Data Table 1: Benthic Chlorophyll From Failon et al. 2020: To estimate benthic algal biomass, a benthic chlorophyll a sample was taken to a depth of 3 mm from the sediment surface (volume = 0.29 mL) and placed in a cooler of ice. The samples were then stored in a -80C freezer to await further processing. Chlorophyll a was extracted in 10 mL of 90% acetone for 24 h and filtered through a 0.45 μm Acrodisc with absorbance measured at 630, 647, 664, 665, and 750 nm against a 90% acetone blank (Brush MJ, personal communication). An additional acidification step allowed for phaeophytin correction. Calculations are presented in Failon et al. 2020.
Data Table 2: Carbon and Nitrogen
Spartina alterniflora (SPAL) and Spartina cynosuroides (SPCY) Snail Experiment
20 individual plants were collected from Taskinas Creek in SPAL and SPCY habitats. Plants were placed in the -80C freezer and later freezedried for a minimum of 72 hours using a Labconco Freezone system. Plant height and dry mass were recorded for later biomass calculations before grinding. Plants were ground to a fine powder in a mini Wiley mill with a 40 mesh sieve. Ground samples were placed into new, clean scintillation vials until further processing. Samples of between 0.8 and 0.9 mg were rolled and processed in a Thermo Scientific FlashEA system
Data Table 3: Grazing Scars
Taskinas Creek Periwinkle Grazing Scar Survey
15 quadrats were haphazardly tossed in each habitat type, S. alterniflora (SPAL) and S. cynosuroides (SPCY), at Taskinas Creek. In each quadrat 5 plants were chosen at random to measure for height and to count the number of scars present from Littoraria irrorata grazing
Data Table 4: Light and Temperature
SPAL SPCY Snail Experiment
4 HOBO loggers were set out at Taskinas Creek on July 11, 2018 at low tide and gathered on August 6, 2018 at low tide. Two of the loggers were in S. alterniflora habitat and two were in S. cynosuroides habitat. Loggers were tied to stake flags with flagging tape to keep them flush with the sediment surface to get accurate light and temperature readings. Loggers were set to take measurements every 5 minutes over the course of the sampling period. Each logger was about 2 meters from the creek bank. Loggers in each habitat were separated by about 5 meters
Data Table 5: Penetrometer (tissue toughness)
SPAL SPCY Snail Experiment
Samples of Spartina alterniflora (SPAL) and Spartina cynosuroides (SPCY) were collected from Taskinas Creek marsh in the summer of 2017.
Within each plant type, twenty 0.0625m^2 quadrats were haphazardly placed along a transect. Stem density and # of standing dead were counted, and plant heights were measured (see plant height data for more information). All quadrats were placed within one meter of the creek/river bank. The tallest plant from each quadrat was set aside for chemical analyses, and the 2nd tallest plant was set aside to collect penetrometer data. The tallest and 2nd tallest plants had to be within a 10cm range in height of one another, or else the 2nd and 3rd tallest plants were collected instead. Exceptions to plant height rule: There are a few quadrats from TC where this does not apply because the rule had not been formulated yet; Also at SH where plants were too patchy to have consistent heights. Plants were transported back to VIMS and placed in the refrigerator until processing.
For each plant: Leaves 1-5 were numbered from youngest to oldest, from the outermost leaf on the plant inwards, alternating from side to side. Leaves were separated from the main stem at the ligule and each leaf was measured for total length. Fifteen centimeters from the ligule, a 5 cm segment of leaf was removed. This segment was measured for leaf width, and then used in the penetrometer to obtain toughness. Penetrometer consists of an insect pin attached to a plastic tray that is suspended above leaf material. A plastic cup is placed on the tray and dry sand is added in small amounts to the cup until the pin pierces the tissue. The amount of sand added to the cup is weighed (with the cup tared prior) and this is the value of toughness. Penetrometer weights: cup = 8.8700g, apparatus = 23.4679g, total weight of penetrometer = 32.3379g.
Data Table 6: Plant Heights
SPAL SPCY Snail Experiment
Five quadrats were haphazardly tossed in each Spartina alterniflora (SPAL) and Spartina cynosuroides (SPCY) habitat. In each quadrat, three plants were chosen at random, measured and clipped. After returning to the lab, the plants were put into the -80 degrees Celsius freezer. The plants were later freezedried and ground in a mini Wiley Mill using a 40 mesh sieve.
Data Table 7: Plant Stem Densities and Invertebrate Survey
Taskinas Creek Invertebrate Surveys
Thirty haphazardly placed 0.0625m^2 quadrats were placed in two vegetation types, Spartina cynosuroides (SPCY) and Spartina alterniflora (SPAL), and surveys were taken. In each quadrat the number of live stems, dead stems, burrows (greater than 1cm), mussels, and snails were counted and recorded.
Data Table 8: Predation Assays
Periwinkle Predation Assays
Naive snails were collected from Taskinas Creek and superglued to fishing line (4 lb. monofilament) tethers (cut to 18 cm and tied to about 15 cm), which were attached to clear plastic rods. 24 snails were deployed in Spartina alterniflora (SPAL) habitat and 24 snails were deployed in Spartina cynosuroides (SPCY) habitat. The tether poles were sunk into the sediment so that the snail was flush with the sediment surface. Tethers were deployed at low tide and then retrieved 24 hours later at the following day's low tide. Snails were marked present or absent to indicate predation. Snails were deployed in three rows of 8, with each row increasing in distance from the creek bank. The total distance from the first row of tethers to the farthest row of tethers was 2 meters. Following the assay any remaining snails were removed from their tethers and let free in the marsh. This assay was repeated for a total of 3 times, each assay using experimentally naïve snails.
Data Table 9: Snail Measurements
Taskinas Creek Invertebrate Surveys
Periwinkle snails (Littoraria irrorata) were collected from two vegetation types, Spartina cynosuroides (SPCY) and Spartina alterniflora (SPAL). Collected snails were taken back to the lab and measured for shell height (operculum to tip of shell) and shell width (widest point of shell) with digital calipers.
Data Table 10: Total Phenolic Concentrations
SPAL SPCY Snail Experiment
S. alterniflora (SPAL) and S. cynosuroides (SPCY) plants were collected from Taskinas Creek, Plants were frozen in a -80C freezer, freeze dried, weighed, ground in a mini Wiley mill, and then analyzed with a modified Folin-Ciocalteu phenolics assay.
Data Table 11: Total Soluble Protein
SPAL SPCY Snail Experiment
S. alterniflora (SPAL) and S. cynosuroides (SPCY) plants were collected from Taskinas Creek. Plants were frozen in a -80C freezer, freeze dried, weighed, ground in a mini Wiley mill, and then analyzed with a modified Bradford protein assay. Protein mass per unit dry weight was calculated by converting mg/mL units to mg/g by multiplying by the starting protein extractant volume (1mL) and dividing by the starting dry plant sample (0.005g), this gives you the dry weight.
