Long-term performance of seagrass restoration projects in Florida, USA

Abstract

Seagrass restoration is a common tool for ecosystem service enhancement and compensatory mitigation for habitat loss. However, little is known about the long-term performance of these projects. We identified seagrass restoration projects by reviewing historic permitting documents, monitoring reports, and studies conducted in Florida, USA, most of which have not been cited previously in peer-reviewed literature. We then revisited 33 seagrass restorations ranging in age from 3 to 32 years to compare seagrass percent cover, species diversity, and community structure in restored and contemporary reference seagrass beds. We found that 88% of restoration projects continued to support seagrass and, overall, restored percent cover values were 37% lower than references. Community composition and seagrass percent cover differed from references in projects categorized as sediment modification and transplant restorations, whereas all vessel damage repair projects achieved reference condition. Seagrass diversity was similar between restored and reference beds, except for sediment modification projects, for which diversity was significantly lower than in reference beds. Results indicate that restored seagrass beds in Florida, once established, often exhibit long-term persistence. Our study highlights the benefit of identifying and surveying historic restorations to address knowledge gaps related to the performance and long-term fate of restored seagrass beds.

Figure 1

Map of seagrass restoration sites visited in this study, with restoration type (sediment modification, transplant, vessel damage repair) indicated. Map generated using QGIS (version 3.0.1, http://qgis.osgeo.org).

Figure 2

Mean percent cover of seagrass from restored and reference beds across sites (10% increments; n = 33).

Figure 3

Mean and 95% confidence interval differences of seagrass percent cover between restored and reference bed in each site (Δµ = µ_Restored − µ_Reference). Values represent percentage points (pp), with sample size and adjusted permutation test P-values (α = 0.05; bold) annotated (no test = no seagrass in restoration or references) (A). Bootstrap distribution of overall and restoration type-specific mean differences in seagrass cover between restored and reference beds (0.5 increments) (B). Mean (bold) and 95% bootstrap confidence intervals are annotated; means with confidence intervals that do not include 0 are considered significantly different.

Figure 4

Mean and 95% confidence intervals of differences between restored and reference seagrass bed values for inverse Simpson diversity index (1/λ) within each restoration site (Δµ = µ_Restored − µ_Reference), with sample size and adjusted permutation test P-values (α = 0.05; bold) annotated (tests were not conducted for monospecific sites = m.sp) (A). Bootstrap distribution of overall and type-specific mean difference in species number per sample values between restored and reference beds (0.01 increments) (B). Mean (bold) and 95% bootstrap confidence intervals are annotated; means with confidence intervals that do not include 0 are considered significantly different.

Figure 5

Mean ± SE of average cover values of seagrass species in restored and reference beds by site (A). Non-metric multidimensional scaling plots (nMDS) of Bray-Curtis dissimilarity between restored and reference beds based on site average cover data (square root transformed) (B). Species abbreviations: Halodule wrightii = Hw; Thalassia testudinum = Tt; Syringodium filiforme = Sf; Ruppia maritima = Rm; Halophila decipiens = Hd; Halophila johnsonii = Hj.