Modelling seagrass growth and development to evaluate transplanting strategies for restoration (original) (raw)
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Open Coast Seagrass Restoration. Can We Do It? Large Scale Seagrass Transplants
Frontiers in Marine Science, 2019
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 timescale 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 m 2) transplanted plot of Z. marina persisted over a long time, increasing to 103 m 2 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 (PUs) from one donor population persisted and expanded. It is recommended that in future habitat restoration efforts large PUs are considered.
Global analysis of seagrass restoration: the importance of large-scale planting
Journal of Applied Ecology, 2015
1. In coastal and estuarine systems, foundation species like seagrasses, mangroves, saltmarshes or corals provide important ecosystem services. Seagrasses are globally declining and their reintroduction has been shown to restore ecosystem functions. However, seagrass restoration is often challenging, given the dynamic and stressful environment that seagrasses often grow in. 2. From our worldwide meta-analysis of seagrass restoration trials (1786 trials), we describe general features and best practice for seagrass restoration. We confirm that removal of threats is important prior to replanting. Reduced water quality (mainly eutrophication), and construction activities led to poorer restoration success than, for instance, dredging, local direct impact and natural causes.
Proceedings of the 11th International Conference on Simulation and Modeling Methodologies, Technologies and Applications
A massive decrease in seagrass coverage in the Philippines has been observed in the past several years due to coastal eutrophication and typhoons. It is key to observe the changes and probable damage in seagrass habitat and develop a way to scientifically back up recovery strategies such as transplantation to increase the probability of rehabilitation success. This study describes the framework development of a transplantation scenario evaluation tool that performs Thalassia hemprichii growth simulation within an uproot site in Palawan as a case study. The growth parameters used include shoot leaf area, spacer length, plastochrone interval, and life expectancy, and horizontal apex density. Base scenario and three scenarios with varying combinations of transplantation density and distribution were applied to the three 4 x 4 grid plots with 24 x 24 cm cell size from classified drone imagery. Results show that transplantation distribution has a greater weight than density with respect to the percent cover responses. Based on the mean and standard deviation of percent cover responses, scenario 1 having 4 transplants with 24 cm intervals is the most suitable for plots 1 and 2, while scenario 2 having 8 transplants (2 per cell) with 24 cm intervals for plot 3.
Limited effects of source population identity and number on seagrass transplant performance
PeerJ, 2017
Global declines in coastal foundation species highlight the importance of effective restoration. In this study, we examined the effects of source population identity and diversity (one vs. three sources per plot) on seagrass (Zostera marina) transplant success. The field experiment was replicated at two locations in Massachusetts with adjacent natural Zostera marina beds to test for local adaptation and source diversity effects on shoot density. We also collected morphological and genetic data to characterize variation within and among source populations, and evaluate whether they were related to performance. Transplants grew and expanded until six months post-transplantation, but then steadily declined at both sites. Prior to declines, we observed variation in performance among source populations at one site that was related to morphological traits: the populations with the longest leaves had the highest shoot densities, whereas the population with the shortest leaves performed the...
A model for the biomass–density dynamics of seagrasses developed and calibrated on global data
BMC Ecology
Background: Seagrasses are foundation species in estuarine and lagoon systems, providing a wide array of services for the ecosystem and the human population. Understanding the dynamics of their stands is essential in order to better assess natural and anthropogenic impacts. It is usually considered that healthy seagrasses aim to maximize their stand biomass (g DW m −2) which may be constrained by resource availability i.e., the local environment sets a carrying capacity. Recently, this paradigm has been tested and reassessed, and it is believed that seagrasses actually maximize their efficiency of space occupation-i.e., aim to reach an interspecific boundary line (IBL)-as quick as possible. This requires that they simultaneously grow in biomass and iterate new shoots to increase density. However, this strategy depresses their biomass potential. Results: to comply with this new paradigm, we developed a seagrass growth model that updates the carrying capacities for biomass and shoot density from the seagrass IBL at each time step. The use of a joint biomass and density growth rates enabled parameter estimation with twice the sample sizes and made the model less sensitive to episodic error in either of the variables. The use of instantaneous growth rates enabled the model to be calibrated with data sampled at widely different time intervals. We used data from 24 studies of six seagrass species scattered worldwide. The forecasted allometric biomass-density growth trajectories fit these observations well. Maximum growth and decay rates were found consistently for each species. The growth rates varied seasonally, matching previous observations. Conclusions: State-of-art models predicting both biomass and shoot density in seagrass have not previously incorporated our observation across many seagrass species that dynamics depend on current state relative to IBL. Our model better simulates the biomass-density dynamics of seagrass stands while shedding light on its intricacies. However, it is only valid for established patches where dynamics involve space-filling, not for colonization of new areas.
International Journal of Ecology, 2012
Donor meadow recovery is important in deciding whether removal of material from natural seagrass meadows is a sustainable activity. Thus an investigation into meadow regrowth was undertaken as part of a large-scale seagrass rehabilitation effort in Cockburn Sound, Western Australia. Several plug extraction configurations were examined in Posidonia sinuosa and Posidonia australis meadows to monitor shoot growth into plug scars. No significant differences in shoot growth between extraction configurations were observed, and both species increased their shoot numbers over two years, with P. sinuosa showing a significantly better recovery rate than P. australis. P. sinuosa shoot recovery into extracted areas was 2.2 ± 0.1 shoots over 24 months, similar to shoot changes in controls (2.3 shoots over the same period). P. australis shoot recovery for each configuration was 0.8 ± 0.3 shoots in 24 months compared with 1.5 shoots in the controls. Based on the number of regrowing shoots, the predicted recovery time of a meadow is estimated at 4 years for P. sinuosa and three years for P. australis. Different plug extraction configurations do not appear to affect meadow recovery, and it can be concluded that established meadows of both species are sustainable providers of planting units for rehabilitation measures.
Effect of Planting Unit Size and Sediment Stabilization on Seagrass Transplants in Western Australia
Restoration Ecology, 2003
The effect of increasing planting unit size and stabilizing sediment was examined for two seagrass planting methods at Carnac Island, Western Australia in 1993. The staple method (sprigs) was used to transplant Amphibolis griffithii (J. M. Black) den Hartog and the plug method was used to transplant A. griffithii and Posidonia sinuosa Cambridge and Kuo. Transplant size was varied by increasing the number of rhizomes incorporated into a staple and increasing the diameter of plugs. Planting units were transplanted into bare sand, back into the original donor seagrass bed, or into a meadow of Heterozostera tasmanica , which is an important colonizing species. Sprigs of A. griffithii were extracted from a monospecific meadow; tied into bundles of 1, 2, 5, and 10 rhizomes; and planted into unvegetated areas. Half the units were surrounded by plastic mesh and the remainder were unmeshed. All treatments were lost within 99 days after transplanting, and although larger bundles survived better than smaller ones, no significant differences could be attributed to the effects of mesh or sprig size. Plugs of P. sinuosa and A. griffithii were extracted from monospecific meadows using polyvinyl chloride pipe of three diameters, 5, 10, and 15 cm, and planted into unvegetated areas nearby. Half the units were surrounded by plastic mesh and the remainder were unmeshed. Posidonia sinuosa plugs were also placed within a meadow of H. tasmanica (Martens ex Aschers.) den Hartog. Only 60% of A. griffithii plug sizes survived 350 days after transplanting back into the donor bed; however, survival of transplants at unvegetated areas varied considerably, and analysis of variance indicated a significant two-way interaction between treatment and plug size. Transplants survived better when meshed (90% survived) and survival improved with increasing plug size. Posidonia sinuosa transplants survived poorly (no plugs survived beyond 220 days in bare or meshed treatments) regardless of size. Survival of 10-and 15-cm plugs was markedly better than the 5-cm plugs in vegetated areas, including the H. tasmanica meadow. The use of large seagrass plugs may be appropriate for transplantation in high-energy wave environments.
Influence of Spacing on Mechanically Transplanted Seagrass Survival in a High Wave Energy Regime
Restoration Ecology, 2003
The wave-exposed nature of much of the southwestern Australian coastline considerably reduces the protective influence of seagrasses, and sediment movement appears to be relatively unaffected by their presence. Present seagrass restoration efforts focus on the deployment of large mechanically transplanted "sods" of seagrass as a means of combating the negative effects of water motion on transplant survival. The aim of this study was to investigate the combined role of wave energy and transplant spacing on sediment movement and transplant survival to provide guidance for seagrass transplantation in areas of high wave energy. One hundred sixty sods (0.25 m 2 ) of seagrass were mechanically extracted from a mixed meadow consisting of Amphibolis griffithii (Cymodoceaceae) and Posidonia coriacea (Posidoniaceae) and planted in a high wave energy site with the treatments configured as three replicates of 16 sods placed in 4 ϫ 4-meter squares at distances of 0.5, 1.0, and 2.0 meters apart. An additional 16 single sods were planted randomly throughout the site. Monitoring was conducted at two monthly intervals and consisted of count-ing the number of sods surviving and measuring the shoot density of seagrass species within each surviving sod. Sediment height was monitored using a series of sediment plates and an electronic sediment level sensor. Sod spacing had no significant effect upon transplant survival, which remained above 90% for 4 months after transplantation and then declined with the onset of winter (June to August). After 14 months individual sod survival was between 9% and 40%. Initial shoot densities were 200 to 500 shoots/m 2 and declined to less than 50 shoots/m 2 . Sediment fluctuations up to 35 cm were noted, occasionally taking place over a matter of hours, and storms during winter caused significantly increased sediment movement. This probably curtailed rhizome extension and prevented the expansion of the transplants. This study indicates that the ability of seagrasses to influence sediment would appear to vary with the prevailing hydrodynamic regime and that a reappraisal of the notion that all seagrass communities trap sediment is necessary.
Restoration Ecology, 2008
Restoration has become an integral part of coastal management as a result of seagrass habitat loss. We studied restoration of the seagrass (Halodule wrightii) near Tampa Bay, Florida. Experimental plots were established in June 2002 using four planting methods: three manually planted and one mechanically transplanted by boat. Seagrass cover was recorded at high resolution (meter scale) annually through July 2005. Natural seagrass beds were concurrently examined as reference sites. We also evaluated the suitability of a commonly used protocol (Braun-Blanquet scores, BB) for comparing the development of seagrass cover using the planting methods and quantifying spatial patterns of cover over time. Results show that BB scores mirrored conventional measures of seagrass characteristics (i.e., shoot counts and above- and belowground biomass) well when BB scores were either low or very high. However, more caution may be required at intermediate cover scores as judged by comparison of BB scores with direct measurement of seagrass abundance. Significant differences in seagrass cover were detected among planting methods and over time (2002–2005), with manual planting of rubber band units resulting in the highest cover. In contrast, the peat pot and mechanical planting methods developed very low cover. Recovery rates calculated from development of seagrass spatial cover were less than those reported for natural expansion. Importantly, time to baseline recovery may be substantially greater than 3 years and beyond standard monitoring timelines. Prolonged recovery suggests that the rate of service returns, critical for estimating compensatory restoration goals under habitat equivalency analysis, may be severely underestimated.
Seagrass Restoration in Australia
This paper will briefly examine the current status of seagrass restoration in Australia and, after some definitions have been dispensed with, describe where most of the efforts have been located and their relative 'success'. Attention is placed more upon the lessons regarding transplant failure we have learned from past studies, as opposed to an in-depth study of each project. In addition, factors contributing to variable success rates with different techniques (seedlings, sprigs and cores) will be highlighted using examples from Western Australia – where many transplant efforts have been located. Examples will then be given of the most recent rehabilitation studies in Western Australia, focusing on mechanical transplanter development, refinement and operation. Concluding comments are then made regarding suggestions to maximise success in future transplantation programmes along with a basic list of requirements.