More than 1,000 non-indigenous aquatic spe- cies have been recorded, in total, from coastal Europe, i.e. navigational inland waterways for ocean-going ves- sels and adjacent water bodies in close proximity. Re- gions considered in this overview range from European Arctic waters to the Mediterranean Sea and Irish waters to the Black Sea. The majority of introduced taxa have been first recorded since the 1950s. Approximately 600 taxa (ranging from unicellular algae to vertebrates) are established with self-sustaining populations. The dominating group of exotic species across all seas is zoobenthos organisms. Introduction vectors are pre- dominantly shipping (ballast water and hull fouling) and species movements for aquaculture or stocking purposes.

/pdf/overview-on-introduced-aquatic-species-in-european-180hix8ugd.pdf

Overview on introduced aquatic species in European navigational and adjacent waters

In Europe, the last 20 years have seen a spectacular increase in accidental introductions of marine species, but it has recently been suggested that both the actual number of invaders and their impacts have been seriously underestimated because of the prevalence of sibling species in marine habitats. The red alga Polysiphonia harveyi is regarded as an alien in the British Isles and Atlantic Europe, having appeared in various locations there during the past 170 years. Similar or conspecific populations are known from Atlantic North America and Japan. To choose between three competing hypotheses concerning the origin of P. harveyi in Europe, we employed rbc L sequence analysis in conjunction with karyological and interbreeding data for samples and isolates of P. harveyi and various congeners from the Pacific and North Atlantic Oceans. All cultured isolates of P. harveyi were completely interfertile, and there was no evidence of polyploidy or aneuploidy. Thus, this biological species is both morphologically and genetically variable: intraspecific rbc L divergences of up to 2.1% are high even for red algae. Seven rbc L haplotypes were identified. The four most divergent haplotypes were observed in Japanese samples from Hokkaido and south-central Honshu, which are linked by hypothetical ‘missing’ haplotypes that may be located in northern Honshu. These data are consistent with Japan being the centre of diversity and origin for P. harveyi . Two non-Japanese lineages were linked to Hokkaido and Honshu, respectively. A single haplotype was found in all North Atlantic and Mediterranean accessions, except for North Carolina, where the haplotype found was the same as that invading in New Zealand and California. The introduction of P. harveyi into New Zealand has gone unnoticed because P. strictissima is a morphologically indistinguishable native sibling species. The sequence divergence between them is 4‐5%, greater than between some morphologically distinct red algal species. Two different types of cryptic invasions of P. harveyi have therefore occurred. In addition to its introduction as a cryptic sibling species in New Zealand, P. harveyi has been introduced at least twice into the North Atlantic from presumed different source populations. These two introductions are genetically and probably also physiologically divergent but completely interfertile.

rbcL sequences reveal multiple cryptic introductions of the Japanese red alga Polysiphonia harveyi

Many non-indigenous species have been found during recent decades in the Lagoon of Venice; many of these species are rapidly becoming both widespread and abundant. Reported here is the invasion of an accidentally introduced bryozoan Tricellaria inopinata, which dominated the Lagoon's fouling community within seven years of its initial detection. Recent declines in its population as well as those of indigenous bryozoans illustrate the importance of placing invasions in the context of the hydrological, chemical and biotic changes that occur in the Lagoon environment.

Biotic Invasions in a Mediterranean Lagoon

A total of ten red seaweed species are recognized as introduced into the North Sea from other parts of the world. These areAsparagopsis armata andBonnemaisonia hamifera (Bonnemaisoniales),Grateloupia doryphora (Halymeniales),Antithamnionella spirographidis, Antithamnionella ternifolia, Anotrichium furcellatum, Dasya baillouviana, ?Dasysiphonia sp.,Polysiphonia harveyi andPolysiphonia senticulosa (Ceramiales). The oldest of these isB. hamifera, introduced prior to 1890, while the most recent,?Dasysiphonia sp., was first found in 1994 and still requires taxonomic investigation. A variety of distribution patterns is seen, with geographical ranges varying from general within the North Sea to very restricted. The diversity of introduced red algae on eastern coasts of the North Sea is much greater than in the west. The most likely explanation for this pattern is that French coasts were the initial site of introduction for many of the seaweeds, which were then distributed northwards by the residual surface currents. Their increasing success in the Netherlands has probably been promoted by the drastically changed local hydrodynamic conditions which have also permitted the recent introduction of many native European species. Of the biological features of species that may favour their success as introductions, clonal vegetative propagation, often with specialized propagules or fragmentation mechanisms, is almost ubiquitous. Low-temperature tolerances can be inferred, but data are sparse. Many of the alien red algae in the North Sea contain anti-grazing compounds such as bromophenols, which may contribute to their invasive potential by deterring grazing sufficiently to permit establishment of an inoculum.

/pdf/red-algal-exotics-on-north-sea-coasts-3h1ocyo2o4.pdf

Red algal exotics on North Sea coasts

The calcareous sponge Paraleucilla magna has been detected at different Mediterranean sites (Taranto, Porto Cesareo, Brindisi and Naples). Its record in well studied areas where several benthic surveys have previously been carried out suggests a recent introduction of the species into the Mediterranean Sea. Until now this sponge has only been recorded from the Brazilian coast. It shows different morphologies, varying from tubular to an irregular massive shape with several folds occurring on its surface. The colour is white-cream. The surface is smooth. The consistency is friable. The oscula are 10–20 mm in diameter and located at the top of tubular protrusions. The skeleton consists of cortical and subatrial triactines and tetractines, together with atrial triactines, differently distributed in the sponge body. Paraleucilla magna is abundant in eutrophic environments, where seasonally it may reach very high frequency values and large dimensions. It is resistant to pollution, but it is also able to live in clean waters. The inclusion of this species among Mediterranean alien invasive species is suggested.

Occurrence of Paraleucilla magna (Porifera: Calcarea) in the Mediterranean Sea

Introduced species in European coastal waters : report on an international workshop organised jointly by the environment programme of DGXII of the European Commission and the Commission Internationale pour l'Exploration Scientifique de la Mer Méditerranée (CIESM)

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Introduced species in European coastal waters : report on an international workshop organised jointly by the environment programme of DGXII of the European Commission and the Commission Internationale pour l'Exploration Scientifique de la Mer Méditerranée (CIESM)