Erichsonella attenuata (Harger, 1873)
Family: Idoteidae
Common names: Eelgrass Isopod
Erichsonella attenuata image
Erichsonella attenuata  

Species Description: Erichsonella attenuata is a small, slender, elongate idoteid isopod. Like other isopods, E. attenuata has seven pairs of legs. Two pairs of antennae are present, and one of these is notably elongated (around half the body length). It is a member of the suborder Valvifera, whose members posess two door-like structures below the abdomen that serve to protect the delicate gill structures (Rupert and Fox 1988).

Potentially Misidentified Species: The slender, elongate body and small body size aid in distinguishing Erichsonella attenuata from other Florida marine isopods.

Regional Occurrence: Bostršm and Mattila (1999) report the US distribution of E. attenuata extending from New Jersey to Florida (possibly discontinuously) and the Gulf of Mexico. The GBIF database [] indicates a somewhat broader western Atlantic distribution, from Maine south along both coasts of Florida and west along the Gulf of Mexico to south Texas.

IRL Distribution: Erichsonella attenuata may be found in seagrass habitats throughout the IRL system (Kensley et al. 1995, Bostrom and Mattila 1999).

Age, Size, Lifespan: Lipson and Lipson (2006) indicate Erichsonella attenuata is a small isopod, attaining a length of approximately 13 mm.

Abundance: Kensley et al. (1995) indicate Erichsonella attenuata is one of the three most common invertebrate species in Indian River Lagoon Halodule beaudettei seagrass beds. It is also a numerical dominant in Zostera marina and Ruppia maritima beds of lower Chesapeake Bay, representing more than 40% of total macroinvertebrate secondary production (Fredette et al. 1990). Marsh (1973) includes E. attenuata as one of the 5 most abundant non-colonial epifaunal inhabitants of the York River, VA, Zostera community he studied.

Reproduction: Details on the reproductive ecology of Erichsonella attenuata from the literature are lacking. General information on reproduction in marine isopods is provided by Barnes (1987). Sexes are separate, and fertilization is internal. Males use modified copulatory pleopods to inject sperm into each of the female's two sternal gnopores. Eggs are fertilized in the oviduct and brooded in a marsupium. In many species, copulation occurs during or following a female molt.

Embryology: Eggs and embryos are brooded in a marsupium and there is no free-living larval stage. Rather, young emerge as a postlarval stage called the manca stage whose last pair of legs is incompletely developed (Barnes 1987, SERTC undated).

Temperature: Marsh (1973) notes that a number of epifaunal species, including Erichsonella attenuata, appear to migrate into bottom sediments during the winter months in the York River, VA, but does not indicate whether this is a response to low temperature, dieback of above-ground seagrass biomass, or both.

Salinity: Erichsonella attenuata is a euryhaline estuarine species. Its presence within the gut contents of young-of-the-year yellow perch (Perca flavescens) captured from the Severn River, a low salinity Chesapeake Bay tributary, suggests E. attenuata can persist at salinities of 7 ppt, and possibly as low as 2 ppt (Muncy 1962). Similarly, Hoese (1960) reports the presence of E. attenuata at salinities ranging from 13.4 ppt down to as low as 2.4 ppt in Mesquite Bay, TX.

Trophic Mode: Erichsonella attenuata is an epiphyte-grazing organism and is an important link in seagrass food webs due to its abundance. Although it appears to feed primarily on epiphytic microalgae, E. attenuata may also be capable of directly utilizing seagrass as a food resource in the absence of alternatives (Howard and Short 1986, Bostršm and Mattila 1999). Duffy et al. (2001) experimentally demonstrated that E. attenuata was quite capable of reducing the epiphyte load on seagrass by grazing.

Surface scrapings of Zostera marina by Marsh (1973) revealed epiphytic material consisted of nematodes, rotifers, diatoms and other microorganisms, sediment and detritus. The author noted E. attenuata as among the grazers utilizing this heterogeneous resource.

Predators: Erichsonella attenuata is an important food resource for predatory seagrass community members. At times, they are consumed in large numbers by seagrass-associated fish predators. A study by Ryer and Orth (1987) in lower Chesapeake Bay, for example, reveals E. attenuata to be the fall seasonal dominant prey item for seagrass-associated northern pipefish (Syngnathus fuscus). In another lower Chesapeake Bay study, Orth and Heck (1980) determined E. attenuata was also a component in the diets of juvenile black sea bass (Centropristis striata).

In the presence of a predatory fish, E. attenuata has been observed under experimental conditions to occupy habitat based on refuge value over food value. In the absence of immediate predation threat, food value was the primary determinant of habitat preference (Bostršm and Mattila 1999).

E. attenuata is also preyed upon by other macroinvertebrates. McDermott (1976) reported predation on E. attenuata by the nemertean worm Zygonemertes virescens under laboratory conditions.

Habitats: Erichsonella is a tropical to warm-temperate genus occupying vegetated marine habitats from the intertidal to 20 m (Pires 1984, Ruppert and Fox 1988). E. attenuata preferentially selects habitats based largely on food value (Bostršm and Mattila 1999). Field manipulations conducted in Waquoit Bay, MA, Zostera beds revealed an increase in macroalgal density appeared to increase the abundance of E. attenuata and other free-swimming macroinvertebrates (O'Brien et al. 1990).

Barnes. 1987. Invertebrate Zoology. 5th edition. CBS College Publishing, NY. 893 p.

Bostrom C and J Mattila. 1999. The relative importance of food and shelter for seagrass-associated invertebrates: A latitudinal comparison of habitat choice by isopod grazers. Oecologia 120:162-170.

Duffy JE, MacDonald KS, Rhode JM, and JD Parker. 2001. Grazer diversity, functional redundancy, and productivity in seagrass beds: An experimental test. Ecology 82:2417-2434.

Fredette TJ, Diaz RJ, Van Montfrans J, and RJ Orth. 1990. Secondary production within a seagrass bed (Zostera marina and Ruppia maritima) in lower Chesapeake Bay. Estuaries 13:431-440.

Hoese HD. 1960. Biotic changes in a bay associated with the end of a drought. Limnology and Oceanography 5:326-336.

Howard RK and FT Short. 1986. Seagrass growth and survivorship under the influence of epiphyte grazers. Aquatic Botany 24:287-302.

Lippson AJ and RL Lippson. 2006. Life in the Chesapeake Bay. Johns Hopkins University Press, MD. 324 p.

Kensley B, Nelson WG, and M Schotte. 1995. Marine isopod biodiversity of the Indian River lagoon, Florida. Bulletin of Marine Science 57:136-142.

Marsh AG. 1973. The Zostera Epifaunal Community in the York River, Virginia Chesapeake Science 14:87-97.

McDermott JJ. 1976. Observations on the food and feeding behavior of estuarine nemertean worms belonging to the Order Hoplonemertea. Biological Bulletin 150:57-68.

Muncy RJ. 1962. Life history of the yellow perch, Perca flavescens, in estuarine waters of Severn River, a tributary of Chesapeake Bay, Maryland. Chesapeake Science 3:143-159.

Kristin MA, O'Brien M, Deegan LA, Finn JT, and SG Ayvazian. 1990. The effects of macroalgae on the abundance and diversity of free-swimming invertebrates in eelgrass beds of Waquoit Bay. Biological Bulletin 179:219-235.

Orth RJ and KL Heck. 1980. Structural components of eelgrass (Zostera marina) meadows in the lower Chesapeake Bay: Fishes. Estuaries 3:278-288.

Pires AM. 1984. Taxonomic revision and phylogeny of the genus Erichsonella with a discussion on Ronalea (Isopod, valvifera). Journal of Natural History 18:665-683.

Rupert EE and RS Fox. 1988. Seashore Animals of the Southeast. A Guide to Common Shallow-Water Invertebrates of the Southeastern Atlantic Coast. University of South Carolina Press. 429 p.

Ryer CH and RJ Orth. 1987. Feeding ecology of the northern pipefish, Syngnathus fuscus, in a seagrass community in the lower Chesapeake Bay. Estuaries 10:330-336.

Southeastern Regional Taxonomic Center (SERTC). Undated. Isopod Crustaceans. 5 p.

Swartz RC. 1972. Biological criteria of environmental change in the Chesapeake Bay. Chesapeake Science 13:517-541.

Erichsonella attenuata image
Erichsonella attenuata  
Erichsonella attenuata image
Erichsonella attenuata  
Erichsonella attenuata image
Erichsonella attenuata  
Erichsonella attenuata image
Erichsonella attenuata  
Erichsonella attenuata image
Erichsonella attenuata  
Erichsonella attenuata image
Erichsonella attenuata