SALT AND WATER BALANCE IN LUGWORMS (POLYCHAETA:ARENICOLIDAE), WITH PARTICULAR REFERENCE TO ABARENICOLA PACIFICA IN COOS BAY, OREGON

¹ Institute of Marine Biology, University of Oregon, Charleston, Oregon; and Zoology Department, Pomona College, Claremont, California 91711

1. The lugworm Abarenicola pacifica can tolerate salinities as low as 23% SW in the laboratory, but is unlikely to survive more than brief exposure to salinities lower than 50% SW in the field.

2. Over this salinity range, Ab. pacifica is an osmotic conformer, but the coelomic fluids are slightly hyperosmotic to the medium. The literature suggests that other members of the family have a similar osmotic behavior.

3. At all salinities, the coelomic fluids of Ab. pacifica are slightly hypo-ionic to the medium with respect to Cl^- and Na⁺. Ion regulation appears to be very limited in all members of the family.

4. Ab. pacifica has very little ability to control its water content and volume in different salinities.

5. The relationship of the osmotic physiology of lugworms to their distribution in estuaries is discussed. While lugworms may be able to avoid contact with overlying waters of too low salinity for perhaps a few days, they are unlikely to form permanent populations in those parts of estuaries where the interstitial salinities drop below 50% SW during any part of the year.