DOI: 10.3391/ai.2025.20.2.153623

Authors: Andrew A. Davinack

Abstract: The assumption that elevated genetic diversity in a population directly correlates with its native range is a common but flawed approach in ecological studies. This practice is based on the belief that native populations, having been exposed to local evolutionary pressures over long periods, should exhibit higher genetic diversity, while introduced populations experience founder effects or bottlenecks that reduce genetic variation. However, multiple introductions and genetic admixture in non-native regions can artificially inflate genetic diversity, challenging the assumption that regions with high genetic diversity are the native ranges. This issue, which has been recognized for nearly two decades, remains prevalent in the literature despite strong evidence to the contrary. Studies on a variety of marine invertebrates demonstrate how introduced populations may exceed native ones in genetic diversity. In contrast, bottlenecks in native populations due to environmental stressors can mask the true genetic history of species. This letter argues for an integrative approach when determining native ranges, combining genetic data with historical, ecological and biogeographical analyses. This broader framework helps avoid misinterpretations of genetic diversity, which could lead to inaccurate conclusions about species’ native ranges and misinform conservation and management strategies.

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DOI: 10.3391/ai.2024.19.2.124566

Authors: Marinus van der Gaag, Gerard van der Velde, Rob S. E. W. Leuven

Abstract: The invasive alien false mussels Mytilopsis leucophaeata cochleata and Dreissena polymorpha (Dreissenidae) have established populations in the North Sea canal in the Netherlands that connects the harbours of Amsterdam with the North Sea. The favourable and unfavourable salinity ranges of both species were earlier studied in long-term outdoor mesocosm experiments. Their occurrence in salinity gradients in estuaries or canals connecting seaways to freshwater harbours provides information on their salinity tolerance under field conditions. By the combination of laboratory experiments and field data using the same source population a high predictability can be expected for establishment of the gradients facilitated by constructions. The reliability of experimentally derived salinity-tolerance limits for both dreissenid species was tested using data on their distribution in a salinity gradient of the littoral zone along the North Sea canal. The mussels used for the survival experiments in mesocosms were also collected from this canal. Favourable salinity ranges for adult survival in the mesocosms were 0.2 – 17.5 for M. leucophaeata cochleata and 0.2 – 6.0 for D. polymorpha. Unfavourable salinities were outside these ranges and led to high and fast mortality of these species. Mytilopsis leucophaeata cochleata was present over nearly the whole length of the North Sea canal with the highest densities close to the sea sluices where also the highest salinities and water temperatures were measured. Their densities in the canal decreased gradually at larger distances from the sea. Dreissena polymorpha co-exists with M. leucophaeata cochleata at the east end of the canal with low salinity due to the influence of freshwater of the river Rhine. The occurrence of D. polymorpha was restricted to a salinity below 4 and M. leucophaeata cochleata only occurred at a salinity above 1.5 (maximum value measured in the canal 9.2). Shorter salinity gradients with lower salinity ranges provided additional information on the co-existence of both species. Co-existence was observed at a salinity range of 1.5–3.3 (own data), 1.0–3.5 (Van Couwelaar and Van Dijk 1989), both in the North Sea canal, and 0.2–2.8, in the Canal through Voorne (Janssen and Janssen-Kruit 1967). These data correspond with studies of both species by Walton (1996) in the Hudson River (salinity range 0–3). Found salinity ranges in the North Sea canal for both species match with the tolerance results obtained by mesocosm experiments. A new invading dreissenid mussel Dreissena rostriformis bugensis and a mytilid Ischadium recurvum occur in the North Sea canal since 2006 and 2012, respectively. Competition between recent and earlier invaders is likely when salinity tolerances are similar. It has already been observed that D. rostriformis bugensis outcompetes D. polymorpha under freshwater conditions (Bij de Vaate et al. 2014; Matthews et al. 2014). Ischadium recurvum has the potential to colonize large parts of the canal and to be a strong competitor of M. leucophaeata cochleata (Goud et al. 2019). Since January 2022, the new ‘Zeesluis IJmuiden’ with the biggest locks in the world is in use, affecting the probability of population establishment of new introduced and invasive alien mussel species.

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DOI: 10.3391/ai.2023.18.4.113092

Authors: Anna Stępień, Anna M. Jażdżewska, Romeu S. Ribeiro, Rafael Santos, Macarena Ros

Abstract: A major challenge in invasion science is detecting overlooked introductions, their pathways of introduction and spread. One of the most successful introduced taxa in aquatic ecosystems are peracarid crustaceans. There are a growing number of reports of accidental introductions of peracarids worldwide, mostly related to human transport hubs (e.g., ports and marinas). Tanaidaceans are especially abundant in these communities. Most frequently given examples of natural and anthropogenic passive dispersers belong to the family Tanaididae. However, their wide distribution requires confirmation. Most records come from 70–80’ of last century, when identification of the species relied only on morphological characters. The small size and large intraspecific variation of tanaidids generate a high taxonomic uncertainty, as in the case of Zeuxo turkensis. Population of this species was previously known from Turkish, Japanese, and Australian coasts. In the two last places this tanaidid was identified as Hexapleomera sasuke, despite there were some premises that it should be synonymized with Z. turkensis. Here we investigate specimens that resembled both Hexapleomera sasuke and Zeuxo turkensis collected in marinas around the Iberian and Moroccan coasts. Integrating morphological and molecular methods (barcoding) we confirmed: (1) the first record and presence of well-structured populations of Z. turkensis in Spain, Portugal and Morocco, representing the first record of the species for Atlantic waters; (2) the conspecificity between H. sasuke and Z. turkensis, which should be synonymized; and (3) the wide distribution of Z. turkensis associated with human transport hubs (i.e. marinas) in the study area, showing its potential for introduction and spread. Integrated approaches and greater taxonomic support are key to advancing knowledge on the origin and invasion patterns of this and other small and poorly known human-mediated widespread species.

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DOI: 10.3391/ai.2023.18.3.104556

Authors: Sungtae Kim, Cheol Yu, Jennifer Ruesink, Jae-Sang Hong

Abstract: Smooth cordgrass (Spartina alterniflora Loisel.), an aggressive non-native species worldwide, colonized tidal flats on the west coast of Korea in two regions differing in tidal amplitude between 1990–2004. By the time of our study in 2015, expansion had occurred both clonally and through formation of new patches, providing an opportunity to determine intertidal range, which is a key component of understanding the threat posed by S. alterniflora through competition with native halophytes or transformation of unstructured mudflat. At Ganghwa (5.69 m tidal range), S. alterniflora ranged from 3.52 to 1.34 m above Mean Sea Level (MSL). At Jindo (2.02 m tidal range), S. alterniflora ranged from 1.57 to -0.18 m relative to MSL. Thus, a wider absolute intertidal range was occupied by S. alterniflora at the megatidal vs mesotidal region, but the lower limit of S. alterniflora did not extend below MSL under megatidal conditions, a pattern that now appears to emerge consistently in both the native and introduced range. In both study regions, S. alterniflora occurred at the same elevations as other salt marsh plants, occupying an upper zone with Phragmites australis (non-native) and middle zone with several native species including Suaeda japonica. S. alterniflora occurred below native marsh vegetation at all sites, which would result in transformation of the extensive mudflats along the Korean coast.

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