The number of prokaryotes and the total amount of their cellular carbon on earth are estimated to be 4-6 ؋ 10 30 cells and 350-550 Pg of C (1 Pg ‫؍‬ 10 15 g), respectively. Thus, the total amount of prokaryotic carbon is 60-100% of the estimated total carbon in plants, and inclusion of prokaryotic carbon in global models will almost double estimates of the amount of carbon stored in living organisms.

Active heterotrophic bacterial communities exist in all marine environments, and although their growth rates or respiratory rates may be limited by the interaction of low substrate concentrations with temperatures near their lower limit for growth, temperature and substrate concentrations are rarely considered together as limiting factors. Moreover, attempts to evaluate metabolic limits by both temperature and substrate concentration have sometimes led to confusing conclusions, because, while we can measure dissolved organic carbon (DOC) concentrations in natural waters, much of it is not readily available to heterotrophic bacteria. In spite of this procedural limitation, it can be helpful to regard temperature and substrate concentration as potential limiting factors that interact. In temperate ocean surface waters and estuarine waters, where bacterial growth is often reduced in winter, growth and respiration may be increased experimentally either by raising the temperature or by increasing organic substrate concentrations, providing indirect evidence that the limitation is an effect of temperature on substrate uptake or assimilation. Experimental work with bacterial isolates also has shown a temperature-substrate interaction. In permanently cold polar waters, most heterotrophic bacteria appear to be living at temperatures well below their optima for growth. Nevertheless, bacteria in permanently cold surface waters can achieve activity rates in summer that are as high as those in temperate waters. In sea ice, rates of bacterial production are most often low, even though concentrations of substrates, including free amino acids, are sometimes much higher than they are in seawater. This suggests that at sea ice temperatures heterotrophic bacteria have lowered ability to take up or utilize organic substrates. KEY WORDS: Temperature · Substrates · Heterotrophic bacteria · Limiting factorsResale or republication not permitted without written consent of the publisher

The energetic demand of microorganisms in natural waters and the flux of energy between microorganisms and metazoans has been evaluated by empirical measurements in nature, in microcosms and mesocosms, and by simulation models. Microorganisms in temperate and tropical waters often use half or more of the energy fixed by photosynthesis. Most simulations and some experimental results suggest significant energy transfer to metazoans, but empirical evidence is mixed. Considerations of the range of growth yields of microorganisms and the number of trophic transfers among them indicate major energy losses within microbial food webs. Our ability to verify and quantify these processes is limited by the variability of assimilation efficiency and uncertainty about the structure of microbial food webs. However, even a two-step microbial chain is a major energy sink.As an energetic link to metazoans, the detritus food web is inefficient, and its significance may have been overstated. There is not enough bacterial biomass associated with detritus to support metazoan detritivores. Much detritus is digestible by metazoans directly. Thus, metazoans and bacteria may to a considerable degree compete for a common resource. Microorganisms, together with metazoans, are important to the stability of planktonic communities through their roles as rapid mineralizers of organic matter, releasing inorganic nutrients. The competition for organic matter and the resultant rapid mineralization help maintain stable populations of phytoplankton in the absence of advective nutrient supply.At temperatures near 0 °C, bacterial metabolism is suppressed more than is the rate of photosynthesis. As a result, the products of the spring phytoplankton bloom in high-temperate latitudes are not utilized rapidly by bacteria. At temperatures below 0 C microbial food webs are neither energy sinks or links: they are suppressed. Because the underlying mechanism of low-temperature inhibition is not known, we cannot yet generalize about this as a control of food web processes.Microorganisms may operate on several trophic levels simultaneously. Therefore, the realism of the trophic level concept and the reality of the use of ecological efficiency calculations in ecosystem models is questionable.

A Water Quality Index (WQI) is a numeric expression used to evaluate the quality of a given water body and to be easily understood by managers. In this study, a modified nine-parameter Scottish WQI was used to assess the monthly water quality of the Douro River during a 10-year period (1992-2001), scaled from zero (lowest) to 100% (highest). The 98,000 km(2) of the Douro River international watershed is the largest in the Iberian Peninsula, split between upstream Spain (80%) and downstream Portugal (20%). Three locations were surveyed: at the Portuguese-Spanish border, 350 km from the river mouth; 180 km from the mouth, where the river becomes exclusively Portuguese; and 21 km from the mouth. The water received by Portugal from Spain showed the poorest quality (WQI 47.3 +/- 0.7%); quality increased steadily downstream, up to 61.7 +/- 0.7%. In general, the water quality at all three sites was medium to poor. Seasonally, water quality decreased from winter to summer, but no statistical relationship between quality and discharge rate could be established. Depending on the location, different parameters were responsible for the episodic decline of quality: high conductivity and low oxygen content in the uppermost reservoir, and fecal coliform contamination downstream. This study shows the need to enforce the existing international bilateral agreements and to implement the European Water Quality Directive in order to improve the water quantity and quality received by the downstream country of a shared watershed, especially because two million inhabitants use the water from the last river location as their only source of drinking water.

Fine jets of water can be used to remove coral tissue quantitatively from skeleton in a form suitable for a variety of chemical analyses, including that of total organic carbon.

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Two herbivorous fishes of the genus Kyphosus (family Kyphosidae) possess unique digestive tracts among fishes, with well-developed caecal pouches and a complex gut-resident microflora. The presence of high concentrations of volatile fatty acids in the gut confirms fermentative digestion in fishes for the first time.

AbstructA formal approach is presented of ordering the time scales of the dominant fluxes of material in an estuary and then accordingly choosing the spatial and temporal resolution of the sampling program. In this way bounds can be derived for the internal turnover times, boundary exchange rates, and import or export fluxes of a particular substance purely from measurements of the standing stock values in the estuary water. Application of this methodology to an experiment in the Duplin River, Georgia, showed that if the effects of the water motion and mixing are extracted from the variation of a biological component, then the variability of the residual can be successfully interpreted. For a typical summer condition it was shown that ammonium was cycled rapidly within the marsh water, its distribution was very patchy, and only its decomposition products left the marsh; that the refractory dissolved organic carbon (DOC) component was steadily exported by longitudinal mixing while labile DOC was rapidly recycled in the water; that silicate was produced in large amounts in the marsh and exported by longitudinal mixing; that particulate organic carbon (POC) concentrations were almost completely determined by the turbulence intensity in the water; and that compared to this internal cycling, export was of minor significance.bution 398 of the University of Georgia Marine Institute.