In Elkhorn Slough, a tidal estuary draining into Monterey Bay, California, the intertidal is occupied by a conspicuous orange sponge known by the name Hymeniacidon sinapium. This same species is found in the rocky intertidal zone of the outer coast of California, and is described herein from subtidal kelp forests of Southern California. Farther afield, morphologically and ecologically indistinguishable sponges are common in estuaries and intertidal areas in Asia, Europe, South America, and Africa. Here I use morphological, ecological, and genetic data to show that these sponges are all members of the same globally-distributed species, which should be known by the senior synonym H. perlevis. Though previous authors have remarked upon the morphological, ecological, and/or genetic similarity of various distant populations, the true scope of this sponge’s distribution appears to be unrecognized or unacknowledged in the literature. Limited larval dispersal, historically documented range expansion, and low genetic variation all support a hypothesis that this sponge has achieved its extraordinary range via human-mediated dispersal, making it the most widely-distributed exotic sponge known to date.

Giant salvinia (Salvinia molesta Mitchell, Salviniaceae) is a free-floating fern native to Brazil that alters natural processes in aquatic ecosystems, causing ecological problems for water resource managers. Due to its ease of dispersal through fragmentation and rapid growth, giant salvinia can quickly become problematic, requiring persistent management efforts. If left unmanaged, giant salvinia creates a thick mat of vegetation, which limits sunlight penetration, reducing aquatic macrophytes, lowering dissolved oxygen and stressing aquatic organisms. Giant salvinia was first reported in Lago Las Curias, Cupey, San Juan, Puerto Rico, USA, in 2016 and covered the entire 19 ha waterbody in 2018. In 2019, we conducted surveys to examine the extent of the invasion and quantify ecological damage to the aquatic environment. We found that the lake is lacking in dissolved oxygen, with a mean concentration of 0.38 mg L^-1, and mean concentrations of nitrate, ammonium, and phosphate were < 1 mg L^-1. Mean pH in 2019 was 6.4, down from 7.6 in years prior to giant salvinia. We estimated total fresh giant salvinia biomass to be 3,449 metric tons and dry biomass to be 51 metric tons. Other floating vegetation associated with the giant salvinia mat included Pistia stratiotes, Pontederia crassipes, Typha sp., Oxycaryum cubense, Cyperus esculentus and Mikania sp. Uncontrolled growth of giant salvinia impeded access to the waterbody and degraded resource quality in the aquatic ecosystem. The lack of dissolved oxygen and decreasing pH creates conditions for sedimentary nutrients release, creating a potential internal loading of phosphorus. To control an infestation of this magnitude we suggest biological control with the salvinia weevil (Cyrtobagous salviniae) which has proven successful in controlling giant salvinia, and at a fraction of the cost of other control methods. Ultimately, an integrated management plan, including chemical and mechanical control, needs to be established to control giant salvinia and other invasive free-floating plants, and monitor the restoration of ecological services at Lago Las Curias. As a long term goal, nutrient fluxes into the lake must be reduced by eliminating non-point sources of pollution throughout the watershed.

Tolerance and resistance to environmental stresses determine the invasion success of alien plants under disturbed conditions. Colonization time and environmental heterogeneity have been thought to contribute to the invasiveness of alien plants. However, few previous studies have synthesized disturbance, environmental heterogeneity and colonization time in the exploration of the invasion mechanisms of invasive clonal plants. In the present study, the performance of the invasive clonal wetland plant Alternanthera philoxeroides was compared under undisturbed (UD), homogeneous burial (HoD) and temporal heterogeneous burial (HeD) conditions at the early and late phases of colonization. Using functional traits including biomass allocation and plant physiology as indicators of invasive performance, we found that in the early phase A. philoxeroides showed phenotypic maintenance in stolon mass ratio (SMR), root mass ratio (RMR), root-shoot ratio and non-structural carbohydrate content of stolon (NSCCstolon) after either HoD or HeD; leaf mass ratio (LMR), specific leaf area (SLA), the maximal fluorescence (Fv/Fm), nitrogen content per leaf mass (Nmass) and leaf carbon/nitrogen (C/N) ratio after HoD; chlorophyll content (Cht) and leaf construction cost per leaf area (CCarea) after HeD. We found that CCarea varied HoD while LMR, SLA, Fv/Fm, Nmass and C/N ratio varied after HeD in the early phase. In the late phase, A. philoxeroides showed phenotypic maintenance in LMR, SMR, RMR, root-shoot ratio and Fv/Fm after either HoD or HeD; Cht and NSSCstolon after HoD. Moreover, we found that SLA, Nmass, C/N ratio and CCarea varied after either HoD or HeD while Cht and NSSCstolon after HeD in the late phase. Both tolerance (phenotypic maintenance) and resistance (phenotypic variation) to the burial disturbance are trait dependent and facilitate the invasion of A. philoxeroides. In addition, the heterogeneity of the disturbance exerted facilitative or insignificant impacts on its invasive performance. These mechanisms may explain the broad invasion of A. philoxeroides into diverse habitats.

Alien aquatic macroinvertebrates, especially invasive crustaceans and molluscs, have heavily impacted native species and ecosystem processes in freshwaters worldwide. Knowledge on alien species distribution is necessary to understand their dispersal dynamics and prevent future invasions, and to predict and reduce undesirable impacts. Literature data on alien macroinvertebrate species (AMS) in Croatia are sparse and a complete inventory of alien macroinvertebrates in Croatian freshwaters has never been conducted. The aim of this study was to present a database of AMS in Croatian freshwaters and to analyse their origin, pathways of introduction and distribution. The AMS database was built based on literature data and the authors’ unpublished data, and included a total of 1,411 records from 689 sites across Croatia. In total, 29 AMS were recorded until 2019, belonging to five major taxonomic groups: subphylum Crustacea (16 species) and phyla Mollusca (7 spp.), Annelida (4 spp.), Cnidaria (1 sp.), and Platyhelminthes (1 sp.). The area of origin of most species is the European Ponto-Caspian region (19 spp., 66%), and the rest originate from North America (5 spp.), Asia (4 spp.) and New Zealand (1 sp.). The most important pathways of unintentional primary introductions were stowaway-shipping (20 spp., 69%) and contaminant-fish stocking (6 spp., 21%). All 29 AMS species were found in the Black Sea Basin (Danube Basin) and five of those were also recorded in the river catchments of the Adriatic Sea Basin. For most AMS, the Sava and Drava Rivers are the main river corridors for their westward spread from the Danube. Since studies of AMS dispersal mechanisms are lacking and only a few studies report the impacts of invasive AMS in Croatia, future studies should be focused on the dispersal dynamics and ecological impact of invasive macroinvertebrates in Croatian freshwaters.

A multisource approach to assessing freshwater biodiversity reveals the first occurrence of the Asian freshwater snail Sinotaia cf. quadrata (Gastropoda, Viviparidae) in inland waters of the northern Iberian Peninsula (Spain) and south-western France. We present a detailed characterization, combining morphological traits and molecular tools for a genetic identification, and illustration of the species and its ultrastructure, as well as key information regarding its reproductive biology and ecology at the new locations. We discuss the most plausible introduction pathways and vectors, its potential invasiveness and the subsequent impacts that it may generate in the receiving localities. Our preliminary results raise concerns about the threat of Sinotaia cf. quadrata to human health and ecosystem dynamics, since this species acts as an intermediate host for several parasite species. Finally, this study confirms once again the usefulness of an integrative taxonomical approach for shedding light on hidden biodiversity and the invasion of freshwater ecosystems.

The Asian clam Corbicula fluminea is self-compatible, hermaphroditic, androgenetic, and ovoviviparous. Androgenesis is a type of asexual male reproduction; although it involves genetic recombination, the offspring retain the same genome as their male parent. Despite this unique reproductive character of C. fluminea, considerable morphological diversity and internal shell color were observed among specimens collected from six locations in Taiwan. We investigated these specimens through morphological examination and amplified fragment length polymorphism (AFLP). Twenty-three AFLP genotypes were found in 48 individuals by using only one primer combination. AFLP was applied for identifying the clonal lineage of C. fluminea successfully. Our results showed that among specimens with different genotypes, external shell color could be affected by environmental factors, such as substrate, showing the same pattern, but internal shell color was determined purely by genetics. This relationship between the inner shell color variation and genotype in C. fluminea can be easily used to study the dispersal of this invasive species and in breeding for aquaculture.

The importation of non-native fish species into Malaysia began as early as the 19th century, when a substantial number of non-native fishes were introduced from southern China, heralding the beginning of aquaculture in Malaysia. In this review, we analyzed the available literature on the history, checklists, current status, production trends, and potential ecological and socioeconomic impacts of non-native freshwater fishes in Malaysia. We identified a total of 30 non-native food fishes belonging to 12 families, with Cichlidae occurring the most frequently. Moreover, 173 species from 40 families of non-native freshwater ornamental, recreational and biological control fishes were also listed. The aquaculture production and wholesale value were significantly higher (p < 0.05) for non-native species, as compared to native species. Approximately 93% (1,317,990 metric tonnes (MT)) of aquaculture production and 85.6% (RM 7.4 billion) of wholesale value are from non-native species. However, for inland freshwater captured fisheries, the landing and wholesale values were significantly higher (p < 0.05) for native species than the non-native species. Non-native species only occupied approximately 28.6% (18,227 MT) of the landing, and 14.2% (RM 110 million) of wholesale value, respectively. For the ornamental fish production, the highest value was recorded in the year 2012 (RM 629 million), but dipped to its lowest value in 2017 (RM 327 million). The cyprinids that are mostly represented by non-native species recorded the highest value (RM 112 million) in the year 2018, followed by osteoglossids that are mainly represented by the native Asian arowana (RM 108 million). Despite the massive economic contribution from these non-native fishes, some of these fish present important ecological and socioeconomic threats to Malaysia. Several recommendations are proposed for a win-win situation between the economic gains and environmental threats caused by these non-native fishes.

Fifteen non-indigenous species have been recorded in Icelandic waters over the past decades, of which six have been classified as invasive or potentially invasive. One of these potentially invasive species is the European flounder (Platichthys flesus). Platichthys flesus is a recent arrival that was firstly identified in 1999 and has, since then, established a population around the whole country. In this study we evaluated if there is niche overlap between juvenile P. flesus and native juvenile European plaice (Pleuronectes platessa) on nursery grounds at three sites in west Iceland. Considering the presumed clockwise spread of P. flesus’ population around the country, the southernmost site, Borgarfjörður, was treated as the site of earlier settlement of P. flesus. Similarly, the northernmost site, Önundarfjörður, was treated as the site of later settlement. We used stomach content and stable isotope analyses to examine if there was a significant niche overlap between P. flesus and P. platessa and to examine if the extent of niche overlap varied between sites. Multiple cohorts of P. flesus and native P. platessa were present at all sites and there was high niche overlap between species with no indication of trophic niche segregation nor change with time from establishment of P. flesus. The current study has shown the co-occurrence and niche overlap of non-indigenous P. flesus and native P. platessa on nursery grounds in Iceland and highlighted the establishment of P. flesus in Iceland as a rare case study to investigate colonisation processes of non-indigenous fish species in sub-arctic marine environments.

Sessile invasive species often efficiently exploit anthropogenic structures, such as harbour walls and pontoons, which can lead to increased vector contact (i.e. contact with boats), and therefore spread rate. The round goby (Neogobius melanostomus) is a bottom-dwelling invasive fish species which was never documented on boats or habitats near the water surface. In this study, we wanted to find out if this fish makes use boat hulls and other vertical anthropogenic structures, which could act as invasion beachheads. We inspected boats close to harbour walls in the river Rhine in Basel, Switzerland, to search for gobies on them and documented the position of the boat and the ways the gobies could have reached the hull. We observed round goby presence on three different boats, with up to 28 goby sightings on one boat hull in the course of 45 minutes. Additionally, we recorded gobies on walls between one and five meters above the ground. Based on these observations, we investigated the behaviour of round gobies using vertical walls as habitat and compared the observed behaviours to those exhibited by gobies on the bottom. Gobies used the habitat along a wall in a generally similar fashion to the habitat on the bottom. However, they sat still for less time and moved more on walls than on the bottom, while feeding activity was similar in both habitats. The results raise questions about the drivers for using vertical structures as habitat in the usually bottom-dwelling round gobies and the plasticity of this behaviour. Our study documents round gobies in direct contact with boats for the first time. Potentially, gobies could find hiding places or suitable structures to nest on boats. This study therefore provides support for the theory that boat hulls are potential vectors for the translocation of round gobies. Our observations should lead to an increased awareness about fish and their eggs on boat hulls and stimulate efforts to implement measures like the check-clean-dry routine for commercial as well as private boats.