File:American malacological bulletin (1987) (18156382765).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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LOPEZ AND HOLOPAINEN: SUSPENSION-FEEDING BY PISIDIUM 23 second method involved placing top 2 cm of a core into cen- trifuge tubes and centifuging for 10 minutes at 750 x g. The supernate was decanted and allowed to settle for 15 minutes to remove larger mineral grains. The interstitial suspension prepared in this manner typically constituted approximately 50% of the total sediment volume. In the third method, 5 cc of sediment was placed into a 10 ml syringe, and pore water squeezed through a 3 nm nuclepore filter fitted in a Swinnex filter holder. INGESTION AND ABSORPTION OF BACTERIA BY PISIDIUM CASERTANUM AND P. CONVENTUS Laboratory experiments were conducted to determine whether or not these two species ingest and absorb interstitial bacteria. ABSORPTION EFFICIENCY OF INTERSTITIAL BACTERIA Several experiments were conducted, but because results were similar, only one is described here. An interstitial suspension was prepared by centrifugation (see above) of sediment collected from 18 m depth in Lake Paajarvi. There were 8.2 x 107 cells x ml"1 in the suspension. A 12 ml sample was then labelled for 20 hours with 30 /*Ci 14C-glucose and 37 nCi 51CrCI3 (see Lopez and Cheng, 1983 for details of radiolabeling methodology). Unincorporated isotopes were removed from the suspension by repeated centrifugations and rinsings with filtered lake water, and then the suspension was brought back to its original volume. Animals had been collected from Lake Paajarvi and allowed to acclimate to laboratory temperature (approximately 18° C) for several days. Sixteen specimens of each species were placed in the labelled suspension and allowed to feed for 1 hour. Half of the animals were then sacrificed to determine 51Cr:14C of the ingested material, while the rest were allowed to feed on an unlabelled interstitial suspension for 2 hours. Fecal pellets were then collected and prepared for liquid scintillation counting. Animals and pellets were solubilized in tissue solubilizer (NCS, Amersham). The scin- tillation cocktail consisted of (9:1) mixture of PCS (Amersham) and 1M HCI. Samples were counted on an LKB liquid scintilla- tion counter using standard two-channel technique with ex- ternal standards corrections. (Wightman, 1975; Cammen, 1977). Absorption efficiency was estimated by the 14C:51Cr twin-tracer method (Calow and Fletcher, 1972; Cammen, 1980b; Lopez and Cheng, 1983). INGESTION/ABSORPTION OF INTERSTITIAL AND SEDIMENT-BOUND BACTERIA A series of experiments was conducted to determine whether or not Pisidium casertanum or P. conventus preferen- tially feed upon interstitial bacteria over particle-bound bacter- ia . Interstitial suspensions and sediment were separated by centrifugation. Interstitial suspensions and sediment suspen- sions were then split into two, and 5 ml subsamples of each were labelled either with 3H (thymidine or glucose) or with 14C- glucose. (20/*Ci 3H, 10/iCi 14C). After approximately 5 hours of labelling, labelled suspensions were then centrifuge-rinsed to remove unincorporated isotopes, and brought up to original volumes. Then interstitial and sediment suspensions were
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Fig. 1a. Fecal pellet from Pisidium conventus. A few mineral grains, some as large as 20 jtm (arrow) are visible. The pellet is 175 long. 1b. Extremely loose pellet produced by Pisidium conventus consisting almost entirely of small (<5 ^m) globular particles. Mineral grains are very rare. The pellet is 110 ^m long. mixed together in a 1:1 proportion, thereby producing a sedi- ment with approximately natural water content. In treatment I, interstitial bacteria were labelled with 3H and particle-bound bacteria with 14C, while in treatment II, suspensions were labelled in the reciprocal manner. For each treatment, 3 groups of 4 Pisidium casertanum or P. conventus were placed in 2 ml of mixture in small wells of a multiwell dish. After 2.5 hours, animals were transferred to lake water, allowed to crawl for several minutes to remove much of the adhering sediment, then moved to unlabelled sediment for 1 hour. Animals were then prepared for liquid scintillation counting, first taking care to remove shell encrustations. Isotope incor- poration in animal tissue is a measure of the amount of bacteria absorbed from each fraction. In trial 1, sediment collected from 8 m was labelled with 3H-thymidine and 14C-glucose, and offered to Pisidium casertanum. In trial 2, 14 m sediment, labelled as above, was offered to both species. In trial 3, 18 m sediment was labelled with 3H- and 14-C glucose, and offered to both species.

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