Benthic response to sedimentation events during autumn to spring at a shallow water station in the Western Kiel Bight

Seasonal variations in bacterial populations (total number, biomass, biomass-spectrum, number of dividing cells) as well as in concentrations and decomposition rates of particulate organic material were followed in a sandy mud sediment of the Western Kiel Bight (Baltic Sea; FRG). The strong seasonal variations observed could be traced back to the effect of certain ecological situations and events in the sediment from which the input of the phytoplankton blooms in autumn and spring, respectively, the accumulation of organic material during winter, and the spring development of the benthic fauna turned out to be the most important. Bacterial carbon net production following the breakdown of the phytoplankton blooms ranged between 9 g (autumn) and 16 g (spring) per g of dry weight sediment per day. The consequences of shifts in the size composition of the bacterial populations as well as the importance of the measurement of enzymatic decomposition rates of particulate organic material in sediments are demonstrated and discussed in relation to the events mentioned above.Publication No. 420 of the Joint Research Program at Kiel University (Sonderforschungsbereich 95 der Deutschen Forschungsgemeinschaft)     

Effect of algal bloom deposition on sediment respiration and fluxes

Using sediment cores collected in November 1989 from Aarhus Bight, Denmark, the fluxes of O₂, CO₂ (total CO₂), NH ₄ ⁺ , NO ₃ ^– +NO ₂ ^– and DON (dissolved organic nitrogen) across the sediment-water interface were followed for 20 d in an experimental continous flow system. On day 7, phytoplankton was added to the sediment surface, to see the result of simulated algal bloom sedimentation. Benthic O₂ consumption and CO₂ efflux, 38 to 41 mmol O₂ m^-2 d^-1 and 25 to 30 mmol CO₂ m^-2 d^-1, respectively, immediately increased by 39% and 100% after the algal addition, but gradually declined to the orginal level. Fluxes of NH ₄ ⁺ (1.0 to 1.2 mmol m^-2 d^-1) and DON (0.3 to 0.9 mmol m^-2 d^-1) increased due to the organic substrate addition. NH ₄ ⁺ and NO ₃ ^– flux changed direction, becoming an efflux and influx, respectively, for a few days and a large amount of DON (max. rate 4.0 mmol m^-2 d^-1) was immediately produced either by bacterial hydrolytic activity or from autolysis of the algae. DON was the most significant nitrogen component in pore water and in terms of N-flux from sediment. A temporary stimulation of anaerobic respiration processes (sulfate reduction and denitrification) and a decrease in nitrification were indicated. After the effect of the organic addition had declined, the fluxes gradually reverted to the original rates. The halflife of the added algal material, of which 20 to 30% was very labile, was estimated to be 2 to 3 wk.     

The plankton tower. II. Release of nutrients from sediments due to changes in the density of bottom water

Results of an enclosure experiment carried out in Kiel Bight are presented. A water column of about 30 m³, extending from the surface to the bottom over a 3 m² patch of sediment (coarse sand), was isolated and observed over a period of 33 days. Considerable water exchange took place with the surroundings partly because of near-surface openings that appeared in the enclosure but mainly because of density changes due to salinity fluctuations in the surrounding water. This denser water entered the enclosure through the sediments, displacing the lighter water through the near-surface openings. Very high nutrient and low oxygen values were measured in the bottom water immediately following this higher-density water influx. The same effect was observed outside the enclosure, but this phenomenon was not marked here, probably due to greater turbulent mixing obscuring this effect. It is postulated that interstitial, water is flushed out of coarse-grained sediments by gravity displacement due to changes in the density of bottom water. In certain areas this mechanism of nutrient release from the sediments is presumably of great ecological importance, both for the phytoplankton and the benthos.Publication no. 83 of the Joint Research Program at Kiel University (Sonderforschungsbereich 95 der Deutschen Forschungsgemeinschaft).     

The common jellyfish Aurelia aurita: standing stock,excretion and nutrient regeneration in the Kiel Bight,Western Baltic

The population dynamics, ammonia and inorganic phosphate excretion, and nutrient regeneration of the common jellyfish Aurelia aurita was investigated from 1982 to 1984 in the Kiel Bight, western Baltic Sea. During summer 1982, medusae abundance ranged between 14 and 23 individuals 100 m^-3, biomass was estimated at about 5 g C 100 m^-3 and the mean final diameter of individuals was 22 cm. Abundance, based on numbers, in 1983 and 1984 was an order of magnitude lower; biomass was less than 2 g C 100 m^-3 and jellyfish grew to 30 cm. During the summers of 1983 and 1984, A. aurita biomass constituted roughly 40% of that of the total zooplankton>200 m. In 1982, for which zooplankton data were lacking, it was assumed that medusae biomass was greater than that of all other zooplankton groups. Total ammonia excretion ranged between 6.5 and 36 mol h^-1 individual^-1, whereas inorganic phosphate release was 1.4 to 5.7 mol h^-1 individual^-1. Allometric equations were calculated and exponents of 0.93 for NH₄–N release and 0.87 for PO₄–P excretion were determined. Nitrogen and phosphorus turnover rates were 5.4 and 14.6% d^-1, respectively. In 1982, the medusae population released 1 100 mol NH₄–N m^-2 d^-1, about 11% of the nitrogen requirements of the phytoplankton. The inorganic phosphate excretion (150 mol m^-2 d^-1) sustained 23% of the nutrient demands of the primary producers. In the other two years the nutrient cycling of the medusae was much less important, and satisfied only 3 to 6% of the nutrient demands. It is suggested that in some years A. aurita is the second most important source of regenerated nutrients in Kiel Bight, next to sediment.     

Is benthic trophic structure affected by food quality? The Dogger Bank example

The aim of this study was to evaluate the relationship between food quality and trophic structure of macrobenthic communities of the Dogger Bank. Therefore, 21 stations along different depth gradients (a transect across the central Dogger Bank and at a station cross in the north-eastern part) were sampled and analysed for macrofauna trophic structure and food supply, indicated by phytopigment composition and organic matter contents of the sediment. The study revealed differences in the trophic structure of the benthic community in areas with contrasting food supply. The trophic structure reflected differences in relative quality of organic matter. The sandy sediments on top of the bank receiving intermediate quantities of high food quality were inhabited by high abundances of interface feeders and sand-licking amphipods of the genus Bathyporeia. The southern stations characterised by a comparatively high amount of intermediate food quality were dominated by interface feeders such as Amphiura filiformis. The northern and north-eastern stations showing the highest diversity of feeding types were characterised by a comparatively low, but highly variable input of intermediate-quality organic matter consisting of both fresh and degraded organic matter. Results are discussed with a special emphasis on specific Dogger Bank features such as benthic primary production and frontal system characteristics.Communicated by O. Kinne, Oldendorf/Luhe     

Factors affecting respiration and photosynthesis by the benthic community of a subtical siliceous sediment

In a shallow, subtidal, siliceous sediment, benthic microalgal biomass (g chlorophyll a cm^-3) is influenced by light and physical sediment dynamics. The microalgal community is relatively dense, despite adverse conditions (7.0 g chlorophyll a cm^-3), and is able to respond rapidly to favorable conditions. Productivity of this community is significantly correlated (P0.05) with benthic light. In addition, productivity is influenced by temperature and bottom water NH₄ ⁺ and PO₄ ^-3 concentrations, especially as the concentrations fall to levels approaching the K _s (halfsaturation constant) of the microalgal community. Metabolic activity in this environment is dependent upon a continuous supply of organic carbon. Temperature is significantly correlated with respiration rate, but other factors (e.g. biomass and organic matter supply) are important also. Community respiration responds to overlying phytoplankton productivity in the same manner as deep-water benthic environments. Bacterial enumeration using CFU (colony-forming units) does not measure accurately the number of in situ metabolically active bacteria.This research was supported by Energy Research and Development Administration Contract AT (11-1) 3279, US AEC Contract AT (11-1) GEN 10, P.A. 20 and NOAA Sea Grant No. 04-3-158-22.     

Shallow-water benthic and pelagic metabolism:

Pelagic primary production and benthic and pelagic aerobic metabolism were measured monthly at one site in the estuarine plume region of the nearshore continental shelf in the Georgia Bight. Benthic and water-column oxygen uptake were routinely measured and supplemented with seasonal measures of total carbon dioxide flux. Average respiratory quotients were 1.18:1 and 1.02:1 for the benthos and water column, respectively. Benthic oxygen uptake ranged from 1.23 to 3.41 g O₂ m^-2 d^-1 and totalled 756 g O₂ m^-2 over an annual period. Water column respiration accounted for 60% of total system metabolism. Turnover rates of organic carbon in sediment and the water column were 0.09 to 0.18 yr^-1 and 6.2 yr^-1, respectively. Resuspension appeared to control the relative amounts of organic carbon, as well as the sites and rates of organic matter degradation in the benthos and water column. Most of the seasonal variation in benthic and pelagic respiration could be explained primarily by temperature and secondarily by primary productivity. On an annual basis, the shelf ecosystem appeared to be heterotrophic; primary production was 73% of community metabolism, which was 749 g C m^-2 yr^-1. The timing of heterotrophic periods through the year appeared to be closely related to both river discharge and the periodicity of growth and death of marsh macrophytes in the adjacent estuary. The results of this study support the estuarine outwelling hypothesis of Odum (1968).This is Contribution No. 530 from the University of Georgia Marine Institute. This work was supported by the Georgia Sea Grant College Program maintained by the National Oceanic and Atmospheric Administration, US Department of Commerce     

Seasonal changes of benthic bacteria in a seagrass bed (Posidonia oceanica) of the Ligurian Sea in relation to origin,composition and fate of the sediment organic matter

Variations in number and biomass of benthic bacteria were examined in the surface sediments of a Mediterranean seagrass bed [Posidonia oceanica (L.) Delile] in the Gulf of Marconi (northwestern Mediterranean Sea) from 1990 to 1991. The annual dynamics of benthic bacterial density and biomass were compared to changes in elemental (organic C and total N) and biochemical (lipids, proteins, carbohydrates) composition of sediment organic matter, as well as to microphytobenthic biomass, dissolved inorganic nutrients and ATP. Bacterial densities exhibited marked seasonal variations (5.12 to 322.7x10⁸ cells g^-1 sediment dry wt) with highest values in late spring. Bacterial standing stocks (15.8 to 882.33 g C g^-1 of sediment dry wt) were high. Bacterial biomass did not correlate with organic C, total N or to specific biochemical components, but correlated significantly with chlorophyll a, ATP and porewater phosphate concentrations. There is evidence that benthic bacteria were responding to variations of algal biomass. Bacterial biomass accounted, on average, for 30% of total living carbon (calculated on the basis of the ATP concentrations) and 8.4% of total organic carbon.     

Detrital pathways in a coral reef lagoon

Coral reef lagoons have generally been regarded as sinks for organic matter exported from more productive reef front and reef flat zones. The object of this study was to examine the importance of detritus as a carbon source for benthic communities in the lagoon at Davies Reef, central Great Barrier Reef. We report the results of seasonal measurements, taken in 1986, of bacterial numbers and production, protozoan numbers, community primary production and respiration in the sediments of Davies Reef lagoon. Deposition rates of organic matter in the lagoon were also measured. Deposition rates (±1 SE) of carbon ranged from 9.2 (±1.5) to 140.7 (±10.3) mg Cm^-2d^-1. Deposition rates were highest in winter and spring, lowest in summer. Rates of bacterial production ranged from 4.7 (±0.2) pmol thymidine incorporated g^-1 dry wt (DW) h^-1 in winter to 23.5 (±1.0) pmol thymidine incorporated g^-1 DW h^-1 in spring. The number of ciliates ranged from 65 (±10) to 356 (±50) cm^-3 through the year and the number of large (20 m) flagellates from 38 (±7) to 108 (±16) cm^-3. There were no clear relationships between the sediment organic content, detrital input or temperature and the rates of bacterial processes, community metabolism or the standing stocks of microbes in the lagoon. The relative significance of detritus and in situ primary production as sources of carbon in the lagoon varied with season. In summer and autumn, detritus was less important than primary production as a source of carbon (4 to 27% of total carbon input). In winter and spring, detritus input became more significant in supply of carbon to the sediments (32 to 67% of the total carbon input). The lagoon does not simply act as a sink for carbon exported from the reef flat. We calculate that only 5% of the net reef flat primary production reached lagoon sediments in summer, but nearly 40% in winter.     

The annual cycle of heterotrophic planktonic ciliates in the waters surrounding the Isles of Shoals,Gulf of Maine: an assessment of their trophic role

Macrofauna living on subtidal rocks reefs in southern California excrete ammonium, a potentially important nutrient for benthic algae. Ammonium excretion rates of eleven macroinvertebrate and five fish taxa were determined from a total of 324 in situ incubations conducted between October 1984 and August 1985 at 14 to 17 m depths off Santa Catalina Island, California. Total ammonium excretion ranged from over 100 mol h^-1 by the kelp bass Paralabrax clathratus to less than 0.1 mol h^-1 by the gastropod Conus californicus. Weight-specific ammonium excretion generally ranged from 0.5 to 4 mol g^-1 h^-1 in invertebrates and from 3 to 7 mol g^-1 h^-1 in fishes. Intraspecific excretion rates varied substantially. Coefficient of variation of excretion rates were higher than reported for laboratory studies and multiple regression indicated that 50 to 90% of the variation in ammonium excretion rates of five species studied in detail could not be explained by the combined variation in dry weight, water temperature, time of day, and incubation dates. The excretion data, along with estimates of population densities and size-frequency distributions, indicate that benthic macrofauna release a total of 25 to 30 mol NH ₄ ⁺ m^-2 h^-1 both day and night. The species that generally make the largest contributions are a gobiid fish (Lythrypnus dalli), followed by three gastropods (Astraea undosa, Tegula eiseni, and T. aureotincta) and a sea urchin (Centrostephanus coronatus). The amount of ammonium excreted by these macrofauna on rocky reefs is insignificant compared to our previously published data on the nighttime excretion of blacksmith (Chromis punctipinnis), a pomacentrid fish that feeds in the water column during the day and shelters on the reef at night. Including blacksmiths, we estimate that the amount released by rocky-reef macrofauna at night is >280 mol m^-2 h^-1, a rate that is similar to that for many other marine communities. Additional studies are required to determine if benthic algae utilize ammonium released by these macrofauna, especially at night.Contribution No. 58 of the Ocean Studies Institute; Contribution No. 123 of the Catalina Marine Science Center     

Microbial RNA and DNA synthesis in marine sediments

A technique for measuring rates of RNA and DNA synthesis in sedimentary microbial communities has been adapted from methods developed for marine and freshwater microplankton research. The procedure measures the uptake, incorporation and turnover of exogenous [2, ³H]-adenine by benthic microbial populations. With minor modification, it is applicable to a wide range of sediment types. Measurement of nucleic acid synthesis rates are reported from selected benthic marine environments, including coral reef sediments (Kaneohe Bay, Oahu, Hawaii), intertidal beach sands (Oahu and southern California) and California borderland basin sediment (San Pedro Basin), and comparisons are made to selected water-column microbial communities. Biomass-specific rates of nucleic acid synthesis in sediment microbial communities were comparable to those observed in water-column assemblages (i.e., 0.02 to 2.0 pmol deoxyadenine incorporated into DNA [ng ATP]^-1 h^-1 and 0.2 to 8.9 pmol adenine incorporated into RNA [ng ATP]^-1 h^-1). DNA synthesis rates were used to calculate carbon production estimates ranging from 2 g C cm^-3 h^-1 in San Pedro Basin sediment (880 m water depth) to 807 g C cm^-3 h^-1 in coral reef sediment from the Kaneohe Bay. Microbial community specific growth rate, (d^-1), estimated from DNA synthesis rates in surface sediments ranged from 0.1 in San Pedro Basin to 4.2 in Scripps Beach (La Jolla, California) intertidal sand.     

The influence of macrofauna on estuarine benthic community metabolism: a microcosm study

Effects of benthic macrofauna (Corophium volutator, Hydrobia sp., Nereis virens) on benthic community metabolism were studied over a 65-d period in microcosms kept in either light/dark cycle (L/D-system) or in continuous darkness (D-system). Sediment and animals were collected in January 1986 in the shallow mesohaline estuary, Norsminde Fjord, Denmark. The primary production in the L/D-system after 10 d acted as a stabilizing agent on the O₂ and CO₂ flux rates, whereas the D-system showed decreasing O₂ and CO₂ flux throughout the period. Mean O₂ uptake over the experimental period ranged from 0.38 to 1.24 mmol m^–2 h^–1 and CO₂ release varied from 0.80 to 1.63 mmol m^–2 h^–1 in both systems. The presence of macrofauna stimulated community respiration rates measured in darknes, 1.4 to 3.0 and 0.9 to 2.0 times for O₂ and CO₂, respectively. In contrast, macrofauna lowered primary production. Gross primary production varied from 1.06 to 2.26 mmol O₂ m^–2 h^–1 and from 1.26 to 2.62 mmol CO₂ m^–2 h^–1. The community respiratory quotient (CRQ, CO₂/O₂) was generally higher in the begining of the experiment (0–20 d, mean 1.89) than in the period from Days 20 to 65 (mean 1.38). The L/D-system exhibited lower CRQ (ca. 1) than the D-system. The community photosynthetic quotient varied for both net and gross primary production from 0.64 to 1.03, mean 0.81. The heterotrophic D-system revealed a sharp decrease in the sediment content of chlorophyll a as compared to the initial content. In the autotrophic L/D-system, a significant increase in chlorophyll a concentration was observed in cores lacking animals and cores with C. volutator (The latter species died during the experiment). Due to grazing and other macrofauna activities other cores of the L/D-system exhibited no significant change in chlorophyll a concentration. Community primary production was linearly correlated to the chlorophyll a content in the 0 to 0.5 cm layer. Fluxes of DIN (NH₄ ⁺+NO₂ ^–+NO₃ ^–) did not reveal significant temporal changes during the experiment. Highest rates were found for the cores containing animals, mainly because of an increased NH₄ ⁺ flux. The release of DIN decreased significantly due to uptake by benthic microalgae in the L/D-system. No effects of the added macrofauna were found on particulate organic carbon (POC), particulate organic nitrogen (PON), total carbon dioxide (TCO₂) and NH₄ ⁺ in the sediment. The ratio between POC and PON was nearly constant (9.69) in all sediment dephts. The relationship between TCO₂ and NH₄ ⁺ was more complex, with ratios below 2 cm depth similar to those for POC/PON, but with low ratios (3.46) at the sediment surface.     

Bacterial activity related to sedimenting particulate matter

The rates of sedimentation of particulate matter were measured at a station in the Eckernförde Bight, Baltic Sea, using sediment traps. Different parameters (C, N, chlorophyll a, phaeopigments, adenosine triphosphate (ATP), heterotrophic activity (glucose maximum uptake velocity, v_max), biological oxygen demand (BOD), and electron-transport-system (ETS) activity) were measured during a 1-year period to evalnate the composition, vertical distribution, and activity of microorganisms associated with sedimenting particulate matter. Measurements indicated that the organic fractions of particulate sedimenting matter were transformed considerably during sedimentation. The seasonal fluctuations showed higher heterotrophic activity durang summer and lower activity during winter. Laboratory experiments also indicated that an important part of planktonic particulate material was susceptible to mineralization within a short period of time: phytoplankton was mineralized by about 35% and zooplankton by about 18% per day, at 20°C; at 5°C mineralization was considerably lower (about 3 and 8%, respectively).Please address all correspondence to: Dr. R. Zimmermann, Institut für Meereskunde an der Universität Kiel, Abteilung Marine Mikrobiologie, Düsternbrooker Weg 20, 2300 Kiel 1, Germany (FRG)     

Nutrient regeneration in shallow-water sediments of the estuarine plume region of the nearshore Georgia Bight,USA

Benthic community respiration and the cycling of N and P were seasonally investigated in the unprotected, sandy sediments (Z5m) of the nearshore zone of the Georgia Bight, USA in 1981 and 1982. Nutrient exchange across the sediment-water interface was calculated from a diffusive model, measured by in-situ enclosure experiments and estimated from whole core incubations. Seasonally changing pore water profiles indicated that the sediments were not in steady-state with respect to N and P and showed the characteristics of enhanced interstitial water movement by benthic animals. Over an annual period the total flux of nitrogen measured in situ averaged 1812 mol m^-2 d^-1 from the sediments. NH ₄ ⁺ flux accounted for the vast majority of the total directly measured N flux (77%), followed by nitrate + nitrite (14%), and dissolved organic nitrogen (9%). Phosphorus flux averaged 537 mol m^-2 d^-1. A large ratio of in-situ fluxes to calculated diffusive fluxes (5.2:1) indicated flux enhancement due to benthic animal activity. ammonium fluxes measured in situ did not agree well with the rate of NH ₄ ⁺ produced in incubated whole cores (11.7 mmol m^-2 d^-1). Relative rates of C, N and P release throughout the year fluctuated considerably. Generally, nutrient fluxes were not simply related to respiration or temperature. As respiration was highly correlated with temperature, however, this suggested that respiration-regeneration was temporarily decoupled from exchange across the sediment-water interface. The annual C-N-P flux stoichiometry was 130:3.1:1. Using the rate at which NH ₄ ⁺ was produced in incubated cores the stoichiometry was 120:21:1. The anomalously low N flux measured in situ was attributed to a combination of denitrification and wave-and current-induced sediment nutrient flushing. The potential for sediment flushing is high as experiments showed that sediments were fluidized or resuspended down to 25 cm during large storms. Benthic nutrient flux contributed 40% to the annual P but only 11% to the annual N requirements of the pelagic primary producers.This is Contribution No. 558 from the University of Georgia Marine Institute. This work was supported by the Georgia Sea Grant College Program maintained by the National Oceanic and Atmospheric Administration, US Department of Commerce, under Grant No. NA80AA-D-00091     

Effects of detrital non-native and native macroalgae on the nitrogen and carbon cycling in intertidal sediments

The decay of non-native and native seaweed mixing may modify sediment biogeochemistry and organic matter transfers within benthic food webs according to their composition and biomass. The non-native species Sargassum muticum was deliberately added to the sediment of an intertidal sandflat at different biomass and mixed to the native species Ulva sp. and Fucus vesiculosus. The sediment porewater was then ¹³C and ¹⁵N enriched to test whether both detrital diversity and biomass influenced the transfer of porewater carbon and nitrogen to the sediment and to the macrofauna consumers. More ¹⁵N-nitrogen was mobilized to sediments and macrofauna when the 3-species detrital mixing was buried, probably because this mixing provided species-specific compounds such as polyphenols due to the presence of S. muticum and F. vesiculosus, as well as large amounts of nitrogen due to the presence of Ulva. Our study revealed the importance of detrital diversity and non-native seaweeds for the nitrogen cycling in the benthic food web.     

Uptake of glucose by bacteria in the sediment

A method is described for the incubation of undisturbed sediment cores under in situ conditions with the addition of low concentrations of ¹⁴C-glucose. Data are presented for respiration, gross uptake and actual uptake rate of glucose by bacteria in sandy, wave-washed beaches of the Baltic Sea. On the average, the bacteria respired 8% of the total glucose taken up. The gross uptake measured was between 2.3×10^-3 and 6.8×10^-3 g ¹⁴C-glucose g sediment^-1 (dry weight) h^-1 (average 4.7×10^-3 g g^-1 h^-1). Minima in the gross uptake rate corresponded with maxima in the concentration of natural free dissolved glucose. For the actual uptake rate, however, very similar uptake rates were calculated for the sediments examined (between 1.4×10^-1 and 1.9×10^-1 g glucose g^-1 h^-1, average 1.7×10^-1 g g^-1 h^-1).Publication No. 183 of the Joint Research Program at Kiel University (Sonderforschungsbereich 95 der Deutschen Forschungsgemeinschaft).     

Fluctuations and interactions of bacterial activity in sandy beach sediments and overlying waters

Fluctuations and interactions of the following microbiological variables and sediment properties were investigated on samples from sandy beaches of the Baltic Sea: bacterial number and biomass, net uptake and respiration rate of ¹⁴C-glucose (U), concentration of natural free dissolved glucose and fructose, actual uptake rate and turnover time of glucose, sand-grain size and shape, water and organic matter content of the sediment. Spearman rank correlation analysis demonstrated significant relationships between cell number, biomass and actual uptake rate of glucose. The concentration of natural glucose varied with sand-grain shape, and the uptake rates of glucose were inversely correlated with the water content of the sediment. In the overlying water, cell number and/or biomass were significantly correlated with both concentration and uptake rates of glucose. Partial correlation analysis, however, indicates that, in the water overlying the sediment at least one of the standing crop variables (bacterial number or biomass) is independently variable with uptake activity. The sediment bacterial standing crop does not necessarily reflect metabolic activity. Various significant interactions were noted between mainly sediment properties (water content, organic matter content, grain size) and variables in the water above (cell number, biomass, concentration and uptake rates of glucose).Publication No. 206 of the Joint Research Program at Kiel University (Sonderfor-schungsbereich 95 der Deutschen Forschungsgemeinschaft).     

Abundance and biomass of macrobenthos in the vicinity of Carson Submarine Canyon,northwest Atlantic Ocean

The abundance, biomass and mean weight of macrofauna in the Carson Canyon region (Lat. 45°30N, Long. 48°40W) of the Grand Banks were estimated from 40 quantitative infaunal samples taken at 15 stations in June 1980. In contrast to other areas, there were no significant differences in these values between samples taken in and outside of the canyon. Abundance ( = 716 individuals m^-2), biomass ( = 10.9 gm^-2), and mean weight ( = 0.03 g individual^-1) displayed no consistent relationship with depth, but stations grouped according to sediment type had differing dominant taxa. Biomass and abundance at the edge of the Grand Banks are unexpectedly low. Larger animals, including fishes, that forage there must depend more on pelagic than on benthic food sources.     

Relationships between microbial distributions and the anaerobic decomposition of organic matter in surface sediments of long Island Sound,USA

Relative rates of the anaerobic decomposition of organic matter in the upper 10 cm of sediment from two stations in central Long Island Sound, USA, were compared. Sediment samples from discrete depth intervas were incubated anoxically and changes in SO ₄ ⁼ , NH ₄ ⁺ , bacterial numbers, extractable adenosine triphosphate (ATP), organic matter, and organic carbon were measured as a function of time and temperature. At both stations (15 and 34 m water-depths, respectively), the calculated rates of SO ₄ ⁼ reduction and NH ₄ ⁺ production decreased exponentially (approximately) with depth below the sediment-water interface. Over the same depth interval, ATP concentrations dropped by a factor of 6 to 7 and bacterial numbers were lower by a factor of 2 to 3. These decreases in SO ₄ ⁼ reduction, NH ₄ ⁺ production, bacterial numbers, and ATP, reflect a change in the physiological state of microbial populations with depth in the sediment and are consistent with the conclusions that the quantity of easily utilizable organic matter changes rapidly below the sediment surface and that food limitation controls the basic depth distribution of microbial activity. The average rates of SO ₄ ⁼ reduction, 29 to 39 mM year^-1 (22°C), in the top 10 cm are similar at both stations studied here, as well as at an additional station from a previous study. In contrast, average NH ₄ ⁺ production differs by a factor of 2 at the two stations, reflecting differences in the C:N ratio of the organic matter supplied to the sediment surface and differences in particle reworking by macrofauna at each site. The apparent activation energy of SO ₄ ⁼ reduction was 19±1 kcal mole^-1 and that of NH ₄ ⁺ production, 18±3 kcal mole^-1. The overall quantity of carbon required to support the calculated average SO ₄ ⁼ reduction rate in the top 10 cm is 23 g C m^-2 year^-1 and represents 36% of all the carbon available to the benthos annually and 11% of the net primary production in the water column. Directly measured fluxes of NH ₄ ⁺ from sediments to overlying water at both stations agree well with those predicted from production rates obtained by the incubation techniques.     

Resting eggs of zooplankton (Copepoda and Cladocera) from the Kiel Bay and adjacent waters (southwestern Baltic)

Resting eggs of four species of calanoid copepods and three species of cladocerans were collected from sediments up to 5cm depth from the Kiel Bay and adjacent waters in the southwestern Baltic Sea during April–May 1994. All but one species of cladoceran was successfully hatched/reared in the laboratory. In the Kiel Bay, egg abundances varied from 1.8x10⁵ to 7.4x10⁵ m^-2. Hatching success of copepod eggs collected from all depths was high (49 to 94%), but was 0 to 79% for cladoceran eggs. Darkness did not seem to affect hatching. Eggs found in the 4 to 5 cm layer of sediment were estimated to be about 15 yr old, showing the presence of an egg bank in the Baltic. Formation of resting eggs may be a genetic trait acquired during the ice ages.