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Soft waters are characterized by low Ca concentrations, and the distribution and relative success of Ca-demanding invertebrates could be limited by low Ca in extreme softwater localities. A further Ca depletion caused by reversed acidification could thus seriously affect freshwater crustaceans. Experimental studies on the calcification and Ca content of Daphnia magna clearly suggested the potential of a Ca limitation. Saturated calcification was reached at Ca concentrations [is greater than] 0.13 mM. Individuals reared in media with lower Ca concentrations were unable to compensate by, increasing the period of postmolt Ca uptake and thus had a lower specific Ca content. Specific Ca content decreased from 4.2% to 1% of dry weight over the range 0.25-0.013 mM Ca. Even at the low Ca concentrations, only 10% of total Ca was reclaimed upon molting, the rest was lost with the old exuviae (~40%) or to the ambient medium (~50%). This incomplete calcification under low ambient Ca concentrations could represent a competitive drawback in Ca-poor waters.

The impact of colony formation on cellular nutrient supply was calculated for Phaeocystis in a turbulent environment using a diffusion--reaction model. The model included diffusive boundary layer as predicted by Sherwood numbers in mass transfer to a sphere. Literature values for nutrient uptake ([V.sub.max], [K.sub.m]) of single cells and colonies and the size dependence of cell numbers in colonies were used in the model. Colony formation was shown to decrease nutrient uptake by Phaeocystis cells because of the presence of diffusive boundary layers with concentration gradients surrounding the colonies. At diffusion limitation, this concentration gradient was reflected by an apparently higher half-saturation constants for nutrient uptake, [K.sub.M], for colonial cells compared with that for single cells. The diffusion limited supply of inorganic nitrogen and orthophosphate from the bulk water phase with concentrations of 2 and 0.2 [micro]M, respectively, was sufficient to support nutrient demands for 1 cell doubling in colonies in 6-10 h, respectively, at a shear rate of 0.1 [s.sup.-1]. The same nutrient concentration levels could theoretically support nutrient demands of single cells for one cell doubling within 2-3 h. It was concluded that the lower grazing pressure in the size class of colonies relative to that of single free-living cells may be more important for colony formation than nutrient concentrations.

We have examined the role of microbial communities on the surface of submersed macrophytes and in the underlying sediment for nitrification and denitrification in light and dark in [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] microcosm systems using isotope pairing and dilution techniques. Potamogeton pectinatus L. and intact sediment cores were collected in a shallow reservoir receiving treated municipal wastewater and containing dense submersed vegetation. Chambers containing P. pectinatus shoots, sediment, or both P. pectinatus shoots and sediment were exposed to 6 h of darkness, 6 h of light, and 6 h of darkness. [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] were added at ambient concentrations of 15 and 5 mg N [liter.sup.-1], respectively. [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] was primarily nitrified in the epiphytic microbial communities, and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] was denitrified in the underlying sediment. In chambers containing macrophytes, there was a net production of [O.sub.2] and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] in light and a net consumption in dark, and nitrification was higher in light than in dark. In chambers with only sediment, there was always a net consumption of [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], and nitrification was similar in light and dark. The results show that submersed macrophytes can be important for the N metabolism in [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] freshwaters (e.g., wastewater treatment systems) by stimulating nitrification through providing surfaces for attached nitrifying bacteria and possibly also through diurnal changes in the water chemistry.

A new method is presented to determine the rates of oxygen consumption, net oxygen metabolism (defined as photosynthesis minus oxygen consumption), and gross photosynthesis at high vertical resolution in benthic phototrophic communities. The rates of oxygen consumption and of net oxygen metabolism as a function of depth and time are calculated from the dynamics in oxygen concentration, as measured with oxygen microsensors during light--dark cycles, by numerically solving the general non--steady state diffusion-reaction equation. The results, as obtained for a temperate intertidal microbial mat, strongly suggest that the vertical distribution and the dynamics in oxygen consumption are controlled by the supply of both oxygen and oxidizable substrates from different sources. The depth distribution of gross photosynthesis, as obtained by the cycling procedure, showed reasonable agreement with the photosynthesis profile, as measured with the conventional light--dark shift method prior to the light-dark cycling experiment, thus supporting the applicability of the method.

Concentrations and bacterioplankton uptake of dissolved free monosaccharides (DFCHO) in relation to bacterioplankton production and phytoplankton biomass were studied in mesotrophic Lake Constance, Germany, from August 1995 to December 1996. Concentrations of total DFCHO, measured by high-performance liquid chromatography (HPLC) and pulsed amperometric detection, ranged from [is less than] 20 to 440 [micro]M and exhibited pronounced spatiotemporal variations. Enhanced concentrations of DFCHO were often associated with the breakdown of phytoplankton blooms and periods of low phytoplankton growth. Bacterial uptake rates of DFCHO were also enhanced during such events, as well as at peaks of bacterioplankton production (BP). Ratios of uptake of DFCHO/BP, however, indicated that DFCHO concentrations were relatively more important as substrates during periods of low bacterial growth than during phases of intense bacterial growth. Ratios of bacterial uptake of DFCHO/BP from spring to fall ranged from 0.22 to 0.39 in the layer 0-10 m, from 0.17 to 0.56 at 20 m, and from 0.22 to 0.46 at 50 m, respectively. Glucose, galactose, and mannose dominated the DFCHO pool and constituted ~55 to ~70 mol%. The analysis of individual turnover times of five DFCHO concentrations from August to November 1995 at 3, 10, and 50 m revealed that the glucose pool turned over most rapidly, followed by galactose and mannose. Glucosamine and fructose always exhibited substantially longer turnover times. Comparisons to previous studies show that DFCHO concentrations are of similar significance for bacterioplankton growth as dissolved free amino acids (DFAA), even though temporal uptake patterns of both substrates are different.

Photoresponses involved in the descent phase of nocturnal diel vertical migration of brine shrimp (Artemia franciscana) naupliar larvae were measured in a laboratory system that mimicked the underwater angular light distribution. The test hypothesis was that kairomones from fish that activate photoresponses involved in DVM include degradation products of polysaccharides in their external mucus. Studies focused on the glycosaminoglycans heparin, chondroitin sulfate A, and hyaluronic acid and their repeating disaccharide units. Active molecules were identified by their activation of the descent photoresponse. Mucus from the mummichog (Fundulus heteroclitus) activated photoresponses at concentrations down to [10.sup.-5] g wet weight of mucus [L.sup.-1]. Water that had previously contained this species had (1) active molecules that were [is less than] 10 kDa in size, (2) polysaccharides in the [is greater than] 10-kDa, [is less than] 30-kDa fraction that could be acted upon by heparinase and chondroitinase to produce active molecules, and (3) enzymes in the [is greater than] 30-kDa, [is less than] 100-kDa fraction that acted on heparin and chondroitin sulfate polysaccharides to produce active molecules. The repeating disaccharide subunits of heparin, chondroitin sulfate A, and hyaluronic acid-induced photoresponses. The disaccharide subunit of hyaluronic acid was the most potent disaccharide, as it activated photoresponses at concentrations as low as [10.sup.-9] M. Tests with different subunits found that compounds with the most potent biological activity were disaccharides with either a sulfamino or acetylamino group on carbon 2 of the hexoseamine. Collectively, the results support the hypothesis and indicate that enzymatic degradation products of sulfated and acetylated fish mucus can serve as kairomones.

To trace the flow of nitrogen through the foraminifera-symbiont system, juvenile specimens of the symbiont-beating planktonic foraminifera, Orbulina universa were collected by SCUBA divers off the coast of Santa Catalina Island, California, and grown in filtered seawater solutions spiked with [sup.15]N-labeled nitrate. Our work isolated each pathway of this symbiotic system to determine the amount of nitrogen translocated to the foraminifera from its endosymbionts and its captured diet. Our model results show that when the nitrate uptake by the symbionts is at a maximum, between 50 and 57% of the foraminiferal nitrogen was translocated from the symbionts and the remainder was derived from the captured diet. In nitrate-deficient environments, when the symbiont nitrate uptake was at a minimum, ~90-100% of the nitrogen was transferred to the foraminifer by the symbionts from the recycled nitrogen ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) pool. In nitrate-deficient conditions, the primary role of the captured diet may be to provide the system with phosphorous. Highly efficient nutrient use is particularly important to the foraminifera-symbiont system, especially when nutrient concentrations are low. The results indicate a limited correlation between the isotopic composition of the [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] in the culture solutions and the [Delta][sup.15]N values of the foraminifera. However, the [Delta][sup.15]N values of the foraminifera much more strongly reflect the [Delta][sup.15]N values of the [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] recycled through the system. It appears that recycled nitrogen ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) is a more important source of nitrogen to the symbionts and the foraminifera than nitrate; therefore, the [Delta][sup.15]N values of the foraminifera may not reflect the isotopic composition of the surface-water nutrients. Understanding the nitrogen flow within modern foraminifera-symbiont associations is also important to ancient marine systems, because symbiont-bearing foraminifera are ubiquitous in the fossil record. This study shows that analysis of individual, symbiont-bearing foraminifera species is a necessary first step toward the development of more reliable use of nitrogen isotopes for paleoceanographic reconstructions.

To test the hypothesized inhibition of high-latitude marine bacteria living at lower temperatures when organic matter is scarce, the effects of temperature and organic substrate concentration on pelagic microbial heterotrophy were investigated in the perennially cold surface waters of a summertime arctic polynya. Utilization (incorporation plus respiration) of radiolabeled amino acids was measured as a function of increasing added substrate concentration at in situ (subzero) temperature and under short-term warming. Results analyzed using analysis of variance (ANOVA) showed that increased substrate concentration had a significant effect on utilization rates at all stations, suggesting that communities were always living well below saturating levels of substrate. About half of the communities sampled revealed a significant temperature response using ANOVA; interactions between temperature and substrate concentration were detected only rarely. Kinetic parameters, used to link microbial activity and substrate utilization with temperature sensitivity, exhibited mixed responses to short-term warming. Maximum specific utilization rates showed the greater temperature sensitivity, with [Q.sub.10] values ranging from 0.25 to 13. Specific affinities responded to temperature significantly at only about half of the stations in the polynya. Psychrophilic behaviors (e.g., highest specific affinities and oligotrophic capacities at lower incubation temperatures) were observed at stations most likely to be influenced by direct Arctic Ocean outflow. Complete agreement with the hypothesis of enhanced substrate requirement by bacteria living at subzero temperature was not found. An improved understanding of the diversity of cold-tolerant and cold-loving microorganisms is needed before generalizing or predicting the role of temperature in the cycling of organic matter at high latitudes.

There has been much discussion and some controversy regarding the role of nutrient enrichment versus other factors, such as altered rates of herbivory, in the degradation of coral reef ecosystems. The resolution of this controversy has been hampered by the lack of manipulative field studies testing the effects of ecologically relevant levels of nutrient enrichment on coral reef communities. We present a new method for adding ecologically relevant levels of nutrients to experimental substrates on coral reefs. The method elevates nutrients for sustained periods of time ([is greater than] 41 d without replenishment of nutrients) and allows for testing interactions of nutrients and altered levels of herbivory. Results from an offshore reef in Key Largo, Florida, show strong effects of excluding large herbivorous fishes, negligible effects of nutrient enrichment--or effects that are opposite of predictions, and no interaction between nutrient levels and herbivory in affecting algal abundance. Patterns observed for this reef did not confirm predictions of previously proposed models that frondose macroalgal or crustose algal abundance would be enhanced with nutrient enrichment or that dominance of filamentous turfs would be greater in unenriched conditions. In contrast to previous predictions, the abundance of larger macroalgae at this site was not increased by elevating nutrients above predicted threshold response levels of 1.0 [micro]M for total inorganic nitrogen or 0.10 [micro]M for soluble reactive phosphate. Also conflicting with some models, filamentous, nitrogen-fixing cyanobacteria were enhanced, rather than suppressed, by nutrient enrichment.

It is known that the zooplankter Daphnia induces colonies in the alga Scenedesmus. As Daphnia grazes on Scenedesmus, it has been postulated that colony formation represents an algal defense mechanism. This induction of Scenedesmus coenobia/colonies by Daphnia could be associated with a substance exuded by the animals that acts as a specific infochemical (kairomone) for Scenedesmus. However, the chemical nature of such a substance is still unknown. Because coenobia can be formed in the absence of Daphnia kairomone, as a result of different N concentrations in the algae and media, we checked different nitrogen excretory products of Daphnia as potential candidates. In this paper we test the hypothesis that ammonia and urea excreted by zooplankters (Daphnia) may induce coenobia formation in Scenedesmus. Using experiments with dialysis separation of Daphnia and algae we show that one of the excretory products of zooplankters, urea, can induce colony formation in Scenesdesmus, whereas ammonia has no effect. Although the effect of urea on coenobia formation may simply be a nutrient effect, this does not exclude the possibility that it results in grazing protection of the algae. Hence, urea produced by zooplankton may serve as a colony inducer to algae.

Estimates of the sources and wet deposition fluxes of inorganic nutrients ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) have been made using a long-term wet atmospheric deposition measurement at three sites along the Mediterranean coast of Israel. The nutrient composition in rainwater indicated a dominant anthropogenic source for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and a continental, natural, and anthropogenic, rock/soil source for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. The calculated long-term dissolved inorganic N (IN) and inorganic P (IP) fluxes were 0.28 and 0.009 g [m.sup.-2] [yr.sup.-1] to the coastal zone and estimated as 0.24 and 0.008 g [m.sup.-2] [yr.sup.-1] to the Southeast (SE) Mediterranean, with a possible increasing pattern of the annual dissolved IN fluxes. Concentration of total and seawater leachable IP (LIP) from dust was examined on 20 Whatman 41 filters collected during 1996. The mean total IP concentration in dust was 0.13 [+ or -] 0.11% (geomean = 0.09%), with a mean of 387 [+ or -] 205 [micro]g IP per g of dust leached by seawater. LIP from dust varies between 6 and 85% (mean of 38%) of the dry total IP. Dust of desert-type (Saharan) events exhibited lower LIP solubility in seawater (~25%, median) than air masses of European origin (~45%, median). The calculated ratio of wet deposition to total (wet and dry) deposition here of 0.2 showed the importance of dry deposition of P in the SE Mediterranean basin compared to atmospheric inputs into the northwestern basin. The total IP and seawater LIP fluxes from dry deposition were estimated as 0.04 and 0.01 g [m.sup.-2] [yr.sup.-1], respectively. Atmospheric inputs of bioavailable N and P represent an imbalanced contribution to the new production of 8-20 and 4-11%, respectively, and reinforce the unusual N: P ratios (~27) and possible P limitation in the SE Mediterranean.

Methods for quantifying total dissolved phosphorus (TDP) were reevaluated. High-temperature ashing/hydrolysis (Ash/Hydrol.) and Acid Persulfate methods were examined for their ability to quantitatively convert a range of organic-P compounds to orthophosphate. The Ash/Hydrol. method recovered on average 99% of organic-P compounds tested, including phosphonates (compounds with C-P bonds). Contrary to concerns voiced in prior studies, we found no P loss due to volatilization in seawater samples. Poor recovery by the Acid Persulfate method was observed for two compound classes: phosphonates and phospholipids. The Ash/Hydrol. method is recommended for routine TDP analyses. The hydrolysis of dissolved organic phosphorus (DOP) during the phosphomolybdate-blue reaction and the subsequent overestimation of dissolved inorganic phosphorus (DIP) have long been a concern. Extent of hydrolysis of standard DOP compounds was evaluated both during this reaction and over long-term acidified (pH 1.0)/refrigerated and unacidified/frozen storage. Eleven of 12 compounds tested hydrolyzed [is less than] 2% during the phosphomolybdate-blue reaction. Phospholipid, phosphosugar, and nucleotide mono- and diphosphate standards stored acidified/refrigerated over 2.5 months were [is less than] 5% hydrolyzed; compounds with higher energy phosphate bonds (e.g., phosphocreatine) hydrolyzed to a greater extent. A natural seawater sample showed no hydrolysis over 80 d, however, suggesting that refrigerated storage of acidified samples is a viable option. Seasonal DOP profiles from the Eel River Shelf quantified by the Ash/Hydrol. and Acid Persulfate methods yielded comparable results, indicating that the DOP pool at this site did not contain significant phospholipids or phosphonates, which are underrecovered by the Persulfate method. Recoveries using a third method, Nitrate Oxidation, were on average 7% lower. Surface-water DOP exceeded DIP in summer and was apparently related to biological productivity, underscoring the need to include organic species when evaluating nutrient limitation and creating nutrient budgets.

The phosphate sorption capacity of intertidal vegetated marsh sediments was measured along a salinity gradient in the Cooper River estuary, South Carolina. The phosphate sorption capacity of the surface sediments (0-10 cm) of a freshwater marsh was higher than the sorption capacity of sediments from brackish and saline marshes, and surface sediments had greater sorption capacity than subsurface (10-20 cm) sediments. These trends were opposite that of available phosphorus, which increased downstream and with depth. Freshwater marsh sediments trap phosphorus in a less-bioavailable form as evidenced by the low zero equilibrium phosphorus concentration (ZEPC) of the ambient sediment and low exchangeable phosphorus found there. Soil ZEPC values were similar to the in situ mean pore-water phosphate concentrations, which shows that sorption has a major effect on the spatial distribution of pore-water phosphorus along the estuarine salinity gradient. The magnitude of phosphorus sorption by the freshwater marsh sediments greatly reduced the pore-water phosphate concentration, while the phosphorus sorption properties of brackish and salt marsh sediments maintained in situ equilibrium pore-water phosphorus concentrations at surplus levels (with respect to its availability to plants). These differences in P sorption properties of the sediments can be explained on the basis of their physical and chemical characteristics. For instance, approaching the sea, the surface area of sediments declined, with freshwater marsh sediments (0-10 cm) supporting 8.5 x higher surface area than the salt marsh sediments. However, the sorption capacity of freshwater sediments was 33 x greater than that of salt marsh sediments, which indicates that other properties such as sediment mineral composition are important. The concentrations of important elements such as Al and Fe in sediments also declined downstream. The results suggest that the differences in phosphorus exchange properties among these marshes are a function of sediment type and sedimentary concentrations of Fe and Al. These in turn are related to the changes in ionic strength and associated parameters (e.g., pH) and physical sorting mechanisms.

The effect of ultraviolet radiation on the bioavailability of dissolved organic matter (DOM) to marine bacterioplankton was investigated in the Mediterranean Sea (Strait of Gibraltar, South and North Aegean Sea) and in the Caribbean Sea off Curacao. Surface-water samples (collected between 1 and 85 m in depth) exposed to solar radiation did not show a distinct pattern in subsequent bacterial growth. However, samples collected from a pronounced chlorophyll maximum (two stations in the Strait of Gibraltar and four stations in the Aegean Sea) displayed in a 50% lower bacterial activity in the radiation-exposed treatments compared with the dark controls. In contrast, mesopelagic water samples (200-350 m in depth) exposed to surface solar radiation exhibited a two- to fourfold increase in bacterial activity compared with the corresponding dark controls. Addition of the model protein bovine serum albumin (BSA) to mesopelagic-water samples and subsequent exposure to solar radiation resulted in a 50% lower rate of bacterial activity compared with the dark treatments, thus indicating the occurrence of photochemically induced changes to this labile compound. This decrease in bacterial activity in BSA-amended, irradiated water was also detectable in surface waters sampled off Curacao, whereas BSA amendment to surface water from the Mediterranean Sea did not result in a distinct pattern of bacterial activity. Our data indicate that exposure of DOM to solar radiation causes a reduced bioavailability of the exposed DOM to bacterioplankton, if the bacterial activity: dissolved organic carbon (DOC) concentration ratio is high (indicative of labile DOM). If the bacterial activity: DOC ratio is low (indicative of more refractory DOM), the bioavailability of the DOM is increased upon exposure to solar radiation.

Several aspects of bacterial glucose assimilation and bacterial production (BP) were investigated over 2 d in the upper 300 m of the Gulf of Mexico. Glucose concentrations ranged from 2 to 15 nM in surface seawater; glucose utilization rates were 1-3 nM [d.sup.-1] in the upper 150 m of the water column and 0.02-0.8 nM [d.sup.-1] in deeper water (150-300 m). Turnover of glucose and bacteria were similar and were in the range of 0.01-0.4 [d.sup.-1]. Measured glucose assimilation rates imply that glucose supports ~5-10% of the observed BP in surface waters. The limiting factors for bacterial glucose utilization varied with depth. Glucose assimilation seemed to be limited by availability of inorganic N in the chlorophyll maximum. Additions of nitrate or ammonium had similar effects on glucose assimilation. BP was limited by C below and above the chlorophyll maximum. Additions of high-molecular-weight (HMW) dissolved organic matter (DOM) decreased bacterial glucose uptake rates, indicating that substances competing with glucose assimilation were derived from HMW DOM extracellularly. Thus, the measurement of free glucose assimilation appears to integrate bacterial utilization of combined glucose and indicates that many of the free sugars in seawater may be derived from polymers. The higher glucose assimilation rates achieved with inorganic nutrient additions indicate that bacterial degradation of C-rich organic matter (OM) could vary between ocean regions with varying inorganic nutrient concentrations.

Using oligonucleotide probes for Eubacteria and four eubacterial subgroups, we monitored changes in bacterial community composition (BCC) with different degrees of grazing pressure, as follows: unfiltered water (UNF, all bacterivores present); [is less than] 20 [micro]m (bacteria, heterotrophic nanoflagellates [HNF], and small ciliates); [is less than] 5 [micro]m (bacteria and HNF only); and [is less than] 1 [micro]m or [is less than] 0.8 [micro]m (bacteria only), incubated in dialysis bags. Experiments were conducted in the Rimov Reservoir (South Bohemia) during the clearwater phase (experiment I), a period of low protistan grazing pressure on reservoir bacterioplankton, and during the late summer phytoplankton peak (experiment II), a period of high protistan grazing pressure. In both experiments, there was a significant shift in BCC in the [is less than] 5 [micro]m treatments, which came in the form of increased proportions of alpha subclass of the class Proteobacteria (ALF) and Cytophaga/Flavobacterium group (C/F), corresponding with increased bacterivory of the ungrazed HNF populations. Changes in BCC in other experimental treatments were related to preincubation protistan grazing pressure. In experiment I, bacterioplankton were subjected to negligible protistan bacterivory in the reservoir and did not show a change in BCC in the predator-free treatment ([is less than] 1 [micro]m), while BCC changed in treatments that yielded increases in protistan bacterivory compared with that in the ambient reservoir water. In experiment II, a significant shift in BCC was induced when bacterioplankton that were subjected to heavy predation pressure in the reservoir were transferred into the predator-flee treatment. Treatments that induced small changes in protistan grazing pressure ([is less than] 20 [micro]m and UNF in experiment II) did not show significant BCC shifts. Proportions of filamentous bacteria ([is greater than] 4 [micro]m) increased in treatments that yielded large increases in bacterivory. Filament formation also showed season-specific features; in experiment I, all filaments belonged into ALE whereas in experiment II, most of them hybridized with the C/F probe. We conclude that the sudden shifts that violate the established balance between bacterial production and the protist-induced bacterial mortality led to the significant shifts in cell morphology and BCC.

Colonies of Stylophora pistillata maintained for four years in indoor aquaria in the near absence of ultraviolet radiation (UVR) contained only small amounts ([is less than] 5 nmol [mg.sup.-1] protein) of 10 identified mycosporine-like amino acids (MAAs, which act as UV sunscreens), the largest number reported in any organism. The concentrations of most MAAs increased linearly or exponentially when colonies were exposed to ultraviolet-A (UVA) and ultraviolet-B (UVB) for 8 h [d.sup.-1] in the presence of photosynthetically active radiation (PAR). Total MAA concentration reached 174 nmol [mg.sup.-1] protein after 30 d, with palythine and mycosporine-2 glycine constituting more than half of the final total. UVB specifically stimulated MAA accumulation: after 15 d, MAA levels in colonies exposed to PAR alone and to PAR and UVA did not differ (7 and 5 nmol MAA [mg.sup.-1] protein, respectively), while those in colonies exposed to PAR and UVA + UVB were significantly higher (28 nmol [mg.sup.-1] protein). Glyphosate, an inhibitor of the shikimate pathway, eliminated or reduced the UV-induced accumulation of most MAAs during 7 d of exposure, providing the first experimental evidence of their synthesis via this pathway in a coral symbiosis. Densities of zooxanthellae in colonies of S. pistillata, Acropora sp., and Seriatopora hystrix exposed to UVR for 15 d were only one-third of those in control colonies unexposed to UVR. This net decrease in the number of zooxanthellae in the corals (bleaching) occurred despite UV-stimulated increases in algal cytokinesis and in the host cell-specific density of zooxanthellae in hospite, increases that apparently destabilized the symbiosis and caused expulsion of the zooxanthellae.

During the cruise ECOANTAR 94 photosynthesis versus irradiance relationships, phytoplankton spectral absorption, quantum yield of carbon fixation, and water column light regime were determined in the eastern Bransfield Strait and surrounding areas of the Weddell Sea and Weddell-Scotia Confluence, to determine if photosynthesis is light limited in these areas. There were no significant differences in the light-saturated chlorophyll-specific rate of photosynthesis [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], light-limited slope ([[Alpha].sup.B]), light saturation parameter ([E.sub.kPAR]), and the maximum quantum yield ([[Theta].sub.m]) between surface and subsurface water for several water masses in the area, which indicates that the photosynthetic response in the upper mixed layer was uniform. There were also no significant differences between the spectral light saturation parameter ([E.sub.kPUR) and the mean absorbed irradiance by phytoplankton in the upper mixed layer ([E.sub.umlPUR])). These similarities suggest that phytoplankton photosynthesis was not light limited in this Antarctic region during the cruise period. This was also affirmed by the fact that the average operational quantum yield of the water column (0.03 mol C [[mol photons].sup.-1]) was half of the mean maximum quantum yield (0.06 mol C [[mol photons].sup.-1]). Primary production is underestimated by 24% when broadband models are compared with spectral ones. These results have important implications for the modeling of carbon flows in the Southern Ocean.

Substitution of the noniron protein flavodoxin for the iron-sulfur protein ferredoxin is an iron-stress response employed by a variety of unicellular organisms, including many phytoplankton. The relative abundance of these two proteins has been shown to vary with the severity of growth limitation by iron in marine diatoms. During the IronEx II mesoscale iron-enrichment experiment, large volume (100-600 liters) phytoplankton samples were collected for analysis of community ferredoxin and flavodoxin abundance using a high-pressure liquid chromatography (HPLC) technique. In addition, three pennate diatom species isolated from the fertilization-induced phytoplankton bloom were used for follow-up laboratory experiments, which examined their iron physiology. Prior to iron enrichment, biomass levels were insufficient to obtain any ferredoxin or flavodoxin signals. Measurements were successful after iron enrichment, with unexpected results. The strength of the HPLC signal tracked the biomass levels of the IronEx II phytoplankton bloom. Chromatographic peaks were evident on the fifth day following enrichment and persisted throughout the experiment before they declined and eventually disappeared following the last iron infusion. The main chromatographic peak was identified as flavodoxin; there was no evidence of ferredoxin in any of the samples. Pennate diatom clones isolated from the fertilization-induced bloom and grown in the laboratory retain the ability to make ferredoxin when iron-replete and induce flavodoxin when iron-stressed. When iron-limited, they are able to completely repress flavodoxin expression in about 1 d in response to iron resupply. Thus, the unexpected absence of ferredoxin and the persistence of flavodoxin during IronEx II, despite the observed increases in biomass and photosynthetic efficiency, suggest that the iron additions were insufficient to completely relieve physiological iron limitation.

The effects of inorganic nutrients (P and N), organic C, and metazoan zooplankton on bacterioplankton production and abundance and on phytoplankton biomass were studied in five experiments (from May to September) in Lake Erken. In addition, the seasonal dynamics of bacterioplankton and phytoplankton were followed in the lake from April to November. Bacterioplankton production was P limited from May to August. N alone never stimulated bacterioplankton production, but bacterioplankton growth was close to colimited by P and N in July and August. Organic C stimulated bacterial production in June and September. Zooplankton enhanced bacterioplankton production in June, when bacterioplankton production was limited by P and C and the phytoplankton biomass in the lake was low. N alone stimulated phytoplankton growth in all experiments. In addition, P alone stimulated phytoplankton growth in May and July, and the combination of P and N stimulated phytoplankton growth in July and August. Zooplankton additions resulted in a decrease in phytoplankton biomass in May and September, mainly owing to grazing on Cryptophyceae. The experimental results indicate that bacterioplankton and phytoplankton growth were uncoupled during most of the open-water period because P primarily limited bacterioplankton growth and N limited phytoplankton growth. The response of the bacterioplankton community was most likely a direct effect of nutrient additions. Primary production and bacterioplankton production were correlated during the season, but partial correlations analysis indicates that this relationship can be attributed to the fact that both primary production and bacterioplankton production showed strong positive correlations with temperature. We suggest that uncoupling of bacterioplankton production and phytoplankton production may be a common phenomenon in lakes.

Rather than seeing the oceans as an expansive void, researchers using acoustic technologies can detect the heterogeneity of biological resources and view the marine environment as a three-dimensional landscape. Underwater remote sensing, using acoustics, provides high resolution maps of the spatial distribution of organisms in aquatic ecosystems. Analyzing the spatial pattern of species distribution within the water column and the impact of that organization on ecological processes bridges the fields of fisheries and spatial analysis. Tools and concepts familiar to geographers, such as remote sensing, GIS, and landscape ecology, contribute to the investigation of large lake and marine ecosystems. Key Words: spatial analysis, remote sensing, aquatic ecology, fisheries acoustics, oceans.

A uniform national policy has to be put into action to save the topography of the seafloor harmed due to pollution. The approaches United States should adopt for managing its oceans with the help of geochemists are discussed.

Research is presented concerning the tectonic process which resulted in the exhumation of the rocks of a basement beneath the southern Iberia Abyssal Plain. Ocean Drilling Program results from this area are discussed.

An assembly of 3000 untethered floats will be released globally 2 kilometers underwater by 2004. The value of the information obtained by the floats for weather forecasting, study of climate and ocean behavior is discussed.

A study was conducted to analyze the biomass, species, and chemical composition of the mesozooplankton and their impact on lower food levels along a transect across the Arctic Ocean. Results indicated that mesozooplankton accounted for about 40% of the total particulate organic carbon in the upper 100 m of the water column. Findings also showed that the species composition was homogeneous along the transect.

A study was conducted to analyze the depth distribution, diversity and abundance of pelagic nemerteans from the Pacific Ocean west of Pt. Conception, CA, and west of Hawaii. Results indicated that the number of nemertean individuals and species were greater between 625 and 1750 m off California, and 1300 to 2500 m off Hawaii. Moreover, the abundance of nemerteans off California was about 10 times that off Hawaii.

A study was conducted to examine the nitrogen isotope biogeochemistry of sinking particles from the margin of the Eastern North Pacific that includes the waters of Monterey Bay, San Pedro Basin and the Gulf of California. Results indicate that the region's nitrogen isotopic ratio is quite different from previous open-sea observations. It was observed that the eastern North Pacific margin's nitrogen isotopic ratio is loosely linked to the transient indicators of the surface ocean.

The effects of seasonally changing sedimentation rates of organic matters to the benthic community were assessed in the north-east Atlantic. The study was done from March to August 1992 by the METEOR expedition 21. Benthic biomass, phytodetritus deposition, accumulated adenylates and phospholipids and vertical flux at 3599 m depth were measured while hydrolytic enzyme activities and changes in chloroplastic concentration were observed. Results indicate that even small sedimentation changes cause metabolic activity elevations and small biomass generation of benthic community.

Thermodynamic and kinematic computations of water mass transformation rates derived from the Atlantic Ocean's air-sea fluxes have been reconciled. Results indicate that the vertical diffusive fluxes at the base of the winter mixed layer and in the seasonal thermocline substantially alters transformation because of the mixing action on the body of fluid between the sea surface and the control surface.

A study was conducted to analyze the distribution of dimethylsulfide in surface seawater and vertical profiles at 19 stations in the Nansha Islands sea area of the South China Sea. Results indicated that the phytoplankton species influence higher concentrations of dimethylsulfide. Findings also showed a clear diel variation in dimethylsulfide concentration in late afternoons. In addition, the sea-to-air flux of dimethylsulfide was pegged at 7.5 micron-mol m(super -2)d(super -1).

A study was conducted to analyze seasonal and interannual variations in mixed-layer carbon dioxide in the Southern Ocean. The temperature, salinity and chlorophyll time series were utilized as constraints on a box framework to extrapolate total dissolved inorganic carbon, oceanic carbon dioxide fugacity and total alkalinity. Results indicated that the rate of increase in the impact of the anthropogenic atmospheric carbon dioxide correlated with half that of the oceanic CO2 fugacity.

A study was conducted to analyze mesoscale eddy fluxes and their association with the gradients of the mean flow. A numerical framework of a baroclinically unstable jet in a zonally periodic channel was utilized. Results indicated that the mixing coefficient for potential vorticity was similar to the mixing coefficient of tracer anomalies on isopycnals. Findings also encouraged future studies on determining a parameterization based on true mixing of potential vorticity.

Several research groups have found that iron is necessary for phytoplankton growth in the world's oceans. Phytoplankton plants consume carbon dioxide but they cannot do this in ocean areas with low levels of iron. Three areas have been identified - the sub-arctic Pacific, the equatorial Pacific and the Southern Ocean of Antarctica. The effect on phytoplankton has a ripple effect on the whole of the sea-life food chain. The Big Sur, on the Californian coast, has an abundance of nutrients but there is not enough iron to allow them to be used by phytoplankton.

The Axial Volcano hot spot and the ridge crest segments of the Juan de Fuca Ridge are under study as part of the National Oceanic and Atmospheric Administration's VENTS program. Observing and analyzing underwater earthquakes, venting, and megaplumes, scientists are hoping to discover the causes of hydrothermal venting and its impact on the ocean environment. Expeditions to the site are being conducted using the most sophisticated oceanographic research ship called Ronald H. Brown.

Scientific researchers led by Falkowski have discovered that nitrogen is the ultimate controlling nutrient that limits carbon fixation in oceanic plants. To arrive at this conclusion, Falkowski examined the origin of enzyme systems involved in the fixation and denitrification of nitrogen. The low solubility of iron limited the fixation of nitrogen in oceanic waters during a certain period in the Earth's history.

It is possible to prove that large-scale bischofite formation took place during the Messinian salinity crisis by analyzing brines taken from the Discovery Basin in the eastern Mediterranean. It was discovered that the brine is basically a concentrated solution of MgCl2, and it was established that the brine is homogeneous throughout the basin. The chemistry of the brine indicates that there were extreme evaporite conditions in the eastern Mediterranean during the late Messinian.

Data from the Hawaiian Ocean Time Series (HOT) station ALOHA was used to indicate that the structure and productivity of the subtropical North Pacific's pelagic ecosystem had significantly changed. The validity of this assumption is questioned because the ALOHA station may not represent the anticyclonic central gyre. However, the ALOHA station was established as an oligotrophic ocean benchmark by the US Joint Global Ocean Flux Study and no equivalent, synoptic oceanographic data set has been proposed to replace ALOHA's data.

Three separate oceanic studies have established that the operations of the Atlantic Ocean's conveyor belt underwent rapid and recurring changes during the last glaciation. Results also suggest a correlation between changes in the operations of the Atlantic conveyor and climatic changes. The instability and erratic behavior of the Atlantic's conveyor as suggested by the results is consistent with the results achieved by simulations. Possible causes for the discrepancies in the results of the three studies are discussed.