Biogeochemistry of Mangrove Soil Organic Matter: a Comparison BetweenRhizophoraandAvicenniaSoils in South-eastern Brazil

Soil core samples fromRhizophora mangleL. andAvicennia schauerianaStapf & Leech forests from south-eastern Brazil were analysed for their total organic matter content and their sugars, amino acid and amino sugars composition. Organic carbon and nitrogen contents were higher inAvicenniathan inRhizophorasoils. The contribution of sugars and amino acids to the total organic carbon pool was constant with depth inRhizophorasoils whereas inAvicenniasoils it increased. Spectral distribution of sugars and amino acids showed a dominance of Ca-affine monomers, particularly acidic amino acids, and the sugar arabinose. Biogeochemical indicators derived from ratios of individual sugar and amino acid monomers confirm previous studies which showed that organic matter in both soils is mainly of mangrove origin. The results further suggest accumulation of organic matter inRhizophorasoils and a continuing degradation of organic matter inAvicenniasoils. The latter may thus release more nutrients to adjacent ecosystems thanRhizophorasoils.     

改性粘土絮凝后残留的太平洋亚历山大藻(Alexandrium pacificum)毒素变化研究

改性粘土法是一种高效、环保的有害藻华应急处置技术,可通过絮凝作用有效去除水体中藻华生物。但利用改性粘土絮凝产毒藻后,水体中胞内外藻毒素的变化情况目前尚不清楚。文章考察了I型改性粘土(MCI)絮凝典型产毒甲藻——太平洋亚历山大藻(Alexandriumpacificum)后,水体中残留藻细胞内和胞外麻痹性贝类毒素(paralytic shellfish toxins, PSTs)含量、组分的变化情况。实验结果表明, MC I对密度为6.11×10~3 cells/mL的A. pacificum 3小时去除率达62%,水体中残留藻细胞单细胞毒素含量和PSTs组分与对照组无显著差异,但水体中总PSTs含量大大降低,其中由絮凝沉降导致的胞内PSTs被去除量占水体中PSTs总减少量的90%以上。另外,针对MC I对胞外PSTs吸附效果的研究发现,低于0.5 g/L的MC I对胞外PSTs无明显吸附效果,而在利用0.2 g/L MC I絮凝去除大部分亚历山大藻后,水体中胞外PSTs含量无明显变化。由此可以推测该用量下的MC I未造成大量藻细胞破裂向水体中释放毒素。该研究结果将为改性粘土治理有毒甲藻藻华的现场应用提供科学依据。     

具产电性能光合细菌DH-3的分离及其对多种底物污水处理能力的评价

本文通过传统微生物分离培养方法从富营养化环境中分离培养出可高效处理多种底物的污水并具备胞外电子传递能力和产电潜力的兼性厌氧光合细菌。在光照培养条件下,利用改良的能够将光合细菌富集/分离的培养基分离培养光合细菌,从形态学和16S rDNA的分子生物学角度鉴定菌株。运用多个指标检测光合细菌处理不同底物的污水培养基的能力,如化学需氧量（chemical oxygen demand,COD）、总氮（total nitrogen,TN）、总磷（total phosphate,TP）,并在电化学工作站检测光合细菌的产电能力。结果表明,获取的光合细菌菌株DH-3与光合细菌类球红细菌（Rhodobacter sphaeroides）有97%的相似性。该菌株拥有在多种底物的污水培养基中生长的能力,其中在以乙酸为底物的培养基中生长最好。通过检测发现该菌株对污水的COD、TN和TP均具有较高的去除率。电化学工作站检测结果表明,菌株DH-3的最大产电流量能达到7.5mA/m²,最大功率密度达到0.056W/m²。由此可见,光合细菌DH-3在污水处理及资源再循环利用等方面具有十分重要的应用潜力。     

Extracellular release of small and large molecules by phytoplankton in the Southern Bight of the North Sea

Extracellular release by phytoplankton of small and large metabolites (molecular weight 〈and〉 500 d) is determined kinetically in various marine ecosystems including the eutrophic Scheldt estuary, the Belgian coastal zone and the oligotrophic English Channel. Kinetic curves show that while small metabolites are immediately released in the external medium, a lag phase is always observed in the release of large metabolites. Results indicate that 9–48% of the total excreted amount ends up in the small metabolites pool with no dependence on light intensity or nutritive conditions. Relative rates of heterotrophic uptake of the phytoplankton extracellular metabolites are calculated from the time dependent distribution of ¹⁴C labelled extracellular products. The data indicate that small molecules with high turnover rates (up to 25% h^?1) may occasionally be excreted by phytoplankton cells. The turnover time of high molecular weight excreted compounds is much longer. A correlation is found between the rate of production of these large extracellular metabolites and the exoenzymatic activity of the bacterial populations.     

Photoadaptation of carboxylating enzymes and photosynthesis during a spring bloom

Properties of the light saturation curve of photosynthesis and ribulose-1,5-bisphosphate carboxylase (RuBPC) activity are shown to change qualitatively in a natural population of marine phytoplankton during a spring bloom. Evidence is presented to show that these changes constitute photoadapative responses to increasing irradiance. As irradiance increased during the bloom, both the level of light-saturated photosynthesis (P_m) and the initial slope of the light saturation curve (α = photosynthetic efficiency) increased whether those parameters were normalized to chlorophyll a concentration (P_m^b, α^b) or to cell numbers (P_m^c, α^c). The magnitudes of these changes were such that I_k (= P_m/α, the photoadaptation parameter) did not change, but I_m, the light intensity at which photosynthesis becomes saturated, increased. RuBPC activity, both chlorophyll a (RuBPC^b) and cell number normalized (RuBPC^c), also increased during the bloom. We suggest that these adaptations were achieved by simultaneously increasing the number of photosynthetic units, proportionately decreasing the photosynthetic unit size, and increasing both the concentrations of the enzymes of the dark reactions and possibly also of photosynthetic electron transport components.We also observed diminished levels of photoinhibition in the high light adapted cells late in the bloom and have suggested that this was a consequence of the same suite of physiological changes.In situ carbon fixation per cell increased during the bloom whereas no change occurred in this parameter when normalized to chlorophyll a concentration. Although these photoadaptive responses thus permitted carbon to be fixed in situ more rapidly per cell, at a constant efficiency with respect to investment of energy in the photosynthetic apparatus, they did not result in a change in growth rate. Based on consideratios of the role of time scale in physiological adaptation, however, it is suggested that the observed alterations in photosynthesis with increasing irradiance might permit a cell to more rapidly fill an energy quota for division, possibly an advantage in a mixing environment in which energy is patchily distributed, both spatially and temporalyy.Phosphoenolpyruvate carboxylase activity when normalized to chlorophyll a (PEPC^b) did not change during the bloom while chlorophyll a normalized dark carbon fixation decreased sharply and was quantitatively small compared to PEPC^b. On this basis and considering that RuBPC^b increased during the bloom, it is suggested that, although PEPC may be involved in dark carbon fixation, its most important quantitative role is probably an indirect one in light dependent photosynthesis.We have also considered the relevance of laboratory results on photoadaptation to interpretations of field studies and have suggested that batch culture studies must be treated with caution but that turbidistat and semi-continuous methods provide reasonable simulations of natural conditions.     

Trichodesmium in the East China Sea

A study is made on the surface distribution ofTrichodesmium thiebautii Gomont in the East China Sea during the years 1961–1967.

1. This alga is very scarce or absent in the period from January to March, and begins to increase in May and June, reaching the maximum population density from July to September, and again decreases in October and November.
2. In summerT. thiebautii is predominantly distributed in the area along the Kuroshio current with high densities of 10²–10³ filaments/l, occasionally exceeding 10³ filaments/l. This alga is estimated to occupy the major part or almost all the parts of chlorophylla in situ contained in the surface water of this season.
3. The occurrence ofT. thiebautii off the southern coasts of Central Japan seems to be caused rather by the multiplication in its own habitat than by the transportation by the Kuroshio current from the East China Sea.

     

Resuspension-induced partitioning of organic carbon between solid and solution phases from a river–ocean transition

Laboratory experiments were conducted to evaluate the net exchange of organic carbon (OC) between sediments and overlying water during episodes of resuspension. Surface sediment samples collected from six locations within the Hudson River Estuary and the Inner New York Bight were resuspended in their respective bottom waters for periods ranging from 30 s to 2 h. After resuspension, dissolved organic carbon (DOC) concentration generally reached levels greater than that predicted by conservative mixing of pore water and bottom water, indicating net release of OC from the sediment particles. The amount of OC released during the 1-h extractions comprised ≤0.1% of the total sediment pool, but correlated positively (R²=0.65, P<0.052) with the amount of particulate organic carbon (POC) found in the high-density fraction of the sediment matrix. This suggests that the mineral-bound fraction of sedimentary OC was the major source for the excess DOC released into solution, and that across various sedimentary environments, only a small (but fairly constant) fraction of the total sedimentary POC may be poised for rapid transfer to the water column.     

Ammonium input to the sea via large sewage outfalls-Part 2: Effects of ammonium on growth and photosynthesis of southern California phytoplankton cultures

Cultures of six marine phytoplankton were grown at ammonium concentrations ranging up to 200 μg-atom NH₄---N litre⁻¹. Only the growth of dinoflagellates, Gymnodinium splendens and Gonyaulax polyedra was inhibited at the two highest concentrations used. In 3-h photosynthetic ¹⁴CO₂ uptake experiments, only Gymnodinium was inhibited at concentrations of NH₄---N greater than 100 μg-atom litre⁻¹. We conclude that the increased ammonium concentrations found near Southern California sewage outfalls would not be inhibiting to phytoplankton in the vicinity of such outfalls.     

Photo-inhibition of phytoplankton photosynthesis as a function of exposure time

The photo-inhibition of phytoplankton photosynthesis at higher intensities was examined with a cultured marine diatom,Phaeodactylum tricornutum, and natural samples. The question was to determine whether photo-inhibition results from excretion of photosynthetic products from cell or from an actual decrease in photosynthetic rate. P. tricornutum cultured at 15 klux showed very little photo-inhibition up to 70 klux, and, in the sample cultured at 1 klux, most marked photo-inhibition was observed in 3 hours experiment. Extracellular release was less than 30% of particulate fixation, and did not show any extreme increase to supplement photosynthesis depression at higher light intensities. When the photosynthesis was measured during 10 minutes, both samples showed no photo-inhibition. The photosynthesis by low light sample lost the linearity of time-course with prolonged exposure at high light intensity. Observed photo-inhibition, therefore, we explained with the actual decrease in photosynthetic rate. Similar photo-inhibition could be seen in marine phytoplankton samples concentrated by filtration.     

水母(沙海蜇)降解与营养盐(氮、磷)释放的模拟与实证

The aim of this study was to investigate nitrogen and phosphorus released in the process of the decomposition of giant jellyfish in the laboratory and found the evidence to verify the influence of nutrients released by the decomposition of jellyfish on the ecosystem in the field. The release of nitrogen and phosphorus from the decomposition of Nemopilema nomurai was examined in a series of experiments under different incubation conditions such as different p H values, salinity values, temperatures and nitrogen and phosphorus concentrations. The results showed that the complete decomposition of Nemopilema nomurai generally took about 4–8 d. The release of nitrogen and phosphorus from the decomposition of Nemopilema nomurai could be divided into two stages: the early stage and the later stage, although the efflux rate of nitrogen was one order more than phosphorus. In the early stage of the decomposition of Nemopilema nomurai, the concentrations of dissolved nitrogen, dissolved phosphorus, total nitrogen and total phosphorus in seawater increased rapidly, and the concentration of nitrogen could reach the highest level in the whole degradation process. In the later stage of the decomposition, the concentrations of dissolved nitrogen and total nitrogen declined slowly, while the concentration of phosphorus in water could reach a maximum in the degradation process. High p H, low salinity,high temperature and N/P will promote the release of nitrogen; low p H is unfavorable to the release of nitrogen but favorable to the release of phosphorus. In addition, we found the concentrations of ammonium and phosphate in the bottom water were higher than those in the surface water during the period of jellyfish bloom in the Jiaozhou Bay, proving that nutrients released by the decomposition of jellyfish have significant influence on nitrogen and phosphorus in the field. For the whole Yellow Sea, nutrients released by jellyfish carcasses may reach up to(2.63±2.98)×107 mol/d of dissolved nitrogen(DN) and(0.74±0.84)×106 mol/d of dissolved phosphorus(DP) during the period of jellyfish bloom. The values are comparable to riverine inputs in a day, but much higher than sediment–water exchange flux in the Yellow Sea. The great amounts of nutrients must have significant influence on the nutrients balance of the Yellow Sea during the period of jellyfish dead and decomposition. Both the experimental data and field observations proved that the decomposition of jellyfish may release a great amount of nutrient to the surrounding environment during the period of jellyfish decomposition.     

Serum biochemical and cellular responses to experimental cupric ion challenge in mussels

Our intent has been to develop rapid and sensitive bioassay procedures for laboratory and field applications based on hemolymph factors in animals such as the bay mussel, Mytilus edulis. We found that mussel hemolymph could be easily and repeatedly sampled from individual animals in sufficient amounts to allow analyses for lysozyme, proteolytic activity, total protein and hemocyte counts. In static tests there seemed to be graded responses indicating release of increasing amounts of the above factors into the hemolymph in roughly direct proportion to Cu²⁺ concentration at lethal and sublethal levels. We interpreted this to be evidence for increased lysosomal and cellular disruption as cupric ion exposure was increased or prolonged. At the same time, Cu²⁺ concentrations in the mussel hemolymph increased up to an order of magnitude above ambient in the range of 26 to 267 ppb. We felt that this was evidence for the release of Cu-binding proteins into the mussel hemolymph. Simultaneously with the above events the serum granulocytes increased in numbers above control values by factors of 3 or 4 in response to copper challenge while macrophage (terminology of Moore & Lowe, 1977) counts, including controls, declined precipitously.     

Distribution of pelagic blue-green algae in the North Pacific Ocean

The distribution of pelagic blue-green algae, especially ofTrichodesmium thiebautii, was investigated on the basis of the collection of theHakuhō Maru Cruise KH-69-4 along 155°W (50°N-15°S) in the North Pacific Ocean from September to November 1969.

1. Five species were identified:Trichodesmium thiebautii (most predominant),T. erythraeum, Oscillatoria sp.,Katagnymene spiralis andRichelia intracellularis.
2. T. thiebautii was most abundant in the western North Pacific central water and abundant next to it in the equatorial water, but it did not occur in the subarctic water.
3. T. thiebautii was ubiquitously distributed in the lower layer of 100–200 m in the equatorial water, though not in a large quantity.
4. T. thiebautii inhabited only the water warmer than 20°C. In its main habitat, nitrate and nitrite were almost zero, but ammonia and phosphate were present. There was not found any correlation between its occurrence and the salinity.
5. Blue-green algae were generally thinly populated in the water rich in diatoms.

     

Accumulation of total CO2 during stagnation in the Baltic Sea deep water and its relationship to nutrient and oxygen concentrations

Accumulation of total CO₂ (C_T) was investigated in the sub-halocline deep water of the Gotland Sea (Baltic Sea) during a period of stagnation from 1995 to 1999. Depth profiles for C_T, nitrate, phosphate, and oxygen were measured during seven cruises in a grid consisting of 26 stations. The mean C_T increased by more than 60 μmol/kg from October 1995 to July 1999 corresponding to a mean accumulation rate of 1.1 mol/m² year. Taking into account vertical mixing, the vertical distribution of the C_T accumulation was used to determine mineralization rates at different depths. High rates immediately below the halocline indicated the existence of a fraction of organic matter, which is rapidly mineralized during sinking through the water column. A second fraction is more refractive and accumulates at the sediment surface in the deep center of the basin where it is slowly mineralized and partly buried. Phosphate release rates in anoxic waters and especially at the redoxcline were substantially higher than those estimated on the basis of the carbon mineralization and the Redfield C/P ratio. This is attributed to non-Redfield mineralization ratios and the dissolution of iron oxide/phosphate associates. The formation of nitrate by mineralization under oxic conditions was almost completely compensated by denitrification. Using the carbon mineralization rates and a C/N ratio of 8.4, a denitrification rate of 280 mmol/m² year was obtained, which approximately balances the input of nitrate/ammonia into the surface water. Relating the apparent oxygen utilization (AOU) to the C_T fraction that was generated by mineralization yielded a carbon mineralization/O₂ consumption ratio of 0.83.     

Photochemical degradation of petroleum hydrocarbon surface films on seawater

Surface films of a crude-oil fraction were exposed to irradiation from different light sources. The physical behaviour is described. Degradation products were isolated and identified. Primarily they are aliphatic and aromatic acids and to a lesser extent alcohols and phenols. Acids were converted into their methylesters and identified by combined gas chromatography and mass spectrometry. The amount of oxidation products in the surface film was estimated by measurement of the CO-infrared absorption in the 1700 cm^?1 region with “Attenuated Total Reflection” (ATR) infrared spectroscopy¹. Comparison between the original crude-oil fraction and degradation products lead to an estimation of the decomposition rate under natural environmental conditions.     

Enhanced carbohydrate production by Southern Ocean phytoplankton in response to in situ iron fertilization

Storage carbohydrates (e.g., water-extractable β-1,3-d-glucan in diatoms) are of key importance for phytoplankton growth in a variable light climate, because they facilitate continued growth of the cells in darkness by providing energy and carbon skeletons for protein synthesis. Here, we tested the hypothesis that synthesis of storage carbohydrates by phytoplankton in the Southern Ocean is reduced by low iron and light availability. During the EisenEx/CARbon dioxide Uptake by the Southern Ocean (CARUSO) in situ iron enrichment experiment in the Atlantic sector of the Southern Ocean in November 2000, we studied the dynamics of water-extractable carbohydrates in the particulate fraction over the period of 3 weeks following the iron release. The areal amount (integral between 0- and 100-m depth) of carbohydrates increased from 1400 to 2300 mg m⁻² inside the iron-enriched patch, while remaining roughly constant in the surrounding waters. Most of the increase inside the patch was associated with the fraction of large (>10 μm) phytoplankton cells, consistent with the shift in the community structure towards larger diatoms. Deck incubations at 60% of the ambient irradiance revealed that the diurnal chlorophyll a (Chl a)-specific production rates of water-extractable polysaccharides were significantly higher for “in-patch” than for “out-patch” samples (0.5 vs. 0.3 μg C [μg Chl a]⁻¹ h⁻¹, respectively). Together with the higher photochemical efficiency of photosystem II (F_v/F_m), this indicates enhanced photosynthetic performance in response to iron fertilization. In addition, the nocturnal polysaccharide consumption rates were also enhanced by iron release, causing a striking increase in the diel dynamics of polysaccharide concentration. An iron-stimulated increase in diel dynamics was also observed in the fluorescence and size of pico- and nanophytoplankton cells (measured by flow cytometry) and is indicative of enhanced phytoplankton growth. Diurnal polysaccharide production by phytoplankton inside the patch was light-limited when they were incubated at intensities below ca. 200 μmol m⁻² s⁻¹ (daytime average). These irradiance levels correspond to those at 20- to 30-m depth in situ, whereas the upper mixed layer was frequently several-fold deeper due to storms. Therefore, these first measurements of phytoplankton carbohydrates during an in situ iron release experiment have revealed that both light and iron availability are the key factors controlling the synthesis of storage carbohydrates in phytoplankton and, hence, the development of diatom blooms in the Southern Ocean.     

Decomposition characteristics of particulate organic matter in hiroshima bay

The decomposition characteristics of particulate organic matter (POM) sampled with plankton nets in Hiroshima Bay were investigated under aerobic conditions in a laboratory experiment.The POM derived from plankton consisted of both a labile fraction (70–80 % of the whole) and a refractory fraction (20–30%). The labile fraction was completely decomposed within 40 days at 20°C. Although the concentrations of particulate organic carbon (POC) decreased gradually with time, an apparent lag phase was recognized in the decomposition of particulate phosphorus (PP) at an early stage, which might result from a specific uptake of dissolved inorganic phosphorus (DIP) by bacteria. A comparison of the metabolic activity between dissolved organic matter (DOM) and POM by measuring ATP contents showed that the former was one order of magnitude larger than the latter.On the other hand, there was no significant difference among the decomposition rates of POM collected at various depths. The change of the first-order rate constant (k) for the POM decomposition by temperature was expressed ask=0.0329 exp(0.0644T), and the Q₁₀ value was 1.94. There were fairly large variances ink values obtained from the various plankton species. Thek values averaged 0.144 day^–1 and ranged from 0.078 to 0.20 day^–1 at 20°C.     

Acclimations of macroalgae as reflected in photosynthetic parameters derived from PAM fluorometry, and possible implications for abundance patterns

The presences of the common macroalgae Ulva sp. and Jania rubens vary between seasons along the Israeli Mediterranean intertidal zone. To reveal some of the potential acclimation mechanisms of these algae, we examined their photosynthetic traits during the year using rapid light curves (RLC) derived from pulse amplitude modulated (PAM) fluorometry. In addition, the relationships between those photosynthetic traits and the relative abundances of the two algae were investigated. Ulva sp. showed high maximal electron transport rates (ETR_max) (49.7–68.8 μmol electrons m⁻² s⁻¹) and onsets of light saturation values (E_k) (75.8–85.6 μmol photons m⁻² s⁻¹) in the winter months of December–February, while low values were found in the summer months of June–July (5.2–20.6 μmol electrons m⁻² s⁻¹ and 6.0–23.7 μmol photons m⁻² s⁻¹, respectively). At noon time (during the highest irradiance of the day), the maximal effective quantum yield (Y₀) did not vary significantly during the year. These results indicate that seasonal irradiance influences the number of reaction centres per thallus area. Both algae showed depressions in Y₀ at noon (23.8% for Ulva sp. and 20.3% for Jania rubens), indicating an efficient non‐photochemical quenching mechanism. A positive correlation between the relative abundance and the photosynthetic parameter Y₀ was found for Jania rubens when Y₀ was sampled in the morning or noon, indicating that growth rate and primary production for this alga can be estimated from RLCs. No such correlation was found for Ulva sp., indicating that, in addition to photosynthetic traits, the relative seasonal abundance of this alga is influenced by other factors such as grazing and/or catastrophic events.     

Evidence for the grazing hypothesis: Grazing reduces phytoplankton responses of the HNLC ecosystem to iron enrichment in the western subarctic pacific (SEEDS II)

A mesoscale iron-enrichment study (SEEDS II) was carried out in the western subarctic Pacific in the summer of 2004. The iron patch was traced for 26 days, which included observations of the development and the decline of the bloom by mapping with sulfur hexafluoride. The experiment was conducted at almost the same location and the same season as SEEDS (previous iron-enrichment experiment). However, the results were very different between SEEDS and SEEDS II. A high accumulation of phytoplankton biomass (∼18 mg chl m⁻³) was characteristic of SEEDS. In contrast, in SEEDS II, the surface chlorophyll-a accumulation was lower, 0.8 to 2.48 mg m⁻³, with no prominent diatom bloom. Photosynthetic competence in terms of F _v/F _m for the total phytoplankton community in the surface waters increased after the iron enrichments and returned to the ambient level by day 20. These results suggest that the photosynthetic physiology of the phytoplankton assemblage was improved by the iron enrichments and returned to an iron-stressed condition during the declining phase of the bloom. Pico-phytoplankton (<2 μm) became dominant in the chlorophyll-a size distribution after the bloom. We observed a nitrate drawdown of 3.8 μM in the patch (day 21), but there was no difference in silicic acid concentration between inside and outside the patch. Mesozooplankton (copepod) biomass was three to five times higher during the bloom-development phase in SEEDS II than in SEEDS. The copepod biomass increased exponentially. The grazing rate estimation indicates that the copepod grazing prevented the formation of an extensive diatom bloom, which was observed in SEEDS, and led to the change to a pico-phytoplankton dominated community towards the end of the experiment.     

Primary productivity in coastal water adjacent to the Kuroshio off Shimoda

The primary productivity in coastal water adjacent to the Kuroshio off Shimoda was measured as part of the International Biological Program. The total amount of chlorophylla in the euphotic zone varied widely from 20 mg/m² to 60 mg/m² throughout the year and the maximum values were measured in early summer. These values were higher than those in the Kuroshio but agreed with those in the Oyashio. Vertical differentiation of photosynthetic characteristics was well developed and it was strongly related to the stratification of the water column. The light-saturated photosynthetic rate of surface phytoplankton varied from 5.8 mg C/(mg chl.h) in May to 2.0 mg C/(mg chl.h) in January. These rates were higher than those in the Kuroshio. The daily primary production was estimated by the chlorophyll method. Highest value was 0.5–1.5 g C/(m²day) in early summer and the lowest was 0.2 g C/(m²day) in winter. The primary productivity in the coastal water studied accorded fairly well with that in the Oyashio.Contribution No. 239 from Shimoda Marine Biological Station. This study is part of JIBP project entitled Studies on the Dynamic Status of the Biosphere, a Special Research Project supported by the Ministry of Education.     

Blooms of <Emphasis Type="Italic">Trichodesmium erythraeum</Emphasis> in the South Eastern Arabian Sea during the onset of 2009 summer monsoon

This study presents in situ evidence for the blooms of Trichodesmium erythraeum observed in the shelf waters of the South Eastern Arabian Sea (SEAS) during the onset of the southwest monsoon in June 2009. Evidence showed that water surface discoloration was caused by the accumulation of T. erythraeum, and that the water column contained a colony of T. thiebautii. The surface water color in the bloom region varied from pale brown to pinkish red. Pale brown indicated healthy algae at the peak of its photosynthetic activity, while pinkish red indicated the presence of photosynthetically less active filaments. Zooplankton abundance, especially copepodites, in the bloom area substantiated the theory that Trichodesmium filaments are excellent epiphytes to which the copepodites cling. The bloom area was very fertile with copious quantities of dissolved oxygen (6.85 ml L^?1), PO₄-P (0.108 μmol L^?1) and SiO₄ (1.29 μmol L^?1). Lower NO₃-N (0.028 μmol L^?1) values in the bloom area did not appear to affect Trichodesmium growth from molecular nitrogen fixation. However, lower NO₃-N values altered the normal phytoplankton composition of this area.