Species Description: Gobiosoma robustum is a small, unscaled goby that is somewhat variable in coloration. The body typically bears several irregular, interconnected dark bands with pale spots that give a chain-like appearance. A distinctive series of dark dots and dashes occur along the mid-side (Robbins et al. 1986). The resemblance of these markings to a visual representation of Morse code gives the animal its common name. The outer row of teeth is enlarged in the upper and lower jaws (GRI undated). The body depth is typically 16-23% of standard length (Hoese and Moore 1977).
Dawson (1966) notes the species typically possesses 9-11 anal rays, 11-13 second dorsal rays, and 15-17 pectoral rays. Robbins et al. (1986) cite the most common count as: 12 dorsal rays; 10 anal fin rays; 16-17 pectoral fin rays. The first dorsal typically has a spine count of VII and a pelvic spine and ray count of I, 5 (GRI undated).
Potentially Misidentified Species: Code gobies co-occur throughout their range with a very large number of other small, very similar gobiid fishes. Positive differentiation among these typically requires close examination and comparison of ray and scale counts and body part measurements by experienced biologists. Ray counts and size measurements overlap to a great degree with some co-occurring species such as Gobiosoma bosci, and microhabitat preferences of the various species may be helpful in making identifications (e.g., see Dawson 1966).
Regional Occurrence: Gobiosoma robustum is a subtropical western Atlantic species reported in Florida from Cape Canaveral to the Florida Keys, and throughout the Gulf of Mexico. Accounts from the Bahamas and Jamaica are likely erroneous (GRI undated).
IRL Distribution: The published northern distributional limit of this species is somewhat south of the northernmost limits of the Indian River Lagoon system, although it is common in the IRL from Cape Canaveral south.
Age, Size, Lifespan: Brown-Peterson et al. (1993) report a size range for Gobiosoma robustum of 11.3-45.2 mm SL, and a median size of 22.4 mm SL. Robbins et al. (1986) give a maximum total length of the species as 50 mm.
The maximum reported age for the species is one year (Froese and Pauly 2008).
Abundance: Tolan et al. (1997) list Gobiosoma robustum as among the top five most abundant fish in a seasonal seagrass study from Redfish Bay, TX. Llanso et al. (1998) report G. robustum as one of two benthic rank dominant fish from Double Branch Bay, Upper Tampa Bay, FL. Florida Bay trawl collections conducted in 1984-1985 reveal a density of 4.5 individuals/ha, and collections made a decade later yielded 7.5 individuals/ha (Thayer et al. 1999). Sampling within seagrass beds themselves yields a considerably higher mean density of 1-4 individuals per square meter (Matheson et al. 1999).
Reproduction: Reproduction in Gobiosoma robustum is sexual, and the sexes are separate. As with most gobies, G. robustum is a demersal spawning species in which breeding males and females both care for the eggs [from generalized family info on: http://reefkeeping.com/issues/2002-09/hcs3/index.php ] (Smith 1997).
Garcia et al. (1988) notes that spawning occurs throughout the year in a population from a lagoon in Campeche, Mexico, with maximal spawning occurring in the cold, dry season when salinity levels become elevated.
Embryology: Details regarding embryologic development are lacking. Eggs are elliptical, around 1.5 mm long and 0.5 mm wide (Coleman et al 1991).
Temperature: Code gobies are restricted in their distribution to the subtropics (Froese and Pauly 2008). Dawson (1966) discovered a pronounced seasonality in the presence of Gobiosoma robustum im Mississippi Sound, and noted individuals were scarce in mid-winter. Water temperatures during this author's study ranged from 13°C to nearly 35°C. Springer and Woodburn (1960) cite 10°C as the lower temperature limit for the species.
Salinity: Gobiosoma robustum is a eurythermal estuarine species. Dawson (1966) reports collecting individuals from environments of low salinity (6.2 ppt) in Mississippi Sound, although 83% of individuals were collected at salinities of 22.3-32.3 ppt. Kilby (1955) observed salinity extremes of 7 ppt and 37.6 ppt for the secies. Gunter (1956) included G. robustum in his revised list of euryhaline American fishes, in which he strictly defined euryhaline species as those that have been recorded from both fresh water and pure seawater by competent observers. Bailey et al. (1954), by contrast, indicate G. robustum is a facultative invader of low salinity waters but does not enter fresh water except as a temporary straggler or very young animal.
Trophic Mode: Gobiosoma robustum preys on several small invertebrate species, including shrimp, gammaridean amphipods, and caprellid amphipods (Caine 1983).
Competitors: Schofield (2003) experimentally demonstrated that G. robustum was able to competitively displace clown gobies (Microgobius gulosus), forcing them out of structured (artificial seagrass) habitat and into bare sand. The results of this study suggest that habitat selection of these two species is modified in areas where they co-occur.
Predators: Llanso et al. (1998) note that red drum (Scaenops ocellatus) often prey on Gobiosoma robustum, while McMichael and Peters (1989) report G. robustum is a component in the diet of spotted seatrout (Cynoscion nebulosus).
Laboratory experiments by Schofield (2005) reveal that G. robustum remained susceptible to predation by toadfish (Opsanus beta) regardless of the presence or absence of structurally complex seagrass in which to seek refuge.
Parasites: Hutton and Sogandares-Bernal (1960) list Diphterostomum americanum (Platyhelminthes: Digenea) as a known parasite of code gobies in Florida.
Habitats: Code gobies are cryptic benthic fishes commonly encountered within seagrass meadows and algal mats of shallow, protected waters (Robbins et al. 1986, Froese and Pauly 2008). The species is demersal but non-burrowing, as compared, for example, to the co-occurring burrowing goby Microgobius gulosus (Schofield 2005). Hoese and Moore (1977) indicate Thalassia testudinum as the preferred seagrass habitat. They appear to be less sensitive than canopy-dwelling species to declines in seagrass cover (Matheson et al. 1999, Fourqurean and Robblee 1999). Less commonly, code gobies can be found in mangrove habitats (Lorenz 1999).
Patrick and Palavage (1994) list G. robustum as a pollution-tolerant species.
Economic Importance: A number of commercially and recreationally important species depend on G. robustum as a food source.
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