(full paper is archived in the Miller Library)
Title: Field and laboratory studies of the effects of chlorinated and unchlorinated sewage on the hermit crab Pagarus samuelis (Stimpson, 1859)
Student Author(s): Remsen, Van
Faculty Advisor(s): Abbott, Donald
Location: Final Papers Biology 175H
Date: June 1970
Keywords: sewage pollution
Abstract: 1) Pagurus is absent within a 100 foot radius of the Pacific Grove sewage outfall. No abnormalities in the patterns of distribution of Pagurus were found outside the 100 foot radius. 2) field cages containing P. samuelis placed within a 100 foot radius of the outfall showed 100% mortality in 28 days. Beyond this distance, mortalities did not exceed those in unpolluted areas. 3) Chlorinated sewage (residual chlorine 15-45 ppm) was the only one of several solutions tested in the laboratory (including dechlorinated sewage) showing significant mortality in 20% and 105 concentrations. Chlorine was probably the cause of deaths recorded in field cages within 100 feet of the outfall; laboratory studies showed sewage without chlorine could not account for this mortality except in concentrations above 50%. 4) Fresh water is a component of sewage toxic to P. samuelis at salinities of 0 -17 o/oo, but not toxic at 27 o/oo and above in 15 days. 5) Other toxic components are present in sewage since mortality exceeding that of controls was recorded in sewage which was dechlorinated and osmotically balanced. 6) P. samuelis tends to move away from solutions with salinities at 27 o/oo or below, but this alone probably cannot explain the absence of this species within the 100 foot radius of the outfall. 7) P. samuelis is not a sensitive indicator for unchlorinated sewage, but is very sensitive to chlorinated sewage. If sewage is not chlorinated, P. samuelis could survive for prolonged periods in 20% concentration of sewage.