Exploration of Antifouling Potential of the Brown Algae <Emphasis Type="Italic">Laminaria</Emphasis> ‘Sanhai’

Seaweeds are one of the largest producers of biomass in the marine environment. It has been well known that marine algae, especially brown algae was a rich source of biogenic compounds with antifouling potential that could be ideal alternatives of tributyltin (TBT). In this paper, antifouling potential of the brown algae Laminaria ‘sanhai’ was explored. Firstly, the dried alga was extracted and the antialgal and antilarval activities were investigated. The EC₅₀ and LC₅₀ values of crude extract of Laminaria ‘sanhai’ against diatom (Skeletonema costatum) and barnacle larval (Chthamalus challengeri) were 8.9 μg mL^?1 and 12.0 μg mL^?1 respectively. Then, guided by bioassay, the bioactive substances were isolated by liquid-liquid extraction. The antialgal and antilarval activities of isolated fraction were improved with the EC₅₀ value of 7.4 μg mL^?1 against S. costatum and LC₅₀ value of 9.7 μg mL^?1 against C. challengeri larvae. Identification by IR, Q-TOFMS and GC-MS of the isolated bioactive substances revealed the abundance of fatty acids. These fatty acids, most with 16, 18 or 20 carbon atoms, contained myristic, hexadecanoic, oleic, linolenic, arachidonic and eicosapentaenoic acids. The results indicated that both the crude extract and the isolated bioactive substances had high antialgal and antilarval activities with no highlighted cytotoxicity which made the brown algae Laminaria ‘sanhai’ a promising source of the environmentally friendly antifoulants.     

Effects of different phosphorus concentrations and N/P ratios on the growth and photosynthetic characteristics of <Emphasis Type="Italic">Skeletonema costatum</Emphasis> and <Emphasis Type="Italic">Prorocentrum donghaiense</Emphasis>

The effects of different phosphorus (P) concentrations (0.36, 3.6, and 36 μmol/L corresponding to low-, middle-, and high-P concentration groups, respectively) and nitrogen (N)/P ratios on the growth and photosynthetic characteristics of Skeletonema costatum and Prorocentrum donghaiense were studied. For both species, the high-P (HP) concentration group showed the greatest algal density and highest specific growth rate. Changes in the maximum efficiency of photosystem II (F _v /F _m ) were monitored under the various P and N/P conditions. The largest decrease in F _v /F _m was in the low-P (LP) group in S. costatum and in the HP group in P. donghaiense. There were high rapid light curves and photochemical quantum yields (Φ _PSII) for S. costatum in the HP group, while the actual photosynthetic capacity was higher in P. donghaiense than in S. costatum in the MP group. Under eutrophic but relatively P-restricted conditions, P. donghaiense had higher photosynthetic activity and potential, which could cause this dinoflagellate to increasingly dominate the phytoplankton community in these conditions. Under the same P concentration and N/P ratio, P. donghaiense had a larger relative maximum rate of electron transport and higher Φ _{PS II} values than those of S. costatum. These differences between P. donghaiense and S. costatum may explain the interaction and succession patterns of these two species in the Changjiang (Yangtze) River estuary from a photosynthesis perspective.     

Antifouling effect of bioactive compounds from selected marine organisms in the Obhur Creek,Red Sea

Three species of sponges and a tunicate were collected from Obhur creek of Jeddah coast for this bioactivity study. In order to assess the antifouling efficacy of selected marine organisms, methanolic extracts of these organisms were tested against different fouling bacterial forms and II-instar stage of the barnacle, Balanus amphitrite. Antibiosis, bioactivity and followed by multivariate analyses were carried out to check the efficacy of antifouling effect of the selected marine organisms. Principal component analysis revealed the exemplary antifouling efficacy of the sponge extracts of Stylissa sp. observed followed by Hyrtios sp. against bacterial forms in the laboratory study. De-trended correspondence analysis confirmed that the contribution of antifouling efficacy of the selected sponge extracts was observed to be more towards Bacillus sp., Vibrio sp. and Alteromonas sp. Moreover, the efficacy of Hyrtios sp. extract(20.430 μg m L~(-1)) followed by Stylissa sp.(30.945 μg m L~(-1)) showed higher against barnacle instar compared with other extracts in the bioactivity assay. Bray-Curtis cluster analysis under paired linkage categorized all the sponge extracts into one major cluster with 75% similarity, and one outlier tunicate. More than 80% similarity observed between Hyrtios sp. and Stylissa sp. Fourier transform infrared spectroscopy(FTIR) showed that the contribution of major peaks found in the marine organisms were towards sulfones, sulfoxides, cyanates and ketones.     

Significance of different microalgal species for growth of moon jellyfish ephyrae, <Emphasis Type="Italic">Aurelia</Emphasis> sp.1

The scyphozoan Aurelia aurita (Linnaeus) sp. l., is a cosmopolitan species-complex which blooms seasonally in a variety of coastal and shelf sea environments around the world. The effects of different microalgal species on the growth of newly-released Aurelia sp.1 ephyrae were studied under laboratory conditions. We fed ephyrae with four different microalgal species (diatom, autotrophic dinoflagellate, heterotrophic dinoflagellate, and chlorophyta) plus Artemia nauplii for 12-24 d at 18°C. Results showed that the growth rate diverged significantly for Artemia nauplii compared to other food types. In addition, there was no significant variation between the growth rates for Skeletonema costatum and Prorocentrum donghaiense, and no significant variation was found in the growth rates for N. scintillans and P. subcordiformis. Artemia nauplii could support the energy requirement for the newly-released ephyrae to develop to meduase, and the ephyrae with Artemia nauplii showed a significant average growth rate of 25.85% d^?1. Newly-released ephyrae could grow slightly with some species of microalgae in the earliest development stage. Chain diatom Skeletonema costatum and autotrophic dinoflagellate Prorocentrum donghaiense, could not support the growth of the ephyrae, while heterotrophic dinoflagellate Noctiluca scintillans and chlorophyta Platymonas subcordiformis could support the growth of the ephyrae. However, none of the ephyrae fed with the tested phytoplankton could mature to medusae.     

Molecular weight controllable degradation of <Emphasis Type="Italic">Laminaria japonica</Emphasis> polysaccharides and its antioxidant properties

In this study, molecular weight controllable degradation of algal Laminaria japonica polysaccharides（LPS） was investigated by ultrasound combined with hydrogen peroxide. Three main factors, i.e., ultrasonic power（A）, ultrasonic time（B）, and H₂O₂ concentration（C） were chosen for optimizing parameters by employing three-factors, three-levels BBD. The influence of degradation on structure change and antioxidant activities was also investigated. A second-order polynomial equation including molecular weight（Y） of Laminaria japonica polysaccharides and each variable parameter, i.e., ultrasonic power（A）, ultrasonic time（B）, and H₂O₂ concentration（C）, was established: Y=20718.67-4273.13A-4000.38B-1438.75C+2333.25AB+1511.00AC+873.00BC+2838.29A² + 2490.79B²+873.04C². The equation regression coefficient value（R² = 0.969） indicated that this equation was valid. The value of the adjusted determination coefficient（adjusted R² = 0.914） also confirmed that the model was highly significant. The results of selected experimental degradation conditions matched with the predicted value. FT-IR spectra revealed that the structures of LPS before and after degradation were not significantly changed. Antioxidant activities of LPS revealed that low Mws possessed stronger inhibitory than the original polysaccharides. The scavenging effects on superoxide radicals was the highest when IC50 of crude LPS was 4.92 mg mL^-1 and IC50 of Mw 18.576 KDa was 1.02 mg mL^-1, which was fourfold higher than initial polysaccharide.     

Genetic transformation of <Emphasis Type="Italic">Nannochloropsis oculata</Emphasis> with a bacterial phleomycin resistance gene as dominant selective marker

The gene ble from Streptoalloteichus hindustanus is widely used as a selective antibiotic marker. It can control the phleomycin resistance, and significantly increase the tolerance of hosts to zeocin. The unicellular marine microalga Nannochloropsis oculata is extremely sensitive to zeocin. We selected ble as the selective marker for the genetic transformation of N. oculata. After the algal cells at a density of 2×10⁷ cells mL^?1 was digested with 4% hemicellulase and 2% driselase for 1 h, the protoplasts accounted for 90% of the total. The ble was placed at the downstream of promoter HSP70A-RUBS2 isolated from Chlamydomonas reinhardtii, yielding a recombinant expression construct pMS188. The construct was transferred into the protoplasts through electroporation (1 kV, 15 μS). The transformed protoplasts were cultured in fresh f/2 liquid medium, and selected on solid f/2 medium supplemented with 500 ng mL^?1 zeocin. The PCR result proved that ble existed in the transformants. Three transformants had been cultured for at least 5 generations without losing ble. Southern blotting analysis showed that the ble has been integrated into the genome of N. oculata. The ble will serve as a new dominant selective marker in genetic engineering N. oculata.     

The impact of atmospheric deposition of cadmium on dominant algal species in the East China Sea

Cadmium(Cd) mainly derived from anthropogenic emissions can be transported through atmospheric pathway to marine ecosystem,affecting the phytoplankton community and primary productivity.In this study,we identified the toxicity threshold of Cd for phytoplankton under seawater conditions of the coastal East China Sea(ECS) through both laboratory and in situ mesocosm incubation experiments.The mesocosm experiment showed that Cd in low concentration(0.003 μg per μg chl a) was conducive to the growth of natural community and increased chl a productivity.In high concentration(0.03 μg per μg chl a) Cd acted as an inhibiting factor which decreased the total chl a productivity.The diatom community was found to be more sensitive to Cd toxicity than dinoflagellate,as the low concentration Cd showed toxicity to diatom but enhanced dinoflagellate growth.We noticed that the soluble Cd estimated from atmosphere deposition to the coastal ECS was below the toxicity threshold and the Cd deposition might promote phytoplankton growth in this region.In our laboratory experiments,adding Cd,similar to aerosol deposition,stimulated the growth of both dominant algal species Prorocentrum donghaiense Lu(dinoflagellate) and Skeletonema costatum(diatom).Adding Cd on a higher level inhibited the growth of both the species,but Skeletonema costatum seemed obviously more sensitive to toxicity.This indicates the potential impact of atmospheric deposition Cd on phytoplankton community succession in the ECS.     

Carbon budget of bastard halibut<Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> in relation to body weight and temperature

The effects of body weight and temperature on the carbon budget of the juvenile bastard halibut ,Paralichthys olivaceus ,were studied at temperature 13.5,18,21.5 and 24℃,respectively.The carbon intake,faecal and growth carbon were measured ,and the carbon respiration was calculated using the carbon budget equation (Cc=Gc Fc Rc),The combined relationship between different components of the carbon budgent,body weight and temperature could be described by regression equations:Cc=1.0206 W^0.8126E^0.1483T;Gc=0.0042w^1.4096(-5.11 T^3 285.90T^2-5173.72T 30314.03);Fc=0.0485W^0.7711e^0.1624T;Uc=1.4333W^0.6715e^0.1487t,Body weight had no significant effect on the carbon absorption efficiency and the conversion efficiency.     

Biodegradation of <Emphasis Type="Italic">Enteromorpha</Emphasis> polysaccharides by intestinal micro-community from <Emphasis Type="Italic">Siganus oramin</Emphasis>

Micro-communities are supposed to have more potential functions of biodegradation of polysaccharides than single strain; however, the intestinal micro-communities involved in the biodegradation of Enteromorpha polysaccharides (EP) were seldom reported. In order to obtain the EP-degrading micro-community, the intestines of Siganus oramin was obtained to isolate the micro-communities, which were enriched by 0.3% of EP as the sole carbon source. A stable micro-community with EP degradative capability was achieved after seven generations of subculture, named H1. Results showed that H1 was able to degrade 75% of EP within 24 hours, and the activity of EP lyases reached 500 U mL^?1 in 32 hours. With denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene clone library analysis, ten bacteria closely related to Marinomonas pontica, Microbacterium sp., Leucobacter chironomi, Cyclobacterium sp., Algoriphagus winogradskyi, Pseudoalteromonas sp. and Vibrio sp. were determined. Furthermore, compared with the DGGE bands sequence and the clone library analysis, the dominant bacteria of the EP-biodegrading micro- community were Pseudoalteromonas sp. and Vibrio sp., with the respective proportion of 38% and 46%, and they should play an important role in EP degradation together with other degrading bacteria in the micro-community H1.     

Impact of several harmful algal bloom (HAB) causing species,on life history characteristics of rotifer <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> Müller

In recent years, harmful algal blooms (HABs) have occurred frequently along the coast of China, and have been exhibiting succession from diatom- to dinoflagellate-dominated blooms. To examine the effects of different diatom and dinoflagellate HABs, the life history parameters of rotifers (Brachionus plicatilis Müller) were measured after exposure to different concentrations of HAB species. The HAB species examined included a diatom (Skeletonema costatum) and four dinoflagellates (Prorocentrum donghaiense, Alexandrium catenella, Prorocentrum lima and Karlodinium veneficum). Compared with the control treatment (CT), the diatom S. costatum showed no adverse impacts on rotifers. Exposure to dinoflagellates at densities equivalent to those measured in the field resulted in a reduction in all the life history parameters measured. This included a reduction in: lifetime egg production (CT: 20.34 eggs/ind.) reduced to 10.11, 3.22, 4.17, 7.16 eggs/ind., life span (CT: 394.53 h) reduced to 261.11, 162.90, 203.67, 196 h, net reproductive rate (CT: 19.51/ind.) reduced to 3.01, 1.26, 3.53, 5.96/ind., finite rate of increase (CT: 1.47/d) reduced to 1.16, 1.03, 1.33, 1.38/d, and intrinsic rate of population increase (CT: 0.39/d) reduced to 0.15, 0.03, 0.28, 0.32/d, for the dinoflagellates P. donghaiense, A. catenella, P. lima and K. veneficum, respectively. The results showed that the diatom S. costatum had no detrimental consequences on the reproduction and growth of B. plicatilis, however, the four dinoflagellates tested did show adverse effects. This suggests that dinoflagellate HABs may suppress microzooplankton, resulting in an increase in algal numbers.     

Temporal and spatial variations of abundance of phycocyanin- and phycoerythrin-rich <Emphasis Type="Italic">Synechococcus</Emphasis> in Pearl River Estuary and adjacent coastal area

Three surveys were carried out in Pearl River Estuary and adjacent coastal area in May, August, and November, 2013, to investigate the temporal and spatial variations of abundance of phycoerythrin-rich Synechococcus (PE-rich SYN) and phycocyanin-rich Synechococcus (PC-rich SYN). The effects of environmental factors on the alternation of the different Synechococcus groups were also elucidated. PE-rich SYN was detected in three surveys, whereas PC-rich SYN was detected in May and August, but not in November. The highest abundances of PE-rich SYN and PC-rich SYN were recorded in August and May, with mean values of 74.17×10³ and 189.92×10³ cells mL^?1, respectively. From May to November, the relative abundance of PE-rich SYN increased, whereas that of PC-rich SYN declined. PE-rich and PC-rich SYN presented similar horizontal distributions with high abundance in the southern estuary in May, and in the western estuary in August. The abundances of PE-rich and PC-rich SYN were high at 27–32°C and salinity of 10–20. PC-rich SYN was not detected at < 24°C, and PC:PE-rich SYN decreased in abundance with salinity increase. When less than 20 mg L^?1, suspended particulate matter (SPM) was helpful for Synechococcus growth. PE-rich SYN decreased in abundance when the concentration of dissolved inorganic nitrogen increased in May and November, and the concentration of phosphate increased in November. However, PC-rich SYN abundance and nutrients showed no correlation. Principal component analysis and regression analysis indicated that PE-rich SYN significantly correlated with the principal components that were affected by environmental factors.     

The metabolite profiling of coastal coccolithophorid species <Emphasis Type="Italic">Pleurochrysis carterae</Emphasis> (Haptophyta)

Pleurochrysis carterae is a calcified coccolithophorid species that usually blooms in the coastal area and causes aquaculture losses. The cellular calcification, blooming and many other critical species specific eco-physiological processes are closely related to various metabolic pathways. The purpose of this study is to apply the unbiased and non-destructive method of nuclear magnetic resonance (NMR) to detect the unknown holistic metabolite of P. carterae. The results show that NMR spectroscopic method is practical in the analysis of metabolites of phytoplankton. The metabolome of P. carterae was dominated by 26 metabolites involved in a number of different primary and secondary metabolic pathways. Organic acids and their derivatives, amino acids, sugars, nucleic aides were mainly detected. The abundant metabolites are that closely related to the process of cellular osmotic adjustment, which possibly reflect the active ability of P. carterae to adapt to the versatile coastal niche. DMSP (dimethylsulphoniopropionate) was the most dominant metabolite in P. carterae, up to 2.065±0.278 mg/g lyophilized cells, followed by glutamate and lactose, the contents were 0.349±0.035 and 0.301±0.073 mg/g lyophilized cells respectively. Other metabolites that had the content ranged between 0.1–0.2 mg/g lyophilized cells were alanine, isethionate and arabinose. Amino acid (valine, phenylalanine, isoleucine, tyrosine), organic acid salts (lactate, succinate), scyllitol and uracil had content ranged from 0.01 to below 0.1 mg/g lyophilized cells. Trigonelline, fumarate and formate were detected in very low content (only thousandths of 1 mg per gram of lyophilized cells or below). Our results of the holistic metabolites of P. carterae are the basic references for the further studies when multiple problems will be addressed to this notorious blooming calcifying species.     

Seasonal variations in the phytoplankton community and the relationship between environmental factors of the sea around Xiaoheishan Island in China

Seasonal variations in the phytoplankton community and the relationship between environmental factors of the sea area around Xiaoheishan Island are investigated in the present study. Xiaoheishan Island is located at 37°58′14″N and 120°38′46″E in Shandong Province, China. A total of 65 species of phytoplankton belonging to three phyla and 27 genera were identified, with Bacillariophyta having the largest number of species. The annual average chlorophyll a concentration for this area was 3.11 μg/L, and there occurs a Skeletonema costatum bloom in winter. The Shannon-Weaver indexes(log_2) of the phytoplankton from all stations were higher than 1, and the Pielou indexes were all higher than 0.3. The results of the canonical correspondence analysis(CCA) indicated that water temperature, PO_4~(3ˉ) and Cu were the environmental factors that had the greatest influence on the distribution of the phytoplankton community throughout the entire year. Although the concentration of heavy metal is well up to the state standards of the first grade of China(GB 3097-1997), these metals still have an impact on the phytoplankton community from this area.     

Inbreeding depression on growth and survival of full-sib family of Manila clam (<Emphasis Type="Italic">Ruditapes philippinarum</Emphasis>)

In present study, the inbreeding depression (ID) of growth and survival of Manila clam (Ruditapes philippinarum) was investigated at larval and juvenile stages. Nine inbred families (A ₂, B ₂, C ₂, D ₂, E ₂, F ₂, G ₂, H ₂ and I ₂) were established by mating within nine full-sib families with expected inbreeding coefficient of 0.25. Inbred families showed significant differences in shell length and hatching rate of D-larvae (straight-hinged larvae). The larvae of the nine inbred families grew slower than those of control group (CG), and their ID value ranged from 0.81% ± 6.09% to 16.10% ± 1.49%. The ID value of larval survival rate varied between 27.47% ± 9.36% and 70.50% ± 13.66%. The ID was also detected for juvenile growth in A ₂, B ₂, C ₂, and D ₂, which ranged from 4.60 ± 2.21 to 17.71 ± 7.73. The A ₂ family maintained the highest juvenile survival rate, whereas the other inbred families exhibited ID values varying between 62.79% ± 4.54% and 96.14% ± 0.87%. The linear relationship of estimated ID between growth and survival was negatively correlated (R = ?0.434, P < 0.05). The results of this study suggested that the ID of growth was common at the larval stage but was less prevalent at juvenile stage. In contrast, the ID of survival increased from larval to juvenile stage. A better understanding of the effect of inbreeding may aid to selective breeding of Manila clam.     

Free polyamine content during algal bloom succession in the East China Sea in spring 2010

We measured the concentrations and distribution of major polyamines(spermine, putrescine and spermidine) in seawater during successive spring algal blooms in an area of frequent harmful blooms in the East China Sea. Spermine, putrescine, and spermidine concentrations were analyzed by high performance liquid chromatography and ranged from 1–64, 7–81, and 0–19 nmol/L. Spermine was present at the highest concentrations, followed by putrescine and spermidine. In late April, when a diatom bloom dominated by Skeletonema costatum dispersed, polyamine concentrations increased, presumably as a result of diatom decomposition. In early May, when a dinoflagellate bloom dominated by Prorocentrum donghaiense occurred, the polyamine concentration decreased from the level seen in late April. The abundant polyamines that decomposed and were released during the diatom bloom in late April may have promoted the growth of P. donghaiense, resulting in its dominance.     

Diel variation in metabolism and ammonia excretion of <Emphasis Type="Italic">Marphysa sanguinea</Emphasis> (Polychaeta: Eunicidae)

Polychaetes provide an excellent food resource for fish and represent the dominant zoobenthos in marine ecosystems. Diel variation in the rates of metabolism and ammonia-N excretion of Marphysa sanguinea were studied. The worms were grouped according to their wet body weight into small (S; 1.24±0.06 g), medium (M; 4.00±0.30 g), and large (L; 8.54±1.08 g) categories. Their weight-specific metabolic rates, based on aerobic respiration (R), were measured at 16°C (±0.2°C) and classed as either routine (R _R) or standard (R _S) rates. Both respiration types decreased with increasing body weight. Respiration was described by R = a W ^b, where b was -0.400 9 and -0.532 0 for R _R and R _S, respectively. Diurnal changes in R _S for each group was relatively flat, with a slightly increasing trend with time, but was relatively stable as a whole. R _R of the diurnal variation of worms was higher than R S, but both had similar overall trends. The peak values of specific dynamic action (SDA) (R _SDA) in the S, M, and L groups were 2.704, 1.149, and 0.682 mg/(g?h), respectively. The durations of SDA were 13, 6, and 6 h, respectively and the energy expenditures of SDA were 377.98, 117.34, and 74.94 J/g, respectively. These data indicate that the metabolic rates were higher in smaller individuals, which is advantageous for their rapid growth.     

Leaf stable carbon isotope composition in <Emphasis Type="Italic">Picea schrenkiana</Emphasis> var. <Emphasis Type="Italic">tianschanica</Emphasis> in relation to leaf physiological and morphological characteristics along an altitudinal gradient

To understand the effects of leaf physiological and morphological characteristics on δ ¹³C of alpine trees, we examined leaf δ ¹³C value, LA, SD, LNC, LPC, LKC, Chla+b, LDMC, LMA and N_area in one-year-old needles of Picea schrenkiana var. tianschanica at ten points along an altitudinal gradient from 1420 m to 2300 m a.s.l. on the northern slopes of the Tianshan Mountains in northwest China. Our results indicated that all the leaf traits differed significantly among sampling sites along the altitudinal gradient (P<0.001). LA, SD, LPC, LKC increased linearly with increasing elevation, whereas leaf δ ¹³C, LNC, Chla+b, LDMC, LMA and N_area varied non-linearly with changes in altitude. Stepwise multiple regression analyses showed that four controlled physiological and morphological characteristics influenced the variation of δ ¹³C. Among these four controlled factors, LKC was the most profound physiological factor that affected δ ¹³C values, LA was the secondary morphological factor, SD was the third morphological factor, LNC was the last physiological factor. This suggested that leaf δ ¹³C was directly controlled by physiological and morphological adjustments with changing environmental conditions due to the elevation.     

Biodeposition,respiration, and excretion rates of an introduced clam <Emphasis Type="Italic">Mercenaria mercenaria</Emphasis> in ponds with implications for potential competition with the native clam <Emphasis Type="Italic">Meretrix meretrix</Emphasis> in Shuangtaizi estuary,China

This study aimed to evaluate the potential impacts of an introduced clam Mercenaria mercenaria on estuarine ecosystem, and implications for the niche competition with a native clam Meretrix meretrix. The biodeposition, respiration, and excretion rates of M. mercenaria were determined seasonally using a sediment trap and a closed respirator in field. The biodeposition rates of M. mercenaria were 0.06–0.37 g/ (ind.·d), and the respiration rates were 0.31–14.66 mg/(ind.·d). The ammonia and phosphate excretion rates were 0.18–36.70 and 1.44–14.87 μg/(ind.·d), respectively. The hard clam M. mercenaria may discharge dry deposits up to 2.1×10⁵ t, contribute 18.3 t ammonia and 9.0 t phosphate to culture ponds, and consume 7.9×10³ t O₂ from ponds annually. It suggested that the hard clam M. mercenaria might play an important role in pelagic-benthic coupling in pond ecosystem through biodeposition and excretion. A comparison of the key physiological parameters of the introduced clam M. mercenaria and the native clam Meretrix meretrix suggested that M. mercenaria had a niche similar to that of Meretrix meretrix in Shuangtaizi estuary and might have a potential competition with Meretrix meretrix for habitat and food if M. mercenaria species escaped from the culture pond or artificially released in estuarine ecosystem.     

Effects of nitrogen and phosphorus on the growth of <Emphasis Type="Italic">Levanderina fissa</Emphasis>: How it blooms in Pearl River Estuary

Effects of nitrogen (N) and phosphorus (P) from different sources and at different concentrations on the growth of Levanderina fissa (= Gyrodinium instriatum) were studied in laboratory conditions. The findings might explain the recurrent blooms of this species in Pearl River Estuary, China. Results showed that nutrient limitation significantly inhibited the growth of L. fissa. The values of specific growth rate (μ _max) and half-saturation nutrient concentration (K _S) were 0.37 divisions/d and 8.49 μmol L^?1 for N, and 0.39 divisions/d and 1.99 μmol L^?1 for P, respectively. Based on K _S values, dissolved inorganic N level in PRE was sufficient to support the high proliferation of L. fissa, while dissolved inorganic P concentration was far lower than the minimum requirement for its effective growth. L. fissa was not able to utilize dissolved organic N (DON) compounds such as urea, amino acids, and uric acid. However, it grew well by using a wide variety of dissolved organic P (DOP) sources like nucleotides, glycerophosphate, and 4-nitrophenylphosphate. The results from this study suggested that the ability in DOP utilization of L. fissa offers this species a competitive advantage in phytoplankton communities. The high level and continuous supply of DIN, enrichment of DOP, together with warm climate and low salinity in the Pearl River Estuary provided a suitable nutrient niche for the growth of L. fissa, and resulted in the recurrent blooms in the estuary.     

Antioxidant response of ridgetail white prawn <Emphasis Type="Italic">Exopalaemon carinicauda</Emphasis> to harmful dinoflagellate <Emphasis Type="Italic">Prorocentrum minimum</Emphasis> exposure and its histological change

The dinoflagellate Prorocentrum minimum, one of the most widespread red tide causing species, affects marine aquaculture and ecosystems worldwide. In this study, ridgetail white prawn Exopalaemon carinicauda were exposed to P. minimum cells (5 × 10⁴ cells mL^?1) to investigate its harmful effects on the shrimp. Antioxidant activities and histological changes were used as indicators of health status of the shrimp. In 72 hours, the mortality of E. carinicauda was not affected, but its antioxidant response and histology were statistically different from those of control. Elevated superoxide dismutase (SOD) and glutathione peroxidase (GPX) activities and depressed catalase (CAT) activity were observed in gill; while increased SOD, glutathione S-transferase (GST), CAT activities and modulated GPX activity were observed in hepatopancreas. Thus, antioxidant activities in gill and hepatopancreas seem to respond differentially to harmful alga exposure. Increased malondialdehyde (MDA) content in early a few hours indicates the damage of the antioxidant defense system. Although MDA content recovered to a low level thereafter, a series of histological abnormalities including accumulation or infiltration of hemocytes, tissue lesions and necrosis were discovered in gill and hepatopancreas. Exposure to P. minimum induced sublethal effects on E. carinicauda, including temporary oxidative damage and histological injury.