Biogeography of wood boring organisms in European coastal waters and evaluation of new approaches to controlling borer attack
Information of the biogeography and severity of attack provoked by wood boring species in
European coastal waters was surprisingly scarce. Two of the outstanding questions that
this work tried to answer were: which wood boring species occur in European coastal
waters and what is the severity of their attack at each site. Therefore, a number of sites -
as far north as Iceland and as far south as Turkey - were investigated. In addition three
important European wreck sites located in the Netherlands, Germany and Finland were
also investigated for species of wood borers present and severity of their attack. Pinus
sylvestris panels were used as baits at each test site. At the wreck sites panels of recent
cut oak and archaeological oak were also deployed. Wood borers that recruited to the
panels were identified to the species level. The evaluation of the severity of attack in the
test panels was based on X-rays of the panels and visual assessment under a stereo
microscope. The rates varied from 0, no attack, to 4, panels destroyed, according to the
categories described in EN 275 (1992).
Six species of wood boring Bivalvia were found in the test sites. The most widely distributed
species in northern Europe was Teredo navalis occurring in nine of the 15 sites surveyed.
In southern Europe, Lyrodus pedicel/atus was clearly the dominant species in all the sites,
except in the Black Sea where the sole bivalve species was Teredo navalis. Other bivalve
species were more restricted in their distribution, occurring in only one or two of the sites:
Psiloteredo megotara, Nototeredo norvagica, Teredo bartschi and Bankia carinata.
In Iceland, the attack in test panels was provoked by Limnoria Iignorum (Isopoda:
Crustacea). This species occurred only in the northernmost sites: Iceland, Sweden, Norway
and Netherlands. Limnoria tripunctata, on the other hand, was found in the southernmost
sites, Portugal and Turkey. Limnoria quadripunctata was found only in Langstone Harbour,
Lyrodus pedicel/atus, Teredo navalis and Limnoria tripunctata were the most destructive
species in this study. Complete failure of the wood panels occurred in Sweden,
Netherlands, England, Croatia, Portugal and Turkey. No signs of boring activity were found
in the Gulf of Riga, probably due to the very low salinity of its waters (0.2 to 3.75 PSU).
The use of preservatives for use in the marine environment has been subject to ever
increasing restrictions. In addition, naturally durable species of wood for use in maritime
construction are becoming increasingly difficulty to obtain, due to the pressure imposed by
the governments. The test of new timbers according to the five-year test period specified in
EN 275, is too long a period for screening tests to be economically viable. Thus, in this
study, laboratory screening tests, using Limnoria quadripunctata as the test organism, were
optimised. The optimisation of the tests involved the investigation of the optimum conditions
of temperature and light for Limnoria quadripunctata. The screening tests were then used
to assess the durability of a large number of lesser utilised timber species and chemically
modified wood for their potential for use in the marine environment. In all tests, the
durability was assessed by measuring the production of faecal pellets by the crustacean
Limnoria quadripunctata under forced feeding conditions over a fifteen-day period. The
number of pellets produced by animals feeding on Scots pine sapwood, which is nondurable,
was used as a basis for comparison. Lower pellet production rates and higher
mortality rates were taken as measures of durability.
The Ghanaian and Brazilian timbers balau, bompagya and jatoba had an antifeedant effect
in L. quadripunctata and the water-soluble extractives produced by these timber species
caused enhanced mortality on test organisms. Timbers such as ayan, Bruguiera, louro
gamela, acariaquara, favinha prunelha and uchi torrado and their leachates were toxic to
Treatments of PBTC with urea 1 were resistant to wood borers in laboratory tests and in
the field trial. Wood treated with one of the formulations of PBTC with urea 2 and urea 2
alone showed also enhanced resistance against L. quadripunctata. However, none of the
wood modifications mentioned above were leach-resistant. To be of practical interest for
use in the marine environment, treatments need to be very leach-resistant otherwise they
will lose their resistance with time.
In European coastal waters three main wood borer species cause great destruction: Teredo
navalis, Lyrodus pedicellatus and Limnoria tripunctata. Therefore before the introduction of
alternative wood materials it should be ensured that they are resistant against these wood
boring species. Some of the wood speCies mentioned above and also some of the wood
modifications may be good alternatives for maritime construction.