Ophiactis savignyi Lineage B

Invasion History

First Non-native North American Tidal Record: 2002
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 2002

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General Invasion History:

Ophiactis savignyi is considered the world's most common and widely distributed brittle star. It was first described from the Red Sea in 1842, and later found to be widely distributed in the tropical and sub-tropical Indian, Pacific, and Atlantic Oceans. It inhabits marine fouling communities, especially sponges, and has been frequently found on ship hulls, buoys, and marine structures. It has a long-lived planktonic larva, with the potential for ballast water transport (Roy and Sponer 2002). In addition to sexual reproduction, it also reproduces asexually by fission, which is an advantage in colonizing new locations where the possibility of fertilization is low (McGovern 2003). Roy and Sponer (2002) found that most of the Atlantic specimens that they examined, including many from the Indo-Pacific and Atlantic, could be divided into two lineages, A and B. Atlantic specimens of lineage B (from Florida, Bermuda, and the Caribbean coast of Panama) were identical to their Indo-Pacific counterparts (from Philippines, Sri Lanka, Rarotonga, and Samoa), and strongly distinct from lineage A. They considered the possibility of natural invasion around Africa, from the Indian Ocean, but concluded that dispersal by currents was not likely, because this species would not survive the cold waters of the Benguela current. The degree of genetic similarity over a very wide range supported a recent, anthropogenic invasion for lineage B. Lineage A, found from Bermuda and Florida to Brazil, was not found in the Indo-Pacific samples tested, but its occurrence there could not be excluded (Roy and Sponer 2002) so it should be regarded as cryptogenic in the Atlantic. Clark (1919), cited by Roy and Sponer (2002), suggested that O. savignyi was introduced to the Atlantic before the mid-19th century.

We have treated O. savignyi as native to the Indo-Pacific, where it ranges from Japan to the Red Sea, South Africa, and French Polynesia. Further west in the Pacific, where we consider it cryptogenic, O. savignyi ranges from California to Peru, and also occurs in Hawaii, the Galapagos, and Easter Island. It was first collected in the Eastern Pacific in 1854 at Cabo San Lucas, Mexico (United States National Museum of Natural History 2008).

North American Invasion History:

Invasion History on the East Coast:

Ophiactis savignyi was collected in the Western Atlantic at least as early as 1875 in Brazil, 1882 in Bermuda, and 1884 on the East and Gulf Coasts of North America. In RV 'Albatross' cruises in 1884-1885, it was collected from off Cape Lookout, North Carolina; and the Dry Tortugas, Goodland Point, and Sarasota, Florida (US National Museum of Natural History 2011). Roy and Sponer (2002) found two lineages in the Western Atlantic, one (Lineage A) unique to the region and one (Lineage B) found in Florida, Bermuda, and the Caribbean coast of Panama which apparently represents a cryptic introduction from the Indo-Pacific. Roy and Sponer (2002) did not give specific locations for samples, so we have considered all locations with US National Museum specimens on the Florida Peninsula from Cape Canaveral on the Atlantic Coast and Cedar Key on the Gulf Coast, southward to the Florida Keys to contain the introduced lineage B, and other Atlantic sites with O. savignyi collections, to be cryptogenic.

Invasion History Elsewhere in the World:

Ophiactis savignyi is considered a recent invader in the Mediterranean, which it apparently colonized through the Suez Canal, reaching Israel by 1948 (Galil 2007). In the Mediterranean, it is known from the Aegean Sea (in 1994, Pancucci-Papadopoulou et al. 2005), and the Gulf of Gabes, Tunisia (in 1973, United States Museum of Natural History 2008). One specimen was found in Banyuls-sur-Mer, France (in 1968, Guile 1968). It also occurs in the East Atlantic on Madeira (Jesus and Domingos 1998) and Senegal (United States National Museum of Natural History 2011).

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Description

Ophiactis savignyi has a disk diameter of 2.5 - 5 mm, usually with six arms 13-20 mm in length. This brittle star reproduces by fission, and can regenerate lost arms, so numbers of arms can vary from 1-7. Small spines are scattered over the disk surface. On the ventral side of the disk, three scale-like oral papillae are present around the mouth, and the oral shields are large. On the dorsal side of the disk, the radial shields are large. The aboral arm plates are elliptical with rounded lateral margins, and a convex distal edge with a median lobe made prominent by a dark spot on either side. There are 5-6 arm spines on each arm segment. Body color ranges from brown to brown-green and cream. The radial shields are darker than the rest of the disk and generally have a patch of white along the outer tip. The arms are banded due to the dark markings on distal portions of the arm plates (Smithsonian Marine Station 2011; Stöhr 2011).

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Taxonomy

Ecology

General:

Ophiactis savignyi is a brittle star which reproduces sexually, broadcasting eggs and sperm, but it can also reproduce asexually by fission. Animals inhabiting sponges tend to be of one sex, dominated by immature animals, and appear to be dependent on asexual reproduction. There appears to be a trade-off between sexual and asexual reproduction, with asexual reproduction being more likely in populations with a lower probability of fertilization. Males are more likely to divide than females, which are more likely to lose their gonads after fission, resulting in a skewed sex ratio (McGovern 2002; McGovern 2003). Ophiactis savignyi can be found in a variety of habitats including rocky shores and seaweed beds, the interior of sponges, mangroves, corals, docks, and boat hulls (Roy and Sponer 2002; McGovern 2003).

Food:

detritus, foraminfera, benthic invertebrates

Trophic Status:

Deposit Feeder

DepFed

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Habitats

General Habitat	Coral reef	None
General Habitat	Grass Bed	None
General Habitat	Marinas & Docks	None
General Habitat	Vessel Hull	None
General Habitat	Rocky	None
General Habitat	Unstructured Bottom	None
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Subtidal	None
Vertical Habitat	Epibenthic	None

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Tolerances and Life History Parameters

Maximum Duration	30	Larval duration, approximate, Roy and Sponer 2002
Minimum Length (mm)	28.5	Adult radius (disk + arms)
Maximum Length (mm)	45	Adult radius (disk + arms)
Broad Temperature Range	None	Warm temperate-Tropical
Broad Salinity Range	None	Polyhaline-Euhaline

General Impacts

No direct impacts have been reported for this species, but they could be substantial, given the high abundance of this brittle star in some locations.

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References

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Zibrowius, Helmut (2002) Assessing scale and impact of ship-transported alien fauna in the Mediterranean?, CIESM Workshop Monographs 20: 63-68

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