Climate oscillations drive nutrient availability and seagrass abundance at a regional scale

Abstract

Seagrasses are increasingly recognized for their ecosystem functions and services. However, both natural and anthropogenic stressors impact seagrass functional traits, for example by altering nutrient regimes. Here, we synthesize 27 yr of data from regional, long-term seagrass and water quality monitoring programs of south Florida to investigate the impacts of relative nutrient availability on seagrass abundance (as expressed by percent cover) across an oligotrophic seascape. We employ linear mixed-effect models and generalized additive models to show that seagrass abundance is driven by interannual variations in nutrient concentrations, which are ultimately controlled by climate oscillations (El Niño Southern Oscillation Atlantic Multidecadal Oscillation) via regional rainfall-runoff relationships. Our study suggests that climate oscillations drive interannual variations in seagrass cover on a regional scale, with high-rainfall years leading to increased nitrogen availability and higher seagrass abundance in typically nitrogen-limited backreef meadows. Conversely, these periods are associated with reduced seagrass cover at the more P-limited inshore sites and in Florida Bay, with yet unknown consequences for the provision of seagrass ecosystem services. We show that nutrient delivery from runoff can have diverging impacts on benthic communities, depending on spatial patterns of relative nutrient limitation, with some N-limited seagrass meadows showing resilience to periodic nutrient enrichment.