西沙群岛珊瑚礁海域浮游动物群落结构初步分析*

为了解西沙群岛珊瑚礁海域浮游动物的群落特征, 于2015年5月末至7月初在西沙群岛8个岛礁(七连屿、永兴岛和东岛3个岛屿以及浪花礁、盘石屿、玉琢礁、华光礁和北礁5个环礁)进行了浮游动物采样, 分析了浮游动物的多样性、丰度和群落结构特征, 并比较了5个环礁潟湖内和向海礁坡区浮游动物群落组成的差异。调查海域共鉴定浮游动物180种(包括浮游幼虫13个类群), 其中桡足类最多, 达83种, 其次是水母类(38种)、浮游软体类(14种)、毛颚类(11种)和浮游被囊类(7种); 浮游动物平均丰度为256.4±117.8个·m^-3, 桡足类占总丰度的51.08%, 其次是浮游幼虫(16.30%)、浮游被囊类(13.22%)和毛颚类(7.70%)。浮游动物种数、多样性和均匀度指数、丰度在岛屿和环礁之间以及环礁的潟湖区和向海礁坡区均存在差异; 浮游动物多样性和丰度在东岛、玉琢礁和华光礁较高, 而在七连屿和北礁较低; 5个环礁向海礁坡区的浮游动物多样性和丰度皆高于潟湖区的。多元统计分析结果表明调查岛礁的浮游动物可划分两个聚群(相似水平85%); 岛屿近岸及环礁的潟湖群落(Ⅰ)和岛屿远岸及环礁的向海礁坡群落(Ⅱ); 两个聚群浮游动物组成差异较显著(r=0.832, p<0.001); 前者的种数、多样性指数、总丰度和主要浮游动物类群如桡足类、毛颚类和浮游幼虫的丰度显著低于后者。环礁潟湖区和向海礁坡区的空间异质性和生态环境差异可能是导致浮游动物群落结构呈现不同特征的主要因素。     

Top–down and bottom–up regulation of macroalgal community structure on a Kenyan reef

Top–down and bottom–up regulation in the form of grazing by herbivores and nutrient availability are important factors governing macroalgal communities in the coral reef ecosystem. Today, anthropogenic activities, such as over-harvesting of herbivorous fish and sea urchins and increased nutrient loading, are altering the interaction of these two structuring forces. The present study was conducted in Kenya and investigates the relative importance of herbivory and nutrient loading on macroalgal community dynamics, by looking at alterations in macroalgal functional groups, species diversity (H′) and biomass within experimental quadrats. The experiment was conducted in situ for 42 days during the dry season. Cages excluding large herbivorous fish and sea urchins were used in the study and nutrient addition was conducted using coated, slow-release fertilizer (nitrogen and phosphorous) at a site where herbivory is generally low and nutrient levels are relatively high for the region. Nutrient addition increased tissue nutrient content in the algae, and fertilized quadrats had 24% higher species diversity. Herbivore exclusion resulted in a 77% increase in algal biomass, mainly attributable to a >1000% increase in corticated forms. These results are in accordance with similar studies in other regions, but are unique in that they indicate that, even when prevailing nutrient levels are relatively high and herbivore pressure is relatively low, continued anthropogenic disturbance results in further ecological responses and increased reef degradation.     

夏威夷群岛的地貌特征

本文根据实地考察并结合有关资料,对夏威夷群岛地貌的一些特点进行探讨。首先,分析了这些岛群的大地地貌特征;其次,介绍了灾害性地质地貌现象的控制和利用;最后,对夏威夷群岛的地貌演变趋势进行了探讨。这对大地地貌的研究以及对我国海岛开发将有所借鉴。     

西沙海区新近纪碳酸盐岩台地地震响应特征和控制因素

利用西沙海域最新采集的高分辨率二维地震资料及钻井资料,结合前人研究成果,建立了西沙海区高精度层序地层格架;并在西沙海区新近纪识别出点礁、塔礁、台地边缘礁和环礁这4种不同类型生物礁,总结了不同生物礁的地震反射特征。早中新世时,西沙碳酸盐岩台地开始发育,台地数量较少且规模有限;中中新世,随着海平面的持续上升,海平面上升速率和碳酸盐岩的生长速率接近,此时碳酸盐岩台地发育规模达到最大;晚中新世以后,海平面继续上升,海平面上升速率远大于碳酸盐岩的生长速率,随着水深的快速增加,台地进入淹没阶段,不适合碳酸盐岩台地及生物礁发育,仅在部分构造高部位继续发育,生物礁主要为大型的环礁。控制西沙碳酸盐岩台地发育的影响因素为构造作用和相对海平面变化。     

Caractéristiques du feutrage algal des récifs coralliens de Polynésie française soumis à différentes intensités de bioérosion

This study deals with the colonisation of experimental Porites blocks by epilithic and endolithic algal community in two atoll lagoons and two high-island lagoons in French Polynesia, exposed to different environmental conditions during a 5-year period. A qualitative analysis of the community (cyanobacteria and micro-algae) was carried out, and the relationship between the epilithic and endolithic strata observed. HPLC analysis of chlorophyll pigments was used to quantitatively determine the plant biomass, which was then compared to that of the algal turf of neighbouring reefs. The results show that these blocks are colonised according to two factors: the reef structure (atoll or high-island) and the degree of human disturbance. The epilithic and endolithic population dynamics differ.The density of the epilithic algal community and the species diversity increase with the degree of eutrophication and the amount of borers (sea-urchins, parrotfish), while the proportion of endolithic species remains low (34 %–59 %). This is especially marked in the high-island lagoons, where leaching has caused enhanced nutrient levels. An extreme case is the station at Faaa, a highly polluted harbour, where increased sea-urchin levels (44 ind. m⁻²) meant that the blocks disappeared completely in less than five years due to bioerosion. In the oligotrophic waters of the atoll lagoons, the losses of CaCO₃ by bioerosion do not exceed 35 % per block, and the algal community is made up mainly of endolithic species (66 %–85 %). The algal biomass is lowest in the Takapoto atolls (10–11 μg cm⁻²) and maximum in Tikehau atoll (23 and 56 μg cm⁻²). The first microborers to settle in the ecological succession of the community are the cyanobacteria. These are gradually replaced by Ostreobium (Chlorophyceae borers), which become dominant in the blocks exposed to the lowest bioerosion rate. The richness and the density of the algal turf reflect the convergence of many ecological factors: it seems that the covering of epilithic algae or the richness of endolithic flora could be used as a global indicator of the quality and the health of a reef.     

Phosphogenesis on selected low atolls in the near-equatorial part of the Western Indian Ocean

The compositions, structures, and microstructures of different types of phosphorites and poorly phosphatized rocks from low atolls in the near-equatorial part of the Western Indian Ocean are described. The rocks were examined under optical and scanning microscopes using microprobing techniques and etching of selected samples with weak solvents as well as with the help of chemical analyses. It is proved that phosphorites have been formed owing to the uneven phosphatization of the primary carbonate rocks; the degree of their phosphatization ranges from traces to 40% P₂O₅. In the phosphorites, numerous organic remains were encountered; they included fragments of plankton, debris of tortoise shells, and coccoidal and filamentous bacteria-like formations. It is suggested that the phosphorites were formed due to the high local biological productivity over the outer edges of coral reefs and are not related to guano accumulation or to endoupwelling.     

南海生物礁及礁油气藏形成的基本特征

南海是我国生物礁最发育的海区，在地质历史上，中新世已发现生物礁有百余个，第四纪生物礁有118个。生物礁类型有塔礁、补丁礁、块礁、台地边缘礁、环礁。其中中新世发育的各种类型的生物礁很多成为重要的油气聚集的场所，如曾母盆地的L礁油藏、珠江口盆地的流花11-1礁油藏。进一步研究南海生物礁形成的特征与成藏的条件，为今后南海油气勘探提供依据。     

Submarine groundwater springs are characterized by distinct fish communities

The inflow of terrestrial groundwater into the ocean is increasingly recognized as an important local source of nutrients and pollutants to coastal ecosystems. Although there is evidence of a link between fresh submarine groundwater discharge (SGD)-derived nutrients and primary producer and primary consumer abundances, the effects of fresh SGD on the productivity of higher trophic levels such as ichthyofaunal communities remain unclear. To further investigate this relationship, we sampled three sites inside a coral reef lagoon in Mauritius: One site entailing six distinct groundwater springs, a site highly influenced by freshwater influx through the springs, and a strictly marine control site. Using remote underwater video surveys, we found that fish abundances were significantly higher at the groundwater springs than at the other two sampling sites.Principal component analyses showed that the springs and the spring-influenced part of the lagoon were best described by elevated water nutrient loadings, whereas the control site was characterized by higher water salinity and pH. Macroalgae cover was highest at the control site and the springs. Herbivores and invertivores dominated the fish community at the springs, in contrast to generalists at the control site. At the spring-influenced site, we mainly encountered high coral/turf algae cover and high abundances of associated fish feeding groups (territorial farmers, corallivores). Our results provide evidence of a fresh SGD-driven relationship between altered hydrography and distinct fish communities with elevated abundances at groundwater springs in a coral reef lagoon. These findings suggest that the management and assessment of secondary consumer productivity in tropical lagoons should take into account the effects of groundwater springs.     

Calcareous Sands from a Coral Atoll-Should It Be Mined or Not?

Many lagoons of coral atolls contain huge reserves of very pure calcareous sands in an easily exploitable form that can be used in a number of industries. It is well known that the geomorphic situation in these coral islands is very delicate. With reference to the calcareous sand deposits in the coral atolls of Lakshadweep, a diversity of opinion exists on the aspect of exploitation, though the reserves were proved more than 20 years ago. Elsewhere calcareous sands have been used for several purposes. No raw materials other than coral sands and corals are available in these islands for developmental work such as construction of building and jetties. Several recommendations have been made to keep the system undisturbed to maintain the ecosystem. It is suggested that an attempt should be made to determine an optimum depth of exploitation of these sands without affecting the reef growth and balance of the ecosystem. This will improve the island economy and better quality of life for the islanders. The strategy will help development elsewhere also.     

Reducing Environmental Impact of Aggregate Excavation in Small Tropic Pacific Islands

Excavating sands and gravel on land in combination with constructing reservoirs for storing fresh water is an ideal approach in atolls. Appropriate mining of gravel from the prograding gravel beach is acceptable. Digging reef rock close to the edge of the wide ocean reef flat without surface loose sediments on it or sand beach can be accepted. Excavating sand from some depths in lagoon is a scientific approach particularly important for urbanized atolls. However, selecting appropriate sites for mining sand other than at some depths in lagoon is suitable to rural islands without dense populations. These sites include up drift side of long groin on the reef flat,partly filled access channel-port, outlet of artificial channel and lagoon margin on the prograding coast.     

Carbon and nitrogen dynamics of the intertidal seagrass, <Emphasis Type="Italic">Zostera japonica</Emphasis>, on the southern coast of the Korean peninsula

Seagrasses require a large amount of nutrient assimilation to support high levels of production, and thus nutrient limitation for growth often occurs in seagrass habitats. Seagrasses can take up nutrients from both the water column and sediments. However, since seagrasses inhabiting in the intertidal zones are exposed to the air during low tide, the intertidal species may exhibit significantly different carbon (C) and nitrogen (N) dynamics compared to the subtidal species. To examine C and N dynamics of the intertidal seagrass, Zostera japonica, C and N content and stable isotope ratios of above- and below-ground tissues were measured monthly at the three intertidal zones in Koje Bay on the southern coast of Korea. The C and N content and stable isotope (δ¹³C and δ¹⁵N) ratios of seagrass tissues exhibited significant seasonal variations. Both leaf and rhizome C content were not significantly correlated with productivity. Leaf δ¹³C values usually exhibited negative correlations with leaf productivity. These results of tissue C content and δ¹³C values suggest that photosynthesis of Z. japonica in the study site was not limited by inorganic C supply, and sufficient inorganic C was provided from the atmosphere. The tissue N content usually exhibited negative correlations with leaf productivity except at the upper intertidal zone, suggesting that Z. japonica growth was probably limited by N availability during high growing season. In the upper intertidal zone, no correlations between leaf productivity and tissue elemental content and stable isotope ratios were observed due to the severely suppressed growth caused by strong desiccation stress.     

基于Ecopath模型的七连屿礁栖性生物的生态承载力分析

生态承载力评估是开展生物资源增殖放流, 维持珊瑚礁生态系统健康的基础和前提。本文基于2019年渔业资源和生态环境的综合调查数据, 构建了七连屿珊瑚礁海域生态系统的生态通道(Ecopath)模型, 分析和探讨了相关功能组增殖放流的生态承载力。结果显示, 七连屿珊瑚礁海域生态系统各功能群营养级范围为1.00~3.81; 生态系统的总能量转化效率为13.45%; 生态系统以牧食食物链占据主导地位, 直接来源于初级生产者的能流占比为57%。系统总初级生产量/总呼吸量为2.54; 总初级生产量/总生物量为19.07; 系统连接指数和系统杂食性指数分别为0.36和0.22, 表明当前七连屿珊瑚礁海域生态系统的成熟度和稳定性偏低, 系统对于外界的干扰抵抗能力较弱。在未改变七连屿珊瑚礁生态系统结构和功能的前提下, 各功能组中珊瑚、双壳类和植食性鱼类的生态承载力分别为25.09~53.77t•km^-2、2.55~39.95t•km^-2和4.89~17.94t•km^-2, 因此仍具有较大的增殖空间。珊瑚礁鱼类群落的最大生态承载力同珊瑚礁无脊椎动物群落的增殖密切相关, 在未来的珊瑚礁渔业管理中应从生态系统整体结构的角度综合考虑增殖放流的方法设计。     

Effects of reef morphology variations on wave processes over fringing reefs

Many low-lying tropical and sub-tropical atolls fringed by coral reefs are susceptible to coastal inundation during extreme wave events. Previous studies have shown that the infragravity (IG) wave is the dominant component of shoreline run-up compared to the sea and swell (SS) wave and the wave-induced setup. To better understand both the SS and IG wave dynamics over a fringing reef with various morphologies, a series of laboratory experiments were conducted in a wave flume based on an idealized fringing reef profile. The shoreline responses of waves to different reef morphologies with/without the reef crest, the lagoon and the reef surface roughness were examined. IG wave resonance on the reef flat was identified by a spectral analysis of the shoreline wave records. Subsequently, a numerical model based on the Boussinesq equations was validated by the experimental data. The model was then applied to investigate the impacts of varying reef morphologic features (fore-reef slope, reef-crest width, lagoon width, and reef roughness coefficient) on the shoreline wave motions.     

Coastal ecosystem dynamics: Relevance of benthic processes

It is believed that the ecological balance and productivity of marine coastal environments are directly related to nutrient supplies from various sources including riverine-estuarine-coastal exchange, upwelling, precipitation, nitrogen fixation, and nutrient regeneration. In south Texas coastal waters, where phytoplankton productivity is comparable to other high productive coastal areas, many nutrient sources are suspected, but are not equally important in supplying sufficient nutrients to drive coastal production dynamics. Nitrogen regeneration from the benthos is implicated from a 2.5-y study of the nutrient cycling processes important in contributing to production levels in these waters. Sediments of the south Texas coastal habitat appear to exhibit a sensitive coupling with overlying waters, where a strong negative correlation exists between the random periodicity of external supplies of ‘new’ nitrogen to the coastal system and the rate at which nitrogen is recycled by sediments. This pattern buffers these waters against extended periods of low input of nutrients from external sources. The development of a conceptual scheme for nutrient cycling in this coastal habitat has provided a more holistic framework from which we can derive an objective assessment of the importance of mechanisms in the system. All data collected so far suggest that the primary production of organic matter and passage through the benthic habitat of these coastal waters is an important pattern responsible for the continued maintenance of productivity in the south Texas coastal ecosystem.     

Water circulation dynamics, water column nutrients and plankton productivity in a well-flushed tropical bay in Kenya

Water circulation, water column nutrients and plankton productivity were studied in a tropical bay with high rates of water exchange (60% to 90% per tide) and short residence times (3 to 4 h). The water circulation is predominantly affected by the semi-diurnal tides, which cause strong and reversing currents in the mangrove creeks (0.60 m·s⁻¹) and currents of low magnitude in the neighbouring seagrass and coral reef zones (< 0.30 m·s⁻¹). Tidal asymmetry, with relatively stronger ebb than flood flows in the mangrove creeks, promotes the net export of nutrients from the river mouth and of organic matter from the mangroves to the seagrass beds. The main sources of the dissolved inorganic nutrients are two rivers (the Kidogoweni and Mkurumuji) which discharge (up to 17.0 m³·s⁻¹) in the upper and lower regions of the bay. The increased input of nutrients did not cause eutrophic conditions since nutrients were rapidly flushed out of the bay. The mangrove biotope generated small amounts of dissolved nutrients which are likely to be used for primary production within the mangrove zone. The production of nutrients in the mangrove zone was masked by high rates of flushing, such that no appreciable nutrient signal was detected in the dry season when the influence of the rivers diminished. The rates of primary production were low in the mangrove, seagrass, and coral reef biotopes in the dry season. Primary production increased slightly during the rainy season. The level of chlorophyll a in the mangrove biotope increased during ebb tides and decreased during flood tides. The highest zooplankton densities, which could not be related directly to primary production in the water-column, occurred at the seagrass station during the wet season.     

南海九章环礁中牛轭礁和西门礁新生沙洲沉积特征与动态

南沙群岛的珊瑚礁以环礁形式存在, 拥有各具特色的地貌形态。九章环礁中的牛轭礁和西门礁是两座发育有新生沙洲的环礁, 代表灰沙岛形成前一个重要的过渡性地貌演化阶段。这两处新生沙洲表层沉积物样品的粒度分析表明: 沉积物主要组分为珊瑚碎屑, 长轴中值粒径在14~45mm之间, 属于砾石级别; 样品分选系数在4.5~31之间, 分选性很差; 球度值为0.52~0.68, 球度差。粒度特征值中, 中值粒径具有随着到水边线距离的增大而升高的趋势, 而分选性和球度与距水边线距离关系不大。整体上中值粒径与分选系数呈正相关关系, 而与球度呈负相关关系。历史文献记载和卫星图像表明, 牛轭礁和西门礁上的新生沙洲都是近年来才形成的, 与风暴过程及冬季风有关。牛轭礁上沙洲向北迁移, 同时其长轴向东南方向延伸; 西门礁上沙洲整体向东南方向迁移, 并形成回弯形沙嘴形态。新生沙洲的出现与珊瑚碎屑物质供给变化或风暴浪作用变化的关系还需进一步探讨。     

Controls on the ratio of mesozooplankton production to primary production in marine ecosystems

An ecosystem model was used to (1) determine the extent to which global trends in the ratio of mesozooplankton production to primary production (referred to herein as the “z-ratio”) can be explained by nutrient enrichment, temperature, and euphotic zone depth, and (2) quantitatively diagnose the mechanisms driving these trends. Equilibrium model solutions were calibrated to observed and empirically derived patterns in phytoplankton biomass and growth rates, mesozooplankton biomass and growth rates, and the fraction of phytoplankton that are large (>5 μm ESD). This constrained several otherwise highly uncertain model parameters. Most notably, half-saturation constants for zooplankton feeding were constrained by the biomass and growth rates of their prey populations, and low zooplankton basal metabolic rates were required to match observations from oligotrophic ecosystems. Calibrated model solutions had no major biases and produced median z-ratios and ranges consistent with estimates. However, much of the variability around the median values in the calibration dataset (72 points) could not be explained. Model results were then compared with an extended global compilation of z-ratio estimates (>10 000 points). This revealed a modest yet significant (r=0.40) increasing trend in z-ratios from values ～0.01–0.04 to ～0.1–0.2 with increasing primary productivity, with the transition from low to high z-ratios occurring at lower primary productivity in cold-water ecosystems. Two mechanisms, both linked to increasing phytoplankton biomass, were responsible: (1) zooplankton gross growth efficiencies increased as their ingestion rates became much greater than basal metabolic rates and (2) the trophic distance between primary producers and mesozooplankton shortened as primary production shifted toward large phytoplankton. Mechanism (1) was most important during the transition from low to moderate productivity ecosystems and mechanism (2) was responsible for a relatively abrupt transition to values >0.1 in high productivity ecosystems. Substantial z-ratio variations overlying these mean trends remained unexplained by these mechanisms. Potential sources of this variability include zooplankton patchiness, unresolved effects of advection and unsteady dynamics, unresolved shifts in mesozooplankton sizes and species, and unresolved aspects of zooplankton bioenergetics. Comparison of the modeled z-ratio patterns and mechanisms diagnosed herein with those obtained using models with expanded biological dynamics embedded in global circulation models will help further elucidate the causes of this variation.     

北冰洋西部沉积物有机碳、氮同位素特征及其环境指示意义

通过对楚科奇海及邻近的北冰洋深水区表层沉积物中有机碳同位素含量(δ13C)、氮同位素含量(δ15N)及生物成因SiO₂(BSiO₂)含量分析,结果表明海源和陆源有机质的分布受海区环流结构和营养盐结构所制约.楚科奇海中西部和楚科奇海台受太平洋富营养盐海水的影响,海洋生产力高,沉积物中海源有机质和BSiO₂含量高;靠阿拉斯加一侧海域海水的营养盐含量和生产力都偏低,沉积物中陆源有机质比重增加;在研究区北部和东北部的楚科奇高地和加拿大海盆,冰封时间较长,营养盐供应少,海洋生产力低,但来自马更些河和阿拉斯加北部的陆源有机质增多,沉积物中BSiO₂含量小于5%,海源有机质百分含量小于40%.由于亚北极太平洋水通过楚科奇海向北冰洋海盆输送,研究区营养盐池表现为开放系统,营养盐的利用率与它的供应成反比,与海洋生产力成反比.     

Effects of epibionts on Sabellaria alveolata (L.) biogenic reefs and their associated fauna in the Bay of Mont Saint-Michel

Biogenic structures built by ecosystem engineers such as corals, bivalves, polychaetes, and sea grasses provide habitat for benthic vertebrates and invertebrates. The polychaete Sabellaria alveolata is an important foundation species whose reef structure adds topographic complexity and high levels of biodiversity to the otherwise low-relief, low diversity, soft-bottom environments in the Bay of Mont Saint-Michel, France, where the largest such reef formations in Europe are found. In this bay, reefs are being increasingly colonised by oysters (Crassostrea gigas) from local aquaculture operations and by green algae (Ulva sp.) due to the increasing inputs of nitrates from terrestrial origin. The purpose of this study was to investigate the possible impacts of epibiotic oysters and green algae on the S. alveolata population and reef community structure in the Bay of Mont Saint-Michel, France. Univariate and multivariate comparisons of macrofauna were conducted for five reef types: controls (no epibionts), low oyster density, high oyster density, green algae, and oyster and green algae. Results showed that all the three reef types with oysters had significantly higher species richness and diversity values than control and algae-only reef types. Pairwise ANOSIM and SIMPER comparisons of controls versus the four reef types with epibionts revealed that all three of the reef types with oysters were significantly different from controls, but there was no significant difference between controls and algae-only reef types. A striking feature of the reef comparisons is that no single species in this species-rich system contributed more than 8.86% to the dissimilarity between the reef types. Thus, k-dominance curves for species abundances were not effective in revealing differences among the reef types. Our results demonstrate that recent anthropogenic inputs of oysters affect the reef species assemblage more strongly than algal epibionts. In addition, epibionts, especially green algae, alter S. alveolata population structure, causing a reduction in new recruits that over the long run may cause significant damage to the reef structure itself. These results are a first step towards understanding anthropogenic threats to S. alveolata reefs and may be useful in the development of strategies for their protection and management.     

Spatial variation of nutrients and primary productivity in the Rufiji Delta mangroves,Tanzania

Determinations of spatial and temporal variations in organic matter and nutrient dynamics in water and sediments are crucial for understanding changes in aquatic bodies. In this study, we (i) determine the spatial dynamics of dissolved inorganic nutrients, during the transition from the dry to the rainy season, and (ii) provide future productivity predictions for the Rufiji Delta mangroves, Tanzania, based on the input of various nutrients. Water samples were collected from six locations, three times per year between April 2012 and January 2014, and analysed for dissolved nutrients, total organic and inorganic carbon, chlorophyll a, chlorophyll b and total carotenoids. The prediction of future net primary productivity in the Rufiji mangroves was undertaken using the software STELLA. The mean nutrient concentrations were of the order: nitrate > phosphate > ammonium > silica > dissolved organic carbon. The study revealed that high nutrient concentrations occurred in the northern part of the Rufiji Delta as a result of anthropogenic influence in the watershed. Modelling of nutrient inputs into the delta indicated enhanced primary productivity, which is expected to increase the vulnerability of water quality in the near future due to eutrophication.