Benthic Communities as Indicators of Geological and Biogeochemical Processes in the Gulf of Papua

Benthic communities inhabiting Gulf of Papua deposits play important roles in determining remineralization and material cycling processes at the seafloor. Faunal abundances, size-frequency distributions, functional groups, and vertical distributions reflect a spectrum of diagenetic depositional environments produced by variations in local sediment transport dynamics and coastal morphology. Thus faunal properties provide a basis for comparison of factors influencing sediment - overlying water interactions, elemental cycling, and material storage. During mid NW monsoon periods (Jan-Feb), macrofaunal densities at Gulf stations are generally low (260 to 1270 m^{-2 }), large macroinfauna are absent in the upper ∼25 cm, and small (< 0.5 mm) surface deposit-feeding polychaetes and tubiculous amphipods dominate, reflecting a frequently destabilized seabed and high sedimentation / erosion rates. Although significant numbers of macrofauna have generally been found to be absent over large areas due to frequent physical disturbance, sedimentary structures demonstrate that many regions of the GoP deltaic complex are periodically extensively bioturbated by relatively large and deep-burrowing infauna. Additionally, faunal samples from February 2003 have significantly increased numbers of opportunistic polychaete and crustacean species relative to 1999 and 2000, indicating that there are periods of faunal colonization and community expansion. These changes may correlate with decreased riverine sediment input associated with El Niño conditions. While the macrofaunal community is relatively depauperate and apparently subject to inhibition by inhospitable physical conditions, the microbial community is highly active, diverse, and abundant throughout the upper ∼1m. The dominance of bacteria and microfauna rather than macrofauna in wet tropical environments like the GoP, contrasts with many reactive continental shelf mud deposits in temperate regions.