Competition between co‐occurring invasive and native consumers switches between habitats

The genome sequence of the Pacific oyster, Magallana gigas (Thunberg, 1793)

We present a genome assembly from an individual Magallana gigas (the Pacific oyster; Mollusca; Bivalvia; Ostreida; Ostreidae). The genome sequence is 564.0 megabases in span. Most of the assembly is scaffolded into 10 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 18.23 kilobases in length.

Alien species revises systematic status: integrative species delimitation of two similar taxa of Symbrenthia Hübner, [1819] (Lepidoptera, Nymphalidae)

Introduction of organisms to new range may impose detrimental effects on local organisms, especially when closely related species are involved. Species delimitation employing an integrative taxonomy approach may provide a quick assessment for the species status between taxa of interest, and to infer ecological competition and/or introgression that may be associated with the introduction. A nymphalid butterfly, Symbrenthia lilaea lunica, was recently introduced to Taiwan, where a closely related local taxon, S. l. formosanus, can be found. We employed multiple species delimitation methods to study the species status between the two taxa, and the results revealed that they can be recognized as two distinct species, revised to S. l. lilaea (syn. nov.) and S. formosanus (stat. rev.) respectively. We further performed a niche modeling approach to investigate the ecological interaction between the two species. The taxonomic status of the two taxa, now elevated to species, has been revised and conservation facing rapid expansion of the introduced species discussed.

Biotic resistance of native fouling communities to bioinvasions could not be demonstrated by transplant experiments in Northern Italy

Biotic resistance is considered an important driver in the establishment of non-indigenous species (NIS), but experiments in the marine environment have led to contradictory results. In this context, a transplant experiment of fouling communities was carried out over five months. Settlement panels were moved from low impact (species-rich native communities) to high impact sites by NIS in two Italian areas to test the biotic resistance hypothesis. Fouling communities displayed significant differences among treatments before and after the transplant, thus indicating the maintenance of a peculiar fouling community in transplanted panels. On the other hand, newly recruited species were similar between treatments and neither a facilitation nor a mitigation role from native fouling communities on NIS was observed. Our results highlight the importance to better investigate the factors affecting the high variability obtained in experiments testing this hypothesis, with the aim to identify potential solutions for NIS management in ports.

Occurrence and abundance of invasive and native Arion slugs in three types of habitats in urban area of Wrocław (SW Poland)

Arion vulgaris and Arion rufus are two cryptic slug species whose ranges overlap in vast areas of Europe. In Poland, A. rufus is native; it reaches the eastern border of its range near Wrocław, while the invasive A. vulgaris was previously not recorded in this area. The study aimed to map the distribution of both species in the city of Wrocław and determine the size and abundance of their populations. Twenty-six sites were surveyed in 2019-2020. They represented three types of habitats: natural, semi-natural and anthropogenic. Because the investigated species are externally indistinguishable, their identification was based on the genital organs. Among 280 analysed specimens, 72% were identified as A. vulgaris, 23% as A. rufus and 5% were classified as hybrids. The hybrids and A. vulgaris were most abundant in semi-natural (83%) and anthropogenic habitats (95%), while A. rufus most often occurred in natural habitats (51%). Arion vulgaris occupied most of the sites (88.5%), and in 50%, it was collected alone. Arion rufus occurred in 46% of the sites (in 11.5% alone), and the hybrids were noted in 27%. In Wrocław A. vulgaris dominates in most sites, and its populations are much more abundant than those of A. rufus where the two species co-occur. This finding indicates that A. vulgaris, with its better adaptive skills and competitive abilities, may negatively impact the native species and, consequently, the latter’s displacement. Although the recorded frequency of hybridisation was very low (5%), it may also have an effect on the local extinction of A. rufus. Interspecific hybridisation is assumed to foster invasions, and climate change may further exacerbate displacement; therefore, they should continue to be monitored.

Gastrointestinal Parasite Community and Phenotypic Plasticity in Native and Introduced Alien Lagomorpha

The Convention on Biological Diversity classifies "Invasive Alien Species" as those whose introduction and spread represents a threat for biodiversity. Introduction of alien pathogens, including parasites, is one of the main consequences of the introduction of invasive alien species. The objective of this work was to assess the parasite community composition in native lagomorphs (Lepus europaeus and Lepus timidus varronis) in sympatric and non-sympatric conditions with an alien lagomorph (Sylvilagus floridanus), and to evaluate the phenotypic traits of exotic parasites in such conditions. We firstly describe the characteristics of the parasite community in the different host species (richness, prevalence, abundance and intensity), and, secondly, the phenotypic traits of the observed parasite species in each host. Nine helminths were reported on: eight nematodes (Obeliscoides cuniculi, Trichostrongylus calcaratus, Trichostrongylus retortaeformis, Trichostrongylus affinis, Trichuris leporis, Trichostrongylus colubriformis, Passalurus ambiguus, and Nematodirus sp.) and one unidentified cestode. In addition, exotic parasites showed significantly different phenotypic plasticity after spillover from S. floridanus to L. europaeus, whereas endemic parasite species were not isolated in the alien S. floridanus. Our results highlight that the community of autochthonous and allochthonous Lagomorpha in northwestern Italy represents an extremely interesting system for modelling ecological and evolutionary interactions between parasites and their hosts.

Marine heat waves differentially affect functioning of native (Ostrea edulis) and invasive (Crassostrea [Magallana] gigas) oysters in tidal pools

The frequency and duration of short-term extreme climatic events, such as marine heat waves (MHWs), are increasing worldwide. The rapid onset of MHWs can lead to short-term stress responses in organisms that may have lethal or sub-lethal effects. In addition, increased temperature variability and extremes are predicted to favour and facilitate the spread of non-native species, altering rates of key ecosystem processes and functions. It is possible, however, that compensatory mechanisms, such as increased feeding rates, may enable the maintenance of metabolic functioning and prevent detrimental temperature effects. Using a mesocosm-based approach, we experimentally tested for the effects of MHWs in tidal pools on the mortality, individual length, width and biomass, and respiration rates for both a native oyster, Ostrea edulis, and invasive oyster, Magallana gigas, with or without food supply. No mortality was recorded for either O. edulis or M. gigas for the duration of the four week experiment. Increases in length were greater in O. edulis compared to M. gigas but were not affected by temperature or food supply. Increases in width, however, did not differ between species but were reduced overall in heat wave treatments regardless of food supply. O. edulis gained more biomass than M. gigas in ambient treatments regardless of food supply but, in heat wave treatments, only gained greater biomass than M. gigas at additional levels of food supply. Respiration rates did not reflect changes in temperature or food supply in either species but differed through time, with greater rates post-heat wave in all treatments. Thermal responses of O. edulis and M. gigas to MHWs thus appear to be context dependent and, if food supply is sufficient, O. edulis may be able to maintain its presence in the intertidal. The ability of M. gigas to remain unaffected by fluctuating environmental conditions, however, suggests future resilience of invasive populations to climatic extremes that may result in competitive exclusion and a further decline in native oyster populations. This information is critical for developing effective management plans to ensure the sustainability of natural oyster populations whilst maintaining key ecosystem functioning.

Foraging of the sea urchin Paracentrotus lividus (Lamarck, 1816) on invasive allochthonous and autochthonous algae

Attempts to control marine invasive alien species (IAS) with native predators gained contrasting results, so far. To explore the feasibility of this approach to control the invasive marine alga Caulerpa cylindracea, we investigated the foraging behaviour of the sea urchin Paracentrotus lividus on three native macroalgae (Ulva sp., Penicillus capitatus and Cystoseira compressa) and on C. cylindracea. The consumption rate of C. cylindracea fresh biomass resulted larger than that of the other algae, when offered separately or in combination. C. cylindracea, however, was not the most attractive food item. The larger consumption rates of C. cylindracea can be explained by its specific caloric content (as assessed by its biochemical composition) that is lower than that of the other algae. Our results confirm that P. lividus can feed on C. cylindracea, but do not fully support its use to control C. cylindracea, unless in conditions where this alga is largely dominant because of other factors.

Food-web modification in the eastern Gulf of Finland after invasion of Marenzelleria arctia (Spionidae, Polychaeta)

The paucity of data on non-indigenous marine species is a particular challenge for understanding the ecology of invasions and prioritising conservation and research efforts in marine ecosystems. Marenzelleria spp. are amongst the most successful non-native benthic species in the Baltic Sea during recent decades. We used stable isotope analysis (SIA) to test the hypothesis that the dominance of polychaete worm Marenzelleria arctia in the zoobenthos of the Neva Estuary after its invasion in the late 2000s is related to the position of this species in the benthic food webs. The trend towards a gradual decrease in the biomass of Marenzelleria worms was observed during 2014–2020, probably due to significant negative relationships between the biomass of oligochaetes and polychaetes, both of which, according to SIA, primarily use allochthonous organic carbon for their production. The biomass of benthic crustaceans practically did not change and remained very low. The SIA showed that, in contrast to the native crustacean Monoporeia affinis, polychates are practically not consumed either by the main invertebrate predator Saduria entomon, which preys on M. affinis, oligochaetes and larvae of chironomids or by benthivorous fish that prefer native benthic crustaceans. A hypothetical model for the position and functional role of M. arctia in the bottom food web is presented and discussed. According the model, the invasion of M. arctia has created an offshoot food chain in the Estuary food webs. The former dominant food webs, associated with native crustaceans, are now poorly developed. The lack of top-down control obviously contributes to the significant development of the Marenzelleria food chain, which, unlike native food chains, does not provide energy transfer from autochthonous and allochthonous organic matter to the upper trophic levels. The study showed that an alien species, without displacing native species, can significantly change the structure of food webs, creating blind offshoots of the food chain.

Competitive feeding interactions between native Ostrea edulis and non-native Crassostrea gigas with implications of introducing C. gigas into commercial aquaculture in the eastern Adriatic Sea

In order to detect the possible regulatory effect of non-native C. gigas on the native O. edulis, under aquaculture conditions, feeding interactions between them were investigated in a highly productive environment of Lim Bay (Adriatic Sea). The present study uses a multi-methodological approach, including stomach content, DNA barcoding and stable isotope analysis to elucidate the feeding ecology of two oyster species. The research confirmed a high overlap throughout the year in the feeding traits among native and non-native oyster species. Competition for food was not the only relationship that exists between the investigated species as the presence of O. edulis larvae in C. gigas stomach content was confirmed by DNA analysis. Findings are not in favour of introducing C. gigas to commercial aquaculture in any new areas in the Adriatic Sea and support the need to improve the existing O. edulis aquaculture and conserve its wild stocks.

Niche Models Differentiate Potential Impacts of Two Aquatic Invasive Plant Species on Native Macrophytes

Potamogeton crispus (curlyleaf pondweed) and Myriophyllum spicatum (Eurasian watermilfoil) are widely thought to competitively displace native macrophytes in North America. However, their perceived competitive superiority has not been comprehensively evaluated. Coexistence theory suggests that invader displacement of native species through competitive exclusion is most likely where high niche overlap results in competition for limiting resources. Thus, evaluation of niche similarity can serve as a starting point for predicting the likelihood of invaders having direct competitive impacts on resident species. Across two environmental gradients structuring macrophyte communities—water depth and light availability—both P. crispus and M. spicatum are thought to occupy broad niches. For a third dimension, phenology, the annual growth cycle of M. spicatum is typical of other species, whereas the winter-ephemeral phenology of P. crispus may impart greater niche differentiation and thus lower risk of native species being competitively excluded. Using an unprecedented dataset comprising 3404 plant surveys from Minnesota collected using a common protocol, we modeled niches of 34 species using a probabilistic niche framework. Across each niche dimension, P. crispus had lower overlap with native species than did M. spicatum; this was driven in particular by its distinct phenology. These results suggest that patterns of dominance seen in P. crispus and M. spicatum have likely arisen through different mechanisms, and that direct competition with native species is less likely for P. crispus than M. spicatum. This research highlights the utility of fine-scale, abundance-based niche models for predicting invader impacts.

Can an invasive species compensate for the loss of a declining native species? Functional similarity of native and introduced oysters

The widespread introduction of the Pacific oyster, Magallana gigas, has raised concerns regarding its potential impact on the functioning of invaded ecosystems. Concurrently, populations of the European oyster, Ostrea edulis, are in decline. We quantified the functional role of the native oyster, O. edulis, in terms of nutrient cycling and associated infaunal biodiversity and compared it directly to that of the invading oyster, M. gigas. The presence and density of both species were manipulated in the field and we tested for differences in concentration of ammonium, phosphate, total oxidised nitrogen and silicate in pore-water; total organic nitrogen and carbon in sediment; microbial activity; chlorophyll concentration; and the assemblage structure and richness of associated benthic taxa. No differences in nutrient cycling rates or associated benthic assemblages were identified between both oyster species. Nutrient concentrations were mostly affected by differences in oyster density and their significance varied among sampling events. Our findings suggest that M. gigas could compensate for the loss of ecosystem functions performed by O. edulis in areas where native oysters have been extirpated.

Assessment of the population of Ostrea edulis in Sweden: A marginal population of significance?

The European flat oyster Ostrea edulis is an economically and ecologically important species subjected to extensive protection and restoration efforts, due to sharp population declines in Europe. In Sweden, O. edulis occurs at the northern fringe of its range. Knowledge of the distribution and abundance of the species is limited, and the size of the population has never been estimated. Oyster fishery sustainability has never been assessed.Using a random sampling approach and towed video, we collected data on oyster occurrence at 435 sites to estimate abundance and distribution of O. edulis in the Swedish Skagerrak region. Furthermore, the size of the population was assessed and the current management and legislation strategy of the species was analyzed.Living O. edulis was found in 27% of all sampled sites above 6 m, and the size of the population was estimated to 36.6 ± 16.3 million individuals (total population ± SE). The distribution was patchy, and approximately 60% of the population was found in oyster bed densities (≥5 oysters/m2), which corresponds to around 1% of the sampled sites.The nondestructive sampling method and representative design provided useful estimates of population size and error, which indicate that the marginal population of O. edulis in Sweden constitutes a significant part of the remaining European population. We argue that the relatively good status of the Swedish population can be explained by (a) private ownership of fishing rights, (b) a small-scale fishery that exploits <0.5% of the estimated population annually, conducted using nondestructive methods, and (c) parasite-free waters, potentially due to effective prevention of spread of infection.

OPEN RESEARCH BADGES

This article has earned an Open Data Badge for making publicly available the digitally-shareable data necessary to reproduce the reported results. The data is available at https://osf.io/jgpxw/?view_only=d070b45802a4426da028efffde3d0f76.