Occurrence of Paraprionospio sp. (form A) larvae (polychaeta: spionidae) in hypoxic water of an enclosed bay

Spatial and temporal distribution of larvae of Paraprionospio sp. (form A), an indicator of organic pollution in Japanese coastal waters, was investigated from May 1982 to November 1982 in Kumihama Bay, an area where oxygen-deficient water develops from late spring through autumn. This species has a less opportunistic life history represented by a seasonal peak in recruitment (September–October 1982). Simultaneously with the deoxygenation in May, larvae appeared in the bottom layer and were subsequently found through November almost exclusively in water layers with oxygen levels below 1 mg l−1. Larvae displayed no changes in vertical distribution in a 24-h study conducted in August 1980. These observations indicate that larvae have the ability to tolerate anoxic or hypoxic water throughout their entire development. It is hypothesized that the adaptation of larvae to hypoxic water may explain the high abundances of Paraprionospio sp. (form A) in organically polluted sediments.