Title: The Biological bulletin
Identifier: biologicalbullet208mari (find matches)
Year: [1] (s)
Authors: Marine Biological Laboratory (Woods Hole, Mass. ); Marine Biological Laboratory (Woods Hole, Mass. ). Annual report 1907/08-1952; Lillie, Frank Rattray, 1870-1947; Moore, Carl Richard, 1892-; Redfield, Alfred Clarence, 1890-1983
Subjects: Biology; Zoology; Biology; Marine Biology
Publisher: Woods Hole, Mass. : Marine Biological Laboratory
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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SYMBIONT POPULATIONS IN SEEP AND VENT MUSSELS 147 post-larval and juvenile mussels, fresh, sieved material was sorted under a dissecting microscope. Mussels were separated into classes based on shell color, shell morphology, and shell length. The smallest size class consisted of post-larval mussels with pinkish-red prodis- soconchs (I and II) and with shell lengths within the range of 0.12 to 0.60 mm. Early juveniles, herein referred to as "Jl", were characterized by the presence of a narrow band of yellow dissoconch shell and by shell lengths within the range of 0.6 to 1.2 mm. Four additional juvenile size classes were designated, with shell lengths in the following ranges: J2: 1.2-2.4 mm; J3: 3.6-4.8 mm: J4: 4.8-6.0 mm; and J5: 6.0-8.4 mm. Transmission electron microscop\ A 0.5-cm-wide section of tissue was dissected from the middle of the gill of adult and larger juvenile specimens. Where mussels were too small to be dissected (i.e.. post- larvae and juvenile stages J-l and J-2), the shells were cracked to allow fixative to penetrate the tissue. Bath\mo- diolus azoricus tissues were fixed for about 3 weeks in 3% glutaraldehyde with 0.1 M cacodylate buffer and 0.4 M NaCl (pH 7.8). Bathymodiolus heckerae tissues were fixed for about 48 hours in 3% glutaraldehyde with 0.1 M phos- phate buffer and 0.25 M sucrose (pH 7.4). Samples were rinsed in 0.1 M phosphate buffer containing 0.25 M sucrose and were post-fixed in a I7c osmium tetroxide solution. The shells of post-larvae and juveniles were dissolved by a 24-h immersion in 2.5 g EDTA/100 ml buffer solution. Speci- mens were dehydrated in a graded acetone series and stained en bloc with 2% uranyl acetate. Gill tissue or whole individuals were infiltrated with Embed 812 epoxy embed- ding medium, polymerized, cut into 70-nm to 80-nm thin sections, and stained with lead citrate. Gill sections were viewed with a Zeiss 109 transmission electron microscope. Densities of bacterial morpliotvpes The density of bacterial morphotypes is defined here as the number of methanotrophic or chemoautotrophic cells per 15.5 /iirr within the apical region of bacteriocytes in transverse section (Fig. 2). The areal dimension and location were chosen because they approximately cover the region of a bacteriocyte that contains symbionts. For each specimen, three transverse sections were cut through the middle of the gill filaments (3 to 6 gill filaments per section) at intervals greater than the maximum diameter of the bacteria (i.e.. ^ 2.0 jam) to ensure that a particular bacterial cell was counted only once. Fifteen 15.5-jLtm2 areas per section were haphaz- ardly selected at low magnification (240X ) for bacterial cell counts. Where an area selected haphazardly at low magni- fication was not located in the apical region of a bacterio- cyte, the specimen was adjusted until the apical region of that bacteriocyte filled the field of view. Counts were earned fc
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. Figure 2. Transmission electron micrograph mosaic of a transverse section through a post-larval specimen of Bathymodiolus azoricus (0.12 to 0.60 mm in shell length) gill filament, ce, ciliary cell; fc, frontal cilia; Ic. lateral cilia; lu, lumen; ly. lysosomal-like residual body; n, nucleus; m, methanotrophic morphotypes; arrowheads, chemoautotrophic morpho- types; double-ended arrow, apical region of bacteriocyte. Scale bar = out at high magnification (48.000X) and included all bac- terial cells that were in the field of view and those cells that were intersected by the upper and right margins. The density of bacterial morphotypes was estimated for mussels of different sizes within each species, as follows: Bathymodiolus azoricus—3 post-larvae, 5 Jl, 5 J2, 5 J3, and 4 adults; B. heckerae—3 post-larvae, 5 Jl, 4 J2, 5 J3. and 4 adults. The Kruskal-Wallis nonparametric test for a one- way design was used to assess variations in median density of each morphotype within a mussel species (a = 0.05). Stable isotope analvses Foot, gill, and mantle tissue was dissected, variously, from adult mussels (>20 mm in shell length) and placed in a drying oven (70 °C) for 24 h. Due to their small size, post-larval and juvenile mussels (<8 mm in shell length) were pooled (post-larvae: 35 individuals per pooled sample; juvenile size classes (Jl through J5): 2 individuals pet- pooled sample). These pooled samples were dried whole, then soaked in 10% HCI to remove the shell carbonate, and then re-dried. Subsamples of dried, acidified tissues were

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