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R E S E A R C H A R T I C L E
Effects of Sediment Fertilization and Burialon Cymodocea nodosa Transplants; Implicationsfor Seagrass Restoration Under a Changing ClimateElena Balestri1,2 and Claudio Lardicci1
Abstract
Sediment fertilization is recommended for improving sea-grass restoration efforts, but few studies have evaluated theefficacy of such practice. Increasing storm frequency due toglobal change could lead to greater sediment mobilization.Understanding how this alteration will interact with fertil-ization to affect transplants is essential for future restora-tion planning. We examined the individual and combinedeffects of nutrients (ambient vs. repeated addition) andburial (control vs. increased frequency and intensity) onthe performance and biomass partitioning of transplantsof the seagrass Cymodocea nodosa at two sites within anorth-western Mediterranean meadow. Fertilization stim-ulated the production of shoots, total biomass, and branch-ing. Burial increased leaf sheath length in one site whilereduced shoot number, leaf number, leaf sheath length,total biomass, net shoot gain, and root-to-shoot ratio in theother site. Regardless of the site, fertilization and burial
interaction reduced the length of vertical internodes andhorizontal rhizomes, and the net shoot gain. Our researchdemonstrates that sediment fertilization ensures rapid col-onization of restoration sites, providing C. nodosa plantsup to eight times larger than controls in one growing sea-son. However, it also indicates that interaction of increasedburial and nutrients reduced the gain in terms of veg-etative expansion and depressed vertical growth, makingplants more vulnerable to subsequent disturbances. There-fore, seagrass restoration practitioners should account forchanges in sediment elevation at transplanting sites whenplanning restoration programs and carefully evaluate theopportunity of applying fertilizers in sites subjected togreater sediment accumulation to avoid failure.
Key words: global change, interactive effect, nutrientaddition, revegetation, seagrass transplantation, sedimentdeposition.
Introduction
Seagrasses are among the most productive ecosystems ofthe world (Duarte & Chiscano 1999) and provide multipleessential services (Costanza et al. 1997). However, seagrassmeadows are declining worldwide (Waycott et al. 2009), andpredictions indicate that the rate of decline will accelerate inthe next century due to global change (Jorda et al. 2012).Given the scale of habitat loss and the value of seagrasses,there is considerable interest in restoring damaged meadows.Although progress has been made in developing revegetativetechniques (Fonseca et al. 1998; Piazzi et al. 1998; Palinget al. 2009; Golden et al. 2010; Orth et al. 2012; Reynoldset al. 2012), for most species the revegetation success isstill limited by slow colonization rates and vulnerability tostresses (Balestri et al. 1998, 2011; Lepoint et al. 2004).Because transplants may suffer from nutrient deficiency due
1Department of Biology, University of Pisa, Via Derna 1, Pisa, 56126, Italy2Address correspondence to E. Balestri, email [email protected]
© 2013 Society for Ecological Restorationdoi: 10.1111/rec.12052
to the lack of physiological integration and immature rootsystem (Lepoint et al. 2004; Balestri & Lardicci 2006; Balestriet al. 2010), addition of fertilizers to sediments has beenrecommended for transplantation (Fonseca et al. 1994).
Experiments have shown seagrass growth limitation bynutrients, e.g. nitrogen (N) and/or phosphorus (P) (Duarte1990; Short et al. 1990; Perez et al. 1991; Fourqurean et al.1992; Duarte & Sand-Jensen 1996; Balestri et al. 2009), andattempts have been made to examine the efficacy of fer-tilization on transplants (i.e. Kenworthy & Fonseca 1992;Sheridan et al. 1998; Worm & Reusch 2000; Hovey et al.2012). These studies suggest caution in applying fertiliz-ers to sediments because nutrient status, light and reducedsediment redox conditions at restoration sites could inter-fere with nutrient uptake and assimilation, resulting in littleor no increase in transplant survival and growth (Peraltaet al. 2003; Cambridge & Kendrick 2009). However, it isunknown whether fluctuations in sediment elevation mayalso influence the growth response of transplants to nutrientenrichment.
In sandy environments, storm disturbance may frequentlyexpose seagrasses to burial by sediments. Seagrasses may
240 Restoration Ecology Vol. 22, No. 2, pp. 240–247 MARCH 2014
Fertilizer and Burial Effect on Sea Grass Transplant
respond to gradual burial through an increase in growthof vertical structures (internodes, leaves and leaf sheaths;Marba & Duarte 1994; Marba & Duarte 1995), but sud-den burial events may cause high mortality rates in mostspecies (Cabaco et al. 2008; Manzanera et al. 2011). Trans-plants are particularly susceptible to burial because their car-bohydrate reserves may be insufficient to support the highgrowth rates required for a shoot to emerge from burial.Hence, their capacity to cope or recover from burial couldbe improved by addition of nutrients to sediments. How-ever, modification of the sediment plant micro-environmentand light intensity reduction following burial could affect rootrespiration and inhibit nutrient uptake by transplants. Pre-dictions indicate that storm frequency will increase due toglobal warming (Young et al. 2011) leading to the poten-tial for recurrent deeper burial. Therefore, understanding howthe interaction of fertilization and burial influences transplantgrowth is critically important in planning future restorationinterventions.
The aim of this study was to evaluate the effectiveness offertilizer application for seagrass restoration under increasedsediment accumulation conditions. Specifically, we examinedthe performance and biomass allocation of Cymodoceanodosa (Ucria) Ascherson transplants either subjected to theapplication of fertilizer to sediments or left at ambient nutrientavailability, and exposed to two burial regimes over theirsecond growing season. This small relatively fast-growingspecies was selected as a model because of growing interestin restoring damaged meadows (Zarranz et al. 2010; Balestri& Lardicci 2012). As environmental conditions may varywithin a meadow (Balestri et al. 2003; Balestri 2004), theexperiment was conducted in two sites of a north-westernMediterranean meadow. To minimize possible confoundingdue to different plant nutritional status and avoid any impacton existing populations, fragments from cultivated plantswere used as transplants.
Methods
Study Locality and Transplantation Procedure
The experiment was conducted within a Cymodocea nodosameadow located at Rosignano Solvay (Italy, 43◦19′01.75N,10◦27′52.76E). The substrate is composed of rock intermingledwith patches of carbonate sand. The tide amplitude is typicallylow. Sea surface water temperature varied from 12◦C in winterto 27◦C in summer and salinity ranged from 37.5 to 38. InJune 2010, apical rhizome fragments of C. nodosa (8 cm inlength, with two shoots) were excised from nursery grownplants (Balestri & Lardicci 2012) and transplanted in two sites,hundreds of meters apart, at similar depth (0.20–0.30 m). Ineach site, fragments (16) were planted at randomly chosenplaces several meters apart using galvanized iron staples thatwere removed four months after planting. The species showsa unimodal annual growth cycle, with a peak during Juneand July and a cessation of rhizome growth from Octoberto January (Caye & Meinesz 1985).
Experimental Design
In June 2011, successfully established plants were assignedat random to one of four experimental treatments accordingto a factorial combination of fertilization (two levels, ambientnutrient vs. nutrient addition) and burial regime (two levels,control vs. increased frequency and intensity). Since somefragments failed to initiate patches, the number of experi-mental plants per site was reduced to 12. There were threereplicate plants in each site per treatment combination. In thefertilizer addition treatments, one stick of slow-release fertil-izer (COMPO, K + S Agricoltura Spa, N-to-P ratio of 13:6 g/g)was inserted into the sediment close to each plant (1 g of fer-tilizer per plant) using plastic tubes (3 mm in diameter) at10 cm below the sediment surface. The tubes were removedsoon after fertilizer application and the hole made by tubeswas covered with the substrate. Before the experiment (May2011), a nutrient release test was made to check the appliednutrient concentration. Fertilizer sticks were inserted into sixunvegetated plots (30 × 30 cm) randomly chosen within themeadow, and two samples of sediment were collected in eachplot with minicores (2.5 cm of diameter) in two separate dates,3 days and 6 days after fertilizer addition, respectively. Threedifferent fertilized plots were chosen on each date. Ambi-ent sediment nutrient concentration was also determined inthree randomly chosen plots. Samples from each plot werehomogenized to reduce the effect of the nutrient patchinessin the sediment, and analyzed by standard colorimetric meth-ods for nutrient content. Results showed that 3 days afterfertilization, the concentration of N (0.23 ± 0.001 mg/g drysediment) and P (0.21 ± 0.007 mg/g dry sediment) was sig-nificantly higher (t-test for independent samples, t = 5.29,p < 0.01 for N; t = 4.94, p < 0.05 for P) than that ambi-ent one (0.13 ± 0.01 N mg/g dry sediment and 0.16 ± 0.006 Pmg/g dry sediment), but after 6 days the concentrations of N(0.18 ± 0.02 mg/g dry sediment) and P (0.18 ± 0.01 mg/g drysediment) were similar to those in unfertilized ones (t = 3.04,p = 0.12 for N and t = 1.14, p = 0.45 for P). Due to the rapidloss of nutrients, the fertilization procedure was repeated everyweek over the experiment (i.e. seven times). Each nutrientaddition supplied 1.44 g N and 0.66 g P to each plot, cor-responding to a total loading of 10 g N m−2 and 4.6 g P m−2
which was within the range of annual nutrient requirement forseagrass growth (6.6 to 50 g N and 0.7 to 5.5 g P m−2 (Hem-minga et al. 1991; Erftemeijer & Middelburg 1995). This loadwas established to ensure that the level of P was not limitingas previous studies have shown that the summer growth ofC. nodosa is strongly P-limited in carbonate sediments due tobinding of phosphate in the sediment (Perez et al. 1991). Inplants maintained at ambient nutrient conditions, no fertilizerwas added and the sediment was punched with a plastic tubeto simulate stick insertion.
In the burial treatments, sediment was manually spread overplants to reach a height of 4 cm (equivalent to 90–100% ofplant height), corresponding to twice the maximum sedimentdeposition recorded at the study locality in spring–summer(unpublished study). No container or frame was used tomaintain initial burial height to avoid any potential effect
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on plant growth, as well as to realistically simulate burialevents, which are usually followed by sediment resuspension.At weekly intervals, a ruler was gently pushed into the addedunconsolidated sediment up to the transplant rhizome stratumso to measure deviations in height from the experimentallyimposed level. Fresh sediment was re-added or removedto re-establish the burial level. In total, eight burial eventswere imposed to transplants. This frequency was to twotimes that of storms (with daily wind speed >10.8 m/s,corresponding to waves at least 3–4 m in height according tothe Beaufort scale) recorded in summer in the last decade atthe study locality (data available from http://www.ilmeteo.it),and considered strong enough to cause complete burial. Thesediment was collected from the shoreline in front of themeadow, homogenized and sieved (through a 1 mm mesh)to remove extraneous material prior to the use. In plantsmaintained at ambient sedimentation, no sediment was added.
Before the start of the experiment, morphological charac-teristics (number of shoots, horizontal rhizome length, numberand length of branches, number of leaves per shoot and lengthof the longest leaf) were measured. At the end of the experi-ment (August 2011), plants were carefully extracted from thesubstrate and transported to the laboratory for measurementsof morphological characteristics (number of live shoots perplant, length of internodes on vertical shoots, horizontal rhi-zome length, number and mean length of branches, number ofleaves per shoot and length of longest leaf and sheath). Verti-cal internode length was estimated by measuring the length ofthe three youngest internodes (i.e. nearer to the leaf meristem)produced by one randomly chosen shoot per plant. Biomassesof separate structures (roots, rhizomes, and shoots) were alsodetermined after drying plants to constant weight at 60◦C (dryweight, DW) and root-to-shoot ratio was calculated by divid-ing belowground by aboveground biomass (g/g DW). Finally,shoot mortality was determined as percentage of shoots thathad died of the total number of shoots produced by each plant,and the net shoot gain was calculated as difference betweenthe number of newly produced shoots (i.e. recruitment) andthe number of dead shoots per plant.
Statistical Analysis
To check for homogeneity in morphology of plants assigned tothe different treatments in each site at the start of the experi-ment, initial morphological data were analyzed by using multi-variate analyses of variance by permutation (PERMANOVA)according to a mixed model univariate analysis of variance(ANOVA) design that included three orthogonal factors, fer-tilization (two levels, fixed), burial (two levels, fixed), and site(two levels, random). The same analysis was performed withdata recorded at the end of the experiment.
Prior to PERMANOVA, data were normalized and dissim-ilarities calculated as Euclidean distances. Significance lev-els were calculated from 9,999 permutations of the residualsunder the reduced model. Whenever possible, post hoc pool-ing of mixed terms of the model was performed to increasethe analysis power. Since significant effects were detected
in PERMANOVA, separate ANOVAs followed by Student-Newman-Keuls (SNK) test at p < 0.05 were performed forthe investigated variables to determine any significant dif-ferences between means of the different treatments. SeparateANOVAs were also conducted on total plant biomass, root-to-shoot ratio, and net shoot gain. Prior to performing theANOVAs, data were tested for normality and homoscedastic-ity, and transformed if necessary. Whenever data transforma-tion failed to achieve homogeneity of variances, the analysiswas performed on untransformed data with (α = 0.01). Posthoc pooling of mixed interaction terms was applied wheneverpossible. PERMANOVA was run through PRIMER v6 withPERMANOVA software while R version 2.12.2 software andR package “GAD” were used for ANOVA.
Results
Before treatment application, plants randomly assigned tothe different treatments and site did not statistically differ inmorphology (F [3,16] = 1.32, p = 0.39; F [1,16] = 0.76 p = 0.58).They had 5.9 ± 0.4 (mean ± SD) shoots, 2.3 ± 0.1 leavesper shoot and 1.5 ± 0.4 branches. All plants survived tothe end of the experiment. At whole plant level, both themain effect of fertilization (F [1,16] = 4.2, p = 0.009) and theinteraction between burial and site (F [1,16] = 4, p = 0.006),were significant. For five plant characteristics, the maineffect of fertilization was significant (Figs. 1 & 2). Fertilizedplants had on average a higher number of live shoots(F [1,16] = 9.1, p < 0.01) and branches (F [1,16] = 7.3, p < 0.05),longer branches (F [1,16] = 5.1, p < 0.05) and greater root(F [1,16] = 5.9, p < 0.05) and rhizome biomass (F [1,16] = 9.6,p < 0.01) that those at ambient nutrient conditions. For sixcharacteristics, the interaction between increased burial andsite was significant (non-additive effect). Buried plants hada lower number of shoots (F [1,16] = 5.4, p < 0.05) and leavesper shoot (F [1,16] = 6.6, p < 0.05), shorter leaves (F [1,16] = 6,p < 0.05) and leaf sheaths (F [1,16] = 18.5, p < 0.001),and smaller shoot (F [1,16] = 20.3, p < 0.001) and rhizomebiomasses (F [1,16] = 5.3, p < 0.05) compared to unburied onesin one site (thereafter referred as Site 1; Figs. 1 & 2). Incontrast, in the other site (Site 2), buried plants had longerleaf sheaths and leaves than unburied ones (Fig. 1). Buriedplants grown in Site 2 also had a higher number of leaves, andlonger leaves, and sheaths than those in Site 1 (Fig. 1). Fortwo characteristics, vertical internode length and horizontalrhizome length, the interaction between fertilization andburial was significant (F [1,16] = 6.3, p < 0.05; F [1,16] = 4.4,p < 0.05). Under enhanced nutrient availability, unburiedplants produced longer horizontal rhizomes and vertical rhi-zome internodes than buried ones irrespective of site (Fig. 1).Under buried conditions, fertilized plants formed shortervertical internodes than unfertilized ones at both sites (Fig. 1).
For total biomass, both the main effect of fertilization(F [1,16] = 0.2, p < 0.05) and the interaction between burial andsite were significant (F [1,16] = 6.4, p < 0.05). Fertilized plantshad a larger biomass than those grown at ambient nutrient
242 Restoration Ecology MARCH 2014
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Figure 1. Morphological variables of Cymodocea nodosa transplants subjected to the individual and combined effects of nutrients (ambient vs. repeatedaddition) and burial (control vs. increased frequency and intensity) in each of the two restoration sites (Sites 1 and 2). Different letters above columnsindicate significant differences between burial levels (capital letters) for each of two nutrient levels and between nutrient levels (lowercase letters) for eachof two burial levels in each site. N−, ambient nutrients; N+, nutrients added; NB, no burial, control; B, increased burial. Bars are mean ± 1 SE (n = 3).
conditions. Unburied plants produced a larger biomass thanburied ones only in Site 1 (Fig. 3). A significant interactionbetween site and increased burial treatment was also detectedfor root-to-shoot ratio (F [1,16] = 19.4, p < 0.001). Higher root-to-shoot ratio in buried plants compared to unburied ones was
observed in Site 1. Under burial conditions the plant root-to-shoot ratio in Site 1 was higher than that in Site 2 (Fig. 3)due to higher shoot mortality. Finally, a significant interactionbetween fertilization and burial (F [1,16] = 6.4, p < 0.05) aswell as between burial and site (F [1,16] = 4.6, p < 0.05) was
MARCH 2014 Restoration Ecology 243
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Figure 2. Biomass of shoots, rhizomes, and roots of Cymodocea nodosatransplants subjected to the individual and combined effects of nutrients(ambient vs. repeated addition) and burial (control vs. increasedfrequency and intensity) at the two restorations sites (Sites 1 and 2).Different letters above columns indicate significant differences betweenburial levels (capital letters) for each of two nutrient levels and betweennutrient levels (lowercase letters) for each of two burial levels in eachsite. N−, ambient nutrients; N+, nutrients added; NB, no burial, control;B, increased burial. Bars are mean ± 1 SE (n = 3).
detected for net shoot gain. Fertilized plants, when unburied,had a greater net increase in shoot number than thoseunfertilized irrespective of site. Fertilized unburied plants alsohad greater net shoot gain than those buried (Fig. 3). Buriedplants had lower net increase in shoot number comparedto unburied ones but only in Site 1. Because of sedimentresuspension by wind generated waves, sediment height waslower than that experimentally imposed (4 cm). Sedimentheight in Site 1 was on average 0.5–1 cm higher than in Site2 from July to the end of the experiment (Fig. 4).
Discussion
This is the first field study to address the effect of fertilizerapplication and its potential interaction with increased burial
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Figure 3. Total biomass, root-to-shoot ratio, shoot mortality, and netshoot gain of Cymodocea nodosa transplants subjected to the individualand combined effects of nutrients (ambient vs. repeated addition) andburial (control vs. increased frequency and intensity) at the tworestorations sites (Sites 1 and 2). Different letters above columns indicatesignificant differences between burial levels (capital letters) for each oftwo nutrient levels and between nutrient levels (lowercase letters) foreach of two burial levels in each site. For shoot mortality, treatmenteffects were not reported because data were not analyzed. N−, ambientnutrients; N+, nutrients added; NB, no burial, control; B, increasedburial. Bars are mean ± 1 SE (n = 3).
severity for seagrass restoration in the context of changingsedimentary conditions due to global change. The study pro-vides evidence that Cymodocea nodosa transplants respondquickly to sediment fertilization. A consistent increase in themean number of shoots and branches, and total biomass pro-duction was found in transplants under enhanced nutrient
244 Restoration Ecology MARCH 2014
Fertilizer and Burial Effect on Sea Grass Transplant
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Figure 4. Variations in artificially imposed burial height (4 cm, dottedline) at the two restorations sites (Sites 1 and 2) during the experimentalperiod. Bars are mean ± 1 SE (n = 6).
conditions compared to those grown at ambient conditions.These responses are in line with previous studies whichshowed stimulating effects of sediment fertilization on sea-grass meadows (Short et al. 1990; Perez et al. 1991; Ken-worthy & Fonseca 1992; Touchette & Burkholder 2000),and they confirm the hypothesis that the growth C. nodosatransplants was strongly limited by nutrients at least intheir first years. No shift in biomass allocation to shootsreported in these previous studies was detected here. This sug-gests that C. nodosa could have evolved a form-conservativestrategy for maximizing exploitation of resources and hor-izontal space occupation under favorable growing condi-tions during the early phases of establishment, similarly tosome clonal plants growing on coastal sand dunes (Frosiniet al. 2012).
The responses of C. nodosa to increased burial weresite-dependent and presumably related to hydrodynamics.Significant stimulatory burial effects on leaf and sheath growthwere evident in Site 2 where sediment resuspension resulted inlower sediment height (1.5–3 cm) than that imposed. Previousstudies have shown that C. nodosa may tolerate sedimentdeposition rate of 1–2 mm/day caused by the continuousmigration of submerged sand dunes in natural stands (Marba &Duarte 1995), but sudden burial events derived from storms oranthropogenic activities may cause substantial shoot mortalityand alteration of population dynamics (Cabaco et al. 2010).Compensatory growth responses (increased rates of verticaland horizontal rhizome elongation, leaf turnover and leafsheath growth) have been observed in the surviving shootsonly below the 50% burial threshold (4 cm; Marba & Duarte1994). Thus, the positive effects detected here in Site 2 wereconsistent with previous reports. On the other hand, negativeburial effects on number of shoots, leaf sheath and leaves, leafnumber, biomass production, root-to-shoot ratio and net shootgain were found in Site 1 where sediment height remainedclose (3.5–4.5 cm) to that imposed, and thus equal or slightlyhigher than the 50% threshold of the species.
Although the variability between sites did not permit anunequivocal test of burial on transplants, the interaction offertilization and burial was significant for some of the plantgrowth-related variables analyzed regardless of site. Specif-ically, under enhanced nutrient conditions unburied plantsshowed a nearly 8-fold increase in mean horizontal rhizomelength (117 cm vs. 14 cm) and up to 10 times higher netincrease in shoot number (70 vs. seven shoots per plant)compared to buried ones. This indicates that transplants wereunable to react to increased nutrient availability through vege-tative expansion when buried, presumably because insufficientenergy and C-skeletons to meet the enhanced demand result-ing from increased nutrient assimilation under the reducedlight conditions imposed by burial. Moreover, fertilizationdepressed internode elongation in vertical rhizomes underburied conditions, and thus diminished the ability of trans-plants to adjust their height to subsequent changes in thesediment environment. Such inhibitory effect could be dueto the production of toxic compounds, such as sulfides, underreduced oxygen availability and higher temperatures in sedi-ments due to burial, which have inhibitory effects on apicalmeristems of short shoots in seagrasses (Peralta et al. 2003;Borum et al. 2005; Holmer & Kendrick 2013).
In summary, the present experiment demonstrates thatapplication of fertilizers to sediments allows a clear gainin terms of faster substrate cover in transplantation sites,providing higher productive and larger C. nodosa plants inonly one growing season in absence of sudden burial episodes.This contrast with previous studies which reported no effectof fertilizers on seagrass transplants (Kenworthy & Fonseca1992; Worm & Reusch 2000; Cambridge & Kendrick 2009).The frequency and method of application employed here maybe not practical of large-scale transplantation due to increasedcosts (the cost estimate for fertilizing 10,000 transplant unitswas about 19,200 E). However, this study was designed toexamine interactive effects of fertilizers and burial on plants,rather than to evaluate whether the fertilization practice canbe scaled up to a commercial application. Additional studiesshould focus on how to reduce the frequency of fertilizeraddition and/or to develop methods that ensure slow releaseor enhanced permanence of nutrients into the root zone. Thisstudy also indicates that sediment fertilization requires specialattention to local sedimentary dynamics. Guidelines currentlyproposed to identify optimal seagrass restoration sites arebased on the evaluation of a particular set of environmentalconditions that include sediment geochemistry and movement(van Katwijk et al. 2009; Cunha et al. 2012) under theimplicit assumption that such conditions are consistent at thesites. However, storm frequency will increase in the comingdecades and cause greater sediment mobility. Sudden burialevents, even of moderate intensity but occurring at a higherfrequency than presently observed, could counteract somebenefits from fertilization, providing lower benefit in termsof vegetative expansion. More importantly, suppression ofvertical growth due to burial and fertilization interactioncould make transplants more vulnerable to subsequentdisturbances.
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Implications for Practice
• The success of Cymodocea nodosa planting may beimproved by fertilizer application, but cost benefit anal-ysis must be considered prior to undertaking restorationefforts.
• Species-specific and location-specific effects of fertiliz-ers and impacts of sediments associated with climatechange or other factors, like dredging, harbor construc-tion, and beach replenishing need to be evaluated priorto planning seagrass restoration.
• Fertilizer application in sites subjected to frequent burialshould be avoided. Alternatively, some kind of structurefor protecting transplants against excessive sedimentdeposition during the early stages of restoration isrecommended.
Acknowledgments
We thank the Solvay Chimica Italia (Rosignano Solvay, Italy)for financially supporting parts of the study. Many thanksare due to Silvia Frosini and Flavia Vallerini for technicalassistance throughout the experiment.
LITERATURE CITEDBalestri, E. 2004. Flowering of the seagrass Posidonia oceanica in a north-
western Mediterranean coastal area: temporal and spatial variations.Marine Biology 145:61–68.
Balestri, E., and C. Lardicci. 2006. Stimulation of root formation in Posidoniaoceanica cuttings by application of auxins (NAA and IBA). MarineBiology 149:393–400.
Balestri, E., and C. Lardicci. 2012. Nursery-propagated plants from seed: anovel tool to improve the effectiveness and sustainability of seagrassrestoration. Journal of Applied Ecology 49:1426–1435.
Balestri, E., L. Piazzi, and F. Cinelli. 1998. Survival and growth of transplantedand natural seedlings of Posidonia oceanica (L.) Delile in a damagedcoastal area. Journal of Experimental Marine Biology and Ecology228:209–225.
Balestri, E., F. Cinelli, and C. Lardicci. 2003. Spatial variation in Posidoniaoceanica structural, morphological and dynamic features in a northwest-ern Mediterranean coastal area: a multi-scale analysis. Marine EcologyProgress Series 250:51–60.
Balestri, E., S. Gobert, G. Lepoint, and C. Lardicci. 2009. Seed nutrientcontent and nutritional status of Posidonia oceanica seedlings in thenorth western Mediterranean Sea. Marine Ecology Progress Series388:99–109.
Balestri, E., F. Vallerini, and C. Lardicci. 2010. Effect of seed density andsediment nutrient heterogeneity on recruitment and early patch growthin the seagrass Cymodocea nodosa . Marine Ecology Progress Series417:63–72.
Balestri, E., F. Vallerini, and C. Lardicci. 2011. Storm-generated fragments ofthe seagrass Posidonia oceanica from beach wrack—a potential sourceof transplants for restoration. Biological Conservation 144:1644–1654.
Borum, J., O. Pedersen, T. M. Greve, T. A. Frankovich, J. C. Zieman, J. W.Fourqueran, and C. J. Madden. 2005. The potential role of plant oxygenand sulphide dynamics in die-off events of the tropical seagrass, Thalassiatestudinum . Journal of Ecology 93:148–158.
Cabaco, S., R. Santos, and C. M. Duarte. 2008. The impact of sediment burialand erosion on seagrasses: a review. Estuarine, Coastal and Shelf Science79:354–366.
Cabaco, S., O. Ferreira, and R. Santos. 2010. Population dynamics of theseagrass Cymodocea nodosa in Ria Formosa lagoon following inletartificial relocation. Estuarine, Coastal and Shelf Science 87:510–516.
Cambridge, M. L., and G. A. Kendrick. 2009. Contrasting responses ofseagrass transplants (Posidonia australis) to nitrogen, phosphorus andiron addition in an estuary and a coastal embayment. Journal ofExperimental Marine Biology and Ecology 37:34–41.
Caye, G., and A. Meinesz. 1985. Observations on the vegetative development,flowering and seeding of Cymodocea nodosa (Ucria) Ascherson, on theMediterranean coast of France. Aquatic Botany 22:277–289.
Costanza, R., R. d’Arge, R. deGroot, S. Farber, M. Grasso, B. Hannon, et al.1997. The value of the world’s ecosystem services and natural capital.Nature 387:253–260.
Cunha, A. H., N. Marba, M. M. van Katwijk, C. Pickerell, M. Henriques, G.Bernard, M. A. Ferreira, S. Garcia, J. M. Garmendia, and P. Manent.2012. Changing paradigms in seagrass restoration. Restoration Ecology20:427–430.
Duarte, C. M. 1990. Seagrass nutrient content. Marine Ecology Progress Series6:201–207.
Duarte, C. M., and C. L. Chiscano. 1999. Seagrass biomass and production: areassessment. Aquatic Botany 65:59–174.
Duarte, C. M., and K. Sand-Jensen. 1996. Nutrient constraints on establishmentfrom seed and on vegetative expansion of the Mediterranean seagrassCymodocea nodosa . Aquatic Botany 54:279–286.
Erftemeijer, P. L. A., and J. J. Middelburg. 1995. Mass balance constraints onnutrient cycling in tropical seagrass beds. Aquatic Botany 50:21–36.
Fonseca, M. S., W. J. Kenworthy, F. X. Courtney, and M. O. Hall. 1994. Sea-grass planting in the southeastern United States: methods in acceleratinghabitat development. Restoration Ecology 2:198–212.
Fonseca, M. S., W. J. Kenworthy, and G. W. Thayer. 1998. Guidelinesfor the conservation and restoration of seagrasses in the United Statesand adjacent waters. NOAA Coastal Ocean Program, Silver Spring,Maryland.
Fourqurean, J. W., J. C. Zieman, and G. V. N. Powell. 1992. Phosphoruslimitation of primary production in Florida Bay: Evidence from the C:N:Pratios of the dominant seagrass Thalassia testudinum . Limnology andOceanography 37:162–171.
Frosini, S., C. Lardicci, and E. Balestri. 2012. Global change and response ofcoastal dune plants to the combined effects of increased sand accretion(burial) and nutrient availability. PLoS One 7:e47561.
Golden, R. R., K. E. Busch, L. P. Karrh, T. A. Parham, M. J. Lewandowski, andM. D. Naylor. 2010. Large-scale Zostera marina (eelgrass) restoration inChesapeake Bay, Maryland, USA. Part II: a comparison of restorationmethods in the Patuxent and Potomac Rivers. Restoration Ecology18:501–513.
Han, Q., T. J. Bouma, F. G. Brun, W. Suykerbuyk, and M. M. vanKatwijk.2012. Resilience of Zostera noltii to burial or erosion disturbances.Marine Ecology-Progress Series 449:133–143.
Hemminga, M. A., P. G. Harrison, and F. vanLent. 1991. The balance ofnutrient losses and gains in seagrass meadows. Marine Ecology ProgressSeries 71:85–96.
Holmer, M., and G. A. Kendrick. 2013. High sulfide intrusion in five temperateseagrasses growing under contrasting sediment conditions. Estuaries andCoasts 36:116–126.
Hovey, R. K., M. L. Cambridge, and G. A. Kendrick. 2012. Season andsediment nutrient additions affect root architecture in the temperateseagrasses Posidonia australis and P. sinuosa . Marine Ecology ProgressSeries 446:23–30.
Jorda, G., N. Marba, and C. M. Duarte. 2012. Mediterranean seagrass vulner-able to regional climate warming. Nature Climate Change 2:821–824.
van Katwijk, M. M., A. R. Bos, V. N. deJonge, L. S. A. M. Hanssen, D. C. R.Hermus, and D. J. De Joung. 2009. Guidelines for seagrass restoration:importance of habitat selection and donor population, spreading ofrisks, and ecosystem engineering effects. Marine Pollution Bulletin58:179–188.
246 Restoration Ecology MARCH 2014
Fertilizer and Burial Effect on Sea Grass Transplant
Kenworthy, W. J., and M. S. Fonseca. 1992. The use of fertilizer to enhancegrowth of transplanted seagrasses Zostera marina L. and Halodulewrightii Aschers. Journal of Experimental Marine Biology and Ecology163:141–161.
Lepoint, G., D. Vangeluwe, M. Eisinger, M. Paster, P. vanTreeck, J. M.Bouquegneau, and S. Gobert. 2004. Nitrogen dynamics in Posidoniaoceanica cuttings: implications for transplantation experiments. MarinePollution Bulletin 48:465–470.
Manzanera, M., T. Alcoverro, F. Tomas, and J. Romero. 2011. Response ofPosidonia oceanica to burial dynamics. Marine Ecology Progress Series423:47–56.
Marba, N., and C. M. Duarte. 1994. Growth response of the seagrassCymodocea nodosa to experimental burial and erosion. Marine EcologyProgress Series 107:307–311.
Marba, N., and C. M. Duarte. 1995. Coupling of seagrass (Cymodocea nodosa)patch dynamics to subaqueous dune migration. Journal of Ecology83:381–389.
Orth, J. R., K. A. Moore, S. R. Marion, D. J. Wilcox, and D. B. Parrish.2012. Seed addition facilitates eelgrass recovery in a coastal bay system.Marine Ecology Progress Series 448:177–195.
Paling, E. I., M. Fonseca, M. M. vanKatwijk, and M. vanKeulen. 2009. Sea-grass restoration. Pages 687–713 in G. Perillo, E. Wolanski, D. Cahoonand M. Brinson, editors. Coastal wetlands: an integrated ecosystemapproach. Elsevier, Amsterdam, the Netherlands.
Peralta, G., T. J. Bouma, J. vanSoelen, J. L. Perez-Llorens, and I. Hernandez.2003. On the use of sediment fertilization for seagrass restoration: amesocosm study on Zostera marina L. Aquatic Botany 75:95–110.
Perez, M., J. Romero, C. M. Duarte, and K. Sand-Jensen. 1991. Phosphoruslimitation of Cymodocea nodosa growth. Marine Biology 109:129–133.
Piazzi, L., E. Balestri, M. Magri, and F. Cinelli. 1998. Experimental trans-planting of Posidonia oceanica (L.) Delile into a disturbed habitat in theMediterranean Sea. Botanica Marina 41:593–601.
Reynolds, L. K., M. Waycott, K. J. McGlathery, R. J. Orth, and J. C. Zieman.2012. Eelgrass restoration by seed maintains genetic diversity: casestudy from a coastal bay system. Marine Ecology Progress Series 448:223–233.
Sheridan, P., G. McMahan, K. Hammerstrom, and W. Pulich. 1998. Factorsaffecting restoration of Halodule wrightii to Galveston Bay, Texas.Restoration Ecology 6:144–158.
Short, F. T., W. C. Dennison, and D. G. Capone. 1990. Phosphorus-limitedgrowth of the tropical seagrass Syringodium filiforme in carbonatesediments. Marine Ecology Progress Series 62:169–174.
Touchette, B. W., and J. M. Burkholder. 2000. Review of nitrogen andphosphorus metabolism in seagrasses. Journal of Experimental MarineBiology and Ecology 250:133–167.
Waycott, M., C. M. Duarte, T. J. B. Carruthers, R. Orth, W. Dennison, S.Olyarnik, et al. 2009. Accelerating loss of seagrasses across the globethreatens coastal ecosystems. Proceedings of the National Academy ofSciences of the United States of America 106:12377–12381.
Worm, B., and T. B. H. Reusch. 2000. Do nutrient availability and plant densitylimit seagrass colonization in the Baltic Sea? Marine Ecology ProgressSeries 200:139–166.
Young, I. R., S. Zieger, and A. V. Babanin. 2011. Global trends in wind speedand wave height. Science 332:451–455.
Zarranz, M. E., N. Gonzalez-Henríquez, P. García-Jimenez, and R. R. Robaina.2010. Restoration of Cymodocea nodosa (Uchria) Ascherson seagrassmeadows through seed propagation. Germination in vitro, seedlingsculture and field transplants. Botanica Marina 53:173–181.
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