Moss distribution in streams of the Quebec Laurentian Mountains

To model the distribution of aquatic mosses, we measured their cover in 33 Quebec streams. The variation in moss cover among streams was explained mostly (42%) by substratum size (percentage >25 cm in diameter). Water pH and depth also explained a significant amount of variation (9 and 10%, respectively). Within a stream, moss cover was again positively correlated to the availability of large substrata and negatively to water depth. There was a strong inverse relationship between covers of moss and of the filamentous cyanobacterium Stigonema, suggesting a competitive interaction. This study confirms previous observations that moss distribution is mainly controlled by substratum size. Chemistry explains part of the among-stream variation. Stigonema-moss competition partly accounts for the patchy distribution within a stream.Key words: aquatic mosses, Fontinalis, streams, Quebec.

Interaction between the effects of Substratun, Velocity and location on Stream Benthos: and experiment

Patches of large and small pebbles were created in three riffles (fast current velocities) and three pools (slow velocities). It was expected that patches with different sizes of pebbles in the two velocity regimes would vary in the entrapment of fine sediments and organic matter, which in turn would result in differences in benthic community structure. This was not the case, for although deposition of fine material was greater in pools, there were appreciable location-specific differences in the fauna unrelated to the variables monitored in the experiment. Functional feeding groups did not respond predictably to the distribution of detritus. Generally, the community was least influenced by substratum size, with any differences being inconsistent across locations. Most other substratum effects were attributable to the presence of epilithon on undisturbed control patches. Velocity was the most influential factor, with riffles having higher total abundances and higher species richness. Some taxa showed strong location- specific differences. At the level of a small patch of pebbles, the colonization dynamics of the fauna are probably a mixture of species- and location-specific dispersal and selection mechanisms. At larger spatial scales, however, community structure is more predictable, with pools differing substantially from riffles.