Ecology of Polydora cornuta Bosc, 1802 (Spionidae: Polychaeta) in the Eutrophic Port of Fukuyama, with Special Reference to Life Cycle, Distribution, and Feeding Type

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Fukuyama Port is a semi-enclosed harbor located in the central region of the Seto Inland Sea. During June 1998, no dissolved oxygen (DO) was present at the bottom layer of the water column. Low DO conditions continued until October, coinciding with a period of high water temperature. A study of the life cycle, distributive characteristics, and feeding type of Polydora cornuta Bosc, 1802, inhabiting the organically polluted port area, was performed. Polydora cornuta which lives in mud tubes in bottom sediments, was found to be unevenly distributed in the innermost part of the port. Taxonomic characteristics are modifications of setiger 5, which includes major heavy spines. Predicted life-cycle duration, based on the 11.5 - 18.2°C temperature of bottom mud during the normal life period for this species, was 40 to 59 days. Appearance of benthic life-stage individuals was limited to winter and spring (i.e., January to May). However, pelagic larval individuals were present throughout the year. The distribution and density of P. cornuta reflected the DO conditions of the bottom layer and sediment. Stable carbon and nitrogen isotope analysis indicated that this species is a suspension feeder.