Effects of habitat complexity on the structure of macrobenthic

. Abstract: The structure and seasonal variability 01'macrobenthic associations in four different patches on a Spartilla altemiflora bed at Arrozal Point, Canan6ia, São Paulo State are described and compared. In the local intertidal marsh, densities 01'S. a!temiflora plants appear in sparsely or densely arranged patches, both in tall and short forms. Thc infaunal polychaetes Capitella capitata, Isolda plllchella, Ncreisoligohalina and Laconereis aClltaaccounted for 44.0% 01'the total individuais while epifaunal forms such as Heleobia allstralis, Littorina anglllifera, Tholozodiu11l r/wmbofrolltalis and Sphaeromopsis l1l011rei were the second most abundant components with 39.5%. Classification analyses 01'sampling time in the same sampling patch indicated that species groups were formed basically by spatial similarity and peak densities aI' macrofauna and secondarily by temporal patterns. Temporal variations were evident with higher number 01'species in colder months (winter and spring). Specics diversity and evenness did not show c\ear seasonal patterns, although they were signilicantly diffcrcnt in sampling patches and time. Heleobia allstralis, Littorina allgulifera and Allomalocardia brasiliellsis were dominant in tall sparse S. altemiflora with density peaks occurring in wintcr/spring periods. 17wlozodium r/lOmbofrolltalis and Sphaeromopsis n!ourei were dominant in short sparse S. altemiflora with dcnsity peaks in summer. In tall, densely distributed S. altemiflora plants the higher densities occurred in winter and the dominant species were Nereis oligo/wlilla, [solda plllchella and Capilella capitata. The species H. allstralis, L. allglllifera and A. brasiliellsis predominated in the short S. altemiflora plants densely distributed, with faunistic peaks recorded in spring. The results suggest that differenccs in form and aggregation 01' S. altemiflora impart changes in the structure 01' macrobenthic fauna associated to this vegetation.