A comparative study of photoadaptation in four diatoms isolated as endosymbionts from larger foraminifera

Four endosymbiotic diatoms were isolated from 2 species of larger foraminifera collected in the Red Sea and Hawaii. The photoadaptive responses of the cultured diatoms were measured at 312, 19 and 7 W cm^-2. Two of the diatoms (Fragilaria shiloi and Nitzschia laevis), both isolated from Amphistegina lessonii, grew fastest at 312 W cm^-2. The other two diatoms (N. valdestriata and N. panduriformis) which were isolated from Heterostegina depressa, grew best at 19 W cm^-2. Of the four diatoms, F. shiloi grew best at high light levels. Also in F. shiloi, chlorophyll c content per cell was directly proportional to light intensity; in contrast chlorophyll a and carotenoids increased to maxima at 19 W cm^-2. The chlorophyll a and c and carotenoid content of N. valdestriata were also maximal at 19 W cm^-2. Photosynthetic rates, measured by respirometry, suggested that the diatoms were photoinhibited at higher light intensities and did well at moderately low light intensities (175W cm^-2). The photocompensation points of all 4 diatoms were about 2% of the light available in the spring at 1-m depth at Elat on the Red Sea. At Elat the photocompensation point would lie between 40 and 50 m if the algae were free in nature. The amount of attenuation of light by the shells of the host has not yet been measured. Presumably photocompensation of the algae within hosts is reached at depths less than 40 m.     

Abundance and production rates of floating diatom mats (Rhizosolenia castracanei and R. imbricata var. shrubsolei) in the Eastern Pacific Ocean

Abundance and production rates were measured on freefloating mats composed of the diatoms Rhizosolenia castracanei and R. imbricata var. shrubsolei in the California Current and boundary waters of the central North Pacific during October, 1980. Mats ranged from 3.0 to 10.6 cm in maximum length and had a mean volume of 6.4 ml. Production rates of the diatom mats averaged 4.0 g C colony^-1 h^-1, more than 10³ times higher than that of an equal volume of surrounding water. However, because of their low density at these sites, about 1 mat m^-3, diatom mats contributed only about 1% of the total primary production. The two large Rhizosolenia species comprised almost all of the phytoplankton biomass within the mats. Rhizosolenia species rarely occurred in seawater between mats, where the phytoplankton community was dominated by a diverse array of nannoplankton. The Rhizosolenia species in the mats appeared to be in healthy condition and contained intracellular bacteria. The very high production rates of the colonies indicate high nutrient demand and, since these particular diatoms lack the symbiotic cyanobacterium Richelia intracellularis, which is implicated in N-fixation in other species of Rhizosolenia, our results indicate that other nutrient sources must be present. We discuss the potential role of the intracellular bacteria in nitrogen fixation.     

Effects of food quality on the reproductive success of Acartia tonsa and Acartia hudsonica: laboratory observations

The effect of the chemical composition of food on the reproductive success of the copepods Acartia tonsa Dana and A. hudsonica Pinhey was studied in the laboratory. Laboratory-reared individuals were fed one of three monoalgal diets at different stages of growth: the diatom Thalassiosira weissflogii, the flagellate Rhodomonas lens and the dinoflagellte Prorocentrum minimum. The diet was analyzed for carbon, nitrogen, protein, carbohydrate and fatty acid content. Reproductive success was measured as eggs female^-1 day^-1 (E _r) and as the hatching success of the eggs. The E _r of Acartia spp. was correlated with protein and specific fatty acids [16:17 (negative), 20:53, 22:63, and 18:0 (positive)] and, especially, the fatty acid composition of the algae expressed as the 3:6 and 20:22 fatty acid ratios. The youngest diatom cultures and exponentially-growing flagellates displayed the highest E _r; the lowest E _r was recorded for females fed the senescent diatom cultures. The development time of eggs was affected by the age of the phytoplankton culture fed to the female. Hatching success of eggs decreased with the age of the algal culture, but no correlation was found with the meansured chemical components of the food.     

Food ingestion and growth of the diatom-feeding nematode Chromadorita tenuis

Feeding rates and growth of the free-living brackish water nematode Chromadorita tenuis (G. Schneider, 1906) was studied throughout its life cycle. Populations were fed with the pennate diatom Nitzschia palea var debilis (Kütz.) Grunow in the laboratory at 18°C in agar plates based on seawater of 6 S. On the average, during the first day after hatching they ingest 1 g of cell contents, equal to 20 times the body weight, and the body weight increased from 3.6 to 6.9 ng C. During the entire 12.5 d of juvenile life the weight increased 40 times, whereas the weight only doubled during adult life, which is almost entirely devoted to reproduction. Adult virgins are larger than mated females. The large size of adult virgins indicates that about 50% of the gonad energy might be transferred to somatic growth. The size-frequency distribution of adult body lengths of a laboratory grown population as compared to four wild populations shows that the food offered to the laboratory population was of a poor quality.     

Effects of host-tissue homogenate of the scleractinian coral Plesiastrea versipora on glycerol metabolism in isolated symbiotic dinoflagellates

Symbiotic dinoflagellate algae (Symbiodinium sp.) isolated from the scleractinian coral Plesiastrea versipora and incubated in homogenized host tissue released 4 to 7 times as much glycerol (14 to 46 nmol glycerol/10⁶ algae) as those incubated in seawater (3 to 6 nmol glycerol/10⁶ algae) after 4 h incubation in the light. During this period, no release of triglycerides was detected. Intracellular glycerol increased 2- to 3-fold in algae incubated in host homogenate, but remained unchanged in algae incubated in seawater at a concentration of 0.82 ± 0.47 nmol glycerol/10⁶ algae. In each incubation condition, intracellular triglyceride levels increased. However, in algae incubated in host homogenate, the intracellular levels of triglycerides reached only about 75% of the amount reached in algae incubated in seawater (max. 18.55 ± 2.40 nmol glycerol/10⁶ cells). Host homogenate did not stimulate the release of glycerol from algae during dark incubation. These data show that the glycerol released by algae incubated in host-tissue homogenate was derived from increased synthesis of glycerol or from diversion of some glycerol or other photosynthetic intermediates from incorporation into algal triglyceride stores, and did not come from existing stores. Received: 20 December 1996 / Accepted: 9 January 1997     

Quantitative separation of benthic diatoms from sediments using density gradient centrifugation in the colloidal silica Ludox-TM

A quantitative density separation method for benthic diatoms is described in detail. Both epipelic and epipsammic diatoms have been separated from inorganic sediment components including empty diatom frustules. The method is based on differences in specific weight, using medium speed centrifugation on a step gradient of the colloidal silica Ludox-TM. Results obtained with this new method have been compared with those obtained by the lens tissue method. For the density method, applied to samples preserved with a mixture of acrolein, glutaraldehyde and tannic acid, a mean recovery of 82.3% chlorophyll a was found. In the lens tissue harvest-experiments, mean chlorophyll a harvests ranged from 29.1 to 53.2%. Moreover, the standard deviation was several times larger for the lens tissue harvest experiments than for the acrolein series processed by the density method. With the density method, sand fractions were removed entirely, while the clay fractions were removed almost completely. The remaining organic carbon (detritus), with a mean value of 42.3% of the original sample, does not interfere with diatom identification and counting, since all organic matter can be fully oxidized. The density method was found to be applicable to widely different kinds of estuarine sediment and varying quantities of benthic diatom biomass present in the samples. The method can also be used for some other algal groups such as Euglenophyceae and Cyanophyceae.Publication No. 19 of the project Biological Research in the Ems-Dollard Estuary.Communicated by O. Kinne, Hamburg     

Dissolution rates of silica from diatoms decomposing at various temperatures

In a study of silica dissolution from diatoms, the rate coefficient (K) h^-1 of raw diatom cells was estimated as 4 to 5 times smaller than that of the acid-digested siliceous skeletons. The dissolution rate coefficient at early stage (K₁) can be predicted as a function of temperature (T°C): in K₁=+T, where is the frequency factor depending on the properties of diatom species, ranging from -7.35 to-`0.38, and the temperature coefficient is 0.0833 for all species. Activation energies were calculated to be 1.37 to 1.38 Kcal mol^-1. This equation suggests that the rate coefficient K₁ increases by a factor of 2.27 for each 10 C° rise in temperature. This equation will also be applied to a new approach for the fate and behavior of biogenous silica settling through a water column by introducing the term temperature into a model.     

Biochemical composition of Nyctiphanes australis and its possible use as an aquaculture feed source: Lipids,pigments and fluoride content

Nyctiphanes australis contained, on a dry weight basis, an average of 52% crude protein and 5.0 to 9.5% lipid. The fatty acid profile of N. australis was markedly unsaturated, with a mean total 3 fatty acid content of 48.6±2.4% of total fatty acids. N. australis contained high levels of the essential long-chain polyunsaturated fatty acids eicosapentaenoic (EPA, 20:53) and docosahexaencic (DHA, 22:63), ranging from 16.6 to 36.5% and 11.1 to 24.8%, respectively. The concentration of total carotenoids ranged from 137 to 302 g g^–1 dry wt, with no significant differences in concentrations found with season or life stage. The carotenoids were comprised of 79.5% astaxanthin and 20.5% canthaxanthin. The lipid and pigment compositions of N. australis suggest that the species could serve as a suitable feed source for cultured salmonids. Like other euphausiids, N. australis contained high levels of fluoride, with a seasonal range between 277 and 3507 g g^–1 dry wt. The high fluoride levels found in N. australis would not detract from its potential as a feed source for salmonids because ingested fluoride is largely absorbed by the skeleton.     

Diets of some deep-sea brittle stars in the Rockall Trough

The stomachs of 1 165 individuals of the species Ophiacantha bidentata (Retzius), Ophiactis abyssicola (M. Sars), Ophiocten gracilis (O. Sars), Ophiura irrorata (Lyman), O. ljungmani (Lyman) and Ophiomusium lymani Wyville Thomson, collected from the general area of the Rockall Trough from 1973 to 1983, were examined; 47% contained material. This varied in nature and in volume between individuals, but overall, the diets of the 6 species showed quite high similarity. The few differences evident are interpreted as reflecting different lifestyles. Except for Ophiocten gracilis, the probably motile, epifaunal species (Ophiura irrorata, O. ljungmani and Ophiomusium lymani) showed the greatest variety in items, and the lowest similarity with the remaining species; they are probably unselective omnivores, eating whatever small prey or organic detritus they are able to find. Ophiacantha bidentata and Ophiactis abyssicola showed both the least dietary variety, and the highest similarity to each other. This probably reflects their more sedentary lifestyle, feeding on current-borne particles and small prey from perches on sessile fauna. The stomach contents of Ophiocten gracilis consisted mainly of amorphous organic material and mineral particles, indicating a microphagous feeding mechanism. With O. gracilis, the proportion of stomachs with food decreased markedly in summer, this coinciding with seasonal gonadal development when stomachs frequently appeared ruptured or compressed. The possible importance of seasonal sedimentation of fast-sinking particulates from the surface is discussed in relation to finds of flocculent organic material, often containing diatom frustules, in stomachs of all 6 species. Some doubts remain as to whether our results are biased by specimens egesting stomach contents on capture. As in shallow water, deep-sea ophiuroids seem to be trophic generalists lacking in dietary specialization. Brief notes on parasites encountered are also given.     

The eye and some effects of light on locomotor activity in Nephrops norvegicus

The compound eye of Nephrops norvegicus (L.) is of the superposition type, well-adapted to the low levels of light prevailing at the sea bed during the activity periods of the species. Only the proximal retinal shielding pigment responds to light, the distal retinal shielding pigment being in the dark-adapted position at all times. The response of the proximal pigment appears to vary seasonally. Field observations compared light intensity at the sea bed with the numbers of N. norvegicus caught by trawl at various times of day in the Irish Sea in summer and winter. Laboratory experiments were combined with these field data to indicate that light is an important modulator of locomotor activity in this species.     

Growth rates of summer nanoplankton (<10 μm) populations in lower Narragansett Bay,Rhode Island,USA

Growth rates of summer (June–September) phytoplankton assemblages and constituent species were measured in 30 diffusion culture experiments. Size-fractionated (<10 m) phytoplankton assemblages were incubated in situ or under simulated in-situ conditions in outdoor tanks connected to a running seawater system. Doubling rates of important species and groups (such as microflagellates) were compared to community biomass doubling rates estimated from ¹⁴C uptake and changes in chlorophyll a concentrations. Division rates of dominant diatom species generally equalled or exceeded community biomass doubling rates, while those of flagellates and non-motile ultraplankters were slower. Maximum division rates of sixteen common diatom species exceeded 2.1 divisions d^-1, while nine had maximum division rates in excess of 3 d^-1. Mean division rates of 12 diatom species exceeded 1 d^-1. Maximum division rates of flagellated species, uncharacterized microflagellates and non-motile ultraplankton assemblages were 2.1, 1.5 and 1.4 d^-1, respectively. Microflagellate and non-motile ultraplankton assemblage doubling rates were less than 0.5 d^-1 in over half of all growth experiments.     

Selective particle ingestion by oyster larvae (Crassostrea virginica) feeding on natural seston and cultured algae

I investigated selective particle ingestion by oyster larvae (Crassostrea virginica) feeding on natural seston from Chesapeake Bay and laboratory-cultured algae of different sizes or chemical content. In 15 of 16 experiments with complex natural suspensions as food, small(<150 m) and large (>150 m) larvae selected most strongly for small (2 to 4 m) food particles, but in the presence of a large (>10 m)-cell dinoflagellate bloom, large larvae strongly selected much larger (22 to 30 m) food material (presumably dinoflagellates). When fed simplified mixtures of four cultured algal species (Synechococcus bacillaris, Isochrysis sp., Dunaliella tertiolecta, and Prorocentrum minimum) ranging in size from 1 to 11 m, small larvae preferred 1 m algae while large larvae preferred 11 m algae. In experiments with algal mixtures, and with suspensions of natural particles and added algae, large larvae preferred algal species harvested from exponential-phase cultures over other species from stationary-phase cultures. Larval ingestion rates of the cultured alga Thalassiosira pseudonana were about three times higher for cells with a low carbon:nitrogen ratio (7.2:1) than for high C:N ratio (16.2:1) cells when these cells were offered separately in suspensions of equal concentration. As a result, more algal cells, algal C, and algal N was ingested by larvae fed low C:N cells. However, larvae did not show a significant preference for either type of cell when they were offered in a 1:1 cell mixture. Feeding patterns of C. virginica larvae in natural food suspensions can vary with the composition of these complex suspensions, and ingestion seems dependent not only on the size, but on the growth rate and chemical quality of food particles.     

Some factors influencing selective release of soluble organic material by zooxanthellae from reef corals

Studies were carried out to determine optimum conditions for the investigation of symbiotic zooxanthellae in vitro and to gain insight into factors influencing release of photosynthate by the symbionts. Zooxanthellae isolated from the reef coral Agaricia agaricites and incubated with an homogenate of host tissue release twice as much photosynthate as controls in seawater. The animal homogenate retained its stimulatory activity for 3 h at room temperature (ca. 26°C). Release of photosynthate was markedly influenced by time after isolation of algae from the host, variation in homogenate concentration, and prolonged exposure to homogenate. Release was not influenced by cell concentration, light intensity, or glycerol in the incubation medium. If zooxanthellae are labelled in vitro with glucose ¹⁴C, the principle product released is alanine ¹⁴C. The mechanism of action of homogenate on zooxanthellae in vitro is discussed in terms of its effect on algal cell membrane permeability. A preliminary fractionation of host homogenate is described.     

Persistent blooms of surf diatoms along the Pacific coast,USA

Productivity was studied in two diatom species, Chaetoceros armatum T. West and Asterionella socialis Lewin and Norris, which form persistent dense blooms in the surf zone along the Pacific coast of Washington and Oregon, USA. Past observations have shown that surf-diatom standing stock usually declines in summer along with concentrations of nitrate and ammonium. Using the ¹⁴C method, photosynthetic rates in natural surf samples were measured monthly for one year (October 1981 through September 1982) at a study site on the Washington coast. Also measured were temperature, salinity, dissolved nutrients, particulate carbon and nitrogen (used as estimates of phytoplankton C and N), and chlorophyll a. Assimilation numbers (P _max) were higher in summer (5 to 8 g C g^-1 chl a h^-1) than in winter (3 to 4gC). Specific carbon incorporation rates (µ_max) showed no obvious seasonality, mostly falling within the range of 0.09 to 0.13 g C g^-1 C(POC) h^-1. The discrepancy between the seasonal trends for chlorophyll-specific and carbon-specific rates reflects a change in the carbon-to-chlorophyll ratio. Because of seasonal differences in daylength and light intensity, daily specific growth rates () are thought to be higher in summer than in winter. Neither ammonium enrichment assays nor particulate carbon-to-nitrogen ratios provided convincing evidence for nitrogen limitation during summer, and the observed changes in diatom abundance cannot be explained on this basis. Both the high diatom concentrations and their seasonal variations probably are due mainly to factors other than growth rates; two factors considered important are diatom flotation and seasonal changes in wind-driven water transport. C. armatum usually dominates the phytoplankton biomass in the surf zone, and evidence suggests that this species is strongly dominant in terms of primary production.Contribution No. 1391 of the School of Oceanography, University of Washington, Seattle, Washington, USA     

Dinoflagellate infections of Favella panamensis from two North American estuaries

Favella panamensis Kofoid and Campbell, 1929 is seasonally abundant in meso- to polyhaline waters of Chesapeake Bay and Indian River, Florida, USA, where it reaches densities of 10³ cells l^-1. During the summers of 1986–1992. F. panamensis populations of the two estuaries were commonly infected by the parasitic dinoflagellate Duboscquella aspida Cachon, 1964. The intracellular phase of the parasite reached maturity in 21 h (30 °C) and consumed 35% of the host's biomass. Infections were not typically lethal to F. panamensis, but sometimes forced the host from its lorica. Several D. aspida were found in the cytoplasm of many hosts, and the number of parasites infection^-1 was directly related to infection level. Parasite prevalence averaged 24.0 and 11.5% with mean number of parasites infection^-1 being 1.5 and 1.3 for Chesapeake Bay and Indian River samples, respectively. D. aspida was estimated to remove up to 68% of host standing stock d^-1 with a mean of 10% for all samples. The average impact of parasitism on F. panamensis populations was somewhat less than would be expected from copepod grazing.     

Nitrogen regeneration by two surf-zone mysids,Mesopodopsis slabberi andGastrosaccus psammodytes

Nitrogen regeneration by two surf zone mysids,Mesopodopsis slabberi andGastrosaccus psammodytes, was determined under laboratory conditions. The mysids were collected from the lower Sundays River estuary, South Africa, from early spring 1984 to late summer 1985. The forms of nitrogen excreted and the effects of mass, temperature and feeding on excretion rate were determined for each species at three experimental temperatures. Comparison of the forms of nitrogen excreted revealed only slight differences between species, with ammonia the major form and urea and amino acids the secondary excretory products in both cases. Mass significantly influenced the rate of ammonia excretion at all experimental temperatures, with no significant difference in slope (common b=0.602) detected between species. During the day sediment deprivation resulted in a 15% and 20% increase in mean ammonia excretion rates of juvenile and adultG. psammodytes respectively, whereas no significant differences were found at night. The mean ammonia excretion rates of fedM. slabberi andG. psammodytes were 2 and 2.5 times higher than starved excretion rates, respectively.G. psammodytes andM. slabberi recycle 139 to 150 g N per running meter of surf zone per year and 1 007 to 1 208 g N m^-1 yr^-1, respectively. Togehter this constitutes 10% of total phytoplankton nitrogen requirements in the surf zone.     

The “red tides” of Malta

A 5 year survey of Marsamxetto Harbour, Malta, was carried out to investigate some factors contributing to red tides and to identify the causative organisms. Red tides occurred usually in May but, less predictably, also during June – August. Causative organisms included the diatom Chaetoceros sp., and the dinoflagellate genera Prorocentrum, Peridinium, Ptychodiscus, Gonyaulax, Ceratium and Cochlodinium. Early summer red tides occurred at a time of increasing insolation, and water temperature, prevailing onshore winds and salinities in the range 34.4 to 36.6 A consistent feature was a quick rise in sea temperature of more than 2 C^o during the week preceding red water. Red tides later in the year coincided with higher temperatures and salinities and calm weather.     

Bathymetric distribution of chaetognaths in the South Eastern Pacific Ocean

The bathymetric distribution of chaetognath fauna observed at planktonic stations in the South Eastern Pacific Ocean during three different expeditions, is presented quantitatively. The material from the cruises IFOP-01 (October–December, 1964) and IFOP-04 (November–December, 1965) was collected by vertical closing net, at regular intervals, from 2000 and 1000 m depth, respectively; the R.V. A. Bruun Cruise 13 data include vertical samples at usual depth intervals from 3000 m (see Table 12), Isaac-Kidd Midwater Trawl (IKMT) and surface collections. They allowed us to identify, for the first time, the meso and bathypelagic species of this region and to extend the longitudinal distribution of the epipelagic species, which had been previously limited to the coastal areas. Among the epiplanktonic species, it was shown that two, Sagitta serratodentata and S. bipunctata, do not penetrate into the Peru Coastal Current region, where the endemic S. bierri is to be found extending westwards to the west boundary of the Peru Coastal Current, and that both mesopelagic species, previously reported for the epipelagic level of this area, S. decipiens and Eukrohnia hamata, inhabit the upper mesopelagic level in the oceanic region, but also rise to the epipelagic level near the coast, where upwellings do occur. The lower mesopelagic levels (500 to 1000 m) are occupied by E. fowleri and S. macrocephala, this latter species being reported for the first time in the South Eastern Pacific Ocean. The other mesopelagic species, S. zetesios and S. bathypelagica, also found for the first time in this region, were not found in large enough numbers to obtain a correct view of their stratification. Eukrohnia bathyantarctica, described for the Southern Ocean and previously reported only in the bathypelagic levels of the Gulf of Mexico and Caribbean Sea, was found at only bathypelagic levels. The faunistic data from the R.V. A. Bruun Cruise 13, were compared with the corresponding hydrographical profiles.     

Grazing and ingestion rates of nauplii,copepodids and adults of the marine planktonic copepod Calanus helgolandicus

The average grazing and ingestion rates of all stages of the marine planktonic copepod Calanus helgolandicus (Calanoida) from nauplius stage IV to adults were measured experimentally at 15°C in agitated cultures. The chain-forming diatom Lauderia borealis and the unarmoured dinoflagellate Gymnodinium splendens were offered as food. The food concentrations were close to natural conditions and ranged from 36 to 101 g of organic carbon per liter. The medium body weights expressed in g of organic carbon of almost all larval stages raised at 49 g C/1 were identical with the weight of the same stages caught in the Pacific Ocean off La Jolla, California, USA. In a log-log system, grazing and ingestion rates increased almost linearly with increasing body weight. Grazing rates ranged from 4 to 21 ml/day/nauplius stage IV to 286 ml to 773 ml/day/female. Ingestion rates increased from 0.2 g to 0.8 g C/day/nauplius stage IV to 18 g to 69 g C/day/female. Grazing and ingestion rates per unit body weight decreased gradually with increasing body weight. The daily ingested amount of food decreased from 292 to 481% of the body weight (g C) of nauplius stage V to 28–85% of the body weight of adult females. Grazing and ingestion performances of all stages increased with increasing particle size. Grazing rates decreased and ingestion rates increased with increasing food concentrations. The published data on food intake of the different age groups of C. helgolandicus show that the young stages of herbivorous planktonic copepods can play a major part in the consumption of phytoplankton in the sea due to their high grazing and ingestion rates.     

Role of bacteria in decomposition of faecal pellets egested by the epiphyte-grazing gastropod Gibbula umbilicaris

The significance of the microheterotrophic utilization of faecal pellets derived from Gibbula umbilicaris — one of the most important gastropod species in the Posidonia oceanica ecosystem around the Isle of Ischia (Italy) — was investigated by means of microcosm-experiments. Initial total organic carbon (TOC) content of faecal pellets was 32 gC (mg faeces dry wt)^-1 and declined continuously over a 2-month incubation period. The low values of TOC coincided with SEM observations of pellets which were found to consist mainly of diatom frustules and other slowly utilizable material. In a long-term experiment freshly egested faecal pellets were rapidly colonized by bacteria, which reached densities of up to 14x10⁵ cells (mg faeces dry wt)^-1 within 12 h. Thereafter bacterial numbers declined and fluctuated in a very narrow range between 2 and 3.5x10⁵ cells (mg faeces dry wt)^-1 during the two months of the investigation period. In short-term experiments (over 5 d) similar trends were observed. Peak densities of attached bacteria were followed by a decline of this population. Concurrently the number of free-living bacteria increased. This observation was confirmed by O₂ consumption measurements of freshly egested faecal pellets over 24 h, where the highest O₂ consumption rates were obtained after 12 h, followed by a rapid decline, thus supporting the view that detachment of bacteria may occur. Moreover, the respiration data indicate that about 4% of faecal TOC are remineralized within the first day.