The Sediment Reworking of the Mud Shrimp Laomedia sp. (Crustacea: Laomediidae) with Tidal Conditions in the Intertidal Sediments of Gomso Bay, Korea

Although the thalassinidean mud shrimp Laomedia sp. is one of the most abundant species in the upper tidal flats along the west coast of Korea, little is known of its ecological characteristics and bioturbation effects on intertidal sediments. This study estimated the sediment reworking rate (SRR) of Laomedia sp. by quantifying in situ sediments ejected from the burrows via direct entrapment and evaluated the effects of tidal conditions on the SRR. The amount of expelled sediments from individual burrows was significantly related to the duration of submergence, whereas SRR showed an increasing trend as elevation increased. The SRR of Laomedia sp. was estimated to be 40 g ind.−1 d−1 and the annual SRR of this species was 72.2 kg m−2 yr−1 based on the density in the study area, which is very high compared to other thalassinidean shrimp. These findings suggest that Laomedia sp. is an important bioturbator in intertidal sediments, and tidal conditions should be considered when evaluating the SRR of this species.

Holocene environmental change inferred from multiple proxies in the mouth of Gomso Bay on the west coast of South Korea

A sediment core (14DH-C01) obtained from the mouth of Gomso Bay, on the west coast of South Korea, was used to obtain high-resolution palynomorph, grain-size, and14C age data to investigate the Holocene sedimentary environment. The results indicated a transgressive depositional process with four stages controlled by sea-level change, as follows: river-dominated fluvial deposition from the early Holocene to 8.48 cal ka BP; tide-dominated tidal channel fill transgression from 8.48 to 8.08 cal ka BP; tide- to wave-dominated tidal channel fill transgression from 8.08 to 6.98 cal ka BP; and wave-dominated marine transgression from 6.98 cal ka BP to the present. Tidal channel filling was the primary mid-Holocene depositional process, accounting for the high sedimentation rate observed. The different hydrodynamics of the river-dominated, tide-dominated, tide- to wave-dominated, and wave-dominated processes following the changes in sea level may have controlled the transgressive depositional process. This transgressive sedimentary model differs from those of other large river mouth areas (e.g., the Changjiang River) since the mid-Holocene, perhaps resulting from the limited sediment supply in the study area.