Ecological Engineering 18 (2001) 107–113

Short communication

Improving mechanical seagrass transplantation

Eric I. Paling a,*, Mike van Keulen a, Karen D. Wheeler a, Jim Phillips b,Roger Dyhrberg c, Des A. Lord d

a Marine and Freshwater Research Laboratory, En�ironmental Science, Murdoch Uni�ersity, Murdoch, WA 6150, Australiab Ocean Industries (WA) Pty. Ltd., 8 Sparks Road, Henderson, WA 6166, Australia

c Di�er I Di�er II Co., Lot 30, Satino�er Way, Wandi, WA 6167, Australiad DA Lord and Associates, PO Box 3172, LPO Broadway, Nedlands, WA 6009, Australia

Received 25 August 2000; received in revised form 14 December 2000; accepted 18 December 2000

Abstract

Until recently seagrass transplantation efforts have met with limited success in areas with high wave energies.Survival in Western Australia has been markedly improved by the deployment of large, mechanically transplantedunits which provide sufficient anchorage to overcome water motion. ECOSUB1 was an underwater seagrassharvesting and planting machine designed to extract and plant large seagrass units with minimal disturbance. Over2000 sods have been planted, with an average survival of approximately 70% over 3 years. New machines(ECOSUB2) have now been constructed to improve efficiency; these are located semi-permanently on the seafloor andallow for concurrent seagrass harvesting and planting. © 2001 Elsevier Science B.V. All rights reserved.

Keywords: Seagrass; Western Australia; Transplantation

www.elsevier.com/locate/ecoleng

1. Introduction

Environmental agencies and regulatory authori-ties assessing activities with potential to impactcoastal environments have become increasinglyconcerned with the loss of seagrass, and the provi-sion for some form of seagrass rehabilitation is

often a condition for project approval (Gordon,1996). Considerable research has taken place inFrance using Posidonia oceanica, and the USAusing Zostera marina, with varying degrees ofsuccess over the last few decades (Molenaar et al.,1993; Fonseca et al., 1998). Far less success hasbeen achieved in Western Australia where ex-posed seagrass habitats and species, such as Am-phibolis sp. and Posidonia sp., are considerablydifferent in morphology from those in the north-ern hemisphere. The apparent reason for failure ishigh water motion, which, combined with insuffi-

* Corresponding author. Tel.: +61-8-93606121; fax: +61-8-93104997.

E-mail address: paling@essun1.murdoch.edu.au (E.I. Pal-ing).

0925-8574/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.

PII: S 0925 -8574 (01 )00065 -9

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cient anchoring of the planted seagrass, results inthe removal of planted units regardless of themethod employed (Lord et al., 1999). The mostsuccessful method to date has used cores of sea-grass containing intact rhizomes and sediment(�50%). This is likely to be due to the improvedanchoring properties and reduced mechanical andphysiological disturbance of the rhizomes (Palinget al., 2000a).

Loss of seagrass occurs in WA as a result ofcommercial dredging work. Cockburn CementLimited operates the largest lime manufacturingworks in Australia. The company dredges carbon-ate shellsand from shallow unconsolidated marinedeposits close to shore (Success Bank, 32°03� S,115°45� E) to produce lime for the Western Aus-tralian alumina and gold industries. Some of theareas dredged contain seagrass (D.A. Lord andAssociates, 1999) and approval for dredging wascontingent upon detailed investigations into thefeasibility of rehabilitation. To maximise the suc-cess for seagrass transplantation and subsequentmitigation it was considered that a large trans-plant unit would have the greatest chance ofremaining in place and surviving in the moder-ately exposed coastline. The approach taken wasto develop a machine capable of transplantinglarge units of seagrass and associated sediment, inorder to minimise disturbance to the rhizosphereand maximise stability of the plantings in theprevailing hydrodynamic conditions.

2. Methods

An underwater seagrass harvesting and plant-ing machine (‘ECOSUB1’), the first of its type inthe world, was designed to extract large seagrass‘sods’ (0.25 m2 in surface area and 0.5 m deep)and plant them with minimal disturbance to theleaves, roots and rhizomes contained within them(Paling et al., 2001). A prototype was developedand tested by the end of September 1996 andtransplantation commenced in November 1996.Over 2040 sods had been planted to December1999.

ECOSUB1 was a prototype, largely designed toassess the technical feasibility of transplanting

seagrass both at depths up to 15 m and undersometimes extreme wave events (Paling et al.,2001). ECOSUB1 was capable of cutting seagrasssods at the donor site (meadows from whereseagrass is extracted), storing nine of them on-board and then transporting and planting them ata recipient site (unvegetated areas to which mate-rial is transplanted). The exercise is inefficientbecause cutting, storing and planting operationscombined take less than 1 h, whereas transport ofthe machine and its deployment at the recipientsite may take up to 3 h. Most time is spent towingthe machine between donor and recipient sitesrather than cutting or planting seagrass. Due tothese constraints, nine sods (2.25 m2) are usuallycut and planted in 1 day.

ECOSUB1 had semi-permanently mountedflotation tanks to facilitate towing; this posesseveral difficulties for its operation. Divers work-ing the unit must do so in a confined space (�1m3). In addition, as the machine has a largevolume (5 long×3 wide×3 m high), oscillatorywater flow, creating drag, causes considerable me-chanical stresses between the machine frame andthe cutting head, which is buried in the sandduring operation.

A new system, referred to collectively as ‘ECO-SUB2’, has been designed and constructed toimprove transplantation rate. ECOSUB2, like itspredecessor, comprises a hydraulically operatedcutting head mounted on a wheeled frame, movedabout the seabed by on-board hydraulic winches.However, whereas ECOSUB1 was a single ma-chine, moved about in its entirety, ECOSUB2consists of two identical machines (Fig. 1), as-signed to either harvesting sods of seagrass orplanting them. The harvested seagrass material(now 0.55 m2 in area) is placed in a shuttle thatcan be separated from the harvesting machine andtransported to the planting machine (Fig. 2). Thegeneral dimensions of the machines are 5.5long×2.95 wide×2.75 m high with a mass of 2.4tonnes (not including the buoyancy module,which is removed during operations to reducevolume and thus drag under oscillatory flow). Theshuttle dimensions are 4.75 long×2.97 wide×2.75 m high, each masses 1800 kg when emptyand accommodates 12 sods.

E.I. Paling et al. / Ecological Engineering 18 (2001) 107–113 109

The transplantation process comprises a cuttingstage and a planting stage. During the cutting stageECOSUB2 is winched forward through the targetseagrass patch while the cutting head is pushed intothe seabed. As the machine moves forward, a blockof seagrass (approximately 76 long×72 wide×35cm deep, twice the area of the sods in ECOSUB1),including aboveground material, roots, rhizomesand surrounding sediment, is enclosed in a metaltray. Once cut, end plates are lowered into place,enabling the sod to be removed intact from theseabed. The sod is then placed into the shuttle,which is docked to the cutting machine duringoperations. This process is continued until theshuttle is full, at which point it is raised from theseabed and towed to the recipient site. The harvest-ing machine remains at the donor site, and cancontinue harvesting operations by docking anothershuttle to it. Planting the sods is the reverse of theextraction process (Paling et al., 2001). Once plant-ing is complete, the machine is then moved forward

to plant the next sod. As with ECOSUB1, sods canbe planted in any configuration, although initialtrials place the sods in a line. Capital costs of bothmachines (excluding operating costs) wasA$100 000 and the approximate cost per sod (in-cluding operational costs) is A$200, although thisis expected to reduce because ECOSUB2 is moreefficient at planting sods.

Monitoring of planted sods, initially conductedat 2-monthly intervals, included measures of sur-vival, areal cover, shoot density, spreading andgrowth pattern (Paling et al., 2000b). These charac-teristics were compared to those obtained fromreference sites, established in natural Posidoniacoriacea and Amphibolis griffithii meadows. As thenumber of transplanted sods has increased, themonitoring now takes place on representative sub-sets of the transplanted sods (Paling et al., 2001).All sod records were reviewed in December 1999,and it was noted that there were several sods whichappeared in the planting records that were never

Fig. 1. One unit of ECOSUB2 (left) and a sod shuttle (right).

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Fig. 2. Seagrass sods (Amphibolis griffithii and Posidonia coriaceae) being placed from the cutting machine into the sod shuttle.

found by the monitoring team. It had originallybeen assumed that these sods did not survive thetransplantation process and were recorded as fail-ures. It has now been determined that they werenever planted. This means that the overall sur-vival of sods has improved, compared with previ-ously plotted survival data. This is why survivaldata (Fig. 3) appear to increase.

3. Results and discussion

Overall, survival of mechanically transplantedsods of all species is approximately 70% (�4.9S.E., Fig. 3). This is considerably higher thanachieved in other transplantation exercises inWestern Australia (Lord et al., 1999). Many sodshave now survived for as much as 3 years and are

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showing signs of expansion (Paling et al., 2001).Results suggest that seagrasses transplanted inspring or summer are more likely to survive thanif planted in autumn or winter. Survival appearsdependent on the species being transplanted;Posidonia species have shown good survival todate, with P. sinuosa and P. coriacea plants show-ing 76.8 and 75.8% survival, respectively, 2 yearsafter transplantation. Shoot density data indicatethat the seagrass transplants follow normal uni-modal, seasonal variations in shoot density (Pal-ing et al., 2001). This suggests that thetransplantation process is not significantly dis-turbing their natural growth patterns.

The transplantation of A. griffithii sods hasbeen less successful, with a 44.3% survival after 2years. Survival of this species appears to be verydependent on planting technique and winterstorm damage after transplanting (Paling et al.,2001). The structure of Amphibolis differs fromPosidonia in that its roots and rhizomes are more

wiry, and substantially less bulky than the above-ground biomass (Paling and McComb, 2000).Once the leaves of Amphibolis are trapped beneaththe sand, they are less likely to be freed from itthan the roots and rhizomes, the end result beingthat the plants may orientate upside down. Incontrast, Posidonia plants have strap-like leavesthat readily escape the sand if buried and a rootmass that is more bulky and easily cut. Thisresults in plants maintaining a correct orientation.

Since its deployment in early 2000, ECOSUB2has planted 280 sods to June with 100% survival.It is anticipated that the machines will be able totransplant up to 75 sods (or almost 40 m2 of 100%cover) per day when fully operational. Sods willbe planted in the appropriate configuration (ap-proximate spacing of 0.5 m apart) to allowspreading and coalescence. Survival is expected tobe better than for ECOSUB1 (Fig. 3) since sodsplanted by ECOSUB2 are twice the area.

Fig. 3. Mean percent survival of all sods transplanted mechanically. For clarity, each year has been given a consistent shade, andeach season has been given a consistent symbol and line style.

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The mechanical seagrass transplants to datehave shown a remarkable rate of survival whencompared to other transplants in the high energywaters of south Western Australia (Paling, 1995).Present data show a mean survival rate of 70%,with some transplant groups surviving at rates ofgreater than 50% for more than 3 years. Influxesof large numbers of seagrass seedlings (Posidoniacoriacea, P. sinuosa, Heterozostera tasmanica andHalophila o�alis) have been observed into therecipient site on several occasions (Paling et al.,2000b). It appears that the artificial generation ofa 50% cover seagrass meadow sufficiently modifiesthe hydrodynamic regime to enable settling andestablishment. The infilling of the recipient sites issuch that the oldest sites are now difficult todistinguish from natural surrounding meadows.Infilling (seedling establishment), combined withrhizome extension by the transplants (rates of upto 20 cm year−1 have been measured), shouldeventually generate substantial new areas of sea-grass meadow.

Although it is difficult to compare these datadirectly with overseas transplantation work, as thehydrodynamic conditions here are considerablyrougher, the survival rates recorded in this studyare higher than the median value of 50% recordedfrom United States studies (Fonseca et al., 1998).Few Australian seagrass planting efforts have re-ported significant transplant survival beyond afew months and survival beyond 2 years has beenvirtually non-existent (Lord et al., 1999). Theresults presented here are therefore very encourag-ing and suggest that the premise of using largesods to overcome high wave energies is wellfounded. The technique, essentially one of sal-vage, conforms to recommendations proposed byLewis (1987) to ensure successful, non-destructivemeadow restoration and creation. Mechanicaltransplantation of large sods appears to provide akey to transplantation success in the exposedmarine environment of Western Australia. Thetechnology described here can be easily modifiedfor other environments, species and depths, andwould appear applicable to seagrass environmentsworldwide, particularly those in high-energy con-ditions where other transplant methods have metwith limited success.

Acknowledgements

The authors wish to thank Cockburn CementLtd. for their continued support, without which aproject of this magnitude could not have suc-ceeded. Photograph for Fig. 2 was taken by BrianRichards.

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