Food webs in forest and pasture streams in the Waikato region,New Zealand: A study based on analyses of stable isotopes of carbon and nitrogen,and fish gut contents

Abstract

Stable isotopes of carbon (C) and nitrogen (N) were studied in 11 stream communities in the Waikato region of New Zealand. From comparisons of mean δ¹³C and δ¹⁵N values, food webs in the shaded, forest streams were clearly based on allochthonous material (conditioned leaf litter and terrestrial invertebrates). Autotrophs in forest streams were not a significant C source for the food webs. However, the C source of food webs in the unshaded pasture streams appeared to be a mixture of allochthonous and autochthonous material. Conditioned leaf litter appeared to contribute to the pasture stream food webs, and the δ¹³C and δ¹⁵N of some samples of epilithic diatoms indicated their consumption by invertebrates in pasture streams. Fish ate a wide range of aquatic invertebrates; longfinned eels (Anguilla dieffenbachii) and banded kokopu (Galaxias fasciatus) also had a large proportion of terrestrial invertebrates in their diet. Filamentous green algae were found only at pasture sites, where they were sometimes abundant. The wide range of δ¹³C values of filamentous green algae (‐18.8 to ‐29.7‰) complicated understanding of their role in the stream food webs. The δ¹³C values of Cladophora were related to water velocity, with more ¹³C‐enriched values in pools than in runs (‐23.2‰ in pools, mean velocity 0.12 m s^?1; ‐28.1‰ in runs, mean velocity 0.24 m s^?1). Crayfish and the gastropod mollusc Potamopyrgus appeared to be the only invertebrates to eat filamentous green algae.     

Fatty acid composition of surface sediments in the subtropical Pearl River estuary and adjacent shelf,Southern China

Surface sediments (10 cm) of the subtropical Pearl River estuary and adjacent shelf, Southern China were collected. Fatty acids and compound-specific carbon isotopic analyses were determined to infer their sources and biogeochemical cycle of this lipid in the subtropical Pearl River estuary and adjacent northern South China Sea (SCS). The total concentrations of fatty acids ranged from ∼1.28 to ∼42.25 μg g⁻¹ dry weight. The levels of polyunsaturated fatty acids (PUFA) were low (0.2–4.8% of total fatty acids), suggesting that fatty acids derived from algae were effectively recycled during the whole settling and depositing process. Bacterial fatty acids were significantly high and terrigenous fatty acids were low in the sediments. Principal component analysis (PCA) of the data also indicates that a clear separation of the biogeochemical sources can be seen. The δ¹³C values of bacterial fatty acids, i.e., i/aiC₁₅ (−22.9‰ to −29.4‰) suggest that bacteria within the sediments mainly utilize a labile pool of organic matter derived from algae for their growth in the subtropical Pearl River estuary system.     

Effects of salinity,temperature, and light intensity on the growth rates of two halophilic phytoflagellates in mixed culture

Growth rates of two halophilic phytoflagellates, Dunaliella euchlora Lerche and D. salina Teodoresco, were studied in mixed batch cultures grown in filtered, axenic brines from Lake Grassmere, New Zealand. Forty‐five combinations of temperature, salinity, and light intensity were used. A maximum growth rate of 1.50 doublings day^‐1 was attained by D. salina at 26°C, 190 × 10^‐3S at a light intensity of 126 μE m^‐2 s^‐1. D. euchlora showed maximum growth rate of 1.16 doublings day^‐1 at 20°C, 120 × 10^‐3S at a light intensity of 180 μE m^‐2s^‐1. Predicted maximum values of 1.41 and 1.14 doublings day^‐1 respectively were obtained from regression models based on 45 replicate treatment combinations. In decreasing order of importance, temperature, salinity, and light intensity influence growth rates of brine algae. The optimum temperature for growth of both species increased as the salt concentration increased but decreased with increasing light intensity.     

Carbon fluxes through major phytoplankton groups during the spring bloom and post-bloom in the Northwestern Mediterranean Sea

The carbon flux through major phytoplankton groups, defined by their pigment markers, was estimated in two contrasting conditions of the Northwestern Mediterranean open ocean ecosystem: the spring bloom and post-bloom situations (hereafter Bloom and Post-bloom, respectively). During Bloom, surface chlorophyll a (Chl a) concentration was higher and dominated by diatoms (53% of Chl a), while during Post-bloom Synechococcus (42%) and Prymnesiophyceae (29%) became dominant. The seawater dilution technique, coupled to high pressure liquid chromatography (HPLC) analysis of pigments and flow cytometry (FCM), was used to estimate growth and grazing rates of major phytoplankton groups in surface waters. Estimated growth rates were corrected for photoacclimation based on FCM-detected changes in red fluorescence per cell. Given the 30% average decrease in the pigment content per cell between the beginning and the end of the incubations, overlooking photoacclimation would have resulted in a 0.40 d^?1 underestimation of phytoplankton growth rates. Corrected average growth rates (μ_o) were 0.90±0.20 (SD) and 0.40±0.14 d^?1 for Bloom and Post-bloom phytoplankton, respectively. Diatoms, Cryptophyceae and Synechococcus were identified as fast-growing groups and Prymnesiophyceae and Prasinophyceae as slow-growing groups across Bloom and Post-bloom conditions. The higher growth rate during Bloom was due to dominance of phytoplankton groups with higher growth rates than those dominating in Post-bloom. Average grazing rates (m) were 0.58±0.20 d^?1 (SD) and 0.31±0.07 d^?1. The proportion of phytoplankton growth consumed by microzooplankton grazing (m/μ_o) tended to be lower in Bloom (0.69±0.34) than in Post-bloom (0.80±0.08). The intensity of nutrient limitation experienced by phytoplankton indicated by μ_o/μ_n (where μ_n is the nutrient-amended growth rate), was similar during Bloom (0.78) and Post-bloom (0.73). Primary production from surface water (PP) was estimated with ¹⁴C incubations. A combination of PP and Chl a synthesis rate yielded C/Chl a ratios of 34±21 and 168±75 (g:g) for Bloom and Post-bloom, respectively. Transformation of group-specific Chl a fluxes into carbon equivalents confirmed the dominant role of diatoms during Bloom and Synechococcus and Prymnesiophyceae during Post-bloom.     

4 种经济海藻脂肪酸组成分析

采用改进的Bligh-Dyer法提取脂溶性成分,气相色谱-质谱联用法(GC-MS)进行分离和鉴定,C19:0内标确定总脂及各组分含量,研究了鼠尾藻(Sargassum thunbergii)、浒苔(Enteromorpha prolifera)、龙须菜(Gracilaria lemaneiformis)和红毛菜(Bangia sp.)4种经济海藻的脂肪酸组成及含量。结果表明,4种海藻都检测出C14-C22脂肪酸,总脂含量在12～19 mg/g之间,不饱和脂肪酸为主要组成成分,含量均超过60%。不饱和脂肪酸中以多不饱和脂肪酸(PUFAs)为主,富含n-3和n-6系列PUFAs,n-6与n-3系列PUFAs之比均低于2。比较4种海藻脂肪酸组成特点表明,鼠尾藻以C16、C18和C20为主要组成成分,具褐藻类脂肪酸组成特征;浒苔以C16和C18为主要组成成分,具绿藻类脂肪酸组成特征;龙须菜和红毛菜以C16和C20类脂肪酸为主,具典型红藻类脂肪酸组成特征,同时二者又有不同之处,分别显示真红藻与原始红藻脂肪酸组成的特点。     

Inorganic nitrogen acquisition by the tropical seagrass Halophila stipulacea

The tropical seagrass Halophila stipulacea is dominant in most regions of the Indo‐Pacific and the Red Sea and was introduced into the Mediterranean Sea after the opening of the Suez canal. The species is considered invasive in the Mediterranean Sea and has been progressively colonizing new areas westward. Growth and photosynthetic responses of H. stipulacea have been described but no information is yet available on the nitrogen nutrition of the species. Here we simultaneously investigated the uptake kinetics of ammonium and nitrate and the internal translocation of incorporated nitrogen in H. stipulacea using ¹⁵N‐labelled substrates across a range of N_i levels (5, 25, 50 and 100 μm ). The ammonium uptake rates exceeded the nitrate uptake rates 100‐fold, revealing a limited capacity of H. stipulacea to use nitrate as an alternative nitrogen source. The uptake rates of ammonium by leaves and roots were comparable up to 100 μm ¹⁵NH₄Cl. At this concentration, the leaf uptake rate was 1.4‐fold higher (6.22 ± 0.70 μmol·g^?1 DW h^?1) than the root uptake rate (4.54 ± 0.28 μmol·g^?1 DW h^?1). The uptake of ammonium followed Michaelis–Menten kinetics, whereas nitrate uptake rates were relatively constant at all nutrient concentrations. The maximum ammonium uptake rate (V_max) and the half‐saturation constant (K_m) of leaves (9.79 μmol·g^?1 DW h^?1 and 57.95 μm , respectively) were slightly higher than that of roots (6.09 μmol·g^?1DW h^?1 and 30.85 μm , respectively), whereas the affinity coefficients (α = V_max/K_m) for ammonium of leaves (0.17) and roots (0.20) were comparable, a characteristic that is unique among seagrass species. No substantial translocation (<2.5%) of ¹⁵N incorporated as ammonium was detected between plant parts, whereas the translocation of ¹⁵N incorporated as nitrate was higher (40–100%). We conclude that the N_i acquisition strategy of H. stipulacea, characterized by a similar uptake capacity and efficiency of leaves and roots, favors the geographical expansion potential of the species into areas with variable water‐sediment N levels throughout the Mediterranean.     

Growth rates and ecology of coralline rhodoliths from the Ras Ghamila back reef lagoon,Red Sea

Rhodoliths are important marine carbonate producers that provide habitat for several marine organisms, and are threatened by ongoing global climate change. Meter‐sized sedimentary patches rich in living rhodoliths, interspersed among corals, were discovered in the back reef of Ras Ghamila lagoon, Southern Sinai, at less than 1 m water depth. In this shallow and relatively sheltered subtropical environment, rhodoliths were found to be monospecific or oligospecific, spheroidal, 3.5 to 9.4 cm in maximum diameter, with warty/lumpy or fruticose (protuberance degree IV) growth forms, and corresponded to the unattached branches or praline type. They grew in bright light under seasonal, moderate, wind‐driven water motion. The dominant rhodolith‐forming species recorded were: Lithophyllum kotschyanum, Porolithon onkodes, Hydrolithon sp. and three species of Neogoniolithon: Neogoniolithon fosliei, Neogoniolithon brassica‐florida, and an undescribed species noted in the text as Neogoniolithon sp. A total of 38 Alizarin‐stained rhodoliths was released in the field and collected after 1 year. They showed different banding patterns (alternating long and short cells) that revealed seasonal growth, with the lowest rates occurring in winter for all species, and an additional summer growth slackening in Neogoniolithon fosliei. Lithophyllum kotschyanum presented evidence of occasional growth cessation, possibly due to temporary burial. The observed annual growth rate of rhodoliths was unrelated to their size. The mean accretion rates were 1.08 mm · year^?1 in L. kotschyanum, 0.75 mm · year^?1 in P. onkodes, 0.49 mm · year^?1 in Hydrolithon sp., 0.85 mm mm · year^?1 in N. fosliei, 0.63 mm · year^?1 in N. brassica‐florida and 0.57 mm · year^?1 in Neogoniolithon sp. The annual mean marginal elongation rate for these taxa was respectively 8.74, 13.92, 3.59, 9.40 and 9.25 mm · year^?1, with the exception of Neogoniolithon sp., for which this parameter was not recorded. Maximum marginal elongation occurred in P. onkodes pointing out its greater ability as a space competitor in comparison with the other rhodolith species. The highest accretion rate and common presence of L. kotschyanum indicate its importance as carbonate producer in tropical reef.     

小球藻对不同盐度海水养殖尾水的净化效果研究

微藻处理养殖尾水已成为热点研究方向,有关一定盐度范围内海水养殖尾水的微藻处理研究较少。本试验调配了两种盐度(16和26)的海水养殖尾水,以空白组作对照,设置小球藻(Chlorella salina)初始接种密度梯度(5×10⁵、1×10⁶、2×10⁶和3×10⁶个/mL),研究小球藻对海水养殖尾水中不同形态氮和磷的去除效果。结果表明,小球藻在海水养殖尾水中生长良好,可有效去除尾水中的氮磷营养盐,16盐度组中各初始藻密度组对NH₄⁺、NO₃^-和总溶解态氮(total dissolved nitrogen,TDN)的去除率分别为85.03%~85.87%、60.87%~63.70%和54.53%~57.64%,组间无显著差异(P>0.05);26盐度组中除5×10⁵组外,其余藻密度组对NH₄⁺、NO₃^-和TDN的去除率分别为87.23%~88.16%、56.70%~57.79%和53.31%~54.62%,且组间无显著差异(P>0.05),表明小球藻初始接种密度对尾水中氮盐的去除无显著影响。除5×10⁵个/mL组外,16与26盐度组中对TDN的去除率无显著差异,表明盐度变化对氮的去除无影响。随着初始藻密度的升高,16和26处理组对总溶解态磷(total dissolved phosphorus,TDP)的去除率均上升,分别为76.13%~99.53%和63.72%~96.83%,表明藻初始接种密度的升高可促进尾水中磷的去除,且盐度升高没有影响小球藻对磷的去除。本研究获得了不同初始接种密度小球藻对一定盐度范围的海水养殖尾水的吸收利用特点,可为海水养殖尾水的生态化处理提供一定的理论基础。     

The application of isotopic and biogeochemical markers to the study of the biochemistry of organic matter in a macrotidal estuary, the Loire, France

The biogeochemistry of organic matter in a macrotidal estuary, the Loire, France, has been studied for two years during different seasons. Both particulate matter and sediment have been sampled in the riverine zone, in the maximum turbidity zone and in the ocean near the river mouth. Two techniques have been used: carbon isotopic ratio determination and analysis of lipid-marker signatures in the n-alkane, n-alkene and fatty acid series. For the period corresponding to the output of the maximum turbidity zone in the ocean, the complete change of organic matter, continental in nature in the inner estuary, pure marine in the outer estuary is well illustrated by the decrease of δ¹³C values and of carbon preference index of n-alkanes. Input sources of organic matter by continental plants, plankton and micro-organisms are discussed from biogeochemical-marker analyses data along with the processes of accumulation of particles and their evolution with the season. Some criteria for evidencing the nature of various organic-matter pools are assessed and compared in different chemical-marker series as follows: high molecular weight n-alkanes and fatty acids, perylene for continental imprints, polyunsaturated 18-, 20- and 22-carbon fatty acids, n-C₁₇, n-alkenes and squalene for algae imprints, branched iso and anteiso fatty acids, Δ11-C_18:1 for microbial imprints.     

Saldanha Bay,South Africa II: estimating bay productivity

Saldanha Bay is a narrow-mouth bay on the west coast of South Africa linked to the southern Benguela upwelling system. Bay productivity was investigated by use of the conventional light-and-dark bottle oxygen method, and, for comparison, through assimilation of the stable isotope tracer ¹³C. Gross community production GCP and net community production NCP, as determined from the oxygen method, were respectively 2.6 and 2.4 times higher than estimates determined from the stable isotope method. Chlorophyll a (Chl a) concentrations increased with the onset of spring and well-defined subsurface maxima developed in association with increasingly stratified conditions (mean water column Chl a concentrations ranged from 5.4 to 31.5?mg m^?3 [mean 15.5?mg m^?3; SD 7.6]). A sharp decline in photosynthetic rates P* (GCP normalised to Chl a concentration) with depth was attributed to light limitation, as demonstrated by the high vertical attenuation coefficients for downward irradiance K_d, which varied from 0.29 to 0.70?m^?1 (mean 0.48?m^?1; SD 0.12). Productivity maxima were consequently near-surface despite the presence of deeper subsurface biomass maxima. The community compensation depth Z_cc, where gross community production balances respiratory carbon loss for the entire community, ranged from 2.9 to 9.2?m (mean 5.8?m; SD 2.2), and was typically shallower than the 1% light depth for PAR (photosynthetically available radiation), Z1%PAR, which is traditionally assumed to be the depth of the euphotic zone and which ranged from 6.6 to 15.9?m (mean 9?m; SD 2.6). Autotrophic communities, where organic matter is produced in excess of respiratory demand, were confined on average to the upper 5.8?m of the water column, and often excluded the bulk of the phytoplankton community, where light limitation is considered to lead to heterotrophic community metabolism. Estimates of integrated water column productivity ranged from 0.84 to 8.46?g C m–2 d^?1 (mean 3.35?g C m^?2 d^?1; SD 1.9).     

Dominant amphipods of Posidonia oceanica seagrass meadows display considerable trophic diversity

Gut content examination and trophic markers (fatty acids, stable isotopes of C and N) were combined to delineate the diet of the dominant species of amphipods from Mediterranean Posidonia oceanica seagrass meadows and to highlight trophic diversity among this community. Our results indicate that, although all dominant species heavily relied on macroalgal epiphytes, considerable interspecific dietary differences existed. Carbon stable isotope ratios notably showed that some of the amphipod species favored grazing on epiphytes from leaves or litter fragments (Apherusa chiereghinii, Aora spinicornis, Gammarus aequicauda), while others such as Dexamine spiniventris preferred epiphytes from rhizomes. The remaining amphipods (Caprella acanthifera, Ampithoe helleri and Gammarella fucicola) readily consumed both groups. In addition, SIAR modeling suggested that most species had a mixed diet, and relied on several food items. Fatty acid analysis and gut contents revealed that contributions of microepiphytic diatoms and of benthic and suspended particulate organic matter to the diet of amphipods were anecdotal. None of the examined species seemed to graze on their seagrass host [low 18:2(n‐6) and 18:3(n‐3) fatty acids contents], but Gammarus aequicauda partly relied on seagrass leaf detritus, as demonstrated by the lesser ¹³C‐depletion of their tissues. Overall, our findings suggest that amphipods, because of their importance in the transfer of organic matter from primary producers and detritus to higher rank consumers, are key items in P. oceanica‐associated food webs.     

An experimental study of microflagellate bacterivory: further evidence for the importance and complexity of microplanktonic interactions

By simulating an upwelling event in a laboratory microcosm, it was possible to promote the development of a natural and diverse planktonic community. An initial bacterioplankton community which developed in response to phytoplankton growth was dominated by small coccoid forms (0,14–0,2 μm³) of the genera Vibrio and Pseudomonas. This group was heavily exploited by the heterotrophic microflagellate Pseudobodo sp. (30 μm³). Later, the bacterioplankton community was dominated by large rods (0,7 μm³) which the flagellates seemed unable to exploit. A Lotka-Volterra predator-prey model fitted to the observed data indicated that the flagellates consumed 2,4 times their carbon body mass per day or 19 bacteria·flagellate^?1·h^?1 when prey were not limiting. Clearance rates were inversely proportional to prey density and ingestion rate, ranging from 2 × 10^?3 to 20 × 10^?3) μ?·flagellate^?1·h^?1. At typical field densities of bacteria and heterotrophic flagellates in the southern Benguela region, between 5 and 30 percent of the water column could be cleared per day. Specific growth rates of the flagellates were positively related to prey density, the maximal rate being 0,84 · d^?1. Their initially faster growth rates allowed bacteria to increase in numbers despite predation. The growth yield of the flagellates (34–36 per cent) was also positively related to food density. Such low values suggest inefficient transfer of carbon to higher trophic orders but considerable nitrogen regeneration. Nitrogen excretion rates were approximately 6–7 μg N·mg dry weight^?1·h^?1, comparable to other flagellates but faster than ciliates. These rates are comparable with in situ measurements of NH⁺₄-N excretion in pycnoclinal regions based on ¹⁵N isotope studies but are only about 20 per cent of measured rates in surface waters. This is interpreted to mean that, in pycnoclinal regions where the relative input of "new" nitrogen is high, there are few regenerative steps and the model describes them satisfactorily. In surface waters, observed rates of excretion can only be accounted for by many regenerative steps in a highly complex food chain in which the cumulative total of nitrogen excretion at each step amounts to that based on ¹⁵N labelling studies.     

Nutritional condition of two coastal rocky fishes and the potential role of a marine protected area

Knowledge of the nutritional conditions of coastal commercial fish populations is key to understanding stock health status, and is essential when making reasonable exploitation and management plans. Here, we present the first results on the condition and feeding preferences of two coastal fish species, Diplodus sargus (Linnaeus, 1758) and Pagellus erythrinus (Linnaeus, 1758). Using stable isotope and biochemical analyses, we tested the potential effects of a marine protected area (MPA) and the occurrence of a dramatic coastal storm on the condition and quality of nutrition. The results suggest that both condition (lipids) and nutrition quality (fatty acids, FAs) in P. erythrinus and D. sargus depend upon on food availability in the area in which they were captured. Pagellus erythrinus individuals inside the MPA stored higher quantities of lipids [46.73 ± 19.00 μg lipid·mg organic matter (OM)^?1] than those outside the MPA (15.63 ± 5.30 μg lipid·mg OM^?1) only before the storm. Diplodus sargus showed different FA signatures inside and outside the MPA before and after the storm. These results suggest that D. sargus increased their quality of nutrition inside (16.62 ± 3.17 μg FA·mg OM^?1) versus outside (7.88 ± 2.36 μg FA·mg OM^?1) the MPA, owing to increased food diversity and availability. Conversely, P. erythrinus did not show differences in nutritional quality inside (18.12 ± 1.13 μg FA·mg OM^?1) or outside (18.81 ± 1.42 μg FA·mg OM^?1) the MPA, possibly because of the increase in ingestion not affecting the studied parameters. In P. erythrinus, the FA concentration decreased after the storm, but in D. sargus, a change in lipid composition was observed. These results suggest that P. erythrinus appears to be more impacted by food quality (different saturated and unsaturated FAs) than D. sargus, owing to a more restrictive diet. We hypothesize that the observed differences between inside and outside the MPA are not only related to the degree of protection, but also to the feeding preferences and behaviour of both fishes.     

Effect of temperature on an alga‐grazer trophic transfer: A dual stable isotope (13C, 15N) labeling experiment

In this study, we examined the impact of temperature on the carbon and nitrogen trophic transfers from a macroalga to a macro‐grazer by the use of dual ¹³C‐ and ¹⁵N‐labeling. Using an experimental approach in mesocosms, individuals of the urchin Psammechinus miliaris were maintained for 1 month at 17°C (mean summer temperature in the Bay of Brest) and at 20°C (maximum summer temperature) and fed with ¹³C‐ and ¹⁵N‐labeled Solieria chordalis. The results showed that the urchins’ ¹³C uptake was 0.30 µg¹³C g dry weight (DW)^?1 at 17°C and 0.14 µg¹³C g DW^?1 at 20°C at the end of the experiment. The lower uptake at the higher temperature may be attributed to a decrease in metabolic activity at 20°C, involving lower feeding and/or respiration rates. Conversely, no significant effect of temperature was detected on ¹⁵N uptake. At the end of the experiment, the urchins’ ¹⁵N uptake was 0.04 µg¹⁵N g DW^?1 at 17°C and 0.03 µg¹⁵N g DW^?1 at 20°C. This suggests that temperature may affect carbon and nitrogen trophic fluxes differently. The use of dual isotope labeling offers interesting prospects and needs to be further extended in order to better understand trophic interactions in marine communities and the consequences of current environmental changes, such as global warming.     

基于脂肪酸生物标记法探讨中国沿海六群体绒螯蟹(Eriocheir sensu stricto)的种群遗传

水产动物肌肉中的脂肪酸组成可用于评价其种群遗传。本研究通过测定和比较辽河(LH)、黄河(HH)、长江(YZ)、瓯江(OJ)、闽江(MJ)和南流江(NLJ)水系野生绒螯蟹(Eriocheir sensu stricto)肌肉中的脂肪酸组成,进一步分析了6群体间的遗传多样性和亲缘关系。结果显示:(1)在6水系群体中检测出26种脂肪酸,其中C20:5n3、C18:1n9、C22:6n3、C16:0、C20:4n6、C18:2n6和C18:0为主要种类,其总和占总脂肪酸的74%以上;(2)逐步判别分析法筛选出8种判别贡献较大的脂肪酸,分别是C17:0、C18:0、C20:0、C22:1n9、C18:3n3、C18:3n6、C20:2n6和C22:5n3,据此分别建立判别方程,综合判别准确率为98.33%;(3)聚类分析显示:OJ与MJ群体的欧氏距离最小, HH与YZ群体的欧氏距离比OJ与MJ群体的要大,NLJ群体与其他5个群体的欧氏距离相对最大;(4)6群体间脂肪酸含量的变异系数在2.99%—30.00%之间,遗传多样性指数变化幅度在3.2732—3.3204之间。综上,基于脂肪酸生物标记法表明6水系绒螯蟹群体遗传多样性指数均较高,脂肪酸可以有效鉴别6水系野生绒螯蟹种群,整体上南流江群体和其余5群体间相距最远;本研究结果可为绒螯蟹种质资源评价和开发利用等提供基础资料。     

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.     

Growth,feed conversion and faecal discharge of yellowtail kingfish (Seriola lalandi) fed three commercial diets

Abstract

A study was undertaken to provide data on growth, feed conversion ratio (FCR) and faecal discharge of yellowtail kingfish (Seriola lalandi) fed three commercial diets used previously to culture this species in New Zealand. Fish were raised in tanks from 0.4 to 1.2 kg over the spring (water temperature 14–17°C) and summer (17–22°C) periods. There were considerable differences in volumetric and mass‐specific feed intake, and energy intake amongst diets. Daily crude protein intake was similar amongst diets, although it increased from the cold (4.05–4.50 g protein kg^?1 day^?1) to warm period (6.48–7.67 g protein kg^?1 day^?1). The biological and economical FCR varied with diet (BFCR 1.22–2.17, EFCR 1.30–2.62), as did the cost of feed per unit biomass produced (NZ$38–3.78 kg^?1). Growth rates were broadly similar amongst diets, and the warmer summer temperature period greatly improved both growth (increase from 0.51–0.64% to 1.18–1.23% mass gain day^?1) and BFCR (decrease from 1.37–2.17 to 1.22–1.46). The Salmofood ESF diet resulted in only half of the faecal setüeable solids and settleable total nitrogen (T N) and total phosphorus (T P) output compared with Skretting NME, which was in turn only half or less of that of Reliance SF     

Effects of some representative petroleum refinery effluent compounds on photosynthesis and growth of natural marine phytoplankton assemblages: Part 1—cresols

The effects of cresols on the photosynthesis and growth of natural marine phytoplankton assemblages from the Scripps Pier at La Jolla, California, USA were measured. In two experiments, in which dinoflagellates were the dominant algae, photosynthesis (measured by ¹⁴C uptake) was inhibited at concentrations > 100 μg litre^?1 and the concentration giving half-maximal photosynthesis was 10,000 μg litre^?1. In a third experiment, in which diatoms were dominant, photosynthesis was not inhibited until levels > 10,000 μg litre^?1 were reached and the half-maximal concentration was 20,000 μg litre^?1. These experiments suggested that dinoflagellates were more sensitive to cresols than diatoms. However, the reverse was true in an experiment using cultures. In a long-term growth experiment (natural assemblages from the Scripps Pier), only a level of 88,000 μg litre^?1 completely inhibited growth. There was a two-day lag in growth at 8500 μg litre^?1, but the algae recovered and grew as well as the controls which contained no cresols. This experiment was started with a mixed diatom-dinoflagellate-microflagellate population but only the diatoms grew. High concentrations of cresols (> 900 μg litre^?1) resulted in a decrease in the diatom Skeletonema costatum, compared with the controls. Otherwise there was no selection for resistant species. In these experiments, cresols were measured by extraction with methylene chloride from seawater followed by measurement by UV absorption. In all experiments cresol levels decreased with time. This was attributed to uptake by phytoplankton and bacterial degradation.     

Abundance, Biomass, C- and N- Content of Flaccisagitta enflata and Mesosagitta minima (Chaetognatha)

Abstract The annual variability in abundance and biomass of Flaccisagitta enflata (Grassi, 1881) and Mesosagitta minima (Grassi, 1881), along with the C‐ and N‐content of their different maturity stages, were investigated in the South Adriatic Sea on a weekly basis throughout 1996. Increases in abundance and biomass of F. enflata [maximum 554 indiv. · (10 m³)^–1 and 16.3 mg C · (10 m³)^–1] and M. minima [maximum 336 indiv. · (10 m³)^–1 and 3.1 mg C · (10 m³)^–1] were found in summer and autumn, a time of intense reproduction for these species. Mean carbon content (as a percentage of dry weight) varied from 30.41 to 40.39 % among maturity stages for F. enflata, and from 27.73 to 39.31 % for M. minima. Nitrogen contents of both species were ～ 3 to 3.5 times less than carbon contents and varied less. Accurate estimates of chaetognath biomass as carbon should be based on the separate contribution of each maturity stage present in the total population.     

Limnology of Lake Rotokawa and its outlet stream

Abstract

The water chemistry, flora, and fauna of Lake Rotokawa (38° 37.8’ S, 176° 11.2'E) was studied in 1975–76. The mean pH is 2.1 and thermal inflows may elevate the mean summer temperature of the surface waters 4.2°c above that of nearby cold water Lake Rotongaio (18.9°c). The temperature range of surface water was from 10.1 °c in winter to 23.1°c in summer. The major anions were SO₄ ^2? 679 g.m^?3, and Cl‐ 314 g.m^?3. Mean concentrations of major cations were Na⁺ 224 g.m^?3, K⁺ 28.9 g.m^?3, Ca²⁺ 13.3 g.m^?3, and Mg²⁺ 2.6 g.m^?3.

Two species of flagellate algae were recorded, of which Euglena anabaena was predominant. Only two benthic macroinvertebrates were found, larvae of Chironomus zealandicus, mean density 253 per square metre, and Helobdella sp., 1.3 per square metre.

The Parariki Stream was influenced by thermal springs in its upper and lower reaches, being cooler (24–25°c) about halfway along its length than near its source (27.8–39.0°c) or confluence (26.5°‐28.0°c) with the Waikato River. In the cooler stretch of the stream where unidentified benthic algae were not limited by high temperature, chlorophyll and total pigment increased from 3.9 to 377.9 mg.m^?3 and from 17.5 to 534.4 mg.m^?3 respectively, and nutrient levels fell (NO₃‐N, 22–10.5 mg.m^?3; NH₄‐N, 6440–230 mg.m^?3; and PO₄‐P, 51–19 mg.m^?3).