Network analysis to inform invasive species spread among lakes

Often facilitated by human-mediated pathways,aquatic invasive species are a threat to the health and biodiversity of global ecosystems.We present a novel approach incorporating survey data of watercraft movement in a social network analysis to reconstruct potential pathways of aquatic invasive species spread between lakes.As an example,we use the green alga Nitellopsis obtusa,also known as starry stonewort,an aquatic invasive species affecting the Great Lakes region in the United States and Canada.The movement of algal fragments via human-mediated pathways(i.e.,watercraft)has been hypothesized as the primary driver of starry stonewort invasion.We used survey data collected at boat ramps during the 2013 and 2014 openwater seasons to describe the flow of watercraft from Lake Koronis,where N.obtusa was first detected in Minnesota,to other lakes in the state.Our results suggest that the risk of N.obtusa expansion is not highly constrained by geographic proximity and management efforts should consider highly connected lakes.Estimating human movement via network analysis may help to explain past and future routes of aquatic invasive species infestation between lakes and can improve evidence-based prevention and control efforts.     

Network analysis to inform invasive species spread among lakes

Often facilitated by human-mediated pathways,aquatic invasive species are a threat to the health and biodiversity of global ecosystems.We present a novel approach incorporating survey data of watercraft movement in a social network analysis to reconstruct potential pathways of aquatic invasive species spread between lakes.As an example,we use the green alga Nitellopsis obtusa,also known as starry stonewort,an aquatic invasive species affecting the Great Lakes region in the United States and Canada.The movement of algal fragments via human-mediated pathways(i.e.,watercraft)has been hypothesized as the primary driver of starry stonewort invasion.We used survey data collected at boat ramps during the 2013 and 2014 openwater seasons to describe the flow of watercraft from Lake Koronis,where N.obtusa was first detected in Minnesota,to other lakes in the state.Our results suggest that the risk of N.obtusa expansion is not highly constrained by geographic proximity and management efforts should consider highly connected lakes.Estimating human movement via network analysis may help to explain past and future routes of aquatic invasive species infestation between lakes and can improve evidence-based prevention and control efforts.     

Network analysis to inform invasive species spread among lakes

Often facilitated by human-mediated pathways,aquatic invasive species are a threat to the health and biodiversity of global ecosystems.We present a novel approach incorporating survey data of watercraft movement in a social network analysis to reconstruct potential pathways of aquatic invasive species spread between lakes.As an example,we use the green alga Nitellopsis obtusa,also known as starry stonewort,an aquatic invasive species affecting the Great Lakes region in the United States and Canada.The movement of algal fragments via human-mediated pathways(i.e.,watercraft)has been hypothesized as the primary driver of starry stonewort invasion.We used survey data collected at boat ramps during the 2013 and 2014 openwater seasons to describe the flow of watercraft from Lake Koronis,where N.obtusa was first detected in Minnesota,to other lakes in the state.Our results suggest that the risk of N.obtusa expansion is not highly constrained by geographic proximity and management efforts should consider highly connected lakes.Estimating human movement via network analysis may help to explain past and future routes of aquatic invasive species infestation between lakes and can improve evidence-based prevention and control efforts.     

Spread and status of seven submerged pest plants in New Zealand lakes

The distribution of seven submerged aquatic pest plants is reported. Lake vegetation surveys recorded pest plants in 27.9% of 344 lakes, with two species co‐occurring in 5.8%, and three species in 2.6% of lakes. Egeria densa was most frequent (15.4% of lakes), followed by Ceratophyllum demersum (9.0%), Lagarosiphon major (7.3%), and Utricularia gibba (5.5%). Spread since 2000 has continued for five pest plants, with 34 lakes invaded by U. gibba over 2004–08 alone. Early regional sites in proximity to human population centres were likely plant liberations and numerous potential founder colonies remain in garden ponds. Human activities were important for inter‐lake dispersal, with the exception of bird‐dispersed U. gibba. Significant lake associations between pest plants, and with presence of six exotic fish species, suggest common dispersal pathways and similar introduction risks. Therefore, predictions of future spread should be possible based on sources, dispersal pathways, and identifying key risk factors for lakes.     

Habitat selection of stone and starry flounders in an estuary in relation to feeding and survival

Juveniles of both stone flounder Platichthys bicoloratus and starry flounder Platichthys stellatus utilize estuaries as nursery grounds. To understand their habitat selection and the functions of habitats such as food supply, we defined the seasonal distribution of recently settled fish of these species in shallow nursery areas and investigated their feeding habits in the Natori River estuary, Japan. Distribution of stone flounder was limited to the lower estuary (<3 km upriver from the mouth) and stone flounder were most abundant near the mouth. Recently settled starry flounder were first detected further upstream in areas characterized by low salinity <10 and by the absence of the predatory sand shrimp Crangon uritai. Early juvenile stone and starry flounders consumed mainly siphons of the bivalve Nuttallia olivacea and the mysid Neomysis awatschensis, respectively; however, 1- and 2-yr-old fish of both stone and starry flounders fed mainly on the bivalve siphons. These results indicate that habitat selections of juvenile stone and starry flounders enable utilization of preferred prey and predator avoidance, respectively, and that non-overlap of these species' habitats results in avoidance of inter-specific competition for food between these two species.     

Quantitation of CYP1A expression in two flatfish species showing different prevalences of contaminant-induced hepatic disease

English sole (Pleuronectes vetulus) and starry flounder (Platichthys stellatus) are two sympatric flatfish species which show markedly different responses to chemical contaminant exposure. Whereas English sole develop hepatic neoplasms, the prevalences of which are strongly linked to exposure to polycyclic aromatic hydrocarbons (PAHs), evidence of neoplasia is virtually nonexistent in starry flounder, even those residing in areas with very high levels of PAH in the sediments. Because PAHs are activated to genotoxic forms by the action of cytochrome P450 1A (CYP1A) in teleosts, we are examining the hypothesis that variation in the hepatic expression of this major inducible cytochrome P450 isozyme may contribute to the differential contaminant response. These two species were captured in the Duwamish Waterway, a contaminated area of Puget Sound, Washington. Catalytic activity of CYP1A [determined as aryl hydrocarbon hydroxylase (AHH) activity] was measured in the liver to quantitatively assess the relative induction of CYP1A in these two species, and AHH activity was significantly higher in English sole than in starry flounder (p = 0.015). Cellular expression of CYP1A was determined by immunohistochemical localization of tissues, using an avidin-biotin peroxidase complex method, with polyclonal rabbit anti-cod CYP1A. The results showed a markedly reduced expression of CYP1A in hepatocytes of starry flounder, which is consistent with the apparent resistance of this species to the development of hepatocellular neoplasia. This reduced expression of CYP1A in hepatocytes of contaminant-exposed fish was previously seen in oyster toadfish from the Elizabeth River, Virginia, and this species is also apparently resistant to hepatocellular neoplasia.     

Regime shifts between clear and turbid water in New Zealand lakes: Environmental correlates and implications for management and restoration

We reviewed lakes in New Zealand reported to have undergone regime shifts between macrophyte‐dominated clear water states and de‐vegetated, turbid states. Regime‐shifting lakes (RSLs) occurred along a wide latitudinal gradient. We obtained catchment land‐use data as well as data on the occurrences of introduced (non‐indigenous) macrophytes and herbivorous and benthivorous fish for the 37 RSLs and for 58 lakes with similar maximum depths and climates, but which had not been reported to have undergone regime shifts. All RSLs had a maximum depth <20 m and mean annual surface air temperature between 9 and 16°G Regime shifts were positively related to the percentage of the catchment in pasture and negatively related to the percentage of the catchment in forest. The occurrences of the introduced macrophyte Egeria densa and the introduced fish, Ameiurus nebulosus (catfish), Carassius auratus (goldfish), Scardinius erythrophthalmus (rudd), Cyprinus carpio (koi carp), and Tinca tinca (tench), were significantly correlated to regime shifts in lakes. Although the presence of other introduced aquatic macrophytes was not significantly correlated with RSLs, the number of exotic fish taxa present in lakes was strongly positively correlated with increasing prevalence of regime shifts. The strength of the correlations between land use and introduced species versus regime shifts illustrates a number of factors which could be managed to reduce the susceptibility of lakes to regime shifts and to restore lakes that have become de‐vegetated. Our findings also suggests that regime shifts in lakes were unlikely to have been common in New Zealand lakes before anthropogenic deforestation and introductions of introduced aquatic taxa.     

Biomass, species composition and diversity of benthic diatoms in mangroves of the Houyu Bay, China

The biomass, species composition and diversity of benthic diatom assemblages in mud-flat soils in Kandelia candel (L.) Druce communities with and without vegetation were studied seasonally at the Houyu Bay in Fuding City, Fujian Province, China. A total of 103 taxa were identified (including varieties). Eighty-four taxa were found in the mud-flat with vegetation and 74 taxa in the mud-flat without vegetation, while the biomass was large in January and April and decreased from July to October. The most abundant species in the mud-flat with vegetation are Nitzschia cocconeiformis, Gyrosigma scalproides and N. fasciculata, compared with G. scalproides and N.obtusa var. scalpelliformis in the mud-flat without vegetation. High/P values at 2 sites during all seasons suggest that diatom assemblages in the sediments of the Houyu Bay represent an original environment. Multi-dimensional scaling of diatom assemblages from mud-flats with and without vegetation shows that a slight seasonal change and only a single association occur in the mangroves.     

Limnology of Lake Ngahewa,North Island,New Zealand

The water chemistry, flora, and fauna of Lake Ngahewa are described. Its waters are coloured by humic material from a flax swamp and the mean carbon: nitrogen ratio of the sediments lies in the range for dystrophic lakes. Thermal stratification is very weak or absent during summer, although deoxygenation occurs at depths below 3 m in late summer. The lake is highly productive and has a diverse phytoplankton and zooplankton population, which is different in species composition from other nearby eutrophic lakes; some algal species common in nearby eutrophic lakes are absent, and there is a high ratio of rotifers to cladocerans and copepods.

The high levels of dissolved phosphorus (42.2 mg.m^‐3) and nitrogen (up to 36.1 mg.m^‐3 NO3‐N) in the lake waters, and the differences in the flora and fauna compared with neighbouring lakes give only weak support to its tenuous classification as a dystrophic lake on the basis of water colour and sediment carbon values. The concept of dystrophy is discussed.     

Genetic variability of the Lessepsian migrant mussel Brachidontes pharaonis (Bivalvia: Mytilidae) in Tunisia

The present study used two mitochondrial markers (16S rRNA and COI) to assess the genetic diversity of a newly founded Lessepsian migrant mussel, Brachidontes pharaonis, in Tunisian waters. The species appears to be restricted to only one population in Rades Harbour, in the northern part of the country. Phylogenetic analyses revealed the monophyly of B. pharaonis in Tunisia. Both molecular markers revealed high genetic variability of the B. pharaonis population. Haplotype networks and demographic analyses confirmed the recent expansion events within this population. Multiple human-mediated introduction events involving several founder populations and intensive population growth rates are probably the main causes of the high polymorphism observed within this invasive mollusc.     

Ecological performance and possible origin of a ubiquitous but under-studied gastropod

Invasions by non-indigenous species (NIS) have been suggested to alter local, regional and global biota on unprecedented scales. To manage NIS, it is pivotal to identify whether a species is introduced or native, but even today the geographical origin of thousands of species worldwide remain uncertain. Most of these ‘cryptogenic species’ are inconspicuous and rare, but in a few instances, they can also be abundant and conspicuous species, with large impacts on community structure. The identification of cryptogenic species, and summarizing information on their most likely origin, is an important task in invasion biology, and can highlight the need for research and management. Here, we document that the gastropod Batillaria australis in the Swan River estuary (Perth, Western Australia) is a conspicuous species of uncertain origin. A literature review combined with new survey data revealed that all evidence point to a recent human-mediated transfer; for example, it is absent from the fossil record, was first collected in 1954, has a low parasite diversity, has increased its population size dramatically in recent times, is separated by >3000 km from conspecifics, has no long-distance dispersal mechanisms, and existing ocean currents run against a natural range extension. Surprisingly, despite political and scientific focus on NIS hardly any ecological data have been published on this species from Western Australia. We show that B. australis is highly abundant in both seagrass beds (424 ± 29 ind m⁻²) and on unvegetated sand flats (92 ± 22 ind m⁻²) being orders of magnitudes more abundant than any native gastropod in the Swan River. Experiments showed that high resistance to predation and environmental stress potentially explains its success. From our survey data, we calculated that >3.6 billion invasive snails today occupy the Swan River. This large snail populations support other organisms; for example, almost 1 billion macroalgae are found attached to living B. australis and >100 million hermit crabs occupy its empty shells. Given Battilaria’s high abundance, wide distribution, large size, persistent shells that support other organisms and bioturbating behavior, it seems inescapable that this potential invader has impacted the ecosystem functioning of the Swan River. We argue that the search for abundant species of uncertain origin should continue, and that these species generally should be treated with the same interest as high status invaders to mitigate impacts in already invaded systems and to avoid secondary spread into neighboring ecosystems.     

Nitrogen loads to New Zealand aquatic receiving environments: comparison with regulatory criteria

ABSTRACT

There is concern about the deteriorating nutrient status of aquatic receiving environments in New Zealand. We estimated the amount by which current nitrogen (N) concentrations and loads exceed criteria in rivers, lakes and estuaries nationally. Criteria corresponded to national ‘bottom-line’ (i.e. minimal) environmental objectives set by government policy. Three metrics were evaluated: (1) degree of compliance describes the current TN loads in receiving environments relative to criteria; (2) catchment N status describes the acceptability of catchment N loads compared to criteria; and (3) excess load indicates the amount by which the N load exceeds the maximum allowable load (kg yr^?1). Non-compliance with N criteria was broadly distributed nationally particularly in low-elevation catchments. Catchments with unacceptable N status constituted at least 31% of New Zealand’s land area, which corresponds to at least 43% of the country’s agricultural land. The national excess load was estimated to be at least 19.1 Gg yr^?1. We are 97.5% confident that estimated excess loads exceed zero for nine of 15 regions and for the nation as a whole. The analyses provide a strategic assessment of where reductions in N emissions are required to achieve the minimal national objectives.     

Establishing habitat-specific indicator species in Tierra del Fuego with freshwater macroinvertebrates

As a tool to understand Tierra del Fuego’s basic ecology and detect changes due to human pressures, this study develops habitat bioindicators. We compared the freshwater benthic macroinvertebrates at 61 study sites in six habitat types: grassland streams, urbanised streams, forested streams, beaver ponds, lakes and peat bog ponds. Forty-nine taxa were identified; insects were the most diverse group. Beaver pond, lake and grassland stream assemblages were similar, as were those from lakes, grassland streams and peat bog ponds. Fourteen taxa were habitat-specific. In forests, these included mayfly scrapers (Andesiops, Meridialaris) and blackfly filterers (Gigantodax). In lakes, two copepod filterers were indicators, and in urban streams, one shredder (Aphroteniella) and three collector-gatherers (springtail, earthworm, aquatic worm). Predators (Corixa, Aeshna) were characteristic of peat bog ponds. Beaver ponds had no indicator species. Establishing links between species and ecosystems constitutes the beginning of a broader effort to understand anthropogenic impacts to Fuegian watersheds.     

Feeding ecology of five commercial shark species of the Celtic Sea through stable isotope and trace metal analysis

In order to trace their feeding habits, stable carbon and nitrogen isotope ratios (delta15N and delta13C), as well as trace metal concentrations (Zn, Cd, Fe, Cu, Se and Hg) were analysed in the tissues of five commercial shark species from the Celtic Sea: the tope shark Galeorhinus galeus, the black-mouthed catshark Galeus melastomus, the starry smooth hound Mustelus asterias, the spiny dogfish Squalus acanthias and the lesser-spotted dogfish Scyliorhinus canicula. Our results were compared to previously described stomach contents and isotopic composition of potential preys. Isotopic ratio delta15N suggested that tope sharks fed at a higher trophic level (16.7 per thousand in the muscle) than the other species, reflecting its piscivorous diet. The lower values of spiny dogfish (11.6 per thousand in the muscle) might be explained, amongst other things, by either its migratory behaviour or its preference for preys from lower trophic levels. Cd and Hg were correlated with isotopic ratios delta13C and delta15N, and were shown to be diet-related whereas Zn, Fe and Cu seemed much more linked to species-specific metabolism. Although this multidisciplinary approach is revealed as a useful tool for the study of shark ecology, the lack of known trophic fractionation suggests that isotopic data be compared to traditional diet analyses.     

罗布泊第四纪湖泊沉积序列及钾盐资源的形成

为在我国新生代大陆沉积盆地开展区域找矿及钾盐资源预测提供科学依据, 采用地球卫星遥感资料和地面调查与化学测试以及区域盐湖卤水演化环境的演绎分析等手段, 综合方法, 揭示了罗布泊盆地第四纪沉积层序和湖泊气候环境变化的基本特征与古湖泊湖水及现代湖水的饱和流结晶路线及成盐成矿演化趋势.区域盐湖卤水演化环境和地质钻探资料及相图表明, 罗布泊地区钾盐矿床的成盐矿物以钾的硫酸盐矿物为主, 并没有出现真正意义上的钾盐沉积阶段(即氯化物钾盐析出阶段), 而钾盐卤水矿床却是一个积极的找矿方向.根据断裂组合及深部地质作用的分析, 这一地段是现代地质作用条件下形成的呈北东向展布的地堑构造系统, 富钾卤水蕴藏在地堑构造系统的中央断裂带内.综合分析表明, 通过地堑构造系统的中央断裂的贯通作用, 使深层卤水以及表层渗滤水向断裂破碎部位聚集, 并由于深部卤水的运动, 使深层盐岩系地层发生选择性溶解和表层渗滤水, 使浅部疏松堆积物的易溶性氧化钾溶解, 从而导致富钾卤水的富集而形成超大型液体钾盐矿床.     

大亚湾夏季浮游植物群落结构及对淡澳河输入的响应特征*

浮游植物是水生生态系统的基础生产者, 其群落结构直接影响到生态系统的健康和安全。河流输入是人类活动影响大亚湾水体环境最重要的途径之一, 淡水输入改变了水体温度、盐度、浊度和营养盐等环境因子, 对浮游植物群落结构产生影响。文章调查研究了2015年河流输入最强的夏季丰水期大亚湾的水体环境因子和浮游植物群落结构, 分析了在较强河流输入影响下浮游植物群落结构的动态变化及其对环境因子的响应。结果发现, 夏季大亚湾淡澳河的输入使湾顶淡澳河口区域形成层化的低盐、高温、低透明度、高营养盐的水体, 湾中部表层水体则受一定强度河流羽流影响, 而湾口和湾中部底层水体主要受外海水影响。淡澳河淡水输入是夏季大亚湾外源性氮、磷营养盐的主要来源, 而硅酸盐除河流输入外, 外海水也输入较多的营养盐使得底层水体硅酸盐浓度较高。夏季大亚湾水体营养比例失衡较严重, 溶解无机磷是限制浮游植物生长的重要因子。硅藻是大亚湾夏季浮游植物的优势类群, 调查发现3种优势种[极小海链藻(Thalassiosira minima)、中肋骨条藻(Skeletonema costatum)和圆海链藻(Thalassiosira rotula)]均为硅藻。通过聚类分析, 可将大亚湾夏季浮游植物群落主要分为3种类型, 分别为: 浮游植物丰度较大的极小海链藻藻华暴发的群落, 位于淡澳河口, 受河流输入影响明显; 中肋骨条藻占据优势的群落, 分布在受一定强度的河流及其羽流影响的湾顶和湾中部区域; 浮游植物丰度较低的群落, 无明显优势种, 主要分布在湾口海水影响区域。淡澳河口的水体环境有利于小型链状硅藻极小海链藻的快速繁殖并暴发了藻华, 藻华发生时的海水环境条件为: 温度30~31°C, 盐度17‰~31‰, 水体透明度0.45~1.2m。硅藻对不同营养盐利用的差异以及随后的生物碎屑和颗粒沉降过程导致藻华发生区域Si∶N值略降低, N∶P值显著升高。河流输入影响下, 单一物种大量生长使得浮游植物群落种类组成丰度分布极不均匀, 从而导致淡澳河口浮游植物群落的种类多样性和均匀度指数降低, 种类多样性和均匀度指数均从淡澳河口向湾口逐渐增大。     

Forecasting the consequences of climate-driven shifts in human behavior on cetaceans

While climate change is expected to affect cetaceans primarily via loss of habitat and changes in prey availability, additional consequences may result from climate-driven shifts in human behaviors and economic activities. For example, increases in shipping, oil and gas exploration and fishing due to the loss of Arctic sea ice are highly likely to exacerbate acoustic disturbance, ship strikes, bycatch and prey depletion for Arctic cetaceans. In the tropics, climate change may result in increased hunting pressure on near-shore dolphins and whales off Asia, Latin America, Africa, and elsewhere as the availability of other marine resources diminishes. This study explores the range of potential consequences to cetaceans worldwide from predicted climate-driven shifts in human behavior, and evaluates the risks to particular species given their geographic ranges and habitat preferences. While concern about impacts of climate change on cetaceans has largely focused on polar species, the analysis presented here suggests tropical coastal and riverine cetaceans such as the Irawaddy dolphin, Indo-Pacific humpback dolphin, and finless porpoise are particularly vulnerable to those aspects of climate change that are mediated by changes in human behavior. Policy recommendations include the following: (1) information about cetacean populations should be incorporated into national, regional and international climate adaptation decisions wherever possible (for example, via GEF-sponsored adaptation initiatives); and (2) human-mediated impacts of climate change should be included in cetacean conservation and management plans, such as the management procedures of the International Whaling Commission (IWC), where possible. Because human responses to climate change are likely to evolve rapidly over the coming years and decades, it is important that local, regional and international cetacean conservation and management plans include regular reviews to allow them to adapt to new information.     

多目标渔业资源科学调查的分层方案设计优化

渔业资源科学调查常用于收集高质量的生物学和生态学数据以进行渔业资源评估与管理。渔业资源调查设计优化十分必要,其有助于在经济有效的采样努力量下提高调查估计量的精度。对于估计单鱼种资源量指数和物种多样性指数为主的多目标渔业资源调查设计,本研究应用模拟方法评价和优化了分层随机采样设计的分层方案。在不同月份,对于不同调查目标,分别比较了不同分层方案设计的表现。对于大多数指标,与简单随机采样设计相比,分层方案设计可以提高调查估计量的精度。目前采用的具有5层的分层随机采样设计表现最好。通过分层方案设计可以补偿由于采样努力量降低造成的估计量精度的下降,采样努力量的减少有助于降低调查成本、减轻调查拖网对于种群数量较低鱼种的不利影响。本研究表明对于不同的调查目标,最优化的分层方案设计不同。调查后分析有助于改善渔业资源调查的分层方案设计。