Littoraria feeding preference:
Littoraria were collected from marshes on
Galveston Island and three snails each were placed in 20 specimen
cups with 10 mL of 20 ppt salinity water. Live
Spartina leaves, standing dead
Spartina stems, and live and dead
Avicennia leaves were collected at the same
time as the snails. Plants were rinsed with distilled water, then
one leaf of each type (Spartina leaves were cut
to 4 cm long sections) was photographed and placed in each specimen
cup. Snails were allowed to feed freely for two weeks with a water
change halfway through. Leaves were photographed again at the end of
two weeks, and area loss from feeding was calculated as the change
in area between the before and after photos, as measured in ImageJ.
Littoraria food quality:
Littoraria were collected from marshes on
Galveston Island and placed in one of six tanks (20-30 snails per
tank). Three tanks were assigned to an
Avicennia diet and the other three were
assigned to a Spartina diet. Each diet
consisted of both live and dead leaves from the source plant.
Littoraria were kept on their assigned diet for
60 days with weekly water changes. At the end of 60 days,
Littoraria were frozen in the lab. Each
individual’s shell length across the longest point was measured,
then body tissue was dissected out of shells, rinsed with distilled
water, blotted dry, and weighed to obtain the wet weight. Body
tissue was then dried in a 60°C oven for 48 hours and re-weighed to
obtain the dry weight. Dry-weight density was calculated as the
ratio of the dry to wet weight for each snail.
Field collected consumers: Littoraria and
Uca were collected from experimentally
manipulated plots in Port Aransas, Texas with varying levels of
mangrove cover (Guo et al., 2017, Coastal regime shifts: Rapid
responses of coastal wetlands to changes in mangrove cover,
Ecology). Ten Littoraria and five
Uca were collected from three low mangrove
cover (0%, 11%, 22%) and three high mangrove cover (77%, 88%, 100%)
plots. Additional Littoraria were collected
from two nearby unmanipulated survey sites, one with mangroves
present and one with mangroves absent. All consumers were frozen
until return to the lab. Littoraria were
processed in the same way as those from the food quality experiment
to determine the shell length and dry weight density.
Uca were weighed, then dissected to obtain the
hepatopancreas. The hepatopancreas was then weighed to calculate the
hepatosomatic index, which is a ratio of the hepatopancreas weight
to the body weight.
Stable isotope data: Ten Littoraria from the
lab food quality (five from each diet) and twelve field collected
Littoraria (two from each study plot) were
analyzed for stable isotopes. The muscular foot was dissected from
each individual, rinsed with distilled water, and dried in a 60°C
oven for 48 hours. Tissue was then ground into a fine powder and
sent to the UC Davis stable isotope laboratory for analysis of
δ13C and δ15N
isotopes.