Vertical distribution of nematodes (nematoda) and harpacticoid copepods (Copepoda : Harpacticoida) in muddy and sandy bottom of intertidal zone at Lok Kawi, Sabah, Malaysia

The approach taken in the present study was to perform a sampling of the ne matodes and harpacticoid copepods and to measure certain pore water paramet ers in muddy and sandy sediments. The Redox Potential Discontinuity (RPD) l ayer in muddy sediment occurred within the top few millimetres. This contra sted strongly with the deep RPD layer found at the similar tidal height on the sandy sediment. The difference in redox conditions between the muddy an d sandy sediments is possibly due to the differences in hydrodynamism. The bulk of nematodes in sandy was found a little deeper than muddy areas. The activity of the many burrowing animals in the muddy and sandy areas may pla y a role in the oxidation of the sediments and thus influence the vertical distribution of the nematode and harpacticoid copepods. The vertical nemato de species showed zonation vertically from the surface to the 30 cm depth o f the sediment. The occurrence of the nematode species below the RPD layer indicated their ability to tolerate sulfides and to utilize the high densit y of microbial organisms in this layer. The presence of low concentration o f dissolved oxygen of the pore water was also responsible for the vertical distribution. The nematodes feeding groups 1A (selective deposit feeders), 1B (non-selective deposit feeders) were abundant in the top 15 cm, whereas the 2A (epigrowth feeders) group was abundant in the top 5 cm of the sedime nt layer. Their distribution was related to the availability of food such a s benthic diatom and other algae in the sediment.