Species Description: The grass cerith, Bittiolum varium, is a small cerithiid gastropod with an elongate, turreted shell consisting of around 10 whorls. The aperture is notably rounded, with a smooth lip and a short, distinct siphonal canal. The intersections of the spiral lines and axial ribs form raised nodules. Color is highly variable, ranging from light to dark brown to gray-white to bluish black to reddish, sometimes with darker flecks or mottling. The soft tissues of the animal itself are often colored similarly to the shell and the sole of the foot is white with opaque spots. The operculum is light brown and translucent (Qurban 2000, STRI undated, BMSM undated).
Potentially Misidentified Species: A number of cerithid gastropods co-occur with Bittiolum varium. The descriptive information provided above should be sufficient to allow amateur naturalists to identify specimens with a reasonable degree of certainty.
Regional Occurrence: Bittiolum varium occurs along the east coast of the Americas from Maryland to Brazil, along the Gulf coast to Texas, and throughout much of the Caribbean (Houbrick 1993, Rosenberg 2005).
IRL Distribution: The species occurs throughout the lagoon.
Age, Size, Lifespan: The maximum confirmed reported size for this species is 6.5 mm, although unconfirmed reports of 10 mm specimens exist (Rosenberg 2005).
Marsh (1976) reports the life span of Bittiolum varium is around 1.5 years, although typically many individual do not survive to this age.
Abundance: Bittiolum varium has been reported to be often abundant (1.7 individuals per square cm) in the summer, and considerably more rare during the winter (Qurban 2000). Mikkelsen at al. (1995) report that Bittiolum varium was the most frequently collected and numerically abundant mollusc of the Indian River Lagoon, based on collection and literature resources dating primarily from 1974 to 1982.
Brewster-Wingard et al. (2001) report that Bittiolum varium is one of the two most numerically abundant molluscs in vegetated habitats of Florida Bay. It and the bivalve mussel Brachidontes exustus together accounted for 95% of live molluscs sampled during this study. Core studies indicate Bittiolum varium has been a dominant component of molluscan assemblages in Florida Bay for the last 200 years (Trappe and Brewster-Wingard 2001).
Reproduction: Bittiolum varium is a dioecius (separate sexes) and fertilization is internal, although males lack a functional penis. Sperm from males may instead be taken into females via inhalent water currents (Webber 1977).
The species is oviparous, with females depositing egg masses onto a variety of suitable substrata, including seagrass blades, drift algae, and rock surfaces. In the IRL, eggs are deposited from spring through early fall (Qurban 2000).
Embryology: Marcus and Marcus (1963) and Thiriot-Quievreux (1979) describe Bittiolum varium larvae as planktotrophic, with a small, transparent shell and a pale, colorless velum.
Planktonic larval Bittiolum varium persist within the water column for more than three weeks before metamorphosis and settlement to the benthos. B. varium water column larvae in the IRL were most abundant in the spring through early fall, becoming increasingly rare in late fall and winter (Qurban 2000).
Pronounced annual abundance peaks are reflective of seasonal high rates of recruitment. Size-frequency analysis of IRL B. variolum by Qurban (2000) revealed the presence of distinct cohorts that could be tracked as they entered into and matriculated through the population.
Temperature: The warm-temperate to subtropical/tropical range of this species may be temperature-driven. Marsh (1973, 1976) noted the presence of large numbers of individuals within bottom sediments during winter months, possibly as an avoidance response to cold temperature.
Salinity: Miller et al. (2007) report a low salinity limit of 10 ppt for Bittiolum varium.
Trophic Mode: Cote et al. (2001) identify Bittiolum varium as a micrograzer. Van Montfrans et al. (1982) report the species is seasonal grazer on diatoms, coralline algae, and other epiphytes of seagrass blades in Chesapeake Bay.
Competitors: During periods of peak abundance, competition for spatial and dietary resources may conceivably occur.
Predators: Juvenile blue crabs (Calinectes sapidus) inhabiting seagrass nursery habitats consume large numbers of Bittiolum varium and other micrograzing snails, and may influence the population dynamics of prey species (Wright, R. A., Crowder 1996, Cote et al. 2001). Field and laboratory studies indicated that blue crabs preferentially consumed B. varium over the gastropod Astyris lunata (Cote et al. 2001).
In addition to blue crabs, Martin et al. (1989) considered spot (Leiostoma xanthurus) to be a major predator of B. varium.
Habitats: Bittiolum varium is a widespread epifaunal inhabitant of marine and estuarine seagrass beds and is a dominant faunal component of Indian River Lagoon seagrass and drift algal communities (Houbrick 1993, Qurban 2000). Ferguson (2005) notes that Florida Bay B. varium shows increased abundance in Halodule wrightii (= wrightii) beds compared to Thalassia testudinum beds.
Wells (1961) and Rothchild (2004) report the species as an oyster associate, and it has also been observed on hydroid-covered algae in shallows near shore (STRI undated).
In at least some portions of the IRL, juveniles and adults appear to overwinter in greater numbers within unattached benthic drift macroalgae than among seagrass blades, and few adults overwinter within the sediment (Qurban 2000).
Special Status: None.
Economic/Ecological Importance: Due to their seasonal high abundance, B. varium is an important grazing faunal community component. When abundant, the species is also important as a dietary resource for benthic predators.
Bailey-Matthews Shell Museum. Undated. Bittiolum varium species profile. Available online.
Brewster-Wingard GL, Stone JR, and CW Holmes. 2001. Molluscan faunal distribution in Florida Bay, past and present: An integration of down-core and modern data. Bulletins of American Paleontology, special volume361:199-231.
Cote J, Rakocinski CF, and TA Randall. 2001. Feeding efficiency by juvenile blue crabs on two common species of micrograzer snails. Journal of Experimental Marine Biology and Ecology 264:189-208.
Ferguson CA. 2005. The appearance of change: Searching for an environmental transition in an accumulating subfossil assemblage. Abstract presented at the 2005 Geological Society of America annual meeting, Salt lake City, UT.
Houbrick R. 1993. Phylogenetic relationships and generic review of the Bittiinae (Prosobranchia: Cerithioidea). Mlacologia 35:261-313.
Marcus E and E Marcus. 1963. Mesogastropoden von der kusts von Sao Paulo. Abhandl. Math. Nnaturwissensch. Klasse akad. Wiss. and Lit. Mainz. 1:1-105.
Marsh G. 1973. Zostera epifaunal community in the York River Virginia. Chesapeake Science 14:87-97.
Marsh G. 1976. Ecology of the gastropod fauna of eelgrass in a Virginia estuary. Chesapeake Science 17:182-187.
Martin TH, Wright RA, and LB Crowder. 1989. Non-additive impacts of blue crabs and spot on their prey assemblages. Ecology 70:1935-1942.
Mikkelsen P, Mikkelsen PS, and DJ Karlen. 1995. Molluscan biodiversity in the Indian River Lagoon, Florida. Bulletin of Marine Science 57:94-127.
Miller AW, Ruiz GM, Minton MS, and RF Ambrose. 2007. Differentiating successful and failed molluscan invaders in estuarine ecosystems. Marine Ecology Progress Series 332:41-51.
Rosenberg G. 2005. Malacolog 4.1.0: A Database of Western Atlantic Marine Mollusca. Available online.
Rothschild SB. 2004. Beachcomber's Guide to Gulf Coast Marine Life: Texas, Louisiana, Mississippi, Alabama, and Florida. Taylor Trade Publications, MD. 200 p.
Smithsonian Tropical Research Institute (STRI). Undated. Bittiolum varium species profile. Bocas del Toro Species Database. Available online.
Thiriot-Quievreux C. Identification of some planktonic prosobranch larvae present off Beaufort, North Carolina. Veliger 23:1-9.
Trappe CA and GL Brewster-Wingard. 2001. Molluscan fauna from core 25B, Whipray Basin, central Florida Bay, Everglades National Park. Open-File Report 01-143. U.S. Geological Survey OFR-01-143. U.S. Geological Survey, Reston VA.
Van Montfrans J, Orth RJ, and SA Vay. 1982. Preliminary studies of grazing by Bittium varium on eelgrass periphyton. Aquatic Botany 14:75-89.