IQ. 61 CD 61.5 35-70 62 62.5 59 58 1O5 35-70 57 56 55 54 53 Longitude (W) AMLR program: Phytoplankton distribution and species composition around Elephant Island, Antarctica, January to March 1994 VIRGINIA E. VILLAFAISIE, E. WALTER HELBLING, and OSMUND HOLM-HANSEN, Polar Research Program, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093-0202 HUMBERTO DfAz, Instituto de Oceanologla, Universidad de Valparaiso, Viña del Mar, Chile ;rogram, a part of the Antarctic Marine Living Resources (AMLR) phytoplankton studies were carried out near Elephant Island, Antarctica, to evaluate the biomass, species composition, and size distribution of the food reservoirs for herbivorous zooplankton, especially antarctic krill (Euphausia superba Dana). This research was performed in a 91-station grid that was occupied two times, once during each leg (Leg I, 12 January to 9 February; Leg II, 14 February to 15 March). Details on the cruise track and station grid are given in Rosen- berg, Hewitt, and Holt (Antarctic Journal, in this issue). Water samples were obtained at 11 standard depths [from 5 to 750 meters (m)] from 10-liter Niskin bottles (with Teflon-covered springs) mounted on a rosette (General Oceanics). The rosette also contained the following: • conductivity, temperature, and depth (CTD) sensors, • a photosynthetic available radiation sensor (PAR, 400-700 nanometers), • a 25-centimeter pathlength transmissometer (Sea Tech), and • a pulsed fluorometer (Sea Tech). Phytoplankton biomass was estimated by two methods: measurements of chlorophyll-a (chl-a), which were done at all stations and at all depths, and measurments of carbon content (at 12 selected stations in each leg), obtained through direct microscopical methods. For chl-a measurements, 100 milliliters (mL) of sample were filtered through a Whatman GF/F glass fiber filter (25 millimeters), and the pigments were extracted in 10 mL of absolute methanol (Holm-Hansen and Riemann 1978). The total chl-a concentration was then obtained by fluorometric techniques (Holm-Hansen et al. 1965). The chl-a concentra- tion in the nanoplankton fraction (cell size less than 20 micrometers) was obtained in a similar way, but the sample was first prefiltered through a nylon mesh fabric (Nitex) with a mesh opening of 20 micrometers. Water samples for floristic analyses were poured into 125 mL brown glass bottles and preserved with buffered formalin. The identification and counting of phytoplankton taxa was done by using inverted microscope techniques (Utermöhl 1958). The phytoplankton carbon content was obtained by calculating cell volumes (Kovala and Larrance 1966) and then applying Strathmann's equations (1967). The patterns of distribution of chl-a at 5 in were fairly similar to those of integrated chl-a (0 to 100 in as was observed in previous studies (Helbling, Villefañe, and Holm-Hansen in press), so only the latter values are shown here (figure 1). During Leg I (figure 1A) integrated chl-a val- ues were rather low throughout the study area at less than 70 milligrams of chl-a per square meter (mg chl-a rn- 2 ), except for a small patch of relatively high values (70 to 105 mg chl-a M-2) in the area between Elephant and Clarence Islands. During Leg II (figure 1B) the pattern of chl-a distribution resembled that in Leg I in that the lowest values were found in the northwestern portion of the grid. There was, however, a great increase in phytoplankton biomass throughout the rest of the grid as compared to values during Leg I, with some stations in Bransfield Strait waters exceeding integrated chl-a values of 200 mg chl-a m 2 . This increase in phytoplankton biomass was also observed in chl-a and phytoplankton car- bon concentrations at 5 in as shown in figure 2. The 60 A <35 60.5 60 B <35 60.5 35-70 çQ. 61 70-10 I 61.5 , . -- . 14O-175 105-14IL 62 62.5 -----______________ -_________________________________ 59 58 57 56 55 54 53 Longitude (W) Figure 1. Integrated chlorophyll-a (milligrams per square meter) from 0 to 100 m depth throughout the AMLR study area. A. Survey A (17-28 January 1994). B. Survey D (25 February to 09 March 1994). ANTARCTIC JOURNAL - REVIEW 1994 191
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IQ. 61CD
61.535-70
62
62.55958
1O535-70
5756555453Longitude (W)
AMLR program: Phytoplankton distribution and speciescomposition around Elephant Island, Antarctica,
January to March 1994VIRGINIA E. VILLAFAISIE, E. WALTER HELBLING, and OSMUND HOLM-HANSEN, Polar Research Program, Scripps Institution of
Oceanography, University of California at San Diego, La Jolla, California 92093-0202HUMBERTO DfAz, Instituto de Oceanologla, Universidad de Valparaiso, Viña del Mar, Chile
;rogram,a part of the Antarctic Marine Living Resources (AMLR)
phytoplankton studies were carried out nearElephant Island, Antarctica, to evaluate the biomass, speciescomposition, and size distribution of the food reservoirs forherbivorous zooplankton, especially antarctic krill (Euphausiasuperba Dana). This research was performed in a 91-stationgrid that was occupied two times, once during each leg (Leg I,12 January to 9 February; Leg II, 14 February to 15 March).Details on the cruise track and station grid are given in Rosen-berg, Hewitt, and Holt (Antarctic Journal, in this issue).
Water samples were obtained at 11 standard depths[from 5 to 750 meters (m)] from 10-liter Niskin bottles (withTeflon-covered springs) mounted on a rosette (GeneralOceanics). The rosette also contained the following:• conductivity, temperature, and depth (CTD) sensors,• a photosynthetic available radiation sensor (PAR, 400-700
nanometers),• a 25-centimeter pathlength transmissometer (Sea Tech),
and• a pulsed fluorometer (Sea Tech).
Phytoplankton biomass was estimated by two methods:measurements of chlorophyll-a (chl-a), which were done atall stations and at all depths, and measurments of carboncontent (at 12 selected stations in each leg), obtained throughdirect microscopical methods.
For chl-a measurements, 100 milliliters (mL) of samplewere filtered through a Whatman GF/F glass fiber filter (25millimeters), and the pigments were extracted in 10 mL ofabsolute methanol (Holm-Hansen and Riemann 1978). Thetotal chl-a concentration was then obtained by fluorometrictechniques (Holm-Hansen et al. 1965). The chl-a concentra-tion in the nanoplankton fraction (cell size less than 20micrometers) was obtained in a similar way, but the samplewas first prefiltered through a nylon mesh fabric (Nitex) witha mesh opening of 20 micrometers.
Water samples for floristic analyses were poured into 125mL brown glass bottles and preserved with buffered formalin.The identification and counting of phytoplankton taxa wasdone by using inverted microscope techniques (Utermöhl1958). The phytoplankton carbon content was obtained bycalculating cell volumes (Kovala and Larrance 1966) and thenapplying Strathmann's equations (1967).
The patterns of distribution of chl-a at 5 in werefairly similar to those of integrated chl-a (0 to 100 inas was observed in previous studies (Helbling, Villefañe, andHolm-Hansen in press), so only the latter values are shownhere (figure 1). During Leg I (figure 1A) integrated chl-a val-
ues were rather low throughout the study area at less than 70milligrams of chl-a per square meter (mg chl-a rn-2), exceptfor a small patch of relatively high values (70 to 105 mg chl-aM-2) in the area between Elephant and Clarence Islands.During Leg II (figure 1B) the pattern of chl-a distributionresembled that in Leg I in that the lowest values were foundin the northwestern portion of the grid. There was, however,a great increase in phytoplankton biomass throughout therest of the grid as compared to values during Leg I, with somestations in Bransfield Strait waters exceeding integrated chl-avalues of 200 mg chl-a m 2. This increase in phytoplanktonbiomass was also observed in chl-a and phytoplankton car-bon concentrations at 5 in as shown in figure 2. The
Figure 1. Integrated chlorophyll-a (milligrams per square meter) from 0to 100 m depth throughout the AMLR study area. A. Survey A (17-28January 1994). B. Survey D (25 February to 09 March 1994).
ANTARCTIC JOURNAL - REVIEW 1994191
Figure 2. Mean phytoplankton biomass concentrations at 5 m depth during Sur-veys A and D. A. Total chl-a (dark bar) and chl-a in the nanoplankton fraction (lightbar). B. Total phytoplankton carbon (dark bar) and carbon in the nanoplanktonfraction (light bar). The lines on top of the bars indicate 1 standard deviation.
Diatoms
DinoflageltatesLeg
FlagellatesLeg II
t-igure . I-'nytoplanKton carbon content (at 5 m depth) in the main taxonomic groups (diatoms,dinoflagellates, and flagellates) as percentages of the total cellular carbon, as determined by micro-scopical analysis. The numbers represent the percentage of the total.
mean chl-a values at 5 in (figure 2A)increased from 0.4 mg chl-a rn 3 during Leg Ito 1.6rng chl-a rn-3 during Leg II, whereas phytoplanktoncarbon (figure 2B) increased from 28.4 to 55.2 mgrn-3. Data in figure 2 also show a change in cell-sizedistribution between Legs I and II. There was a rela-tive increase in the rnicroplankton fraction fromLeg I to Leg II as seen both from chl-a measure-ments (figure 2A) and phytoplankton carbon con-centrations (figure 2B).
These remarkable differences between Leg Iand II in regard to the amount and size distributionof phytoplankton were related to differences in phy-toplankton species composition, as shown in figure3. During Leg I, the phytoplankton crop was domi-nated mainly by flagellates (77 percent); stations inBransfield Strait waters were generally dominatedby cryptophytes, whereas stations in Drake Passagewaters were dominated by naked dinoflagellatesand other flagellates (as prymnesiophytes and/orchlorophytes). The high biomass patch foundbetween Elephant and Clarence Islands during Leg I(figure 1A), however, was dominated by pennatediatoms, such as Pseudonitzschia spp. (rangingbetween 20 and 50 micrometers in size), and centricdiatoms, such as Chaetoceros neglectus and Thalas-siosira sp. In general, these same diatom specieswere the ones that dominated and accounted for 80percent of the biomass, on average, throughout thestudy area during Leg II. This drastic change in thespecies composition was also observed during theAMLR 1990 and 1991 cruises; flagellates were domi-nant during January to February (Leg I) anddiatoms during February to March (Leg II) (Vii -lafane 1993). The reasons for the intra-annual tern-
nnriI and sntii1 unrinhilitir
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jobserved in the AMLR study areaare not clear, but we suggest that acombination of factors, such asnutrient variations in differentwater masses, grazing by zooplank-tonic species, and degree of stratifi-cation, could account for theseobservations.
This research was supported byNational Oceanic and AtmosphericAdministration (NOAA) CooperativeAgreement number NA47FR0030.We thank the officers and crew ofNOAA ship Surveyor for excellentsupport during field operations.Grateful acknowledgment is alsomade to Marcel Ramos (UniversidadCatOlica de Valparaiso, Chile), PedroBaron (Universidad Nacional de LaPatagonia, Argentina), and ChristianBonert (Servicio Hidrografico de la
Armada, Chile) for their generous help onboard ship. Ship-board personnel included E. Walter Helbling (12 January to 9February), Virginia Villafañe (12 January to 9 February), Hum-berto DIaz (12 January to 15 March), and Osmund Holm-Hansen (14 February to 15 March).
References
Helbling, E.W., V.E. Villafane, and 0. Holm-Hansen. In press. Variabili-ty of phytoplankton distribution and primary production aroundElephant Island, Antarctica, during 1990-1993. Polar Biology.
Holm-Hansen, 0., C.J. Lorenzen, R.W. Holmes, and J.D.H. Strickland.1965. Fluorometric determination of chlorophyll. Journal de Con-seil pour L'Exploration de laMer, 30(1), 3-15.
Holm-Hansen, 0., and B. Riemann. 1978. Chlorophyll-a determina-tion: Improvements in methodology. OIKOS, 30(3),438-447.
t'
Kovala, P.E., and J.D. Larrance. 1966. Computation of phytoplanktoncell numbers, cell volume, cell surface and plasma volumes perliter, from microscopical counts (Special Report 38). Seattle:Department of Oceanography, University of Washington.
Rosenberg J.E., R.P. Hewitt, and R.S. Holt. 1994. The U.S. AntarcticMarine Living Resources (AMLR) program: 1993-1994 field seasonactivities. Antarctic Journal of the U.S., 29(5).
Strathmann, R.R. 1967. Estimating the organic carbon content of phy-toplankton from cell volume or plasma volume. Limnology andOceanography, 12(3), 411-418.
Utermöhl, H. 1958. Toward the improvement of the quantitative phy-toplankton method. Mitteilungen-Internationale Verein igung fürTheoretische undAngewandte Limnologie, No. 9,1-38. (In German)
Villafañe, V.E. 1993. Patterns of distribution of phytoplankton speciesand biomass in the vicinity of Elephant Island, Antarctica, duringsummer 1990-1992. (Masters of Science Thesis, University of Cali-fornia at San Diego).
AMLR program: Distribution of phytoplankton in the upperwater column in relation to different water masses
E. WALTER HELBLING and OSMUND HOLM-HANSEN, Polar Research Program, Scripps Institution of Oceanography, Universityof California at San Diego, La Jolla, California 92093-0202
;rogram,part of the Antarctic Marine Living Resources (AMLR)
our phytoplankton project conducted intensivestudies in the area around Elephant Island, Antarctica,onboard the National Oceanic and Atmospheric Administra-tion (NOAA) ship Surveyor, January through March 1994. Thecruise track and station positions are given in Rosenberg,Hewitt, and Holt (Antarctic Journal, in this issue). In thispaper, we present information on the distribution of phyto-plankton with depth as related to the major water masses pre-sent in the AMLR study area.
Detailed biological-physical-optical data were obtainedthroughout the upper water column [0 to 750 meters (m)] atevery station using a General Oceanics rosette equipped with1110-liter Niskin bottles and the following:• a conductivity-temperature-depth sensor (CTD, Sea Bird
Inc., SBE-9),• a pulsed fluorometer (Sea Tech),• a 25-centimeter pathlength transmissometer (Sea Tech),
and• a photosynthetically available radiation (PAR) sensor.A profiling PUV-500 unit (Biospherical Instruments, Inc.) wasalso deployed at every daylight station (when weather permit-ted) down to 100 m to obtain information on the attenuationof solar radiation at 305, 320, 340, and 380 nanometers in theultraviolet region of the spectrum, in addition to PAR at400-700 nanometers. The instantaneous rate of photosynthe-sis was estimated using the 683 nanometers upwelling radia-tion sensor located on the bottom of the PUV-500 unit(Chamberlin et al. 1990).
Various water masses are normally encountered in theElephant Island area (Amos and Lavender 1992), but the ones
that are most evident and widespread in the upper 200 inthe water column are those characterized as Drake Passagewaters, Bransfield Strait waters, and Bransfield-Scotia Conflu-ence waters (Silva et al. in press). Data from representativestations in Drake Passage and Bransfield Strait waters are dis-cussed below.
Station D04 (figure 1) was located in the Bransfield Straitand presented a relatively shallow upper mixed layer (UML)of about 30 m, as estimated from the density profile. Chloro-phyll-a (chl-a) concentrations were high within the UML atup to 1.3 milligrams per cubic meter (mg rn- 3) but decreasedrapidly below it (figure 1A). Some photoinhibition of chl-a flu-orescence was evident down to 25 m, but no inhibition of theinstantaneous rate of primary production was noted (figure1B). The depth of the euphotic zone (1 percent of surface irra-diance) for this station was about 68 m.
Station D51 (figure 2), located in Bransfield Strait watersto the northeast of King George Island, had a deeper UML of50 in was much richer in regard to phytoplankton bio-mass. Chl-a concentrations were high in the upper 50 inthe water column (up to 4 mg rn- 3) and were still fairly high(1.8 mg rn-3) at 75 in 2A). Instantaneous productionrates were also high in the upper part of the UML with ratesexceeding 500 nanornoles of carbon fixed per cubic meter persecond (nmole C rn-3 s_1) (figure 2B); these high rates equateto an assimilation value of approximately 5.4 mg C mg chl-a'hr'. The 1 percent light level for this station was about 35 m.
In contrast to stations in Bransfield Strait waters, stationslocated in Drake Passage waters showed a subsurface chl-amaximum below the pycnocline. Data from Station D43 (fig-ure 3) show that chl-a was higher between 50 and 100 in
