Circumpolar dispersal by rafting in two subantarctic kelp-dwelling crustaceans

Abstract

Long-distance oceanic rafting is frequently invoked as an explanation for broad geographic distributions of sedentary marine taxa, but evidence for this ecological process remains elusive. We explored empirically the potential of rafting as a dispersal mechanism by comparing circumpolar mtDNA variability in 3 codistributed subantarctic taxa: 2 direct-developing epifaunal crustacean species (Limnoria stephenseni, Parawaldeckia kidderi) and their macroalgal host (Durvillaea antarctica). A previous study of D. antarctica suggests that its subantarctic populations were established only postglacially, and we predict that the epifaunal invertebrates associated with it experienced a parallel island-colonization episode, facilitated by kelp-rafting. We generated and analysed mtDNA sequence data (cytochrome oxidase subunit I [COI] gene, > 900 base pairs) from 89 L. stephenseni and 62 P. kidderi specimens and reanalysed previously published comparable data for D. antarctica. Both epifaunal species exhibited wide-scale circumpolar distributions of a single haplotype. Little sequence diversity was found within island samples, with the exception of P. kidderi in the Falkland Islands. The phylogeographic diversity and structuring of the invertebrates was very similar to that of their kelp host and consistent with a scenario of subantarctic recolonization and population expansion. The dependence of these otherwise non-dispersive crustaceans on macroalgal holdfasts for food and habitat, as well as the great abundance of D. antarctica adrift in the Antarctic Circumpolar Current (ACC), support rafting as their most plausible recolonization mechanism. We suggest that macroalgal rafting may explain similarities in the species composition of intertidal marine communities across the subantarctic.

Patrones de diversidad y estructura genética en especies antárticas y subantárticas de Nacella (Nacellidae)

“…En Subantártica, la marcada diferenciación entre los linajes de Patagonia e Isla Kerguelén contrastan con los resultados registrados en otros invertebrados que muestran altos niveles de conectividad entre provincias geográficamente alejadas. Distintos grupos de invertebrados incluyendo mitílidos (Gérard et al 2008), crustáceos (Nikula et al 2010), equinodermos (Díaz et al 2011) y gasterópodos pulmonados (Cumming et al 2014) muestran evidencia de conectividad contemporánea entre provincias subantárticas geográficamente alejadas. De esta forma, para Nacella la distancia geográfica, los patrones oceanográficos y rasgos de historia de vida como su modo de desarrollo representan una barrera infranqueable para la conectividad a lo largo de Subantártica (González-Wevar et al 2010).…”

“…Por un lado, la CCA actúa como una gran barrera para la mayoría de los invertebrados marinos entre provincias antárticas y subantárticas (Shaw et al 2004;Page & Linse, 2002;Griffiths et al 2009;González-Wevar et al 2012a;Poulin et al 2014). Por otro lado, a lo largo de Subantártica la CCA actúa como un importante medio de transporte entre provincias geográficamente distantes, especialmente para organismos con alta capacidad dispersiva (Gérard et al 2008;Waters, 2008;Fraser et al 2009;Díaz et al 2011) y para aquellos que viven asociados a macroalgas (Nikula et al 2010;Fraser et al 2011;Cumming et al 2014). El segundo periodo durante el Mioceno medio (~ 14 Ma) se asocia a un incremento en la formación de aguas de profundidad en el OA, la intensificación de CCA y al re-establecimiento de una capa de hielo permanente en Antártica Este y en el margen Pacífico de Península Antártica (Lawver & Gahagan, 2003;Verducci et al 2009).…”

Spatio-temporal distribution of floating objects in the German Bight (North Sea)

“…seaweed and wood) and anthropogenic debris (e.g. plastics items) have been suggested as dispersal vectors for a wide range of species from marine and terrestrial environments (Ingólfsson, 1995;Barnes and Milner, 2005;Johansen and Hytteborn, 2001;Waters, 2008); recent molecular studies have added support to this view (Muhlin et al, 2008;Nikula et al, 2010). Anthropogenic floating objects (mainly plastic debris) may facilitate long-distance dispersal of invasive species, and furthermore impact marine wildlife (e.g.…”

Kelp rafts in the Humboldt Current: Interplay of abiotic and biotic factors limit their floating persistence and dispersal potential

“…In contrast, species without planktonic larvae rely on other mechanisms to reach new habitats. Rafting on floating algae has been suggested as an important dispersal mechanism for these invertebrates (Nikula et al 2010). Here dispersal depends not only on the organisms themselves but also on the floating substratum and its persistence at the sea surface.…”