A silent invasion

Abstract

Invasions mediated by humans have been reported from around the world, and ships' ballast water has been recognized as the main source of marine invaders worldwide. Some invasions have dramatic economic and ecological consequences. On the other hand, many invasions especially in the marine realm, can go unnoticed. Here we identify a human mediated, worldwide introduction of the hydrozoan species Turritopsis dohrnii. The normal life cycle of hydrozoans involves the asexual budding of medusae from colonial polyps. Medusae of Turritopsis, however, when starved or damaged, are able to revert their life cycle, going back to the polyp stage through a process called transdifferentiation. They can thus easily survive through long journeys in cargo ships and ballast waters. We have identified a clade of the mitochondrial 16S gene in Turritopsis which contains individuals collected from Japan, the Pacific and Atlantic coasts of Panama, Florida, Spain, and Italy differing from each other in only an average of 0.31% of their base-pairs. Fifteen individuals from Japan, Atlantic Panama, Spain, and Italy shared the same haplotype. Turritopsis dohrnii medusae, despite the lack of genetic differences, are morphologically different between the tropical and temperate locations we sampled, attesting to a process of phenotypic response to local conditions that contributes to making this grand scale invasion a silent one.

Molecular phylogenetics reveals differential divergence of coastal snails separated by the Isthmus of Panama

“…However, sequence divergence between these snails is extremely low (0.8% in the COI gene and 0.2% in the 16S gene), suggesting that a potential dispersal event occurred between the Pacific and Atlantic after the final closure of the Isthmus and introgressive hybridization occurred recently between these two species. There are several examples which suggest that dispersal between the Pacific and Atlantic occurred after the Isthmus rose, by the breaching (Lessios etal., 2001) and by human activities (Roy and Sponer, 2002;Miglietta and Lessios, 2009). We are currently sampling more extensively across the Americas to fully evaluate this possibility and the potential pathways for recent dispersal events between the Pacific and Atlantic coasts.…”

Seasonal fluctuations of some biological traits of the invader <i>Caprella scaura</i> (Crustacea: Amphipoda: Caprellidae) in the Mar Piccolo of Taranto (Ionian Sea, southern Italy)

“…Invading organisms may affect marine systems by altering ecosystem processes, disrupting trophic dynamics, disturbing and degrading habitats, or directly competing, parasitizing, or preying upon native species (Ruiz et al 1999). The success of introduced organisms depends on many factors, including their adaptability to new environments and survival under unfavourable conditions, linked to lifecycle features such as high reproductive potential and dispersal ability (Miglietta and Lessios 2009). Polluted or physically degraded environments are more exposed to invasion than pristine ones (Galil 2007).…”

First record of the invasive stinging medusa Gonionemus vertens in the southern hemisphere (Mar del Plata, Argentina)

“…Although there are few described occurrences of gelatinous zooplankton that have successfully invaded different coastal environments of the world (Graham & Bayha, 2007), some of these invasions had dramatic economic and ecological consequences (Miglietta & Lessios, 2009). Examples include high concentrations of medusae clogging fishing nets and stinging species creating problems along recreational beaches (Graham et al, 2003;Graham & Bayha, 2007).…”

“…Examples include high concentrations of medusae clogging fishing nets and stinging species creating problems along recreational beaches (Graham et al, 2003;Graham & Bayha, 2007). Hydromedusae (Cnidaria, Hydrozoa) can be transported through ballast water, but if the species has a meroplanktonic life cycle, their benthic stage can also be introduced as a part of the ship's fouling fauna (Rees & Gershwin, 2000;Genzano et al, 2006;Miglietta & Lessios, 2009). …”