PARENT SESSION
Oral Session #61: Aquatic Ecology: Fish - Communities and interactions. Presiding: J. Chick.
Thursday, August 9, 2001. 8:00 AM to 11:45 AM. Hall of Ideas F.

Assembly of fishes and macroinvertebrates in a large neotropical floodplain river: The role of structural habitat complexity.

Arrington, Albrey¹, Winemiller, Kirk¹, ¹

ABSTRACT- Large floodplain rivers are poorly studied components of the biosphere that contribute significantly to biodiversity and production worldwide. We examined the role of habitat complexity in structuring local fish and macroinvertebrate assemblages in the Cinaruco River, Venezuela. The Cinaruco is a relatively pristine lowland floodplain river that harbors a diverse fish fauna (>225 species) and experiences dramatic seasonal fluctuations in water levels (>5m) that directly affect habitat availability. Over 6 months, early dry season thru early wet season, we collected monthly samples from shore-line habitats of varying structural complexity in the main river channel and in lagoons, with seven replicate locations sampled each month for each habitat. Detrended correspondence analysis of 215 samples containing 46,292 individual fishes and macroinvertebrates indicated a consistent, non-random pattern of assemblage structure associated with structural complexity of small-scale (<5m) habitat patches. Although samples were nested within locations and subject to spatial auto-correlation, habitat type and complexity and not geographic location explained assemblage structure. Fishes and macroinvertebrates were assembled primarily along an axis of structural habitat complexity, and secondarily affected by flow velocities. We believe the 3-dimentional structural complexity of habitat units is a primary factor influencing recruitment into local assemblages, with abiotic (e.g., flow) and biotic factors further constraining membership in local assemblages.

KEY WORDS: Assemblage structure, Habitat complexity, Neotropical floodplain river, Fishes