RECONSTRUCTING HISTORICAL ECOLOGY OF KANE'OHE BAY (HAWAII) USING SURFICIAL MOLLUSK-DOMINATED SHELL ACCUMULATIONS

There is a growing realization that surficial shell accumulations can provide reliable historical ecological data on the past states of aquatic ecosystems, including diversity, spatial ecosystem structure, and long-term stability of marine benthic associations. The surficial accumulations typically represent multi-centennial or multi-millennial records of local communities potentially archiving a long-term historical record of local and regional ecosystems.

Using this approach, we are currently investigating historical ecology of Kāneʻohe Bay, which is situated on the southeast coast of O’ahu Island. The bay is the largest sheltered body of water present on the main Hawaiian Islands and also harbors one of the two Hawaiian barrier reefs. Diverse habitat types, including reefs, soft-bottom lagoons, forereef hardgrounds, and diverse shoreline settings are present in the bay.

A total of 21 bulk samples were collected by SCUBA, with multiple replicate samples acquired for each major habitat type present in the study area. Samples were sieved using 1mm mesh size and all shells were identified to species level, when possible. Preliminary analyses based on 11 samples (933 specimens total) point to high regional biodiversity (89 species). In addition, local (alpha) diversity varies notably across sites: standardized species diversity (n = 35 specimens) ranges from 7.2 to 17.5 species per sample. The highest diversity was recorded in shallow reef-associated habitats and the lowest was recorded in muddy soft-bottom lagoon habitats. This is consistent with surveys of living communities carried out concurrently at the same sites. Multivariate ordinations of shell samples clearly delineate habitats indicating that faunal composition varies predictably across different environmental settings present in the bay. These preliminary results suggest that despite time-averaging and post-mortem transport surficial shell accumulation preserve faithfully spatial structuring of marine benthic associations and indicate that major habitats present in the bay must have been relatively stable spatially in the most recent centuries.