[Show abstract][Hide abstract] ABSTRACT: The Henry’s Law constant (k) for phosphine in seawater was determined by multiple phase equilibration combined with headspace gas chromatography. The effects of pH, temperature, and salinity on k were studied. The k value for phosphine in natural seawater was 6.415 at room temperature (approximately 23°C). This value increases with increases in temperature and salinity, but no obvious change was observed at different pH levels. At the same temperature, there was no significant difference between the k for phosphine in natural seawater and that in artificial seawater. This implies that temperature and salinity are major determining factors for k in marine environment. Double linear regression with Henry’s Law constants for phosphine as a function of temperature and salinity confirmed our observations. These results provide a basis for the measurement of trace phosphine concentrations in seawater, and will be helpful for future research on the status of phosphine in the oceanic biogeochemical cycle of phosphorus.
Full-text · Article · Jul 2013 · Chinese Journal of Oceanology and Limnology
[Show abstract][Hide abstract] ABSTRACT: To verify the feasibility of high-affinity nitrate transporter gene (Nrt2) as an indicator of nitrogen status, changes in the transcript levels of transcripts associated with phosphate starvation and different nitrate concentrations were studied using real-time quantitative reverse-transcription PCR (QRT-PCR) technology in batch cultures of Skeletonema costatum. The results show that compared with P-replete condition, P starvation could reduce the Nrt2 transcript levels apparently. Nrt2 transcript levels had a significant negative linear correlation with nitrate concentrations below 40 µmol/L. The results of 48 h short-term incubation experiment under different nitrate concentrations confirmed this correlation, and the following regression equation is built: y = −3.305x +98.95, R
2 = 0.988, where x represents nitrate concentrations (<40 µmol/L) and y represents the Nrt2 transcript levels.
No preview · Article · Jun 2013 · Acta Oceanologica Sinica -English Edition-
[Show abstract][Hide abstract] ABSTRACT: Harmful algal blooms (HABs) are harmful to coastal ecosystems, fisheries, the aquaculture industry, and even human health, thus they have received great attention worldwide. In this study, geostatistical tools in Geographic information system (GIS) were used to analyze HAB data collected over the last 11 years in the southwest Bohai Sea with the goal of detecting spatial and temporal characteristics of HAB events in this area. The seasonality, trend of HAB occurrences and the spatial pattern of HAB events were examined by time-series analysis and nearest neighbor analysis, respectively. The frequency of HAB occurrences was mapped using kernel density estimation, and the harm caused by HAB events was assessed and then categorized using a characteristic-based empirical model. The occurrences of HABs not only exhibited significant seasonality and a “single peak” trend in time but also were clustered in space. HABs had both a high frequency of occurrence and a high harm in the north Bohai Bay and the Yellow River estuary. In addition, HABs posed a high harm in the nearshore area near the city of Huanghua in Bohai Bay and the offshore area in the middle Bohai Bay; thus, HAB monitoring and/or management should be concentrated in these locales. Compared to previous descriptions, this research utilized a visualizable approach to more fully identify the scope, distribution, and characteristics of HAB occurrences in the southwest Bohai Sea, thus providing useful information to support the implementation of a monitoring and management program for HABs.
No preview · Article · May 2013 · Continental Shelf Research
[Show abstract][Hide abstract] ABSTRACT: Phosphine, which is released continuously from sediment, can affect the eco-physiological strategies and molecular responses of phytoplankton. To examine the effects of phosphine on phosphorus uptake and utilization in Thalassiosira pseudonana, we examined the transcriptional level of the phosphate transporter gene (TpPHO) and the activity of alkaline phosphatase (AKP) in relation to supplement of various concentrations of phosphine. TpPHO expression was markedly promoted by phosphine in both the phosphate-deficient and phosphate-4 µM culture. However, high phosphine concentrations can inhibit TpPHO transcription in the declining growth phase. AKP activity was also higher in the phosphine treatment groups than that of the control. It increased with increasing phosphine concentration in the range of 0 to 0.056 µM but was inhibited by higher levels of phosphine. These responses revealed that phosphine can affect phosphate uptake and utilization in T. pseudonana. This result was consistent with the effect of phosphine on algal growth, while TpPHO expression and AKP were even more sensitive to phosphine than algal growth. This work provides a basic understanding for further research about how phosphine affects phytoplankton.
[Show abstract][Hide abstract] ABSTRACT: The photosynthetic capacity of phytoplankton is frequently limited by the availability of nutrients. To explore the mechanism of the effect of nutrient availability on photosynthesis, batch cultures of a marine diatom Skeletonema costatum (Greville) Cleve were carried out under different nitrate (N: 0-220.75 mu M) and phosphate (P: 0-9.075 mu M) concentrations. Changes of photosynthetic characters, including the photosynthetic rate (measured by O-2 evolution) and the rbcL mRNA content (encoding the large subunit of the Calvin cycle enzyme, RuBisCO), were both studied. Within the range tested, both the photosynthetic rate and rbcL transcript levels correlated significantly with N and P concentrations in the medium. Additionally, the photosynthetic rates and rbcL transcript levels were both growth dependent. Significant correlations were also found between the abundance of rbcL mRNA and the photosynthetic rate (R-2 = 0.800), rbcL and growth rate (R-2 = 0.855), the photosynthetic rate and growth rate (R-2 = 0.815). These results are consistent with N and P nutrition-regulating photosynthesis from the transcriptional levels of rbcL. The rbcL transcript level has the potential to be a good marker of algal growth and primary productivity.
Preview · Article · Dec 2012 · Journal of Plankton Research
[Show abstract][Hide abstract] ABSTRACT: Hypoxia has become an overwhelming phenomenon in the coastal environment off the Changjiang (Yangtze River) estuary. Seasonal data were obtained in the Changjiang estuary during 2003, 2004, 2005, and 2009 and during an additional cruise between April and May in 2007 on the dissolved oxygen distribution of the bottom water, on hypoxic events, and on their potential causes. Dissolved oxygen was less than 3.0 mg L⁻¹ in the summer and less than 5.0 mg L⁻¹ in the spring and autumn in the topographic trough and was generally lower than that in the surrounding bottom water of the Changjiang estuary. In the summer, there was a positive correlation (r² = 0.57) between dissolved oxygen concentration and temperature, contrary to the observations in the autumn and winter. A strong halocline and thermocline appeared in the spring and summer. A change in temperature structure was observed in an additional cruise in 2007; the vertical transport of dissolved oxygen flux, which was restricted by stratification, reached 2.77 g m⁻² d⁻¹ .Large nutrient inputs and phytoplankton seem to contribute to hypoxia in the Changjiang estuary.
No preview · Article · Nov 2011 · Journal of Coastal Research
[Show abstract][Hide abstract] ABSTRACT: Responses of growth, cellular total protein, carbohydrates and pigment composition in batch cultures of the marine dinoflagellate, Prorocentrum donghaiense, isolated from the Changjiang Estuary were studied in relation to concentrations of nitrate (0–256 μM) and phosphate (0–16 μM). The results showed that growth and biochemical composition of P. donghaiense were affected by changes in concentrations of N and P. Results showed luxury P consumption in all treatments. Algal division rates were strongly dependent on nitrogen and phosphorus concentrations. An increase in the initial N-added concentrations of the media led to an increase in the cellular total protein, ranging from 0.931 to 0.575 ng/cell during stationary phase. P concentration did not have an obvious effect on protein. Cellular carbohydrates significantly accumulated in both N-limited and P-limited conditions. There was a significant negative correlation between cellular carbohydrates and the specific growth rate. Nutrient availability influenced pigment synthesis. Cellular pigment contents in N-0 and P-0 treatments were significantly lower than that for high nutrient treatments during stationary phase. In addition, pigment ratios changes with different growth phases and nutrient status. Relationship between these biochemical parameters and initial nutrient concentrations showed the potential for specific ratios, including cellular protein/carbohydrate, cellular β-carotene/Chlorophyll a, cellular carbohydrate/cellular total P and protein/cellular total P, to be used as indicators of physiological status of P. donghaiense.Research highlights► Cellular protein content was closely related to the availability of N. ► Nutrient limitation can induce the accumulation of carbohydrates in the cell. ► Pigments ratios changed with different growth phases and nutrient status. ► Specific ratios could indicate the nutritional status of phytoplankton.
No preview · Article · Aug 2011 · Journal of Experimental Marine Biology and Ecology
[Show abstract][Hide abstract] ABSTRACT: Algal allelopathy is an ecological/physiological phenomenon that has focused attention on the interactions among algae and
the production of algal toxins. We investigated the allelopathic interactions between the dinoflagellate genus Prorocentrum micans and diatom genus Skeletonema costatum and between P. micans and dinoflagellate genus Karenia mikimotoi using bi-algal cultures. Because the effects were species-specific and size-dependent, we evaluated the effect of different
initial densities. At low densities of P. micans and high densities of S. costatum inoculated into the same medium, the growth of P. micans was weakly restrained, whereas the growth of S. costatum was significantly suppressed. S. costatum and K. mikimotoi were strongly inhibited by P. micans, in both the bi-algal cultures and enriched filtrates. Direct cell-to-cell contact was not necessary to gain a competitive
advantage, thus, our results suggest that P. micans inhibited the growth of S. costatum and K. mikimotoi by the release of allelochemical(s). Last, a mathematical model was used to simulate growth and interactions between P. micans and S. costatum and between P. micans and K. mikimotoi in bi-algal cultures.
–bi-algal culture–enriched filtrate culture
No preview · Article · Jul 2011 · Chinese Journal of Oceanology and Limnology
[Show abstract][Hide abstract] ABSTRACT: Eutrophication has emerged as a key environmental problem in Chinese coastal waters, especially in the Changjiang (Yangtze)
River estuary. In this area, large nutrient inputs result in frequent harmful algal blooms and serious hypoxia in bottom waters.
Four cruises were made in the estuary in 2006 to assess the concentration and distribution of dissolved inorganic nitrogen
(DIN) and phosphorus (DIP). The concentration of DIN decreased gradually in a linear relationship with salinity from the river
mouth to outer waters, while DIP was relatively more dispersed. A modified box budget method was used to estimate nutrient
fluxes in the estuary and its adjacent waters. Water and nutrient budgets as well as primary production and denitrification
rates were estimated from the box budget model. Estimated water residence time in the estuary was about 11 d. The turbid mixing
zone released 33% of DIN and 49% of DIP, while in the adjacent outer sea 17.9 mmol DIN/m2·d and 0.36 mmol DIP/m2·d were fixed. Dissolved inorganic phosphorus was imported from the deep open sea waters, supporting primary production and
population growth in this zone. Net ecosystem production (NEP) was calculated at 38.2 mmol/m2·d in the outer estuary and the estimated rate (N-fixation minus denitrification) was negative (1.92 mmol/m2·d), implying that a large amount of input nitrogen was taken up by algae and recycled through denitrification in bottom water
Keywordnitrogen–phosphorus–nutrients–transport–budget model–Changjiang (Yangtze) River estuary
No preview · Article · Jul 2011 · Chinese Journal of Oceanology and Limnology
[Show abstract][Hide abstract] ABSTRACT: Matrix-bound phosphine (MBP) has been measured in sediment from two cores in Lake Illawarra on the south east coast of Australia. The sediments were also dated in the upper layers. MBP concentrations found range from 142 to 1813 ng kg(-1), dw (dry weight of sediment) with some values being amongst the highest ever measured. Values of MBP in deeper sediments were higher than for near surface samples, but the patterns with depth were not consistent. Strong correlations were noted between MBP and organic phosphorus (OP, r>0.8) and with total phosphorus (TP, r>0.7), but only moderate correlations were found with organic carbon (OC, r>0.5). No correlations were found between MBP concentrations and the age of the sediments. It was confirmed that high MBP concentrations are indicative of a phosphorus rich environment. The results tend to support the premise that MBP is generated by microbial attack on OP under anaerobic conditions.
Full-text · Article · Jun 2011 · Marine Pollution Bulletin
[Show abstract][Hide abstract] ABSTRACT: The impact of harmful algal blooms (HABs) on public health and related economics have been increasing in many coastal regions
of the world. Sedimentation of algal cells through flocculation with clay particles is a promising strategy for controlling
HABs. Previous studies found that removal efficiency (RE) was influenced by many factors, including clay type and concentration,
algal growth stage, and physiological aspects of HAB cells. To estimate the effect of morphological characteristics of the
aggregates on HAB cell removal, fractal dimensions were measured and the RE of three species of HAB organism, Heterosigma akashiwo, Alexandrium tamarense, and Skeletonema costatum, by original clay and modified clay, was determined. For all HAB species, the modified clay had a higher RE than original
clay. For the original clay, the two-dimensional fractal dimension (D
2) was 1.92 and three-dimensional fractal dimension (D
3) 2.81, while for the modified clay, D
2 was 1.84 and D
3 was 2.50. The addition of polyaluminum chloride (PACl) lead to a decrease of the repulsive barrier between clay particles,
and resulted in lower D
2 and D
3. Due to the decrease of D
3, and the increase of the effective sticking coefficient, the flocculation rate between modified clay particles and HAB organisms
increased, and thus resulted in a high RE. The fractal dimensions of flocs differed in HAB species with different cell morphologies.
For example, Alexandrium tamarense cells are ellipsoidal, and the D
3 and D
2 of flocs were the highest, while for Skeletonema costatum, which has filamentous cells, the D
3 and D
2 of flocs were the lowest.
Keywordharmful algal blooms–modified clay–fractal dimensions–
No preview · Article · May 2011 · Chinese Journal of Oceanology and Limnology
[Show abstract][Hide abstract] ABSTRACT: The effects of in vivo exposure of Mytilus galloprovincialis to two anionic surfactants (SDBS and SDS) on the molecular biomarker system were studied. After continuous exposure for 72 days, activities/levels of GST, GPx and GSH were significantly higher than in corresponding control groups following exposure to 3.000 mg/L SDS and SDBS. Activities of SOD and CAT were significantly inhibited by experimental SDBS (except CAT in 0.100mg/L group), but not by SDS. Statistical analysis of enzyme activities/levels suggested that there were significant positive relationships between GST and GPx, and negative relationships were found between GSH and CAT, GSH and SOD. Amplified fragment length polymorphism (AFLP) results showed that a greater genotoxic effect was observed for SDBS than for SDS. Based on the above results, the biomarker system of mussels can be affected by the two anionic surfactants (>or=3.000 mg/L); it was more easily affected by SDBS than by SDS.
No preview · Article · Jul 2010 · Ecotoxicology and Environmental Safety
[Show abstract][Hide abstract] ABSTRACT: Both nitrate (NO3−) and soluble reactive phosphate (PO43−) concentration in the freshwater end-member at the mouth of the Changjiang River have increased dramatically since the 1960s.
Within the same period in the sea area, with surface salinity>30, NO3− concentration has shown an obvious increase, PO43− has not changed greatly and dissolved reactive silica (SiO32−) has deceased dramatically. An examination of the elemental ratio of NO3− to PO43− at the mouth of the Changjiang River did not show a systematic trend from the 1960s to 2000s largely because both nutrients
increased simultaneously. In comparison, the elemental ratio of dissolved inorganic nitrogen (DIN) to PO43− in surface seawater, with salinity>22, has shown a clearly increasing trend. Furthermore, an overall historical change of
the SiO32−:PO43− ratio has undergone a reverse trend in this area. Based on the changes of SiO32−:PO43− and DIN:PO43− ratios, we can conclude that an overall historical change of SiO32−:DIN ratio has decreased in this area from the 1950–1960s to 2000s. The argument that phytoplankton productivity in the Changjiang
estuary has been enhanced by increasing nutrient input from the riverine transport was supported by these results. A comparative
study analyzing the shift of phytoplankton composition from the mid-1980s to 2000s was also made. The results indicated that
the average yearly percentage of diatom species in the Changjiang estuary has decreased from 84.6% during 1985–1986 to 69.8%
during 2004–2005. Furthermore, the average yearly percentage of diatom abundance in the Changjiang estuary decreased from
99.5% during to 75.5% over the same time period, while the abundance of dinoflagellates has increased dramatically, from 0.7%
Keywordeutrophication-nutrients-phytoplankton community-Changjiang estuary
Full-text · Article · Jul 2010 · Chinese Journal of Oceanology and Limnology
[Show abstract][Hide abstract] ABSTRACT: The nitrogen isotopic composition of dissolved nitrate (δ15N-NO3−) in surface water of the Yangtze River estuary was determined in four seasons of 2006. δ15N-NO3− ranged from 0.4‰ to 6.5‰ and varied with seasons and geographic regions, reflecting the dynamics of nitrogen cycling in the estuarine ecosystem. δ15N-NO3− was markedly lower in February than in other seasons and exhibited conservative mixing, which was probably attributed to the NO3− being sourced from the atmospheric deposition and agricultural fertilizer. In the upper estuary, the influence of riverine inputs was important during all surveys. In the turbidity maximum zone, nitrification was found with nitrate depleted in 15N in May, whereas denitrification resulting in heavy δ15N-NO3− played an important role in August. More enriched δ15N-NO3− values coinciding with losses of nitrate concentrations based on the conservative mixing model were found in the adjacent marine area in May, and may reflect obvious phytoplankton assimilation of dissolved nitrate. In this manner, δ15N-NO3− may be a sensitive indicator of nitrogen sources and biogeochemical processing existing in this estuary in conjunction with the variations of dissolved nitrate and other environmental factors.
No preview · Article · Dec 2009 · Estuarine Coastal and Shelf Science
[Show abstract][Hide abstract] ABSTRACT: From November 2002 to 2006, five cruises were undertaken in the Yangtze River Estuary and the adjacent East China Sea to compare the nutrient concentrations, ratios and potential nutrient limitation of phytoplankton growth before and after impoundment (June 2003) of the Three Gorges Dam (TGD). Concentrations of dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP) and total nitrogen (TN) exhibited an increasing trend from 2002 to 2006. In contrast, total phosphorus (TP) concentration exhibited a decreasing trend. The mean concentrations of DIN, SRP, and TN in the total study area increased from 21.4 microM, 0.9 microM, and 41.8 microM in 2002 to 37.5 microM, 1.3 microM, and 82.2 microM in 2006, respectively, while TP decreased from 2.1 microM to 1.7 microM. The concentration of dissolved reactive silica (DRSi) had no major fluctuations and the differences were not significant. The mean concentration of DRSi in the total study area ranged from 52.5 to 92.3 microM. The Si:N ratio decreased significantly from 2.7 in 2002 to 1.3 in 2006, while TN:TP ratio increased from 22.1 to 80.3. The area of potential P limitation of phytoplankton growth expanded after 2003 and potential Si limitation appeared in 2005 and 2006. Potential P limitation mainly occurred in an area of salinity less than 30 after 2003, while potential Si limitation occurred where the salinity was greater than 30. By comparison with historical data, the concentrations of nitrate and SRP in this upper estuary during November 1980-2006 increased obviously after impoundment of TGD but DRSi decreased. Meanwhile, the ratios of N:P, Si:N and Si:P decreased obviously.
No preview · Article · Sep 2009 · Science of The Total Environment
[Show abstract][Hide abstract] ABSTRACT: Variations of cellular total lipid, total carbohydrate and total protein content of two dominant bloom-forming species (Skeletonema costatum and Prorocentrum donghaiense) isolated from the Yangtze River Estuary were examined under six different nutrient conditions in batch cultures. Daily samples were collected to estimate the cell growth, nutrient concentration and three biochemical compositions content during 7 days for S. costatum and the same sampling procedure was done every other day during 10 days for P. donghaiense. Results showed that for S. costatum, cellular total lipid content increased under phosphorus (P) limitation, but not for nitrogen (N) limitation; cellular carbohydrate were accumulated under both N and P limitation; cellular total protein content of low nutrient concentration treatments were significantly lower than that of high nutrient concentration treatments. For P. donghaiense, both cellular total lipid content and total carbohydrate content were greatly elevated as a result of N and P exhaustion, but cellular total protein content had no significant changes under nutrient limitation. In addition, the capability of accumulation of three biochemical constituents of P. donghaiense was much stronger than that of S. costatum. Pearson correlation showed that for both species, the biochemical composition of three constituents (lipid, carbohydrate and protein) had no significant relationship with extracellular N concentration, but had positive correlation with extracellular and intracellular P concentration. The capability of two species to accumulate cellular total lipid and carbohydrate under nutrient limitation may help them accommodate the fluctuating nutrient condition of the Yangtze River Estuary. The different responses of two species of cellular biochemical compositions content under different nutrient conditions may provide some evidence to explain the temporal characteristic of blooms caused by two species in the Yangtze River Estuary.
No preview · Article · Jan 2009 · Journal of Experimental Marine Biology and Ecology
[Show abstract][Hide abstract] ABSTRACT: Matrix-bound phosphine (MBP) concentrations in surface sediments collected from 37 stations along the coast of China in 2006 are reported. MBP was found in all samples and the average concentration was 6.30ngkg(-1)dry weight (dw). The distribution of MBP showed certain spatial variation characteristics with high MBP concentrations at stations near to the coast. The average concentrations of MBP in the northern Yellow Sea (NYS), the southern Yellow Sea (SYS), the northern area of East China Sea (NECS), the southern area of East China Sea (SECS), and South China Sea (SCS) were 5.57+/-3.78, 3.78+/-2.81, 5.27+/-3.07, 5.48+/-4.05 and 13.52+/-7.86ngkg(-1)dw, respectively. The correlations between MBP and influencing factors, such as the sedimentary environmental characteristics (sediment type, the grain size, contents of phosphorous, organic matters and redox potential) and the aquatic environmental characteristics (temperature, salinity, depth and hydrodynamics) were studied. The results indicated that MBP was strongly influenced by various factors, such as total phosphorus (TP), organic phosphorus (OP), organic carbon (OC), the grain size and hydrodynamics, all of which not only offered reasonable interpretations for the distribution characteristics of MBP but also provided evidence to support the viewpoint that phosphine originated from OP decomposition. This work is the first comprehensive study of the distribution of MBP along the coast of China and its relationships with environmental factors which will lead to a better understanding of the phosphorus (P) biogeochemical cycle in the sea.
[Show abstract][Hide abstract] ABSTRACT: Sediment is commonly considered as a source of phosphine, which is a highly toxic and reactive atmospheric trace gas. This study aims to investigate the seasonal and spatial distribution of matrix-bound phosphine (MBP) and its relationship with the environment in the Changjiang River Estuary. A total of 43 surface sediments were collected in four seasons of 2006, and concentrations of MBP and relative environmental factors were analyzed. MBP ranged from 1.93 to 94.86ng kg(-1) dry weight (dw) with an average concentration of 17.14ng kg(-1)dw. The concentrations of MBP in the upper estuary were higher than those in the lower estuary, which could be attributed to greater pollutant inputs in the upper estuary. The concentrations of MBP also varied with season, with November > August > May > February. Significant correlations existed between MBP and total phosphorus (TP), organic phosphorus (OP), inorganic phosphorus (IP), organic carbon (OC), total nitrogen (TN), the grain size, and redox potential (Eh), suggesting that these sedimentary environmental characteristics played an important role in controlling the MBP levels in the sediments. Notably, there were positive linear relationships between the concentrations of soluble reactive phosphorus (SRP), TP, and chlorophyll a (Chl a) in bottom water and MBP in sediments. These relationships might be very complicated and need further exploration. This work is the first comprehensive study of the seasonal and spatial distribution of MBP in sediments and its relationships with environmental factors in a typical estuary, and will lead to deeper understanding of the phosphorus (P) biogeochemical cycle.
[Show abstract][Hide abstract] ABSTRACT: We studied the possible role that marine microalgae may play during the outbreaks of WSS (white spot syndrome). In order to elucidate the possibility of marine microalgae carrying WSSV (white spot syndrome virus), six marine microalgae (Isochrysis galbana, Skeletonema costatum, Chlorella sp., Heterosigma akashiwo, Scrippsiella trochoidea, Dunaliella salina) were co-cultured with adult Marsupenaeus japonicus infected with WSSV and were assayed daily by nested-PCR to study whether they could carry WSSV. Further experiments were conducted to investigate whether the virus carried by microalgae could re-infect juvenile M. japonicus. Results showed that all of the experimental microalgae, except H. akashiwo could carry WSSV, and among them, Chlorella sp. and S. trochoidea had the strongest WSSV-carrying ability. Unlike other invertebrate carriers of WSSV, the WSSV detections in microalgae, which were positive after 1 and 3 days, were negative after 10days of incubation. WSSV detection results in juvenile M. japonicus showed that the juvenile shrimp were re-infected by co-cultured Chlorella sp., although the juvenile M. japonicus carried so small an amount of WSSV that it could only be detected by nested-PCR. The results of this experiment suggest that microalgae might be one possible horizontal transmission pathway for WSSV. Further research, however, is required to better understand the factors behind the different carrying abilities and virus-carrying mechanisms of different microalgae.
[Show abstract][Hide abstract] ABSTRACT: The effects of fresh thalli and culture medium filtrates from two species of marine macroalgae, Ulva pertusa Kjellm (Chlorophyta) and Gracilaria lemaneiformis (Bory) Dawson (Rhodophyta), on growth of marine microalgae were investigated in co-culture under controlled laboratory conditions. A selection of microalgal species were used, all being identified as bloom-forming dinoflagellates: Prorocentrum donghaiense Lu sp., Alexandrium tamarense (Lebour) Balech, Amphidinium carterae Hulburt and Scrippsiella trochoide (Stein) Loeblich III. Results showed that the fresh thalli of either U. pertusa or G. lemaneiformis significantly inhibited the microalgal growth, or caused mortality at the end of the experiment. However, the overall effects of the macroalgal culture filtrates on the growth of the dinoflagellates were species-specific (inhibitory, stimulatory or none) for different microalgal species. Results indicated an allelopathic effect of macroalga on the co-cultured dinoflagellate. We then took P. donghaiense as an example to further assess this hypothesis. The present study was carried out under controlled conditions, thereby excluded the fluctuation in light and temperature. Nutrient assays showed that nitrate and phosphate were almost exhausted in G. lemaneiformis co-culture, but remained at enough high levels in U. pertusa co-culture, which were well above the nutrient limitation for the microalgal growth, when all cells of P. donghaiense were killed in the co-culture. Daily f/2 medium enrichment greatly alleviated the growth inhibition on P. donghaiense in G. lemaneiformis co-culture, but could not eliminate it. Other environmental factors, such as carbonate limitation, bacterial presence and the change of pH were also not necessary for the results. We thus concluded that allelopathy was the most possible reason leading to the negative effect of U. pertusa on P. donghaiense, and the combined roles of allelopathy and nutrient competition were essential for the effect of G. lemaneiformis on P. donghaiense.