Abstract
The vertical distribution of meiofauna in estuarine sand and mud sediments was investigated over a period of 14 mo. Statistically significant differences were found between fluctuations of meiofauna inhabiting different depth zones in the top 20 cm of the sediment. The shallow populations are affected more drastically during times of adverse conditions but they have the ability to respond rapidly to favorable conditions. A combination of physiological adaptation and changes in species composition, rather than seasonal vertical migrations, are responsible for the observed patterns.