International Work
AUSTRALIA
Utilization of Nitrogen and Carbon by Phytoplankton in Moreton Bay, Australia.
O'Donohue, M.J., P.M. Glibert, and W.C. Dennison. 2000. Mar. Freshwat. Res. 51(7): 703-712.
ABSTRACT: Increasing nutrient inputs to waters of coastal embayments and river systems are changing aquatic diversity and nutrient cycling processes of near-coastal systems worldwide. Nitrogen may be a major element controlling plant productivity in coastal ecosystems and anthropogenic inputs can lead to eutrophication. In this study, the seasonal and spatial changes in inorganic carbon and nitrogen transformation were determined within Moreton Bay, a shallow subtropical embayment in southeastern Queensland (Australia). Water samples were collected within river mouths, at river plume sites and at well flushed ocean-influenced sites. Rates of inorganic nitrogen and carbon uptake were determined across temporal and spatial scales. Strong gradients in carbon and nitrogen dynamics from oligotrophic to river-influenced waters with seasonal flows is likely to exist in many tropical and subtropical coastal waters in Australia.
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Tracing the Fate of 15N-enriched Feed in an Intensive Shrimp System.
Burford, M.A., N.P. Preston, P.M. Glibert, and W.C. Dennison. 2002. Aquaculture 206(3-4): 199-216. PDF by request
ABSTRACT: The fate of 15N-nitrogen-enriched formulated feed fed to shrimp was traced through the food web in shallow, outdoor tank systems (1000 l) stocked with shrimp. Triplicate tanks containing shrimp water with and without sediment were used to identify the role of the natural biota in the water column and sediment in processing dietary nitrogen (N). A preliminary experiment demonstrated that 15N-nitrogen-enriched feed products could be detected in the food web. Based on this, a 15-day experiment was conducted. The ammonium (NH4+) pool in the water column became rapidly enriched (within one day) with 15N-nitrogen after shrimp were fed 15N-enriched feed. By day 15, 6% of the added 15N-nitrogen was in this fraction in the 'sediment' tanks compared with 0.4% in the 'no sediment' tanks. The particulate fraction in the water column, principally autotrophic nanoflagellates, accounted for 4-5% of the 15N-nitrogen fed to shrimp after one day. This increased to 16% in the 'no sediment' treatment, and decreased to 2% in the 'sediment' treatment by day 15. It appears that dietary N was more accessible to the phytoplankton community in the absence of sediment. The difference is possibly because a proportion of the dietary N was buried in the sediment in the 'sediment' treatment, making it unavailable to the phytoplankton. Alternatively, the dietary N was retained in the NH4+ pool in the water column since phytoplankton growth, and hence, N utilization was lower in the 'sediment' treatment. The lower growth of phytoplankton in the 'sediment' treatment appeared to be related to higher turbidity, and hence, lower light availability for growth. The percentage 15N-nitrogen detected in the sediment was only 6% despite the high capacity for sedimentation of the large biomass of plankton detritus and shrimp waste. |
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BALTIC SEA
Variability in Inorganic and Organic Nitrogen Uptake Associated with Riverine Nutrient Input in the Gulf of Riga, Baltic Sea.
Berg, G.M., P.M. Glibert, N.O.G. Jørgensen, M. Balode, and I. Purina. 2001. Estuaries 24(2): 204-214. PDF by request
ABSTRACT: Concentrations and rates of uptake of dissolved organic nitrogen (DON, free amino acids, and urea) and inorganic nitrogen (DIN, nitrate, and ammonium) were measured along two transects in the Gulf of Riga, a sub-basin of the Baltic Sea, during May and July 1996. Concentrations of total dissolved nitrogen (TDN) were 23 plus or minus 3 µg-at N l-1 in the northern region (mouth) and 41 plus or minus 5 µg-at N l-1 in the southern region (head) of the Gulf. Rates of nitrogen uptake, determined with 15N-labeled substrates, reflected differences in TDN concentration between the regions. In May, uptake of DIN+DON measured 0.17 and 0.43 µg-at N l-1 h-1 in the northern and southern parts of the Gulf, respectively. In July, DIN+DON uptake measured 0.38 and 0.68 µg-at N l-1 h-1 in the north and south, respectively. Most of the variability in total nitrogen flux between the northern and southern regions was due to heterogeneity of DON utilization. Uptake of urea and dissolved free amino acid were up to 6 and 3 times greater in the south compared to the north. As evidenced by size-fractionation, plankton size structure appeared to play a role in the uptake of DON. The community in the southern part was largely composed of cells < 5 µm, while up to 67% of the community in the northern part was composed of cells > 5 µm. Our results indicate that DON was a major source of nitrogen to phytoplankton, particularly in the southern part of the Gulf. |
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BRAZIL
New and Regenerated Production in the South Atlantic off Brazil.
Metzler, P.M., P. M. Glibert, S.A. Gaeta, and J.M. Ludlam. 1997. Deep-Sea Res. I 44(3): 363-384. PDF by request
ABSTRACT: Rates of assimilation of NH4+,NO3- and urea were determined at eight oceanic stations in March 1994 and one inshore station in December 1994 in the South Atlantic off Brazil by performing 15N tracer experiments on microbial populations from two depths (50% and 1% of surface light penetration). Carbon uptake rates were determined by 14C tracer experiments at the same depths. At each sampling site temperature and salinity profiles were obtained and ambient nutrient and phytoplankton biomass were measured. Concentrations of chlorophyll a were <0.3 µg l-1 in the oceanic region and varied from 0.12 to 1.41 µg l-1 in the inshore region. On average NO3- was the main form of nitrogen available for phytoplankton (64-86% of total nitrogen) in oceanic waters, while at the inshore station, NO3- represented less than 32% of total nitrogen supply. Nonetheless, primary production was dominated by regenerated production. Uptake of reduced forms of nitrogen represented on average 74% of total nitrogen utilized by phytoplankton in the oceanic region and 96% at the inshore station. In oceanic waters, the mean f-ratio (contribution of new to total production) was 0.16 and 0.30 at subsurface (50% Io) and bottom (1% Io) of the euphotic zone, respectively. At the inshore station the mean f-ratio was 0.05 at the subsurface and 0.10 at the bottom of the euphotic zone. Temperature and salinity measurements showed occasional injections of NO3- into the euphotic zone, resulting from the intrusion of the South Atlantic Central Water on the continental shelf. Episodic enrichment of the base of the euphotic zone with NO3- enhanced the contribution of new to total production and led to a maximum f-ratio of 0.86 in oceanic waters and 0.26 in coastal waters.
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Contrasting Effects of Substrate and Grazer Manipulations on Picoplankton in Oceanic and Coastal Waters off Brazil.
Metzler, P.M., P. M. Glibert, S.A. Gaeta, and J.M. Ludlam. 2000. J. Plankton Res. 22(1): 77-90. PDF by request
ABSTRACT: In two contrasting regions off the coast of Brazil, picoplankton (<1 µm) responses to removal of larger grazers and to the additions of glucose and amino acids were determined. Effects of glucose and amino acid additions (1 µM) on particulate nitrogen and chlorophyll a concentrations, and on rates of NH4+ uptake and regeneration, were observed after 5 h pre-incubation. In the oceanic waters, removal of the >1 µm fraction had no significant effect on the chlorophyll a of the picoplankton after 5 h. However, the addition of glucose stimulated both uptake and regeneration by a mean of 27%, and the addition of arginine led to significant decreases in the rates of NH4+ uptake and regeneration. In contrast, in the coastal waters, significant increases in chlorophyll and particulate nitrogen concentrations were found after 5 h incubation in both the amended samples and in the controls, and mean rates of NH4+ uptake and regeneration were affected to a lesser degree by the additions of either glucose or amino acids than in the oceanic waters. The oceanic responses were suggestive of carbon limitation of heterotrophic bacteria. In the coastal region, on the other hand, the supply of organic carbon and nitrogen was likely to have been sufficient to meet the nutritional requirements of the heterotrophic bacteria and cyanobacteria. Grazing by larger organisms on the picoplankton appeared to play a more significant role in the nitrogen cycle in the coastal waters than in the oceanic waters.
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CHINA
Nitrogen Uptake Rates During a Dinoflagellate Bloom in the East China Sea, 2005: Variation with N:P ratio.
Li, J., P.M. Glibert, S. Lu, D. Lu, X. Shi, and C. Zhang. Proceedings of the 2006 XII International HAB Conference. In press.
ABSTRACT: During late spring and early summer of 2005, large scale (>15,000 km2) mixed dinoflagellate blooms developed in the coastal East China Sea. Karenia mikimotoi was the dominant HAB species in the first stage of the bloom and was succeeded by Prorocentrum donghaiense. Samples were collected from different stations along both north-south and west-east transects during 3 cruises of the Chinese Ecology and Oceanography of Harmful Algal Blooms (CEOHAB) Program, before and during the bloom progression. Nitrogen isotope methods were used to measure rates of NO3-, NH4+, urea, and glycine uptake during the blooms. The progression of the blooms was related to a change in available nitrogen (N) and phosphorus (P) composition. As the ambient N:P decreased from > 50 to ~16, bloom strength increased. Reduced nitrogen, especially NH4+ and urea were preferentially taken up during the blooms, and supplemental phosphorus enrichment increased the rates of nitrogen uptake, suggesting phosphorus limitation in the bloom area.
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KUWAIT
First Record of a Fish-killing Gymnodinium sp. Bloom in Kuwait Bay, Arabian Sea: Chronology and Potential Causes.
Heil, C.A., P.M. Glibert, M.A. Al-Sarawi, M. Faraj, M. Behbehani, and M. Husain. 2001. Mar. Ecol. Prog. Ser. 214: 15-23. PDF by request
ABSTRACT: Significant natural and aquaculture fish deaths in Kuwait Bay occurred from September to October of 1999 and were attributed to a bloom of the dinoflagellate Gymnodinium. A chronology of the bloom event suggests that a period of low winds and stable water-column structure preceded the bloom. Maximum cell concentrations of Gymnodinium (>6 x 106 cells l-1) were also immediately preceded by a more than 20-fold increase in mean inorganic nitrogen concentrations (up to 60 µM) and elevated inorganic phosphate concentrations. This, combined with elevated inorganic and organic nutrient concentrations within the bloom, suggests that coastal nutrient eutrophication was likely to have contributed significantly to bloom development and support. Termination of the Gymnodinium bloom coincided with a bloom of the non-toxic ciliate Mesodinium rubrum, which appeared as large red patches in Kuwait Bay. While no adverse human health effects were associated with the bloom, closure of shellfish and selected finfish (largely mullet Liza macrolepis) markets resulted in significant economic losses to the region. The occurrence of this toxic algal bloom event, the first within the Arabian Sea, highlights the need for monitoring and research programs in the Arabian Sea and Kuwait Bay that focus on nutrients and eutrophication, in addition to oil related pollution issues.
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A Fish Kill of Massive Proportion in Kuwait Bay, Arabian Gulf, 2001: The Roles of Bacterial Disease, Harmful Algae, and Eutrophication.
Glibert, P.M., J.H. Landsberg, J.J. Evans, M.A. Al-Sarawi, M. Faraj, M.A. Al-Jarallah, A. Haywood, S. Ibrahem, P. Klesius, C. Powell, and C. Shoemaker. 2002. Harmful Algae 1: 215-231. PDF by request
ABSTRACT: In August and September, 2001, Kuwait Bay, a semi-enclosed embayment of the Arabian Gulf, experienced a massive fish kill involving over > 2500 metric tons of wild mullet (Liza klunzingeri), due to the bacterium Streptococcus agalactiae. In the Bay, this event was preceded by a small fish kill (100-1000 dead fish per day) of gilthead sea bream (Sparus auratus) in aquaculture net pens associated with a bloom of the dinoflagellate Ceratium furca. Sea bream were found to be culture positive with S. agalactiae, but did not show any visible signs of disease. Unusually warm temperatures (up to 35oC) and calm conditions prevailed during this period. As the wild fish kill progressed, various harmful algae were observed, including Gymnodinium catenatum, Gyrodinium impudicum, and Pyrodinium bahamese var. compressum. Cell numbers of G. catenatum and G. impudicum exceeded 106 l-1 in some locations. All fish tested below the limits of detection for paralytic shellfish poisoning (PSP) and brevetoxins. Clams (Circe callipyga) were positive for PSP but at levels below regulatory limits. Nutrient concentrations, both inorganic and organic, were highly variable with time and from site to site, reflecting inputs from sewage outfalls, the aquaculture operations, a high biomass of decomposing fish, and other sources. It is hypothesized that many factors contributed to the initial outbreak of the bacterial disease, including unusual warm and calm conditions. The same factors, as well as enriched nutrient conditions, also apparently were conducive to the subsequent HAB outbreaks.
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Characterization of Beta-haemolytic Group B Streptococcus agalactiae in cultured seabream, Sparus auratus L., and Wild Mullet, Liza klunzingeri (Day), in Kuwait.
Evans, J.J., P.H. Klesius, P.M. Glibert, C.A. Shoemaker, M.A. Al-Sarawi, J. Landsberg, R. Duremdez, A. Al-Marzouk, and S. Al-Zenki. 2002. J. Fish Dis. 25: 505-513.
ABSTRACT: Streptococcus agalactiae was isolated from cultured gilthead seabream, Sparus auratus L., and diseased wild Klunzinger's mullet, Liza klunzingeri (Day), in Kuwait Bay, Arabian Gulf. Isolates were catalase negative, Beta-haemolytic Gram-positive cocci and serogroup B. Experimental infectivity trials with mullet and seabream brain isolates in Nile tilapia, Oreochromis niloticus L., caused 100 and 90% mortality, respectively, within 7 days post-inoculation indicating virulent S. agalactiae as the bacterial pathogen responsible for the epizootic in Kuwait Bay. PDF by request |
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