COS 40-6 - Assessing long-term seagrass monitoring data to determine sampling frequency in a sub-tropical estuary

Wednesday, August 10, 2016: 9:30 AM
Grand Floridian Blrm A, Ft Lauderdale Convention Center
Jerry Metz, Elizabeth W. Stoner and D. Albrey Arrington, Loxahatchee River District, Jupiter, FL

Seagrasses are some of the most productive ecosystems in the world, acting as ecosystem engineers, creating quality habitat and contributing to ecosystem function. The Anthropocene epoch will likely be characterized as a period in which seagrasses declined at alarming rates, typically driven by anthropogenic activities. Seagrass monitoring efforts, therefore, are increasingly important as scientists and natural resource managers map extant seagrass beds, quantify seagrass losses, and identify key stressors driving seagrass declines. Frequent seagrass monitoring is costly, so resource managers are not able to adequately characterize temporal and spatial patterns in seagrass occurrence and/or loss.

Here, we use our extensive seagrass monitoring dataset, spanning an eleven year continuous period of record, to design a seagrass sampling strategy that maximizes attainment of high quality seagrass data while minimizing costs. Seagrass data were collected every other month from 2003 to 2014 in the Loxahatchee River estuary, Florida, within defined extant seagrass beds across a salinity gradient. We then systematically excluded sample periods (e.g., all February samples), and re-analyzed the dataset to determine if reduced sampling frequency affected our estimates of maximum spatial extent of our dominant seagrasses (Syringodium filiforme, Halodule wrightii, and Halophila johnsonii) by year. 


Maximum annual occurrence of S. filiforme, H. wrightii, and H. johnsonii were heavily influenced by month. Peak H. wrightii abundance occurred from June through August with a sharp decline in the fall and winter months. The federally threatened H. johnsonii occurrence peaked in April with distinct declines through the summer months. Maximum canopy height among S. filiforme and H. wrightii seagrass also occurred most frequently from June through August before subsiding in October and throughout the winter months. Our evaluation shows a systematic seagrass monitoring program with targeted sampling effort occurring in April (H. johnsonii), June, and August (S. filiforme and H. wrightii) will allow regional natural resource managers to efficiently and effectively characterize optimal annual patterns of seagrass occurrence. Such patterns will be more than adequate to quantify expected degradation as we experience and document the Anthropocene. More optimistically, these data will be sufficient to strategize necessary ecosystem enhancement and restoration projects to turn back the tide of seagrass losses.