ABSTRACT

Seagrasses provide unique biodiverse communities in shallow water, essential habitat for juvenile fishes, and provide shore protection against erosion by stabilizing offshore sediments (Brasier 1975)� Seagrass clones can grow for thousands of years (Arnaud-Haond et al� 2012), but they are in serious decline worldwide (Short et al� 2011) and in the Mediterranean (Procaccini et al� 2003)�

Part of this decline is due to direct damage by dredging and anchors, but the major part results from land-based sources of pollution, mainly by both nutrients from inadequately treated sewage, which causes seagrasses to be overgrown and smothered by weedy algae (Lapointe et al� 1994), and erosion of sediments from land after deforestation, which causes sediment buildup in the water that kills seagrasses by decreasing the light they need for photosynthesis and by direct smothering�

Restoration of seagrass communities has long been seen as a priority in many coastal areas, because loss of seagrass beds plays a major role in loss of coastal fisheries habitat-especially for juvenile fish populations-and in accelerating coastal erosion� But in general, most restoration have proven to be expensive failures, because when seagrasses are transplanted into areas where previously existing seagrass beds had been killed by deteriorating water quality, transplanted seagrasses usually die for the same reasons as the previous populations� There are few locations where water quality deterioration has been permanently reversed and improved so that transplanted seagrasses are able to survive�

CONTENTS

Introduction ������������������������������������������������������������������������������������������������������������������������������������ 161 Materials and Methods ������������������������������������������������������������������������������������������������������������������ 162 Results �������������������������������������������������������������������������������������������������������������������������������������������� 163

Giovinazzo �������������������������������������������������������������������������������������������������������������������������������� 163 Torre Guaceto ���������������������������������������������������������������������������������������������������������������������������� 165 Otranto Electroduct ������������������������������������������������������������������������������������������������������������������� 165

Conclusions ������������������������������������������������������������������������������������������������������������������������������������ 166 References �������������������������������������������������������������������������������������������������������������������������������������� 167

Because of the slow growth or poor survival with conventional methods of seagrass restoration in most locations (Curiel et al� 1994; Faccioli 1996; ICRAM 2001; Boudouresque et al� 2006; Uhrin et al� 2009; Paling et al� 2009; van Katwijk et al� 2009), improved methods are needed that increase seagrass growth rates, attachment, and survival in order to successfully restore this important habitat� Our results with restoration of Posidonia oceanica in the Adriatic Seawaters of the Province of Bari, Puglia, Italy, show that such technology is now available�

MATERIALS AND METHODS

Seagrass transplantation projects using electrified mesh substrates were carried out from June to September 2008 at two very different locations, Giovinazzo and Torre Guaceto� The depth, habitat, and power sources were different at each site (Table 14�1)� At each site, three or four pieces of metal mesh, 50 cm on each side, were nailed to hard substrate or laid over soft substrate� Mesh spacing was 4 cm, and seagrass plants with roots were planted in the spaces, attached by ties to the mesh to secure them against wave surge until established�

At Giovinazzo (Figure 14�1), the shallow (1�5 m) station was located in sand patches created by erosion between nearby Posidonia oceanica beds� The deeper station was located on dead Posidonia root mats that had been overgrown by Nanozostera noltii, also close (about 1 m away) to living Posidonia beds� At Giovinazzo, these two seagrasses occur in patches mixed with a third species, Cymodocea nodosa� The deepest site, at Torre Guaceto (Figure 14�2), was free of seagrasses because the seagrass could not attach to the limestone hardground due to lack of sufficient sediment and high wave action� The bottom was largely covered with algae�

Detailed descriptions of these sites, including bathymetry, sedimentology, and biology, are included in Vaccarella and Ciccolella (2008) and in Vaccarella and Goreau (2008)�

In addition, comparison was made with an underwater high-voltage direct current transmission line, the Otranto electroduct (Figure 14�3)� This was an uninsulated copper cable at a depth of 40 m, and more than 8 cm thickness of soft minerals, almost entirely brucite, grew over it in 3 years�

RESULTS

Giovinazzo

Minerals grew very rapidly on the meshes because of the high power from the transformer� Time series color photos of the results at all sites are included in the appended CD� The transplanted Posidonia began growing well, but by the end of the experiment the thickness of mineral growth completely filled in the spaces between the meshes and smothered most of the seagrass plants (Figure 14�4)� The shallower station meshes, which had shorter cables than the deeper ones, drew more current and grew and filled in faster, taking about two months to fill in, while the deeper ones took about four months (Figure 14�5)� Samples of material were analyzed by X-ray diffraction and found to be 91% brucite (magnesium hydroxide), 7�5% aragonite (calcium carbonate), and the rest composed of sand and mud cemented by the mineral growth (Figure 14�6)�

In September, the power was terminated and the meshes left in the water for two years� By that point, the soft minerals had turned hard and cemented themselves to the substrate, making their

retrieval very hard� They were extensively covered with marine life, including algae (Caulerpa racemosa and Halopteris filicina), barnacles (Balanus perforatus), oysters (Anomia ephippium), chitons, and serpulids� An Octopus vulgaris had created a den under one of the meshes� Color photos of these organisms are included in the CD in the back of the book�

Torre Guaceto

At Torre Guaceto marine-protected area, the power was supplied by a solar panel in a direct mode, with no battery, so it received power only when it was sunny� It was clear that the power was very much less than at Giovinazzo, the minerals grew much more slowly and harder, and they achieved a thickness of only 1�5 mm (Figures 14�7 and 14�8)� The mesh cemented itself to the hard bottom� The Posidonia transplants grew very well, and after only three months all the plants added new young and intermediate leaves, and about 80% of them showed clear root growth, from 6�2 to 79�7 mm (Figure 14�9a and b)�

Organisms found on and around the Biorock meshes are shown in Table 14�2�

Otranto Electroduct

The copper cable remained free of corrosion despite being in the sea for years� The organic or inert material aggregated by the deposits of brucite was overgrown by vegetal and/or calcareous residues of Posidonia oceanica, Cladocora caespitosa, Filigrana implexa, Bittium reticulatum, Laevicardium oblungum, Myriapora truncata, Pentapora fascialis, Retepora septentrionalis,

spines, and plates of echinoidea� Apart from the biogenic components, there were also aggregated mineral components, sand, and mud�

Among the organisms detected on the magnesium hydroxide deposits, the alga Codium tomentosum; the porifera Axinella polypoides; the annelids Filigrana implexa, Sabella penicillus, and Sabella spallanzani; the bryozoan Pentapora fascialis; and the echinoderm Echinaster sepositus were also observed� The organisms that covered the deposits of magnesium hydroxide showed healthy development, and the fish swam without any problem near the electroduct together with molluscs (Tonna galea)�

CONCLUSIONS

Biorock meshes grown at a low charging rate were able to produce healthy and rapid growth of Posidonia oceanica on hardground where they normally could not attach� Meshes that were overcharged grew too fast and overgrow the seagrass� In all cases, the minerals hardened, cemented themselves to the substrate, and attracted colonization by a wide variety of local marine life�

These results suggest that the Biorock method can be used to restore biodiverse seagrass habitat in a wide variety of settings, including those where inappropriate substrate or high wave energy would normally prevent their establishment and growth� Further experimentation is needed to optimize the method and apply it to restoration of damaged seagrass habitats�

REFERENCES

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