Abstract
Little is known about meiofaunal responses to Low- versus High-Water-Level (L- vs HWL) particularly in the subtropics. Meiofaunal reaction was evaluated in three locations (deeply-different) in two man-made freshwater channels in (Rowaina and Shalma) Northern Nile Egyptian delta: 50, 100, & 150, and 900, 950, & 1000 metres distances from the sluice, respectively. LWL and HWL were in January and July 2019 respectively. Eight vs ten and nine vs eleven major taxa were noted in Rowaina H- vs LWL and Shalma L- vs HWL, respectively. Taxa had different susceptibilities to L- vs HWL. Nematode, hydracarina, and oligochaetes dominated in L- and HWL, (Shalma), and in HWL (Rowaina). Whereas Nematoda, Copepod, and Oligochaeta prevailed in LWL (Rowaina). Oligochaeta biomass was generally high in LWL and HWL. Hydracarina in LWL, and Nematode & Copepod in HWL had low biomasses in Rowaina and Shalma respectively. Abundances and biomasses were significantly different within and among channels. Environmental variables were significantly different only between water levels. It could be concluded that L- vs HWL has both direct and indirect (variabilities in environmental factors) impacts on meiofauna. Channel width & morphology, may impose extra influences. This study may enhance invertebrate surveys with hydrologically different freshwater bodies.

Key words: abundance, biomass, meiofauna, water level.