THE INTERNATIONAL RESEARCH GROUP ON WOOD PROTECTION. Section 1. Biology. Wood boring species present in the Tagus Estuary and the severity ...
IRG/WP 08-10664
THE INTERNATIONAL RESEARCH GROUP ON WOOD PROTECTION Section 1
Biology
Wood boring species present in the Tagus Estuary and the severity of their attack on wooden piles exposed in the area: a case study 1
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L M S Borges , L Nunes , A A Valente and P Palma
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1. Institute of Marine Sciences, School of Biological Sciences, University of Portsmouth, Ferry Road, Portsmouth PO4 9LY, UK 2. Laboratório Nacional de Engenharia Civil, Av. do Brasil, 101, 1700-066 Lisbon, Portugal
Paper prepared for the 39th Annual Meeting Istanbul, Turkey 25 – 29 May 2008
IRG SECRETARIAT Box 5609 SE-114 86 Stockholm Sweden www.irg-wp.com
Wood boring species present in the Tagus Estuary and the severity of their attack on wooden piles exposed in the area: a case study L M S Borges1, L Nunes2, A A Valente2 and P Palma2 1. Institute of Marine Sciences, School of Biological Sciences, University of Portsmouth, Ferry Road, Portsmouth PO4 9LY, UK 2. Laboratório Nacional de Engenharia Civil, Av. do Brasil, 101, 1700-066 Lisbon, Portugal
ABSTRACT Wood exposed in the marine environment is subject to degradation by wood boring organisms. This is probably one of the reasons why wood has been substituted by concrete and steel in maritime structures in many European coastal areas. Wooden piles obtained from a wharf exposed in the Tagus Estuary, Porto Brandão (Almada, Portugal) provided an opportunity to understand the main agents of biodeterioration of wood, as wooden structures in the area are rare.
The examination of the piles revealed severe deterioration by wood boring organisms. Major destruction caused by limnoriids was observed in the outer layers of the piles. The species was identified as Limnoria quadripunctata but a field survey in wooden structures nearby the area where the piles were obtained, revealed also the presence of Limnoria tripunctata. Thus, it is possible that this last species was also responsible for the degradation observed. The piles were also attacked by teredinids but the severity of their attack was less extensive than that by limnoriids. Two teredinid species were identified, Lyrodus pedicellatus and Nototeredo norvagica. N. norvagica was previously reported from test panels exposed in the Tagus in the 1980’s. However, this was the first time L. pedicellatus was reported in this area. The increase in water temperature surface due to global warming might be responsible for the increased activity in southern European waters of L. pedicellatus, a warm water species. The higher activity of limnoriids in the Tagus Estuary in later years might be related not only with warmer
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water temperatures but also with an increase in salinity in the area, as limnoriids appear to be restricted to waters with salinities close to that of seawater.
The development of adequate methods of wood protection requires accurate identification to define the borer hazard at various sites. In this study the Tagus Estuary is used as a case study. Species identification also assisted in the documentation of the activity of particularly damaging species, which enabled biodeterioration to be related with defined organisms.
Keywords: marine borers, limnoriids, teredinids, wooden structures, biodegradation, Tagus Estuary.
1. INTRODUCTION For many centuries wood had been the material used for maritime construction, possibly due to its wide availability, relative ease of fabrication and repair (Cragg, 1996). However, in the 20th century other materials became more popular and wooden structures have been substituted by concrete and steel structures. These latter two materials are now dominant in marine developments in countries such as the UK (Reynolds, 2004) and Portugal (Borges, pers. obsv.). Nevertheless, the properties of wood, such as resilience, favourable strength-to-weight ratio, relatively low energy costs of production and renewability, make it an attractive material for engineers to design with and specify (Cragg, 1996). Wood also suffers much less from the effect of the salt in the seawater than for instance steel or concrete (Williams et al., 2004). In addition, the production of cement and steel alone accounts for over 10% of global annual greenhouse gas emissions whereas, processing of wood for construction has much lower CO2 emissions: a growing tree absorbs more carbon from the atmosphere than it emits and it processing also requires less energy (Burnett, 2006). In line with the commitment of European Union to reduce the emission of greenhouse gases this demands an immediate re-evaluation of the environmental costs of processing of rawmaterials used for construction, both in terrestrial and in marine environments.
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Therefore, wood obtained from sustainable sources is more environmentally friendly and its use in marine construction should be favoured.
The destruction caused by wood borers is probably one of the main reasons for the substitution of timber by other materials in maritime structures. Although a number of preservatives have been used to protect wood exposed in the sea, the control of wood borers remains an unresolved problem. In addition, the recent EU directive (European Commission, 2003) is now limiting the use of traditional preservatives such as creosote and copper chromium arsenate (CCA) for wood in marine construction. Therefore, other approaches to ensuring an adequate service life for timber place in the sea need to be explored. One approach has been the investigation of the natural durability of lesser utilised timbers species using laboratory tests (Borges, 2008) or field trials (Bultman et al., 1988; Edmondson, 1955; Haderlie, 1983; Southwell & Bultman, 1971). Another approach, which has been developed in recent years, is the modification of wood for use in the marine environment (Borges et al., 2004, 2005; Borges, 2007; Westin & Rapp, 2005). However, this latter method needs to be developed further to provide wood with effective anti-borer protection. One of the keys to develop an effective modification method against wood borers is without doubt the understanding of their biology. In particular, attention should be focused on modes of nutrition of borers (Daniel et al., 1991; Dymond et al., 2003; Morton, 1978) and on their interrelationship with microorganisms (Distel, 2003). Also of particular importance are taxonomic studies, which form the foundation of all biological studies (Cragg et al., 1999). Thus, defining borer hazard for timber in various sites and documenting the spread of particularly damaging species, including their ecology and behaviour, is required if anti-borer trials are to be effectively conducted.
Recently, Laboratório Nacional de Engenharia Civil (LNEC) had access to three wooden piles, which had been exposed in the Tagus Estuary (Fig. 1) at Porto Brandão (Almada, Portugal) for a period of sixteen years. During this period, the piles suffered from severe wood boring attack and consequently they were removed and substituted by concrete piles. The analysis of the biodeterioration in the piles offered an excellent
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opportunity to gain insight on the reasons of the substitution of timber by other materials such as concrete and steel in maritime structures in the Tagus Estuary. The main aim of this study was to accurately identify the wood boring organisms in the piles and in the wooden structures surveyed and documentation of particularly damaging species in order to define the biohazard for wooden structures in the area. The second aim was to compare the wood boring species presently occurring in the Tagus Estuary with those identified during the trials conducted by researchers from LNEC in the 1960’s and 1980’s (Franco, 1968, 1975 Franco & Farinha, 1968; Reimão & Cockroft, 1985). This comparison highlighted changes in the composition of boring species in the Tagus Estuary, which may be related to changes in the water temperature and salinity due to global warming. The information obtained in this study was valuable to the research programme ‘Marine Environment Damage to Atlantic Coast Structures and Buildings: Methods of Assessment and Repair’ (MEDACHS), which has been developed by LNEC since 2005. It also assists with the mapping of wood boring hazard in European coastal waters initiated by Borges (2007).
Trafaria
Setúbal
SPAIN
Porto Brandão
PORTUGAL
ATLANTIC
40.00
39.00
38.00
37.00 N 9.00
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7.00
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Figure 1 Location of sites were the field surveys were conducted.
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5.00 W
2. EXPERIMENTAL METHODS
2.1 Piles retrieved from Porto Brandão, Almada, Portugal Each pile was divided in three areas – supratidal, intertidal and subtidal – to facilitate the determination of the severity of wood boring attack. Each area was inspected for signs of damage by limnoriids and teredinids. The level of damage was rated using the visual assessment categories described in EN 275 (1992).
On their arrival at LNEC, the wooden piles were checked externally for the presence of Limnoria. The animals were extracted and identified according to the keys in Menzies (1957). Some superficial calcareous teredinid tubes were also removed. Unfortunately, the soft bodies of the teredinids had already rotten away, because the piles were inspected only after one year of being retrieved from the field. Thus, they were checked for the remaining pallets of the teredinids in order to identify the species causing the attack. The pallets were observed under the stereo microscope and identified using the description and keys in Turner (1966; 1971).
2.2 Wooden test panels from marine trials in the 1960´s Test panels (Fig. 2) of different wood species – mainly African woods – which were exposed in the Tagus Estuary in the 1960´s (LNEC’s collection) were observed under a light microscope. Some remaining pallets were found and, when possible, teredinid species were identified. The reports from those trials were also revised to get information on the wood boring species identified at the time.
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Figure 2 Wood panel (Nesogordonia leplaei) exposed in the Tagus Estuary (Arsenal do Alfeite) in the 1960’s.
2.3 Field survey around the coast of Lisbon and surrounding areas Field surveys were conducted at Porto Brandão, Trafaria and Setúbal (Fig. 1). At Porto Brandão, a wooden structure attacked by wood borers was sampled (Fig. 3).
Figure 3 Collecting samples of a wooden structure attacked by wood borers at Porto Brandão.
At Trafaria, there were no wooden structures visible in the harbour but pieces of attacked wood were found on the beach and some samples were collected.
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No wooden structures were found at the fishing and commercial harbours in Setúbal except a small wooden ladder at the fishing harbour (Fig. 6). Small samples of the parts of the ladder attacked by wood borers were collected to be analysed in the laboratory.
Figure 6 Wooden ladder, Setúbal fishing harbour, showing attack by wood borers (arrows). Note that the position of the ladder is reversed.
3. RESULTS
3.1 Piles from Porto Brandão The piles retrieved from Porto Brandão showed sever wood boring attack (Fig. 7) on the intertidal and subtidal areas. Both areas were rated 4 for limnoriids attack and 3 to 4 for teredinid attack, according to the categories defined in EN 275 (1992).
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a b
c
Figure 7 Piles retrieved from Porto Brandão showing sever limnoriid attack. a- supratidal; b-intertidal; c- subtidal.
The intertidal area showed an hourglass shape (Fig. 7 zone b and Fig. 8a), while the subtidal area (Fig. 7 zone c and Fig. 8b), exposed above the bottom line, had a characteristic pencil-point shape.
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b
Figure 8 Detail of sections of the piles retrieved from Porto Brandão; a- intertidal area showing hourglass shape; b- subtidal area showing pencil-point shape.
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These shapes are characteristic of Limnoria attack. Indeed, the specimens extracted from the pile were all Limnoria quadripunctata Holthuis (Fig. 9).
Figure 9 Limnoria quadripunctata found in piles retrieved from Porto Brandão (notice the arrows pointing the four punctae on the pleotelson).
Some shipworm attack was also visible in some areas of the pile, with the calcareous tubes protruding through the wood surface. It was not possible to find complete specimens but several shells and pallets were recovered form the tunnels. Pallets found in these tubes were identified as belonging to Nototeredo norvagica (Splenger) (Fig. 10).
Figure 10 Pallets of Nototeredo norvagica (left) and a piece of the calcareous tube showing concammerations (right). 9
Pallets found in the smaller tubes with no concammerations, were identified as belonging to Lyrodus pedicellatus (Quatrefages) (Fig. 12).
Figure 12 Pallets of Lyrodus pedicellatus found in piles retrieved from Porto Brandão, Almada, Portugal.
3.2 Wooden test panels from marine trials in the 1960´s Most of these test panels were severely attacked by teredinids and, to a smaller extent, by limnoriids. Although the determination of the wood boring species was not the main objective of the study at the time, there are references, in the numerous reports produced, to Limnoria tripunctata and Teredo navalis (Franco, 1968, 1975 Franco & Farinha, 1968).
The observation of the panels under the stereo microscope revealed some remaining pallets and even some dried specimens of Limnoria. Some pallets appeared to be of Teredo navalis and others of Lyrodus pedicellatus. However there was uncertainty in these identifications as some pallets had lost their periostracum and were very dry. The intact features of the pleotelson of some dry limnoriids found in the old panels made it possible to identify them as Limnoria tripunctata.
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3.3 Survey at Porto Brandão, Trafaria and Setúbal Wooden structures were very rare in these three areas. Most harbours and fishing ports use alternative materials for maritime construction, such as concrete and steel, as it can be seen in Figure 13.
Figure 13 Setúbal’s commercial harbour (left) and fishing harbour (right). No wooden structures were found in these harbours.
Wooden samples taken from the old shipwharf at Porto Brandão showed severe attack by limnoriids (Fig. 3) and, in some areas, also by teredinids. The specimens of Limnoria obtained from the samples, were of Limnoria tripunctata (Fig. 14). tunnels, Chelura terebrans was also found (Fig. 16).
Figure 15 Several live specimens of Limnoria tripunctata in a piece of wood, collected during the survey at Porto Brandão. Note the three punctae in the pleotelson of one of the specimens (arrow).
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In some of the
Figure 16 Chelura terebrans found in wood samples collected in the field survey at Porto Brandão.
At Trafaria no wooden structures were found. The samples of wood collected were taken from wood found on the beach. They were also attacked by limnoriids and teredinids but no specimens were found.
The areas surveyed at Setúbal, had no wooden structures, apart from a wooden ladder – turned upside down – attacked both by limnoriids and teredinids. Samples of the ladder were taken but no limnoriid specimens were found. The pallets found in the samples belonged to Lyrodus pedicellatus.
4. DISCUSSION AND CONCLUSIONS The extensive limnoriid deterioration observed in the piles retrieved from Porto Brandão was unexpected. In previous trials (Franco, 1968, 1975 Franco & Farinha, 1968; Reimão & Cockroft, 1985) limnoriids were not considered a threat to wooden structures in the Tagus Estuary. At the time, teredinids – mainly Teredo navalis – were the most wood destructive agencies in the area. It is clear from the comparison of species found in the present study with those found on the early trials, that a great change in boring species composition have occured in the Tagus Estuary.
The finding of Limnoria quadripunctata in the piles from Porto Brandão was also unexpected, as this area is out of the known range of distribution of the species in
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Europe (Borges, 2007). Since the species was first found along the coasts of The Netherlands and described by Holthuis (1949), it was only found in Europe along the coasts of Britain (Borges, 2007; Hall & Saunders, 1967; Hockley & Eltringham, 1958; Jones, 1963) and at Trieste, Italy (Menzies & Becker, 1957). A key factor determining geographical distribution of limnoriids is temperature (Cragg et al., 1999). The optimum temperature for L. quadripunctata survival ranges between 15 to 25˚C (Borges, 2007), which coincides with the range of temperatures registered annualy in the Tagus Estuary. The absence of this species in test panels exposed in the Tagus Estuary during the 1960’s and 1980’s may be related with the limited capability of dispersion of these organisms and, therefore, their potential to exploit climatically suitable environments (Cragg et al., 1999). It is also possible, however, that the increased surface water temperature in European coastal waters accompanied by a rise in salinity in southern European waters (Eisenreich, 2005) has been responsible for the increased limnoriid activity observed in the area. Indeed, limnoriids appear to be restricted to waters with salinity close to that of seawater (Cragg et al., 1999).
The wooden structures found during the survey carried out at Porto Brandão, were severely attacked by L. tripunctata (Fig. 3), which seems to corroborate the hypothesis that the present conditions of temperature and salinity in the Tagus are favouring the activity of limnoriids. The area surveyed at Porto Brandão was very near to the place where the piles were retrieved. This suggests that the two species – L. quadripunctata and L. tripunctata – coexist in the area, similarly to what was observed in Southampton waters, UK by Eltringham & Hockley (1958). Therefore, it is not improbable that the damage observed in the piles might have been caused by both limnoriids species. The great severity of limnoriid attack inflicted onto the three piles confirms laboratory findings that L. quadripunctata – when in optimal conditions of temperature and salinity – can cause severe damage to wood, similar to damage by Limnoria tripunctata (Borges, 2007; Cookson, 1990), which was considered to be the most destructive limnoriid species (Menzies, 1957).
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The third crustacean – Chelura terebrans – found at Porto Brandão has been established as a wood borer (Barnard, 1955). However, there is no information reporting this species as a threat for wooden structures in marine environments (Borges, 2007). From the results of the present study, it was not possible to ascertain whether the damage observed in the wooden structure surveyed was caused by C. terebrans and L. tripunctata or whether it was inflicted by this last species alone.
The second most destructive species found in the piles was Nototeredo norvagica. Although the number of specimens of Lyrodus pedicellatus was greater than that of N. norvagica, the large dimensions which these latter organisms attained were the cause of the extensive teredinid damage observed in the inner layers of the piles. The relative low number of specimens of N. norvagica found in the piles suggests that either the population is small in the area, due perhaps to climatic conditions, or that these organisms are not very active at these depths (Borges, 2007). Indeed a large number of organisms of this species could have destroyed these wooden structures very quickly due to their large dimensions. It is not possible to ascertain whether there is a permanent population in the Tagus Estuary but the fact that N. norvagica was found previously in the area (Reimão & Cockroft, 1985) suggests that it occurs, at least sporadically.
Lyrodus pedicellatus was found for the first time in the Tagus Estuary in the present study. In the 1960’s reports, the only teredinid species found in the Tagus Estuary was Teredo navalis (Franco, 1968; Franco & Farinha, 1968). In a historical review of the literature concerning wood borers in European waters, L. pedicellatus was mentioned in several studies but did not seem to be a very active species in European coastal waters (Borges, 2007). However, in later years L. pedicellatus is the most destructive species in southernmost waters as far North as the English Channel (Borges, 2007). In the three areas surveyed (Porto Brandão, Trafaria and Setúbal) this was no exception confirming the trend observed by Borges (2007). The fact that not many studies concerning wood borers were undertaken in southern European waters previous to the study of Borges (2007), might explain why the great damage caused by this species had not been
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documented previously. However, it is also possible that this species is becoming more active in later years with the increasing of the temperature of sea surface in Europe (Eisenreich, 2005).
The present case study clearly shows that the destruction of wood caused by marine borers is the main reason why wooden structures have been progressively substituted in the marine environment by other materials thought to be more durable. In southern European waters, the destruction by xylotrophic organisms is, in general, more severe than in northern European coasts (Borges, 2007), which might explain the almost total abandoning of wood as material for maritime construction along the Portuguese coast (Borges, pers. obsv.). The definition of the borer hazard – 4 to limnoriids and 3 to 4 to teredinids, according to EN 275 (1992) – and documentation of the activity of particularly damaging species – Limnoria tripunctata, L. quadripunctata, Lyrodus pedicellatus and Nototeredo norvagica – may be the basis for the development of effective protection for wood to be use in marine construction in the Tagus Estuary.
ACKNOLEDGMENTS We would like to thank the International Research Group on Wood Protection for funding the Short Scientific Mission in Lisbon of the senior author. The financing provided by the Project INTERREG IIIB Espaço Atlântico nº 197 – MEDACHS is also acknowledge.
REFERENCES Barnard, J. L. (1955) The wood boring habits of Chelura terebrans Philippi in Los Angeles Harbor: 87-97. Borges, L. M. S. (2007) Biogeography of wood boring organisms in European Coastal waters and new approaches to controlling borer attack. PhD thesis, Portsmouth University, Portsmouth, UK. Unpublished. Borges, L. M. S., Cragg, S. M., Bergot, J., Williams, J. R., Shayler, B. & Sawyer, G. (2008) Laboratory screening of tropical hardwoods for natural resistance to the marine borer Limnoria quadripunctata with an investigation of the role of leachable and nonleachable factors. Holtzforschung 62:99-111.
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Borges, L. M. S., Cragg, S. M., Williams, J. R. (2003) Comparing the resistance of a number of lesser known species of tropical hardwoods to the marine borer Limnoria using a short-term laboratory assay. International Research Group on Wood Preservation IRG/WP/03-10500: 1-11 Borges, L. M. S., Cragg, S. M., Zee van der, M. (2004) Evaluating the potential of modified wood for use in the marine environment, using a short-term laboratory bioassay. International Research Group on Wood Preservation IRG/WP/04-10: 1-14. Borges, L. M. S., Cragg, S. M., Zee van der, M., Homan, W. (2005) Laboratory and field tests of the potential for use in marine environments of wood modified with dimethyloldihydroxyethyleneurea (DMDHEU) and phosphobutane tricarboxylic acid (PBTC). Proceedings of the 2nd Conference on Wood Modification, Goettingen, Germany. ISBN 3-00-017207-6. British Standard EN 275 (1992) Wood preservatives. Determination of the protective effectiveness against marine borers. 16pp. Bultman, J. D., Beal, R. H., Purushothan, A. (1988) Evaluation of some Indian woods for natural resistance towards wood destroying organisms. In: Marine Biodeterioration. Eds. Thomson, M. –F., Sarojini, R., Nagabhushanam, R. Oxford IBH Publishing, New Delhi. 673-681. Burnett, J. (2006) Carbon benefits of timber in construction. A report by the Edinburgh Centre for Carbon Management Ltd. 26pp. Cookson, L. J. (1990) A laboratory bioassay method for testing preservatives against the marine borers Limnoria tripunctata, L. quadripunctata (Crustacea) and Lyrodus pedicellatus (Mollusca). International Research Group on Wood Preservation IRG/WP/4159: 1-5. Cragg, S. M. (1996) Timber in the marine environment. Timber Trades Journal 376: 2628. Cragg S. M., Pitman A. J., Henderson S. M. (1999) Developments in the understanding of the biology of the marine wood boring crustaceans and in methods of controlling them. International Biodeterioration and Biodegradation 43: 197-205. Daniel, G., Cragg, S. M., Nilsson, T. (1991) Ingestion of wood-degrading microorganisms by Limnoria lignorum. International Research Group on Wood Preservation IRG/WP/4169: 1-13. Distel, D. L. The biology of marine wood boring bivalves and their bacteria endosymbionts (2003). In: B. Goodell, D. D. Nicholas, T. P. Schultz (eds.), Wood Deterioration and Preservation. Washington D. C., American Chemical Society Press. 845pp. Dymond, J., Guille, M. J., Cragg, S. M. (2003) Isolation of a putative endogenous
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endo-β-1,4-glucanase (cellulase) from the midgut diverticulae of the wood-boring crustacean, Limnoria quadripunctata. International Research Group on Wood Preservation IRG/WP/03-10494: 1-12. Edmondson C. H. (1955) Resistance of woods to marine borers in Hawaiian waters. Bernice P. Bishop Museum occasional papers 217: 1-91. Eisenreich, S. J. (2005) Climate change and the European water dimension. European Commission- Join Research Centre. EU 21553 EN. 253pp. www.http//europa.eu.int Eltringham, S. K., Hockley, A. R. (1958) Coexistence of three species of the woodboring Isopod Limnoria in Southampton water. Nature 4624: 1659-1660. European Commission (2003) Directive 2003/2/EC of 6 January 2003 relating to restrictions on the marketing and use of arsenic (10th adaptation to technical progress to Council Directive 76/769/EEC). Official Journal of European Communities 9.1.2003: L4/9-L4/11. Franco, S. E. (1968) Resistęncia natural de madeiras tropicais aos xilófagos marinhos. Unpublished report. Franco, S. E. (1975) Estudo do comportamento de madeiras imersas (durabilidade natural). Décimo primeiro relatório. Unpublished report. Franco, S. E. & Farinha, M. M. (1968) Programa I. Identificaçăo e distribuiçăo geográfica de organismso xilófagos e incrustantes. O.C.D.E. Programas de Pesquisa em Cooperaçăo . 1° Relatório. Haderlie, E. C. (1983) Long-term natural-resistance of some Central America hardwoods to the attack to Bankia setacea (Tryon) and to the griblle Limnoria quadripunctata Holthuis in Monterey Harbor. Veliger 25: 182-184. Hall, G. S., Saunders, R. G. (1967) Incidence of marine borers round Britain's coasts. Timber Research and Development Association. Unpublished report. Hockley, A. R., Eltringham, S. K. (1958) Migration and reproduction of Limnoria in Southampton water. Annual Report Challenger Society 3: 22. Holthuis, L. B. (1949) The Isopoda and Tanaidacea of the Netherlands, including the description of a new species of Limnoria. Zoologische Mededelingen 30: 163-190. Jones, L. T. (1963) The geographical and vertical distribution of British Limnoria (Crustacea: Isopoda). Journal of the Marine Biological Association of the United Kingdom 43: 589-603. Menzies, R. J. (1957) The marine borer family Limnoriidae (Crustacea, Isopoda). Part I:
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northern and central America: systematics distribution, and ecology. Bulletin of Marine Science of the Gulf and Caribbean 7: 100-200. Menzies, R. J., Becker, G. (1957) Holzzerstörende Limnoria-Arten (Crustacea, Isopoda) aus dem Mittlmeer mit Neubeschreibung von L. carinata. Z. Angew. Zool. 44: 85-92. Morton, B. (1978) Feeding and digestion in shipworms. Oceanography and Marine. Biology: an Annual Reveview 16: 107-144. Reimăo, D., Cockroft, R. (1985) Wood preservation in Portugal. Swedish National Board for Technical Development (STU). Informat. No 487. Reynolds, T. (2004) UK timber for marine and geotechnical applications. INFD6SFENH. Retrieved March 3, 2005 from http://www.forestry.gov.uk/forestry Southwell, R.C & Bultman, J. D. (1971) Marine wood boring resistance of untreated woods over long periods of immersion in tropical waters. Biotropica 3: 81-107. Turner, R. D. (1971) Methods d'identification des perforants et des cahmpignons en millieu marin. In: Jones, E. B. G. & Eltringham, S. K. (eds.) Les Perforants, les Champignons et les Salissures du Bois en Millieu Marin. OECD, Paris: 69-73. Turner, R. D. (1966) A survey and illustrated catalogue of the Teredinidae. The Museum of Comparative Zoology, Harvard University, Cambridge, M.A. 265pp. Westin M. & Rapp A. O. (2005) Resistance of modified wood to marine borers: results from a five year field test according to EN 275. In: H. Militz & C. Hill (eds.) Wood Modification: Processes, Properties and Commercialisation, Gottingen, Germnay. Williams J. R., Cragg S. M., Borges L. M. S., Shayler B. (2004) Evaluating the natural durability of a number of lesser known species of Ghanaian hardwoods using a short term laboratory assay. International Research Group on Wood Preservation IRG/WP/04-10540:1-7.
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