Natural recovery of a marine foundation species emerges decades after landscape-scale mortality

Margaret O Hall,Bradley T Furman,Michael J Durako,Susan S Bell

doi:10.1038/s41598-021-86160-y

Abstract

Globally, the conditions and time scales underlying coastal ecosystem recovery following disturbance remain poorly understood, and post-disturbance examples of resilience based on long-term studies are particularly rare. Here, we documented the recovery of a marine foundation species (turtlegrass) following a hypersalinity-associated die-off in Florida Bay, USA, one of the most spatially extensive mortality events for seagrass ecosystems on record. Based upon annual sampling over two decades, foundation species recovery across the landscape was demonstrated by two ecosystem responses: the range of turtlegrass biomass met or exceeded levels present prior to the die-off, and turtlegrass regained dominance of seagrass community structure. Unlike reports for most marine taxa, recovery followed without human intervention or reduction to anthropogenic impacts. Our long-term study revealed previously uncharted resilience in subtropical seagrass landscapes but warns that future persistence of the foundation species in this iconic ecosystem will depend upon the frequency and severity of drought-associated perturbation.

Highlights

The conditions and time scales underlying coastal ecosystem recovery following disturbance remain poorly understood, and post-disturbance examples of resilience based on long-term studies are rare
Rankin Key (RAN) and Johnson Key (JON) Basins, which had highest incidence of severe die-off, exhibited three discrete phases of turtlegrass recovery: (1) a stagnant recovery or depressed phase during post-die-off algal blooms, (2) a recovering phase during which turtlegrass biomass increased, and (3) a recovered phase where turtlegrass biomass was relatively stable over several years
Seagrass biomass decreased during the first phase [i.e., JON and Rabbit Key (RK) Basins], suggesting bloom-induced secondary mortality, but biomass subsequently increased to levels similar to those recorded in the recovered phase of severely affected basins (Fig. 2A–H)

Summary

Introduction

The conditions and time scales underlying coastal ecosystem recovery following disturbance remain poorly understood, and post-disturbance examples of resilience based on long-term studies are rare. We documented the recovery of a marine foundation species (turtlegrass) following a hypersalinity-associated die-off in Florida Bay, USA, one of the most spatially extensive mortality events for seagrass ecosystems on record. The mass mortality (i.e., die-off) of Thalassia testudinum (turtlegrass) in Florida Bay, USA in 1987, provided a unique opportunity to examine the recovery capacity of a subtropical seagrass ecosystem following landscape-scale disturbance (Fig. 1). This seagrass die-off represented one of the most spatially extensive mortality events of a marine foundation species reported to date[11]. During the algal bloom period, secondary losses of the climax species, turtlegrass, and all other seagrass taxa were recorded, including the early colonizers Halodule wrightii (shoal grass) and Syringodium filiforme (manatee grass), effectively halting the beginning stages of successional recovery in locations severely affected by die-off[13]

Methods

Results

Conclusion