Habitat quality of estuarine nursery grounds: Integrating non-biological indicators and multilevel biological responses in Solea senegalensis

Estuaries are highly valuable ecosystems that provide various goods and services to society, such as food provision and supporting nursery habitats for various aquatic species. Estuarine habitat quality assessment is thus critical in managing both ecological and economic value. In this work, various biological and non-biological indicators of habitat quality in estuarine nursery areas were determined, encompassing local environmental conditions, chemical contamination, anthropogenic pressures, juvenile Solea senegalensis condition, biomarkers response to contamination and juvenile density. The various indicators provided an integrated view on habitat quality and their responses were broadly concordant. Nursery quality assessment based on anthropogenic pressure indicators and fish biomarker responses were very similar, signaling nursery areas with higher anthropogenic pressure in Tejo and Ria de Aveiro estuaries. Yet, favorable environmental conditions across all sites could have contributed to lessen the potential hazardous biological effects of exposure to anthropogenic stressors, resulting in soles’ fairly good condition and generally high juvenile density. Nevertheless, a mismatch between high juvenile density and high estuarine contribution to adult coastal populations was observed in areas with higher anthropogenic pressures. Although a causal relationship cannot be established, the results emphasize the need to fully understand how the estuarine period spent in estuaries and local processes determine the quantity and quality of juveniles exported to marine adult populations, which is critical to achieve the full potential of the fish production service of estuaries and coastal stock replenishment.     

珠江口伶仃洋中华白海豚栖息地利用对海岸线等变迁的响应

沿岸鲸豚类栖息地易受人类活动的干扰，导致其分布和核心栖息地发生变化。珠江口-漠阳江口中华白海豚种群是目前所知全球范围内最大的种群，其中伶仃洋水域是其重要的栖息地。近年来，珠江口伶仃洋周边城市发展带来的人类活动增加，白海豚的生存压力日益增大，分析伶仃洋中华白海豚对栖息地环境变化的响应，研究对应的保护策略显得非常迫切。以多源陆地资源卫星Landsat为数据源，通过影像分析近43年珠江口伶仃洋围填海造成的海域流失，结合近20年来采用截线抽样法收集的海豚观测数据，运用含障碍核插值（Kernel interpolation with barriers）方法，分析白海豚的分布及核心栖息地的变化。结果显示：1986-2015年期间，研究区域内流失的海域面积为344.08km²；目击分布离人工海岸线的平均距离大于自然海岸线的平均距离，目击分布到自然海岸线和人工海岸线的平均距离均在减小，表明过去20年白海豚的栖息地使用选择发生了一些变化，被迫适应人类活动的干扰；1997-2016年白海豚的分布范围呈现先增加后减小，白海豚栖息地使用的重心偏向伶仃洋东部水域，核心栖息地趋向主航道和无人海岛附近水域萎缩，可能是海豚因海域食物资源减少而迫不得已的选择。不同时期，珠江口中华白海豚国家级自然保护区所覆盖的核心栖息地比例呈递减趋势，占比由79.9%下降到49.4%，当前有必要对保护区范围和功能区作出一些优化调整，以适应栖息地使用的变化格局。     

On the cultivation of free-living marine and estuarine nematodes

Although a large body of literature exists on the systematics and ecology of free-living marine and brackish-water nematodes, key questions on the nature and magnitude of interactions between nematodes and other organisms in the benthos remain unanswered. Relatively few authors have investigated live nematodes in food web studies or in experiments dealing with the nematodes’ response to a varying environment. It is mainly for the latter purpose that attempts have been made to maintain, rear and cultivate selected species. This paper describes the methodology used for the maintenance, rearing, and eventual permanent agnotobiotic cultivation of a variety of estuarine nematodes. Spot plates, where small samples of sediment or macrophyte material are inoculated on a sloppy agar layer, have been used for the purpose of maintenance and initial cultivation. Those species that reproduce on spot plates are then selected for monospecific cultivation on agar layers with different nutrient enrichments and with micro-organisms cotransferred from the spot plates as food. Mixtures of bacto and nutrient agar prepared in artificial seawater were specifically suitable for the xenic cultivation of nine bacterivorous and, when supplied with Erdschreiber nutrients, two algivorous/bacterivorous nematode species. Up to three generations of five other nematode species have been reared under laboratory conditions, and several more were kept alive and active for variable periods of time on agar. Generation times observed on spot plates forAdoncholaimus fuscus andOncholaimus oxyuris were substantially shorter than previously published estimates and suggest a correspondingly higher predatory and scavenging potency for these and related enoplids. A procedure for the long-term storage of nematodes at −80°C with glycerol as a cryoprotectant was successfully used forDiplolaimella dievengatensis, Panagrolaimus sp. 1, andPellioditis marina, but not forDiplolaimelloides meyli. The authors have also summarized the existing literature on the cultivation of marine and brackish-water nematodes. Continuous cultivation appears to have been successful mainly for Aufwuchs and epiphytic nematodes; only few sediment-dwellers have been established in permanent culture. Of only just over 30 species that have ever been cultivated, more than half belong to one family (Monhysteridae) and three are Rhabditida, an order poorly represented in the marine environment. Four species have been grown in monoxenic and one in axenic culture, the latter though with limited success. It is concluded that our understanding of the basic nutritional requirements of marine nematodes is as yet insufficient, and that the culture techniques which have so far mainly deployed agar or liquid substrates, while being suitable for the cultivation of Aufwuchs and epiphytic nematodes, do not accurately enough mimic gradients specific of the natural habitat of many sediment-dwellers.     

Multi-species response to rapid environmental change in a large estuary system: A biochronological approach

The sensitivity of species to environmental change is dependent on their ecological requirements (i.e. specialist v. generalist), and hence likely to be species-specific. Identifying species level variation in environmental sensitivity informs assessments of community vulnerability and assists in developing adaptive management strategies. We investigated species-specific sensitivity in fish to understand the vulnerability of differing life histories and ecological requirements to rapid environmental alteration (i.e. drought). Biochronologies of fish growth, based on increment widths in otoliths, were analysed using a mixed modelling approach. We assessed multi-decadal responses in fish growth to environmental variation in the terminal system of Australia’s largest river, for three long-lived fish species with differing life histories and ecological requirements: a freshwater specialist and two estuarine generalists. Biochronologies were between 20 and 38 years long, spanned a decade of severe drought and showed considerable inter-annual variation in growth. Precipitation influenced the growth of the obligate freshwater specialist, Macquaria ambigua ambigua. Temperature and salinity influenced the growth of the two estuarine generalists: Argyrosomus japonicus (estuarine opportunist) and Acanthopagrus butcheri (estuarine dependent), respectively. These results suggest that generalisations about how species respond to environmental change may mask species-specific responses to dependent on the constraints of their ecological requirements (i.e. specialist v. generalist). These findings also highlight the importance of considering the diversity of life history strategies that inhabit an ecosystem when developing conservation and management strategies.     

Landscape-level seagrass–sediment relations in a coastal lagoon

We investigated the relationships between sediment (subaqueous soil) properties and eelgrass (Zostera marina L.) distribution to develop landscape-level soil-based strategies for choosing eelgrass restoration locations. Subaqueous soils were sampled and eelgrass cover determined for 14 soil-landscape units within a 116 ha area of Ninigret Pond, a coastal lagoon in Rhode Island, USA. Of the 14 soil-landscape units sampled for eelgrass cover, 52% had virtually no eelgrass cover (<10%), while 18% had high eelgrass cover (>90%). The Lagoon Bottom, Shallow Lagoon Bottom, Flood-tidal Delta Slope, and Barrier Cove subaqueous soil-landscape units had the highest eelgrass cover (66–100%). A weak relationship between eelgrass cover and water depths (r² = 0.10) was observed suggesting that properties other than water depth may also control eelgrass distribution. Subaqueous soils on landscapes with >60% eelgrass cover had relatively high levels of acid-volatile sulfides (>90 μg/g), high soil salinity levels (34–44 ppt), fine textures (silt loam), and relatively high total nitrogen levels (>0.15%). Four principal components accounted for 81% of the variability in eelgrass cover. The first component reflected particle-size distribution (i.e. sand, silt, and clay contents) effects and accounted for 43% of the variability. The other components suggested that eelgrass cover is correlated to carbonaceous remains, non-calcareous rock fragments and soil salinity. These data suggest that the current distribution of eelgrass within the study area is strongly influenced by physical and chemical subaqueous soil characteristics. Soil survey techniques proved useful for the delineation of sediment characteristics (e.g. texture, salinity) that influence eelgrass distribution patterns at landscape-level scales.     

Use of a real-time remote monitoring network (RTRM) and shipborne sampling to characterize a dinoflagellate bloom in the Neuse Estuary, North Carolina, USA

The spatial-temporal distribution of a dinoflagellate bloom dominated or co-dominated by Prorocentrum minimum was examined during autumn through early spring in a warm temperate, eutrophic estuary. The developing bloom was first detected from a web-based alert provided by a network of real-time remote monitoring (RTRM) platforms indicating elevated dissolved oxygen and pH levels in upper reaches of the estuary. RTRM data were used to augment shipboard sampling, allowing for an in-depth characterization of bloom initiation, development, movement, and dissipation. Prolonged drought conditions leading to elevated salinities, and relatively high nutrient concentrations from upstream inputs and other sources, likely pre-disposed the upper estuary for bloom development. Over a 7-month period (October 2001–April 2002), the bloom moved toward the northern shore of the mesohaline estuary, intensified under favorable conditions, and finally dissipated after a major storm. Bloom location and transport were influenced by prevailing wind structure and periods of elevated rainfall. Chlorophyll a within bloom areas averaged 106 ± 13 μg L⁻¹ (mean ± 1 S.E.; maximum, 803 μg L⁻¹), in comparison to 20 ± 1 μg L⁻¹ outside the bloom. There were significant positive relationships between dinoflagellate abundance and TN and TP. Ammonium, NO₃⁻, and SRP concentrations did not decrease within the main bloom, suggesting that upstream inputs and other sources provided nutrient-replete conditions. In addition, PAM fluorometric measurements (09:00–13:00 h) of maximal PSII quantum yield (F_v/F_m) were consistently 0.6–0.8 within the bloom until late March, providing little evidence of photo-physiological stress as would have been expected under nutrient-limiting conditions. Nitrogen uptake kinetics were estimated for P. minimum during the period when that species was dominant (October–December 2001), based on literature values for N uptake by an earlier P. minimum bloom (winter 1999) in the Neuse Estuary. The analysis suggests that NH₄⁺ was the major N species that supported the bloom. Considering the chlorophyll a concentrations during October and December and the estimated N uptake rates, phytoplankton biomass was estimated to have doubled once per day. Bloom displacement (January–February) coincided with higher diversity of heterotrophic dinoflagellate species as P. minimum abundance decreased. This research shows the value of RTRM in bloom detection and tracking, and advances understanding of dinoflagellate bloom dynamics in eutrophic estuaries.     

Products of Chlorophyll a Transformation by Selected Benthic Organisms in the Odra Estuary (Southern Baltic Sea)

The transformation of chlorophyll a by two benthic bivalves – Dreissena polymorpha and Mytilus edulis and, for comparison, by the chironomid Chironomus plumosus – was examined. D. polymorpha is a suspension-feeding, freshwater but very salinity-tolerant species, M. edulis a suspension-feeding marine species, and C.␣plumosus a typical detritivorous freshwater species. All three are common in the Odra Estuary. Specimens of the three species were collected from this area in the period 1999–2003. The bivalves were transferred to a compartment on land and kept in tanks filled with water (filtered and unfiltered) collected simultaneously with the organisms, under light and temperature conditions similar to those obtaining in their natural environment. Pigments in the water samples, faeces and pseudofaeces from the tanks, and in the gut content from C. plumosus, were determined with HPLC. The digestion products of the three species were mainly phaeophorbides a, generally thought to originate mainly from zooplankton grazing, and pyrophaeophytin a in minor quantities. The results indicate that the main chlorophyll a derivatives in faeces and pseudofaeces and gut content of the three species were the same as those in the sediments of the Baltic Sea, including the Odra Estuary. Our previous studies have shown that the sediments in this area are richer in phaeophorbides a than sediments from other parts of the southern Baltic Sea. All this suggests that the benthos may play an important role in the transformation of chlorophyll a in the Odra Estuary area.     

闽江河口湿地生物多样性及其保护

根据闽江河口湿地比较系统的调查资料,分析了生物多样性的状况及其受人为活动影响的原因,提出了湿地生物多样性保护的对策。研究表明,闽江河口区西自闽侯竹岐,东至连江川石岛,共划分10个湿地类型,总面积约459.2km2。闽江河口众多的湿地串珠状排列,有6块面积较大的湿地,是鸟类的主要栖息、繁殖和迁徙地。闽江河口湿地的维管束植物107科337属465种,被子植物89科317属438种,大型水生无脊椎动物61种,鸟类29科118种,植被类型4种类型、18个群系和22个群丛。文中分析了环境污染、不合理开发利用、盲目围垦等人为活动对闽江口湿地生物多样性的影响,最后提出了湿地生物多样性的保护对策。     

椒江口海域春秋季虾类资源分布与环境的关系

利用2010年春季(4月)和秋季(10月)椒江口海域渔业资源调查资料,分析了椒江口虾类资源密度的分布,优势种和水团、水深等环境因子对虾类数量和分布的影响.结果表明:椒江口海域春季和秋季虾类平均重量密度分别为7.89和86.20 kg·km-2,尾数密度均值分别为11.04×103和34.41×103 ind·km-2;虾类密度平面分布特征,在春季,调查海域虾类密度西部高于东部,高密度区出现在椒江河口沿岸区域,尤其是受椒江径流影响明显的北部沿海海域;在秋季,东部明显高于西部,尤其是大陈岛东南部受台湾暖流和浙江上升流影响的海域.逐步回归分析表明:椒江口表层温度与虾类重量密度和尾数密度均呈显著的相关关系(Pw =0.004,PN=0.01),但水深与资源密度相关关系不显著;春季,中国毛虾(Acetes chinensis)对虾类尾数密度贡献率最大,对重量密度贡献率也较大,为春季最重要的优势种;秋季,中华管鞭虾(Solenocera crassicornis)对尾数和重量密度贡献率均最大,为秋季最重要的优势种.     

基于GIS的长江口海域生态系统脆弱性综合评价

气候变化、富营养化、生境破碎等是全球普遍面临的生态问题,科学评估生态系统外部压力及其弹性力,对生态系统管理和生态修复具有重要的指导意义。使用空间主成分分析(SPCA)和层次分析法(AHP)构建评价指标体系,结合地理信息系统软件,对长江口海域生态环境脆弱性进行综合评价,并根据生态环境脆弱性指数(EVI)值,将研究区生态环境脆弱性分为5级:微度脆弱(0.5)、轻度脆弱(0.5—0.8)、中度脆弱(0.8—1.0)、重度脆弱(1.0—1.2)、极度脆弱(1.2—1.5)。结果表明:空间尺度上,长江口口门内生态环境脆弱度最高,生态环境脆弱度从口门内向口门外呈显著的降低趋势,近五年,口门内极度脆弱区空间分布南移;评估区域内,约2000 km~2的极度脆弱区发生了转变,极度脆弱区、重度脆弱区面积占比分别下降了7%和5%,长江口海域生态环境脆弱性明显好转。总体上,近年来大量陆源污染物输入以及生态系统结构变化,是导致长江口生态环境脆弱度较高的重要因素。