On the dominance of pre-existing swells over wind seas along the west coast of India

Wave data collected off Goa along the west coast of India during February 1996-May 1997 has been subjected to spectral analysis, and swell and wind sea parameters have been estimated by separation frequency method. Dominance of swells and wind seas on monthly and seasonal basis has been estimated, and the analysis shows that swells dominate Goa coastal region not only during southwest monsoon (93%), but also during the post-monsoon (67%) season. Wind seas are dominant during the pre-monsoon season (51%). The mean wave periods (T_m) during southwest monsoon are generally above 5 s, whereas T_m is below 5 s during other seasons. Co-existence of multiple peaks (from NW and NE) was observed in the locally generated part of the wave spectrum, especially during the post-monsoon season. NCEP reanalysis winds have been used to analyse active fetch available in the Indian Ocean, from where the predominant swells propagate to the west coast of India. A numerical model was set up to simulate waves in the Indian Ocean using flexible mesh bathymetry. The correlation coefficients between measured and modelled significant wave heights and mean wave periods are 0.96 and 0.85, respectively. Numerical simulations reproduced the swell characteristics in the Indian Ocean, and from the model results potential swell generation areas are identified. The characteristics of swells associated with tropical storms that prevail off Goa during 1996 have also been analysed.     

Temporal variation of diatom benthic propagules in a monsoon-influenced tropical estuary

Temporal variations in the diatom benthic propagule (DBP) community and their role in the phytoplankton community in a monsoon-affected tropical estuary, Zuari estuary, Goa (India) are presented. The DBP from the sediments was enumerated using an extinction dilution method (most probable number method), which allows estimation of resting stages through examination of germinated vegetative cells in culture. The DBP community was dominated by planktonic species belonging to the genera Skeletonema, Fragilariopsis, Thalassiosira, and Chaetoceros. Benthic propagules (BPs) of Skeletonema costatum and Fragilariopsis sp. were dominant throughout the year. Between these two species, only S. costatum showed a linear relationship between the BP and planktonic cells, indicating that this species is particularly important in coupling of pelagic and benthic ecosystems. During the onset and restart of monsoon after an intermittent break, water column was stratified, with a low-salinity layer arising from riverine discharge and precipitation at the surface and relatively cold, saline, low-oxygen waters at the bottom. Stratification favored blooming of S. costatum and Fragilariopsis sp. in nutrient-rich surface and bottom waters, respectively. The decline in these blooms ensuing nitrate depletion and salinity change resulted in an increased abundance of BP. Chaetoceros bloom was observed during the monsoon break as well as during non-monsoon period and on both the occasions the decline in bloom was coupled with freshwater discharge. During the non-monsoon season, Thalassiosira blooms were encountered subsequent to high nitrate inputs. These findings suggest that in such shallow tropical regions, physical processes during monsoon (freshwater discharge) and non-monsoon seasons (currents, waves and tides) cause resuspension of diatom BP. Since light is not a limiting factor for germination in such regions, the blooming of resuspended BP depends on nutrient availability.     

丹江口水库浮游植物时空变化特征

为研究丹江口浮游植物的群落特征,探讨影响浮游植物时空分布的环境因子,于2014年5月2015年4月对丹江口水库进行了为期1年的调查.此次调查共采集到浮游植物66种,隶属于7门21科38属.浮游植物全年平均生物量为0.35 mg/L,平均密度为9.08×10~5cells/L.优势种为脆杆藻、小环藻、直链藻和栅藻,其中脆杆藻所占比例最大,平均生物量为0.089 mg/L,占总生物量的25.43%.近些年丹江口水库营养水平的提高可能是脆杆藻生物量升高的主要原因.绿藻和蓝藻在夏季大量繁殖,硅藻为春、秋和冬季优势门类.汉江库区浮游植物生物量大于丹江库区,两个库区的浮游植物种类组成存在明显的差异,丹江库区优势门类为硅藻门,而汉江库区为绿藻门.浮游植物生物量与环境因子的相关分析表明,浮游植物生物量的主要影响因子是总磷浓度、pH值和溶解氧浓度.RDA分析表明,影响浮游植物组成的主要环境因子是溶解氧浓度、pH值、总磷浓度和水温.为控制浮游植物的生物量,防止其异常增殖造成水华,应严格控制外源营养盐特别是磷元素的输入.本研究可为丹江口水库的水质改善及富营养化防治提供一定的科学依据.     

Metazooplankton communities in the Ahe atoll lagoon (Tuamotu Archipelago, French Polynesia): Spatiotemporal variations and trophic relationships

Metazooplankton abundance, biomass (<80μm, 200-500μm and >500μm) and community structure in the Ahe atoll were studied together with their relationships with environmental factors (temperature, salinity, wind) and trophic factors (phytoplankton, bacteria, heterotrophic nanoflagellates (HNF) and ciliates) during three periods in 2008-2009. Meroplankton, mainly bivalve and gastropod larvae, was dominant. Holoplankton was dominated by copepods, the main species being Oithona spp., Paracalanus parvus, Clausocalanus spp., Corycaeus spp., Acartia fossae and Undinula vulgaris. The results suggest a clear wind influence on the structure and horizontal distribution of the zooplankton communities. The metazooplankton appeared to be controlled mainly by food resources, suggesting a bottom-up control. The low nanophytoplankton biomass in contrast to the high abundance of picophytoplankton, HNF and nano-particle grazers (mainly Oithona spp., Paracalanus and bivalve larvae) highlighted the importance of the microbial loop in the food web.     

Time–frequency characterization of sub-divisional scale seasonal rainfall in India using the Hilbert–Huang transform

Time–frequency characterization is useful in understanding the nonlinear and non-stationary signals of the hydro-climatic time series. The traditional Fourier transform, and wavelet transform approaches have certain limitations in analyzing non-linear and non-stationary hydro-climatic series. This paper presents an effective approach based on the Hilbert–Huang transform to investigate time–frequency characteristics, and the changing patterns of sub-divisional rainfall series in India, and explored the possible association of monsoon seasonal rainfall with different global climate oscillations. The proposed approach integrates the complete ensemble empirical mode decomposition with adaptive noise algorithm and normalized Hilbert transform method for analyzing the spectral characteristics of two principal seasonal rainfall series over four meteorological subdivisions namely Assam-Meghalaya, Kerala, Orissa and Telangana subdivisions in India. The Hilbert spectral analysis revealed the dynamic nature of dominant time scales for two principal seasonal rainfall time series. From the trend analysis of instantaneous amplitudes of multiscale components called intrinsic mode functions (IMFs), it is found that both intra and inter decadal modes are responsible for the changes in seasonal rainfall series of different subdivisions and significant changes are noticed in the amplitudes of inter decadal modes of two seasonal rainfalls in the four subdivisions since 1970s. Further, the study investigated the links between monsoon rainfall with the global climate oscillations such as Quasi Bienniel Oscillation (QBO), El Nino Southern Oscillation (ENSO), Sunspot Number (SN), Atlantic Multidecadal Oscillation (AMO) etc. The study noticed that the multiscale components of rainfall series IMF1, IMF2, IMF3, IMF4 and IMF5 have similar periodic structure of QBO, ENSO, SN, tidal forcing and AMO respectively. As per the seasonal rainfall patterns is concerned, the results of the study indicated that for Assam-Meghalaya subdivision, there is a likelihood of extreme rare events at ~0.2 cycles per year, and both monsoon and pre-monsoon rainfall series have decreasing trends; for Kerala subdivision, extreme events can be expected during monsoon season with shorter periodicity (~2.5 years), and monsoon rainfall has statistically significant decreasing trend and post-monsoon rainfall has a statistically significant increasing trend; and for Orissa subdivision, there are chances of extremes rainfall events in monsoon season and a relatively stable rainfall pattern during post-monsoon period, but both monsoon and post-monsoon rainfall series showed an overall decreasing trend; for Telangana subdivision, there is a likelihood of extreme events during monsoon season with a periodicity of ~4 years, but both monsoon and post-monsoon rainfall series showed increasing trends. The results of correlation analysis of IMF components of monsoon rainfall and five climate indices indicated that the association is expressed well only for low frequency modes with similar evolution of trend components.     

Seasonal variations and trophic ecology of microzooplankton in the southeastern Arabian Sea

The seasonal ecological response of microzooplankton in the southeastern Arabian Sea is presented. During the spring intermonsoon period, stratification and depletion of nitrate in the surface waters (nitracline was at 60 m depth) cause low integrated chlorophyll a (av. 19±11.3 mg m⁻²) and primary production (av. 164±91 mgC m⁻² d⁻¹). On the other hand, nutrient enrichment associated with coastal upwelling and river influx during the onset and peak summer monsoon resulted in high integrated chlorophyll a (av. 21±6 mg m⁻² and av. 29±21 mg m⁻², respectively) and primary production (av. 255±94 mgC m⁻² d⁻¹ and av. 335±278 mgC m⁻² d⁻¹, respectively). During all three periods, diazotropic cyanobacterium Trichodesmium erythraeum dominated in the nutrient depleted surface waters. A general increase in abundance of larger diatoms was evident in the surface waters of the inshore region during monsoon periods. The microzooplankton abundance was found to be significantly higher during the spring intermonsoon (av.241±113×10³ ind m⁻²) as compared to onset of summer monsoon (av. 105±89×10³ ind m⁻²) and peak summer monsoon (av.185±175×10³ ind m⁻²). Microzooplankton community during the spring intermonsoon was numerically dominated by ciliates while heterotrophic dinoflagellate was the dominant ones during the monsoon periods. The high abundance of ciliates during the spring intermonsoon could be attributed to the stratified environmental condition prevailed in the study area which favors high abundance of smaller phytoplankton and cyanobacteria, the most preferred food of ciliates. On the other hand, the dominance of heterotrophic dinoflagellates during the monsoon periods could be linked to their ability to graze larger diatoms which were abundant during the monsoon periods. The overall results show low abundance of microzooplankton in the eastern Arabian Sea during the monsoon periods mainly due to a decline in ciliates abundance. This decline during the monsoon periods could be the result of (a) low abundance of smaller phytoplankton and (b) high stock of mesozooplankton predators (av. 245 ml 100 m⁻³).     

青藏高原东南缘高山湖泊藻类响应气候变化和大气沉降的长期特征

高山湖泊远离人类活动直接影响,通常具有面积小、寡营养、食物网单一等特点,对气候变化和营养输入具有较高的敏感性。我国青藏高原东南缘地区氮沉降通量较高、增温幅度显著,已有研究显示该地区可能受湖泊类型、流域特征等影响存在差异性的湖泊响应模式。本研究选择该区域位于树线以下、具有不同水深的3个小型湖泊(盖公错纳、沃迪错、碧沽天池)开展沉积物调查和对比研究,通过钻孔样品测年、理化特征和藻类(硅藻群落、藻类色素)等多指标分析,结合区域气候定量重建和氮沉降等数据收集,评价了过去300年来藻类演替模式的异同特征及湖泊水深的调节作用。结果显示,3个湖泊中硅藻的优势物种与群落组成差异明显。深水型湖泊盖公错纳(最大水深39.4 m)的硅藻群落以浮游种为主(占比达82%),优势种为眼斑小环藻(Pantocsekiolla ocellata)、科曼小环藻(Pantocsekiella comensis);深水型湖泊沃迪错(最大水深20.7 m)的硅藻群落中浮游种和底栖种约各占50%,优势种为眼斑小环藻(Pantocsekiella ocellata)、连结脆杆藻(Saurosira construens);浅水湖...     

Diatom thanatocoenosis in a middle Galician Ría: Spatial patterns and their relationship to the seasonal diatom cycle in the water column and hydrographic conditions

Modern diatom distribution patterns in the surface sediment of the Ferrol Ría and their relationship to the hydrography and diatom patterns in the water column were studied to determine the hydrographic influence on the record of these biogenic components. Diatom abundance in the water column was assessed for different oceanographic periods and compared with the biosiliceous sedimentary record. Very low abundances were found in the water column during the winter, whereas in spring and summer, diatoms proliferated. Chaetoceros spp. formed the bulk of the water column community during spring and summer, followed by Thalassionema nitzschioides and Rhizosolenia spp. Nitzschia longissima represented a significant portion of the winter assemblage, together with Paralia sulcata and benthic taxa. Leptocylindrus danicus, N. longissima and Skeletonema costatum characterized the autumn campaign, when stratification of the waters occurs, with L. danicus being especially abundant in the outer ría.Seasonal hydrographic and associated productivity patterns govern the abundance and assemblage of the diatoms preserved in surface sediments. Samples located in the inner ría area and its margins exhibited the highest abundances of diatoms, and were primarily dominated by benthic species. The freshwater group, crysophycean cysts and phytoliths were present in the landward stations influenced by river runoff. The middle ría was characterized by P. sulcata and Thalassiosira spp., with minor occurrences of the benthic and freshwater group. Chaetoceros R.S., L. danicus R.S. and T. nitzschioides typified the outer ría, an assemblage that corresponds to nutrient-rich coastal areas of high productivity influenced by oceanic waters, demonstrating the impact of oceanic waters flowing into the embayment due to enhanced tidal mixing through the narrow channel. Therefore, sediment diatom assemblages reflect diatom production patterns in the water column of the Ría. However, we must proceed with caution when interpreting the paleorecord in the inner area due to the high contribution of allochthonous taxa, which is indicative of low water depths. This paper contributes to a better understanding of diatom thanatocoenosis in the Galician Rías, where very few studies of this kind have been done to date.     

Seasonal variations of hydrographic conditions of estuarine and oceanic waters adjoining the old Mangalore port

In order to understand the various processes responsible for siltation in the entrance channel and in the sand bar area near the old Mangalore port, variations in temperature, salinity, suspended sediment load, currents and extinction coefficient in the Netravathi-Gurpur Estuary and in the sea near the sand bar were studied in relation to tides during monsoon, post-monsoon and pre-monsoon seasons. The hydrographic characteristics in the estuary showed marked seasonal changes and were influenced by tides to a considerable extent. In the sea, seasonal variations of these parameters were less marked, and the effect of tides was not significant. Salinity and temperature values in the estuary and in the sea were maximum during the pre-monsoon season in general. The suspended sediment load values were always higher in the estuary than in the sea and they were found to be maximum in the monsoon season. Currents in the estuary were controlled by tides as well as by the river flow, particularly in the monsoon season, whereas currents in the sea mostly followed the general circulation pattern. Extinction coefficient values were higher in the monsoon season both in the estuary and in the sea due to increase in the particulate matter from inland drainage.     

Chlorella-bearing ciliates (Stentor, Ophrydium) dominate in an oligotrophic, deep North Patagonian lake (Lake Caburgua, Chile)

The aim of this study was to present quantitative data on the population dynamics of Chlorella-bearing ciliates (Stentor, Ophrydium) compared to the total zooplankton community in a deep, oligotrophic North Patagonian lake. Mixotrophic and heterotrophic ciliates, rotifers and microcrustaceans, and important ecological parameters were sampled during a 1-year study. The results showed a low biodiversity with only a few dominant species in every zooplankton group. Three mixotrophic ciliates - Stentor araucanus, S. amethystinus and Ophrydium naumanni - were found. They peaked in summer and autumn with maximum values of 152-313 Ind L⁻¹ (Stentor) and 1880 Ind L⁻¹ (Ophrydium). Their contribution to the total ciliate abundance was 16±17% (annual average). Both Stentor species displayed a distinct vertical zonation during the stratification period with peak depth between 10 and 15 m (metalimnion). The contribution to total zooplankton biomass was 59.4% on an annual average (Stentor: 41%, O. naumanni: 18.4%) and 83% during the stratification period. Both abundance and biomass of mixotrophic ciliates correlated strongly with temperature and to a lesser degree with copepods, rotifers and small cladocerans. According to this study mixotrophic ciliates were by far the dominant zooplankton group in Lake Caburgua. We report for the first time the importance of O. naumanni in a deep Chilean North Patagonian lake.     

Cold fronts induce changes in phycoperiphyton structure in a shallow lake: Wind forces drive algae succession and nutrient availability

We evaluated wind as the main structuring force in driving phycoperiphyton structure, community composition and succession in a warm, polymictic shallow lake in southern Brazil. Mangueira Lake is continuously mixed due to its exposure to wind, and during cold fronts the wind changes from the dominant NE direction to a SSW direction. Our question was: could changes in wind forces induce phycoperiphyton succession and determine population structure? To answer this question, we studied the phycoperiphyton successional response to a change in wind forces under three different situations: on clean macrophyte leaves in an open site (Open) and in an enclosed site protected from the wind (Enclosure), and the Natural community growing on uncleaned macrophyte leaves in an open site. Cold fronts improved nutrient availability and changed the algal community. The phycoperiphyton natural community was dominated by Epithemia spp bound in gross masses of green filaments during cold fronts. However, the wind direction typically changes when cold fronts are over (NE-E) and wind blowing from the off-shore direction dislodged the attached algae biomass and pushed it toward to lake shore, inducing community changes. The macrophyte bank exhibited rapid colonization and acted as a refuge for phycoperiphyton, providing habitat heterogeneity, whereas the enclosure acted as a buffer against wind forces, delaying the succession derived from settlement of loosely adhered algae. Furthermore, in the enclosure, the succession only started after a strong disturbance (rain and wind > 10 m s⁻¹) in which lake water flooded the mesocosm inducing colonization. Phycoperiphyton showed resilience and recovered rapidly after the disturbance, when the rain supplied inocula and wind favored colonization with growth forms that take advantage of local conditions, depending of wind dynamics.     

广州市区越秀湖浮游纤毛虫群落的季节变化

从 1997年 4月到 1998年 3月之间 ,应用定性观察和定量分析的方法对广州市的城市湖泊——越秀湖进行了浮游纤毛虫群落的种类组成、群落的生物多样性、丰度、生物量、优势种的种群季节变化等群落结构参数进行了研究 .共发现了 76种浮游纤毛虫 ;最大丰度为 6 9.1×10 3 ind.· L-1;最大生物量为 7.16 mg· L-1;群落中的优势种为大弹跳虫 (H alteria grandinella)、尾毛虫 (Urotricha spp.)、尾侠盗虫 (Strobilidium caudatum)、小侠盗虫 (Strobilidium humile)和膜袋虫 (Cyclidium spp.) ;群落的生物多样性指数在 2 .4到 3.0之间 .分析了这个湖泊浮游纤毛虫群落结构参数的季节变化 .通过与文献报道的比较、分析 ,从纤毛虫的优势种、总丰度和生物量确定了该城市湖泊的富营养状况为重度富营养化 .     

Monsoon driven changes in phytoplankton populations in the eastern Arabian Sea as revealed by microscopy and HPLC pigment analysis

Like the rest of the Arabian Sea, the west coast of India is subject to semi-annual wind reversals associated with the monsoon cycle that result in two periods of elevated phytoplankton productivity, one during the northeast (NE) monsoon (November–February) and the other during the southwest (SW) monsoon (June–September). Although the seasonality of phytoplankton biomass in these coastal waters is well known, the abundance and composition of phytoplankton populations associated with this distinct and predictable seasonal cycle is poorly known. Here we present for the first time, the results of a study on the community structure of phytoplankton for this region, derived from HPLC pigment analysis and microscopic cell counts. Our sampling strategy allowed for large spatial and temporal coverage over regions representative of the coastal and offshore waters, and over seasons that included the NE and the SW monsoon. Monthly observations at a fixed coastal station in particular, allowed us to follow changes in phytoplankton community structure associated with the development of anoxia. Together these measurements helped establish a pattern of seasonal change of three major groups of phytoplankton: diatoms, dinoflagellates and cyanobacteria that appeared to be tightly coupled with hydrographic and chemical changes associated with the monsoonal cycle. During the SW monsoon when nitrate concentrations were high, diatoms were dominant but prymnesiophytes were present as well. By October, as nitrate fell to below detection levels and anoxic conditions began to develop on the shelf below the shallow pycnocline, both diatom and prymensiophytes declined sharply giving way to dinoflagellates. In the well oxygenated surface waters, where both nitrate and ammonium were below detection limits, pico-cyanobacterial populations became dominant.During the NE monsoon, a mixed diatom-dinoflagellate population was quickly replaced by blooms of Trichodesmium erythraeum and Noctiluca miliaris with higher amounts of zeaxanthin, β-carotene, Chl b and prasinoxanthin. Trichodesmium trichomes were noticed in the water column as early as December when nitrate concentrations became limiting. The low phytoplankton biomass and high ammonium concentrations argue that active grazing populations may be responsible for preventing diatom-dinoflagellate populations from establishing themselves to bloom proportions in the eastern Arabian Sea during the early NE monsoon. Trichodesmium continued its dominance well into May, when nutrient enrichment associated with its death and decay helped simulate the growth of both diatoms and dinoflagellates. Given that anoxic conditions are becoming more pervasive in the eastern Arabian Sea, our observations in particular, those of a shift towards dinoflagellate dominance during the development of anoxia assume particular importance.     

Temporal changes in Sphingomonas and Mycobacterium populations in mangrove sediments contaminated with different concentrations of polycyclic aromatic hydrocarbons (PAHs)

The change in community diversity and structure of the indigenous, dominant, polycyclic aromatic hydrocarbon (PAH)-degrading bacterial genera, Sphingomonas and Mycobacterium, due to contamination in the environment is not very well known. A combination of PCR-DGGE with specific primers and a cultivation-dependent microbiological method was used to detect different populations of Sphingomonas and Mycobacterium in mangrove sediments. The structure of the entire bacterial community (including Sphingomonas) did not show a shift due to environmental contamination, whereas the diversity of Mycobacterium populations in mangrove sediments with higher PAH contamination increased from exposure between Day 0 and Day 30. The isolated Mycobacterium strains migrated to the same position as the major bands of the bacterial communities in Mycobacterium-specific DGGE. A dioxygenase gene system, nidA, which is commonly found in PAH-degrading Mycobacterium strains, was also detected in the more highly contaminated sediment slurries. The present study revealed that Mycobacterium species were the dominant PAH-degraders and played an important role in degrading PAHs in contaminated mangrove sediments.     

Seasonal variation of microzooplankton (20–200 μm) and its possible implications on the vertical carbon flux in the western Bay of Bengal

Stratification (throughout the year) and low solar radiation (during monsoon periods) have caused low chlorophyll a and primary production (seasonal average 13–18 mg m⁻² and 242–265 mg C m⁻² d⁻¹, respectively) in the western Bay of Bengal (BoB). The microzooplankton (MZP) community of BoB was numerically dominated by heterotrophic dinoflagellates (HDS) followed by ciliates (CTS). The highest MZP abundance (average 665±226×10⁴ m⁻²), biomass (average 260±145 mg C m⁻²) and species diversity (Shannon weaver index 2.8±0.42 for CTS and 2.6±0.35 for HDS) have occurred during the spring intermonsoon (SIM). This might be due to high abundance of smaller phytoplankton in the western BoB during SIM as a consequence of intense stratification and nitrate limitation (nitracline at 60 m depth). The strong stratification during SIM was biologically evidenced by intense blooms of Trichodesmium erythraeum and frequent Synechococcus–HDS associations. The high abundance of smaller phytoplankton favors microbial food webs where photosynthetic carbon is channeled to higher trophic levels through MZP. This causes less efficient transfer of primary organic carbon to higher trophic levels than through the traditional food web. The microbial food web dominant in the western BoB during SIM might be responsible for the lowest mesozooplankton biomass observed (average 223 mg C m⁻²). The long residence time of the organic carbon in the surface waters due to the active herbivorous pathways of the microbial food web could be a causative factor for the low vertical flux of biogenic carbon during SIM.     

Coastal habitat degradation and green sea turtle diets in Southeastern Brazil

To show the influence of coastal habitat degradation on the availability of food for green turtles (Chelonia mydas), we assessed the dietary preferences and macroalgae community at a feeding area in a highly urbanized region. The area showed low species richness and was classified as degraded. We examined stomach contents of 15 dead stranded turtles (CCL = 44.0 cm (SD 6.7 cm)). The diet was composed primarily of green algae Ulva spp. (83.6%). In contrast, the macroalgae community was dominated by the green alga Caulerpa mexicana. We found a selection for red algae, seagrass and Ulva spp., and avoidance for C. mexicana and brown alga Dictyopteris delicatula. The low diversity of available food items, possibly a result of environmental degradation, likely contributed to the low dietary diversity. The nutritional implications of this restricted diet are unclear.     

Impact of flood events on macrobenthic community structure on an intertidal flat developing in the Ohta River Estuary

We investigated the effects of river floods on the macrobenthic community of the intertidal flat in the Ohta River Estuary, Japan, from 2005 to 2010. Sediment erosion by flood events ranged from about 2–3 cm to 12 cm, and the salinity dropped to 0‰ even during low-intensity flood events. Cluster analysis of the macrobenthic population showed that the community structure was controlled by the physical disturbance, decreased salinity, or both. The opportunistic polychaete Capitella sp. was the most dominant species in all clusters, and populations of the long-lived polychaete Ceratonereis erythraeensis increased in years with stable flow and almost disappeared in years with intense flooding. The bivalve Musculista senhousia was also an important opportunistic species that formed mats in summer of the stable years and influenced the structure of the macrobenthic community. Our results demonstrate the substantial effects of flood events on the macrobenthic community structure.     

Occurrence of brackish water phytoplankton species at a closed coral reef in Nansha Islands, South China Sea

The phytoplankton assemblage of Zhubi Reef, a closed coral reef in Nansha Islands (South China Sea, SCS) was studied in June 2007. A total of 92 species belonging to 53 genera and four phyla have been identified. The dominant taxa in the lagoon were the diatom Chaetoceros and cyanobacteria Nostoc and Microcystis, while in reef flats were cyanobacteria Trichodesmium erythraeum, dinoflagellates Gymnodinium and Prorocentrum. The species richness and diversity were consistently lower in the lagoon than in reef flats. Classification and nMDS ordination also revealed significant dissimilarity in phytoplankton community structure between the reef flat and lagoon, with statistical difference in species composition and abundance between them (ANOSIM, p = 0.025). Nutrient concentrations also spatially varied, with ammonium-enrichment in the lagoon, while high Si-concentration existed in reef flat areas. Both nutrient levels and currents in SCS may play important roles in determining the composition and distribution of microalgae in Zhubi Reef and SCS.     

Microbiological composition of native and exotic clams from Tagus estuary: Effect of season and environmental parameters

The influence of seasonal and environmental parameters on the occurrence of bacteria was investigated in two clam species (Venerupis pullastra and Ruditapes philippinarum), water and sediment from the Tagus estuary. Total viable counts (TVC), Escherichia coli, Salmonella spp. and Vibrio spp. were evaluated during one-year. Overall, significant seasonal variations were found in both sampling sites, especially for E. coli and Vibrio spp. levels. In summer, significantly higher Vibrio spp. levels were found in R. philippinarum and sediment samples, but not in V. pullastra clams and water samples. In contrast, significantly higher TVC and E. coli levels were observed in winter months in water and sediment samples. Salmonella spp. was generally isolated when higher levels of E. coli were detected, particularly in R. philippinarum. This study is useful for authorities to develop monitoring strategies for coastal contamination and to estimate human health risks associated with the consumption of bivalves.     

水体叶绿素a和硅藻群落时空分布及影响因子的对比分析——以云贵高原异龙湖为例

藻类是湖泊生态系统中重要的初级生产者,物种多样性高且对水环境变化敏感,其生产力水平与群落构建模式是反映湖泊环境梯度和生态系统特征的可靠指标。其中硅藻优势属种的演替模式及其环境条件识别,是开展湖泊生态健康和环境质量评价的重要内容。本文选择亚热带地区浅水湖泊异龙湖开展季节调查,对20个采样点的叶绿素a和硅藻群落组成等指标开展分布特征及其驱动因子的定量评价,系统分析藻类变化的时空模式、驱动因子及其指标异同。2020年12月一2021年9月,异龙湖水环境特征的季节波动明显,综合营养指数TSI平均为74.76,总体处于富营养水平。在80个水体样品中共发现硅藻21属68种,群落结构以浮游类型(平均占比79.33%±20.69%)的耐中富营养种为主;在4个季节的调查中,膜糊直链藻Aulacoseira ambigua(61.62%±20.26%)为优势种。主成分分析显示,硅藻群落组成存在明显的空间差异和季节变化。冗余分析和方差分解等结果表明,水体营养因子(TN、TP和N:P)是影响叶绿素a浓度空间变化的重要因子(解释方差为19.08%±11.4%),水温和水深梯度的影响较小(9.63%±11.31%...