Environmental hypoxia as a metabolic constraint on fish: the case of Atlantic cod, Gadus morhua

Hypoxia is known to provoke a wide range of effects on aquatic animals. Here we use laboratory and field data on Atlantic cod, Gadus morhua, to illustrate that many of these responses can be explained within the metabolic scope (MS) framework, i.e. taking into account the directive and limiting effects of dissolved oxygen (DO) on the ability of animals to acquire energy for growth and activity. A MS model for cod shows that scope for activity (swimming, feeding, etc.) is proportional to DO and becomes nil, jeopardising survival, when DO is < approximately 20% air saturation. Laboratory studies have confirmed this lethal threshold and demonstrated that growth and food ingestion were significantly reduced below 70% sat. This loss of appetite has been linked to a reduction of the peak value and an increase in duration of postprandial metabolism, in agreement with the MS model. Dwindling MS during hypoxia imposes an upper limit to swimming performance. Cod may also opt to reduce spontaneous swimming activity to spare oxygen for other activities such as digestion. In the Kattegat, the Baltic Sea, and the Gulf of St. Lawrence, eastern Canada, cod completely avoid waters where their MS is near zero. Furthermore, cod density increases exponentially with DO up to approximately 70% sat in the Gulf of St. Lawrence. Although hypoxia results in other direct and indirect effects as well, the MS framework allows modelling of many of the responses to hypoxia for individual cod that ought to be reflected at the population and community levels. The MS framework is also useful to compare species responses. We show that the impact of hypoxia on MS is similar, when expressed as a proportion of MS in normoxia, in cod, European sea bass (Dicentrarchus labrax), the common sole (Solea solea) and turbot (Psetta maxima). Data are required for other species to evaluate how general these findings are.     

Effects of hypoxia on benthic macrofauna and bioturbation in the Estuary and Gulf of St. Lawrence,Canada

The bottom water in the >300 m deep Lower St. Lawrence Estuary (LSLE) is persistently hypoxic in contrast to the normoxic bottom waters in the Gulf of St. Lawrence (GSL). We photographed the seabed at 11 stations in the Estuary and Gulf of St. Lawrence (EGSL) during the summers 2006 and 2007 and analysed the images to identify bioturbation traces (lebensspuren) and benthic macrofauna. The objective was to identify the environmental variables that influence the density and diversity of benthic macrofauna and bioturbation traces, and the differences that exist among regions with high, medium and low oxygen levels in the bottom water. The bottom water oxygen concentration is the variable that best explains the densities of total-traces as well as surface-traces. However, the density of these traces was higher in hypoxic regions than in well-oxygenated regions. The higher density of traces in the hypoxic region of the LSLE is mainly due to the activities of the surface deposit feeder Ophiura sp., which occurs in large numbers in this region. Possible explanations explored are stress behaviour of the organisms in response to hypoxia and different benthic macrofauna community structures between the hypoxic regions of the LSLE and the normoxic regions of the GSL. In the former, surface deposit feeders and low-oxygen tolerant species dominate over suspension feeders and low-oxygen intolerant species.     

Mercury content of mussels from the St. Lawrence Estuary and northwestern Gulf of St. Lawrence, Canada

A first survey of the mercury content of intertidal mussels in the St. Lawrence Estuary and part of the Gulf of St. Lawrence shows means values ranging from 0.160 to 0.629 ppm (dry weight). Highest values (grand mean 0.430 ppm) were found in the upper part of the lower estuary, lowest values (grand mean 0.172 ppm) on the north shore of the estuary and Gulf, and intermediate values along the Gaspé Peninsula. The results indicate a decreasing gradient in mercury levels from the mouth of the Saguenay Fjord seaward.     

Physiological energetics of the fourth instar of Chinese horseshoe crabs (Tachypleus tridentatus) in response to hypoxic stress and re-oxygenation

Hypoxia associated with eutrophication is a potential threat to the Chinese horseshoe crab Tachypleus tridentatus which inhabits intertidal sand flats in Asia. This study investigated the effect of dissolved oxygen level (DO) (6, 4 and 2 mg O₂ l⁻¹) on the physiological energetics in the juvenile T. tridentatus. They were exposed to various oxygen levels for three days and then transferred to normoxia for three days to examine the recovery from low oxygen stress. Feeding rate, respiration rate and scope for growth were reduced at lower DO levels while absorption efficiency and excretion rate were independent of DO levels. Although full recovery of the physiological responses and scope for growth from hypoxis stress was observed when normoxia resumed, their long term survival in suboptimal habitats with frequent occurrence of hypoxia deserves a close monitoring as hypoxia may be even more common in future in a warming world.     

Dissolved oxygen--a target indicator in determining use of the Gulf of Kachchh waters

Spatial and temporal variations of Dissolved Oxygen (DO) and Biochemical Oxygen Demand (BOD) in the Gulf of Kachchh (GoK), India are assessed based on data collected since 1976. DO concentrations in the interior GoK vary within a narrow range (6.05-6.86 mg l(-1)), whereas near-shore waters show wider variations (3.5-7.8 mg l(-1)). The DO concentration levels in the Gulf waters are close to saturation, varying from 75.4% to 108.6%, which is much higher than the 60% saturation level set for the SW-1 waters. BOD-DO simulation shows that when effluents containing a BOD concentration of 50.0 mg l(-1) are introduced at three select locations, DO reduces from 5.1 mg l(-1) to 3.1, 5.0 and 3.8 mg l(-1), respectively, indicating a strong sensitivity to effluent load. Based on the DO analysis, BOD assimilation capacity of coastal waters around the Marine National Park (MNP) and Marine Sanctuary (MS) in the Gulf is determined. DO available for utilization for various categories of water use is illustrated, keeping in mind the ecology of MNP and MS areas. The significance of DO as a target indicator to zone the Gulf for different water use, is highlighted in this study.     

Auroral electrojet dynamics during magnetic storms, connection with plasma precipitation and large-scale structure of the magnetospheric magnetic field

Effect of the equatorward shift of the eastward and westward electrojets during magnetic storms main phase is analyzed based on the meridional chains of magnetic observatories EISCAT and IMAGE and several Russian observatories (geomagnetic longitude ≈110°, corrected geomagnetic latitudes 74°>φ>51°.) Magnetic storms of various Dst index intensity where the main phase falls on 1000 UT - 2400 UT interval were selected so that one of the observatory chains was located in the afternoon - near midnight sector of MLT. The eastward electrojet center shifts equatorward with Dst intensity increase: when Dst ≈ −50 nT the electrojet center is located at φ ≈ 62°, when Dst ≈ −300 nT it is placed at φ ≈ 54°. The westward electrojet center during magnetic storms main phase for intervals between substorms shifts equatorward with Dst increase: at φ ≈ 62° when Dst ≈ −100 nT and at φ ≈ 55° when Dst ≈ −300 nT. During substorms within the magnetic storms intervals the westward electrojet widens poleward covering latitudes φ ≈ 64°–65°. DMSP (F08, F10 and F11) satellite observations of auroral energy plasma precipitations at upper atmosphere altitudes were used to determine precipitation region structure and location of boundaries of various plasma domains during magnetic storms on May 10–11, 1992, February 5–7 and February 21–22, 1994. Interrelationships between center location, poleward and equatorward boundaries of electrojets and characteristic plasma regions are discussed. The electrojet center, poleward and equatorward boundaries along the magnetic observatories meridional chain were mapped to the magnetosphere using the geomagnetic field paraboloid model. The location of auroral energy oxygen ion regions in the night and evening magnetosphere is determined. Considerations are presented on the mechanism causing the appearance in the inner magnetosphere during active intervals of magnetic storms of ions with energy of tens KeV. In the framework of the magnetospheric magnetic field paraboloid model the influence of the ring current and magnetospheric tail plasma sheet currents on large-scale magnetosphere structure is considered.     

Sensitivity of coastal waters to anthropogenic trace metal emissions

Trace metal concentrations in the waters of the Gulf of St. Lawrence and the Scotian Shelf and their sensitivity to changes in the composition of the major contributor of fresh water, the St. Lawrence River, are assessed. Comparison of the levels of trace metals in eastern Canadian coastal waters with those in other coastal waters of the world reveals that the former area generally has lower trace metal concentrations and is, therefore, probably less contaminated than elsewhere. The increased anthropogenic activity in the St. Lawrence drainage basin required to increase the levels of trace metals in receiving coastal waters by detectable amounts is discussed. We demonstrate that faster and more reliable warning of changes due to anthropogenic activity will be revealed through river monitoring than through monitoring of coastal waters. Changes in the marine environment can then be assessed through a thorough understanding of the geochemical behaviour of trace metals in nearshore waters.     

Quartz OSL dating of late Holocene beach ridges from the Magdalen Islands (Quebec,Canada)

Quartz optically stimulated luminescence (OSL) dating has been applied to sandy beach ridge systems from the Magdalen Islands in the center of the Gulf of St. Lawrence (Quebec, Canada) to provide the first chronological framework for these features. Nineteen beach ridges (22 samples) from four different sites throughout the archipelago were investigated. At one of the sites, samples were taken at 9 m and 7.5 m depth using a vibracore. The quartz is dominated by the fast OSL component and a single-aliquot regenerative-dose (SAR) protocol was used to measure the equivalent doses; a low preheat (180°C/10 s) was chosen to avoid the influence of thermal transfer. The average dose recovery ratio of all samples is 1.02 ± 0.02 (n = 130) suggesting that the SAR protocol works satisfactorily on this material. The OSL ages are internally consistent and supported by independent age control (radiocarbon). The OSL ages indicate that the ridges were built between 2.6 ± 0.2 ka and 0.40 ± 0.10 ka, i.e. during a period of sea level rise. This rise eroded adjacent sandstone cliffs, which contributed a significant sediment supply to the littoral drift and beaches. Some low-lying coasts in the archipelago are still prograding, despite a relative sea level increase of ∼1.6 mm/a over the last 600 years. The late Holocene ages obtained in this study indicate that these processes have been active for at least the past two thousand years. This study demonstrates for the first time that OSL dating using quartz has great potential in this area, and is an appropriate method for establishing precise chronologies for coastal sediments in this region of the Gulf of St. Lawrence.     

Hypoxia does not promote naphthalene bioaccumulation in the brown shrimp, Penaeus aztecus

Since increased ventilation is known to be a common strategy used by aquatic animals to cope with hypoxia, we tested in present study the hypothesis that hypoxia can promote the bioaccumulation of naphthalene, a representative polycyclic aromatic hydrocarbon (PAH), in Penaeus aztecus, a penaeid shrimp subject to hypoxia and PAH contamination in the northern Gulf of Mexico. For each of the two naphthalene concentrations, five groups of shrimps were, respectively, subjected to five different conditions, namely, clean seawater under normoxia, seawater containing acetone under normoxia and hypoxia, and seawater containing 10 or 250 μg/L naphthalene under normoxia and hypoxia. Our results suggest that hypoxia does not significantly alter naphthalene bioaccumulation in either the gills or the hepatopancreas of P. aztecus. The absence of a promoting effect of hypoxia on naphthalene bioaccumulation is attributed to the increased disposition of naphthalene when the shrimps are subjected to hypoxia.     

Effect of stratification on tidal circulation over the Scotian Shelf and Gulf of St. Lawrence: a numerical study using a three-dimensional shelf circulation model

A three-dimensional shelf circulation model is used to examine the effect of seasonal changes in water-column stratification on the tidal circulation over the Scotian Shelf and Gulf of St. Lawrence. The model is driven by tidal forcing specified at the model’s lateral open boundaries in terms of tidal sea surface elevations and depth-averaged currents for five major tidal constituents (M₂, N₂, S₂, K₁, and O₁). Three numerical experiments are conducted to determine the influence of baroclinic pressure gradients and changes in vertical mixing, both associated with stratification, on the seasonal variation of tidal circulation over the study region. The model is initialized with climatological hydrographic fields and integrated for 16 months in each experiment. Model results from the last 12 months are analyzed to determine the dominant semidiurnal and diurnal tidal components, M₂ and K₁. Model results suggest that the seasonal variation in the water-column stratification affects the M₂ tidal circulation most strongly over the shelf break and over the deep waters off the Scotian Shelf (through the development of baroclinic pressure gradients) and along Northumberland Strait in the Gulf of St. Lawrence (through changes in vertical mixing and bottom stress). For the K₁ constituent, the baroclinic pressure gradient and vertical mixing have opposing effects on the tidal circulation over several areas of the study region, while near the bottom, vertical mixing appears to play only a small role in the tidal circulation.     

Sources of particulate and dissolved organic carbon in the St Lawrence River: isotopic approach

We investigate sources of both dissolved and particulate organic carbon in the St Lawrence River from its source (the Great Lakes outlet) to its estuary, as well as in two of its tributaries. Special attention is given to seasonal interannual patterns by using data collected on a bi‐monthly basis from mid‐1998 to mid‐2003. δ¹³C measurements in dissolved inorganic carbon, dissolved organic carbon (DOC) and particulate organic carbon (POC), as well as molar C : N in particulate organic matter (POM), are used to bring insight into the dynamic between aquatic versus terrigenous sources. In addition, ¹⁴C activities of DOC were measured at the outlet of the St Lawrence River to its estuary to assess a mean age of the DOC exported to the estuary. In the St Lawrence River itself, aquatically produced POC dominates terrestrially derived POC and is depleted in ¹³C by approximately 12‰ versus dissolved CO₂. In the Ottawa River, the St Lawrence River's most important tributary, the present dataset did not allow for convincing deciphering of POC sources. In a small tributary of the St Lawrence River, aquatically produced POC dominates in summer and terrestrially derived POC dominates in winter. DOC seems to be dominated by terrestrially derived organic matter at all sampling sites, with some influence of DOC derived from aquatically produced POC in summer in the St Lawrence River at the outlet of the Great Lakes and in one of its small tributaries. The overall bulk DOC is relatively recent (¹⁴C generally exceeding 100% modern carbon) in the St Lawrence River at its outlet to the estuary, suggesting that it derives mainly from recent organic matter from topsoils in the watershed. Copyright © 2005 John Wiley & Sons, Ltd.     

Could ocean currents be responsible for the west to east spread of aquatic invasive species in Maritime Canadian waters?

The circulation in the shelf seas of Maritime Canada is predominantly in the northeast–southwest direction. Despite the mean northeast–southwest flow, a number of AIS invasions have been observed to proceed in the opposite direction – from the Gulf of Maine, around Nova Scotia, and into the southern Gulf of St. Lawrence. Flow fields from a numerical circulation model are used to investigate whether these invasions could be due to drift in ocean currents. Particle tracking experiments are performed and probability density functions (PDFs) derived that describe the probability of drifting a given upstream distance in a given drift time. Analysis of these PDFs revealed that for invasions that took 20–40 y to occur, propagule drift in ocean currents could be responsible for the upstream spread, while this was not the case for short timescale invasions (<10 y). Rafting could be responsible for both short and long timescale invasions.     

The Pan-African continental margin in northeastern Africa: evidence from a geochronological study of granulites at Sabaloka, Sudan

Ion microprobe zircon ages, a Nd model age and RbSr whole-rock dates are reported from the high-grade gneiss terrain at Sabaloka on the River Nile north of Khartoum, formally considered to be part of the Archaean/early Proterozoic Nile craton. The granulites, which are of both sedimentary and igneous derivation, occur as remnants in migmatites. Detrital zircon ages range from ≈ 1000 to ≈ 2650 Ma and prove the existence of Archaean to late Proterozoic continental crust in the sedimentary source region. The Nd model age for one sedimentary granulite is between 1.26 (T_CHUR) and 1.70 (T_DM) Ga and provides a mean crustal residence age for the sedimentary precursor. Igneous zircons in enderbitic gneiss crystallized at 719 ± 81 Ma ago, an age that also corresponds to severe Pb loss in the detrital zircons and which probably reflects the granulite event at Sabaloka. The RbSr data indicate isotopic homogenization at about 700 Ma ago in the granulites and severe post-granulite disturbance at ≈ 570 Ma in the migmatites. We associate this disturbance with hydration, retrograde metamorphism and anatexis that produced undeformed granites ≈ 540 Ma ago. The ≈ 700 Ma granulite event at Sabaloka suggests that this part of the Sudan belongs to the Pan-African Mozambique belt while the ancient Nile craton lay farther west. The gneisses studied here may represent the infrastructure of the ancient African continental margin onto which the juvenile arc assemblage of the Arabian-Nubian shield was accreted during intense horizontal shortening and crustal interstacking of a major collision event.     

Sexual maturation as a source of variation in the relationship between cadmium concentration and body weight of Mytilus edulis L.

In order to refine the utilization of Mytilus edulis as a pollution indicator species, the relationship between cadmium concentration and mussel body weight was investigated at different sites in the Estuary and Gulf of the St. Lawrence. Our data show that the regression coefficients become considerably more variable when animals enter adulthood and that the variations are probably related to biochemical changes occurring during the sexual cycle. A substantial improvement of the applicability of mussels for monitoring marine pollution can be achieved by using only immature animals. This should reduce the influence of metabolism on the metal content of mussels and thereby give a more precise indication of ambiant pollution levels.     

Hypoxia impairs embryo development and survival in black bream (Acanthopagrus butcheri)

Coastal environments are threatened by the increasing frequency, extent and severity of hypoxic events. Hypoxia affects vast areas around the world and often causes fish kills, reduced abundance, altered distribution, low benthic biomass and declines in fisheries. In Australia, many fisheries are based on sparid fishes and in the southern states black bream (Acanthopagrus butcheri) is important to both the recreational and commercial sectors. This species completes its entire life cycle in estuaries and annual recruitment is highly variable and very likely influenced by environmental conditions during the spawning season.In a laboratory-based experiment, fertilised black bream eggs (embryos) were exposed to five different levels of dissolved oxygen (DO). The DO levels were maintained in small test wells using nitrogen gas in a novel chamber design. Embryo development was assessed over a 2-day period and hatched larvae were observed until Day 2 post-hatch. Significant differences (p < 0.05) were observed in embryonic development and survival as a function of DO level. In severely hypoxic conditions (30% saturation) survival to 1 day was reduced and no hatching occurred. In moderately hypoxic conditions (45–55%S), both precocious and delayed hatching was observed and hatch rates were reduced, whilst the number of hatched larvae with deformities increased, resulting in reduced larval lengths. No larvae survived to Day 2 post-hatch when held in hypoxic conditions (<55%S). This study demonstrates the detrimental effect that severe hypoxia can have on the early development of black bream which could result in reduced recruitment and lowered abundance. Other species that share similar early life histories may also be at risk.     

Study on subtidal circulation and variability in the Gulf of St. Lawrence,Scotian Shelf,and Gulf of Maine using a nested-grid shelf circulation model

This paper examines the subtidal circulation and associated variability in the Gulf of St. Lawrence, the Scotian Shelf, and the Gulf of Maine (GSL-SS-GOM) in 1988–2004 based on results produced by a nested-grid shelf circulation model. The model has a fine-resolution child model (～ (1/12)°) embedded inside a coarse-resolution parent model (～ (1/4)°) of the northwest Atlantic. The combination of the semi-prognostic method and the spectral nudging method is used to reduce the model seasonal bias and drift. The child model reproduces the general features of the observed circulation and hydrography over the study region during the study period. The child model results demonstrate that the time-mean circulation in the GSL is affected by the time-mean atmospheric forcing and inflow through the Strait of Belle Isle. The temporal variability in atmospheric forcing affects the outflow through western Cabot Strait, which in turn affects the transport of the Nova Scotian Current and the gulf-wide cyclonic circulation in the GOM. The simulated seasonal variability of salinity in the top 30 m of the GSL-SS-GOM is mainly affected by the equatorward advection of low-salinity waters from the lower St. Lawrence Estuary to the GOM through the Scotian Shelf. The simulated intraseasonal variability of circulation in the GSL is affected by the variability in the estuarine circulation in response to the temporal variability in atmospheric forcing. On the Scotian Shelf, the intraseasonal variability is mainly driven by the variability of wind forcing and mesoscale and nonlinear dynamics over the shelf break and slope region. The interannual variability in the simulated temperature and salinity are spatially coherent in the intermediate waters in the GSL, which is caused partially by the local response to atmospheric variability and partially by variabilities over the southern Newfoundland Shelf that enter the GSL through the eastern Cabot Strait. By comparison, on the Scotian Shelf, the interannual variability of simulated circulation is affected by anomalies produced by the nonlinear dynamics which are advected equatorwards by the shelf break jet.     

Sperm swimming in the polychaete Galeolaria caespitosa shows substantial inter-individual variability in response to future ocean acidification

The rapidity of ocean acidification intensifies selection pressure for resilient phenotypes, particularly during sensitive early life stages. The scope for selection is greater in species with greater within-species variation in responses to changing environments, thus enhancing the potential for adaptation. We investigated among-male variation in sperm swimming responses (percent motility and swimming speeds) of the serpulid polychaete Galeolaria caespitosa to near- (ΔpH −0.3) and far-future ocean acidification (ΔpH −0.5). Responses of sperm swimming to acidification varied significantly among males and were overall negative. Robust sperm swimming behavior under near-future ocean acidification in some males may ameliorate climate change impacts, if traits associated with robustness are heritable, and thereby enhance the potential for adaptation to far-future conditions. Reduced sperm swimming in the majority of male G. caespitosa may decrease their fertilization success in a high CO₂ future ocean. Resultant changes in offspring production could affect recruitment success and population fitness downstream.     

The dynamic cusp aurora on 30 November 1997: response to southward turning of the IMF

We document the detailed dynamics of the dayside aurora in the ≈1200–1600 MLT sector in response to a sharp southward turning of the interplanetary magnetic field (IMF) under negative IMF B_y conditions. Features not documented in previous work are elucidated by using two meridan scanning photometers (separated by 2 h) and an all-sky auroral imager in Ny Ålesund, Svalbard (75.5^MLAT) in combination with magnetograms from stations on Svalbard, covering the latitude range 71^–75^MLAT. The initial auroral response may be divided into three phases consisting of: (1) intensification of both the red (630.0 nm) and green (557.7 nm) line emissions in the cusp aurora near 1200 MLT and ≈100 km equatorward shift of its equatorward boundary, at ≈75^MLAT, (2) eastward and poleward expansions of the cusp aurora, reaching the 1430 MLT meridian after 5–6 min, and (3) east-west expansion of the higher-latitude aurora (at ≈77^–78^MLAT) in the postnoon sector. The associated magnetic disturbance is characterized by an initial positive deflection of the X-component at stations located 100–400 km south of the aurora, corresponding to enhanced Sunward return flow associated with the merging convection cell in the post-noon sector. The sequence of partly overlapping poleward moving auroral forms (PMAFs) during the first 15 min, accompanied by corresponding pulsations in the convection current, was followed by a strong westward contraction of the cusp aurora when the ground magnetograms indicated a temporary return to the pre-onset level. These observations are discussed in relation to the Cowley-Lockwood model of ionospheric response to pulsed magnetopause reconnection.     

Distribution and fluxes of metals in the St. Lawrence River from the outflow of Lake Ontario to Québec City

Six anchor stations in the St. Lawrence River from the outflow of Lake Ontario to Quebec City, were occupied for ca. 24 hours in June 1987 during low flow conditions. Samples of water and suspended particulate matter were separated by continuous-flow centrifugation, and were collected every two hours.During this sampling period, fluxes of dissolved forms of zinc, copper and nickel increased in Lac St. François and downstream relative to the sum of the fluxes for the two upstream stations at the outflow of Lake Ontario. Increases in the flux of dissolved zinc and copper were pronounced below Montreal and above Lac St. Pierre. For particulate forms of metals, all five metals show that there are significant inputs in the section of the St. Lawrence River between Lac St. François and the station just above the entrance to Lac St. Pierre.The average concentrations of dissolved cadmium, lead, zinc, copper and nickel ranged from 7–23 ng/l; 9–35 ng/l; 0.434–0.939 g/l; 0.15–0.89 g/l and 0.58–1.12 g/l respectively.Regression analysis of the dissolved and particulate metal concentrations suggests that the concentration of dissolved cadmium, lead, zinc and nickel can be predicted from the regression equation and the determination of particulate metal concentration. This prediction appears to be independent of the suspended particulate matter concentration which varies from ca. 1 to 10 mg/l from the outflow of Lake Ontario to Québec City.     

Man-made storage of water resources—A liability to the ocean environment? Part II

The first part of this article (Mar. Pollut. Bull., 13, 7–12, 1982) described the impact of the seasonal fresh water runoff on bodies of water—such as the Gulf of St. Lawrence and the coastal region—through changes in the salinity and temperature distribution and through changes in the current generated by the density difference between the fresh river water and the ocean. The strength of the current and thus the transport of deep ocean water to the coastal region depends on the amount of fresh water released into the ocean. Therefore modifying the natural seasonal runoff by storing water for power production during the winter interferes with the timing of the physical and dynamic balance of the coastal region. The impact of this interference on the marine life and on the climate of the region is now discussed.