Open Coast Seagrass Restoration. Can We Do It? Large Scale Seagrass Transplants

Diogo Paulo,Emanuel J Gonçalves,Joana Boavida,Alexandra H Cunha,Ester A Serrão,Mark Fonseca

doi:10.3389/fmars.2019.00052

Abstract

Abstract Some of the major challenges in seagrass restoration on exposed open coasts are the choice of transplant design that is optimal for coastlines periodically exposed to high water motion, and understanding the survival and dynamics of the transplanted areas on a long time-scale over many years. To contribute to a better understanding of these challenges, we describe here part of a large-scale seagrass restoration program conducted in a Marine Park in Portugal. The goal of this study was to infer if it was possible to recover seagrass habitat in this region, in order to restore its ecosystem functions. To infer which methods would produce better long term persistence to recover seagrass habitat, three factors were assessed: donor seagrass species, transplant season, source location. Monitoring was done three times a year for 8 years, in which areas and densities of the planted units were measured, to assess survival and growth. The best results were obtained with the species Zostera marina transplanted during spring and summer as compared to Zostera noltii and Cymodocea nodosa. Long-term persistence of established (well rooted) transplants was mainly affected by extreme winter storms but there was evidence of fish grazing effects also. Our results indicate that persistence assessments should be done in the long term, as all transplants were successful (survived and grew initially) in the short term, but were not resistant in the long term after a winter with exceptionally strong storms. The interesting observation that only the largest (11 m2) transplanted plot of Z. marina persisted over a long time, increasing to 103 m2 in 8 years, overcoming storms and grazing, raised the hypothesis that for a successful shift to a vegetated state it might be necessary to overpass a minimum critical size or tipping point. This hypothesis was therefore tested with replicates from two donor populations and results showed effects of size and donor population, as only the larger planting units from one donor population persisted and expanded. It is recommended that in future habitat restoration efforts large planting units are considered.

Highlights

Seagrass restoration has been conducted for nearly 70 years, since the middle of the last century (e.g., Addy, 1947)
Due to the exploratory nature of seagrass restoration on an exposed open costal area, we designed transplant areas to answer the following research questions: (1) which seagrass species? (2) which time of the year is best for transplanting? (3) which donor populations provide higher restoration success? and (4) which initial transplant size? This paper reports on how addressing these questions shaped our understanding of the factors controlling the unvegetated state of the area, allowing us to adaptively overcome stressors that limited seagrass recolonization and eventually led this restoration project to achieve persistent seagrass establishment
Z. noltii collected in Ria Formosa had no significant difference in maximum quantum yield during the experiment (ANOVA P > 0.05)

Summary

Introduction

Seagrass restoration has been conducted for nearly 70 years, since the middle of the last century (e.g., Addy, 1947). Restoration attempts in more wave exposed coasts are still few (Bull et al, 2004; van Katwijk et al, 2009). Open coast large-scale, nonexperimental restoration has only been attempted in Western Australia (Fonseca et al, 1998a; Paling et al, 2003, 2007). Restoration of seagrasses on exposed open coasts poses special challenges, both logistical and environmental (Paling et al, 2003), and the operation of divers and safety issues in open ocean settings raise costs significantly (Calumpong and Fonseca, 2001). High wave energy, whether stochastic or periodic, limits operations and can quickly erode planted areas or mobilize sediments that bury seagrasses, for young meadows that have not yet reached sufficient abundance to reach an equilibrium with the disturbance regime (Den Hartog, 1971; Patriquin, 1975; Fonseca et al, 1983; Marbà et al, 1994; Fonseca and Bell, 1998; Turner et al, 1999; Bryars, 2008)

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Conclusion