Project: RAPID: COLLABORATIVE RESEARCH: Mechanisms of seagrass community injury and resilience post Hurricane Florence: implications for increasingly stormy coasts

NSF Award Abstract:
Seagrass meadows are conspicuous features of many estuarine and nearshore environments. By some estimates, these meadows contribute an average of $20,000 per hectare per year in goods and services. These include nutrient cycling, sediment stabilization, carbon burial, and provision of nursery habitat for juvenile fishes, crabs, and shrimps. Alarmingly, seagrasses are threatened by several environmental and human-driven stressors, and loss of seagrass habitat remains a key concern for conservation and sustainable development programs. Anticipated increases in storminess (frequency and intensity) and rainfall under many climate change modeling scenarios make understanding hurricane impacts on valuable coastal habitats such as seagrass meadows important on local, national, and global scales. Indeed, seagrass meadows potentially serve as a 'canary in the coal mine' regarding the effects of increased hurricane activity as they are found at shallow depths and are affected by turbidity and salinity; seagrasses are also vulnerable to burial or erosion due to large storms. Seagrasses (1) include a suite of species with distinct growth and reproductive strategies; (2) live in a range of meadow sizes and degrees of 'patchiness;' and (3) present divergent seasonal cycles. This represents a tremendous opportunity to explore the conditions and attributes that result in seagrass resilience or vulnerability to hurricanes as a model for coastal ecosystem responses more broadly.

Hurricane Florence made landfall along the NC coast on September 14, 2018. Florence stalled approaching shore, and storm-related winds/rains persisted for >4 days (13th-16th) in southeastern NC. Subsequently, record high sea-level stands (surge + tide) were observed across the NC coastline. Furthermore, Florence became the second wettest US storm, behind only Harvey in 2017, dumping 65 trillion L of rain over land that depressed estuarine salinities for over a month. NC seagrasses are dominated by three species: eelgrass, shoalgrass, and widgeon grass. Meadows exist as polycultures or monocultures, and exhibit a diverse range of spatial configurations. Meadows are also defined by strong seasonality: eelgrass shoots senesce in summer due to heat stress, with sites transformed either into shoalgrass-dominated meadows or mudflats. Subsequent to dieback, eelgrass depends upon a combination of seedbank and surviving apical meristems for regeneration each winter. Using key seagrass datasets collected by the research team dating back decades across ~40 Florence-impacted meadows, several fundamental ecological questions are being addressed: (1) how sexual (eelgrass: seedbank) v. asexual (shoalgrass: vegetative growth and fragment colonization) life histories promote susceptibility or resilience of seagrass to disturbance; (2) how meadow landscape configuration and plant diversity modulate the effect of storms on seedbank retention; (3) how meadow disturbance (intense physical v. more chronic physiochemical drivers) affected community dynamics, with special focus on plant productivity and the critical 'nursery role' of seagrass habitat; and (4) how seasonality and species traits amplify or attenuate the effects of intense disturbance on seagrasses. This research expands upon previous post-hurricane studies by considering the interactive effects of hurricanes, landscape configuration, and biodiversity on ecosystem responses. It also leverages ongoing, NSF-supported work along the TX coast to compare-and-contrast the responses of different seagrass phenology/growth strategies to storm disturbance (e.g., turtlegrass in TX is a "leaf-on" species throughout the year while eelgrass and shoalgrass in NC both exhibit strong seasonality in biomass). Collectively, this work will result in more generalizable models of coastal ecological resilience to storminess.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.