The Ecological Changes of Macrozoobenthos to the Sand Excavation Activities in the Southern Continental Shelf of the Korea Strait

Abstract

The present study aims to detect early changes in the community structures of macrozoobenthos and indications of their recovery following sand excavation activities in the soft bottom of the southern continental shelf area, Korea strait, from August 2002 to October 2005. About 10 million m3 of relict sandy sediments were excavated from a 9 km2 area over 18 months, from June 2002 to April 2004. The sand excavation and collection activities in the study area increased the sand amount in the residual sediments due to the complete loss of fine surface sediments. However, the fine particles in the turbidity flumes produced by sand hopper vessels were deposited in neighboring zones. The overall ecological impacts of the sand excavation activity are the rapid loss of macrobenthic animals in the central region of the excavation area and the decrease in densities of some disturbance-sensitive macrobenthos, such as Ampelisca spp. and Photis longicaudata that are dominant in the marginal parts of the excavation area. The burrowing polychaete Ophelina acuminata and the opportunistic tube-building polychaete Paraprionospio coora were the most predominant species in the central region of the study area following 12 months. The affected regions showed decreases in the abundance and recovery of the macrozoobenthic fauna species depending on the changes in sediment properties induced by the sand excavation activities, such as sediment loss and material deposition materials. One and a half years after the cessation of the sand excavation activities, the density of the most abundant species was increased and comparable to those in the reference area. In addition, the biological characteristics of the macrobenthic community showed indications of recovery to their previous status, with different faunal compositions and densities. Further long-term ecological monitoring of the macrobenthic communities is necessary to comprehensively assess their recovery processes following sand excavation in the study area.