Does surface textural complexity of woody debris in lotic ecosystems influence their colonization by aquatic invertebrates

Abstract

Materials retained by river systems are diverse. Woody debris recruited from the riparian vegetation into streams is of variable sizes and varying surface textural complexity. The main aim of this study was to determine experimentally the colonization of wood recruited into a tropical stream by aquatic invertebrates and relate this to the degree of wood surface textural complexity. Wood, being alien to the wholly-aquatic and semi-aquatic invertebrates, provided an attachment substratum and was increasingly colonized by the invertebrates up to the 178th day. There was an initial increase in the taxa diversity up to the 9th day followed by a drastic decrease thereafter. Wood with smaller surface area had the higher invertebrate densities than those with large surface area, thus contrasting the expected trend. Our results show that the colonization by invertebrates of wood was scale-dependent. Invertebrates occupied the cracks, holes, protrusions, crevices and the small depressions found on the wood surface. Chironomidae (Order Diptera) made small tunnels in the more decayed parts of the wood and at the nodal areas. Wood decomposes slowly but it could cumulatively contribute more energy in its lifespan than the short-lived leaf litter which is more abundant in streams. Aquatic invertebrates encountering woody material in nature would make a trade-off between accepting a long-lasting resource and expending energy in continued search for the more palatable short-lived leafy material. The ecological and economic value of wood texture in streams and riparian vegetation management are poorly known and there is need for further research in the tropics.