The importance of facilitation in the zonation of shrubs along a coastal salinity gradient

Question: What are the interactive roles of abiotic stress and plant interactions in mediating the zonation of the shrub Tamarix chinensis along a salinity gradient? Location: Yellow River estuary (37°46′N, 119°09′E), northeast China. Methods: We surveyed the zonation of T. chinensis along a salinity gradient and quantified its salt tolerance using a pot experiment. In two field experiments, we transplanted T. chinensis seedlings into salt marsh, transitional zone and upland habitats, manipulated neighbours and quantified survivorship and biomass to examine neighbour effects. We also quantified vegetation effects on abiotic conditions in each zone. Results: Tamarix chinensis dominated the transitional zone, but was absent in upland and salt marsh habitats. In the pot experiment, T. chinensis grew well in freshwater treatments, but was inhibited by increasing salinity. Field experiments revealed that competition from neighbours limited T. chinensis growth in the uplands, while T. chinensis transplants were limited, with or without neighbours, in the salt marsh by high soil salinity. In the transitional zone, however, T. chinensis transplants performed better with than without neighbours. Vegetation removal significantly elevated soil salinity in the transitional zone, but not in other zones. Conclusions: Competition, facilitation and abiotic stress are all important in mediating the zonation of T. chinensis. Within its physiological stress tolerance range, or fundamental niche, it is limited by plant competition in low salinity habitats, and facilitated by neighbours in high salt stress habitats, but cannot survive in salt marshes having salinities above its salt stress tolerance limit. Our results have implications for understanding the relationships between facilitation and stress gradients.     

First records of Gastrotricha from South Africa, with description of a new species of Halichaetonotus (Chaetonotida, Chaetonotidae)

During a survey of the biota of the St. Lucia Estuary in the iSimangaliso Wetland Park, South Africa, a number of Gastrotricha were found among samples of meiofauna. Fresh, marine sediment yielded several specimens belonging to a total of seven species. Of these, two are already known from other regions (i.e., Dactylopodola australiensis and Heteroxenotrichula squamosa), one is described as new to science (Halichaetonotus sanctaeluciae sp. n.), while the remaining four (Pseudostomella sp., Halichaetonotus sp.1, Halichaetonotus sp. 2, Xenotrichula sp.) require further collections and analysis, in order to establish the extent of their affiliation to species already described. General appearance, shape of hydrofoil scale and the occurrence of three long spines on the dorsal side make the new species most closely related to Halichaetonotus australis and Halichaetonotus marivagus. The key differences from these taxa and between Halichaetonotus sanctaeluciae sp. n. and Halichaetonotus aculifer are discussed.     

长江口及邻近海域秋冬季小型底栖动物类群组成与分布

对2009年11-12月采自长江口及邻近的东海海域19个站位的小型底栖动物类群组成、丰度、生物量和空间分布及其与沉积环境的关系进行了研究.结果表明,该海域秋冬季小型底栖动物的平均丰度和生物量分别为(1081 ±700)个/10 cm2和(600±374) μg干重/10 cm2,均呈现由北往南、由近岸向外海递减的趋势,且在长江口冲淡水向东海的扩展区域内,小型底栖动物的丰度明显较东海外围海域高.该数量与同一海域春季的研究结果相近,但明显低于夏季.在分选出的12个主要类群中,海洋线虫在丰度上占绝对优势(94.4％),其次是涡虫类(2.3％)和桡足类(2.0％).线虫也是生物量上的最优势类群(占68.1％),其次是涡虫类(14.8％)、桡足类(6.8％)和多毛类(5.8％).在垂直分布上,占总量70.8％的小型底栖动物和69.9％的线虫分布于0-2 cm表层,均高于54％-65％的历史资料.Spearman相关分析表明,小型底栖动物丰度与叶绿素a含量呈显著正相关,与水深、底层水温和底层盐度呈显著负相关.BIOENV分析显示与小型底栖动物类群组成和丰度相关性最高的环境因子组合为水深和脱镁叶绿素a含量.海洋线虫与桡足类数量之比(N/C)可大致反映本海域沉积环境的质量状况,但沉积物类型等因素的影响可造成环境评价的偏差.通过对639条线虫生物体积的测算,获得两个站位的线虫平均个体干重分别为0.104μg/个和0.365 μg/个.研究表明,我国当前普遍采用的0.4 μg/个这一系数估计的线虫生物量将不同程度地高估其实际生物量.     

珠江口超微型浮游植物时空分布及其与环境因子的关系

对珠江口及近海区域进行了夏季和冬季超微型浮游植物(0.2-3μm)调查,分析了其时空分布及其与环境因子的关系.夏季,珠江口浮游植物密度与磷酸盐成显著正相关,且N/P远远高于30,表明浮游植物受到P限制.夏季超微型藻数量比冬季高一个数量级,其丰度与盐度成显著正相关而和营养盐(溶解性无机氮(DIN),PO4-P,SiO4-Si)显著负相关,表明珠江口超微型藻受到径流的负面影响,表现出其数量在虎门附近海域低,随着咸淡水混合程度的加剧逐渐增大的分布特征;超微型浮游植物叶绿素a在总叶绿素a中的比例也表现为河口上游低,到万山群岛附近海域达到最大,推测近海高光照、低营养盐更适宜超微型藻的生长,同时也说明超微型浮游植物适应贫营养环境的生态特点.     

长江口和杭州湾凤鲚胃含物与海洋浮游动物的种类组成比较

2009年6月—8月期间在长江口及杭州湾水域收集了1355尾的凤鲚（Coilia mystus）标本,对其胃含物进行分析,期间采用出现频率（F）、个数百分比（N）、重量百分比（W）、相对重要性指标（IRI）、优势度（Y）公式计算,并进行种类的相似性分析,同步采集了取样点附近的浮游动物,比较了凤鲚胃含物食谱与该海域浮游动物种类组成。结果表明：河口性的长额刺糠虾IRI 为703.25,%IRI为62.94%,远远超过其他种类,甚至超过任何一个桡足类优势种,因而是凤鲚食谱中的最重要的种类。凤鲚摄食的其他主要种类包括：火腿许水蚤（Schmackeria poplesia）（IRI = 261.04）,虫肢歪水蚤（Tortanus vermiculus）（IRI = 107.53）、真刺唇角水蚤（Labidocera euchaeta）（IRI = 27.27）。以上四种浮游动物重要性合计%IRI为98.36%。在主要食物种类占绝对优势。因而是凤鲚饵料中最重要的优势种。种类组成相似性分析结果显示：胃含物和海域浮游动物之间的相似度值大致在0.363—0.365之间;而两者桡足类之间的相似值在0.521—0.575之间。推测凤鲚对个体较小的桡足类摄食方法是过滤性摄食,对种类的选择性较低。而对个体较大的糠虾则是有选择性追逐摄食。     

Spatial heterogeneity in size and parasitism: How it arises in an estuarine snail population

Populations of Ilyanassa obsoleta, a snail abundant in estuaries along the Atlantic coast of North America, exhibit much unobvious spatial heterogeneity. Lifetime dispersal of snails stands to be great, as they live for decades and can make daily moves of tens of meters. They could distribute uniformly, but in many populations there are characteristic spatial distributions of differently sized and trematode-infected snails. This is the case where this work was done in the Savages Ditch habitat of Rehoboth Bay, Delaware, U.S.A.. The study was designed to explain how the spatial heterogeneity in that habitat arises as a consequence of snail movements. Individually marked snails were tested for trematode infections and released from five well-separated positions. Snails released from each position were in three groups: (1) natives, collected from the position area, and (2) large and (3) small “outlanders”, collected from a site in the habitat that was separated from all release positions, had enhanced tidal currents, and where both size classes were available. Locations of found, released snails were noted for up to four years. Depending on collection site, many native snails were parasitized. In any case, they always tended to disperse in the vicinity where initially collected. Large outlanders (∼ 21% infected) dispersed variably, moving back toward their source area from certain release positions, but not from others. Small outlanders (∼ 4% infected), almost regardless of where released, tended to disperse back toward their source area. Dispersals of these snail groups from the five release positions explains much about how the pattern of spatial heterogeneity seen in the habitat arises.     

Natural and anthropogenic changes to mangrove distributions in the Pioneer River Estuary (QLD,Australia)

We analyzed a time series of aerial photographs and Landsat satellite imagery of the Pioneer River Estuary (near Mackay, Queensland, Australia) to document both natural and anthropogenic changes in the area of mangroves available to filter river runoff between 1948 and 2002. Over 54 years, there was a net loss of 137 ha (22%) of tidal mangroves during four successive periods that were characterized by different driving mechanisms: (1) little net change (1948–1962); (2) net gain from rapid mangrove expansion (1962–1972); (3) net loss from clearing and tidal isolation (1972–1991); and (4) net loss from a severe species-specific dieback affecting over 50% of remaining mangrove cover (1991–2002). Manual digitization of aerial photographs was accurate for mapping changes in the boundaries of mangrove distributions, but this technique underestimated the total loss due to dieback. Regions of mangrove dieback were identified and mapped more accurately and efficiently after applying the Normalized Difference Vegetation Index (NDVI) to Landsat Thematic Mapper satellite imagery, and then monitoring changes to the index over time. These remote sensing techniques to map and monitor mangrove changes are important for identifying habitat degradation, both spatially and temporally, in order to prioritize restoration for management of estuarine and adjacent marine ecosystems.     

Effects of salinity and temperature on the expression of enzymatic biomarkers in Eurytemora affinis (Calanoida, Copepoda)

In order to establish effective enzymatic biomarkers that could provide in situ early warning of contaminant exposure in estuarine ecosystems, the potential effects of the principal abiotic factors (temperature and salinity) were investigated on common biomarkers, the acetylcholinesterase (AChE) and the glutathione S-transferase (GST) in Eurytemora affinis. Short term salinity stress effects simulated during an experimental tide indicated that enzymatic activities of this species are characterized by maximum expression related to an optimal salinity range (between 5 and 15 psu). Moreover, longer time exposure to various salinity tanks confirmed the effects of this factor on both AChE and GST activities. Therefore, optimal AChE activity was measured at 10 psu, while optimal GST activity was measured at 5 psu. Furthermore, significant effects of temperature were also recorded, particularly for AChE expression (slight effects were measured on GST expression) with an optimal condition at 11 degrees C. These experiments indicated a more pronounced effect of salinity over temperature especially on the AChE expression and confirmed the need to standardize sampling procedures in relation with environmental parameters for biomonitoring studies based on enzymatic analyses.     

Fish assemblage in the Pearl River Estuary: Spatial‐seasonal variation,environmental influence and trends over the past three decades

The Pearl River Estuary is the largest estuary in South China and plays a considerable role in the local fisheries economy, yet little is known about the current state of fish assemblage in this ecosystem. To quantify spatial‐seasonal variations, environmental influences, and trends over the past three decades of the fish assemblage in the Pearl River Estuary, we sampled 11 sites seasonally from December 2013 to September 2016. Throughout the study, 285 species from 88 families and 195 genera were collected. There were obvious spatial and seasonal variations of the fish assemblage in terms of the dominant species, species richness, and composition of ecological types. Mouth distance, NH₄⁺ N, chlorophyll‐a, flow, DO, salinity and water transparency were the main variables influencing the spatial‐temporal dynamic of fishes within the estuarine systems. Compared with the record of 330 species in the 1980s, the number of fish species in the Pearl River Estuary has declined by 45 fish species. The Jaccard's similarity of fish composition between the historical investigation (the 1980's) and the present investigation (2013–2016) was 0.62, with 95 species undiscovered and 50 species increased in the present study compared to the 1980s, indicating the assemblage structure has obviously changed. However, in term of ecological guilds, there was no significant difference in the composition of all the selected ecological traits between these two periods. Anthropogenic activities including overfishing, introducing alien fish, dam construction and pollution were considered the main disturbance on fish composition over the past three decades. We conclude that there existed pronounced spatiotemporal changes of fish assemblages, which arises from the compounding effects of environmental factors and anthropogenic activities. These findings are beneficial to understanding and developing suitable conservation strategies for the management and protection of fish resources in the Pearl River Estuary.     

闽江河口湿地秋茄叶绿素含量高光谱遥感估算

叶绿素含量是表征植被胁迫状态的一个重要指示因子,同时也是其它生化参数估算的重要基础,对其进行遥感反演具有重要意义。选取闽江口秋茄(Kandelia candel)作为研究对象,分别于2013年4月和7月采集叶片,室内测定其叶片正面和反面反射光谱,同时测定其叶绿素含量(单位面积含量和单位质量含量)。选取13个常用参数进行敏感性分析,并进一步选取与叶绿素相关系数较高的参数建立估算模型。结果表明,秋茄叶片反面反射率高于正面,尤其在绿光波段和近红外波段部分区域(1450—2450 nm)表现较为明显。对所选取的大部分参数而言,其与单位面积叶绿素含量的相关系数要高于与单位质量叶绿素含量的相关系数;基于正面光谱计算的光谱参数与叶绿素含量的相关系数要高于基于反面光谱计算的光谱参数。估算与验证模型结果进一步表明,TCARI、Vog1、Vog2和Vog3能较好的估算不同生长期秋茄叶片的叶绿素含量。此外,在使用GM、Carter2和PSSRb估算叶片叶绿素含量时,可以适当考虑反面光谱的应用。这些结果也预示着利用高光谱遥感数据估算秋茄叶片叶绿素含量是可行的,并且具有较高的估算精度。