Transorchestia enigmatica

Invasion History

First Non-native North American Tidal Record: 1962
First Non-native West Coast Tidal Record: 1962
First Non-native East/Gulf Coast Tidal Record:

---

General Invasion History:

Transorchestia enigmatica is a semi-terrestrial, littoral amphipod, known only from the shorelines of Lake Merritt, in Oakland, California, a tidal lagoon of San Francisco Bay. It was first collected there by James T. Carlton in 1962. This beach-hopper shows close morphological affinities with species from Chile and New Zealand, and was probably transported to San Francisco Bay in dry ballast, cargo, or dunnage (i.e. scrap material used to secure cargo in holds or on deck) (Bousfield and Carlton 1967; Bousfield 1982; Carlton 1979; Cohen and Carlton 1995).

North American Invasion History:

Invasion History on the West Coast:

Transorchestia enigmatica was first collected on the shores of Lake Merritt, Oakland, California in 1962. It was found amongst shore debris such as leaves, rotting wood, vegetation, and washed-up tubes of the serpulid polychaete Ficopomatus enigmaticus. It is now largely confined to one muddy-sandy beach in the lagoon, although it is occasionally found in the channel leading to Oakland Harbor. Transorchestia enigmatica may have been introduced by sailing ships from Chile or New Zealand (Bousfield and Carlton 1967; Bousfield 1982; Carlton 1979; Cohen and Carlton 1995).

---

Description

General features of the family Talitridiae include a laterally compressed, arched body; a short Antenna 1 and long Antenna 2; well-developed eyes and pereiopods (walking legs); hopping locomotion; and the ability to survive exposure to air in beach wrack-lines and debris. Transorchestia enigmatica has a squarish-oval, medium-sized eye. Antenna 1 is short, with its tip not quite reaching the distal end of peduncle segment 2 of Antenna 2. Antenna 2 is sexually dimorphic. In the male, the peduncle is more robust and longer than the flagellum, while in the female, the peduncular segments are more slender and the flagellum is longer than the peduncle. In both sexes, Gnathopod 1 is much smaller than Gnathopod 2. The dactyl (segment 7) of Gnathpod 1 barely overlaps the palm. The propodus (segment 6) is inflated, the palm is slightly concave, and the dactyl is sinuate (both have irregular curves). Pereiopods 3 and 4 are long and slender, with segments 5 about equal to segment 6. Perieopods 5-7 are progressively longer, and their coxal plates larger. The urosome segments are distinct. Uropods 1 and 2 are biramous, while Uropod 3 is uniramous, with the distal segment blunt and spine-like. The telson is spade-like, formed of two medially fused lobes with stout lateral and apical spines. Adult males range from 11 to 15 mm in size and females range from 9-11 mm. In a photograph, this amphipod was pinkish-brown dorsally, and pinkish-white ventrally (Ken-Ichi Ueda, http://www.inaturalist.org/guide_taxa/46735). Description based on: Bousfield and Carlton 1967; Bousfield 1982; Bousfield 2007.

Bousfield (1982) has placed T. enigmatica in the T. chiliensis group, including T. chiliensis (Chile), T. gracilis (Chile), and T. serratula (New Zealand) (Bousfield 1982). This amphipod is presumed to have originated from the Southern Hemisphere (Carton 1979; Bousfield 1982; Cohen and Carlton 1995).

---

Taxonomy

Ecology

General:

Transorchestia enigmatica is a semiterrestrial beach-dwelling amphipod (sand-hopper), living around and under debris on sandy beaches at or above the normal high-tide line, and cannot survive prolonged immersion. It is tolerant of rain and sharp changes in salinity (Bousfield and Carlton 1967; Carlton 1979; Cohen and Carlton 1995). Sexes are separate, the young are brooded, and development is direct (Bousfield 1973). Details of its life history have not been documented.

Food:

Seaweed, carrion, detritus

Trophic Status:

Omnivore

Omni

---

Habitats

General Habitat	Unstructured Bottom	None
General Habitat	Coarse Woody Debris	None
Salinity Range	Mesohaline	5-18 PSU
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	High Intertidal	None
Tidal Range	Supratidal	None
Vertical Habitat	Epibenthic	None

---

---

Tolerances and Life History Parameters

Minimum Length (mm)	9	Adult females range from 9 to 11 mm (Bousfield and Carton 1967; Bousfield 1982).
Maximum Length (mm)	15	Adult males range from 11 to 15 mm (Bousfield and Carlton 1967; Bousfield 1982)
Broad Temperature Range	None	Warm-temperate
Broad Salinity Range	None	Mesohaline-Euhaline

General Impacts

No impacts have been reported for Transorchestia enigmatica in Lake Merritt, California, its only known location.

---

References

Bousfield, E. L. (1982) The amphipod superfamily Talitoidea in the northeastern Pacific region. 1. Family Talitridae: Systemaitcs and distributional ecology, National Museum of Canada Publications in Biological Oceanography 11: 1-73

Bousfield, E. L.; Carlton, James (1967) New records of Talitridae (Crustacea: Amphipoda) from the central California coast, Bulletin of the Southern California Academy of Sciences 66(4): 277-284

Bousfield, Edward L. (2007) The Light and Smith Manual: Intertidal invertebrates from Central California to Oregon (4th edition), University of California Press, Berkeley CA. Pp. 611-12

Carlton, James T. (1979) History, biogeography, and ecology of the introduced marine and estuarine invertebrates of the Pacific Coast of North America., Ph.D. dissertation, University of California, Davis. Pp. 1-904

Carlton, James T. (1987) Patterns of transoceanic marine biological invasions in the Pacific Ocean, Bulletin of Marine Science 41(2): 452-465

Cohen, Andrew N.; Carlton, James T. (1995) Nonindigenous aquatic species in a United States estuary: a case study of the biological invasions of the San Francisco Bay and Delta, U.S. Fish and Wildlife Service and National Sea Grant College Program (Connecticut Sea Grant), Washington DC, Silver Spring MD.. Pp. <missing location>

U.S. National Museum of Natural History 2002-2021 Invertebrate Zoology Collections Database. http://collections.nmnh.si.edu/search/iz/

---