*3.3. Water Quality* Nutrients and Stable Isotopes

Seawater nutrient levels and N stable isotopes of macroalgae were assessed simultaneously to obtain an indication of land-based pollution. Nutrients were not elevated (>10 μM DIN) at the urban sites compared to the rural sites, though there were significant site and depth interactions [two-way MANOVA *F*(3,63) = 3.208, Pillai = 0.398, *p* = 0.0012]. Combined nitrate and nitrite, and phosphate were responsible for these interactions [two-way ANOVA NO3 − + NO2 −: *F*(3,63) = 10.8991, *p* < 0.0001; PO4 <sup>3</sup>−: *F*(3,63) = 4.5597, *p* = 0.0059]. Rural-N 10 m had significantly higher combined nitrate and nitrite (NO3 − + NO2 <sup>−</sup>: 1.05 ± 0.07 μM) and phosphate (PO4 <sup>3</sup><sup>−</sup> 0.15 ± 0.01 <sup>μ</sup>M; Table S6) than all other sites at 10 m, but similar levels of both nutrients at 5 m compared to remaining sites (Figure 6). Variation in DIN was marginally significant with a site and depth interaction [two-way ANOVA *F*(3,63) = 2.7769, *p* = 0.0484], but there were no significant differences in the pairwise test (*p* < 0.05; Figure 6).

**Figure 6.** Seawater nutrient concentrations (top to bottom: dissolved inorganic nitrogen [DIN], NH4 +, NO3 − + NO2 −, PO4 <sup>3</sup>−) sampled in triplicate on each transect at the four sites (Urban-W, Urban-E, Rural-N, Rural-E), two depths (5 m and 10 m), and three transects per depth in Timor-Leste in November 2015. Bold line is the median, box ends are the first and third quartile, lines are 95% confidence interval of the median, and points are Tukey's outliers. Gray points indicate samples. Note differences in scales.

Stable isotope values were consistent across sites, with no elevated values at the urban sites compared to the rural sites. Delta 15N stable isotopes had a significant site difference for both algae species. Urban-E had significantly lower δ15N in both algae species (Table 1). **Table 1.** Delta 15N stable isotope ANOVA results of algae sampled at the four sites (Urban-W, Urban-E, Rural-N, Rural-E), two depths (5 m and 10 m), and three transects per depth in Timor-Leste in 2015. Starred values are significant results with mean, standard error, and post hoc groupings (a, b, or ab) presented per site with "-" indicating no samples collected.

