Modelling habitat preference,abundance and species richness of alien macrocrustaceans in surface waters in Flanders (Belgium) using decision trees

The introduction and the spread of alien invasive species are a worldwide phenomenon causing global ecological and economic damages. Among the invaders, alien macrocrustaceans are known to be very successful invertebrates that colonise new habitats rapidly. Data from different fresh and brackish waters gathered by the Flemish Environment Agency (VMM) were used to build data-driven models predicting habitat preference, abundance and species richness of alien macro-Crustacea present in surface waters in Flanders. Different techniques such as regression and classification trees in combination with several optimisation methods (e.g. pruning) were used to construct the models. The performance of the models was moderate, because a balance between performance, ecological relevance and complexity was strived for. When using a three-fold cross validation it was found that the variation between the folds was limited, which is an indication of the robustness and the good reliability of the constructed models. Based on a sensitivity analysis the importance of conductivity, Kjeldahl nitrogen and shipping were stressed as well as graphically illustrated. Alien macrocrustaceans were predicted as present under brackish water conditions as well as in fresh waters with intensive ship traffic and low levels of organic pollution. The alien species richness was higher in rivers with intensive ship traffic and increased with increasing conductivity. Especially in brackish waters, alien macrocrustaceans reached high abundances. In fresh water, the abundance of alien species was generally lower. An integrated model that combined our habitat suitability model with a water quality model was used to predict the future distribution of alien macrocrustaceans. The predictions indicated that the prevalence and the species richness of alien macrocrustaceans are likely to increase with improving chemical water quality, whereas their abundance will probably decrease slightly. From our analysis, it is clear that models are a useful tool and that decision makers should focus on vulnerable areas such as brackish water areas and areas with intensive ship traffic in order to prevent the further introduction and spread of alien species.     

Four arguments why so many alien species settle into estuaries, with special reference to the German river Elbe

In one of the largest European rivers, the Elbe, from its source in the Czech Republic to the German North Sea, 31 alien macrozoobenthic species have been recorded in total. Most of these species have been introduced by shipping activities. With a total number of 21 species, many of the established aliens occur—partly exclusively—in the brackish area of the Elbe estuary. In order to explain this observed settlement characteristic, four main arguments come into consideration: (1) estuaries with intensive international shipping have a higher potential infection rate than other aquatic zones; (2) brackish water species have, due to specific physiological characteristics, a better chance of being transported alive than euhaline or freshwater species and they also probably have a higher perennation and establishment potential after release; (3) brackish waters have the greatest natural ‘indigenous species minimum’, so that more alien species can potentially establish; and (4) salt-tolerant limnetic alien species introduced into inland water reached the coast at first in the estuaries. It seems that the combination of brackish water with its unsaturated ecological niches and intensive international ship traffic has the highest potential infection rate for aquatic systems with alien macrozoobenthic species. And, estuaries are subjected to a two-sided invasion pressure by alien species, via the ocean (mainly shipping) and via inland waters (mainly shipping canal construction). The identification of such patterns is an important prerequisite for the development of a forward-looking alien monitoring and management strategy.     

Environmental Control on Fish and Macrocrustacean Spring Community-Structure,on an Intertidal Sandy Beach

The inter-annual variability of the fish and macrocrustacean spring community on an intertidal sandy beach near the Canche estuary (North of France) was studied from 2000 to 2013 based on weekly spring sampling over an 11-year period. Twenty-eight species representing 21 families were collected during the course of the study. The community was dominated by a few abundant species accounting for > 99% of the total species densities. Most individuals caught were young-of-the-year indicating the importance of this ecosystem for juvenile fishes and macrocrustaceans. Although standard qualitative community ecology metrics (species composition, richness, diversity, evenness and similarity) indicated notable stability over the study period, community structure showed a clear change since 2009. Densities of P. platessa, P. microps and A. tobianus decreased significantly since 2009, whereas over the period 2010-2013, the contribution of S. sprattus to total species density increased 4-fold. Co-inertia and generalised linear model analyses identified winter NAO index, water temperature, salinity and suspended particular matter as the major environmental factors explaining these changes. Although the recurrent and dense spring blooms of the Prymnesiophyte Phaeocystis globosa is one of the main potential threats in shallow waters of the eastern English Channel, no negative impact of its temporal change was detected on the fish and macrocrustacean spring community structure.     

Using long-term monitoring to investigate the changes in species composition in the harbour of Ghent (Belgium)

The macroinvertebrate community of the harbour of Ghent was studied by analysing 135 samples taken at different sampling locations from 1990 until 2008. The results showed that the current Crustacea and Mollusca communities are mainly represented, in terms of abundances, by alien species. In total, seven alien and four indigenous crustacean species were found. Mollusc diversity was higher, with a total of 14 species, four of which were alien. Macroinvertebrate diversity was very low at the beginning of the 1990s, but increased due to the improvement of the chemical water quality achieved by sanitation and stricter environmental laws. This is reflected by the dissolved oxygen concentration, which increased from an average of 2 mg/l to an average of 9 mg/l, allowing more sensitive species to establish. Since 1993, the number of alien taxa has augmented, whereas the number of native taxa has remained stable. The improvement of the chemical water quality and the simultaneous increase in total number of species were also reflected in an increase of the Multimetric Macroinvertebrate Index Flanders, which is used to assess the ecological water quality in Flanders. Due to intensive international boat traffic and the low species diversity, the harbour of Ghent is highly vulnerable for invasions. Stronger regulations and a better understanding about the contribution of shipping, shortcuts via artificial water ways, habitat degradation and environmental pollution are required to reduce the further spread of alien species.     

Changes in marsh nekton communities along the salinity gradient of the Schelde river, Belgium and The Netherlands

Nekton was sampled in five marshes along the salinity gradient of the Schelde River. The utilisation of three different habitats (large and small creek, marsh pond) by fish and macrocrustacean species was compared among the five sampling sites. In the larger channels fyke nets were deployed to capture fish and macrocrustaceans leaving the marsh at ebb while block nets were set in smaller intertidal creeks. Fish traps passively sampled fish and shrimp in the marsh ponds. The tidal freshwater marsh had a species poor fauna and only a low number of fish was caught. Besides some freshwater species (Alburnoides bipunctatus, Carassius carassius) the European eel, Anguilla anguilla was still present. The four other marshes had a similar community structure although Platichthys flesus was absent from the euhaline area. Among fish species, dominance of Dicentrarchus labrax, Platichthys flesus and Pomatoschistus microps was observed. Carcinus maenas and Palaemonetes varians were the most abundant macrocrustacean species in every marsh. Between the large and small intertidal creeks there was no difference in nekton species composition. The main species used both habitats. Marsh ponds were utilized intensively only by two species, Pomatoschistus microps and Palaemonetes varians in every marsh.     

Early detection of potentially invasive invertebrate species in Mytilus galloprovincialis Lamarck, 1819 dominated communities in harbours

Constan?a harbour is a major port on the western coast of the semi-enclosed Black Sea. Its brackish waters and low species richness make it vulnerable to invasions. The intensive maritime traffic through Constan?a harbour facilitates the arrival of alien species. We investigated the species composition of the mussel beds on vertical artificial concrete substrate inside the harbour. We selected this habitat for study because it is frequently affected by fluctuating levels of temperature, salinity and dissolved oxygen, and by accidental pollution episodes. The shallow communities inhabiting it are thus unstable and often restructured, prone to accept alien species. Monthly samples were collected from three locations from the upper layer of hard artificial substrata (maximum depth 2?m) during two consecutive years. Ten alien macro-invertebrate species were inventoried, representing 13.5% of the total number of species. Two of these alien species were sampled starting the end of summer 2010, following a period of high temperatures that triggered hypoxia, causing mass mortalities of benthic organisms. Based on the species accumulation curve, we estimated that we have detected all benthic alien species on artificial substrate from Constan?a harbour, but additional effort is required to detect all the native species. Our results suggest that monitoring of benthic communities at small depths in harbours is a simple and useful tool in early detection of potentially invasive alien species. The selected habitat is easily accessible, the method is low-cost, and the samples represent reliable indicators of alien species establishment.     

An appraisal of a biocontamination assessment method for freshwater macroinvertebrate assemblages; a practical way to measure a significant biological pressure?

Freshwater invasive or alien species (IAS) can have a major impact on benthic macroinvertebrate assemblage structure and diversity. This has implications for accurate biological monitoring, the assessment of the ecological quality status of rivers and achievement of Water Framework Directive (WFD) objectives. Although IAS constitutes a major biological pressure to WFD objectives, current approaches to ecological status assessment tend to ignore their presence. This problem is compounded as biotic indices such as the Biological Monitoring Working Party (BMWP) score do not distinguish between native and IAS, when IAS tend to be more tolerant of organic pollution than the natives they replace. Biocontamination is the presence of an IAS in a system, and we tested a new method of biocontamination assessment, designed to be used alongside current routine water quality monitoring techniques, by applying it to biological monitoring data from the river monitoring programme of a small Island, The Isle of Man. Although 54% of monitoring sites exhibited no biocontamination, 19% showed low or moderate biocontamination and 27% high or severe biocontamination. Richness contamination was low (only two contaminated families being recorded), but abundance contamination was high in some sites (87% of individuals being IAS). Sites with a greater relative abundance of IAS individuals exhibited lower BMWP water quality. Within invaded sites BMWP monitoring was not responsive to changing chemical water quality, whereas within uninvaded sites it was. In invaded sites, the relative abundance of IAS increased as ammonia and BOD₅ increased. Our study shows current monitoring approaches mask the presence of AIS within assemblages, with some highly biocontaminated sites registering high BMWP biological quality. This new index represents a simple way to integrate the IAS biological pressure into established WFD monitoring programmes, to produce more comprehensive estimates of ecological quality status than are currently being realised.     

Fruit traits of vertebrate-dispersed alien plants: smaller seeds and more pulp sugar than indigenous species

Vertebrates play a major role in dispersing seeds of fleshy-fruited alien plants. However, we know little of how the traits of alien fleshy fruits compare with indigenous fleshy fruits, and how these differences might contribute to invasion success. In this study, we characterised up to 38 fruit morphology, pulp nutrient and phenology traits of an assemblage of 34 vertebrate-dispersed alien species in south-eastern Queensland, Australia. Most alien fruits were small (81% < 15 mm in mean width), and had watery fruit pulps that were high in sugars and low in nitrogen and lipids. When compared to indigenous species, alien fruits had significantly smaller seeds. Further, alien fruit pulps contained more sugar and more variable (and probably greater) nitrogen per pulp wet weight, and species tended to have longer fruiting seasons than indigenous species. Our analyses suggest that fruit traits could be important in determining invasiveness and could be used to improve pre- and post-border weed risk assessment.     

Physico‐chemical variables determining the invasion risk of freshwater habitats by alien mollusks and crustaceans

The aim of this study was to assess the invasion risk of freshwater habitats and determine the environmental variables that are most favorable for the establishment of alien amphipods, isopods, gastropods, and bivalves. A total of 981 sites located in streams and rivers in Germany. Therefore we analyzed presence–absence data of alien and indigenous amphipods, isopods, gastropods, and bivalves from 981 sites located in small to large rivers in Germany with regard to eight environmental variables: chloride, ammonium, nitrate, oxygen, orthophosphate, distance to the next navigable waterway, and maximum and minimum temperature. Degraded sites close to navigable waters were exposed to an increased invasion risk by all major groups of alien species. Moreover, invaded sites by all four groups of alien species were similar, whereas the sites where indigenous members of the four groups occurred were more variable. Increased temperature and chloride concentration as well as decreased oxygen concentration were identified as major factors for the invasibility of a site. Species‐specific analyses showed that chloride was among the three most predictive environmental variables determining species assemblage in all four taxonomic groups. Also distance to the next navigable waterways was similarly important. Additionally, the minimum temperature was among the most important variables for amphipods, isopods, and bivalves. The bias in the occurrence patterns of alien species toward similarly degraded habitats suggests that the members of all four major groups of freshwater alien species are a non‐random, more tolerant set of species. Their common tolerance to salinity, high temperature, and oxygen depletion may reflect that most alien species were spread in ballast water tanks, where strong selective pressures, particularly temperature fluctuations, oxygen depletion, and increased salinity may create a bottleneck for successful invasion. Knowledge on the major factors that influence the invasion risk of a habitat is needed to develop strategies to limit the spread of invasive species.     

Effect of alien riparian vegetation and its removal on a highly endemic river macroinvertebrate community

Invasive alien trees along river banks can reduce indigenous biodiversity, while their removal can restore it. We assessed here family- and species-level responses of river benthic macroinvertebrate assemblages to three riparian vegetation types (natural, alien trees, cleared of alien trees) in the Cape Floristic Region biodiversity hotspot. High species beta diversity of this highly endemic fauna meant that between-river, as well as seasonal effects, dominated assemblage patterns. SASS5, a qualitative, rapid bioassessment technique, based on the sensitivity of the families present, was used as a measure of river health and, indirectly, of water quality. SASS indicated a decline in water quality conditions after alien clearing, a likely response to the greater insolation and apparent erosion of cleared banks, resulting in elevated temperatures and suspended solids and lowered oxygen levels. Overall, cleared and natural sites were more similar to each other than to alien sites, suggesting some post-clearing recovery. However, many sensitive, endemic taxa survived in alien-invaded sites, and more than in the natural sites. These endemic species made use of shady, cool, high-oxygen levels under the alien tree canopy. However, endemics declined in overall abundance in sites cleared of aliens, being replaced by more tolerant, widespread taxa. Clearance of the alien trees opened up the rivers to sunny conditions, which had a major impact on community composition. Vegetation types, oxygen levels and river width were important environmental variables affecting these macroinvertebrate responses. Re-establishment of invertebrate biodiversity matched that of indigenous vegetation, with the most sensitive endemic taxa only recovering after establishment of bushy indigenous and shade-producing fynbos. Therefore, for biodiversity conservation objectives to be achieved, it is essential that indigenous plants are maintained and encouraged during and after clearing to ensure the recovery of endemic and sensitive taxa.     

Linking environmental conditions and ship movements to estimate invasive species transport across the global shipping network

Aim Some nations, and the International Maritime Organization, are moving towards requirements for managing ballast water to reduce the number of alien species transported and released. These and other measures will be most efficient when targeted at ships posing the greatest risks. Here, we analyse world‐wide ship movements and port environmental conditions to explore how these risk components differ across arriving ships. Location Global, with a case study of the Laurentian Great Lakes. Methods We gathered salinity and temperature data for all global shipping ports, and data for all global ship movements during a 12 ‐month period. We applied these data to the Laurentian Great Lakes to determine which global ports may donate new species to the Great Lakes via ship traffic, and which are most environmentally similar to the Great Lakes. Results We show that ships regularly travel to the Great Lakes from all major coastal, and many inland, regions of the world. Most global ports, and thus the species in them, are separated from the Great Lakes by no more than two ship voyages. Combined with a measure of environmental similarity among global ports, we identify ship routes likely to transport species adapted for survival in the Great Lakes and global regions that may be the source of increasing future invasions. Main conclusions The Great Lakes account for a small fraction of global shipping yet are closely connected to all other ports, and the species in them, by the shipping network. Our methods and data allow risks from individual ships to be ranked so that management activities can be targeted at ships most likely to introduce new invaders. Because our data sets are global, they could be applied to ship arrivals at any global port.     

New alien barnacles in the Azores and some remarks on the invasive potential of Balanidae

Global homogenization of biota is underway through worldwide introduction and establishment of non-indigenous (exotic) species. Organisms fouling ship hulls are continually in transit and can affect communities through biodiversity loss and serious damage to economy and public health. In the Azores, for the first time, underwater alien species prospection was conducted in marinas and recreational harbours, at S?o Miguel Island. Populations of three locally previously unknown barnacle species were found: Amphibalanus amphitrite, Amphibalanus eburneus and Perforatus perforatus. These species account for the more than 50% of alien barnacles worldwide that belong to Balanidae family. Hence, some considerations about morphology and life cycle of this family are advanced, discussed and related to their invasive potential.     

Salinity-related distribution of alien amphipods in rivers provides refugia for native species

There are numerous papers upon the range extension, biology and the impact of alien amphipods upon the local fauna. However, there are no studies concerning the alien versus native species distribution patterns at the catchment scale of river systems. In total 125 sites were sampled: 41 in main rivers constituting the Polish section of the central invasion corridor (Bug, Vistula, Notec with canals, Oder) and 84 in their affluents. The conductivity of large rivers was much higher than in their small affluents. The number of alien species and their abundance was higher at sites with raised conductivity values. The reverse situation was noticed when native amphipods were taken into account. Moreover, large rivers were inhabited by alien fauna, whereas in smaller streams only native species were sampled. The absence of alien amphipods in small rivers may be explained by their ecological preference for a higher conductivity of water. Thus in smaller streams the native fauna is free from the pressure posed by alien amphipods. If not degraded by human activity, small affluents may function as refugia for native amphipod species. Otherwise, elevation of salinity related to improper catchment management or sewage treatment may lead to extinction of such local disjunct population of native amphipods.     

Ecological traits and environmental affinity explain Red Sea fish introduction into the Mediterranean

Alien species are considered one of the prime threats to biodiversity, driving major changes in ecosystem structure and function. Identifying the traits associated with alien introduction has been largely restricted to comparing indigenous and alien species or comparing alien species that differ in abundance or impact. However, a more complete understanding may emerge when the entire pool of potential alien species is used as a control, information that is rarely available. In the eastern Mediterranean, the marine environment is undergoing an unparalleled species composition transformation, as a flood of aliens have entered from the Red Sea following the opening of the Suez Canal in 1869. In this study, we compile data on species traits, geographical distribution, and environmental affinity of the entire pool of reef‐associated fish species in the Red Sea and more generally across the Indo‐Pacific. We use this extensive data to identify the prime characteristics separating Red Sea species that have become alien in the Mediterranean from those that have not. We find that alien species occupy a larger range of environments in their native ranges, explaining their ability to colonize the seasonal Mediterranean. Red Sea species that naturally experience high maximum temperatures in their native range have a high probability of becoming alien. Thus, contrary to predictions of an accelerating number of aliens following increased water temperatures, hotter summers in this region may prevent the establishment of many alien species. We further find that ecological trait diversity of alien species is substantially more evenly spaced and more divergent than random samples from the pool of Red Sea species, pointing at additional processes, such as competition, promoting ecological diversity among alien species. We use these results to provide a first quantitative ranking of the potential of Red Sea species to become established in the eastern Mediterranean.     

Hybrid swarm as a result of hybridization between two alien and two native water frog species (genus Pelophylax) in Central Croatia: Crna Mlaka fishpond acting as a species melting pot?

Biological Invasions - Spreading of alien water frog species (genus Pelophylax) has been reported across Europe, posing a severe risk for the replacement or genetic swamping of indigenous species....     

Herbivores,but not other insects,are scarce on alien plants

Abstract Understanding how the landscape‐scale replacement of indigenous plants with alien plants influences ecosystem structure and functioning is critical in a world characterized by increasing biotic homogenization. An important step in this process is to assess the impact on invertebrate communities. Here we analyse insect species richness and abundance in sweep collections from indigenous and alien (Australasian) woody plant species in South Africa's Western Cape. We use phylogenetically relevant comparisons and compare one indigenous with three Australasian alien trees within each of Fabaceae: Mimosoideae, Myrtaceae, and Proteaceae: Grevilleoideae. Although some of the alien species analysed had remarkably high abundances of herbivores, even when intentionally introduced biological control agents are discounted, overall, herbivorous insect assemblages from alien plants were slightly less abundant and less diverse compared with those from indigenous plants – in accordance with predictions from the enemy release hypothesis. However, there were no clear differences in other insect feeding guilds. We conclude that insect assemblages from alien plants are generally quite diverse, and significant differences between these and assemblages from indigenous plants are only evident for herbivorous insects.     

Towards clarifying the presence of alien algae in inland waters — can we predict places of their occurrence?

Small algae are the trophic basis in both marine and freshwater ecosystems. The identification of tiny microorganisms and place of their origin is laborious but necessary. This paper consists of a literature review of 17 species of planktonic algae, with a discussion of taxonomic problems. We also clarify whether these 17 species are non-native, invasive or cryptogenic species, with an indication whether they had been recognised as ‘alien’ in Europe. According to our observations, areas colonized by small and alien algal species, were anthropogenically altered. There were: systems with heated waters (‘heated islands’), which imitated tropical conditions; highly eutrophic to hypereutrophic water ecosystems, easily colonized by alien species, fishponds with intense fish cultivation, where alien species of fish are/had been introduced, which carried also other alien organisms; and inland water ecosystems with high salinity or high conductivity e.g. pits inundated by mine waters, imitating sea or brackish conditions acting as hubs of migration of alien species adapted to brackish or saline waters. We have prepared a map showing areas inhabited by alien species, both of documented places and hypothetical ones, where we would expect alien species to occur.     

Abundance of invasive peacock bass increases with water residence time of reservoirs in southeastern Brazil

Neotropical freshwater ecosystems are experiencing a great expansion in the number of invasive species, which is especially alarming since this region harbours 30% of the world’s fish biodiversity with high levels of endemism. We aimed to evaluate the main predictors of peacock basses (Cichla spp.) abundance outside their native range, which are the Amazon and Tocantins-Araguaia river basins. We used multivariate ordination techniques and multimodel inference to analyse peacock basses abundance in twelve reservoirs of the Paraíba do Sul river basin, southeastern Brazil. Interestingly, reservoirs at higher (southernmost) latitudes, located in more populated areas, had higher water temperature and lower turbidity, due to increased water residence time, and these three variables were also positively correlated with abundance of this warm-water invasive fish. Habitat structure was less important in explaining peacock basses abundance, which was not significantly related to biotic factors (fish species richness and time since peacock basses introduction). We hypothesize that the observed effects of reservoir management on limnological features and peacock bass abundance, particularly water residence time (as a mediator of temperature and turbidity), may apply to other Neotropical basins and could influence the impact of this invader.     

Alien arthropod predators and parasitoids: interactions with the environment

Many species of entomophagous arthropods have been introduced either intentionally (through the practice of biological control) or unintentionally to new regions. We examine interactions of these aliens with their new environments in the context of rapid global change linked to human activity. We consider effects of such interactions on establishment and spread of the alien species and effects on indigenous biota and ecosystems. Major elements of global change that affect alien-environment interactions include landscape modifications by humans (e.g., cultivation, habitat loss and fragmentation) and increases in atmospheric CO₂ and other gases resulting in climate change and other effects (e.g., changes in food quality for herbivores that affect higher trophic levels as well). Alien arthropod predators can alter landscapes for their benefit, to the detriment of indigenous species. A brief review also of blood-feeding alien arthropods makes clear that interactions with the environment critically influence invasions of zoophagous arthropods in general.     

Anostracans and microcrustaceans as potential food sources of waterbirds on sodic pans of the Hungarian plain

Hungarian sodic water bodies have a rich macro- and microcrustacean fauna due to the lack of fish populations. The crustacean population is very abundant, for this reason these wetlands provide good feeding resources for waterbirds. The density of macro- and microcrustacean populations together with feeding waterbirds was investigated in March, April, and May of 2002, on two characteristic sodic pans, “Kelemen-szék” and “Zab-szék”. The following dabbling-filtering waterfowls and pelagic forager wader species were counted: northern pintail (Anas acuta), northern shoveler (Anas clypeata), garganey (Anas querquedula), common teal (Anas crecca), avocet (Recurvirostra avosetta), spotted redshank (Tringa erythropus), greenshank (Tringa nebularia), and marsh sandpiper (Tringa stagnatilis). The dominant macrocrustacean species was the [Anostraca – Branchinectidae] natronophile Branchinecta orientalis, and its density was significantly higher in Zab-szék than in Kelemen-szék. The microcrustacean zooplankton community was also different in the pans, [Cladocera] Daphnia magna density was significantly higher in Kelemen-szék than in Zab-szék, but the density of the [Copepoda] natronophile Arctodiaptomus spinosus, was higher in Zab-szék than in Kelemen-szék. The density of the investigated waterbird species was also significantly higher in Zab-szék than in Kelemen-szék during spring. We can conclude that the macrocrustacean B. orientalis is one of the most important potential food resources for migrating pelagic foraging waders in spring on characteristic Hungarian sodic pans. However, the most abundant available food item for waterbirds are copepod microcrustacean zooplankton, which have a biomass that is larger by approximately one order of magnitude than the macrocrustacean zooplankton biomass. Considering the lack of submerged water vegetation, we suggest that planktonic microcrustaceans are an important food resource for dabbling-filtering ducks because they can utilise the small crustacean biomass more effectively than the less abundant and rapidly moving macrocrustacean B. orientalis.