Ancient globetrotters—connectivity and putative native ranges of two cosmopolitan biofouling amphipods

Abstract

The geographic distributions of some coastal marine species have appeared as cosmopolitan ever since they were first scientifically documented. In particular, for many benthic species that are associated with anthropogenic substrata, there is much speculation as to whether or not their broad distributions can be explained by natural mechanisms of dispersal. Here, we focused on two congeneric coastal crustaceans with cosmopolitan distributions—the tube-dwelling amphipods Jassa marmorata and Jassa slatteryi. Both species are common elements of marine biofouling on nearly all kinds of artificial hard substrata in temperate to warm seas. We hypothesized that the two species’ modern occurrences across the oceans are the result of human shipping activities that started centuries ago. Mitochondrial DNA sequences of the CO1 fragment of specimens from distinct marine regions around the world were analysed, evaluating genetic structure and migration models and making inferences on putative native ranges of the two Jassa species. Populations of both species exhibited considerable genetic diversity with differing levels of geographic structure. For both species, at least two dominant haplotypes were shared among several geographic populations. Rapid demographic expansion and high migration rates between geographically distant regions support a scenario of ongoing dispersal all over the world. Our findings indicate that the likely former native range of J. marmorata is the Northwest Atlantic, whereas the likely former native range of J. slatteryi is the Northern Pacific region. As corroborated by the genetic connectivity between populations, shipping still appears to be the more successful vector of the two species’ dispersal when compared to natural mechanisms. Historical invasion events that likely started centuries ago, along with current ongoing dispersal, confirm these species’ identities as true “neocosmopolitans”.

Global gap-analysis of amphipod barcode library

“…Some amphipod species are well-adapted to anthropogenic environments such as artificial structures used in coastal protection or are part of fouling communities, and have shown a high invasion potential worldwide ( e.g. , Bij de Vaate et al, 2002 ; Kelly et al, 2006 ; Cabezas et al, 2014 ; Rewicz et al, 2015 ; Beermann et al, 2020 ; Sedano et al, 2020 ).…”

An example for transatlantic hitchhiking by macrozoobenthic organisms with a research vessel

“…2 The route of the research vessel from April to September 2019 can also be called a globetrotter. A recent study found that J. marmorata (and also Jassa slatteryi Conlan, 1990) began long ago to colonize the oceans and they call this type "neocosmopolitans" [27]. According to Griffiths et al [28] J. marmorata was already observed in South Africa in the 1950s.…”

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“…None of these species crosses the tropics, which seems to be a natural barrier to these primarily cool and cold water species. Beermann et al (2020) have demonstrated conclusively that J. marmorata and J. slatteryi have crossed the tropics through ship transport. The trans-hemispheric distributions of J. morinoi and J. valida suggest that they have as well.…”

“…Further examination of the trans-hemispheric species suggest possible centres of origin. Jassa marmorata is likely indigenous to the Atlantic coasts of Canada and USA (Beermann et al 2020). Here, it is the sole species of Jassa north of North Carolina where it can be found on natural, relatively pristine exposed coast as well as in bays and harbours on human modified substrates such as docks, pilings and ships.…”