Microheterotrophs in the ice-edge zone: An AMERIEZ study

Data summary: Arthur Harbor studies, December 1984 and January 1985 Station

Chlorophyll a (in micrograms per liter) Total ^ 20 micrometer ^ 10 micrometer ^ 5 micrometer

2.06 1.34 0.97 0.53

4.13 3.59 2.93 2.02

2.85 2.48 2.14 1.40

1.81 1.43 1.18 0.65

Chlorophyll a (percent of total) ^ 20 micrometer ^ 10 micrometer ^ 5 micrometer

65 47 26

87 71 49

87 75 49

79 65 36

Ciliate abundance (number per liter) Tintinnines Other oligotrichs Total ciliates

500 900 1,700

500 1,200 1,800

1,200 2,400 3,700

2,100 2,600 5,100

Frequency of dividing cells (percent of total cells) Cymatocylis spp. Laackmariniella spp.

Codenellopsis glacialis

12.7 31.4 30.1

Microheterotrophs in the ice-edge zone: An AMERIEZ study D.L. GARRISON and K.R. BUCK Center for Marine Studies University of California Santa Cruz, California 95064

Microheterotrophs, such as heterotrophic flagellates and ciliates, are now widely recognized as important components of pelagic food webs (e.g., Taylor 1982). The abundance of these organisms in the ice-edge zone may reflect increased production in ice communities and in ice-edge plankton blooms (Garrison et al. 1984). As part of the Antarctic Marine Ecosystem Research at the Ice-Edge Zone (AMERIEZ) program in November 1983, we began to study microheterotrophs in the ice-edge region of the Weddell Sea. In initial reports, we reported (Buck and Garrison 1984; Garrison, Buck, and Silver 1984; Garrison and Buck 1985) finding a surprising diversity and abundance of microheterotrophs in ice-edge zone, and an apparent increase 136

16.3 38.1 29.2

19.1 46.0 35.5

22.2 53.9 46.2

in microzooplankton at the ice edge. During 1984 and 1985, we have examined approximately 75 ice and water samples. Here, we present a summary of our continued studies. Population studies. The abundance of microheterotrophs in the upper water column for stations under heavy ice cover (stations 5 and 6) and along a transect across the ice-edge zone (stations 15 through 21) is shown in the figure. Most of the microzooplankton biomass was concentrated in the upper 50 meters; abundance dropped markedly below approximately 50 to 60 meters. Microheterotroph populations are much more concertrated in ice than in water but, because ice is limited to the upper 1 t 2 meters, the largest fraction of microheterotrophs will still be found in the water column (table; see Garrison et al. 1984). Our data for early spring conditions overlap the range of values von Brockel (1981) cites for late fall conditions. Our lower range of values suggests a seasonal abundance cycle for microzooplankton. This possibility will be addressed during an AMERIEZ cruise in March 1986. Microheterotroph populations in ice were often dominated by heterotrophic flagellates, (see Buck and Garrison 1984; Garrison et al. 1984), whereas those in water were almost entirely comprised of naked ciliates. We have been able to recognize several forms that occur in both ice and water. However, there are still many forms that we cannot yet identify with certainty, and our efforts to determine the relationships between ice and water is continuing. ANTARCTIC JOURNAl.

Summary of ciliate biomass (in milligrams of carbon per square meter) in ice and water. (Data from von Brockel 1981 was recalculated for the upper 50 meters and is presented for a comparison with values from the present study.)

Sample X Range

were supported by an award to John Corliss from the Smithsonian Sorting Center (Contract No. PC-504011). We thank J.O. Corliss and Richard Snyder for their collaboration.

References

Remarks

Ice cores 13 3-19.9 Ice floes < 1.5 meter Water column 69 24-179 Upper 50 meters Water column 136 11-453 von Bröckel (1981)

Systematic studies of ciliated protozoans. Ciliates from our ice samples have been examined, identified, and described by John Corliss and Richard Snyder, University of Maryland (Corliss 1985). Corliss and Snyder found 26 ciliate species and described seven new species. Other forms in the samples may constitute additional new species, but these could not be described adequately from the present samples. This brief study serves to emphasize how poorly the antarctic ciliates are known. Our population studies suggest that naked ciliates are abundant and probably ecologically important in food webs in the ice-edge regions. On-going studies on microheterotrophs in the ice-edge zone was supported by a National Science Foundation grant (DPP 82-18747) to D.L. Garrison and M.W. Silver. Systematic studies

Brockel, K. von. 1981. The importance of nanoplankton within the pelagic Antarctic ecosystem. Kieler Meeresforsch u ngen Sonderheft, 5, 61 - 67. Buck, K.R., and D.L. Garrison. 1984. Heterotrophic nanoplankton from Antarctic sea ice. (Abstract.) EQS., Transactions American Geophysical Union, 65, 922. Corliss, JO. 1985. Taxonomic identifications and description of Antarctic ciliate fauna from selected samples collected by D.L. Garrison, University of California at Santa Cruz. (Draft report prepared for the Smithsonian Sorting Center. Contract No. PC-504011.) Washington, D.C.: Smithsonian Institution. Garrison, D. L., K. R. Buck, and M. W. Silver. 1984. Microheterotrophs in the ice-edge zone. Antarctic Journal of the U.S., 19(5), 109 - 111. Garrison, D.L., and K.R. Buck. 1985. Microbial communities in pack ice floes in the Antarctic. (Abstract.) (Second International Phycological Congress, Copenhagen, 4 - 10 August 1985.) Nelson, D.M., W.O. Smith, and L.J. Gordon. 1984. Phytoplankton dynamics of the marginal ice-zone of the Weddell Sea NovemberDecember 1983. Antarctic Journal of the U.S., 19(5), 105 - 107. Taylor, G.T. 1982. The role of pelagic heterotrophic protozoa in nutrient cycling: A review. Annales L'Institut Oceanographique (Paris), 58, 227241.

Microzooplank[.on biomass ( mg C / m2) 20e

20

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1 21 19

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15

17

18

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0 Mlcrozooplankton biomass (in milligrams of carbon per square meter) in the upper 50 meters of the water column in the Weddell Sea during November 1983. Stations 5 and 6 were under heavy ice cover. Stations 15-21 were along a transect across the ice-edge zone. Station locations, approximate ice cover, and the location of an ice-edge bloom is given in Nelson, Smith, and Gordon 1984. ("mgCIm2" denotes "milligrams of carbon per square meter?')

1985 REVIEW

137