Supplementary Materials

Appendix 1 Morphological characteristics of the four Spartina alterniflora habitat types. a)

Stem height (mm), b) dry biomass (grams per m2), c) stem density (stems per m2), d)

SPAD value, e) tiller density (stems per m2), and f) marsh snail (Littoraria irrorata) and marsh mussel (Geukensia demissa) plot specific frequency of occurrence (% of plots) across habitat types. Habitat types with the same letter are not significantly different at the p<0.05 level (a-e). Boxplots (a-e) are shown with medians, first, and third quantiles and a range of 1.5 times the interquantile range. Outliers beyond the range are represented as circles. Total dry biomass (grams per m2) of S. alterniflora was obtained for subset of sub-samples from each transect by drying plant matter at 60°C for at least

24 hours (Appendix 2). SPAD value or greenness is a surrogate for chlorophyll content.

Greenness was measured shortly after returning plants to the lab using a Minolta 502

SPAD meter on a subset of randomly selected stems from a subset of transects (3-5 transects per habitat type; Appendix 2). Non-parametric statistics were used to compare stem height (mm), stem density (no. per m2), biomass (grams per m2) and SPAD value among S. alterniflora habitat types (dieback zone, transitional zone, short morph, and tall morph); see methods for detailed description of statistical tests. Appendix 2

Sample size of analyses. Values shown are the amount of transects (number on left), sub-

samples (parenthesized number in center), and stems (bracketed number on right) for a

given figure and analysis. The bold number indicates unit of replication.

Dieback Transitional Short Morph Tall Morph Figure Zone Zone Stem-borer 7 (14) [217] 7 (14) [275] 7 (14) [228] 7 (14) [129] 1 & 2 Frequency Stem Height a 7 (14) [217] 7 (14) [275] 7 (14) [228] 7 (14) [129] A1a Biomass 7 (13) [170] 7 (13) [268] 7 (13) [165] 7 (14) [129] A1b Stem Density b 7 (14) [480] 7 (14) [422] 7 (14) [671] 7 (14) [242] A1c SPAD 4 (7) [44] 4 (6) [51] 3 (5) [31] 4 (6) [46] A1d Tiller Density 6 (12) [50] 6 (12) [99] 6 (11) [33] 5 (10) [27] A1e Stem-borer Frequency (non- 6 (12) [81] 6 (12) [57] 6 (11) [73] 5 (10) [58] A3 tiller)

Footnotes. a The stem height row also indicates total number of transects, sub-samples, and stems collected from the field and analyzed in the laboratory. b The number of stems in the stem density row are for the full quadrat. Appendix 3

Stem borer frequency of occurrence across the four Spartina alterniflora habitat types for old growth or non-tiller stems. Habitat types with the same letter are not significantly different at the p<0.05 level. Boxplots are shown with medians, first, and third quantiles and a range of 1.5 times the interquantile range. Outliers beyond the range are represented as circles. We determined if stems were new growth (tillers) based on the absence of nodes for a subset of transects (5-6 transects per habitat type; Appendix 2).

Prior studies on stem borers did not remove tillers from their assessment of frequency of occurrence (Stiling and Strong 1983). To ensure our data was comparable with past studies, we chose to leave tillers in our analysis (Fig. 1 and Fig. 2). When tillers are excluded, however, a trend of stem-borer frequency following the plant health gradient becomes evident (i.e. high frequency in dieback zone, moderate frequency in transitional zone, and low frequency in healthy short morph). Appendix 4

Stem borer family-specific percent height in Spartina alterniflora stems for the a) dieback zone, b) transitional zone, c) short morph, and d) tall morph. Boxplots are shown with medians, first, and third quantiles and a range of 1.5 times the interquantile range.

Outliers beyond the range are represented as circles. Low sample size precluded adequate statistical analysis of variation in percent height between stem boring families; therefore, data are only shown graphically.