## 3 Results
### Analyses of Mussel CPUIE and Richness  
Principal component analysis followed by the broken stick test resulted in seven interpretable principal components (Table 5). Following [78], we considered 1.050! the threshold for identifying important coefficients, due to our low overall sample size. PC 1 described an upper watershed (i.e., further from the Gulf of Mexico; lower PC scores) to lower watershed (i.e., closer to the Gulf of Mexico; higher PC scores) gradient of water quality, land cover, and geology, specifically temperature (lower upstream), DO (higher upstream), % agriculture (lower upstream), % evergreen forest (higher upstream), % Al-luvium (lower upstream), % High Terraces (lower upstream), % Pascagoula Hattiesburg (higher upstream), and % Citronelle Formation (higher upstream). PC 2 described sites higher in the watershed with greater pH, % deciduous forest, % mixed forest, % wetland, \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Variable** & **Mean** & **Maximum** & **Minimum** \\ \hline
**Geology** & & & \\ \% Alluvium & 20.55\% (0.02) & 57.06\% & 1.39\% \\ \% Prairie Terraces & 22.84\% (0.07) & 98.61\% & 0.00\% \\ \% High Terraces & 56.48\% (0.07) & 95.74\% & 0.00\% \\ \% Deweyville Terraces & 0.13\% (0.00) & 2.02\% & 0.00\% \\ \% Pascagoula Hattiesburg & 69.82\% (0.06) & 85.32\% & 58.61\% \\ \% Citronelle Formation & 19.83\% (0.08) & 32.43\% & 0.00\% \\ \% Coastal Deposits & 10.35\% (0.10) & 41.39\% & 0.00\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._  
Figure 3: Watershed boundaries used to estimate land cover upstream of sampling sites (green circles). Boundaries (black lines) determined from U.S. Geological Survey hydrological units (12 digits codes). Green lines indicate the portion of the watershed upstream of some sampling sites that was analyzed. Otherwise, the entire upstream contributing watershed area was used. Land cover was obtained from U.S. National Oceanic and Atmospheric Agency 2010 C-CAP Regional Land Cover. Land cover types were developed (orange), water (dark blue), agriculture (tan), deciduous forest (light green), evergreen forest (dark green), mixed forest (olive green), wetland (light blue), and barren (yellow). and lower % Coastal Deposits. PC 3 described sites lower in the watershed with lower % agriculture, but higher % alluvium and % Coastal Deposits. PC 4 was negatively associated with % mixed forest. PC 5 was associated with sites with specific geologic conditions (% Deweyville Terraces) and higher pH. PC 6 was negatively associated with % evergreen forest, and PC 7 was positively associated with higher DO. For mussel CPUE, the zero-inflation component of the finite mixture model was statistically significant (\(\beta=1.16\) (\(\pm 0.58\) SE), z = 2.02, \(p=0.04\)) and explained 76.1% of the probability in the model. Water quality, habitat, land cover, and geologic variables only explained 23.9% of Mussel CPUE, which was negatively related to PC 1 (\(\beta=-2.69\) (\(\pm 0.56\) SE), z = \(-4.80\), \(p<0.01\)), PC 2 (\(\beta=-2.42\) (\(\pm 0.44\) SE), z = \(-5.86\), \(p<0.01\)), % less than 0.250 mm (\(\beta=-0.050\) (\(\pm 0.002\) SE), z = \(-3.28\), \(p<0.01\)), and % less than 0.125 mm (\(\beta=-19.40\) (\(\pm 0.470\) SE), z = \(-4.13\), \(p<0.01\)), and positively related to PC 4 (\(\beta=6.47\) (\(\pm 1.23\) SE), z = \(5.25\), \(p<0.01\)), and PC 5 (\(\beta=4.46\) (\(\pm 0.82\) SE), z = \(5.40\), \(p<0.01\)). CPUE was higher in upstream sites with higher DO (PCs 1, 7), pH (PCs 2, 5), % evergreen forest (PC 1), % mixed forest (PCs 2, 4), % Pascagoula (PC 1), % Citronelle Formation (PC 1), and % Deweyville Terraces (PC 5). In contrast, CPUE was lower downstream in sites with higher temperatures (PC 1), % less than 0.250 mm, % less than 0.125 mm, % agriculture (PC 1), % wetland (PC 2), % deciduous forest (PC 2), % alluvium (PC 1), % Coastal Deposits (PC 2), and % High Terrace (PC 1).