Evaluating the genetic effects of the invasive Ocenebra inornata on the native oyster drill Ocenebra erinacea

Studies focusing on the effect of invasive species on the genetic diversity of native marine invertebrates remain scant. Here we report diversity among French populations of the intertidal gastropod Ocenebra erinacea (Linnaeus, 1758) sampled in the presence and absence of the invasive Ocenebra inornata (Recluz, 1851). Between 1999 and 2004, a total of 352 individuals of O. erinacea was collected from 15 sites (five of which had the invasive present) and was genotyped at the mitochondrial locus Cytochrome Oxidase 1 (cox1). No statistical difference was observed between polymorphism levels recorded within native populations exposed to the invasive, compared with populations sampled in the absence of O. inornata. No sign of native population decline was detected in response to the invader. While significant shifts in native O. erinacea population sizes have previously been reported in the literature, genetic effects may take longer to accumulate, or may be undetectable without a larger panel of genetic markers. By contrast, large genetic distances and significant population differentiation were recorded between Atlantic and Mediterranean O. erinacea samples, suggesting that these populations have distinct evolutionary histories. Comparison of genetic divergence within the closely related genus Nucella suggests that the Atlantic populations of O. erinacea and those from Thau Lagoon in the Mediterranean may belong to different species or subspecies.     

Changes in survivorship,behavior, and morphology in native soft‐shell clams induced by invasive green crab predators

Many studies on invasive species show reduced native densities, but few studies measure trait‐mediated effects as mechanisms for changes in native growth rates and population dynamics. Where native prey face invasive predators, mechanisms for phenotypic change include selective predation, or induced behavioral or morphological plasticity. Invasive green crabs, Carcinus maenas, have contributed to declines in native soft‐shell clams, Mya arenaria, in coastal New England, USA. We tested the hypothesis that clam ability to detect chemical cues from predators or damaged conspecifics would induce greater burrowing depth as a refuge from invasive crabs, and greater burrowing would require increased siphon growth. To determine how crab predation affected clam survivorship and phenotypic traits in the field, clams in exclosure, open, and crab enclosure plots were compared. Crab predation reduced clam density, and surviving clams were deeper and larger, with longer siphons. To determine whether the mechanism for these results was selective predation or induced plasticity, phenotypes were compared between clams exposed to chemical cues from crab predation and clams exposed to seawater in laboratory and field experiments. In response to crab predation cues, clams burrowed deeper, with longer siphons and greater siphon mass. Overall, crab predation removed clams with shorter siphons at shallow depths, and crab predation cues induced greater burrowing depths and longer siphons. Longer siphons and greater siphon mass of deeper clams suggests clams may allocate energy to siphon growth in response to crabs. By determining native behavior and morphological changes in response to an invasive predator, this study adds to our understanding of mechanisms for invasive impacts and illustrates the utility of measuring trait‐mediated effects to investigate predator–prey dynamics.     

Myosotella myosotis (Mollusca: Ellobiidae) — an overlooked,but well-established introduced species in South Africa

Myosotella myosotis is shown to be a well-established alien species in South Africa. Discovered in Port Elizabeth more than 100 years ago, it was initially thought to be indigenous and was described under two different names, but subsequent taxonomic work has demonstrated that these are synonyms of the variable and widely introduced European M. myosotis. This information, published in a revision of western Atlantic Ellobiidae, has escaped the attention of the South African marine science community. There has been no recent mention of M. myosotis or its two pseudoindigenous synonyms in the literature pertaining to either the estuaries or the malacofauna of South Africa, or to marine bioinvasions in the region. This example serves to demonstrate that invasion biology has a global context and that taxonomic literature is an important source of pertinent data. The fact that a species, which evidently occurs in abundance, can be overlooked for so long is both surprising and sobering.     

Impact of seawater temperature on growth and recruitment of invasive fouling species at the global scale

Epibenthic fouling communities are dominated by invasive species that are globally distributed and can have substantial ecological and economic impacts in coastal habitats. Little is known about inter‐specific differences in life history strategies that cosmopolitan invasive species employ to acquire space and succeed in invaded habitats. The goal of this study was to examine the impact of seawater temperature on recruitment and growth of several cosmopolitan fouling species including the tunicates Botrylloides violaceus, Botryllus schlosseri and Diplosoma listerianum, as well as the bryozoans Bugula neritina and Watersipora subtorquata. To do this, the iBARGE (Invasive Bryozoan and Ascidian Recruitment and Growth Experiment) program was developed, utilizing a global network of collaborators to examine patterns over a broad geographic scale and a wide range of naturally varying seawater temperatures. This project produced a data set of thousands of photographs from 18 marinas in five countries in summer 2014 and 2015, allowing for recruitment and growth to be tabulated at a variety of temperatures. Thermal growth curves were established for five invasive species, and growth was compared among temperatures across sites, revealing a significant thermal effect. Recruitment was linked to temperature, with generally higher recruitment at warmer seawater temperatures and the highest peak recruitment values for the bryozoan Bugula neritina. Temperature also changed the relative importance of growth and recruitment for several species. These results paint a complex picture of the interactions among invasive fouling species as they relate to seawater temperature.     

Changes in life cycle of the Ponto‐Caspian amphipod Pontogammarus robustoides at in the northernmost part of its range

The aim of this study was to investigate the dynamics of abundance, population structure and reproductive variables of the invasive Ponto‐Caspian amphipod Pontogammarus robustoides in its northernmost population, located in the Baltic Sea. Pontogammarus robustoides population variables were studied every month from May to October over 7 years (2002–2008) at two locations in the eastern part of the Gulf of Finland, one site in the north and one in the south. Observations of macrozoobenthos were also conducted once per year in July at 12 sites in this gulf during 2002–2014. This was to monitor the distribution area of P. robustoides and its abundance/biomass in different parts of the Gulf. The results showed that P. robustoides is a widely spread species in the Gulf, preferring to colonize stone‐sandy, vegetated and littoral habitats, from the shore to a depth of 5 m, with water salinity of 0.2–3 ppt. This species co‐exists with other amphipods, such as the Baikalian Gmelinoides fasciatus, the North Atlantic Gammarus tigrinus and the native Gammarus spp. The abundance of P. robustoides varied between the two study sites and among years (2002–2008), reaching a maximum level of 1000 ind.·m^?2 for adults and 3000 ind.·m^?2 for juveniles. The temperature‐dependent duration of egg development (embryogenesis) in the amphipod and the annual number of generations in P. robustoides populations varied among years. Three generations were recorded in most years and two generations in the coldest years. Clutch size (or fecundity) was dependent on the body length of female and averaged between 33 and 43 eggs per clutch for females ranging in body length from 11.2 to 12.2 mm. A maximum of 75 eggs were observed in a female with a body length of 16 mm. This paper concludes that life‐cycle variables change when P. robustoides spreads from the southern (Ponto‐Caspian region) to northern (Baltic Sea) range areas. In the studied northernmost location, the fecundity and number of generations of this amphipod were 1.5–2‐fold lower compared with the more southern locations. In addition, these variables and P. robustoides abundance were different between the coldest and warmest years at study sites that testify about their distinct dependence on local environmental conditions; further changes in life cycle of this species may be expected together with current climate warming.     

Response of Acartia populations to environmental variability and effects of invasive congenerics in the estuary of Bilbao, Bay of Biscay

The effect of environmental factors (river discharge, water temperature and dissolved oxygen saturation) on the abundance and distribution of Acartia populations and the interactions between their congenerics was evaluated by means of transfer function (TF) models in the estuary of Bilbao during the period 1998–2005. The recorded species were Acartia clausi, Acartia tonsa, Acartia margalefi and Acartia discaudata. Acartia clausi dominated in the entire euhaline region of this estuary until 2003 when it was displaced from the inner part by A. tonsa. This invasive species (A. tonsa) was found for the first time in 2001 and colonized successfully the inner (salinity 30) and intermediate (salinity 33) waters of this estuary since 2003. The TF models revealed an immediate and negative effect of A. tonsa on A. clausi in the intermediate salinity (33) waters, where these species showed the highest spatial overlap. The results indicate that environmental changes from 2003 influenced the abundance of Acartia species, being unfavourable for A. clausi. The decrease of A. clausi abundance in low salinity waters was related to a significant decrease of dissolved oxygen saturation levels, whereas the increase of temperature was linked to a significant increase of A. tonsa. Acartia margalefi and A. discaudata were scarce over the entire period, but they were found to be valuable indicators of hydrological changes, which were associated to climate factors. These two latter species increased in abundance and expanded their seasonal distribution, and in the case of A. margalefi also its spatial distribution, in 2002, coinciding with the period in the time-series when autumn–winter rainfall and summer temperatures were lowest, and dissolved oxygen saturation levels were highest.     

Decadal variability of the shallow Pacific meridional overturning circulation: Relation to tropical sea surface temperatures in observations and climate change models

In this study, we use existing observational datasets to evaluate 20th century climate simulations of the tropical Pacific. The emphasis of our work is decadal variability of the shallow meridional overturning circulation, which links the tropical and subtropical Pacific Ocean. In observations, this circulation is characterized by equatorward geostrophic volume transport convergence in the interior ocean pycnocline across 9°N and 9°S. Historical hydrographic data indicate that there has been a decreasing trend in this convergence over the period 1953–2001 of about 11 Sverdrup (1 Sv = 10⁶ m³ s⁻¹), with maximum decade-to-decade variations of 7–11 Sv. The transport time series is highly anti-correlated with sea surface temperature (SST) anomalies in the central and eastern tropical Pacific, implying that variations in meridional overturning circulation are directly linked to decadal variability and trends in tropical SST. These relationships are explored in 18 model simulations of 20th century climate from 14 state-of-the-art coupled climate models. Significant correlation exists between meridional volume transport convergence and tropical SST in the majority of the models over the last half century. However, the magnitude of transport variability on decadal time scales in the models is underestimated while at the same time modeled SST variations are more sensitive to that transport variability than in the observations. The effects of the meridional overturning circulation on SST trends in most the models is less clear. Most models show no trend in meridional transport convergence and underestimate the trend in eastern tropical Pacific SST. The eddy permitting MIROCH model is the only model that reasonably reproduces the observed trends in transport convergence, tropical Pacific SST, and SST gradient along the equator over the last half century. If the observed trends and those simulated in the MIROCH model are ultimately related to greenhouse gas forcing, these results suggest that the Bjerknes feedback, by affecting pycnocline transport convergences, may enhance warming that arises from anthropogenic forcing in the eastern tropical Pacific.     

The rise of Laminaria ochroleuca in the Western English Channel (UK) and comparisons with its competitor and assemblage dominant Laminaria hyperborea

The distribution of species is shifting in response to recent climate change. Changes in the abundance and distributions of habitat‐forming species can have knock‐on effects on community structure, biodiversity patterns and ecological processes. We empirically examined temporal changes in the abundance of the warm‐water kelp Laminaria ochroleuca at its poleward range edge in the Western English Channel. Resurveys of historical sites indicated that the abundance of L. ochroleuca has increased significantly in recent decades. Moreover, examination of historical records suggested that L. ochroleuca has extended its distribution from sheltered coasts on to moderately wave‐exposed open coasts, where it now co‐exists and competes with the assemblage dominant Laminaria hyperborea. Proliferation of L. ochroleuca at its poleward range edge corresponds with a period of rapid warming in the Western English Channel. Preliminary comparisons between L. ochroleuca and L. hyperborea highlighted some subtle but ecologically significant differences in structure and function. In summer, the average biomass of epiphytic stipe assemblages on L. hyperborea was 86 times greater than on L. ochroleuca whereas, on average, L. ochroleuca had a greater stipe length and its blade supported 18 times as many gastropod grazers (Gibbula cineraria). Differences in summer growth rates were also recorded, with L. ochroleuca being more productive than L. hyperborea throughout July. Comprehensive seasonally replicated comparisons are needed to examine the wider implications of proliferation of L. ochroleuca at its poleward range edge, but our study suggests that local biodiversity patterns and ecological processes (e.g. timing of productivity and trophic pathways) on shallow subtidal reefs may be altered by shifts in the relative abundances of habitat‐forming kelp species.     

DNA and morphological identification of an invasive swimming crab,Charybdis japonica,in New Zealand waters

Mitochondrial DNA sequences were used to identify an invasive swimming crab found in Waitemata Harbour, New Zealand. A 457 base sequence of the cytochrome oxidase 1 gene was compared in New Zealand specimens and nine species of Charybdis from Australia and Asia. The New Zealand specimens aligned with C. japonica. The diagnostic morphological characters of C. japonica were also checked in 54 specimens of the species collected in Waitemata Harbour, and concur with the mtDNA result. This is the first record of C. japonica establishing populations outside its native range. C. japonica, along with C. hellerii and the Lessepsian migrant C. longicollis, are the only known invasive species of Charybdis. C. japonica and C. hellerii are two of the few Charybdis species that inhabit the intertidal zone, and it is likely that the intertidal characteristics of these species contribute to their success as invasive species.     

Does the invasive plant Elymus athericus modify fish diet in tidal salt marshes?

The invasion of Mont-Saint-Michel Bay salt marshes (France) by a grass species (Elymus athericus) has led to important changes in vegetation cover, which is likely to modify the habitat for many invertebrates. Some of them constitute the main food items for several fish species, such as young sea bass (Dicentrarchus labrax) and sand goby (Pomatoschistus minutus), that feed in salt marsh creeks during high tides. As a result, fish nursery functions of salt marshes could be modified by the E. athericus invasion. In order to test this hypothesis, gut contents of the two most abundant fish species (sea bass and sand goby) were compared before and after E. athericus invasion in the same salt marsh creek and using the same methodology. The accessibility and availability of the main food item, the semi-terrestrial amphipod Orchestia gammarella, were estimated and compared between invaded (dominated by E. athericus) and original areas (dominated by Atriplex portulacoides). Gut content analysis showed a significantly greater percentage of fish leaving with empty guts from E. athericus areas than from A. portulacoides areas. The sea bass diet composition study showed a major shift in the relative importance of the main food items: before E. athericus invasion, diets were dominated by the semi-terrestrial species O. gammarella, whereas after the E. athericus invasion they were dominated by a marine mysid Neomysis integer. The same trend was found for sand gobies, with a shift of the main food item from O. gammarella before invasion to the polychaete Hediste diversicolor after invasion. These trophic changes may be explained by the lower accessibility and availability of O. gammarella in invaded communities than in natural ones. The E. athericus invasion, observed throughout northern Europe, is thus likely to disturb trophic function of natural salt marshes for fish. This preliminary study of the E. athericus invasion is also an illustration that invasive species are an urgent problem in conservation biology.     

Interactive effects of pH and temperature on native and alien mussels from the west coast of South Africa

Global warming and ocean acidification influence marine calcifying organisms, particularly those with external shells. Among these, mussels may compensate for environmental changes by phenotypic plasticity, but this may entail trade-offs between shell deposition, growth and reproduction. We assessed main and interactive effects of pH and temperature on four mussel species on the west coast of South Africa (33°48′ S, 18°27′ E) in October 2012 by comparing shell dissolution, shell growth, shell breaking force and condition index of two native species, the ribbed mussel Aulacomya atra and the black mussel Choromytilus meridionalis, and two aliens, the Mediterranean mussel Mytilus galloprovincialis and the bisexual mussel Semimytilus algosus. Live mussels and dead shells were exposed for 42 days to seawater of pH 7.5 or 8.0, at 14 °C or 20 °C. Low pH, high temperature and their combination increased shell dissolution of the two aliens but their growth rates and condition indices remained unchanged. Aulacomya atra also experienced greater shell dissolution at a low pH and high temperature, but grew faster in low-pH treatments. For C. meridionalis, shell dissolution was unaffected by pH or temperature; it also grew faster in low-pH treatments, but had a lower condition index in the higher temperature treatment. Shell strength was not determined by thickness alone. In most respects, all four species proved to be robust to short-term reduction of pH and elevation of temperature, but the native species compensated for greater shell dissolution at low pH by increasing growth rate, whereas the aliens did not, so their invasive success cannot be ascribed to benefits accruing from climate change.     

Impacts of climate variability and change on fishery-based livelihoods

There is increasing concern over the consequences of global warming for the food security and livelihoods of the world's 36 million fisherfolk and the nearly 1.5 billion consumers who rely on fish for more than 20% of their dietary animal protein. With mounting evidence of the impacts of climate variability and change on aquatic ecosystems, the resulting impacts on fisheries livelihoods are likely to be significant, but remain a neglected area in climate adaptation policy. Drawing upon our research and the available literature, and using a livelihoods framework, this paper synthesizes the pathways through which climate variability and change impact fisherfolk livelihoods at the household and community level. We identify current and potential adaptation strategies and explore the wider implications for local livelihoods, fisheries management and climate policies. Responses to climate change can be anticipatory or reactive and should include: (1) management approaches and policies that build the livelihood asset base, reducing vulnerability to multiple stressors, including climate change; (2) an understanding of current response mechanisms to climate variability and other shocks in order to inform planned adaptation; (3) a recognition of the opportunities that climate change could bring to the sector; (4) adaptive strategies designed with a multi-sector perspective; and (5) a recognition of fisheries potential contribution to mitigation efforts.     

Epibiotic traits of the invasive red seaweed Acanthophora spicifera in La Paz Bay,South Baja California (Eastern Pacific)

The aim of this study was to analyze the interaction of a non‐native macroalga (Acanthophora spicifera) with native macroalgae (Sargassum spp.) and sponge assemblages in a subtropical embayment of the Mexican Pacific. The intensity of A. spicifera epiphytism on the native seaweed Sargassum varied significantly over time and was inversely related to the Sargassum density and size. The higher intensity (up to 28 individuals per host plant) occurred when Sargassum was smaller and was lower in density (senescence period). The lower intensity was recorded during the growth period of Sargassum and the subsequent increase in intensity was attributed to a high fragmentation period of A. spicifera, which was evidenced by a decrease in its average size and biomass and by the presence of larger free‐floating accumulations on the subtidal zone. The facultative interaction between A. spicifera and Sargassum appears to be neutral, as no negative or positive effects were found for epiphytic or basibiont seaweeds. However, this invasive seaweed characteristically monopolizes almost all types of hard substrate, and its effects on other algae and benthic organisms should be investigated. Moreover, A. spicifera was often epizoic on epilithic sponges. This invasive seaweed was found anchored on the sponge tissue by rhizome‐like structures. In addition, free‐floating fronds of A. spicifera were frequently found carrying small pieces of the basibiont sponge in its basis (60% of them with eggs and embryos), which suggests a novel facilitation mechanism for some sponge species, as the A. spicifera epizoism could favor fragmentation, dispersal and recruitment of these invertebrates. This study shows that A. spicifera is not only a species that adapts rapidly to the new conditions of the receiving environment but, due to its epibiotic traits, it can directly interact with and influence the life histories of some native species.     

Effect of native and invasive cordgrass on Macoma petalum density, growth, and isotopic signatures

Ecosystem engineers can influence community and ecosystem dynamics by controlling resources, modifying the flow of energy or biomass, or changing physical characteristics of the habitat. Invasive hybrid cordgrass (Spartina alterniflora × Spartina foliosa) is an ecosystem engineer in salt marshes in San Francisco Bay, California, U.S.A. that raises intertidal elevations and may be either increasing C₄ plant carbon input into food webs or tying up carbon in a form that is not usable by consumers. A manipulative experiment compared abundance, growth, and stable isotope (δ¹³C and δ¹⁵N) composition of the clam Macoma petalum (=M. balthica) among native marsh, hybrid Spartina, and mudflats in central San Francisco Bay. We found higher densities (individuals m⁻²) of M. petalum on mudflats compared to either native or hybrid Spartina (p < 0.001). Macoma petalum shell growth was significantly greater in mudflats than in either vegetation type in 2002 (p = 0.005) but not 2003. Differences in shell growth between native and hybrid Spartina were not significant. Stable isotope results showed differences between habitats in δ¹³C but not δ¹⁵N. Carbon signatures of M. petalum placed in Spartina were much more depleted than the isotopic signature of Spartina. Neither native nor hybrid Spartina appears to be a significant carbon source for M. petalum in San Francisco Bay, and we found no evidence that hybrid Spartina contributes carbon to M. petalum beyond what is provided by S. foliosa, despite the hybrid's much greater biomass. Our results show that loss of mudflat habitat, rather than increased input of C₄ carbon, is the greatest effect of the invasion of hybrid Spartina on M. petalum.     

Are invasive species most successful in habitats of low native species richness across European brackish water seas?

European brackish water seas (Baltic Sea, Black Sea and Sea of Azov, Caspian Sea) are subject to intense invasion of non-indigenous species (NIS). In these seas, salinity is the most important range limiting factor and native species seem to reach a minimum species richness at intermediate salinities. This trend, revealed by Remane in 1934 and later on confirmed by many other scientists, was compared to the salinity range of already established NIS in the European brackish water seas. It turned out that most NIS are well adapted to the salinities holding lowest native species richness, already in their native area, and that NIS richness maximum in brackish water seas occurs in the salinity intervals of native species richness minimum. A predictable pattern in the salinity range of NIS can be used as a tool in initial risk assessment of future invasions in brackish water seas, especially when mapping highly potential donor and recipient areas. A product of empty niches, suitable environmental conditions, and availability of proper vectors might be the most effective predictor for the invasibility of brackish water areas.     

Reduction of flatfish habitat as a consequence of the proliferation of an invasive mollusc

Coastal bays provide habitats for juveniles and adults of many marine species. Mont Saint-Michel Bay (MSMB, France) hosts a highly diversified fish community and constitutes one of the most important nursery grounds for many commercially exploited marine species, such as sea bass, flatfish, clupeids and rays in the English Channel. Besides, MSMB also suffers from the massive invasion of an exotic mollusc, the American slipper-limpet (Crepidula fornicata, L.). This species arrived four decades ago and now represents the main filter-feeder biomass in the bay (150 Mt), an order of magnitude larger than local farmed and natural shellfishes. Recent analyses underlined the impact of this small gastropod on the trophic structure of this bay and its negative influence on juvenile sole densities in the nursery grounds. The present study uses a geostatistical approach to explore the effect of the extension of the slipper-limpet on flatfish (common sole Solea solea, L.; plaice Pleuronectes platessa, L.; brill Scophthalmus rhombus, L. and flounder Platichthys flesus, L.) spatial distribution. Data collected during survey of the MSMB at the end of the 1970s and three decades later have been used to build interpolated maps of (1) slipper-limpet and (2) flatfish spatial distributions. Slipper-limpets were concentrated in a small area, in the western part of the MSMB, in the 1970s while today they occupy half of the bay. This rapid proliferation led to the decrease of available surface for flatfishes, which previously occupied the whole bay and are now restricted to its eastern part. The present study highlighted that the negative influence on fish habitat in MSMB is apparently more related to changes in the substratum than to trophic interactions. This invasion has possible consequences on flatfish population renewal at a large scale and may also damage other benthic or demersal species, such as rays.     

Modelling the influence of environmental and weather factors on the density of the invasive polychaete Boccardia proboscidea

The inter‐tidal zone around sewage discharges in a Southwest Atlantic shore (Mar del Plata, Argentina) is currently colonized by extensive inter‐tidal reefs of the invasive spionid Boccardia proboscidea. Understanding the links between both human and natural disturbances and the massive development of non‐indigenous species will help prevent marine bioinvasions, which are already favoured by global oceanic trade. We present herein predictive models for variations in the density of B. proboscidea around sewage discharges of Mar del Plata, using environmental (pH, turbidity, temperature, salinity and total organic matter content), weather (wind direction and storm records), spatial (sites) and temporal (season and year) variables. Density variations were modelled by generalized linear models, and model averaging (multimodel inference) was used to obtain predicted values. The highest predicted values of B. proboscidea density occurred at sites to the south of the sewage effluent in spring. These sites are more affected by urban effluent discharges and they showed increased B. proboscidea density when the north wind was predominant. In addition, B. proboscidea density values were higher in sites with 20–22 °C (seawater temperature), high total organic matter content in sediments and low salinity. The averaged model was only a good ‘predictive model’ for sites to the north of the outfall, but was useful as an ‘explanatory model’ in all sites. Such predictions may help to back up conservation and management policies and decisions.     

秦皇岛河口沉积物砷形态分布特征

河口沉积物在陆源砷向海洋输送过程中具有源和汇的双重作用,分析砷在河口沉积物中的存在形态和分布特征对于掌握砷的毒理效应和污染评价具有重要意义.通过野外调查和样品采集,对秦皇岛典型河流河口沉积物中砷的质量比进行了测定,并采用Tessier五步连续提取法对砷在沉积物中的存在形态进行了提取分析.结果表明,汤河河口表层沉积物中砷的质量比为35.73~46.63 mg/kg,戴河河口表层沉积物中砷的质量比为13.60~16.00 mg/kg,汤河河口沉积物砷含量明显高于戴河河口.总砷含量随沉积深度的增加而有降低的趋势.各形态砷在沉积物中的分布特征基本一致,即以残渣态为主,占其总量的87%以上,其他各形态相对含量较小,其中可利用性最强的可交换态含量最小,平均为1.04%.各形态砷分布与沉积物的pH和有机质含量有一定的相关关系, pH和有机质含量的改变将会影响砷的形态分布特征.     

Capacity,capability and cross-border challenges associated with marine eradication programmes in Europe: The attempted eradication of an invasive non-native ascidian,Didemnum vexillum in Wales,United Kingdom

Increasing recognition of the threat which invasive non-native species present to ecological and economic assets has led to a recent surge in international, regional and national policies. Within the European Union, a draft EU Regulation on the prevention and management of invasive alien species has been developed. The draft Regulation, published in 2013, recommends the creation of a list of invasive alien species of Union concern, wherein any Member State identifying newly establishing populations of these species must implement rapid eradication measures. The first recording of the invasive non-native ascidian Didemnum vexillum in Britain in 2008 in Wales, and subsequent eradication efforts, presents a timely opportunity to evaluate the United Kingdom׳s existing capability and capacity to undertake a rapid eradication in the marine environment in light of the draft EU Regulation, as well as highlighting some of the cross-border challenges facing the EU. Although the UK is often cited within Europe as having made significant progress in the field of invasion management, the lessons learned from the eradication process in Wales highlight that the UK is inadequately prepared to undertake rapid eradication measures in the marine environment and that the lack of a coordinated approach between nations has significant potential to devalue localised eradication efforts. A number of measures are discussed to enhance future capability both in the UK and the wider European Union including enhanced alerting mechanisms, science-based monitoring programmes to enable early detection, increased commitment of resources and the need for cross-border collaboration.