Herbivory is a key structuring force that can have negative, positive, or mixed impacts on seagrasses. The identity and abundance of herbivores, as well environmental conditions such as solar insulation, can influence the impacts of herbivory. To understand the impact of herbivores on turtlegrass in warm, temperate St. Joseph Bay (SJB) in the northeastern Gulf of Mexico, we estimated densities of the most common herbivores: variegated sea urchins and green turtles. We also estimated SJB’s herbivore carrying capacities by estimating annual average turtlegrass production and variegated urchin consumption rates and by using previously calculated juvenile green turtle consumption rates and seagrass area. During summer, turtlegrass exhibited compensatory growth due to urchin herbivory, but during winter, turtlegrass growth was negatively affected by urchin grazing. Given our calculated annual turtlegrass production, urchin ingestion rates, and the average urchin density of 5.89 ± 0.09 (SE) urchins ha−1, the turtlegrass production not consumed by urchins can sustain 278.0 juveniles ha−1, or about 556,010 turtles, putting current average green turtle abundance of 26 ± 3.7 individuals ha−1 at 4.0–14.6% of carrying capacity. Previous work in this system has shown that simulated turtle herbivory can reduce turtlegrass productivity—with this potential reduction in production, SJB could not sustain a green turtle population at current urchin densities. Given the rapid global green turtle increase, evaluating densities and future carrying capacities of herbivores in higher latitude seagrass pastures is critical for updating and achieving recovery goals for both green turtles and globally declining seagrass meadows.