BOSMINA REMAINS IN LAKE WASHINGTON SEDIMENTS - QUALITATIVE HETEROGENEITY OF BAY ENVIRONMENTS AND QUANTITATIVE CORRESPONDENCE TO PRODUCTION

Bay environments differ in productivity and species composition from o pen waters. Transects of surface sediments in Lake Washington (Seattle ) reveal significant morphological gradients in the small pelagic clad oceran Bosmina longirostris. In all bays examined, these bosminids ran ge from shorter featured clones nearshore to longer featured clones of fshore. However, because bays constitute such a limited areal extent o f the lake (4.9%), only 2.3% of remains in midlake sediments came from bay populations. A core taken from midlake waters indicates nearly un iform long-featured morphology of offshore Bosmina over the past 80-12 5 yr. The localized deposition of remains in bays underscores that bio diversity surveys of large lakes need to include bays in addition to o pen-water samples. Clarifying how abundant cladoceran remains are prod uced, transported to, and preserved in sediments is crucial for interp reting historical sequences. A simple vertical model, derived from mol ting and death schedules, accurately predicts relative seasonal fluxes for remains at a midlake site (r = 0.94-0.95). However, the absolute flux is low, <7% of the expected rate, suggesting substantial loss thr ough decomposition and fragmentation. Use of abundant cladoceran micro fossils to reconstruct species-specific or general secondary productio n requires careful calibration studies, although the potential dividen ds are great.