Results of a detailed study on the vertical distribution of fouling and wood-boring organisme of Trondheimefjord at an interval of 3 m from intertidal level to a depth of 30 m, has been presented, based on data collected from two series of panels, exposed from 15-3-1977 to 15-7-1977 (Series I) and from 22-7-1977 to 13-3-1978 (Series II). The intensity of fouling generally decreased with increasing depth. Quantitatively fouling was heavy on panels of Series I than on Series II, although species-wise it was more heterogeneous on panels of Series II. The bulk of the fouling was constituted by Balanus crenatus, Laomedia sp., Mytilus edulis, Modiolus sp. and Hiatella arctica. Incidence of borers and the resultant destruction of timber were heavy on panels of Series II than on those of Series I. The influence of the period of exposure on the above pattern of infestation by foulers and borers has been discussed. Psiloteredo megotara concentrated at the upper levels upto a depth of 15 m, with more settlement between 3 m to 9 m depth. Although Xylophaga dorsalis was present on panels from 3 m to 30 m depth, their intensity abruptly changed from 9 m onwards and continued to increase with increasing depth, with maximum number near the mud level at 30 m. Attack of Limnoria lignorum also was heavy at mud level. On the same panel, while Psiloteredo megotara preferred to settle in more numbers on the lower surface, Xylophaga dorsalis did so on the upper silted surface. The importance of such selective vertical incidence of different borers and their cooperation in the destructive activity have been stressed from the point of wood destruction in the Trondheimsfjord.

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