Seagrasses are “coastal barometers” and frequently used to assess ecosystem health and condition. Monitoring programs worldwide measure a suite of seagrass indicators because they are effective water quality integrators. To be considered robust, an indicator should have a direct relationship with both environmental or anthropogenic drivers and ecosystem function. The main objective of this study was to develop a conceptual ecological model (CEM) by curating a list of the most suitable, affordable, and functional indicators for seagrass ecosystems in the Gulf of Mexico. We conducted a workshop that featured a panel of seagrass experts who evaluated the robustness of the indicators and CEM. We targeted indicators that were repeatable, cost-effective, applicable at multiple scales, easy to explain to managers and addressed multiple management objectives, and currently measured by monitoring programs in the Gulf of Mexico. For each indicator, we identified a measurable metric and formulated a unique set of ratings and assessment points. Metric ratings (excellent/good, fair, poor) and assessment points were determined using long-term monitoring data from Texas and Florida, coupled with the knowledge of the expert panel and an extensive literature search.
Results/Conclusions
We identified 10 indicators and 12 metrics frequently measured by 39 monitoring programs across the Gulf. Using recent data from the Texas Seagrass Monitoring Program to validate the CEM, we found that seagrass percent cover and blade length were sensitive indicators of environmental change. Substantial changes in seagrass cover (> 25% loss) and blade length (> 25%) were linked to large-scale climatic disturbances. Severe drought conditions resulted in a massive die-off of Syringodium filiforme (97% loss) in 2012-2013. In 2017, we documented considerable declines in the cover (-31%) and blade length (-30%) of Thalassia testudinum following a major hurricane. After these disturbances, our model categorized seagrass condition for percent cover and blade length as “poor”. Our proposed CEM can serve as a tool to score seagrass ecosystem condition at the bay or basin scale. Scores can be reported using a red-yellow-green scheme which summarizes information in an accessible format for resource managers, stakeholders and policy-makers. Moreover, the indicators, metrics, and assessment points are amenable to large scale evaluations of ecosystem condition because they are economically feasible. The CEM can be used to provide a comprehensive assessment of the status and trends of seagrass habitats across the entire Gulf of Mexico.