The effect of increasing seagrass root complexity and redox potential on the population of Pillucina vietnamica (Bivalvia: Lucinidae) in southwestern Thailand

Abstract

ABSTRACTIt is well known that seagrasses provide habitat to many bivalves. Pillucina vietnamica is the dominant bivalve (> 4000 inds m−2) in seagrass beds at the Haad Chao Mai National Park, Thailand, where seagrasses are abundant and diverse. This study aimed to determine the relationship of root, rhizome and redox potential to the P. vietnamica population. The study was performed using patches of three seagrass species (Halophila ovalis, Thalassia hemprichii and Cymodocea rotundata), which have different root morphologies and occur in both mono- and multi-specific stands as well as adjacent to areas of bare sand. The results showed that, within the vegetated areas, the abundance of P. vietnamica increased with increased root complexity and redox potential. A high abundance of P. vietnamica was found in patches of the branched root species, C. rotundata, suggesting that the root mats of this species was a preferred habitat for bivalves by providing a complex habitat and sufficient oxygen levels. The size class frequency of the bivalves differed between seasons. They were smaller and distributed bimodally in the summer but were larger and distributed unimodally in the monsoon month, suggesting a shift from the juvenile stage to the mature stage.