The density of five major groups at fouling organisms Ibacteria, diatoms, choanotlagellates, ciliates, macroorganisms) on seven artilicial substrata with surface tensions between 19.0 and 64.5 mN m ' was studied in the Gulf at Thailand. Two series of test panels r the different substrata were immersed into the sea between 3 hours and 64 days (macrotauna 128 days). The results show that surface tension has ,t limited impact on the density of the organisms. Only bacteria settled conlinuously in signilicantly lower numbers on materials within the minimum bioadheslw2 range (20-25 mN m ') than on other substrata. Signifi(:dn[ differences between the substrata may disappear after long exposure, as in series 2 after 16days For diatoms and protozoa, a colonisation pattern similar to thdt of bacteria with a minimum ol 20-25 mN m : was detected alter severdl exposure intervals, l.lowever, it was never recor(ted m more than 3 exl)osure intervals in a row. The colonisation pattern of macroorganisms could not be attributed Io substratum surface tension. An index, called "colonisation degree" is introduced to give a gene.~ral impression at the density of organisms on the materials tested. The colonisation degree did not show any signilicant difference at any exposure interval. The present results clearly suggest that substratum surface tension is easily overshadowed by other factors in colonisation processes under natural conditions.

Carapace wettability and density of fouling organisms (bacteria, diatoms, protozoa, fungi, macro-organisms) were investigated for 45 crustacean species (Hoplocarida, Decapoda) from 15 families in the Gulf of Thailand. The results show that crustaceans can create and maintain characteristic carapace wettabilities. About 21 species (47%) possess highly wettable carapaces with contact angles below 20 • . Contact angles between 20 • and 40 • were recorded for four species (2%), angles between 40 • and 60 • for eight species (4%) and from 60 • to 70 • for 11 (24%) species. One species, Alpheus euphrosyne (Alpheidae, Decapoda), exhibited an extremely low surface wettability (contact angle: 91 • ). Densities of colonisers and contact angles did not correlate. Very low wettability by water (θ > 90 • ) may only contribute little to fouling reduction in A. euphrosyne which showed the most hydrophobic carapace surface and was colonised by the lowest numbers of bacteria among all species and no other colonisers at all. We conclude that surface wettability is of little relevance for antifouling defence in crustaceans.

Carapace wettability and density of fouling organisms (bacteria, diatoms, protozoa, fungi, macro-organisms) were investigated for 45 crustacean species (Hoplocarida, Decapoda) from 15 families in the Gulf of Thailand. The results show that crustaceans can create and maintain characteristic carapace wettabilities. About 21 species (47%) possess highly wettable carapaces with contact angles below 20 • . Contact angles between 20 • and 40 • were recorded for four species (2%), angles between 40 • and 60 • for eight species (4%) and from 60 • to 70 • for 11 (24%) species. One species, Alpheus euphrosyne (Alpheidae, Decapoda), exhibited an extremely low surface wettability (contact angle: 91 • ). Densities of colonisers and contact angles did not correlate. Very low wettability by water (θ > 90 • ) may only contribute little to fouling reduction in A. euphrosyne which showed the most hydrophobic carapace surface and was colonised by the lowest numbers of bacteria among all species and no other colonisers at all. We conclude that surface wettability is of little relevance for antifouling defence in crustaceans.