Direct visualization of mucus production by the cold-water coral <i>Lophelia pertusa</i> with digital holographic microscopy

<i>Lophelia pertusa</i> is the dominant reef-building organism of cold-water coral reefs, and is known to produce significant amounts of mucus, which could involve an important metabolic cost. Mucus is involved in particle removal and feeding processes, yet the triggers and dynamics of mucus production are currently still poorly described because the existing tools to study these processes are not appropriate. Using a novel microscopic technique—digital holographic microscopy (DHM)–we studied the mucus release of <i>L</i>. <i>pertusa</i> under various experimental conditions. DHM technology permits µm-scale observations and allows the visualization of transparent mucoid substances in real time without staining. Fragments of <i>L</i>. <i>pertusa</i> were first maintained in flow-through chambers without stressors and imaged with DHM, then exposed to various stressors (suspended particles, particulate food and air exposure) and re-imaged. Under non-stressed conditions no release of mucus was observed, whilst mucus strings and sheaths were produced in response to suspended particles (activated charcoal and drill cuttings sediment) i.e. in a stressed condition. Mucus strings and so-called ‘string balls’ were also observed in response to exposure to particulate food (brine shrimp <i>Artemia salina</i>). Upon air-exposure, mucus production was clearly visible once the fragments were returned to the flow chamber. Distinct optical properties such as optical path length difference (OPD) were measured with DHM in response to the various stimuli suggesting that different mucus types are produced by <i>L</i>. <i>pertusa</i>. Mucus produced to reject particles is similar in refractive index to the surrounding seawater, suggesting that the energy content of this mucus is low. In contrast, mucus produced in response to either food particle addition or air exposure had a higher refractive index, suggesting a higher metabolic investment in the production of these mucoid substances. This paper shows for the first time the potential of DHM technology for the detection, characterization and quantification of mucus production through OPD measurements in <i>L</i>. <i>pertusa</i>

Has phytodetritus processing by an abyssal soft-sediment community recovered 26 years after an experimental disturbance?

The potential harvest of polymetallic nodules will heavily impact the abyssal, soft sediment ecosystem by removing sediment, hard substrate, and associated fauna inside mined areas. It is therefore important to know whether the ecosystem can recover from this disturbance and if so at which rate. The first objective of this study was to measure recovery of phytodetritus processing by the benthic food web from a sediment disturbance experiment in 1989. The second objective was to determine the role of holothurians in the uptake of fresh phytodetritus by the benthic food web. To meet both objectives, large benthic incubation chambers (CUBEs; 50 × 50 × 50 cm) were deployed inside plow tracks (with and without holothurian presence) and at a reference site (holothurian presence, only) at 4100 m water depth. Shortly after deployment, 13C- and 15N-labeled phytodetritus was injected in the incubation chambers and during the subsequent 3-day incubation period, water samples were taken five times to measure the production of 13C-dissolved inorganic carbon over time. At the end of the incubation, holothurians and sediment samples were taken to determine biomass, densities and incorporation of 13C and 15N into bacteria, nematodes, macrofauna, and holothurians. For the first objective, the results showed that biomass of bacteria, nematodes and macrofauna did not differ between reference sites and plow track sites when holothurians were present. Additionally, meiofauna and macrofauna taxonomic composition was not significantly different between the sites. In contrast, total 13C uptake by bacteria, nematodes and holothurians was significantly lower at plow track sites compared to reference sites, though the number of replicates was low. This result suggests that important ecosystem functions such as organic matter processing have not fully recovered from the disturbance that occurred 26 years prior to our study. For the second objective, the analysis indicated that holothurians incorporated 2.16 × 10−3 mmol labile phytodetritus C m−2 d−1 into their biomass, which is one order of magnitude less as compared to bacteria, but 1.3 times higher than macrofauna and one order of magnitude higher than nematodes. Additionally, holothurians incorporated more phytodetritus carbon per unit biomass than macrofauna and meiofauna, suggesting a size-dependence in phytodetritus carbon uptake

Sink or link? The bacterial role in benthic carbon cycling in the Arabian Sea's oxygen minimum zone

The bacterial loop, the consumption of dissolved organic matter (DOM) by bacteria and subsequent transfer of bacterial carbon to higher trophic levels, plays a prominent role in pelagic food webs. However, its role in sedimentary ecosystems is not well documented. Here we present the results of isotope tracer experiments performed under in situ oxygen conditions in sediments from inside and outside the Arabian Sea's oxygen minimum zone (OMZ) to study the importance of the microbial loop in this setting. Particulate organic matter, added as phytodetritus, was processed by bacteria, protozoa and metazoans, while dissolved organic matter was processed only by bacteria and there was very little, if any, transfer to higher trophic levels within the 7 day experimental period. This lack of significant transfer of bacterial-derived carbon to metazoan consumers indicates that the bacterial loop is rather inefficient, in sediments both inside and outside the OMZ. Moreover, metazoans directly consumed labile particulate organic matter resources and thus competed with bacteria for phytodetritus

De inpassing van de Barbierbeek in het gecontroleerd overstromingsgebied Kruibeke-Bazel-Rupelmonde

This report deals with the possibilities to fit the Barbier-brook in the Controlled lnundation Area of Kruibeke, Bazel en Rupelmonde that was planned according the Sigmaplan. The so called CIA-KBR is situated upstream Antwerp. The CIA-KBR will be inundated when a certain flood on the river Schelde overflows the lowered river dike. The result is a decrease of the peak of the flood. A dike at the polder side will fulfill the defensive function during the period of inundation. This dike is called the "ringdike". The Barbier-brook cuts through the CIA-KBR. Within the CIA the Barbier-brook is diked in since the 13th century. Further on in this text these dikes will be called Barbier-brook dikes. Nowadays, the area between these dikes forms the storage for the Barbier-brook.The study participates in the preparations for the CIA-KBR. Co-ordinated by the Institute of Nature Conservation in Brussels some studies for possibilities of nature development within the CIA-KBR are carried out.In this report the technical possibilities to fit the Barbier-brook in the CIA-KBR as weIl as the perspectives for nature developrnent are studied. The perspectives for nature development can be split in:.nature development influenced by the Barbier-brook.nature development influenced by the Barbier-brook and a controlled reduced tide, controlled reduced tide stands for: a tide controlled by culverts for the in- and outlet of water from the river Schelde with a reduced tide amplitude with an average of 0,25 to 0,5 m.This last perspective corresponds most to the historical natural situation of the area, which consists of freshwater marshes and mud plains.To be able to work out these aspects it is necessary to carry out also a study ofthe water quality and quantity of the Barbier-brook.No discharge data from the Barbier-brook are known at all. Based on the discharge data of the Kleine Molenbeek near Liezele, which has a similar catchment area except the size, the discharge frorn the Barbier-brook could be abstracted. To do so, the surface area of the Kleine Molenbeek is multiplied by a factor 1,43. Frorn these discharge data follows a mean discharge of the Barbier-brook which varies seasonally between 3 and 5 m3/s. These data show also an increase in the annual maximum 24h-discharges starting from approximately 1980.The quality of the water of the Barbier-brook off the CIA-KBR is very bad. The brook is heavily polluted with domestic, industrial and agricultural wastewater. Nearby the site where the brook discharges into the Schelde it is characterised as "biologically dead". The involved communities have made sewerage plans which will decrease the pollution of the Barbier-brook with dornestic wastewater with about 80%. Concerning the houses which are not covered by the sewerage plans the following measures are given: 1) yet inc1ude into the sewerage plans, and 2) provide small-scale biological treatment.After completion of the sewerage plans and the extra measures the following reductions of the pollution by wastewater on the Barbier-brook could be reached:dornestic wastewater: 92%; industrial wastewater: 90%; agricultural wastewater: 31 %To make it technically possible to fit the Barbier-brook in the CIA-KBR it is necessary to compensate the storage of the Barbier-brook in order to prevent the brook to cause trouble at the houses of Bazel that stand close to the brookside. For this reason the following measures will be elaborated:The realisation of a storage along the ringdike which is connected with the CIA by means of a culvert. The surface needed for the storage is regulated by the maximum water level that is tolerated in the storage. From calculations follows that there is enough place to realise a storage that can guarantee a safety for a situation with a return period of 1 per 1000 years. No houses need to be removed.The realisation of a storage in the natural valley of the Barbier-brook situated upstream Bazel and the CIA. This storage needs to be fit in the protected landscape without large works. From calculations follows that the available storage volume is insufficient to guarantee a safety for a situation with a return period of 1 per 1000 years.Placing a pumping station at the ringdike with sufficient capacity to pump over a discharge of the Barbier-brook with a return period of 1 per 400 years which is 8,7 m3/s. It is technically possible to reach this with a "screw-up-pumping station" as well as with a "screw-centrifugal-pumping station”Not until the quality of the water of the Barbier-brook improves strongly, nature development can be effectively worked out. In this study the following perspectives for nature development are elaborated in order to increase the value of nature in that part of the CIA that can be influenced by the Barbier-brook:.Concerning the area between the Barbier-brook dikes possible measures are worked out to improve the present potential values of nature. Thus rich zones along the Creek of Kruibeke can be expected and the higher grounds will be rich in flowering plants. When the dikes around the Barbier-brook are preserved the introduction of a controlled reduced tide is of no influence concerning nature development of the Barbier-brook..Concerning a part of the polder of Kruibeke space will be created for development of a more natural Barbier-brook. The agricultural activities on the other grounds will be preserved. Different measures will make this possible of which one is the removal of the Northern Barbier-brook dike. There will be aimed towards broad and rich developed zones along the brook with gradation in vegetation types. The introduction of a controlled reduced tide is not considered because of the present function of agriculture in the polder ..Concerning the polders of Kruibeke and Bazel measures are worked out to provide a total free development of the Barbier-brook. The most effective measure to reach this is the removal of the Barbier-brook dikes except that part of the dikes between the new ringdike and the natural height in the polder of Bazel. There will be a striving towards a large scaled landscape dominated by reeds and rich developed wetlands. The introduction of a controlled reduced tide is of great influence of the nature development in this situation. It might even re sult in freshwater marshes and mud plains in the CIA-KBR

Ecosystem engineering creates a direct nutritional link between 600-m deep cold-water coral mounds and surface productivity

Cold-water corals (CWCs) form large mounds on the seafloor that are hotspots of biodiversity in the deep sea, but it remains enigmatic how CWCs can thrive in this food-limited environment. Here, we infer from model simulations that the interaction between tidal currents and CWC-formed mounds induces downwelling events of surface water that brings organic matter to 600-m deep CWCs. This positive feedback between CWC growth on carbonate mounds and enhanced food supply is essential for their sustenance in the deep sea and represents an example of ecosystem engineering of unparalleled magnitude. This ’topographically-enhanced carbon pump’ leaks organic matter that settles at greater depths. The ubiquitous presence of biogenic and geological topographies along ocean margins suggests that carbon sequestration through this pump is of global importance. These results indicate that enhanced stratification and lower surface productivity, both expected consequences of climate change, may negatively impact the energy balance of CWCs

Meiofauna metabolism in suboxic sediments: currently overestimated

Oxygen is recognized as a structuring factor of metazoan communities in marine sediments. The importance of oxygen as a controlling factor on meiofauna (32 µm-1 mm in size) respiration rates is however less clear. Typically, respiration rates are measured under oxic conditions, after which these rates are used in food web studies to quantify the role of meiofauna in sediment carbon turnover. Sediment oxygen concentration ([O2]) is generally far from saturated, implying that (1) current estimates of the role of meiofauna in carbon cycling may be biased and (2) meiofaunal organisms need strategies to survive in oxygen-stressed environments. Two main survival strategies are often hypothesized: 1) frequent migration to oxic layers and 2) morphological adaptation. To evaluate these hypotheses, we (1) used a model of oxygen turnover in the meiofauna body as a function of ambient [O2], and (2) performed respiration measurements at a range of [O2] conditions. The oxygen turnover model predicts a tight coupling between ambient [O2] and meiofauna body [O2] with oxygen within the body being consumed in seconds. This fast turnover favors long and slender organisms in sediments with low ambient [O2] but even then frequent migration between suboxic and oxic layers is for most organisms not a viable strategy to alleviate oxygen limitation. Respiration rates of all measured meiofauna organisms slowed down in response to decreasing ambient [O2], with Nematoda displaying the highest metabolic sensitivity for declining [O2] followed by Foraminifera and juvenile Gastropoda. Ostracoda showed a behavioral stress response when ambient [O2] reached a critical level. Reduced respiration at low ambient [O2] implies that meiofauna in natural, i.e. suboxic, sediments must have a lower metabolism than inferred from earlier respiration rates conducted under oxic conditions. The implications of these findings are discussed for the contribution of meiofauna to carbon cycling in marine sediments

Образ города в записках Н. Дуровой “Кавалерист-девица. Происшествие в России”

Статья посвящена анализу записок Надежды Дуровой как путевому дневнику, в котором изображены многие города из разных стран в мирное и военное время. Автор статьи доказывает, что восприятие города зависит от исторического времени, от настроения мемуаристки, от физического состояния; акцентирует внимание на том, что в записках Дуровой нашли отражение обычаи и традиции жизни не только дворянства и высших кругов, но и простого народа, солдат, офицеров. В статье сделана попытка сравнить описание городов у нескольких украинских мемуаристов (Т. Шевченко, С. Капнист-Скалон), показать различный подход в изображении действительности у мемуаристов и писателей.Стаття присвячена аналізу записок Надії Дурової як дорожньому щоденнику, в якому змальовано багато міст з різних країн в мирний і військовий час. Автор статті доводить, що сприйняття міста залежить від історичного часу, від настрою мемуаристки, від фізичного стану; акцентується увага на тому, що в записках Дурової відображені звичаї і традиції життя не лише дворянства і вищих кругів, але й простого народу, солдатів, офіцерів. У статті зроблена спроба порівняти опис міс у декількох українських мемуаристів (Т. Шевченко, С. Капніст-Скалон), показати різний підхід в зображенні дійсності у мемуаристів і письменників.This article analyzes the notes of Nadezhda Durova as travel diary, which shows many cities from different countries in peacetime and wartime. The author of the article proves that the perception of the city depends on the historical time, the mood of the memoirist, on the physical state; focuses on the fact that the notes of Durova reflect customs and traditions of life not only the nobility and the higher circles, but also ordinary people, soldiers, officers . An attempt to compare description of cities by another Ukrainian memorialists (T. of Shevchenko, P. Kapnist-Skalon) is done in the article. А different approach in the image of reality in memoirists and writers is also shown

Contrasting metabolic strategies of two co‑occurring deep‑sea octocorals

The feeding biology of deep-sea octocorals remains poorly understood, as attention is more often directed to reef building corals. The present study focused on two common deep-water octocoral species in the Azores Archipelago, Dentomuricea aff. meteor and Viminella flagellum, aiming at determining their ability to exploit different food sources. We adopted an experimental approach, with three different food sources, including live phytoplankton, live zooplankton and dissolved organic matter (DOM), that were artificially enriched with 13C and 15N (C and N tracers). The presence of tracers was subsequently followed in the coral tissue, C respiration and particulate organic C and N (POC and PON) release. In both species, feeding with zooplankton resulted in significantly higher incorporation of tracers in all measured variables, compared to the other food sources, highlighting the importance of zooplankton for major physiological processes. Our results revealed contrasting metabolic strategies between the two species, with D. aff. meteor acquiring higher amounts of prey and allocating higher percentage to respiration and release of POC and PON than V. flagellum. Such metabolic differences can shape species fitness and distributions and have further ecological implications on the ecosystem function of communities formed by different octocoral species.Versión del edito