Presence of the tunicate Asterocarpa humilis on ship hulls and aquaculture facilities in the coast of the Biobío Region, south central Chile

Abstract

Non-native ascidians are important members of the fouling community associated with artificial substrata and man-made structures. Being efficient fouling species, they are easily spread by human-mediated transports (e.g., with aquaculture trade and maritime transports). This is exemplified by the ascidian Asterocarpa humilis which displays a wide distribution in the Southern Hemisphere and has been recently reported in the Northern Hemisphere (NW Europe). In continental Chile, its first report dates back from 2000 for the locality of Antofagasta (23°S). Although there was no evidence about the vectors of introduction and spread, nor the source, some authors suggested maritime transport by ship hulls and aquaculture devices as putative introduction pathways and vectors. In the present study, we report for the first time the presence of A. humilis on the hull of an international ship in a commercial port in Concepción bay (36°S), south central Chile. We also found one individual associated to a seashell farm, 70 km far from Concepción bay. Further individuals were subsequently identified within Concepción bay: one juvenile settled upon international harbor pilings and a dozen individuals along aquaculture seashell longlines. For the first specimens sampled, species identification was ascertained using both morphological criteria and molecular barcoding, using the mitochondrial gene cytochrome c oxidase subunit I (COI) and a nuclear gene (ribosomal RNA 18S). The nuclear 18S gene and the mitochondrial gene COI clearly assigned the specimens to A. humilis, confirming our morphological identification. Two haplotypes were obtained with COI corresponding to haplotypes previously obtained with European and Northern Chilean specimens. The present study thus reports for the first time the presence of A. humilis in the Araucanian ecoregion, documenting the apparent expansion of this non-native tunicate in Chile over 2,000 km, spanning over three ecoregions. In addition we reveal the potential implication of the international maritime transport as a vector of spread of this species along the Eastern Pacific coast, and the putative role of aquaculture facilities in promoting local establishments of non-native tunicates.

Morphology, genetics, and historical records support the synonymy of two ascidian species and suggest their spread throughout areas of the Southern Hemisphere

“…The presence of A. humilis has been reported in the Southern Hemisphere in both, artificial (Kesteven 1909;Clarke and Castilla 2000;Monniot et al 2001;Schwindt et al 2014;Turon et al 2016b;Page and Kelly 2016;Pinochet et al 2017;this study) and natural habitats (Varela 2007;Page and Kelly 2016; this study). In the Northern Hemisphere, the species is introduced and has been mainly found in harbors (Bishop et al 2013;Kenworthy et al 2018).…”

“…Monniot and Monniot (1983) reported the presence of C. robinsoni in the Magellanic region of Argentina (Franklin Bay), in a presumably natural habitat (F. Monniot personal communication, specimens attached to Pyura legumen from MNHN collection S1 CNE 09). In the SE Pacific, we report for the first time the presence of A. humilis in natural habitats (Table 1), while all the previous records corresponded to artificial settings (Clarke and Castilla 2000;Manríquez et al 2014;Turon et al 2016a, b;Pinochet et al 2017;Leclerc et al 2018).…”

“…We analyzed morphological features, including the number of oral tentacles, number of longitudinal branchial vessels, number and shape of gonads in each side of the body and orientation of gonoducts. They covered the range previously described for A. humilis (Heller 1878;Kesteven 1909;Bovien 1921;Hartmeyer 1922;Hartmeyer and Michaelsen,1927;Brewin 1946;Kott 1952;1985;Millar 1982;Clarke and Castilla 2000;Monniot et al 2001;Varela 2007;Bishop et al 2013;Turon et al 2016b;Pinochet et al 2017) and C. robinsoni (Hartmeyer 1916;Van Name 1945;Diehl 1977) (Table 3). Our analysis of specimens did not reveal a pyloric caecum, a character reported for A. humilis (Clarke and Castilla 2000).…”

“…We compiled and compared the information on these features with descriptions available in the literature. These are for A. humilis : Heller 1878;Kesteven 1909;Brewin 1946;Kott 1952;1985;Millar 1982;Clarke and Castilla 2000;Monniot et al 2001;Varela 2007;Bishop et al 2013;Turon et al 2016a;Pinochet et al 2017;and for C. robinsoni: Hartmeyer 1916;Van Name 1945;Diehl 1977.…”

Spread of the non-native anemone Anemonia alicemartinae Häussermann & Försterra, 2001 along the Humboldt-current large marine ecosystem: an ecological niche model approach

“…For example, a study carried out in the ballast water and hulls of 186 vessels in the North Sea found that 57% of the species recorded were non-native (Gollasch, 2002). Similar studies conducted in the coast of Chile revealed the presence of the invasive ascidian Asterocarpa humilis attached to hulls of international ships, which may explain the rapid spread of this species for more than 2,000 km along the coast (Pinochet et al, 2017).…”