The role of macrophytes as a refuge and food source for the estuarine isopod Exosphaeroma hylocoetes ( )

The role of submerged macrophytes as refugia from fish predation and as possible food sources for the estuarine isopod Exosphaeroma hylocoetes ( Barnard, K.H., 1940) was investigated. Laboratory experiments tested the effectiveness of artificial vegetation, replicating submerged vegetation, in enabling isopods to elude selected fish predators Rhabdosargus holubi, Glossogobius callidus, Monodactylus falciformis and Clinus cottoides. Isopods preferentially hid in the vegetation (>90%), even in absence of fish. The predatory fish had varying success in finding isopods within the vegetation. Isopod mortality ranged from 2% (R. holubi) to a maximum of 87% (C. cottoides) within vegetation, depending on the fish predator present. Stable isotope and fatty acid analyses ruled out the submerged macrophyte Ruppia maritima and inundated fringing grasses as direct food sources, but highlighted the epiphytic biota (mainly diatoms) found on the submerged vegetation and sediments as more likely food sources. These findings are consistent with gut content analyses. The results suggest that the close association of E. hylocoetes with R. maritima is the result of the vegetation providing the isopod with a refuge against fish predation as well as areas of increased food availability.     

Surface evolution and carbon sequestration in disturbed and undisturbed wetland soils of the Hunter estuary,southeast Australia

The aim of this work was to quantify the soil carbon storage and sequestration rates of undisturbed natural wetlands and disturbed wetlands subject to restriction of tidal flow and subsequent rehabilitation in an Australian estuary. Disturbed and undisturbed estuarine wetlands of the Hunter estuary, New South Wales, Australia were selected as the study sites for this research. Vertical accretion rates of estuarine substrates were combined with soil carbon concentrations and bulk densities to determine the carbon store and carbon sequestration rates of the substrates tested. Relationships between estuary water level, soil evolution and vertical accretion were also examined. The carbon sequestration rate of undisturbed wetlands was lower (15% for mangrove and 55% for saltmarsh) than disturbed wetlands, but the carbon store was higher (65% for mangrove and 60% for saltmarsh). The increased carbon sequestration rate of the disturbed wetlands was driven by substantially higher rates of vertical accretion (95% for mangrove and 345% for saltmarsh). Estuarine wetland carbon stores were estimated at 700–1000 Gg C for the Hunter estuary and 3900–5600 Gg C for New South Wales. Vertical accretion and carbon sequestration rates of estuarine wetlands in the Hunter are at the lower end of the range reported in the literature. The comparatively high carbon sequestration rates reported for the disturbed wetlands in this study indicate that wetland rehabilitation has positive benefits for regulation of atmospheric carbon concentrations, in addition to more broadly accepted ecosystem services.     

Observations of Floc Sizes in a Muddy Estuary

Measurements are presented of median floc diameters and associated environmental data over spring-tide tidal cycles at two stations in the muddy Tamar Estuary, UK, for winter, spring and summer conditions. The particulate organic carbon and particulate total carbon contents of mudflats and SPM (suspended particulate matter) at the stations, together with other evidence, indicates that much of the SPM was derived from mud sources that were located between the two stations during winter and spring, and from very mobile sediment sources in the upper estuary during summer. Observed in-situ median floc sizes varied widely, from <50 to >500 μm and rapid settling of particles close to HW and LW (high and low water) left only the smaller flocs in suspension. Time-series of depth-averaged median floc sizes generally were most closely, positively, correlated with depth-averaged SPM concentrations. Floc diameters tended to reach maximum median sizes near the time when SPM concentrations were highest. These high concentrations were in turn largely generated by resuspension of sediment during the fastest current speeds. Although such correlations may have arisen because of SPM-driven floc growth - despite fast tidal currents - there is also the possibility that tough aggregates were eroded from the intertidal mudflats and mudbanks. Although a hypothesis, such large aggregates of fine sediment may have resulted from the binding together of very fine bed particles by sticky extracellular polymeric substances (EPS) coatings, produced by benthic diatoms and by other biologically-mediated activity. A rapid reduction of SPM occurred at the up-estuary station within 2.5 h of HW on the flood, when decelerating currents were still relatively fast. It appears that at least two processes were at work: localised settling of the largest flocs and up-estuary transport in which large flocs were transported further into the estuary before settling into the Tamar's ETM (estuarine turbidity maximum) over the HW-slack period. Up-estuary advection of large flocs and their eventual settling would place the down-estuary edge of the ETM above the upper-estuary station during summer, spring-tide conditions. This position of the ETM was observed close to HW during longitudinal surveys of the estuary.     

厦门东西海域海洋线虫群落种类组成及摄食类型的初步比较研究

2002年6月30日和7月1日在厦门海域2个采样点取样,对厦门东西海域自由生活海洋线虫的群落结构进行了初步比较研究.结果显示:2个站位共鉴定自由生活海洋线虫53种,西海域37种,东海域31种,其中优势种是茅咽线虫Dorylaimopsis variabilis.、萨巴线虫Sabaticria sp.、霍帕线虫Hoppcria sp.、海洋拟齿线虫Parodontophora marina 和星火线虫Marylymnia sp.;对海洋线虫群落结构和生物多样性指数的比较表明,2个站位的群落多样性指数和优势种基本一致,但优势种的优势度有一定差异.西海域站位出现的种类多,但种类分布不均匀;东海域出现的种类少,但种类分布较均匀.非选择性沉积食性者(即1B型)和底上硅藻食性者(即2A型)是该海域两个站位的优势摄食类群.从优势种和摄食类群方面来看,厦门海域与台湾海峡南部、黄河口站位海洋线虫群落有一定的相似性.     

2005年春季广东近岸海域麻痹性贝毒素的特征分析

于2005年3~5月,在广东省近岸海域的27个采样点(从东到西覆盖整个广东省沿海,包括了广东省的12大重点海湾海水养殖区)进行了贝类样品采集,共采集了35个品种120个样品。采用小白鼠生物检测法对麻痹性贝毒素(PSP)的检测结果表明,其3、4和5月采集的样品均检测出毒性值,2005年春季广东近岸海域的PSP呈现出以下主要特征:(1)PSP的检出率和含量值均较低。在120个检测的样品中,只有13个样品检测出PSP毒性数据,检出率为10.8%;检出PSP范围为每100 g贝类软组织含152~198 MU。其中北津港(东平)的托氏毛蚶和神泉港(神泉)的近江牡蛎样品,在1 h内小白鼠的致死率都非常高,但毒性并不强。所有检测出的PSP毒性数据值均大大低于我国目前暂定的警戒标准:每100 g贝类软组织含80μg STXeq(对KM系小白鼠而言,相当于每100 g贝类软组织含约423 MU)。2005年春季广东近岸海域海水水温偏低可能是一个重要原因。(2)感染PSP毒性的生物品种不多。在已检测的35个贝类品种中,只有8个品种检测出PSP毒性数据,占被检测总品种数的22.8%。牡蛎的PSP检出率相对较高,而其它常见品种如文蛤和翡翠贻贝的PSP检出率均较低,华贵栉孔扇贝未检出PSP。(3)PSP的地理分布范围较广。从检测出PSP毒性数据的样品的地理分布来看,范围较广,从东到西几乎包括了整个广东省沿海。其中北津港6个样品中,有2个检测出PSP毒性数据,PSP最高值也出现在北津港(东平)。广东12个大重点海湾海水养殖区,除红海湾、大亚湾、大鹏湾及海陵湾4个大重点海湾海水养殖区外,其它8个大重点海湾海水养殖区均检测出PSP,占12个大重点海湾海水养殖区总数的66.7%。在以前未检出的多处海水养殖区也能检出PSP。并就有关问题进行了讨论。     

粤东-闽南沿岸海域上升流区软水母亚纲一新种和一新记录的记述

报道了2009年5月在粤东-闽南上升流区发现软水母亚纲（Leptomedusae Haeckel,1866）一新种,大腺触丝水母（Lovenella macrogonaLin,XuetHuang,sp.nov.）和我国海域一新记录,脆弱似杯水母[Phi-alella fragilis（Uchida,1938）].大腺触丝水母,新种的鉴别特征如下：伞半球形,外伞上有分散刺细胞,4个大的生殖腺,卵圆形,在辐管中部;4条主辐触手,触手球背部有块状黑色素,具有6~8对侧丝;4个大的间辐位缘疣,球形,具排泄乳突,背部有黑色素分布;24个平衡囊,每个平衡囊具1个平衡石.     

A preliminary investigation of the fish food web in the Gironde estuary,France, using dietary and stable isotope analyses

Carbon and Nitrogen stable isotopes and stomach contents analyses were used to investigate an estuarine fish food web and identify the contribution of these two methods to the knowledge and understanding of the food web's structure and its functioning. The nine most abundant fish species during the warm period in the Gironde estuary (southwest France, Europe) are examined. Observation of the stomach contents reflects a variety of feeding modes between fish species that consume a diverse assortment of prey, with limited dietary overlap. Nevertheless, when regarding the whole fish community, few prey species dominate the stomach contents. Nitrogen isotope ratios indicate a high intraspecific variability inducing an interspecific covering of the signatures. However, a tendency to δ¹⁵N enrichment according to the trophic position of the species studied was observed. Fish assemblages show a trend towards enrichment of their carbon isotopic signatures from the upper estuary (−20.8 ± 1.8‰) towards the lower estuary (−18.3 ± 1.6‰). But whatever the capture zone considered, most of the individual δ¹³C values for each fish analysed are comprised between −22 and −16‰. Only few specimens, belonging to migratory amphihaline species, have significantly lighter values.     

Short-term (≤2 yrs) estuarine mudflat and saltmarsh sedimentation: High-resolution data from ultrasonic altimetery, rod surface-elevation table, and filter traps

Rates of short-term (up to 2 years) bed elevation change and sedimentation from mudflats to salt marshes were measured in a rapidly infilling macrotidal estuary using an original combination of three high-resolution techniques: an ultrasonic altimeter, the Rod Surface-Elevation Table (RSET) method, and filter traps. The Authie estuary is located on a straight, sand-rich coast and is undergoing rapid infill under the influence of flood-dominant tides reinforced by wave action. The estuarine sediment suite consists of both mud and sand derived from the sea, of sand derived from storm wave erosion of dunes lining the north bank of the estuary, and, to a much smaller extent, of mud from the river catchment. Bed elevation change and sedimentation rates show an expected increase with the duration of tidal flooding (hydroperiod) in both space and time. The estuarine bed sediment suite changes from sandy at the mouth to muddy within the low-energy inner estuary, where mudflats are rapidly accreting, paving the way for the formation of increasingly denser and mature salt marshes from the high-sedimentation pioneer zone to the upper marsh where annual sedimentation is very low. Recorded variability in rates of bed elevation change and sedimentation reflect the influence of estuarine macro-scale and local sediment transport and depositional processes in a macrotidal context dominated by high inputs of allochthonous sediments.     

Nutrient concentrations and fluxes in the Changjiang Estuary during summer

In June 2003 and 2006 concentrations of nutrient were determined in the Changjiang Estuary. The data indicated that phosphate and nitrate did not behave conservatively in the estuary, but silicate behaved conservatively. An important mobilization of phosphate and nitrate was observed from the river up to halfway in the estuary. Both input flux (from river to estuary) and output flux (from estuary to coastal zone) of phosphate, silicate and nitrate were calculated from statistical interpretations of the salinity profiles. There was a large discrepancy between input and output fluxes of phosphate and nitrate. The river fluxes of silicate, phosphate and nitrate (f_r) are augmented 5.3%, 28.9% and 36.6% in June 2003 and 1.0%, 62.5%, 31.7% in June 2006 by internal inputs (f_i). The phosphate and nitrate fluxes are enhanced through the estuarine process, while silicate flux is unaltered. The authors present some long-term data for nutrient concentrations and the ratios of silicon to nitrogen to phosphorus in the Changjiang Estuary. Silicate level falled in the last two decades, while concentration of nitrate increased. Phosphate concentration had no significant change.     

山东半岛南部近岸海域富营养化状况的多元评价研究

于2006年至2007年分四个季度月对山东半岛南部近岸海域(35.5°~36.7°N,119.8°~121.3°E)的营养盐和叶绿素a进行了设站调查,分析了该海域上述因子时空分布特征,同时应用主成分分析(PCA)和潜在富营养化评价方法对该海域的富营养化状况进行了分析,初步确定了影响该海域富营养化状况的主要驱动因子。结果表明:(1)在时间分布上,总氮、总磷、活性磷酸盐、溶解态氮与总无机氮和活性硅酸盐的季节变化类似,均表现出秋冬季浓度较高而春夏季较低的趋势,而总磷、溶解态磷的浓度则在冬季最高,在夏秋季较低,叶绿素a浓度的季节变化趋势为春夏季较高,而冬季最低;该海域营养盐与叶绿素a浓度空间分布以胶州湾和丁字湾为中心,总体呈现出由近岸向离岸海域逐渐递减的趋势;(2)应用主成分分析对调查结果进行分析,结果显示10项调查指标(营养盐与叶绿素a)可以转换提取4个主成分,解释82.00%的结果。主成分综合得分可以作为富营养化程度的评价指标,据此得到调查海域富营养化状况的季节变化趋势由高到低依次为秋季、冬季、春季、夏季,总体呈现出以胶州湾和丁字湾为中心,沿岸及北部海域富营养化程度较高的格局;分析结果还表明总无机氮是该海区富营养化形成的主要驱动因子;(3)利用潜在富营养化评价方法对调查海域富营养化状况进行了初步分析,结果表明该海区仅于秋季表现为总体中度营养,在其他季节总体趋势均为贫营养,胶州湾与丁字湾附近海域在春秋季表现为磷限制潜在富营养化。主成分分析法较潜在富营养化评价方法更敏感,不仅能够定量表述海区富营养化状况,而且能够有效确定富营养化驱动因子。