A rare example of non-native chitons: broad intertidal habitat range and large densities of Sypharochiton pelliserpentis show no evidence of habitat engineering effect in South Australia

摘要

There are numerous examples of non-indigenous rocky-intertidal mobile invertebratespecies, but there have been very few instances of introductions of chitons despitetheir often high abundance in fouling assemblages where non-indigenous speciesoriginate. In 2016, it was observed incidentally that the snake-skin chitonSypharochiton pelliserpentis, native to eastern Australia and New Zealand, wasoccurring in Coffin Bay in western South Australia, which is a sheltered bay usedfor oyster farming and far outside the previously documented S. pelliserpentisrange. The main coastal water currents in the region flow from west to east, meaningnatural larval dispersal into Coffin Bay from eastern Australian populations isunlikely. Surveys of population and community dynamics done in 2018 revealedthat a large population has established with the non-native chiton far outnumberinga comparable native chiton (Plaxiphora albida) that may occupy a similar nichespace. The chitons occurred on exposed bedrock habitats as well as cryptic habitatsunderneath boulders; both species were equally abundant between these habitatsexcept at one site where S. pelliserpentis densities specifically underneath boulderswere 10 times greater than other habitat-types or sites. Sypharochiton pelliserpentisin its native range can largely impact sessile assemblages; here we tested thehypothesis that sessile assemblages would differ on boulders with versus withoutthe non-native chiton, but no evidence of any such effect was found. Sypharochitonpellisperpentis is a common epibiont of oyster-reefs and the origin of its introductioninto South Australia may involve transport of oyster-industry materials, which washow introductions of four other non-native benthic invertebrates occurred previouslyinto another Australian region. The geographic extent of S. pelliserpentis in SouthAustralia is unknown at this stage but the chiton was not found during surveys inanother nearby bay. Knowledge that oyster-associated chitons may be spreadingoutside their native ranges, and that they can establish primarily in habitats that arelargely hidden from view, such as underneath boulders, can inform monitoring andmanagement practices for ecology of non-indigenous intertidal species.