Mineral Transformation and Sedimentological Considerations

SEDIMENT INGESTION BY T I G R I O P U S C A L I F O R N I C U S AND OTHER ZOOPLANKTON: MINERAL TRANSFORMATION AND SEDIMENTOLOGICAL CONSIDERATIONS l JAMES P. M. SYVITSKI 2 Department of Geological Sciences Institute of Oceanography University of British Columbia Vancouver, B.C. AND

ALAN G. LEWIS Department of Zoology Institute of Oceanography University of British Columbia Vancouver, B. C. ABSTR^CI: Tigriopus californicus ingest sediment at a rate dependent on the suspension concentration and on particle mineralogy. Ingested minerals undergo chemical and mineralogical transformation that depend on initial mineralogy and residence time in the digestive tract. Clinochiore altered to Mg-chamosite with a reduction in Mg and an increase in Fe. Tremolite partially altered to chamosite with a reduction in both Mg and Ca. Montmorilionite altered to vermiculite and mica with an increase in Mg, Ca, and Fe. Gypsum formed in some mineral-bearing pellets. Such chemical changes may in part explain alteration of minerals in the marine environment. Ingested clays are mostly in the form of flocs. Planktonic pellets settle through the water column much faster than the settling of their component particles. The increased settling rate allows clay-size particles to be deposited where the hydrodynamic conditions suggest only coarse silt and fine sand should occur.

INTRODUCTION

Inorganic particles settling through the water column contribute the largest volume of material to the ocean floor. These particles settle individually or as flocs, their rate of settlement being controlled by their shape and weight. They are exposed to physical, chemical, and biological processes, which may change the particles during and after sedimentation. Clay mineral distribution in bottom sediments has previously been explained by settling rate and chemical changes after deposition. Little work has been done on the biological processes occurring before and after deposition. Most previous studies have been limited to the interaction of sediment and benthic organisms (Verwey, 1952; Lurid, 1957a,; Ani Manuscript received May 4, 1979; revised December 14, 1979. 2Present address: Department of Geology and Geophysics, University of Calgary, Calgary, Alberta.

derson, Jonas and Odum, 1958; Rhoads, 1963; Haven and Morales-Alamo, 1966, 1968, 1972; Rhoads and Young, 1970; Chakrabarti, 1972; Boothe and Knauer, 1972; Pryor, 1975; Cadee, 1976). Accelerated sedimentation of diatoms and coccoliths by incorporation into pelagic zooplankton fecal pellets has been investigated (Schrader, 1971; Roth, MuUin and Berger, 1975; Honjo, 1976; Honjo and Roman, 1978). Feeding activity of pelagic zooplankton may cause rapid sedimentation of small mineral particles, which according to Stokes Law would require years to settle to the sea floor (Lisitsin, 1961; Manheim, Hathaway and Uchupi, 1972). This mechanism may explam the formation of welldefined clay zones related to distinct source areas rather than indistinct mixtures expected from relatively slow deposition and consequent extensive mixing (Lisitsin, 1961). Flat, irregular terrigenous minerals, 1 to 25 v.m m size, were found m the digestive tract of deep-water filter feeding copepods (Harding, 1974). Mauchline and Fisher (1969) noted that

JOURNAL OF SEDIMENTARYPETROLOGY, VOL. 50, NO. 3) SEPTEMBER, 1980, P. 0869-0880. Copyright © 1980, The Society of Economic Paleontologists and Mineralogists 0022-44'72/80/0050-0869/$03.00

870

JAMES P. M. SYVITSK1 AND ALAN G. LEWIS

euphausiids ingest mineral grains along with orgamc debris. Since 70 percent of the suspended particulate material in the ocean is inorganic (Wangersky, 1965), indiscriminate f'flter feeders must ingest inorganic mineral particles (Harding, 1974). Bacteria and organic debris adsorbed on suspended mineral surfaces probably provide nourishment for filter feeding zooplankton (Robinson, 1957; Harding, 1974). Bigham (1974) and Pryor (1975) observed clay agglomerates in fecal pellets and implied that pellets are an important mechanism of marine sedimentation. Such sedimentation by fecal pellets is important inthe transport of trace metals (Johannes and Satomi, 1966; Frankenberg, Coles and Johannes, 1967) and radionucleides (Osterberg, Carrey and Curl, 1963; Fowler and Small, 1972), in the formation of biogenic oozes (Smayda, 1970; Schrader, 1971; Roth et al., 1975; Honjo, 1976), and in nutrient cycling (Honjo and Roman, 1978). Moore (1931) observed that fjords contained a Mgh percentage of zooplankton pellets in the bottom sediment although he did not obtain their inorganic weight percent. Our study evaluates a) the ability of zooplankton to ingest autoclaved sediment, b) the effect of suspension concentration on the rate of pellet egestion, c) whether mineral transformations would occur after particles were ingested, and d) the settling velocity of mineral-beating fecal pellets and its relation to pellet volume. MATERIALS AND METHODS

The main organism used in this study was Tigriopus californicus, a marine intertidal harpacticoid copepod. These were maintained at room temperature (23 ° C) under fluorescent light conditions, in artificial sea water (31%o salinity). Rinsed T. californicus were left in particle-free autoclaved sea water for 4 hours to cleanse their digestive tract before each experiment. The standards were illite from Fithian, Illinois [Ki.2(AI 1.2Mgo.2Feo.6 ) (Si3 A1)O io(OH)2 ], clinochlore from Cotopaxi, Colorado [(Mg4FeA1 ) (Si3A1)Oto(OH)8 ], tremohte [Ca2Mg4.2 Feo.6 Mno.3) (Si7.8 Alo.2)022 (OH)2 ], vermiculite from Africa [(MgL, Ko.7AI 0.5Feo, Cao.2)(S i3.3AI 0.7)O t o (OH)2 4H 2)], muscovite 2M [KA12 (Si 3AI)O J0(OH) 2], montmorillonite

from Cameron, Arizona [(Ko. z Cao.~) (AI L,Mgo.3Feo.,) Si4Olo(OH)2 nH20] kaolinite 1Tfrom Georgia [ A12Si 20 s (OH) 4], microcline [(Ko.gNa0. I )A1Si30 8 ], and quartz (SiO2). The mineralogy of the standards was determined by X-ray powder film. Standards had particle diameters isolated by centrifugation between 0.8 v.m and 35 v~m.

Zooplankton Ingestion of Autoclaved Sediment Suspensions containing 50 ppm of a standard in artificial sea water were autoclaved for 2 hours to reduce the concentration of bacteria; however, contamination did occur during transfer of copepods. Fifty copepods believed necessary to compensate for individual variation (Marshall and Orr, 1955a) were added to each mineral suspension in 1 l Nalgene flasks. Flasks were kept in reduced light at 23°C and were rotated at one RPM to keep the minerals in suspension for the duration of the 48-hour experiment. Copepods were then separated from the mixtures by nylon screens. The minerals were suction-filtered onto 47 mm HA Millipore filters (0.45 I.tm nominal pore size), gently washed with distilled water to remove salts, and air dried in a desiccator. Filters were mounted on glass slides with acetone, after adding a few drops of clearing fluid (1:1:1 hexane:ethylene dichloride: 1,4-dioxane). Filter slides were analyzed with a Zeiss phase contrast microscope where the pellets were counted and their sizes determined with a Zeiss Particle Size Analyzer. Effect of Suspension Concentration on Pellet Egestion The procedure was similar to that previously described. In this experiment, however, various concentrations (0 to 100 mg/1) of the tremolite standard were used. Mineral Transformation of lngested Sediment A special copepod feeding apparatus (Fig. 1) was built to collect T. californicus fecal pellets for mineralogical and chemical analysis. The copepods were free to swim into an elevated holder and feed on the various mineral standards on the bottom of the holder. Egested pellets in the main part of

MINERAL TRANSFORMATION BY ZOOPLANKTON SEDIMENTINGESTION ~ ) j - W a t ch G l a s s

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Ftc. l.--Schematic of an aquarium built to collect inorganic pellets for chemicaland mineral analysis. the aquarium settled past a 300 ixm screen to keep them away from the copepods and thus ensure no ingestion by them. When a sufficient number of pellets had accumulated normally after three weeks, they were removed and prepared for mineral and chemical analysis. Biological activity on the pellets was eliminated with H: O 2 leaving behind the mineral residue. Frustules of diatoms introduced as a result of contamination during the transfer of T. californicus was a source of Si contamination. Each experimental run with any one mineral was replicated four times with control-standards kept under identical temperature (23 ° C) and solution conditions (31%o salinity). The experimental run yielded a pellet residue concentration slightly greater than 2 rag. This amount was equally subdivided for mineral and chemical analysis. Control-standards for chemical analysis were the same weights as the pellet residues and were vacuum filtered as a homogeneous layer with identical thickness (area of filter kept constant). The cellulose f'dters with sample were carbon coated for quantitative analysis by energy dispersive SEM, which provided elemental ratios between the control-standards and the pellet residues. Relative elemental abundances were assumed not to change significantly between standard and pellet residue and result in variable elemental

871

fluorescent interference. With this assumption, element peaks heights of the two sampies were compared directly as cation ratios. Each analysis on the energy-dispersive SEM continued until the largest peak (Si) reached 8000 counts. Since there was Si enrichment in the pellet residue due to diatom contamination, A1 was chosen as the ratio denominator (Table 2) since AI(OH)3 has low solubility (pH 5 to 9). Since tremolite contains little A1, however, Fe was used in its denominator (Table 3). Pellet residues and corresponding standards for XRD analysis were mounted with random orientation onto 13 mm Ag f'dters (0.45 ~m nominal pore size) and fixed with nail polish onto glass slides. This technique is described in detail by Syvitski and Bayliss (1980). Diffractograms were produced from the pellet residues and standards after air drying at 20°C and heat treatment at 300° for 1 hour and 550° for 1 hour. Montmorillonite and vermiculite were also analyzed after glycolation (1,2-ethanediol) before heat treatment. All mounts were analyzed on an X-ray diffractometer with nickel fdtered copper radiation generated at 40 kV and 20 mA. Scan speed was 1/2 ° 20 per minute.

Settling Velocity of Mineral-Bearing Fecal Pellets Approximately 80 mg of each mineral standard was added to individual Erlenmeyer flasks containing 450 ml of artificial sea water. Fifty T. californicus were added to each flask. The pellets, located along the bottom edges of the flask, were removed in small quantities with a micropipette to a watch glass containing sea water. Pellets were individually selected and added to a 1 l graduated cylinder containing sea water. Using a stop watch, each pellet was timed over a predetermined fall distance after it had reached terminal velocity. Before the pellet reached the bottom, it was removed with an extension micropipette to a microscope slide where the cross-sectional area was recorded.

RESULTS Trigriopus californicus will ingest autoclaved particles with a definite mineral preference (Table l). Preferred minerals (mont-

J A M E S P. M. S Y V I T S K I A N D A L A N G. L E W I S

872

TABLE l.--The egestion rate of Tigriopus cahfornieus for various mineral suspensions indicating the number of pellets counted (N), the number of pellets per day produced by one eopepod (NPD), reaction time (RT) and mean pellet size (MPS). The reaction time equals the maximum time some particles would reside in the digestive tract assuming an even rate of pellet ejection

Mineral

N

Montmorilionitte lllite Clinochlore Tremolite Vermiculite Muscovite Kaolinite Microcline Quartz

1900 1300 1200 700 1000 790 700 600 600 420 300 210

RT (hours)

NPD

19 13 12 7 10 8 7 6 6 4 3 2

l 2 2 3 2 3 3 4 4 6 8 I1

MPS (itm)

140 125 120 110 120 120 115 110 110 105 1~0 100

morillonite, iUite, clinochlore, tremolite, and vermiculite) have the lowest residence time in the digestive tract and are packaged in the largest pellets. These preferred minerals are rich in exchangeable divalent cations. Both montmorillonite and illite also had the smallest mean component size (=1 ~m) although their particles flocculated to sizes between 5 and 20 ~m. An increase in a standard (tremolite) concentration causes an initial increase in the production of fecal pellets (Fig. 2) until, at 25 mg/1 of clay concentration, the highest pellet production was attained. Continued increase in the concentration, however, was not paralleled by an increase in pellet production. The pellet size decreased slightly with increasing clay concentration. Table 2 summarizes the chemical and mineralogic changes that occurred during the

ingestion of mineral particles by Tigriopus. Gypsum occasionally formed during the digestive process (Fig. 3). MontmoriUonite (Fig. 4), tremolite (Fig. 5), and vermiculite (Fig. 6) underwent major crystollographic change. There was no increase in the variability about the mean concentration for any one element when comparing pellet residue to the standard from which the residue was produced. Except for microcline, all minerals studied showed some chemical change (Table 3). Mineral-bearing pellets collected from T. californicus had length to width ratios between 4:1 and 5.4:1. The correlation coefficient calculated for pellet volume and pellet settling rate was found to be 0.88. The 95 percent confidence belt for the correlation coefficient was 0.73 to 0.93 (N = 15). The linear regression equation, over the range

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F~o. 2 . - - T h e egestion rate of Tlgriopus cal~fornicus for various tremolite concentrations held in suspension.

F[o. 3.--X-ray dfffractograms of the muscovite standard that remained unchanged at 3 0 0 ° C from 2 0 ° C. The peDet residue sample indicates the presence of gypsum (0.757 nm, 0.379 am) as well as the unchanged muscovite peaks.

MINERA L TRA NSFORMA TION B Y ZOOPLA NKTON

SEDIMENT

INGESTION

873

T^~LE 2.--Summary of chemical and mineral change that occurred during the ingestion of mineral particles Mineralogy Starting Standard

Dominant Chemical Change ( D e t a i l s in T a b l e 3)

Pellet Residue

Microcline lllite (pyrite) Clinochlore

Microcline lllite (pyrite) Mg-Chamosite

none ttone increase in Fe: decrease in Mg

Muscovite

Muscovite

slight decrease in K

Montmorillonite(quartz, Vermiculite.mica, kaolin- increasein Mg, Ca, and Fe; slight kaolinite) ite, quartz decrease in K

Tremolite

Tremolite. ehamosite

increase in AI; decrease in Ca

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not discernable

decrease in Mg, K, Ca and Fe

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001 basal reflection 0.4 nm) decreased; 002 basal reflection (0.71 nm) increased occasional appearance of gypsum reflections (fig. 3) considerably sharper reflections; 001 reflection (I.4 nm) did not expand upon glycolationand contracted during heat treatments; kaolinite (001) reflections intensified (Fig. 4) New appearance of 001 basal reflections of chamosite (Fig. 5) no well-definedX-ray reflections remained (Fig. 6)

of pellets observed, was calculated at Y = X • 10 -4 +4.9, where Y equals the settling rate 3(m/day) and X equals the pellet volume ( ~ m ) . The settling rate of these pellets was found to vary with mineralogy (Table 4). The mean settling rate for the mineral-beating fecal pellets is always greater than the settling rate for the mean particle size ingested, regardless of mineralogy (Table 4). Table 4 also shows these values translated into equivalent spherical sedimentation diameters. DISCUSSION

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Minerals that underwent chemical change had been preferentially selected by the copepods. This implies that the mineral stand a r d s m a y p r o v i d e c a t i o n s (Mg, F e , C a ) to p l a n k t o n i c m a r i n e o r g a n i s m s . T h e o n e exc e p t i o n , t h e illite s t a n d a r d , p r o d u c e d a h i g h mortality rate on feeding copepods compared to o t h e r i n g e s t e d m i n e r a l s . T h e sulfide c o n t a i n e d in t h e s t a n d a r d illite m a y b e toxic. T h e r e s i d e n c e t i m e o f clay p a r t i c l e s in t h e c o p e p o d d i g e s t i v e t r a c t ( T a b l e 1) m a y b e r e s p o n s i b l e f o r d i f f e r e n c e s in t h e d e g r e e o f m i n e r a l t r a n s f o r m a t i o n s ( T a b l e 2). Although previous studies have indicated

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FIG. 4.--X-ray diffractograms of the montmorillonite standard indicate the classical expansion upon glycolafion and contraction upon heat treatment. The peUet residue sample indicates the new presence of vermiculite and mica along with kaolinite and quartz.

J A M E S P. M. S Y V I T S K I

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AND ALAN

G. L E W I S

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particle settling rates (based on the mean size of ingested particles) and their equivalent spherical sedimentation diameter

Mineral Tremolite lnite MontmoriUonite Ctinoehlore Quartz

Equivalent Spherical Setting R a t e Sedimentation (m/dayXi ± S.D.) Diameters(~ra) PeUet P a r t i c l e s Pellet Particles 227 169 142 127 115

± ± ± ± ±

96 66 44 46 56

47 ± 8 .08 ± 12 ND 48 ± 39 34 ± I1

54 47 ND 41 39

25 1 ND 25 21

ND = no data.

and grinding in the digestive tract (Sullivan, 1977), along with the weak acid environment, may further promote alteration of clay minerals. The influence of mechanical pressure is seen by bent vermiculite flakes (Fig. 7B). The iron increase (Table 3) in the clinochlore pellet residue is probably Fe s÷ on the basis of solubility in sea water and the acid environment of the digestive tract. There are no data available on the redox potential of the copepod gut environment. The substitution of Fe 3÷ for the decreased Mg 2÷ may occur in the octahedral layer a n d / o r the brucite layer. This chemical change satisfies the mineral stability (Mg-chamosite formed) and accounts for the X-ray reflections retaining their d-spacing and sharpness. The K/A1 decrease in muscovite (Table 3) may have resulted from interlayer leaching of K as aided by the grinding of the original standard which might reduce the K + ion stability. The cation increase plus the crystal changes of montmorillonite indicate transformation to vermiculite and mica (Fig. 4). The simultaneous formation of illite and chlorite from montmorillonite left for many months in artificial sea water was documented by Whitehouse and McCarter (1958). This has since been supported by Helgeson and Mackenzie (1970) and Dunoyer De Seganzac (1970). The variation in zooplankton transformation of montmorillonite was that the well-defined brucite layer for chlorite was not developed. Tremolite was partly transformed to chamosite (Fig. 5). Since chlorite is a Ca-poor mineral, the C a / F e decrease (Table 3) seems reasonable. Ca(OH)z, being soluble in the copepod digestive tract, would be free to leave with the other digestive fluids or be

875

taken up by the organism. The tremolite standard was ball milled to clay size prior to being fed to the copepods; this plus its high weathering potential (Longham, 1969, p. 60) might explain the apparent case of its partial chemical and mineral transformation. Clay plates formed from the tremolite (Fig. 7C, D). Vermiculite pellet residues showed the largest change in chemistry and mineralogy. No well-defmed X-ray reflections remained indicating at least partial crystallographic destruction (Fig. 6). All metallic cation ratios decreased after ingestion by the copepods (Table 3). The leached cations would have no place to be resorbed in the original crystal structure. Those cations could dissolve in the digestive fluid, or be adsorbed by organic molecules and amorphous compounds, and subsequently either be taken up by the copepods or passed out of the digestive tract. Intracellular concretions of Ca and Fe have been found in another harpacticord copepod (Fahrenbach, 1963) andinthe domestic housefly (Sohal, Peters, and Hall, 1977), suggesting that uptake can occur. Inorganic Particle Uptake The uptake pattern of inorganic particles agrees with studies on food uptake with respect to concentration (e.g., Marshall and Orr, 1955a; Frost, 1975). There thus appears to be an "optimum" concentration at which fecal pellet production is highest and a "threshold" concentration below which pellet production is low. Tigriopus californicus was found to ingest particles that ranged in size from 0.5 o.m to 50 ixm. The lower limit of particles used by copepods was previously found to be about l0 Ixm (Hargrave and Geen, 1970; Frost, 1975; Boyd, 1976; Nival and Nival, 1976). The discrepancy is due to Tigriopus ingesting 5 to 20 jxm floes composed of minute particles which accounts for our lower size limit. Ingestion of floes over discrete particles would also explain why the abundant minerals, quartz, and feldspar, in the water column of Howe Sound (a Canadian west coast fjord near Vancouver), are not the most abundant minerals ingested by the local pelagic zooplankton (Syvitski, 1978). Natural mineral-bearing pellets, primarily clay plates with few quartz and feldspar

MINERAL TRANSFORMATION B Y ZOOPLANKTON SED1MENT INGESTION

particles, have the same basic composition as the natural inorganic flocs (Syvhski, 1978). Particles smaller than 2 ~m caught up in a floc matrix are found in abundance in natural fecal pellets (Fig. 7F). Zooplankton (copepods and euphausiids) collected from Howe Sound produced on an average only half the number of pellets per time as the laboratory cultured T. californicus (Syvitski, 1978). Figure 7A shows a cInochlore pellet produced by a freshly captured zooplankter. A large increase in the number of T. californicus and an increase in swimming activity resulted from their ingestion of montmoriUonite. Original stock populations increased by over 15 times in a one-month period. In the presence of the montmorillonite suspension, the adult coloration changed abruptly from a translucent pearl white to a dark orange red. Yudonova (1940) noted 'red' Calanus occurred in abundance in the Barents Sea near the surface waters during the summer. Marshall and Orr (1955b, p. 93) suggested that a "special food" might trigger the swarms of red Calanus observed in Norwegian fjords and the Barents Sea. Although the "special food" was not identified, the red coloration seen in T. californicus when fed on smectite may occur in nature. Discrete and rich layers of pelagic fecal pellets have been observed in cores collected from the N.W. Pacific near seamounts (Syvitski and Chase, in prep.). Possibly an abundance of volcanic ash in the water column may trigger these freak? plankton blooms producing the pellets. Pellet Settling Rate

Volume, shape, composition, and compaction have been found to influence settling rates (Fowler and Small, 1972; Honjo and Roman, 1978). Holding the other three factors constant, settling rate will increase as pellet volume (size) increases (Fowler and Small, 1972). Smayda (1969) stressed the importance of shape, which appears to be hydrodynamically sound (Lane and Carlson,

877

1954; Graf and Acaroglu, 1966; Komar and Reimers, 1978). Holding pellet volume constunt, mineral-bearing pellet settling rates (Table 4) are greater than values presented by Smayda (1969) although the shape of the mineral-beating peUets (length:width ratios of 4:1 to 5.4:1) would suggest slower settling than the more spherical pellets examined by Smayda. The inorganic composition could account for this increased rate of pellet settling as mineral particles will normally be denser than organic matter. Pellet compaction varies with the composition of the internal particles as well as the concentration of material in the pellet. Compaction is related, then, to particle density and the particle packing coefficient. Marshall and Orr (1955a) and Honjo and Roman (1978) have found that the pellet length differed with diet. This is also suggested by the pellet size variation with mineralogy (Table 1). Pellet size alone, though cannot account for the pellet settling rate variation due to mineralogy (Table 4). Tremolite pellets having the highest particle density (3.1 g • c m - 3 ) have the fastest settling velocity. Illitc, the second fastest setting pellet type, has the next highest particle density (2.8 - 2.9 g • cm -3) which would even be higher because of the pyrite association (density 5.0 g . c m - 3 ) . Montmorillonite pellet settling velocity is due to a combination of low particle density (2.6 g • cm -3) and large pellet size (Table 1). Clinochlore and quartz pellets settled out the slowest, with clinochlore pellets sinking faster due to the larger pellet size and higher particle density. As a practical example, the rate of pellet sedimentation varied from 0.3 percent to 87.0 percent of the total sedimentation rate as determined by suspended sediment collectors in Howe Sound (Syvitski and Murray, 1980). Pellets were composed of 98 percent mineral particles as determined by SEM (Figs. 7E, 8A, B). Although Howe Sound shows changing mineralogy down inlet (Syvitski et al., in prep.), the exact effect of planktonic transformation of ingested minerals as compared to other effects (i.e., hydraulic

Fro. 7.--Scanning electron micrographs of mineral-bearing fecal pellets: A) a chlorite pellet from freshly capturedzooplankter;B) pell©tcontainingbent vermiculiteplates; C) tremolitepelletwith new plate-likestructures which are changed from the standard chain structures, D); E) and its enlargement F) is a mineral-bearing fecal pellet coliectedfrom Howe Sound.

878

J A M E S P. M. S Y V I T S K 1 A N D A L A N G. L E W I S

F[c. 8.--Scanning electron micrographs of mineral-bearing fecal pellets collected from Howe Sound: A) and B) are pellets without an organic covering; C) and its enlargement D) is a pellet with an organic covering.

sorting, flocculation) is still not known. In fact, it may be impossible to sort out the real effect of this study unless a mineral was formed that was completely unique compared to the background of unpelletized sediment. CONCLUSION

Marine zooplankton ingest suspended sediment at a rate dependent on the suspension concentration and on particle mineralogy. Fecal pellets collected from a fjord receiving glacial run-off were mostly composed of clay flakes. Clays that are ingested are largely

in the form of flocs. Mineral particles undergo chemical and mineral transformation in the digestive tract of Tigriopus californicus, depending on particle mineralogy and residence time in the digestive tract. Mineralbearing egested pellets settle through the water column many times faster than the individual component mineral particles. The settling velocity of mineral-bearing pellets has been found to vary with constituent particle densities and pellet volume (related to packing coefficients of the particles). When pellets are rich in minerals, the in-

M I N E R A L TRA N S F O R M A TION B Y Z O O P L A N K T O N S E D I M E N T I N G E S T I O N

creased bulk density causes them to settle more rapidly than fecal pellets composed mostly of organic debris. This increased rate of settling allows clay particles to fall to the bottom and be deposited where the hydrodynamic environment might prevent deposition of particles finer than coarse silt. The chemical changes on the various clay minerals due to Tigriopus californicus ingestion need to be examined with other zooplankton species. The results may in part explain clay pattern anomalies of marine clay minerals (Edzwald and O'Melia, 1975; Jean, 1971). ACKNOWLEDGMENTS

The project was funded by the National Research Council (J. W. Murray 65-6224; J. P. Syvitski 69-2563; A. G. Lewis A-2067) and by INCRA 246 grant. J. D. Milliman and J. W. Murray supplied much of the original stimulus for this project. W. C. Barnes, P. Bayliss, R. L. Chase, S. Honjo, L. M. Laukulich, A. A. Levinson, and W. C. Pryor are thanked for their critical comments. REFERENCES ANDERSON,A. E., JONAS, E. C., Arid OOtJM, H. T., 1958, Alteration of clay minerals by digestive processes of marine organisms: Science, v. 127, p. 190-191. BICHAM,G. H., 1974, suspended sediments contributed to the southeastern U.S. continental shelf: An investigation by scanning electron microscopy: Mere. Inst. Geol. Bassin Aquitaine, v. 7, p. 103-108. BOND, R. M., 1934, Digestive enzymes of the pelagic copepod Calanus finmarchicus: Biol. Bull., v. 67, p. 461--465. BOOVHE, P. N., ANDKNAU~rt, G. A., 1972, The possible importance of fecal material in the biological amplification of trace and heavy metals: Linmology Oceanography, v. 17, p. 270-274. BOYD, C. M., 1976, Selection of particle size by Fdterfeeding copepods: A plea for reason: Limnology Oceanography, v. 21, p. 2,4--38. CADEE, (3. C., 1976, Sediment reworking by Arenicola marina on tidal flats in the Dutchwadden Sea: Netherlands Sea Res., v. 10, p. 440--460. CHAKRASARr|,A., 1972, Beach structures produced by crab pellets: Sedimentoiogy, v. 18, p. 129-134. DUNOWR DE SEOONZA¢, G., 1970, The transformation of clay minerals during diagenesis and low-grade metamorphism: A review: Sedimentology, v. 15, p. 281-346. EDZWALO,J. K., ANn O'MELIA, C. R., 1975, Clay distributions in recent estuarine sediments: Clays Clay Minerals, v. 29, p. 39--44. FAHRENBACn,W. H., 1962, The biology o f a harpacticoid copepod: Le Cellule, v. 62, p. 301-376.

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