).
Fig. 3.31. Distribution of macrobenthic population density in the study area in 2009-2010
Ecological quality status: In recent years, several benthic biotic indices have been proposed as ecological indicators in estuarine and coastal waters. One such indicator, the AZTI Marine Biotic Index (AMBI), was designed to establish the ecological quality of European coasts.
The AMBI has been used also for the determination of the ecological quality status (EQS) within the context of the European Water Framework Directive. In this case this index has been used for determining EQS, the response of soft-bottom benthic communities to natural and man-induced disturbances in coastal environments.
70
Fig. 3.32. Distribution of macrobenthic population biomass in the study area in 2009-2010
AMBI Index is calculated based on the proportions of five ecological groups (EG) to which the benthic species are allocated: EG I the disturbance-sensitive species, EG II the disturbance-indifferent species, EG III the disturbance-tolerant species, EG IV the second- order opportunistic species and EG V the first-order opportunistic species.
Portita: in Portita sector, the state is slightly disturbed in most stations while the benthic community health is unbalanced. In May, only in PO05 station (the Observatory place) and in PO04 in September, the state was moderately disturbed, while benthic community health was a transitional one to pollution (Fig. 3.33). With the exception of PO5 and PO4 stations, the proportion between the Ecological Groups is not significantly different in the two analyzed seasons. The situation slightly improved at PO5 station in autumn, due to the tolerant species. On the other hand, the situation got worse at PO4 in autumn. The explanation is that this station is under the direct influence of the Danube. The other stations were situated towards the coast, thus less impacted by the Danube influence. PO05 – MAY: ~ 45% dominant Ecological groups IV and V (second and first-orderopportunistic species) Heteromastus filiformis, Capitella capitata, Prionospio cirrifera, Anadara inaequivalvis, Polydora cornuta, Dipolydora quadrilobata, Oligochaeta (Fig.3.34). PO05 – SEPTEMBER: ~ 60% dominant Ecological groups III (tolerant species) (Melinna palmata, Ventrosia ventrosa, Abra prismatica, Abra alba, Medicorophium runcicorne)
71
Fig. 3.33. Ecological quality status in Portita area (Upper graph – May: Lower graph – September)
72
Fig. 3.34. Benthic community health in Portita area (Upper graph – May: Lower graph – September)
73 Sf. Gheorghe Area: In both seasons, the AMBI index shows a moderately disturbed state in inshore stations in Sf. Gheorghe sector, situated near the Danube mouths (Fig. 3.35). Benthic community health was transitional to pollution, with moderate disturbance inshore stations and slight disturbance in offshore stations.
There are no significant changes between May and September regarding the proportion of the Ecological Groups. The opportunistic species dominate in coastal stations while the sensitive ones prevail in offshore stations (Fig. 3.35).
Inshore stations with ~ 45% dominant Ecological groups III, IV and V (Melinna palmata, Anadara inaequivalvis, Abra prismatica, Oligochaeta), showing transition to pollution. Offshore stations show unbalanced state with ~ 50% dominant Ecological groups I and II (sensitive species) (Pusillina lineolata, Parvicardium exiguum, Spisula subtruncata, Phtisica marina, Eudorella truncatula, Iphinoe elisae, Upogebia pusilla).
Emergent events in 2010 - Evidences of algal bloom and mass mortality: During the interval 28 - 30 July 2010, mass mortalities of some marine organisms such as fish, molluscs, crustaceans and other animals (jellyfishes) were recorded at the Romanian Black Sea littoral (Table 3.3). These heavy mortalities were generally the result of a stressed environment, generated by oxygen depletion – a direct result of the hot period with average temperatures of 38°C in air and 27°C in seawater and calm weather, no wave motion.
In May - June the coastal marine environment was characterized by low salinity (<10psu) and moderate amounts of oxygen as a result of massive input of freshwater discharge from the Danube River due to floods recorded in Europe.
74
Fig. 3.35. Ecological quality status in Sf. Gheorghe area and benthic Community Health in Sf. Gheorghe area (Upper graph – May: Lower graph – September)
75
Fig. 3.36. Variations of dissolved oxygen on Constanta transect of the Romanian Black Sea coast, July 2010
Fig. 3.37.Hypoxic phenomena recorded at Mamaia Bay in the period 1998-2010, sub-surface depth is ~1 m (after Lazar et al., unpublished data)
In July low O2 concentrations, high temperatures and low salinity values of surface seawater were recorded in stations located in the coastal area in July (Fig. 3.36) and (Fig.3.38). On 28th
July 2010, the lowest O2 concentration of the last 12 years was recorded in the area.
All the events happened in a very short period (3-4 days), being mostly observed in semi- enclosed shallow waters. Oxygen concentration in seawater was extremely reduced at depths greater than 10 m, without affecting the benthic fauna (Fig. 3.37, 3.39).
76
Fig. 3.38. Variations of temperature and salinity on Constanta transect of the Romanian Black Sea coast, July 2010
77 Table 3.3. List of species encountered on the beach at the Romanian coast of the Black Sea during the mortalities recorded in July 2010.
Stations on the beaches Cap Species Corbu Mamaia Constanta Midia FISHES Neogobius cephalarges PALLAS - - ++ +++ Neogobius melanostomus PALLAS - - +++ +++ Mesogobius batracnocephalus PALLAS - - - ++ Gobius sp. + + +++ +++ Solea nasuta PALLAS - - +++ +++ Platichthys fxesus luscus PALLAS - - + - Mullus barbatus ponticus ESSIPOV ++ + +++ +++ Gaidropsarus mediterraneus L. - - ++ +++ Ophidion rochei MULLER - - ++ +++ Scorpaena porcus L. - - + ++ Trachinus draco L. - - + + Parablennius sanguinolentus PALLAS - - + ++ Parablennius tentacularis BRUNNICH - - + ++ Symphodus tinca L. - - + ++ Gymnammodytes cicerellus RAFINESQUE - - + - Syngnathus sp. - - +++ ++ MOLLUSCS Cardium exiguum GMELIN ++ + - - Lentidium mediterraneum COSTA +++ - - - Mya arenaria L. - - - - Mytilus gallaprovincialis LAM. - - - +++ Anadara inequivalvis BRUG. ++ + - - Rapana venosa VALEN. + - - + Donax trunculus L. + - - + CRUSTACEANS Pachygrapsus marmoratus FABR. - - + + Xantho poressa OLIVI - - + + Crangon crangon L. + + + - Palaemon elegans RATHKE - - - ++ VARIA Aurelia aurita L. (Coelenterata) - - ++ -
Main changes in the NW Black Sea benthic communities: A comparison between the information from the 1960s and the data from the present time reveals that nowadays there are signs of benthic ecosystem dysfunctions. While in the 1960s the main benthic communities were extended on large areas, well distributed spatially, at present some of them have been reduced and fragmented (e.g. Phyllophora), others having lost the status of community due to invasive species, which occupied their habitats.
A comparison between the present results and those from the period of increasing ecological pressure in the 1980s-1990s indicates that the 1990s period was characterized by major perturbations of bottom communities in the coastal area, but increased stability in the offshore zone.
78
Fig. 3.39. Sudden warming of seawater and hypoxic events were followed by mass mortality of fishes – goby fish on Mamaia beach (upper picture); species diversity of killed fishes (lower pictures).
At the turn of the century a slow recovery of the benthic communities in the coastal area could be observed (over 10,000 indvs/m-2, see Fig.3.40 - the green area), while the situation remained almost unchanged in the offshore zone (Fig.3.40 - the blue and red area). Increases
79
1980-1990
2003-2010 Fig. 3.40. Comparative maps of the macrobenthos density (indvs.m-2) distribution on theRomanian shelf of the Black Sea in 1980-1990 and 2003-2010 (Bacescu et al., 1971). in the abundance of macrobenthic populations are due to invasive and opportunistic species, such as: Dipolydora quadrilobata, Melinna palmata, Alitta succinea, Heteromastus filiformis, etc. (Fig. 3.40). The biomasses also reflect the above situation. The Danube and Dniestr areas, still under ecological pressure, have higher biomasses represented by the “newcomers“ in the
80 Black Sea, the mollusks Mya arenaria, Anadara inaequivalvis, Rapana venosa and polychaeta Melinna and Neanthes, which have a high potential to endure stressor pressure (Fig.3.41). The current abundance level of opportunistic molluscs species Rapana, Mya and Anadara, highly tolerant to hypoxia, continues to dominate the macrobenthos system; these species represent a rich trophic resource, having potentially, at the same time, a commercial value.
1980-1990
2003-2010 Fig. 3.41. Comparative maps of the macrobenthos biomass (g.m-2) distribution on theRomanian shelf of the Black Sea in 1980-1990 and 2003-2010 (Bacescu et al., 1971).
81 Meiobenthos populations, Assessing the biodiversity of the marine free-living nematodes from the Romanian sector of the Black Sea as indicator species for hypoxia: The Black Sea meiobenthic communities are relatively little studied nowadays. To this category belong gastrotricha, kinorincha, ostracoda, foraminifera, nematodes, halacarida, harpacticticoida, etc. At 100 m depth, macrofauna consists mainly of small holoturia (sea-cucumbers), ascidians (sea-squirts), polychaeta and oligochaeta worms rarely found below 150 m depth and, very rarely, at 200 m depth. In exchange, the meiobenthic communities, such as nematoda, foraminifera, harpacticoida, kinorhyncha, however, can be occasionally found even at 200 m. For the moment, we will deal only with the nematode populations. The first studies dedicated to the Romanian littoral nematodes diversity occurred in the 50s-60s, when 17 species were listed by Băcescu et al (1963), out of a total of 148 forms inventoried at that time. Most of them were known for Sebastopol Bay, due to the great Russian nematodologist Filipjev, 28 species were known for the Bulgarian coast (Platonova, 1968) and two species for the prebosphoric space and Caucasian coast of the Black Sea.
The ecology of nematodes is closely related to the substratum type, Wieser (1959) being the first specialist to identify the major ecological groups of nematodes based on this factor. Similar data were published by Băcescu et al. (1971) after a critical analysis of the information available in the literature at that time and by a comparative study of the researches on the distribution of nematodes in different benthic biocoenoses and sea-floor levels at the Romanian coast. The highest diversity was found in the biocoenosis of Modiolus in the circalittoral level, unlike the deeper periazoic level, where only 12species were listed (Fig. 3.42).
Materials and methods: Meiobenthos sampling was carried out in 2010 (May and September) and 2011 (April). Along four transects crossing the Romanian continental shelf - Sf. Gheorghe, Portita, Constanta and Mangalia (Fig.3.26) 55 meiobenthos samples were collected in 2010 and 32 samples in 2011. In 2011 there were analyzed 9 samples coming from stations located between 36 and 200 m depths and 1 sample from 16 m depth on Sf. Gheorghe transect, and 1 sample from 150 m depth on Mangalia transect. The geographical coordinates of stations in 2010 and 2011 were the same. The multi corer with 4 tubes, Mark II type (tube area - 0.0075 m-2, multiplication factor for 1 m-2 - 133) was used for sampling, being lowered into the sea from R/V “Mare Nigrum” board.
Sediment samples with nematodes were taken from the top 5 cm and occasionally from the next 5 cm of the collected core and preserved with buffered formaldehyde 4% in
82 polypropylene containers. In the laboratory, the samples were washed to remove the mineral sedimentary matrix and extract the meiobenthic organisms, using a sieve of 90 μm mesh-size.
Taxonomic identification was carried out under a microscope, using determination keys after Platonova (1968), Filipiev (1968), Chesunov, 2006, Onciu (1995), Wieser (1953-1956) and online databases (Nemys (http : / / nemys.ugent.be), GBIF (http://www.gbif.org) and OBIS (http://www.iobis.org).
The quantitative structure was expressed and analyzed as number of individuals per square meter (indvs.m-2), by counting all individuals in a sample or more subsamples during the sorting process under microscope. For identification, nematodes were first fixed in glycerol for better observation of the transparent elements of the internal structure which are key identifiers. Statistical calculation was done by univariate and multivariate analyses of the parameters studied. It is worth mentioning that a member of the Hypox team - Mihaela Muresan is working on nematodes at present as a Ph.D. student.
Rationales: Generally, nematodes are considered to be the most resistant meiofauna taxa to low oxygen concentrations and sulphide exposure and copepodes to be more sensitive (Murrell and Fleeger, 1989; Hendelberg and Jensen, 1993). However, this seems to be species specific as the diversity of nematodes may decrease after a hypoxic event (Austen and Widbom, 1991) and some copepod species appear to be tolerant to low oxygen concentrations and sulphide exposure (Vopel et al., 1996). Among the metazoan meiofauna, nematodes, the numerically dominant and least motile meiofaunal taxon in subtidal soft sediment communities, are the most tolerant to low oxygen (Giere, 1993; Cook et al., 2000; Neira et al., 2001a).
Many metabolic studies of free-living and parasitic nematodes (Bolla, 1980) contributed to deeper insights into the complex biochemical events that underpin their life in different stressful conditions. At the base of researchers‟ discovery is the intermediary metabolism, which is responsible for many shifts and adaptive responses. These metabolic shifts can occur instantly, as response to changing environments, or more slowly as e.g. over the course of their life cycle. These aspects were well studied in case of genetic model species Caenorhabditis elegans. In case of free-living nematodes tolerant to hypoxia, as in case of many marine invertebrate, the anaerobic capacities are due to anaerobically functioning mitochondria.
83 Marine invertebrate mitochondria are endowed with especially adapted electron transport systems for anaerobic fermentation of malate, resulting in succinct and short chained organic acids, acetate and propionate, as end-products (reviewed by Grieshaber et al, 1994). It is a well accepted view that a prime function of early mitochondrial activity in an atmosphere of changeable oxygenation was to control intracellular pO2 in diffusion limited organisms, by reducing O2 to water and keeping the production of reactive O2 species low (Brand, 2000; Abele, 2002).
Discovery of alternative oxidase activity in marine invertebrate mitochondria is related to cyanide-insensitive respiratory pathways that are electron transport chains terminating in so called alternative end oxidase (AOX). Alternative oxidase expression is influenced by stress-stimuli cold, oxidative stress, pathogen attack, and by factors restricting electron flow through the cytochrome pathway of respiration, like H2S or cyanide inhibition. Control over the AOX activity is exerted at the levels of gene expression, as well in response to availability of carbon and reducing potential. Recently the gene has been detected in marine ectotherms from the phyla Mollusca, Nematoda and Urochordata, and expression confirmed in different tissues of the tunicate Ciona intestinalis and the oyster Crassostrea gigas (McDonald & Vanlerberghe, 2005). Several alternative electron pathways have been characterized and described for free-living and parasitic nematodes (Paget et al, 1988; Wieser et al, 1974; Paget et al., 1987; Mendis & Evans, 1984), colonizing a micro-oxic/sulphidic habitat: the gut.
Several nematode species are able to withstand anoxic conditions for over 60–78 days, although their densities decline (Wieser and Kanwisher, 1961; Moodley et al., 1997). Recent meiofaunal studies at three shelf and upper slope sites off Chile (309 m; north off Antofagasta, 366 m; central off Concepcion, and 296 m; south off Chiloe) (0–10 cm; Veit- Kohler et al., 2009), and off Callao, Peru (94 m) (0–1 cm; Gutierrez et al., 2008) confirm previous observations for the region (Neira et al., 2001a, 2001b) that nematodes are the dominant meiobenthic group at these depths and that they reach highest densities and biomass during periods of strong oxygen deficiency.
Some results on the richness and distribution of nematodes populations: In the frame of Hypox Project 52 samples taken at different depths from four sectors at the Romanian Black Sea continental shelf were analyzed (Table 3.4):
Sf. Gheorghe transect covering the Danube River influence gradient, depth gradient and coastal-offshore gradient;
84 Portita zone – the more or less protected sector of Hypox Observatory situated south of the Danube Delta; Constanta transect – the “classical” marine area of the Romanian monitoring in the Black Sea; Mangalia transect – the southern sector of the Romanian coast, far from the direct Danube River influence, in the neighbourhood of the frontier with Bulgaria.
A total number of 96 nematode species were identified (Table 3.5); specific diversity of nematode populations varies both geographically from north to south and bathymetrically from coastal shallow waters to offshore deep waters (Fig. 3.42; Fig. 3.26; Table 3.6, 3.7).
The highest nematodologic diversity was recorded on Sf. Gheorghe transect (85 species) and on the bottoms situated at 61 – 100 m depths. The most common species of nematodes at the Romanian Black Sea shelf, usually ranking among the top 10 species, are: Sabatieria pulchra, S. abyssalis, Terschellingia longicaudata, Viscosia cobbi, Spirinia zosterae, Axonolaimus ponticus, Metalinhomoeus zosterae, Sphaerolaimus gracilis, Viscosia minor,Enoplus euxinus etc. (Table 3.5).
Table 3.4. Studying nematodes‟ populations - research efforts and main results. Depth interval - m No. samples Number of species 0-20m 6 28 21-30m 10 48 31-40m 6 44 41-60m 9 53 61-100m 10 60 101-150m 7 44 151-210m 4 15
Table 3.5. List of nematodes‟ populations found in 2010 and April 2011 and their average density on transects
Crt.no. Species Transects Sf. Gheorghe Portita Constanta Mangalia 1 Anoplostoma viviparum 14.78 2 Araeolaimus sp. 193.16 54.94 3 Axonolaimus ponticus 127572.34 151.38 7423.85 4 Axonolaimus setosus 29477.84 2528.64 5 Bathylaimus assimilis 9.37 57.79 3.77 6 Bathylaimus cobbi 118.96 1748.49 128.87 7 Camacolaimus dolichocercus 47.42 19.00 8 Cheironchus bulbosa 8814.25 57.79 9 Chromadora cricophana 546.68 12.73 10 Chromadora gracilis 26.33 5.46 11 Chromadora quadrilinea 268.89
85 12 Chromadorella pontica 15858.99 753.69 41.42 13 Chromadora sp. 9.56 173.57 19.00 14 Chromadorina obtusa 11.21 57.79 8.24 15 Chromadorita sp. 5.78 18.62 16 Chromaspirina pontica 172.87 17 Cobbionema acrocerca 15384.67 695.38 213.26 448.62 18 Cobbia triodonta 118.18 19 Cyatholaimus (Paracanthoncus) caecus 2543.75 2277.68 139.97 771.70 20 Daptonema elegans 592.90 17.32 21 Daptonema setosus 29927.53 218.92 22 Daptonema oxycerca 28245.76 184.62 23 Dichromadora gracilis 28.98 342.51 3.77 24 Desmodora pontica 139491.25 56.48 25 Desmolaimus bulbulus 175.78 26 Desmoscolex minutus 34.64 27 Enoplus maeoticus 26.52 175.53 317.72 28 Eleutherolaimus longus 19199.33 189.80 22.48 1167.30 29 Enoploides amphioxi 176.34 83.23 41.42 30 Enoploides cirrhratus 26.52 118.15 41.42 31 Enoploides brevis 859.21 118.15 34.36 1845.89 32 Enoplolaimus conicus 84.14 33.61 857.98 33 Enoplus euxinus 1691.43 816.78 1434.94 73.15 34 Euchromadora sp. 183.84 249.92 389.39 35 Eurystomina assimilis 535.53 48.32 36 Halalaimus ponticus 17677.38 1648.29 715.87 684.21 37 Halaphanolaimus pellucidus 16645.63 1322.11 286.48 292.89 38 Halanonchus bullatus 189239.16 2693.96 39 Halichoanolaimus clavicauda 17849.54 178.19 40 Halichoanolaimus filicauda 24.51 265.48 19.00 41 Hypodontolaimus ponticus 9.37 1158.13 53.64 42 Linhomoeus filiformis 13578.44 858.88 551.71 73.15 43 Linhomoeus hirsutus 591.64 3778.17 44 Linhomoeus sp. 45.64 531.52 81.72 45 Metalinhomoeus sp. 354.32 34.97 46 Metalinhomoeus zosterae 58.35 134.60 1588.69 47 Metachromadora macroutera 822.20 173.38 74.15 13855.64 48 Metoncholaimus demani 26344.89 622.83 165.67 49 Microlaimus ponticus 74.36 1288.48 19.00 53.23 50 Monhystera sp. 372.92 19.87 51 Nemanema filiforme 191.79 944.87 285.74 52 Neochromadora sp. 96.58 194.62 53 Odontophora angustilaima 1891.60 4767.83 2342.96 7861.78 54 Oncholaimus brevicaudatus 16.15 55 Oncholaimus campylocercoides 6294.12 49.76 5476.55 56 Oncholaimus dujardinii 5.78 34.64 53.20 57 Oxystomina clavicauda 29669.63 74.34 67.69 58 Oxystomina elongata 714.79 177.22 788.92 194.62 59 Quadricoma loricata 258.42 686.17 316.38 60 Quadricoma media 313.86 22.17 61.55
86 61 Quadricoma pontica 54.42 24.16 215.42 62 Quadricoma reinharddi 176.25 98.52 76.00 63 Quadricoma nematoides 133.74 64 Quadricoma sp. 11.57 19.00 65 Pandolaimus ponticus 9.37 66 Paralinhomoeus ostrearum 86.25 116.87 62.51 67 Paramonhystera elliptica 4743.72 223.83 274.24 271.24 68 Paramonhystera setosa 1357.17 1892.99 69 Paroncholaimus zernovi 99.89 3.77 70 Prosphaerolaimus euripharynx? 171.80 17571.81 71 Rhabdodemania pontica 3552.28 57.79 16.77 72 S. abyssalis 388354.39 126174.76 882.76 36137.73 73 Sabatieria longicaudata 14884.62 79.83 325.58 31447.11 74 Sabatieria pulchra 14873.41 11477.82 6426.80 2119.96 75 Sabatieria quadripapilata 25.36 5.46 76 Sphaerolaimus gracilis 939.77 8872.41 78.69 15.96 77 Sphaerolaimus macrocirculus 5214.75 985.86 497.73 1223.60 78 Sphaerolaimus ostreae 346.30 2671.66 224.48 1443.50 79 Sphaerolaimus dispar 26.33 258.57 80 Sphaerocephalum dolichocercus 44227.13 4865.96 81 Spirinia sabulicola 161.24 58.86 19.00 53.20 82 Spirinia zosterae 2372.94 1912.58 353.70 83 Terschellingia antonovi 225.54 84 Terschellingia communis 47.77 34.64 85 Terschellingia pontica 3.75 4112.97 185.87 97.53 86 Terschellingia longicaudata 19211.82 4919.69 7176.99 11456.18 87 Th.longicaudatus 23.56 496.85 88 Theristus latissimus 26.33 19.00 89 Theristus maeoticus 82.83 90 Tricoma platycephala 3548.83 72.19 1965.44 91 Tripyloides marinus 172.76 292.89 92 Viscosia cobbi 13224.57 741.64 3231.39 145.86 93 Viscosia elongata 1762.86 5337.12 19.87 384.81 94 Viscosia glabra 14.78 95 Viscosia minor 87.13 13643.41 96 Viscosia viscosa 2599.26 612.75 Number of species - N sp 87 64 71 35 Average density - indvs.m-2 1265229.76 221016.70 52003.02 129026.08
87
Fig. 3.42. Distribution of nematodes' populations on depth intervals at the RomanianBlack Sea continental shelf.
Fig. 3.43. Distribution of nematodes' populations on depth intervals at the Romanian Black Sea continental shelf.
88 Explanation to the first 10 ranked species on the cumulative curves of populations in Fig.3.43.
Table 3.6. Some indicators of nematodes‟ populations on the bathymetric zones at the Romanian Black Sea continental shelf Indicators Values Bathymetric interval 0-20 m 21-30 m 31.40 m 41-60 m 61-100 m 101-150 m 151-210 m min 11.43 26.68 31.61 41.09 62.75 110.80 161.50 Depth - m Mean 16.37 28.453 33.44 48.13 84.36 132.31 183.43 max 21.51 30.55 36 60.8 98.00 150.50 210.20 min 3 5 9 4 13.0 5 0 N sp Mean 7.5 13.2 14.5 14.7 19.2 13.1 4.8 max 13 20 19 24 35.0 24 8 min 261.3 45804.2 12768.0 33383.1 10773.0 5985.0 0.0 D - indvs.m-2 Mean 3801.5 349561.4 195822.9 157056.0 35481.2 39945.4 2327.5 max 8224.1 1638559.9 324003.5 401128.0 109060.0 106932.0 5852.0
89 Table 3.7.The first 10 or 20 ranked nematodes species on bathymetric zonesaccording to the value of ecological importance index 0 – 20 m Rank. Species name Davg D% 1 Sabatieria pulchra 74,764.40 70.24 2 Terschellingia longicaudata 8,420.90 7.91 3 Viscosia minor 8,439.74 7.93 4 Anoplostoma viviparum 3,726.88 3.50 5 Sphaerolaimus macrocirculus 1,521.52 1.43 6 S. abyssalis 1,691.32 1.59 7 Enoploides brevis 800.66 0.75 8 Chromadorella pontica 974.89 0.92 9 Enoplolaimus conicus 823.27 0.77 10 Oncholaimus brevicaudatus 823.27 0.77 21 - 30 m
Rank Species name Davg D% 1 S. abyssalis 122,049.64 34.92 2 Sabatieria pulchra 72,529.05 20.75 6 Terschellingia longicaudata 31,488.75 9.01 7 Viscosia cobbi 16,790.98 4.80 5 Spirinia zosterae 24,899.19 7.12 3 Sphaerolaimus gracilis 11,609.04 3.32 4 Sphaerolaimus macrocirculus 7,117.49 2.04 8 Viscosia minor 6,164.12 1.76 9 Eleutherolaimus longus 3,046.37 0.87 10 Axonolaimus ponticus 4,719.31 1.35 31 – 40 m
Rank Species name Davg D% 1 S. abyssalis 53014.00 27.07 2 Terschellingia longicaudata 39249.92 20.04 3 Sabatieria pulchra 32708.41 16.70 4 Axonolaimus ponticus 19530.49 9.97 5 Viscosia cobbi 11126.43 5.68 6 Paramonhystera elliptica 4510.94 2.30 7 Metalinhomoeus zosterae 2932.86 1.50 8 Enoplolaimus conicus 1865.30 0.95 9 Cyatholaimus (Paracanthoncus) caecus 1796.06 0.92 10 Spirinia zosterae 2773.81 1.42 41 – 60 m
Rank Species name Davg D% 1 S. abyssalis 62513.12 39.80 2 Sabatieria pulchra 28194.50 17.95 3 Metalinhomoeus zosterae 11093.29 7.06 4 Viscosia cobbi 8155.48 5.19 5 Terschellingia longicaudata 6777.21 4.32 6 Cobbionema acrocerca 1950.50 1.24
90 7 Enoplolaimus conicus 1912.90 1.22 8 Enoplus euxinus 3676.08 2.34 9 Viscosia elongata 2338.95 1.49 10 Halalaimus ponticus 1860.26 1.18 61 – 100 m
Rank Species name Davg D% 1 S. abyssalis 10,504.28 29.61 2 Enoplus euxinus 3,835.37 10.81 3 Quadricoma loricata 3,683.78 10.38 4 Halalaimus ponticus 1,686.03 4.75 5 Metachromadora macroutera 1,600.27 4.51 6 Paramonhystera elliptica 1,826.44 5.15 8 Paralinhomoeus ostrearum 1,104.96 3.11 9 Halanonchus bullatus 921.75 2.60 10 Viscosia cobbi 1,460.87 4.12 11 Sphaerolaimus macrocirculus 588.37 1.66 12 Odontophora angustilaima 456.85 1.29 13 Terschellingia longicaudata 419.90 1.18 14 Cyatholaimus (Paracanthoncus) caecus 512.30 1.44 15 Sphaerocephalum dolichocercus 984.12 2.77 16 Metalinhomoeus zosterae 455.77 1.28 17 Prosphaerolaimus euripharynx? 637.37 1.80 18 Oncholaimus campylocercoides 396.55 1.12 19 Halaphanolaimus pellucidus 225.20 0.63 20 Rhabdodemania pontica 170.69 0.48 101 – 150 m
Rank Species name Davg D% 1 S. abyssalis 11922.065 29.84593 2 Oncholaimus campylocercoides 5835.8521 14.60959 3 Halanonchus bullatus 3844.9631 9.625557 4 Odontophora angustilaima 2736.1739 6.849792 5 Linhomoeus hirsutus 2517.2664 6.301775 6 Sabatieria pulchra 1463.9984 3.665003 7 Desmodora pontica 968.11404 2.423596 8 Cobbionema acrocerca 716.09921 1.792697 9 Metalinhomoeus zosterae 1044.1609 2.613973 10 Tricoma platycephala 507.76085 1.271139 11 Rhabdodemania pontica 850.3 2.128658 12 Linhomoeus filiformis 585.16429 1.464912 13 Eleutherolaimus longus 319.9164 0.800885 14 Spirinia zosterae 315.80424 0.790591 15 Metoncholaimus demani 431.66562 1.08064 16 Axonolaimus ponticus 411.5 1.030157 17 Paralinhomoeus ostrearum 258.80529 0.647898 18 Theristus longicaudatus 523.55556 1.310679 19 Halalaimus ponticus 209.95 0.525593 20 Metachromadora macroutera 381.9 0.956056
91 151-210 m
Rank Species name Davg D% 1 S. abyssalis 731.5 31.42857 2 Sabatieria pulchra 598.5 25.71429 3 Metalinhomoeus zosterae 266 11.42857 4 Terschellingia longicaudata 133 5.714286 5 Tricoma platycephala 133 5.714286 6 Viscosia cobbi 99.75 4.285714 7 Quadricoma sp. 66.5 2.857143 8 Viscosia glabra 66.5 2.857143 9 Axonolaimus ponticus 33.25 1.428571 10 Bathylaimus cobbi 33.25 1.428571
Diversity of nematodes’ populations in the studied area in May and September 2010: In May and September 2010 a diversity richness of 92 species (Table 3.8) belonging to 22 families was found during the two expeditionary research studies. Out of 92 species only few of them have a high value of their indices of ecological significance (W) ensuring more than 70-80% of the total density; Sabatieria abyssalis and S. pulchra dominate by far, Terschellingia longicaudata and Viscosia cobbi being on the third and fourth places (Fig. 3.44). A similar conclusion has come up from Mediterranean Sea studies on nematodes distribution. As so, the most abundant genus in the Mediterranean canyons was Sabatieria, similar to the shelf break and slope stations. According to Vanreusel 1990, Vincx et al., 1990, Sabatieria genus are typically found in muddy sediments, which are anoxic a few millimeters below the surface. Some authors talk about a specific niche that is used by the two con generic species (S. abyssalis and S. pulchra). S. pulchra was mostly abundant down to 80 m in depth, while S. abyssal up to 160 m, but their association in the same site was encountered also. The frequent association with Terschellingia longicaudata and Viscosia genus was frequently noted. Terschellingia sp. is a selective deposit feeder, a part of Linhomoeidae Family. It has a long tail, a slender body and a small buccal cavity, which help it to use efficiently a particular trophic niche constituted of bacterial items. Armenteros et al, 2009 also found in eutrophic parts of the Caribbean Sea a codominance of the two mentioned species. It was reported that T. longicaudata is usually found in anoxic conditions and feeds on bacteria (Wieser, 1953, 1960), and could be also found in the deeper layers of the substrate (Eskin & Palmer, 1985). Viscosia genus are cosmopolitan (about 15 species are considered valid taxons), with no peculiar preferences for any substrata. Therefore, some authors (Meyers & Hopper,1973, Riemann & Schrage, 19781 and Lopez et al., 1979,Heip et al., 1985), consider this genus rather detritv or and necrophagous than predator.
92
Table 3.8. General characteristics of nematodes‟ populations identified in 2010 frequency (F%), mean density (Davg), ecological density (Deco), numerical proportion (D%), index of ecological importance (W), rank of species
1 Anoplostoma viviparum 3,70 414,10 11180,65 0,31 1,07 42 2 Areolaimus sp. 3,70 89,39 2413,61 0,07 0,50 61 3 Axonolaimus ponticus 33,33 3263,18 9789,53 2,42 8,98 5 4 Axonolaimus setosus 1,85 561,92 30343,70 0,42 0,88 46 5 Bathylaimus assimilis 5,56 117,58 2116,40 0,09 0,70 52 6 Bathylaimus cobbi 16,67 908,26 5449,54 0,67 3,35 25 7 Camacolaimus dolichocercus 5,56 27,79 500,26 0,02 0,34 67 8 Cheironchus bulbosa 1,85 12,84 693,50 0,01 0,13 84 9 Chromadora cricophana 11,11 252,94 2276,43 0,19 1,44 37 10 Chromadora gracilis 1,85 11,21 605,50 0,01 0,12 85 11 Chromadora quadrilinea 1,85 114,53 6184,50 0,08 0,40 64 12 Chromadorella pontica 14,81 535,85 3617,00 0,40 2,43 30 13 Chromadora varia 3,70 38,57 1041,39 0,03 0,33 71 14 Chromadorina obtusa 5,56 30,99 557,86 0,02 0,36 66 15 Chromadorita sp. 3,70 16,54 446,65 0,01 0,21 80 16 Chromaspirina pontica 3,70 73,63 1987,97 0,05 0,45 62 17 Cobbionema acrocerca 35,19 646,92 1838,62 0,48 4,11 19 18 Cyatholaimus (Paracanthoncus) caecus 27,78 897,92 3232,51 0,67 4,30 16 19 Daptonema elegans 5,56 292,08 5257,35 0,22 1,10 40 20 Daptonema setosus 7,41 219,81 2967,40 0,16 1,10 39 21 Daptonema oxycerca 3,70 33,07 892,86 0,02 0,30 72 22 Dichromadora gracilis 1,85 3,99 215,41 0,00 0,07 90 23 Desmodora pontica 7,41 112,83 1523,26 0,08 0,79 48 24 Desmolaimus bulbulus 3,70 741,29 20014,71 0,55 1,43 38 25 Desmoscolex minutus 1,85 4,42 238,45 0,00 0,08 88 26 Enoplus maeoticus 1,85 52,95 2859,50 0,04 0,27 76 27 Eleutherolaimus longus 38,89 1031,25 2651,78 0,76 5,45 13 28 Enoploides amphioxi 7,41 106,50 1437,74 0,08 0,76 50 29 Enoploides cirhratus 3,70 31,62 853,85 0,02 0,29 74 30 Enoploides brevis 27,78 712,74 2565,87 0,53 3,83 20 31 Enoplolaimus conicus 38,89 1199,40 3084,16 0,89 5,88 8 32 Enoplus euxinus 29,63 1394,45 4706,26 1,03 5,53 10 33 Euchromadora sp. 1,85 64,90 3504,55 0,05 0,30 73 34 Halalaimus ponticus 46,30 889,41 1921,14 0,66 5,52 12 35 Halaphanolaimus pellucidus 14,81 478,23 3228,05 0,35 2,29 32 36 Halanonchus bullatus 16,67 642,47 3854,81 0,48 2,82 28 37 Halichoanolaimus clavicauda 7,41 110,36 1489,91 0,08 0,78 49 38 Halichoanolaimus filicauda 1,85 2,46 133,00 0,00 0,06 93 39 Hypodontolaimus ponticus 3,70 6,88 185,73 0,01 0,14 83 40 Linhomoeus filiformis 18,52 293,84 1586,73 0,22 2,01 35 41 Linhomoeus hirsutus 11,11 791,38 7122,46 0,59 2,55 29 42 Linhomoeus sp. 5,56 106,39 1915,02 0,08 0,66 55 43 Metalinhomoeus sp. 1,85 57,31 3094,68 0,04 0,28 75 44 Metalinhomoeus zosterae 29,63 2370,83 8001,55 1,76 7,21 7 45 Metachromadora macroutera 25,93 605,23 2334,46 0,45 3,41 24 46 Metoncholaimus demani 3,70 159,88 4316,81 0,12 0,66 54 47 Microlaimus ponticus 7,41 390,37 5269,98 0,29 1,46 36 48 Monhystera sp. 3,70 173,08 4673,13 0,13 0,69 53 49 Nemanema filiforme 5,56 37,04 666,72 0,03 0,39 65 50 Neochromadora sp. 3,70 73,57 1986,47 0,05 0,45 63 51 Odontophora angustilaima 27,78 1007,34 3626,43 0,75 4,55 15 52 Oncholaimus brevicaudatus 3,70 93,94 2536,31 0,07 0,51 59 53 Oncholaimus campylocercoides 12,96 910,99 7027,63 0,67 2,96 26 54 Oncholaimus dujardinii 3,70 13,28 358,63 0,01 0,19 82
93 55 Oxystomina clavicauda 7,41 127,62 1722,81 0,09 0,84 47 56 Oxystomina elongata 16,67 463,16 2778,99 0,34 2,39 31 57 Quadricoma loricata 22,22 746,25 3358,11 0,55 3,51 23 58 Quadricoma media 7,41 145,13 1959,22 0,11 0,89 45 59 Ouadricoma pontica 3,70 39,14 1056,69 0,03 0,33 70 60 Quadricoma sp. 1,85 4,93 266,00 0,00 0,08 87 61 Quadricoma nematodoides 3,70 17,34 468,07 0,01 0,22 79 62 Paralinhomoeus ostrearum 20,37 331,29 1626,35 0,25 2,24 33 63 Paramonhystera elliptica 20,37 923,77 4534,87 0,68 3,73 21 64 Paramonhystera setosa 1,85 79,42 4288,57 0,06 0,33 69 65 Paroncholaimus zernovi 1,85 3,99 215,41 0,00 0,07 90 66 Prosphaerolaimus euripharynx? 7,41 207,25 2797,82 0,15 1,07 41 67 Rhabdodemania pontica 9,26 131,98 1425,40 0,10 0,95 44 68 Sabatieria abyssalis 81,48 42092,18 51658,58 31,18 50,41 1 69 Sabatieria longicaudata 7,41 72,30 976,04 0,05 0,63 57 70 Sabatieria pulchra 70,37 30133,76 42821,66 22,32 39,64 2 71 Sabatieria quadripapilata 1,85 80,24 4332,78 0,06 0,33 68 72 Sphaerolaimus gracilis 16,67 2478,98 14873,90 1,84 5,53 11 73 Sphaerolaimus macrocirculus 24,07 1628,80 6765,78 1,21 5,39 14 74 Sphaerolaimus ostrae 18,52 1284,24 6934,89 0,95 4,20 18 75 Sphaerolaimus dispar 7,41 44,73 603,88 0,03 0,50 60 76 Sphaerocephalum dolichocercus 9,26 1226,81 13249,58 0,91 2,90 27 77 Spirinia sabulicola 7,41 72,62 980,33 0,05 0,63 56 78 Spirinia zosterae 16,67 5217,79 31306,71 3,87 8,03 6 79 Terschellingia antonovi 1,85 39,38 2126,67 0,03 0,23 78 80 Terschellingia communis 1,85 4,42 238,45 0,00 0,08 88 81 Terschellingia pontica 16,67 1005,44 6032,62 0,74 3,52 22 82 Terschellingia longicaudata 57,41 12332,84 21483,01 9,14 22,90 3 83 Theristus moeoticus 1,85 10,74 579,83 0,01 0,12 86 84 Th.longicaudatus 5,56 88,34 1590,03 0,07 0,60 58 85 Theristus latissimus 3,70 13,68 369,25 0,01 0,19 81 86 Tricoma platycephala 9,26 77,20 833,75 0,06 0,73 51 87 Tripyloides marinus 11,11 115,88 1042,94 0,09 0,98 43 88 Viscosia cobbi 57,41 6014,06 10476,10 4,46 15,99 4 89 Viscosia elongata 16,67 1473,49 8840,96 1,09 4,27 17 90 Viscosia glabra 5,56 15,02 270,43 0,01 0,25 77 91 Viscosia minor 18,52 2330,04 12582,20 1,73 5,65 9 92 Viscosia viscosa 9,26 672,96 7267,98 0,50 2,15 34
An increasing diversity was observed at depths that correspond to Modiolus biocoenosis. Similar high values of Margaleff and Shannon diversity indices were obtained for stations at 60 - 114 m depth (Stations: 10SG05, 10SG06, 10SG07, 10SG08); the indices evince suitable biotopic conditions for a rich nematode community, made of small populations of specialized species on different niches. A slightly lower diversity but a little higher density were found at 98 m. The same pattern of diversity indices is seen at 114.5 m but almost a three-time higher density occurred.
94
Fig. 3.44. Cumulative curve of the nematode populations‟ dominance.
Among the most frequent species at 87 m were: S. abyssalis (St. Ma03, St.SG06), Quadricoma loricata (St.10Ma03, St.10CT06), Enoplus euxinus (St.10Ma03, St.10CT06, St. SG06), Halalaimus ponticus (St.10Ma03), Sphaerocephalum dolichocercus (St.10CT06), Sphaerolaimus macrocirculus (St.10SG06a), Prosphaerolaimus euripharynx (St.10Ma03). Around 100 m (St.10SG08and St.10MA02) the dominant species were: Oncholaimus campylocercoides, Halanonchus bullatus, Odontophora angustilaima, S. abyssalis. At 143.4 m (St.10SG09), the dominant species were: Linhomoeus hirsutus, Daptonema elegans, S. pulchra, while at 110.8 m deep (St.10MA02), the dominant ones were: S. abyssalis, Halanonchus bullatus, Rhabdodemania pontica, Oncholaimus campylocercoides, Linhomoeus hirsutus.
A striking feature of nematode assemblages is the large number of species present in anyone habitat, but the highest known species diversity values for them were reported from the deep sea (Soertat et al., 1995), while the lowest nematode diversity was observed in the polluted subtidal muds sites off the Belgian East coast (Vincx, 1990), where at some sites only one species was present.
In 2010, in shallow waters, between 11 - 43 m depth, 34 species were found among the first 15 ranked species in spring. About 11.76% of them (S. abyssalis, Terschellingia longicaudata, Enoplolaimus conicus, S. pulchra) were euconstant species in all profiles (a frequency of 100%); 14.71% (Sphaerolaimus ostreae, Cobbionema acrocerca,Viscosia elongata, Metalinhomoeus zosterae, Viscosia cobbi) – occurred in 75% of stations on
95 profiles), 29.41% (Eleutherolaimus longus, Sphaerolaimus macrocirculus, Cyatholaimus caecus, Microlaimus ponticus, Axonolaimus ponticus, Odontophora angustilaima, Sphaerolaimus gracilis, Sphaerocephalum dolichocercus, Terschellingia pontica, Halaphanolaimus pellucidus) – present in 50% of stations were accessories species, the remaining 44.12% being accidentally encountered species.
Morphometric characteristics, trophic type and substratum affinity of nematodes assemblages: In the shallow zone, changes in nematode size spectrum according to increase of organic input could be caused by changes in the community‟s trophic structure: the increase in proportion of large, non-selective deposit feeders followed with corresponding increase in predators also represented by bigger worms. The most diverse group was that of predators-omnivores (2B) - 47% and non-selective feeders (1B) (29.41%). 2B group of species was dominated by relatively small length stout species, with the exception of very long and slender Viscosia species. Non-selective feeders (1B) were numerically dominated by S. abyssalis (length = 1.65 mm - male; a=33; length = 1.50 mm - female; a=25) and Sabatieria pulchra (length = 1.27 mm – male; a=33; length = 1.62 mm; a=30 -female), of medium length and width. In the same trophic group (1B), a second size class was made of very long and medium width species: Axonolaimus ponticus (length = 3.64mm – male; length = 4.00 mm – female; a=63), Odontophora angustilaima (length = 2.40mm – male; a=50) and a third class of small-sized and medium width species (length to width ratio - >15): Eleutherolaimus longus (length = 1.60 mm – male; a=55); Bathylaimus cobbi (length = 1.40 mm – male; a=30). Dominant biocoenoses belong to Lentidium mediterraneum, Anadara inaequivalvis, Mya arenaria and Melinna palmataon the north western shelf being strongly influenced by Danube organic enrichment, seasonal thermal regime and nutrients and O2 fluxes in the water column and sediments.
Therefore, the dominant substratum is mud, mud mixed with broken-shells and sandy mud, actively bioturbated, favouring the O2 penetration in sediments but also organic mineralization and bacterial thriving. The dominant species were: Sabatieria pulchra, S. abyssalis, Terschellingia longicaudata, which are euriotopic species on all types of substratum. In the southern part of the Romanian continental shelf, the dominants were: S. abyssalis, Terschellingia longicaudata, Sphaerolaimus gracilis, Viscosia elongata, Sabatieria pulchra.
Although free-living nematodes were assumed to be resistant to sediment organic enrichment (Powell 1989; Giere 1993; Duplisea and Hargrave, 1996), the data presented in this study,
96 confirmed by literature (e.g. Essink and Keidel 1998; Mirto et al. 2002; Wetzel et al. 2004), suggest that many nematode species are intolerant to organic loading (e.g., Chromadoridae, Monhysteridae). Thus, it seems likely that the response of natural assemblages to organic enrichment will be dependent on the faunal characteristics of the receiving area (the background community). In this sense, nematode assemblages from organically poor sandy areas subjected to organic enrichment are expected to change more drastically than those derived from the organically rich mud (Schratzberger and Warwick 1998). The population changes caused by eutrophication, weak ventilation and increasing temperature could happen within well known tolerant organisms to organic enrichment.
One example is provided by mussels‟ farm, which induced structural shifts in nematode assemblages. This could be the case of seasonal flooding that brings nutrients, detritic and vegetal material in areas under the Danube‟s influence. The bacterial activity and its community structure could be also a major factor of influence for nematode from the area. The intense biodeposition can change the structure of the assemblages – e.g. the samples taken from mussel farms were numerically dominated by few genera. The three most abundant genera - Terschellingia, Sabatieria and Daptonena - accounted for 65% of the total collected fauna.
The increase in the abundance of the genera Terschellingia, Sabatieria due to intense biodeposition in the areas affected by mussel culture was not a surprise. These nematode genera are regularly found in marine shallow waters, but they are particularly abundant inorganically enriched silt bottoms (Gyedu-Ababio et al., 1999; Fonseca and Netto, 2006; Johnson et al., 2007). They are all characterized by low oxygen consumption rates (Warwick and Price, 1979) and thus, of advantage in oxygen-poor, organically enriched sediments. During the summer the sheltered shallow water localities in the eulittoral zone of Hiddensee Island, Germany (southwest coast of the Baltic Sea) are characterized by regular periods of hypoxia and intense hydrogen sulphide production. Field investigations showed that these biotopes are densely populated by the mud-burrowing harpacticoid copepod Cletocamptus confluens. Unlike other harpacticoids such as Tachidius disciples Giesbrecht 1881, Nitocra spinipes Boeck 1864 and Mesochra lilljeborgi Boeck 1864, these species is often found not only in the top but also in deeper, probably anoxic and sulphidic sediment layers. The nematodes Daptonema trabeculosum (Schneider 1906) and Sabatieria pulchra (Schneider 1906) were far less common.
97 In autumn of 2010, the species diversity from trophic type and size point of view was comparable. Thus, the two profiles analyzed on the same depths revealed a large dominance of species: Sabatieria pulchra, Viscosia cobbi, S. abyssalis, Axonolaimus ponticus, Metalinhomoeus zosterae, Eleutherolaimus longus, Sphaerolaimus macrocirculus etc. The mud inhabitants are mostly relatively small and have short setae (e.g., Sabatieria pulchra). Tita et al. (1999) recorded that the average body width and biomass of nematodes were higher in mud than in sand, resulting in a higher calculated respiration. Soetaert et al. (2002) contended that nematode body length increases when the sediments become little permeable and more cohesive. This was related to organic matter, but probably also to oxygen supply. The typical thiobiotic species from “sulphide layers” has a long, slender and sluggish body with a thin cuticle (e.g., Linhomoeidae) (Jensen, 1978b). This longer and more slender shape has been interpreted as enabling higher mobility, facilitating effective vertical migrations; other advantages of a slender body were considered the enhanced trans-epidermal uptake of oxygen and dissolved food.
In deeper waters, the nematodes communities were sampled from 8 depth points (Stations: 10CT06 - 86.27 m; 10MA03 - 87.96 m; 10MA02 - 110.8 m; 10MA09 - 150.5m; 10MA10 - 210.20 m; 10SG08 - 114.50 m; 10SG09 - 143.40 m and 10SG13 - 161.50m) Nematodes feeding on bacteria are typically found here. The long, slender Linhomoeidae species, 1A trophic type (Linhomoeus hirsutus, Linhomoeus filiformis, Terschellingia longicaudata, Metalinhomoeus zosterae) and the similar morphotypes are some of the most numerous species (Halalaimus ponticus, Nemanema filiforme, Halanonchus bullatus, Viscosia cobbi). Their size varies between 2.9 mm and 4.3 mm length, a >75(length/width ratio).
Small length and stout nematodes form another group. In this category are the nematodes smaller than 1 mm and a<15 (Quadricoma loricata, Q. nematoides, Q. pontica, Tricoma platycephala). Some of the smallest forms were also Chromaoridae species (Chromadorina obtusa, Chromadora gracilis, and Chromadorella pontica) but in very reduced densities. Chromadora species are generally known from a large type of habitats, being tolerant species in a large spectrum of salinities (5 - 30 PSU) and grain size of sediments (0 – 250 μm). Their limited number at these depths in the Black Sea could be assumed on the basis of food preference. They are preferably epibenthic diatoms feeders (2A) as it has been noted by Jensen (1978a) who studied Chromadora tenuis feedinghabits in culture experiments and Tietjen & Lee (1973) who studied Ch. macrolaimoides. The latter selects its food and regulates its ingestion rate according to the food source (14l g of Nitzschia acicularis per day
98 and 27 μg of Nitzschia closterium per day). The largest nematodes as both length and width were: Cheironchus bulbosus, Enoplus euxinus, Metachromadora macroutera, Sphaerocephalum dolichocercus, Enoploide samphioxi, and Oncholaimus campylocercoides. Their length is frequently greater than 2.5 mm up to 4.5 mm and a ~60. In majority, these species are predators with great contribution to diversity and trophic relations structure within the population assemblages at these depths. Oncholaimus campylocercoides was reported from Mediterranean shallow vents in white bacterial mats. This species, considered by some authors (Meyers & Hopper, 1973, Riemann & Schrage, 1978; and Lopez et al., 1979; Heip et al. 1985) rather scavenger than predator, was often found abundant in biotopes where epistrate-feeders dominate, but its presence in rich sulphide biotopes showed that it can also feed on „sulphur-bacteria‟. This case could be in the presence of Oncholaimus campylocercoides at 143 m depth an accident or a trophic niche which offers the energetic support for such big species in a less competitive space, like lack of abundant macrofauna. Other size classes were present also, more or less within medium size morphotypes: S. abyssalis, Desmodora pontica, Eleutherolaimus longus etc. From Desmodoridae Family, Desmodora masira was found in the Oxygen Minimum Zone of the Santa Barbara basin with epicuticular, likely ecto-symbiotic bacteria. We can conclude that the large taxonomic diversity of morphotypes and trophic types present within the nematode communities at these depths, if not unusual in other seas, is a very meaningful fact for the Black Sea, permitting metazoan life up to 180 m depth. The nematodes adaptations could be related to efficient energetic food assimilation or, more than that, to physiological strategies for preventing lethal effects of H2S. Until now no clear evidence was provided for this hypothesis. Some authors pointed to the presence of dark, often multilayered intracellular globules in the intestinal cells of nematode species typical for sulphidic muds (i.e. Sabatieria wieseri, Terschellingia longicaudata, Sphaerolaimus papillatus, Siphonolaimus ewensis, Pontonema vulgare). However, their significance is ambiguous and their adaptive value for the thiobiotic life rather disputed (Jennings, 1970, Thiermann, 1994). The presence of shiny globules in cuticle or patches of granules in epidermal and intestinal cells were observed in this study no only in Metalinhomoeus zosterae cuticle and other Linhomoeidae species but also in Sabatieria species and Oncholaimidae.
On the vertical distribution of nematodes in sediments: The vertical distribution in sediment layers was assessed based on samples taken in September from two profiles: Sf. Gheorghe and Portita. On Sf. Gheorghe profile the depths ranged from 16 m to 87 m. On Portita, the
99 stations depths were not greater than 42 m. The vertical distribution of nematode in sediments extracted in corer tube was assessed for 0 – 5 cm, respectively 5 – 10 cm layers. We were particularly interested in 5- 10 cm layer, which is considered a particular environment for those species that have the capacity of burying themselves into sediments or even living there for a longer time. The results indicate that, as a rule, the top 5 cm layer of sediment has a higher specific diversity of nematodes than the sub-surface layer (Figs. 3.45 and 3.46). In the top layer of the bottom sediments nenatodes‟ population are very abundant, the most common species are listed as below:
Hypoxia can affect the vertical distribution and composition of nematode fauna. On the Swedish west coast, for example, Sabatieria pulchra, a species associated with the redox potential discontinuity migrates vertically and is the only metazoan species present after summer hypoxia (Hendelberg and Jensen, 1993). Species of the same genus dominate bathyal sediments (500 m and 1000 m) off the Kenyan coast in the W Indian Ocean (Muthumbiet al., 2004). Subsurface fauna appear to be affected by hypoxia only in a narrow, shallow depth range, suggesting an upwards migration in response to increasing sulphide concentration (Hendelberg and Jensen 1993).
In the Western Mediterranean (Tyrrhenian Sea), a strong impact on meiofauna assemblages was observed beneath fish cages. The nematode assemblage was highly impacted, with reduced densities, diversity and richness in sediment beneath the farm. There were also changes in functional indices; after 45 days of farming there was an increase in individual biomass and a different nematode assemblage.
In studies regarding meiofaunal recovery following hypoxia, for example, Chandler and Fleeger (1987) showed that copepods and nauplii re-colonized azoic estuarine sediments in only two days, whereas nematodes required 29 days. Subtidal experiments placing azoic sediment trays revealed that copepods required five days to reach background densities, while
100 for nematodes it took seven days (Alongi, 1990). Experimentally-induced hypoxia caused strong changes in nematode community composition on a tidal flat but did not result in complete nematode mortality, as observed for the macrobenthos (Van Colen et al., 2008). Nematode recovery was rapid (1 month) but was strongly influenced over the long term by the dynamics of the macrobenthic bioturbation, grazing and re-suspension (Van Colen et al., 2009).
A literature source gives numerous evidences that the large deep-dwelling nematode species, Sabatieria pulchra shows high tolerance and even tends to increase in hypoxic microcosms. Sabatieria pulchra is commonly found in high densities at depths near the RPD (redox potential discontinuity) layer, and has shown a tolerance to long periods of oxygen deficiency (Wieser and Kanwisher, 1961; Jensen, 1981, 1983; Warwick and Gee, 1984; Olafsson, 1992; Hendelberg and Jensen, 1993).
Fig. 3.45. Species richness in samples from the two layers of sediments:0 - 5 cm and 5 – 10 cm
101
Fig. 3.46. Cumulative curves of the nematodes‟ populations densities inthe surface (0-5 cm) and sub- surface (5-10 cm) layers.
102
Fig. 3.47. Comparative data on the structure and abundance (dominance %) of nematodes‟ populations in the tow layers – surface (0-5 cm) and sub-surface (5-10 cm) – of sediment
103
Fig. 3.48. Average distribution of nematodes' populations in the two layers of sediment 0-5 cm and 5- 10 cm.
Conclusions: On the Romanian continental shelf of the Black Sea there were recorded 92 species in May and September 2010. In 2011 there were identified 33 species in the stations analyzed, 17 of them with the highest diversity being found on the profile Sf. Gheorghe in the stations at 98 m and 114 m depth, respectively; this situation is comparable to that found in May 2010, when the number of species was 20 at 98 m depth and 18 at 114 m depth. A dominant nematodes community tolerant to eutrophication conditions, organic loading and hypoxic conditions, made up of species of S. pulchra, S. abyssalis, Terschellingia longicaudata etc., is spread throughout the whole investigated area, from the shallow waters to the deepest bottoms at the limit of the metazoan life development. In 2011 the dominant species were Sabatieria abysalis, S. pulchra, Desmodora pontica, Halanonchus bullatus, Axonolaimus ponticus and Theristus oxycercus. Specific associations of taxa were identified. The most important factors influencing their formation seem to be: feeding type, sediment type and food availability. The feeding type is implied in the community formation has a secondary role; first role is according to sediment type and food availability. Feeding type plays an important role mostly in the vertical distribution of Nematodes in sediment (Olav, 2009). The taxonomic diversity increases with depth, which may suggest that the nematodes in the Black Sea, under unfavourable conditions, may have an adaptive strategy in response to
104 the lack of resources or in the presence of physiological stress factors. Sinking or vertical migration into sediments, though there is no clear evidence of the residence time in the deeper layers, may suggest that the nematodes can develop different metabolic ways, which include chemosynthetic mechanisms to produce energy and obtain food. Their adaptive capacity enables them to change the food type according to the available trophic resources, such as the species of genus Oncholaimidae. At the Romanian coast, the communities of nematodes were well represented in 2010, which indicates that, in addition to the wide variability of environmental factors, hypoxic events are well tolerated by the local communities.
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3.3. Benthic foraminifera studies in the Amvrakikos Gulf (UPAT)
For site description of the Amvrakikos Gulf in the Ionian Sea, reader is referring to Section 2.5. Benthic foraminifera analyses were carried out in two sediment cores (st13 and st15) from the Amvrakikos Gulf using standard micropaleontological methods (Fig. 3.50). Twenty- five (25) samples have been analyzed from the 30 cm long sediment core St13 and twenty- eight (28) from the 42 cm-long core St15.
Although the resolution of the sediment sampling is still low, preliminary results show that benthic foraminifera assemblages exhibit changes in relation to the decline of oxygen availability at the sea bottom of the gulf (Fig. 3.51). The onset of the interval of low oxygen availability is marked in the core sediments by a lithological change. At this changes, benthic foraminifera diversity start to decrease. Shallow infauna species dominate together with agglutinated foraminifera. The abundance of epifauna species shows a gradual decrease.
109 When the sea bottom is characterized by the minimum oxygen values, the benthic diversity is the lowest. Then deep infauna species are dominant.
The sea bottom recovery (oxygen increase) is characterized by an increase of benthic diversity. Epifauna and shallow infauna species replace the previous microfauna. Many of the benthic species obtained at the onset of the low-oxygen interval are observed also at this stage. This pattern seems to characterize the top black organic layer of the short and long sediment cores analyzed. Furthermore a similar trend has also been obtained in the sediments of the long core at sediment depth interval of 110-115 cm.
Fig. 3.50. Map of Amvrakikos Gulf showing the location of sediment cores St13 and St15.
110
Fig. 3.51. Downcore variability of micropalaeontological parameters in sediment core St13 collected from Amvrakikos Gulf.
References
Ferentinos, G., Papatheodorou, G., Geraga, M., Iatrou, M., Fakiris, E., Christodoulou, D., Dimitriou, E., Koutsikopoulos, C. (2010): Fjord water circulation patterns and dysoxic/anoxic conditions in a Mediterranean semi-enclosed embayment in the Amvrakikos Gulf, Greece. Estuarine, Coastal and Shelf Science 88 (4), pp. 473-481.
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