Environmental Controls on Macrofaunal Community in the Gaoping Submarine Canyon off the SW Taiwan
Date Issued
2016
Date
2016
Author(s)
Chen, Guan-Ming
Abstract
Gaoping Submarine Canyon （GPSC） is the major pathway of terrestrial organic carbon into the deep South China Sea and also an area prone to frequent submarine geohazards. Despite our understanding on the sediment transports in the GPSC has accumulated over the years, their effects on the benthic ecology has never been studied. In order to understand how the spatial and temporal variations of the GPSC environments may affect the community structure of deep-sea macrobenthos, we repeatly sampled the upper GPSC and the adjacent slope （GPS） in April, August and November 2015. A total of 8 stations were sampled from 200 to 1100-m depths for macrofauna, bottom hydrography and sediment geochemistry. A 3-D, hydrostatic, internal tide model was also used to extract the bottom tidal current velocities. Our results suggest that the macrofaunal density, diversity and taxon composition were significantly different between the canyon and slope. Near the head region of GPSC, physical disturbance by hyperpycnal conditions and strong internal tide energy may depressed macrofaunal density and diversity. As the depth and distance increase away from the canyon head, the physical disturbance may be relieved and thus resulted in increase of macrofaunal density and diversity with depths. The internal tide energy was stronger in the canyon than on the slope but in gerneral the energy decreased with depths; therefore, organic carbon associated with the fine grain sediments was less likely to setttle in the canyon and near the shelf breaks, resulting in higher total organic carbon （TOC） contents in the slope sediments, as well as an increase of sedimentary TOC with depths. The macrofauna density on the slope, howerver, displayed a negative relationship with TOC and declined significantly with depth, suggesting that the TOC concentration may be controlled by hydrodnamic engery and not necessary relfected the food availability to the macrofauna. On the slope, the declined in macrofauna density also liklily relieved the compitions, promote coexistence and thus resulted in the significantly increasing diversity with depth. For the taxon composition, polychaetes, nematodes and harpacticoids thrived in both the canyon and slope, but peracarid crustaceans were either rare or disppeared from the canyon and mostly occurred on the relatively stable slope environments. In addition, the abundance-weighted mean vertical distribution of macrofauna was significantly deeper in the canyon sediments than that on the slope sediments, presumably, due to the removal of the epibenthic peracarid crustaceans in the canyon. In the wake of the global climate changes, the changes of storm and precipitations patterns likely lead to changes in frequency and intensity of submarine geohazards in the canyon. This study investigated the interpalys between submarine canyon environemts and benthic communities stucture. The reuslts will enhence our ability to predict the potential climate changes impacts on the submarine canyon ecosystems.
Subjects
Deep Sea Macorfauna
Gaoping Submarine Canyon
Taxon Composition
Grain Size
Organic Carbon
Disturbance
Type
thesis
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