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.     

Variations in sexual and asexual reproduction of Scirpus mariqueter along an elevational gradient

In order to assess the importance of sexual and asexual reproduction during the life history of Scirpus mariqueter, its reproductive and growth characters were concurrently examined along an elevational gradient (from low elevation to high elevation). The proportions of flowering shoot and inflorescence mass, seed : flower ratio and seed weight were used to quantify the investment in sexual reproduction. The proportions of current-year shoot and rhizome mass were used to quantify the investment in asexual reproduction, and the proportion of corm mass was used for growth, respectively. It was found that vegetative propagation predominated at low elevation, whereas sexual reproduction predominated at high elevation; and that sexual reproduction increased with declining asexual reproduction along the gradient. The results suggest that asexual reproduction is relatively favored in the early life stage, whereas sexual reproduction is favored when the population becomes mature and aged, probably because of the functional differentiation between the two reproductive types. Sexual productive characters (i.e. the proportions of flowering shoot and inflorescence mass) were negatively correlated to both growth and asexual reproductive characters along the gradient, indicating there might exist some trade-offs among growth, sexual and asexual reproduction during the life history. However, no obvious pattern was found between asexual reproductive characters and growth characters along the elevational gradient, possibly because of the varied relationships between them at different life stages. The variations in sexual and asexual reproduction in the species and the relationship between them are thought to be of great significance for local population growth, species persistence and evolution.     

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.     

长江口不同水域浮游动物数量特征比较

为了分析长江口浮游动物与环境的关系,从2004年到2006年分别于5月份(平水期)和8月份(枯水期)在长江口水域共设22个观测站进行6次海洋调查.结果显示:长江口浮游动物丰度8月份高于5月份,北支略大于南支,长江口口外大于口内. 在大多数情况下,5月份丰度近海略大于咸淡交错水域,8月份相反.长江口浮游动物丰度和分布具有不确定性,水团的季节变化,外海水和冲淡水交汇的位置是影响长江口浮游动物分布特征的重要因素.对长江口南支水域而言,5月份中华华哲水蚤(Sinocalanus sinensis), 8月份火腿许水蚤(Schmackeria poplesia)是最主要的优势种;咸淡交错水域和北支优势种种类较多,真刺唇角水蚤(Labidocera euchaeta)在5月份和8月份都是主要优势种,其次是小拟哲水蚤(Paracalanus parvus).针刺拟哲水蚤(Paracalanus aculeatus),背针胸刺水蚤(Centropages dorsispinatus),太平洋纺锤水蚤(Acartia pacifica)和火腿许水蚤仅为8月份的主要优势种.对近海而言,中华哲水蚤(Calanus sinicus)是主要的优势种,其次是五角水母(Muggiaea atlantica)和肥胖箭虫(Sagitta enflata).     

In situ feeding rates and grazing impact of Mesopodopsis africana O. Tattersall in the St Lucia Estuary, South Africa

Mesopodopsis africana is an important mysid in southern African coastal zooplankton and a key species in the St Lucia estuarine lake, which is currently undergoing severe desiccation owing to freshwater deprivation. M. africana populations through much of the system are consequently under severe environmental stress. This study investigates the grazing dynamics of this mysid species, in relation to autotrophic food availability and other environmental constraints in two contrasting areas of the St Lucia Estuary, Charters Creek, heavily affected by the desiccation process and the Mouth, virtually under unchanged conditions. Gut evacuation experiments were conducted once each during the day and the night. Evacuation rates were consistently higher during the night, ranging from 0.27 to 0.33 h^-1 at Charters Creek and from 1.13 to 1.24 h^-1 at the Mouth. Ingestion rates were, therefore, higher at the Mouth resulting in population grazing impacts of 2.5% of the total microalgal biomass, while the grazing impact at Charters Creek was only 0.5%. The spatial variation in ingestion rates could be attributed to seasonal differences in gut evacuation rates, differences in the mean size of mysids used, or the physicochemical conditions present at the two stations. It is suggested that mysid populations at Charters Creek are predominantly driven by bottom-up forces, initiated by the harsh environmental conditions. Despite the lower ingestion rates exhibited at Charters Creek, results indicate that these mysids are capable of meeting all their energetic requirements from a microalgal diet alone, although they may also utilise a heterotrophic diet.     

Assessment of Heavy Metal Contamination in the Sediments of the Shuangtaizi Estuary Using Multivariate Statistical Techniques

In order to assess heavy metal pollution of sediment samples collected from Shuangtaizi estuary, contamination factor (CF) and multivariate statistical analyses, including principal component analysis (PCA), cluster analysis (CA) and correlation analysis, are carried out in this paper. CF confirms that Pb, Cu and Hg concentrations are very low and all fall within the range of background, while Zn and Cd demonstrate moderate contamination (in A10, A13, A15, A16 and A17 sites) and very high contamination (in A10, A13, A15 and A17 sites), respectively. The PCA indicates that four significant principal components (PCs) are extracted, explaining 88.959% of total variance, which suggests that Pb, Cu and Zn are mainly associated with organic carbon (OC). The result from CA is consistent with that obtained from PCA, classifying that the heavy metals in two clusters derive from different sources. Correlation analysis supports the conclusions from PCA and CA, elucidating the relationships between heavy metals and particle sizes of the sediments.     

利用导数光谱估算珠江河口水体悬浮泥沙浓度

悬浮泥沙不仅影响水体的生态状况,而且对河口地貌及岸线的演变起到重要作用。高光谱技术可用于船载、机载及星载的光学传感器上,被认为是监测光学复杂水体的有效工具。为研究高光谱技术在河口悬浮泥沙监测应用中的可行性,于2004年5月及2006年8月,在珠江口进行了两个航次的现场水质采样及同步光谱测量。测量的原始遥感反射率光谱的分辨率为0.38nm,处理成为10nm的带宽,并进一步处理成导数光谱。以悬浮颗粒物(SPM)表征悬浮泥沙,分析了SPM和各光谱间的相关性。结果显示,一阶导数光谱,特别是605nm,可用于河口水体的SPM估算。该研究结果可应用到光学复杂河口水体的悬浮泥沙现场监测,并且对Hyperion及环境1号等卫星成像高光谱数据有潜在的应用价值。     

Determining effects of suspended sediment on condition of a suspension feeding bivalve (Atrina zelandica): results of a survey, a laboratory experiment and a field transplant experiment

The horse mussel Atrina zelandica (Gray) is a large, suspension feeding pinnid bivalve, common in coastal and estuarine areas of northern New Zealand. As a suspension feeder, Atrina is likely to be influenced by suspended sediment loads. We conducted a laboratory experiment to determine the effect of short-term elevations in turbidity levels, such as those commonly recorded during storms, on the physiological condition and clearance rates of Atrina. We also conducted a field survey and a 3-month transplant experiment at multiple sites along a gradient of increasing suspended sediment load in a New Zealand estuary. Laboratory clearance rates of Atrina declined above a threshold suspended sediment concentration, and Atrina physiological condition at the end of this experiment was lower in high cf. low turbidity treatments. Decreases in Atrina condition were detected after exposure to elevated levels for only 3 days. The field survey and transplant experiment provided empirical evidence of a strong, negative effect of increasing suspended sediment flux on the physiological condition of Atrina. We suggest that relationships between the physiological condition of suspension feeders and sediment settling flux could provide a link between sediment inputs, which commonly occur as a result of catchment runoff during rainfall events, and the ecological health of estuarine and shallow coastal areas. Our study also demonstrated that Atrina have a natural distribution limit controlled by suspended sediment load. Thus, there is potential for larger-scale functional and structural effects on benthic communities in estuarine and coastal areas with high rates of sedimentation.     

Resolving the origins of invertebrate colonists in the Yangtze River Estuary with molecular markers: Implications for ecological connectivity

Understanding connectivity over different spatial and temporal scales is fundamental for managing of ecological systems. However, controversy exists for wintertime ecological connectivity between the Yangtze River Estuary (YRE) and inner southwestern Yellow Sea. Here, we investigated ecological connectivity between the YRE and inner southwestern Yellow Sea in wintertime by precisely pinpointing the source of the newly colonized populations of a winter‐spawning rocky intertidal invertebrate, Littorina brevicula (Philippi, 1844), on artificial structures along the coast of the Yangtze River Delta (YRD) using mitochondrial ND6 sequences and microsatellite data. Clear phylogeographic and genetic differentiation were detected between natural rocky populations south and north of the YRE, which resulted from the lack of hard substrate for rocky invertebrates in the large YRD coast. For the newly colonized populations on the coast of YRD, most individuals (98%) to the south of ~33.5°N were from natural rocky populations to the south of the YRE and most of those (94%) to the north of ~33.5°N were from the northern natural rocky populations, which demonstrated strong ecological connectivity between the inner southwestern Yellow Sea and the YRE in winter time. We presented the first genetic evidence that demonstrated a northward wintertime coastal current in the inner southwestern Yellow Sea, and precisely illustrated the boundary of the coastal current recently proposed by numerical experiment. These results indicated that the YRE serves as an important source of materials and energy for the inner southwestern Yellow Sea in winter, which can be crucial for the function of the Yellow Sea ecosystem.     

Biotic communities of freshwater marshes and mangroves in relation to saltwater incursions: implications for wetland regulation

An ecosystem-level study was conducted in the Guandu wetlands insubtropical coastal Taiwan to examine how salinity influences the abundance,diversity, and structure of biotic communities. We surveyed eight permanentstudy sites, spanning freshwater marshes, to the gate on the dyke, andmesohaline mangroves representing a gradient of the extent of saltwaterincursions. Analyses of abiotic variables showed that salinity was the primarydetermining factor for discriminating habitat types in the wetlands, butcommunities differed in their sensitivity to salinity. The composition of plantand insect communities was most affected by the salinity gradient, suggestingthe utility of these communities for ecological monitoring of saltwaterincursions. However, spatial changes in communities at higher trophic levels,including macrobenthos, mollusks, fish, and birds, could not be explained simplyby the salinity gradient. Instead, changes in these communities were morerelevant to the composition of other biotic communities. Our results show thatspecies richness and diversity of plant communities were higher in the marshesthan in the mangroves. Nevertheless, insect communities censused in themangroves had higher diversity, despite lower abundance and species richness.Macrobenthos surveyed in the mangroves showed higher biomass and number of taxa.Mollusks and fish were also more abundant at sites near the gate compared to themarsh sites. This suggests that maintaining a tidal flux by means of gateregulation is necessary for conserving the spatial heterogeneity andbiodiversity of coastal wetlands.