In vitro iron enrichment experiments in the Prydz Bay, the Southern Ocean: A test of the iron hypothesis

In "high nitrate, low chlorophyll" (HNLC) ocean regions, iron has been typically regarded as the limiting factor for phytoplankton production. This "iron hypothesis" needs to be tested in various oceanic environments to understand the role of iron in marine biological and biogeochemical processes. In this paper, three in vitro iron enrichment experiments were performed in Prydz Bay and at the Polar Front north of the Ross Sea, to study the role of iron on phytoplankton production. At the Polar Front of Ross Sea, iron addition significantly (P < 0.05, Student's t-test) stimulated phytoplankton growth. In Prydz Bay, however, both the iron treatments and the controls showed rapid phytoplankton growth, and no significant effect (P > 0.05, Student's t-test) as a consequence of iron addition was observed. These results confirmed the limiting role of iron in the Ross Sea and indicated that iron was not the primary factor limiting phytoplankton growth in Prydz Bay. Because the light environment for phytoplankton was enhanced in experimental bottles, light was assumed to be responsible for the rapid growth of phytoplankton in all treatments and to be the limiting factor controlling field phytoplankton growth in Prydz Bay. During the incubation experiments, nutrient consumption ratios also changed with the physiological status and the growth phases of phytoplankton cells. When phytoplankton growth was stimulated by iron addition, N was the first and Si was the last nutrient which absorption enhanced. The Si/N and Si/P consumption ratios of phytoplankton in the stationary and decay phases were significantly higher than those of rapidly growing phytoplankton. These findings were helpful for studies of the marine ecosystem and biogeochemistry in Prydz Bay, and were also valuable for biogeochemical studies of carbon and nutrients in various marine environments.

Spatial distributions and seasonal variations of particulate phosphorus in the Jiaozhou Bay in North China

Based oil the measurements of particulate phosphorus (PP) in the Jiaozhou Bay front May 2003 to April 2004, the spatial distribution, seasonal variation and biogeochemical characteristics of PP Were investigated to Understand the fates and roles of phosphorus in the Jiaozhou Bay ecosystem. The Concentration of the total PP ranged from 0. 07 to 2. 09 mu mol/dm(3). The concentration of POP was from 0. 01 to 1. 83 mu mol/dm(3), with all average of with all average of 0. 33 mu mol/dm(3), which accounted for 50. 4% in total PP. In general, file concentrations of IT in surface water show obvious seasonal variations in the Jiaozhou Bay. POP was the highest in spring, which derived front the accumulation of phyto-detritus and was the lowest ill autumn, which was decomposed into seawaters to participate the recycle of phosphorus. PIP was the highest in spring and summer and Was the lowest in autumn and winter. PLP Was Mainly influenced by river input in the inner bay lint POP derived front autochthonous source in the outer bay. Overkill, the concentrations of IT in the inner bay were higher than those in mouth and the Older bay. In the inner bay. the concentrations of IT with the area near the shore were higher than those in the center of the bay. Totally PP showed the decreasing trend with depth especially in spring and winter. The high value of PP emerged in 20 and 10 in Corresponding to summer and autumn, respectively. The changes of POP showed hysteretic effect compared with the changes of Chl a in the investigated year. However, according to the Change of Chl a, the second high value of POP which should be emerged ill October was missing due to the remineralization of POP and participation in the recycle of phosphorus, which lead to the high concentration of orthophosphate in seawaters.

Growth characters and photosynthetic capacity of Gracilaria lemaneiformis as a biofilter in a shellfish farming area in Sanggou Bay, China

Experiments on growth characters and ecological functions of the macroalgae Gracilaria lemaneiformis, collected from south China, were conducted in polyculture areas of kelp and filter-feeding bivalve in Sanggou Bay in Weihai City, Shandong, in north China from May 2002 to May 2003. The results of 116 days cultivation showed that the average wet weight of alga increased 89 times from 0.1 to 8.9 kg rope(-1), with an average specific growth rate ( based on wet weight) of 3.95% per day. The most favorable water layer for its growth was 1.0 - 1.8 m below the surface in July and August, with an average specific growth rate of 8.2% per day in 30-day experiments. Photosynthetic activity changed seasonally, with an average of 7.3 mg O-2 g dw(-1) h(-1). The maximum rate (14.4 mg O-2 g dw(-1) h(-1)) was recorded in July, or 19.3 mg CO2 g dw(-1) h(-1), while the minimum (0.40 mg CO2 g dw(-1) h(-1)) was in April. This study indicated that the culture of G. lemaneiformis is an effective way to improve water quality where scallops are cultivated intensively.

Studies on growth rate and grazing mortality rate by microzooplankton of size-fractionated phytoplankton in spring and summer in the Jiaozhou Bay, China

Dilution experiments were performed to examine the growth rate and grazing mortality rate of size-fractionated phytoplankton at three typical stations, inside and outside the bay, in the spring and summer of 2003 in the Jiaozhou Bay, China. in spring, the phytoplankton community structure was similar among the three stations, and was mainly composed of nanophytoplankton, such as, Skeletonema costatum and Cylindrotheca closterium. The structure became significantly different for the three stations in summer, when the dominant species at Stas A, B and C were Chaetoceros curvisetus, Pseudo-nitzschia delicatissima, C. affinis, C. debilis, Coscinodiscus oculus-iridis and Paralia sulcata respectively. Tintinnopsis beroidea and T. tsingtaoensis were the dominant species in spring, whereas the microzooplankton was apparently dominated by Strombidium sp. in summer. Pico- and nanophytoplankton had a relatively greater growth rate than microzooplankton both in spring and summer. The growth rate and grazing mortality rate were 0.18 similar to 0.44 and 0.12 similar to 1.47 d(-1) for the total phytoplankton and 0.20 similar to 0.55 and 0.21 similar to 0.37 d-1 for nanophytoplankton in spring respectively. In summer, the growth rate and grazing mortality rate were 0.38 similar to 0.71 and 0.27 similar to 0.60 d-1 for the total phytoplankton and 0.11 similar to 1.18 and 0.41 similar to 0.72 d(-1) for nano- and microphytoplankton respectively. The carbon flux consumed by microzooplankton per day was 7.68 similar to 39.81 mg/m(3) in spring and 12.03 similar to 138.22 mg/m(3) in summer respectively. Microzooplankton ingested 17.56%similar to 92.19% of the phytoplankton standing stocks and 31.77%similar to 467.88% of the potential primary productivity in spring; in contrast, they ingested 34.60%similar to 83.04% of the phytoplankton standing stocks and 71.28%similar to 98.80% of the potential primary productivity in summer. Pico- and nanophytoplankton appeared to have relatively greater rates of growth and grazing mortality than microphytoplankton during the experimental period. The grazing rate of microzooplankton in summer was a little bit greater than that in spring because of the relatively higher incubation temperature and different dominant microzooplankton species. Microzooplankton preferred ingesting nanophytoplankton to microphytoplankton in spring, while they preferred ingesting picophytoplankton to nanophytoplankton and microphytoplankton in summer. Compared with the results of dilution experiments performed in various waters worldwide, the results are in the middle range.

Causes and consequences of changes in nutrient structure in the Jiaozhou Bay

Concentrations and ratios of nutrients in Jiaozhou Bay, China, have changed much in the past decades, with trends indicating an increase in nitrogen and a decrease in silicate. Statistical analysis has shown that the long-term variations of nutrients are associated with agricultural activities, precipitation, and anthropogenic factors. Stoichiometric calculations indicate that the nutrient structure has become more and more unbalanced. There has been almost no possibility for nitrogen limitation since the 1980s, the probability of P limitation has increased, and the probability of Si limitation has also increased markedly from the 1980s to the 1990s. As a consequence of changes in nutrient structure, a decrease in the abundance of net phytoplankton was evident, whereas total chlorophyll a levels have remained roughly unchanged at around 3.55 mu g/L. Thus, it is likely that smaller species have taken the niche vacated by the larger species. Changes in phytoplankton size and species composition may ultimately lead to various functional and structural changes at the system level.

Evolution of nutrient structure and phytoplankton composition in the Jiaozhou Bay ecosystem

The inventories of nutrients in the surface water and large phytoplankton( > 69 pm) were analyzed from the data set of JERS ecological database about a typical coastal waters, the Jiaozhou Bay, China, from 1960s for N, P and from 1980s; for Si. By examining long-term changes of nutrient concentration, calculating stoichiometric balance, and comparing diatom composition, Si limitation of diatom production was found to be more possible. The possibility of Si limitation was from 37% in 1980s to 50% in 1990s. Jiaozhou Bay ecosystem is becoming serious eutrophication, with notable increase of NO2-N, NO3-N and NH4-N from 0.1417 mumol/L, 0.5414 mumol/L, 1.7222 mumol/L in 1960s to 0.9551 mumol/L, 3.001 mumol/L, 8.0359 mumol/L in late 1990s respectively and prominent decrease of Si from 4.2614 mumol/L in 1980s to 1.5861 mumol/L in late 1990s; the nutrient structure is controlled by nitrogen; the main limiting nutrient is probably silicon; because of the Si limitation the phytoplankton community structure has changed drastically.

Dissolved inorganic carbon and CO2 fluxes across Jiaozhou Bay air-water interface

On the basis of data collected in the Jiaozhou Bay in June and July 2003, the DIC distribution in seawater is studied, and an average air-sea flux of CO2 is estimated. The results show that the content of DIC inside the bay is markedly higher than outside the bay in June, but the content of DIC outside the bay is markedly higher than inside the bay in July. The trend of DIC distribution inside the bay is similar, viz. the content is the maximum in the northeast, then decreases gradually toward the west, and the content is the minimum in the west. The total trend of vertical distribution is to increase gradually from surface to bottom. This characteristic of DIC distribution is determined by Jiaozhou Bay hydrology and there is a close relation between DIC and particulate N,P. Average CO2 flux across the air-sea interface is 0.55 mol/(m(2.)a) in June and 0.72 mol/(m(2.)a) in July. Jiaozhou Bay is considered as a net annual source for atmospheric CO2 in June and July, and the total CO2 flux from seawater into atmosphere is about 740 t in June and 969 t in July.

The effects of spring-neap tide on the phytoplankton community development in the Jiaozhou Bay, China

The development of the phytoplankton community was studied in the Jiaozhou Bay during the spring to neap tide in August 2001, through three cruises and a 15 d continuous observation. This investigation indicates that diatom cell abundance increased sharply following the end of a spring tide, from 9 cells/cm(3) to a peak of 94 cells/cm(3). The dominant species composition and abundance show a quick species sequence from spring to neap tide, and the dominant species at the start phase is Skeletomena costatum, then changes to Chaetoceros curvisetus, finally it changes to Eucampia zodiacus. Silicate concentration increases during spring tide, as a result of nutrient replenishment from the water-sediment interface, its initial average concentration in neap tide is 1.39 mumol/dm(3) and reached the peak average concentration of 8.40 mumol/dm(3) in spring tide. But the nitrogen concentration dropped due to dilution by the low nitrogen seawater from the Huanghai Sea, its initial average concentration in neap tide is 67 mumol/dm(3) and decreased to the average concentration of 54 mumol/dm(3) in spring tide. The degree of silicon limitation was decreased and phytoplankton, especially diatoms, responds immediately after nutrient replenishment in the water column. Skeletonmea costatum, as one of the dominant species in the Jiaozhou Bay, shows a quicker response to nutrient availability than Eucampia zodiacus and Chaetoceros curvisetus. It is proposed that dominant species composition and water column stability synchronously determine the development of phytoplankton summer blooms in the Raozhou bay.

Matrix-bound phosphine: A new form of phosphorus found in sediment of Jiaozhou Bay

Matrix-bound phosphine (PH3), a new form of phosphorus, was found in sediment of Jiaozhou Bay in December 2001. Concentration and distribution of PH3 in different layers of sediment with different stations were analyzed. The results show that PH3 concentrations are various with different layers and different stations. PH3 concentrations in the bottom layer of sediment (20-30 cm) are usually higher than those in the surface layer (0-4 cm). The highest PH3 concentration in our investigation reaches 685 ng/kg (dry), which is much higher than those in terrestrial paddy soil, marsh and landfill that have been reported up to now. The correlation analysis indicates that there is no apparent correlation between the concentrations of PH3 and inorganic phosphorus in sediment. However, the correlation between the concentrations of phosphine and organic phosphorus in the bottom layer of sediment is remarkable (R-2=0.83). It is mainly considered that PH3 in sediment of Jiaozhou Bay is produced from the decomposition of organic phosphorus in the anaerobic condition, and so PH3 concentrations are related to organic phosphorus concentration and anaerobic environment in sediment. The discovery of PH3 in sediment will give people some new ideas on the mechanisms of phosphorus supplement and biogeochemical cycle in Jiaozhou Bay.

Summer feeding activities of zooplankton in Prydz Bay, Antarctica

Grazing of dominant zooplankton copepods (Calanoides acutus. and Metridia gerlachei), salps (Salpa thompsoni) and microzooplankton was determined during the austral summer of 1998/1999 at the seasonal ice zone of the Prydz Bay region. The objective was to measure the ingestion rates of zooplankton at the seasonal ice zone, so as to evaluate the importance of different groups of zooplankton in their grazing impact on phytoplankton standing stock and primary production. Grazing by copepods was low, and accounted for less than or equal to 1% of phytoplankton standing stocks and 3.8-12.5% of primary production for both species during this study, even the ingestion rates of individuals were at a high level compared with previous reports. S. thompsoni exhibited a relatively high grazing impact on primary production (72%) in the north of our investigation area. The highest grazing impact on phytoplankton was exerted by microzooplankton during this investigation, and accounted for 10-65% of the standing stock of phytoplankton and 34-100% of potential daily primary production. We concluded that microzooplankton was the dominant phytoplankton consumer in this study area. Salps also played an important role in control of phytoplankton where swarming occurred. The grazing of copepods had a relatively small effect on phytoplankton biomass development.

Historical changes in nutrient structure and its influences on phytoplantkon composition in Jiaozhou Bay

Due to the influence of human activities, nutrient concentrations, nutrient ratios and phytoplankton composition have notably changed in Jiaozhou Bay, China since the 1960s. From the 1960s to the 1990s, nutrient concentrations have increased 1.4 times for PO4-P, 4.3 times for NO3-N, 4.1 times for NH4-N and 3.9 times for DIN. The atomic ratio of DIN:PO4-P increased very rapidly from 15.9 +/- 6.3 for the 1960s, to 37.8 +/- 22.9 for the 1990s. SiO3-Si concentration has remained at a very low level from the 1980s to the 1990s. The high ratio of DIN: PO4-P and low ratios of SiO3-Si:PO4-P (7.6 +/- 8.9) and SiO3-Si:DIN (0.19 +/- 0.15) showed the nutrient structure of Jiaozhou Bay has changed from more balanced to unbalanced during the last 40 years. The possibility that DIN and/or PO4-P as limiting factors of Jiaozhou Bay phytoplankton has been lessened or eliminated and that of SiO3-Si limiting has been increased. The changes in nutrient structure may have led to the decrease of large diatoms and a shift of phytoplankton species composition. It is likely that there is a trend from large diatoms to smaller cells in Jiaozhou Bay. (C) 2001 Academic Press.

Summertime ciliate and copepod nauplii distributions and micro-zooplankton herbivorous activity in the Laizhou Bay, Bohai Sea, China

The abundance and biomass of ciliated protozoa and copepod nauplii were investigated at 21 grid stations and two anchored stations in the Laizhou Bay, Bohai Sea, China in June 1998. Dilution incubations were carried out to investigate micro-zooplankton grazing pressure at the anchored stations during spring tide and neap tide. The dominant species were Tintinnopsis amoyensis, T. chinglanensis, T. pallida and aloricate ciliates. A total of 13 species of tintinnids were found. The total abundance of ciliates and nauplii ranged from 30 to 2390 ind l(-1) at grid stations. Tintinnopsis amoyensis was the only ciliate found at the anchored stations and in concentrations which varied from 0 to 6700 ind l(-1). The spatial distribution of ciliates was patchy. Tintinnopsis amoyensis and T. pallida were distributed in the Weihe River mouth and Xiaoqinghe River mouth respectively. The aloricate ciliates, T. chinglanensis and Codonellopsis ostenfeldi dominated offshore in sequence. The water mixing process may affect the spatial pattern of the dominant ciliate species. The abundance and biomass of copepod nauplii were in the range of 0-140 ind l(-1) and 0-7 mu g C l(-1) respectively, with the peak appearing at grid station 15. The total biomass of ciliates and copepod nauplii was in the range of 1(.)5-25 mu g C l(-1). Water column biomass of ciliates and nauplii varied from 2(.)37 to 52(.)3 mg C m(-2). At the anchored stations, the phytoplankton growth rates ranged from undetectable to 0 21 d(-1) and micro-zooplankton grazing rates from 0 13 to 0(.)57 d(-1). The grazing pressure of micro-zooplankton were 12 to 43% of the chlorophyll standing stock and 84 to 267% of the chlorophyll (C) 2000 Academic Press.

An unidentified haplosporidian parasite of bay scallop Argopecten irradians cultured in the Shandong and Liaoning provinces of China

Since 1988 growers of bay scallop Argopecten irradians in China have been experiencing mortality in their cultured stocks. Although poorly documented, mortality apparently began near Qingdao and has since spread to other areas of Shandong and Liaoning provinces. Samples of cultured scallops were collected from several growing areas in these provinces and analyzed by histological methods for pathogens. An unidentified haplosporidian parasite was observed in a high proportion of scallops from two of the stocks examined. Most infections were of low intensity, but one heavy infection was also observed. Only plasmodia stages were observed; they occurred intercellularly in connective tissues throughout the scallops. Plasmodia were spherical to oval, varied from 4.0 to 17.0 mu m in diameter and contained from 2 to 18 nuclei. Absence of spores prevented generic assignment of the parasite. The source and pathogenicity of the haplosporidian could not be assessed without additional research. No other microbial parasites (i.e. rickettsia-like, chlamydia-like or kidney coccidia) were observed in any of the scallops examined.

Environmental changes reflected by sedimentary geochemistry in recent hundred years of Jiaozhou Bay, North China

Sediment geochemical technique was employed to assess how the sediment records reflect the environmental changes of Jiaozhou Bay, a semi-enclosed bay adjacent to Qingdao, China. In the past hundred years, Jiaozhou Bay has been greatly impacted by human interventions. A dated core sediment by Pb-210 chronology was analyzed for trace metals including Li, Cd, Cr, Pb, Cu, Ni, Co, Zn together with C, N, P and BSi. Based on the research, the development of Jiaozhou Bay environment in the past hundred years can be divided into three stages: (1) before the 1980s characterized by relatively low sedimentation rate, weak heavy metal pollution and scarce eutrophication; (2) from the 1980s to 2000, accelerating in the 1990s, during which high sedimentation rates, polluted by heavy metals and the frequent occurrence of red tide; (3) after 2000, the period of the improvement of environment, the whole system has been meliorated including the heavy metal pollution and hypernutrification. (c) 2006 Elsevier Ltd. All rights reserved.