Influence of topographic heterogeneity and spatial scales on the structure of the neighbouring intertidal endobenthic macrofaunal community

Abstract

The influence of topographic heterogene~ty (boulders of different slzes: 0 75, 1.5, 2.25 m ) on ~ntertldal soft-bottom communlty characteristics [diverstty(H') r~chness, and btomass] was examined In the St. Lawrence Estuary. Canada. The macrofauna, s e d ~m e n t chal-acterist~cs, and flow regime In the zones surrounding boulders were examlned in 6 orlentations (direct~ons] a n d at 3 d~stances from boulders. Flow around boulders and control sites (no boulders) was estimated by the rate of plaster dissolut ~o n of standard plaster cyl~nders. Control sttcs (no boulders) showed the highest spectes dlverslty (H',: based on density) and r ~c h n ~s s These parameters decreased s~gnificantly w ~t h boulder stze and Increased s ~g n ~f ~c a n t l y w ~t h dlstance from boulders. For both small and large boulder slzes, h ~g h e s t and lowest divers~ties were generally observed In oppoute oncntat~ons Overall, b ~o m a s s was not Influenced by boulder slze Plaster d ~s s o l u t ~o n expla~ned more v a r ~a b l l ~t y in d~versity, richness and b~onlass ( u p to 35, 30 and 25'%), r e s p e c t ~v ~l y j than d ~d sediment charactrl-~st~cs (8, 6 and 27",,, r ~s p c c t ~v e l y ) . Specles dominance was sttong dnd PI-obably explained the relatlve constancy of d~verstty among treatments