The response of two spionid polychaetes to natural processes and anthropogenic activities on the San Pedro Shelf, California

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Abstract
The hypothesis tested here was that the distribution and abundance of two spionid polychaetes (Prionospio sp. A and Spiophanes missionensis) are unrelated to an ocean outfall and its operation on the San Pedro Shelf, California from 1985 through 1994. The hypothesis was rejected, but with different results per species. Abundance of Prionospio sp. A was enhanced near the outfall whereas that of Spiophanes missionensis declined towards the outfall. Both species showed definite seasonal peaks and subtle sediment size preferences. Abundance of Prionospio sp. A was more responsive to the outfall while that of S. missionensis seemed more responsive to major environmental events (storms and El Niños). There was an inverse relationship in abundance between the two species from 1985 through 1994. It was concluded that the coincidental response of both species may be a more sensitive measure of both natural and anthropogenic effects than focusing on the response of a single species.