The requirement of Hydroides elegans for suitable hard substratum leads to association with various organisms that provide these substrates such as the eastern oyster Crassostrea virginica.Invasion History: Carlton and Ruckelshaus (1997) and NIMPIS (2002) suggest Australasia and the Indian Ocean as possible centers of origin for the species. The centers of origin for cosmopolitan species are difficult to determine with certainty, but substantial evidence suggests Australia as a likely historical source for Hydroides elegans. ten Hove has presented much of the evidence (ten Hove 1974, BioNet Annelid Archives) and it is summarized here.The species was first described from Sydney Harbor by Haswell (1883), although by 1888 it had also been found in the Italian Mediterranean (Zibrowius 1991). The local distributions of the species in these two areas were very different, however, with Mediterranean populations restricted to harbor and lagoonal communities while historic Australian populations occurred as part of natural coastal communities at a depths of around 20 m (Allen (1953). Moran and Grant (1984) suggest that the more recent rise to prominence of H. elegans in Australian harbor fouling communities is the result of increased pollution loads in the harbors. The natural occurrence of a number of Hydroides congeners in Australia adds weight to the argument implicating this part of the world as the original source of H. elegans.Ship hull fouling is widely suggested as the most important transport vector in the spread of H. elegans, with accidental transport in shipments of harvested wild or cultured bivalves noted as a secondary source of introduction (NIMPIS 2002).The first report establishing the presence of H. elegans in Florida dates to 1971 (Zibrowius 1971, Carlton and Ruckelshaus 1997). ten Hove notes his discovery of H. elegans in Curaçao at the same time. He also notes, however, that reexamination of earlier Curaçao collections (from a Venezuelan ship hull and from floating buoys) from as far back as the mid-1950s reveals the presence and probable establishmentof H. elegans at that time in Curaçao. Potential to Compete With Natives: Hydroides elegans competes with co-occurring fouling community species for space, food, and possibly other resources. For example, NIMPIS (2002) reports that competition by H. elegans for food and oxygen has been implicated in up to 60% mortality for cultured oysters in Japan. The native North American congener H. dianthus has been similarly implicated in the mortality of juvenile oysters from smothering.Additionally, tube-forming species like H. elegans are considered to be "ecosystem engineers" capable of modifying the habitats in which they occur. Architectural habitat modification due to the presence of calcareous tubes would be expected to affect community structure at localized scales. Possible Economic Consequences of Invasion: Direct economic impacts of these tube-dwelling biofoulers include the cost of cleaning ship hulls, aquaculture gear, and other submerged structures. Other costs include decreased operational efficiency of fouled vessels due to drag and of water intake pipes due to clogging (MIMPIS 2002).The economic impact of Hydroides elegans in the IRL is undetermined.
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