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The ampithoid apphipod Cymadusa compta. Illustration modified from Bousfield 1973.

Species Name: Cymadusa compta SI Smith, 1873
Common Name: None
Synonymy: None

    Kingdom Phylum/Division Class: Order: Family: Genus:
    Animalia Arthropoda Malacostraca Amphipoda Ampithoidae Cymadusa

    Species Description

    Cymadusa compta is a small, tube-building gammaridean amphipod of family Ampithoidae. Its most distinguishing feature is its large, ovate, encapsulated and red-tinted eyes which occupy most of the head lobe. The coxal plates are deep and sparingly setose along their lower margins, with the fifth coxal plate being the deepest. There are two pairs of antennae and two pairs of moderately robust gnathopods. The appendages and antennae all bear setae (Bousfield 1973).

    The tubiculous structures C. compta builds and occupies have been described as web-like nests by Marsh (1973).

    Potentially Misidentified Species

    Identification of amphipods to the species level is generally beyond the abilities of amateur naturalists. The large eyes and phytal (plant-associated), tube-dwelling habits of this species are useful aids in identification.


    Regional Occurrence

    Cymadusa compta is widely distributed along the Atlantic and Gulf coasts of the United States, ranging from the Gulf of Maine and Cape Cod south to Florida and west along the Gulf of Mexico to Texas (Bousfield 1973, Morgan and Kitting 1984, Hauxwell et al. 1998).

    IRL Distribution

    Cymadusa compta is widespread throughout the seagrass habitats of the IRL system (Stoner 1983).


    Age, Size, Lifespan

    Females are typically 12-15 mm in length and males are somewhat smaller, 7-11 mm (Bousfield 1973), although animals up to 20 mm have been reported (Hauxwell et al. 1998). Cymadusa compta is an annual species.


    Marsh (1973) notes that Cymadusa compta ranked 9th in abundance of mcroinvrtebrates in a study he conducted in the York River Estuary, VA, and was one of only 6 species present in all 48 samples collected in that study. Fox and Bynum (1975) list C. compta as a common and widespread component of North Carolina estuarine systems. Stoner at al. (1983) report a density of around 200 individuals per square meter in Pensacola Bay grassbeds, while Sheridan and Livingston (1983) indicate a seasonal numerical dominance for the species in Apalachicola Bay occurring from October to February and reaching a peak abundance of more than 4,300 individuals per square meter.

    Nelson et al. (1982) report that C. compta was the dominant seagrass-associated amphipod in all four sampling sites examined by the author within the Indian River portion of the IRL complex. These authors note that C. compta is actually more abundant in the IRL than the ubiquitous seagrass amphipod Gammarus mucronatus, but is not as motile or as conspicuous.


    Cymadusa compta reproduces sexually and the sexes are separate. Bousfield (1973) indicates ovigerous females are present in New England waters from May-September, but the reproductive season is likely to be longer and possibly year-round in the southern portion of the species range.

    Females become ovigerous at approximately 2 weeks old. Clutch size varied from less than 5 eggs/individual to around 25 eggs/ individual and varied with diets of different nutritional value in laboratory experiments (Cruz-Rivera and Hay 2000).


    Limited information on embryology is available. The eggs are contained by the female within a thoracic brood pouch and young hatch out as fully developed juveniles with no free-living larval stage.



    The broad distribution of this amphipod from the Gulf of Maine and Cape Cod southward into Florida indicates the species is eurythermal in its temperature tolerance.


    Boesch and Diaz (1974) list Cymadusa compta as mesohaline to polyhaline in its salinity tolerance, and provides a range of 5-30 ppt corresponding with that designation. Examination of NOAA NBI collection records reveals the species has been collected collected at higher salinities of nearly 44 ppt.

    Feeley (1967) describes seasonal migrations of C. compta and also the amphipod Ampithoe longimana in response to salinity fluctuations in the Chesapeake estuary.


    Trophic Mode

    Cymadusa compta is primarily an epiphyte and macroalgal grazer and detritivore (Luczkovich et al. 2002). Grazing studies by Zimmerman et al. (1979) reveal that C. compta consumed macroepiphytic algae, drift algae, and seagrass detritus, and consumes macroalgae at a higher rate than epiphytes when both are abundant Although it readily shreds phytodetritus, C. compta appears to feed very little on live seagrass (Kelly et al 1990). However, gut content analysis has revealed some vascular plant material (Nelson 1979). Chemically defended seaweeds are actively avoided (Cruz-Rivera and Hay 2003).


    Significantly positive association of Cymadusa compta and Gammarus mucronatus in habitats they share is likely due to the very similar diets of these species (Zimmerman et al. 1979, Rey and Stoner 1984). Detrital material is typically abundant in these habitats, so competition based on limiting food resources might not be expected to occur. An earlier study by Cory (1967), however, makes a case for competition between C. compta and the amphipod Ampithoe longimana in the Patuxent River Estuary, MD. The author notes that where these species co-occur they settled on experimental plates such that all C. compta individuals were located on one side of the panel and all A. longimana confined themselves to the opposite side. Cory suggests this is cogent evidence of territorialism on a microscale.

    The ability of this species to construct tube homes on plant surfaces is likely to minimize space competition with both tube-building and non tube-building heterospecifics.


    Cymadusa compta and other seagrass-associate amphipods are important links in estuary food webs. In the IRL, they are of particular importance to young-of-the-year pinfish (Lagodon rhomboids) and other juvenile fish species (Stoner 1979, 1983 Nelson 1995). It is also a potential prey species for macroinvertebrates such as the nemertean worm Tetrastemma elegans (McDermott 1976).

    C. compta and other amphipods have been observed to preferentially occupy dense seagrass patches over sparse ones, presumably as a way to minimize predation risk (Stoner 1979, 1980).


    Cymadusa compta and other seagrass-associate amphipods are important links in estuary food webs. In the IRL, they are of particular importance to young-of-the-year pinfish (Lagodon rhomboids) and other juvenile fish species (Stoner 1979, 1983 Nelson 1995). It is also a potential prey species for macroinvertebrates such as the nemertean worm Tetrastemma elegans (McDermott 1976).

    C. compta and other amphipods have been observed to preferentially occupy dense seagrass patches over sparse ones, presumably as a way to minimize predation risk (Stoner 1979, 1980).


    Cymadusa compta is a sedentary tube/nest-dwelling species (Marsh 1973). It has been collected from a number of IRL habitat types, including seagrass beds, macroalgae, and sand and mud bottoms. Zimmerman et al. (1979) indicate a habitat preference for Halodule wrightii (=wrightii), while Stoner (1983) reports the highest densities in the Indian River Lagoon in, respectively, Thalassia, Syringodium, and Halodule. On a per biomass basis, experimental animals prefer Halodule over Thalassia and Syringodium, but when seagrass was offered at equivalent surface areas no preference is observed (Stoner 1980).

    Rey and Stoner (1984) also found C. compta on nearly 50% of the sea hare (Aplysia brasiliana) egg masses the examined, and noted that it was one of three species that together accounted for greater than 90% of the individuals collected from egg masses.

    Although primarily a benthic associate, Williams and Bynum (1972) report that C. compta was routinely collected as part of the meroplankton in estuarine surface plankton tows in North Carolina. Nelson and Demetriades (1992) note that C. compta is a very rare component of the peracarid community associated with Sabellariid (Phragmatopoma lapidosa) worm rock.

    Individuals build mucus tubes on the plants they inhabit which limits to a degree their foraging range and mobility (Cruz-Rivera and Hay 2000). Colinization studies using artificial seagrass plots reveal C. compta is a mobile species capable of colonizing available habitat even though it is a tube-dweller (Bartholomew 2002).

    Unlike some other gammaridean amphipods (e.g., Melita elongata), C. compta does not aggregate gregariously, and is more cryptic in appearance as well as behavior (Stoner 1980).

    Activity Time

    Williams and Bynum (1972) collected moderate numbers of water column Cymadusa compta in nighttime surface plankton tows and also collected more individuals during full moons compared to new moons, indicating a degree of nocturnal activity as well as lunar periocicity in terms of behavior.


    Economic Importance

    Fredette et al. (1990) estimate the contribution of Cymadusa compta to secondary production in a 140 ha Chesapeake Bay seagrass bed to be 1.7 x 103 kg/year dry weight, ranking it as the 6th largest macroinvertebrate contributor out of the species examined by these authors.

    In addition to their role as a trophic link between primary producers and secondary consimers (Zimmerman et al. 1979, Nelson 1981a, b), seagrass-associated amphipods have been shown to be important as potential removers of epiphytic algae from seagrass blades. Not all amphipods are equally efficient at reducing seagrass epiphyte loads (van Montfrans et al. 1984, Duffy et al. 2001), and Hootsmans et al. (1984) noted that C. compta exhibited intermediate ability to reduce fouling.


    Bartholomew A. 2002. Faunal colonization of artificial seagrass plots: The importance of surface area versus space size relative to body size. Estuaries 25:1045-1052.

    Boesch DF and RJ Diaz. 1974. New records of peracarid crustaceans from oligohaline waters of the Chesapeake Bay. Chesapeake Science 15:56-59.

    Bousfield EL. 1973. Shallow-water gammaridean Amphipoda of New England. Corell University Press, Ithaca, New York. 312p.

    Cory RL. 1967. Epifauna of the Patuxent River Estuary, Maryland, for 1963 and 1964. Chesapeake Science 8:71-89.

    Cruz-Rivera E and ME Hay. 2000. The effects of diet mixing on consumer fitness: Macroalgae, epiphytes, and animal matter as food for marine amphipods. Oecologia 123:252-264.

    Cruz-Rivera E and ME Hay. 2003. Prey nutritional quality interacts with chemical defenses to affect consumer feeding and fitness. Ecological Monographs 73:483-506.

    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.

    Feeley JB. 1967. The distribution and ecology of the Gammaridea (Crustacea: Amphipoda) of the lower Chesapeake estuaries. Unpublished M.S. Thesis, College of William and Mary. 75 p.

    Fox RS and KH Bynum. 1875. The amphipod crustaceans of North Carolina estuarine waters. Chesapeake Science 16:223-237.

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

    Hauxwell J, McClelland J, Behr PJ, and I Valiela. 1998. Relative importance of grazing and nutrient controls of macroalgal biomass in three temperate shallow estuaries. Estuaries 21:347-360.

    Hootsman MJM, Graveland J., van Montfrass J, and RJ Orth. 1984. Laboratory studies of four peracarid crustacean species grazing on Zostera marina periphyton in the Chesapeake Bay, USA. Botanica Marina.

    Kelly JR, Levine SN, Buttel LA, Carr KA, Rudnick DT, and RD Morton. 1990. The effects of tributyltin within a Thalassia seagrass ecosystem. Estuaries 13:301-310.

    Luczkovich JJ, Ward GP, Johnson JC, Christian RR, Baird D, Neckles H, and WM Rizzo. 2002. Determining the trophic guilds of fishes and macroinvertebrates in a seagrass food web. Estuaries 25:1143-1163.

    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.

    Morgan MD and CL Kitting. 1984. Productivity and utilization of the seagrass Halodule wrightii and its attached epiphytes. Limnology 29:1066-1076.

    Nelson WG. 1995. Amphipod crustaceans of the Indian River Lagoon: current status and threats to biodiversity. Bulletin of Marine Science 57:143-152.

    Nelson WG. 1979. An analysis of structural pattern in an eelgrass (Zostera marina L.) amphipod community. Journal of Experimental marine Biology and Ecology 39:231-264.

    Nelson WG, Cairns KD, and RW Virnstein. 1982. Seasonality and spatial patterns of seagrass-associated amphipods of the Indian River Lagoon, Florida. Bulletin of Marine Science 32:121-9.

    Nelson WG and L Demetriades. 1992. Peracarids associated with sabellariid worm rock (Phragmatopoma lapidosa Kinberg) at Sebastian Inlet, Florida, USA. Journal of Crustacean Biology 12:647-654.

    Rey JR and AW Stoner. 1984. Macroinvertebrate associations on the egg masses of the sea hare, Aplysia brasiliana Rang (Gastropoda: Opisthobranchia). Estuaries 7:158-164.

    Sheridan PF and RJ Livingston. 1983. Abundance and seasonality of infauna and epifauna inhabiting a Halodule wrightii meadow in Apalachicola Bay, Florida. Estuaries 6:407-419.

    Stoner AW. 1979. Species-specific predation on amphipod Crustacea by the pinfish Lagodon rhomboides: Mediation by macrophyte standing crop. Marine Biology 55:201-207.

    Stoner AE. 1980. Perception and choice of substratum by epifaunal amphipods associated with seagrasses. Marine Ecology Progress Series 3:105-111.

    Stoner AW. 1983. Distributional ecology of amphipods and tanaidaceans associated with three sea grass species. Journal of Crustacean Biology 3:505-518.

    Stoner AW, Greening HS, Ryan JD, and RJ Livingston. 1983. Comparison of macrobenthos collected with cores and suction sampler in vegetated and unvegetated marine habitats. Estuaries 6:76-82.

    van Montfrans J, Wetzel RL, and RJ Orth. 1984. Epiphyte-grazer relationships in seagrass meadows: Consequences for seagrass growth and production. Estuaries 7:289-309.

    Williams AB and KH Bynum. 1972. A ten-year study of meroplankton in North Carolina estuaries: Amphipods. Chesapeake Science 13:175-192.

    Zimmerman R, Gibson R, and J Harrington. 1979. Herbivory among gammaridean amphipods from a Florida seagrass community. Marine Biology 54:41-47.

Report by: J. Masterson, Smithsonian Marine Station
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Page last updated: October 1, 2008

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