Invasion History

First Non-native North American Tidal Record: 1993
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 1993

General Invasion History:

The isopod Iais floridana lives commensally in the burrows of Sphaeroma terebrans, an isopod which burrows into mangrove roots and salt marshes (Rehm and Humm 197; Estevez 1995). Sphaeroma terebrans is probably native to the Indo-Pacific, but is now widespread in the tropical and subtropical Atlantic (Carlton and Ruckelshaus 1997). Iais floridana was first collected in Estero Bay, Lee County, on the Gulf Coast, near the tip of Florida, but most collections were made in the Indian River Lagoon (Kensley and Schotte 1999). It has not yet been reported outside of Florida. We suspect that this isopod occurs through much of the range of S. terebrans, and has been overlooked. Iais floridana, like its host, is most likely of Indo-Pacific origin.

At least three species of Iais occur commensally with isopods of the genus Sphaeroma, one example being I. californica, an associate of the New Zealand species S. quoianum. Iais californica was described from S. quoianum introduced to California (Carlton 1979). Iais floridana is closest morphologically to I. singaporensis (Kensley and Schotte 1999).

North American Invasion History:

Invasion History on the East Coast:

Iais floridana was first collected in 1995 on the East Coast in Port St. Lucie, Florida, on the St. Lucie River, a tributary of the Indian River Lagoon. In 1995-1996, many specimens were collected from rotten wood in the St. Lucie River, Taylor Creek, and the St. Sebastian River – tributaries of the Indian River Lagoon. The isopods were collected at 0-15 PSU (Kensley and Schotte 1999).

Invasion History on the Gulf Coast:

One specimen of Iais floridana was first collected in Hendry Creek off of Estero Bay, Lee County, Florida, on the Gulf of Mexico, in 1993. In 1996, 14 more specimens were collected at the mouth of the Estero River. All were found on Sphaeoma terebrans (Kensley and Schotte 1999).


Iais floridana has an elongated elliptical body, which is broadest in pereaonal segment 4 and tapered towards the head. Coxal plates are visible in dorsal view. The head is twice as wide as long, with the anterior-lateral corners rounded. The eyes are medium-sized and consist of two ommatidia. The pleotelson is nearly circular, with long biramous uropods protruding beyond it. Antenna 1 is ~1/8 of the body length and composed of 6 segments, while Antenna 2 is ~1/4 of the body length, with a flagellum of 13 segments. In males, Pleopods 1 and 2 are modified for copulation. Pleopods 1 are fused to form a narrow appendage (the sympod), not widening near the tip and ending in a pair of rounded processes, each bearing 9 setae. Pleopods 2 are not fused, but the inner ramus is modified into a needle-like stylus. The female's brood pouch contains up to eight eggs and is covered by an oval operculum. Males averaged 1.34 mm in length, while the average length for ovigerous females was 1.76 mm (Kensley and Schotte 1999).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Malacostraca
Subclass:   Eumalacostraca
Superorder:   Peracarida
Order:   Isopoda
Suborder:   Asellota
Family:   Janiridae
Genus:   Iais
Species:   floridana


Potentially Misidentified Species

Iais californica
Native to New Zealand, introduced to California

Iais singaporensis
Similar in body shape to I. singaporensis (Bruce and Wong 2015)



Iais floridana is a commensal isopod living on the pleopods of the introduced isopod Sphaeroma terebrans (Kensley and Schotte 1999). It has separate sexes and direct development (Schultz 1969). In this species, as in some other Iais spp., the male practices mate-guarding, when a male clasps a late-juvenile (manca) female and holds her until copulation is possible (Kensley and Schotte 1999). Iais floridana presumably feeds on the detritus and phytoplankton gathered by Sphaeroma terebrans’s suspension feeding, as is suspected for I. californica and I. floridana (Rotramel 1975). Iais floridana is known only from Florida, so its temperature tolerance range is unknown. It has been found over a salinity range of 0 to 15 PSU (Kensley and Schotte 1999).


detritus and phytoplankton


Commensal with Sphaeroma terebrans

Trophic Status:




General HabitatCoarse Woody DebrisNone
General HabitatMangrovesNone
General HabitatMarinas & DocksNone
Salinity RangeLimnetic0-0.5 PSU
Salinity RangeOligohaline0.5-5 PSU
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Minimum Salinity (‰)0Field (Kensley and Schotte 1999)
Maximum Salinity (‰)15Field, highest salinity of collection (Kensley and Schotte 1999). However, this isopod may have a wider salinity range, since its host, (Sphaeroma terebrans, tolerates fresh to full marine waters (Becker 1971).
Maximum Length (mm)1.8None
Broad Temperature RangeNoneSubtropical
Broad Salinity RangeNoneTidal Limnetic-Mesohaline

General Impacts

No impacts have been reported for Iais floridana, although its host organism, Sphaeroma terbrans, is regarded as an important ecosystem engineer in mangroves and is an important wood-borer of human structures (Becker 1971; Rehm and Humm 1973; Davidson et al. 2014). In another closely related isopod pair, Iais californica had poor survival (15-22%) in containers without S. quoianum, but I. californica had little or no effect on the survival of S. quoianum (Rotramel 1975).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 1993 Def Estab
S190 Indian River 1995 Def Estab
G030 North Ten Thousand Islands 1993 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


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Bruce, Niel L.; Wong, Helen P.-S. (2015) An overview of the marine Isopoda (Crustacea) of Singapore, Raffles Bulletin of Zoology Supplement No. 31:: 152-168

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.; Ruckelshaus, Mary H. (1997) Nonindigenous marine invertebrates and algae of Florida, In: Simberloff, Daniel, Schmitz, Don C., Brown, Tom C.(Eds.) Strangers in Paradise: Impact and Management of Nonindigenous Species in Florida. , Washington, D.C.. Pp. 187-201

Davidson, Timothy M.; Rumrill, Steven S.; Shanks, Alan L. S (2008) Colonization and substratum preference of an introduced burrowing crustacean in a temperate estuary., Journal of Experimental Marine Biology and Ecology 354: 144-149

Estevez, Ernest D. (1994) Inhabitation of tidal salt marshes by the estuarine wood-boring isopod Sphaeroma terebrans in Florida., In: Thompson, M.-F. and Nagabhushanam, R.(Eds.) Recent developments in biofouling control. , New Delhi. Pp. 97-105

Kensley, Brian; Schotte, Marilyn (1999) New records of isopods from the Indian River Lagoon, Florida (Crustacea: Peracarida)., Proceedings of the Biological Society of Washington 112(4): 695-713

Rehm, Andrew; Humm, Harold J. (1973) Sphaeroma terebrans: a threat to the mangroves of southwestern Florida., Science 182: 173-174

Rotramel, George L. (1975) Observations on the commensal relations of Iais californica (Richardson, 1904) and Sphaeroma quoyanum H. Milne Edwards, 1840 (Isopoda), Crustaceana 28(3): 247-256