Influence of initial substratum surface tension on marine micro- and macro-fouling in the Gulf of Thailand

Abstract

The density of five major groups of fouling organisms (bacteria, diatoms, choanoflagellates, ciliates, macroorganisms) on seven artificial substrata with surface tensions between 19.0 and 64.5 mN m−1 was studied in the Gulf of Thailand. Two series of test panels of the different substrata were immersed into the sea between 3 hours and 64 days (macrofauna 128 days). The results show that surface tension has a limited impact on the density of the organisms. Only bacteria settled continuously in significantly lower numbers on materials within the minimum bioadhesive range (20–25 mN m−1) than on other substrata. Significant differences between the substrata may disappear after long exposure, as in series 2 after 16 days. For diatoms and protozoa, a colonisation pattern similar to that of bacteria with a minimum of 20–25 mN m−1 was detected after several exposure intervals. However, it was never recorded in more than 3 exposure intervals in a row. The colonisation pattern of macroorganisms could not be attributed to substratum surface tension. An index, called “colonisation degree” is introduced to give a general impression of the density of organisms on the materials tested. The colonisation degree did not show any significant 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. *** DIRECT SUPPORT *** A03B6037 00003