West & Glasby. 2021. Interpreting Long-Term Patterns of Seagrasses Abundance: How Seagrass Variability Is Dependent on Genus and Estuary Type

West, Greg J., and Tim M. Glasby. “Interpreting Long-Term Patterns of Seagrasses Abundance: How Seagrass Variability Is Dependent on Genus and Estuary Type.” Estuaries and Coasts , November 12, 2021. https://doi.org/10.1007/s12237-021-01026-w.

Seagrass habitats are recognised as providing essential ecosystem services and being indicators of estuarine health, and are under increasing threat globally. This study examined the spatial and temporal variability of four dominant seagrass genera ( Posidonia , Zostera , Halophila and Ruppia ) among five geomorphic estuary types and four levels of estuarine maturity in New South Wales (NSW), Australia, over a 40-year period. While there was a decline in total seagrass area across NSW over the last 40 years, this was mostly attributed to Ruppia , the genus with the greatest temporal variability. The composition of seagrasses differed among estuary types and with the maturity of Barrier estuaries. Posidonia was found to be the least temporally variable genus over the last 40 years. The greatest overall annual rate of decline was 1.85% year−1 for Ruppia which is considerably less than the global estimated rate of 5% year−1 over the same time period. Average annual rates of decline were greater over the last 18 years than the last 40 years, but only for the most transient genera and only in some estuary types. Recent declines in Posidonia were greater than those over the last 40 years in two of the most heavily urbanised estuaries. The temporal variability of Zostera differed significantly among estuary types and decreased with increasing water depth across all estuaries. No relationships were found between catchment disturbances, measured as land use or population density, and seagrass change or temporal variability at the estuary scale. Our results highlight the importance of distinguishing among seagrass genera when interpreting changes over time and considering factors such as estuary type, which is effectively a surrogate for environmental conditions.