Is

::

•'.11..:'

McCleave and Timothy E. Targett will determinethe gut contents.

Some echinoderm and fish specimens were col-lected and preserved for taxonomic purposes.Fishes of the families Channichthyidae, Bathydro-conidae, Liparidae, and Zoarcidae were obtainedand will be examined by Hugh H. DeWitt, Uni-versity of Maine. Some heart urchins were col-lected for examination by F. Julian Fell, Univer-sity of Maine, while crinoids and asterozoans willbe determined by Dr. Dearborn.

We extend our appreciation to Captain Pieter J.Lenie and the crew of RJV Hero for their enjoyablecompany, their cooperation, and their excellentfield support. We also thank William Showers, agraduate student at the University of California,Davis, for field assistance. This study was supportedby National Science Foundation grant o pp 74-08565.

Biology of krill(Euphausia superba) and other

antarctic invertebrates

M. A. MCWHINNIE, C. DENYS, and D. SCHENBORNDepartment of Biological Sciences

De Paul UniversityChicago, Illinois 60614

These studies began upon our arrival at PalmerStation on 28 November 1975 and ended when RIVHero departed on 9 March 1976, at the end of theaustral summer. Throughout the season 152pelagic and 16 bottom samples were collected(Isaacs-Kidd midwater and conventional benthictrawls, respectively) aboard Hero (cruise 76-2) dur-ing 24 days at sea. Other benthic and pelagicsampling was accomplished in Arthur Harborusing Zodiak boats. Sampling of krill at five depths,mostly between 500 meters and surface, was usuallyconducted from dusk to dawn. Sampling through

4-

I'II''I

Figure 1. Krill sample being brought aboard RN Hero by Captain Lenle. Figure 2. Krill stations occupied In December 1975 andJanuary 1976 between Daliman Bay of Brabant island and the Argentine islands, north and south of Palmer Station (P).

June 1976 55

LOW"

these hours takes advantage of diurnal migrationsof euphausiids and permits assessment of responsesto changing light intensity by different age classes.During the day, samples were collected when char-acteristic reflections from pelagic densities ap-peared on the sonar record. A moderate degree ofcorrespondence was found between the characterof the sonar "blip" and krill populations. CaptainPieter Lenie of Hero contributed greatly to sonarmonitoring and participated in all sampling (figure1).

Sampling stations occupied in December werereoccupied in January (early and midsummer) toobserve krill distribution characteristics in this areaas the summer advanced (figure 2).

Subsequent collections in February were takenbetween Palmer Station (64°46'S. 64°05'W.) andnorthward to the southeast of Livingston Island(62°36'S 60°30'W.). A southern cruise in earlyMarch reached the north end of Marguerite Bay;the southernmost collection was southwest of Ade-laide Island (67°15'S. 68°30'W.). The easternmostsample taken this season was at 59°35'W.

Euphausiid collections were divided for diversestudies: (1) formalin- preserved for species identifi-cation, for determination of sex differentiation andratios, and for age classes; (2) histological fixationfor study of gonadal development; (3) frozen forstudy of proteins and enzymatic analyses; (4) live

maintenance in seawater tanks aboard Hero forgrowth studies (molting) upon return to the Palmerlaboratory.

Stock euphausiids were maintained at Palmer in aflowthrough tank in the aquarium room where sea-water temperature ranged from 10 to 3°C. Forgrowth rate studies, animals maintained singly ortwo in a container were held within the same tem-perature range. Molting was monitored and all krillwere fed freshly collected phytoplankton at leastonce daily. Most animals molted at least once, whilemany survived a considerable period and somemolted three times during this study. As is charac-teristic of crustacea, some die in the course of molt-ing. The average daily loss from all factors was 1 to3 percent of the group under study (figure 3). Inthe absence of currents from which krill filter phy-toplankton, and under conditions of laboratoryfeeding, the amount of plankton eaten was assessedby visual evidence of food (color and volume) in thedigestive tract of these transparent animals, and byfecal string production. Similar observations weremade with freshly collected animals at sea. Labora-tory survival of krill is considered to have been goodthroughout this study. Some small krill collected inArthur Harbor on 3 December were alive and feed-ing at the end of the season after molting severaltimes in 3 months.

While krill were not generally collected in Arthur

Figure 3. Krill and theirmolted exoskeletons: (a)the animal successfullycompleted molting and hasfed as shown by dark di-gestive tract; (b) the animaldied in the course of molt-

ing.

56 ANTARCTIC JOURNAL

Harbor or in the nearby island groups, much evi-dence of their presence was found in Adélie pen-guin (Torgersen Island) and Dominican gull(Bonaparte Point) colonies.

To determine growth increments, krill werephotographed between molts and body lengthswere measured from these records. This procedurewas adopted to reduce handling, mechanical dam-age, and a rise in temperature, all of which occurduring direct measurement (figure 4). The growthincrement per molt of juvenile to young adultsranged from 0 to 10 percent of the previous inter-molt size.

Initial age class studies of preserved krill indicateat least three size groups collected in AntarcticPeninsula waters during the 1975-1976 australsummer. Krill collected in straits and channelsamong the South Shetland, Palmer Archipelago,and Bisco islands indicated the presence of at leastthree euphausiid species. Breeding adults weresometimes evident through the presence of sper-matophores on either males or females.

A correlation between size and gonadal develop-ment, the criterion of maturity for reproduction,has been reported to be low (for example, occur-ring at body lengths of 27 to 49 millimeters) (Barg-mann, 1937, 1945; Fraser, 1936). Histologicalpreparation of collected specimens will enablematurity determinations relative to size in thesepopulations.

In a second study, the metabolic basis of low tem-perature adaptation was continued using diversemarine invertebrates. Emphasis was on Krebs citricacid cycle oxidations. The oxidation rate of oxa-loacetate (oxA) to malate is at least four timesgreater than that of isocitrate to alpha-ketoglu-tarate. This suggests that a large percentage of thephosphoenolpyruvate, derived from glycolysis,enters Krebs cycle by way of OXA and reduces oxi-dative decarboxylations, thus conserving organiccarbons. The fish Notothenia neglecta shows a similaroxidation of OXA, while the liver and skeletal muscleof warmblooded gentoo penguins (Pygocelis papua)and skuas (Catharacta macconnackii) follow the moreconventional intermediate steps of this cycle. Lungtissue, however, resembles invertebrate tissue oxi-dative patterns. Tissue levels of pyruvic and lacticacids reflect these differences (lower in coldbloodedand higher in warmblooded animals). These resultsextend an earlier study at McMurdo Station(McWhinnie et al., 1975), which demonstrated highglucose utilization through the hexosemonophos-phate shunt, high lipid synthesis, and low carbondioxide production.

While observing large numbers of limpets in tidepools (up to 50 to 100 per square meter), a study of

Figure 4. E. superba on 4 February 1976 (a) and after molt on16 February (b). The size increase between these two dates

was 1 millimeter.

their tolerance to hyposaline media was conducted.Glacial melt in the Palmer Station area during theaustral summer exposes limpets (Patinigera polaris)to dilute seawater in such pools through a 9- to 10-hour low tide period. Tolerance to a hyposalinemedium was studied with animals collected fromthe Kristy Cove area and maintained in seawateraquaria at 10 to 3°C. Survival and tolerance wereexpressed as (1) the time for 50 percent of the ani-mals to die (LD-50), (2) the locomotion and surfaceadherence, and (3) the changes in wet weight whenmaintained in 40-percent seawater. In early sum-mer the LD-50 for small limpets (mean length of31 millimeters) was 58 hours, while it was 48 hoursfor large limpets (mean length of 46 millimeters);in late summer these intervals increased to 76 and62 hours, respectively. Although both size groupsheld in dilute seawater reached a maximum wetweight within 24 hours, small limpets gained sig-nificantly more weight and exhibited greater swell-ing of the foot.

Further, after 12 hours in 40-percent seawater,80 percent of the small limpets retained the abilityto attach firmly to substrate despite a 13.4-percentweight gain and some swelling. Large limpets, how-ever, showed only a 7.4-percent weight gain withlittle swelling. Less than 10 percent of the large lim-pets remained capable of attaching to substrate.

We are grateful to Martin Curran, Holmes andNarver, Inc., for his efforts in support of our pro-

June 1976 57

gram, to William Fraser for collecting skuas for thisstudy, to E. Douglas and R. Lockner for providingpenguin tissues, to the diving team (R. Daniels, Wil-liam Showers, and D. Lame) of the University ofCalifornia, Davis, for providing numerous inverte-brates for these studies, and to Captain Lenie andthe crew of Hero for their willingness to workthrough the night to assist in our krill collections.

This research was supported by National ScienceFoundation grant Opp 73-05890.

References

Bargmann, H. E. 1937. The reproductive system of Euphausiastiperba. Discovery Reports, XIV: 325-350.

Bargmann, H. E. 1945. The development and life-history ofadolescent and adult krill, Euphausia superba. Discovery Re-ports, XXIII: 103-176.

Fraser, F. C. 1936. On the development and distribution ofyoung stages of krill (Euphausia superba). Discovery Reports,XIV: 1-192.

McWhinnie, M. A., S. Rakusa-Suszczewski, and Sr. M. 0. Cahoon1975. Physiological and metabolic studies of antarctic fauna,austral 1974 winter at McMurdo Station. Antarctic Journal ofthe U.S., X(6): 293-297.

sence of a summer bloom on the western side of thesound. Our New Harbor study area thus is quiteunlike most antarctic coastal environments that ex-perience a large, predictable burst of organic pro-duction; as a result, the New Harbor site may havecloser affinities with the deep sea than with themore familiar antarctic benthos.

Much effort was devoted to maintaining, moni-toring, and evaluating numerous experiments(figures 1 and 2) begun during the 1974-1975season to test hypotheses concerning predator-preyinteractions, the natural history of scavengers, or-ganic enrichment, dispersal and mobility of variouslife cycle stages, annual growth patterns, benthicsuccession, and larval settlement and early recruit-ment patterns. One outstanding result is themarked settlement patterns on artificial substrataplaced on the bottom and in the water column. Inparticular, the "filter" effect of Odontaster validuswas clearly demonstrated. Several new experimentswere begun to test hypotheses concerning demersallarvae, larval responses to various disturbances,adult-larval interactions, effects of bacteria on lar-val settlement, dispersal abilities of brooded young,prey refugia, organic enrichment, various otheranimal interactions, and the growth and recruit-ment patterns of several benthic species. Morephotographic transects and other references wereestablished in the sponge community and in soft-

Benthic communities ofMcMurdo Sound

JOHN S. OLIVER, DANIEL J . WATSON,EDMUND F. O'CONNOR, and PAUL K. DAYTON

Scripps Institution of OceanographyUniversity of California, San Diego

La Jolla, California 92093

During the 1975-1976 austral summer we con-tinued and expanded experimental evaluation ofthe organization and maintenance of shallow-waterbenthic marine communities of McMurdo Sound.We also made extensive scuba diving surveys alongwestern McMurdo Sound, sampled the deep ben-thos in the Ross Sea, and observed shallow-waterbenthos beneath the Ross Ice Shelf at White Island.

Measurements of benthic and water column pro-ductivity and chlorophyll levels show a north-southproductivity gradient along Ross Island, a distinctcoastal summer phytoplankton bloom, and the ab-

Figure 1. An array of sediment containers supported by asubsurface float at New Harbor, McMurdo Sound. The rack Is30 meters above bottom and will test hypotheses about themidwater nature of benthic animal larvae. Tuffy scrubbersattached to sides of the racks have proven to be a very attrac-

tive substratum for several suites of animals.

58 ANTARCTIC JOURNAL