Hydroides elegans is a small tube-forming serpulid polychaete worm commonly found in hard-bottom coastal and estuarine fouling communities. The species is present in the IRL and elsewhere in Florida but is an introduced species not native to the United States.Adult H. elegans have 65-80 body segments and an opercular crown with 14-17 spines, each with 2-4 lateral processes and a medial row of short serrations. The opercular crown also has a small central spine. The calcareous tubes produced by H. elegans are white and sinuous, sub-trapezoidal in cross-section and possessing 2 longitudinal ridges and many transverse wrinkles (Imajima 1976, NIMPIS 2002).

Azores, Azores Exclusive Economic Zone, European waters (ERMS scope), Greek Exclusive Economic Zone, Gulf of Mexico, Mediterranean Sea, New Zealand Exclusive Economic Zone, North East Atlantic, North Sea, Portuguese Exclusive Economic Zone, Red Sea, Spanish Exclusive Economic Zone, United Kingdom Exclusive Economic Zone

Hydroides elegans is subtidal to low intertidal fouling organism that utilizes a variety of natural and artificial hard substrates including oyster and rock reefs, wood, concrete pilings, aquaculture cages, intake pipes, and vessel hulls. It is now widely distributed in the topics and subtropics, particularly in harbor fouling communities. The introduced range of the species includes coastal areas on both sides of the Atlantic (NIMPIS 2002). The species was established in parts of the southern Caribbean as early as the mid 1950s, and it was confirmed present in Florida in 1971 (Carlton and Ruckelshaus 1997). Occurrence on India River Lagoon collection blocks in locations ranging from Cape Canaveral to south Hutchinson Island suggests that Hydroides elegans is established and widespread in the Lagoon, although the relatively stenohaline character of the early life history stages (see below) may limit population distribution.

Imajima (1976) reports a maximum body length of 20 mm and a maximum tube length of up to 80 mm. The maximum width at the thorax is 1.5 mm.

Kaplan (1999) estiamates 10-15 Hydroides species occur in the South Atlantic and Caribbean. Individual species distributions are uncertain and identification to species level is difficult and requires examination of the details of the setae and opercular crown. NIMPIS (2002) indicates that the collar setae are a key feature for differentiation and notes that in H. elegans the collar setae are bayonet-shaped and have a denticulate (toothed) subapical zone.

Depth range based on 20 specimens in 1 taxon.
Water temperature and chemistry ranges based on 12 samples.

Environmental ranges
  Depth range (m): 1 - 3889.5
  Temperature range (°C): 13.628 - 27.099
  Nitrate (umol/L): 0.086 - 5.799
  Salinity (PPS): 34.929 - 38.757
  Oxygen (ml/l): 3.866 - 4.657
  Phosphate (umol/l): 0.085 - 0.256
  Silicate (umol/l): 1.887 - 9.347

Graphical representation

Depth range (m): 1 - 3889.5

Temperature range (°C): 13.628 - 27.099

Nitrate (umol/L): 0.086 - 5.799

Salinity (PPS): 34.929 - 38.757

Oxygen (ml/l): 3.866 - 4.657

Phosphate (umol/l): 0.085 - 0.256

Silicate (umol/l): 1.887 - 9.347
 
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Hydroides elegans is a suspension feeder. Adult animals filter phytoplankton and suspended organics from the water column and Udhayakumar and Karande (1996) indicate that diatoms were an important dietary component in the animals they studied. Larvae also feed on water column phytoplankton. Laboratory-cultured H. elegans larvae have been reared on Dunaliella and Isochrysis (NIMPIS 2002).

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.

H.A. ten Hove, annelid expert from the Zoological Museum of the University of Amsterdam, has cited Hydroides elegans as probably the most widespread harbor-fouling serpulid worm of the worldwide tropics and subtropics (BioNet Annelid Archives).Bagaveeva and Zvyagintsev (1999) report that H. elegans biomass may reach several kg/m² by late summer in the northwestern Sea of Japan where it is also believed to be an introduced species.

Reproduction in Hydroides elegans is sexual and the the sexes are separate (NIMPIS 2002), although some sources (e.g., CSIRO 2001) report the species as hermaphroditic. Gametes are released to the environment and fertilization is external (Nishi 1992). Qiu and Qian (1998) report that most reproductive individuals had tube lengths of 12 mm or more and average fecundity ranged between 1100-9050 oocytes per female.Reproductive seasonality varies by location and has been reported as occurring from late summer to early winter in both hemispheres with some populations in milder climates capable of year-round reproduction (Miura and Kajihara 1984, Udhayakumar and Karande 1996, Lewis and Smith 1991). Qiu and Qian (1998) suggest salinities above 25 ppt and temperatures above 20°C are requisite conditions for reproduction.

A planktonic larval period persists for less than a week before settlement-stage Hydroides elegans individuals recruit into hard benthic habitats (NIMPIS 2002).