File:American malacological bulletin (1987) (17533857544).jpg

Title: American malacological bulletin
Identifier: americanmal4519861987amer (find matches)
Year: 1983 (1980s)
Authors: American Malacological Union
Subjects: Mollusks; Mollusks
Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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HORNBACH AND COX: ENVIRONMENTAL INFLUENCES IN PISIDIUM 57 rates. Also, none of the clams from FP reached shell lengths characteristic of their natural habitat (i.e. FP clams often reach sizes > 3.0 mm but none reached this size in these ex- periments). There is, however, an effect of pond of origin on how clams grew in the water of various hardness (Fig. 7). Based on t-tests conducted for each date for each treatment (i.e. water hardness), the following results were found. In pond water, clams from FP generally had larger mean shell lengths from the beginning of the experiments until July 1983 (ap- proximately day 350) at which time there was no significant difference in mean shell length until the clams from RP died. In very soft water, clams from RP had significantly larger mean shell lengths from the beginning of the experiments until February 1983 (approximately day 270). Following this date there were no significant differences. In soft water, again clams from RP had significantly larger mean shell lengths until July 1983 (day 350) and then there was no difference. In hard water there was no significant difference in shell length until September 1982 (approximately day 80) and then clams from FP had significantly greater mean shell lengths than clams from RP. There was no significant difference in shell lengths of clams maintained in very hard water at any time. These results, again are difficult to interpret and show no clear pattern of water hardness effect on growth except that in softer waters clams from RP appeared to grow slight- ly better than clams from FP but in hard water clams from FP seemed to grow better. Part of the inconsistency in pat- tern has to do with differences in survivorship patterns under various treatments. Since clams die at different rates in these treatments (see below) this affects mean shell lengths dif- ferentially. It might have been better to isolate individual clams and follow individual growth rates rather than mean Table 3. Survivorship data, partioned by treatment, for various sizes of Pisidium casertanum from transfer experiments between Riopel Pond (RP) and Farriers Pond (FP). The numbers in parentheses after the median survival times are standard errors. TREATMENT Number of Pond of Origin Median Individuals _ Initial Size Survival at start of Pond of Transfer (mm) Time (Days) Experiment NB* 65.1 12 2) 172 2.5 113.3 (2.4) 40 2.5 49.9 (1.3) 40 2.1 - 2.5 50.4 (2.9) 40 2.5 122.5 (4.3) 6 NB* 51.4 (3.3) 45 2.5 ( - ) 0 'newborns - clams born during the transfer of experiments
Text Appearing After Image:
TIME (DAYS) Fig. 5. Survivorship curves for 5 size categories of Pisidium casertanum involved in transfer experiments between two ponds in southwest Virginia (RP = Riopel Pond; FP = Farriers Pond).

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