This study compared the sizes of zooids in colonies of the cheilostome bryozoan Cribrilina annulata collected from two differing substrata (stones and algae) in three regions of the White and Barents Seas. Zooids of the colonies growing on stones were larger than those in the colonies growing on the thalli of the red alga Odontalia dentata. Size differences of the zooids in the colonies growing on the same substratum in different regions were minor. Three possible explanations for these dimensional differences of zooids are discussed: (1) larvae of different sizes settle on different substrata; (2) ancestrulae of different sizes survive on different substrata; and (3) substrata influence the ancestrulae's size.

The effect of substrate texture on colonization by stream macroinvertebrates was studied in a mountain stream. Experimental patches made of natural substrate, with two levels of cobble and gravel texture (rough and smooth), were subjected to two colonization periods (two hours and one week) within a riffle. Cobble texture affected the number of individuals and taxa colonizing substrate patches, although these relationships depended on time of colonization and some local environmental factors. Texture influence was different for different taxa, and only affected the scraper functional feeding group after one week of colonization, probably in relation to the development of an epilithic layer. These results suggest a significant effect of the surface texture of substrate on colonization by macroinvertebrates, although the effect is complex and needs more careful examination.