|
II. HABITAT AND
DISTRIBUTION
Regional Occurrence:
Cerithidea scalariformis occurs in Georgia, both coasts of Florida,
and Cuba. Its limited distribution is probably due to lack of a planktonic larval stage (Houbrick 1984).
IRL Distribution:
Although probably occurring lagoon wide, a population of Cerithidea
scalariformis was studied at Big Starvation Cove, across the Indian River
from Link Port (Houbrick 1984).
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Several (4 - 5) weeks after hatching, thousands of juvenile snails 1.1 -
13.0 mm in length were observed in the field, and were most numerous in October
and November. By late January, juvenile snails had attained lengths ranging from
2.0 - 8.0 mm and were found in tidal creeks. At this time, adult Cerithidea,
with eroded shells and heavily parasitized with trematodes, were beginning to
die off. Juvenile snails tend to remain submerged while adults tended to stay
above the high water mark occurring along creek banks and can be found a meter
above the high water mark on vegetation (Salicornia and mangroves). By early
spring, immature snails were half adult size while most adults from the previous
generation were gone. By early summer young snails reach adulthood and attain
sexual maturity by August - September (Houbrick 1984).
Probable lifespan of Cerithidea
scalariformis is 1 to 2 (possibly 3) years. Highest growth rates occur in
immature snails (<10.0 mm). The adult snail shows no growth in shell length (Houbrick 1984).
Abundance:
Highest abundance observed for Cerithidea scalariformis at Big
Starvation Cove (Indian River Lagoon) was 1,100 individuals per square meter.
Highest densities are found in the Salicornia zones (Harlos 1976;
Houbrick 1984).
Locomotion:
Crawls. Hatchlings do not display planktonic
stage or swimming
behavior.
Reproduction:
Cerithidea scalariformis, like all
Potamididae, is aphallate and it
is thought that spermatophore transfer occurs via the siphons. Spermatophores
are held in the spermatophore bursa where they eventually disintegrate releasing
sperm. Sperm migrate to the seminal receptacle where egg fertilization takes
place. Eggs are arranged in a loose spiral and encased in long jelly strings, ~
51.0 mm long by 1.13 mm in diameter. This "spawn" is deposited in the
field (on bark, decaying wood and leaves) from late September through November
when hatchlings were also found. A spawn mass can contain up to 350 eggs.
Embryology:
Cerithidea scalariformis, is a direct developer with no planktonic
larval stage (Houbrick 1984). Transparent egg capsules are ~ 0.37 mm in
diameter and the single bright green egg within the capsule is ~ 0.28mm in
diameter. After deposition, cleavage ensues and early embryonic stages appear
green. The veliger stage embryo is reached about 5 days after deposition and
morphologically is typical of direct developers having eyespots, small velar
lobes and a large larval shell. Hatchlings emerge 18 - 22 days after deposition,
crawl on the substratum and metamorphose into tiny snails within one to two
days.
IV. PHYSICAL TOLERANCES
Temperature:
C. scalariformis is highly eurythermal, and
also is able to tolerate periods of desiccation (Houbrick 1984). Temperatures at Big
Starvation Cove (Indian River Lagoon) can vary greatly with sun exposure, and
often reach as high as 50.0 °C in the summer (N. Smith, pers. obs.).
Salinity:
Cerithidea scalariformis is euryhaline,
preferring a salinity of 28.0 ppt. However, at Big Starvation Cove (Indian River Lagoon) normal salinity is 33.0
ppt, and varies substantially depending on season. Substrata
salinities moreso than predation probably determine vertical distribution of
these snails (Harlos 1976 as cited in Houbrick 1984).
Other Physical Tolerances:
Few empty shells of C.
scalariformis were found at Big Starvation Cove (Indian River Lagoon),
possibly due to their dissolution in the ambient, low pH environment (Houbrick
1984), which living C. scalariformis tolerates well.
V. COMMUNITY ECOLOGY
Trophic Mode:
Juvenile and adults both feed on detritus and
microalgae (N. Smith -
pers.
comm.).
Habitat:
Cerithidea scalariformis leads an amphibious existence in muddy
estuarine habitats in tropical and subtropical areas. C. scalariformis
occurs in large numbers along tidal creeks in mangrove and salt marsh habitats.
Associated Species:
Predator avoidance behavior, i.e., climbing vegetation, is less obvious in Cerithidea
scalariformis than in other congeners. At Big Starvation Cove (in the Indian
River Lagoon) young snails had nipped tentacles, suggesting killifish predation,
as was observed by Harlos (1976). Mud crab predation was also observed,
and clapper rails were suspect predators at this later site (Harlos 1976 as
cited in Houbrick 1984) Although other potential predators were observed at this
site, e.g., wading birds, raccoons opossums and fiddler crabs, Houbrick (1984)
observed no visible indications of predation such as drilled or cracked shells.
However, Smith (pers. obs.) believes that blue crabs are the main predators of C.
scalariformis in the Indian River Lagoon.
VI. SPECIAL STATUS
Special Status:
None
Economic Importance:
None
Report by: N. Smith, UCSB
Submit additional information, photos or comments to:
irl_webmaster@si.edu
Page last updated: July 25, 2001
|
