Effect of land development on stream bottom faunas
- Fisheries Laboratory, Marine Department.
The most striking feature of land development in New Zealand has been the removal of the original forest cover from a large proportion of the land, and its replacement by pasture. Although no historical data are available, study of present conditions indicates that this change had comparatively little effect on the bottom fauna of streams. Where clearance has decreased the stability of the bed the average level of abundance has been probably reduced by more frequent and severe flooding. In small streams, on the other hand, clearance has increased the illumination of the stream bed and enabled the attached algae and the fauna feeding on them to increase also. Qualitatively, there appears to have been little change in the fauna, although a few groups such as the stone flies (Plecoptera) and caddisflies of the family Leptoceridae may have decreased.
The less conspicuous changes in land use in recent years which result from more intensive and efficient agriculture are, by contrast, having a pronounced effect upon the bottom fauna, particularly of the fairly rapid, stony, streams which are characteristic of much of New Zealand. The changes arise primarily from the increased supply of nutrients in the water; this increases the quantity of attached algae growing on the stream bed, and changes their nature; the changes in physical environment and food supply so produced cause qualitative changes in the nature of the bottom fauna.