P.S.Z.N.: Marine Ecology, 22 (4): 343±355 (2001)
Blackwell Wissenschafts-Verlag, Berlin
ISSN 0173-9565
Accepted: May 18, 2001
Tintinnids (Ciliophora) and Other
Net Microzooplankton (>
> 30 mm) in Southwestern Atlantic Shelf Break Waters
Gustavo A. Thompson1, 2, *, Viviana A. Alder1, 2, 3 & Demetrio Boltovskoy1, 2, 4
1
Departamento de Ciencias BioloÂgicas, Facultad de Ciencias Exactas y Naturales, Universidad
de Buenos Aires, C1428EHA Buenos Aires, Argentina.
2
Consejo Nacional de Investigaciones CientõÂficas y TeÂcnicas, Avda. Rivadavia 1917, C1033AAJ
Buenos Aires, Argentina.
3
Instituto AntaÂrtico Argentino, Cerrito 1248, C1010AAZ Buenos Aires, Argentina.
4
Museo Argentino de Ciencias Naturales ªBernardino Rivadaviaº, Av. Angel Gallardo 470,
C1405DJR Buenos Aires, Argentina.
With 4 figures and 2 tables
Keywords: Microzooplankton, southwestern Atlantic, Malvinas Current,
biogeography, Tintinnina.
Abstract. Proportions of foraminifers, tintinnids, polycystine radiolarians, pteropods
and crustacean larval stages were estimated in a collection of 76 vertically stratified
(0±100 m) 30 mm net microplankton samples from 16 stations along the Argentine
shelf-slope (around 200 m isobath ± between 40 and 56° S), covered on 13±18 November 1996. Tintinnids were identified to species. Relative abundances of the microzooplankton assessed and chlorophyll a values allow to define two contrasting groups of
stations: `deep' and `shallow'. The former, located in pelagic, purely subantarctic Malvinas Current waters, hosted higher proportions of foraminifers and lower proportions
of tintinnids, as well as less chlorophyll a (all differences were significant at the 0.1 %
level). `Shallow' stations were located in the area of the thermohaline front where the
Patagonian Current comes in contact with the Malvinas Current, and were generally
characterized by higher chlorophyll a levels (up to 3.7 mg Chl a ´ l±1). The distribution
of tintinnid species, on the other hand, allowed no discrimination between these two
areas, although some of the dominant forms showed much higher relative abundances
in one of the two groups of stations. Twenty-six tintinnid taxa were recorded, yet only 6
accounted for 95 % of the specimens identified. Tintinnid taxocoenoses were characterized by a few abundant species and many rare ones. Numbers of tintinnid species and
specific diversity did not differ noticeably with depth and latitude. Cape Horn Current
waters were detected in the area by the presence of expatriated organisms presumably
originating at mid-latitudes in the South Pacific Ocean.
* Author to whom correspondence should be addressed. E-mail: [email protected]
U. S. Copyright Clearance Center Code Statement: 0173-9565/01/2204 ± 0343$15.00/0
344
Thompson, Alder & Boltovskoy
Problem
The hydrology of the southern Southwestern Atlantic Ocean is dominated by subantarctic oceanic waters of the Malvinas Current and shelf waters of the Patagonian Current.
The former is a branch of the West Wind Drift (= Antarctic Circumpolar Current) that
flows north-north-eastward along the Patagonian slope (Peterson & Stramma, 1991;
Piola & Rivas, 1997), while the latter also carries subantarctic, albeit slightly warmer
and less saline waters sluggishly northward over the continental shelf (Brandhorst &
Castello, 1971; Severov, 1990; Piola & Rivas, 1997; see Fig. 1).
Between ca. 36 and 50° S, the Malvinas Current and the Patagonian Coastal Current
are separated by a rather well-defined shelf-break front; active vertical water mixing
along this boundary is responsible for enhanced primary production (Carreto, 1989;
Negri, 1993; Carreto et al., 1995) and high concentrations of zooplankton (Ciechomski
& SaÂnchez, 1983; Boltovskoy et al., 1999). This frontal area is characterized by steep
gradients in planktonic abundance and composition. In spite of its ecological and
economic importance, aside from the few and scattered nutrient and chlorophyll a
measurements and some species distribution data (see review in Boltovskoy, 1999b),
the shelf-break front is poorly investigated.
This paper provides data on tintinnid assemblages and compares them with those recorded in neighboring pelagic waters. These results stress similarities and differences
between the core of the Malvinas Current, sampled for the present work, with nearby
pelagic waters surveyed by similar methods in previous investigations (Fernandes,
1998; Thompson et al., 1999).
Material and Methods
Seventy-six microplankton samples were collected by means of 30 mm-mesh nets from 16 stations located
between 40 and 56° S, along 57±63° W, on 13±18 November 1996 (TABIA V cruise), from the Brazilian
research and support vessel `Ary Rongel' (Fig. 1). The transect covered middle and outer shelf (water depths
< 200 m), slope (200±1000 m) and pelagic (> 1000 m) waters. Depth intervals sampled were: 0±5, 5±15, 15±
30, 30±50 and 50±100 m. Proportions of shell- and skeleton-bearing zooplankters were estimated from subsamples in 10 or 25 ml settling chambers under an inverted microscope. Groups assessed were: foraminifers,
polycystine radiolarians, tintinnids, pteropods (chiefly protoconchs), and early crustacean larvae and moults
(chiefly nauplii). Almost all tintinnids were identified to species (total specimens scanned: 29,587; average
unidentifieds per sample: 0.2 %) according to the classification system proposed by Alder (1999).
Vertical temperature profiles were obtained from XBT launchings. Bottle water samples were collected at
each station from 0, 5, 10, 25, 50, 75, 100 and 125 m for analyses of chlorophyll a (200 ml of water filtered
through Whatmann GF/C filters; filters stored, dried and frozen for subsequent analyses with fluorometric
techniques after extraction with 90 % acetone in the laboratory; Evans & O'Reilly, 1983).
In order to assess structural similarities between stations a cluster analysis based on the relative abundance
of the microzooplanktonic groups surveyed and on the distribution of chlorophyll a was performed using the
correlation coefficient and the Unweighted Pair-Group Method using arithmetic Averages (UPGMA; Romesburg, 1984). Tintinnid species diversity was examined using both the number of species per sample recorded
and Shannon-Wiener's diversity index (Shannon & Weaver, 1949).
Southwestern Atlantic tintinnids
Fig. 1.
Station locations and general hydrological features of the area.
345
346
Thompson, Alder & Boltovskoy
Results
1. Microzooplankton characterization and distribution
According to the water-column depths at the sampled sites, the transect covered middle-outer shelf, slope and open ocean waters. Most of the cruise track roughly followed
the 200 m isobath, which in this area defines a steep depth gradient, so that slight eastwest excursions involve very significant bottom-depth changes (Fig. 1). Thus, almost
all stations were located within this onshore-offshore gradient characterized by strong
differences in bottom depth.
Surface water temperatures increased northward from 5 to 11°C. Vertical stratification in the upper 100 m was generally weak between 40 and 50° S, whereas farther
south it disappeared altogether (Fig. 2A). Concentrations of chlorophyll a were moderately high, with several peaks in excess of 2.5±3 mg Chl a ´ l±1 (Fig. 2B).
The geographic distribution of the microzooplankton was irregular and patchy
(Figs. 2C±G). Metazoans, chiefly represented by crustacean larvae and moults, were
on average somewhat more abundant (60 % of all organisms counted) than the protist
fraction, yet variations among geographic locations and depths were wide (3±96 %).
Tintinnids dominated the > 30 mm protist assemblages (mean: 65 %; range: 5±99 %),
followed by foraminifers (33 %; 0±90 %) and radiolarians (1.4 %; 0±10 %).
The cluster analysis defines two contrasting groups of stations (Fig. 3): `shallow' stations (numbers 1, 2, 9±14, mean bottom depth 543 m) and `deep' stations (3±8, 16,
mean bottom depth 2144 m). Station 15, which according to the analysis falls in the
`deep' group (Fig. 3), hosted atypical microplankton, including presumably expatriated
tintinnids (see Discussion). All tows performed at station 15, located on the Burdwood
Bank (bottom depth 140 m), yielded many benthic foraminifers; the tintinnid assemblages here were dominated by a characteristically neritic species ± Codonellopsis balechi. We contend that the particular bottom topography of this area, associated with a
shallow bottom and strong wind stress prevailing at the time of sampling (ca. 25 kn),
favored the resuspension of bottom materials (Murray, 1965) and/or the advection of
coastal waters; this station was therefore excluded from further comparisons of `shallow' vs. `deep' areas.
Mean chlorophyll a values and microzooplanktonic relative compositions for `shallow' and `deep' stations are shown in Table 1. `Shallow' stations, located in shelf and
Table 1. Comparison of chlorophyll a values (in mg Chl a ´ l-1) and microzooplanktonic proportions in `shallow' and `deep' stations (station 15 excluded, see text).
`shallow' stations
chlorophyll a
Tintinnina
1.5 [0.2±3.7]
`deep' stations
0.4 [0.2±2.5]
P value for t-test
< 0.001
40.8
11.4
< 0.001
Foraminifera
4.3
20.5
< 0.001
Polycystina
0.3
1.1
0.008
pteropods
0.2
1.8
0.008
54.5
65.2
0.004
crust. larvae
Southwestern Atlantic tintinnids
347
Fig. 2. Profiles for temperature (based on 32 XBT launchings, in °C), chlorophyll a and proportions of the
microplankters analyzed. Data for the crustaceans include larvae and moults.
slope waters (Fig. 1), were generally characterized by high chlorophyll a values, especially down to ca. 50 m (mean: 1.5 mg Chl a ´ l±1; Fig. 2B). Generally, tintinnids comprised higher proportions of overall microzooplankton in these samples than elsewhere
(Fig. 2C). Stations of the `deep' group were mostly located at bottom depths deeper
than 1000 m (Fig. 1). Chlorophyll a values here were noticeably lower than at the `shallow' stations (mean: 0.4 mg Chl a ´ l±1), and tintinnid proportions of total net microzooplankton were much lower. On the other hand, foraminifers accounted for higher
fractions of the microzooplankton here than in the `shallow' samples (Table 1, Fig. 2D).
348
Thompson, Alder & Boltovskoy
Fig. 3. Grouping of the stations as indicated by a cluster analysis (correlation coefficient of faunal similarity
and UPGMA) based on percentage data of the microzooplankters surveyed and the distribution of chlorophyll a.
Polycystine and pteropod contributions were variable and generally low, but differed
significantly between the two sample groups, with peak relative numbers at the `deep'
stations (Table 1, Figs. 2E, F). Crustacean larvae accounted for high proportions of the
microzooplankton almost everywhere; the highest values were recorded in the `deep'
station group (Table 1, Fig. 2 G).
2. Distribution of tintinnid species
A list of the 26 tintinnid taxa recorded, their geographic distribution, and their mean
(for the entire collection) and maximum (for any given sample) percentages of all tintinnids are presented in the Appendix. Only 6 taxa accounted for 95 % of the specimens
identified (Acanthostomella norvegica f. typica, mean percentage contribution: 25 %;
Codonellopsis pusilla f. typica, 24 %; Steenstrupiella pozzii, 17 %; Amphorides quadrilineata, 15 %; Codonellopsis balechi, 9 %; Cymatocylis antarctica f. typica, 5 %;
Figs. 4A±F). Helicostomella subulata and Dictyocysta elegans var. lepida represented
3 %, whereas the remaining 18 taxa accounted for 2 % altogether (see Appendix).
The distribution of tintinnid species along the transect was poorly structured and
faunistically dissimilar, discrete regions could not be identified. Several of the most
abundant tintinnids, however, did load differently on the `shallow' and `deep' stations
differentiated on the basis of relative microzooplanktonic compositions (Fig. 3). Thus,
percentages of Acanthostomella norvegica f. typica, Steenstrupiella pozzii and Am-
Southwestern Atlantic tintinnids
349
phorides quadrilineata were 1.6±2.7 higher at the `shallow' stations, whereas those of
Codonellopsis pusilla f. typica were, on average, 6 times higher at the `deep' ones.
However, the proportions of Cymatocylis antarctica f. typica were quite similar in both
sample groups (Figs. 4A±E; Table 2).
The numbers of tintinnid species did not differ noticeably in the various depth intervals. Thus, the four uppermost depth offsets sampled (0±50 m) hosted, on average, 5.8
tintinnid species, and the 50±100 m interval was only slightly more diverse, with 6.3
species per sample. This minor difference can be due to the circumstance that while in
the uppermost depths only surface-dwelling species were collected, farther below (50±
100 m) we retrieved the local population plus a few isolated specimens of epipelagic
taxa exported from the surficial strata. The specific richness of samples from `shallow'
and `deep' stations did not differ much either, oscillating around 6.1 (range: 3 to 10)
species per sample; this is consistent with the lack of faunistically dissimilar discrete
regions. Specific diversity (Shannon-Wiener's formula; ln-based) did not vary noticeably among depth layers and groups of stations either, averaging around 0.978 (range:
0.045 to 1.838).
Fig. 4. Geographic and vertical distribution of the relative contributions of dominant tintinnid species to
their overall taxocoenosis.
350
Table 2. Contribution (%) of the six dominant tintinnid species and comparison with previous data from the same area (The transects sampled are shown in Fig. 1).
Acanthostomella
norvergica f. typica
Amphorides
quadrilineata
Codonellopsis
balechi
Codonellopsis
pusilla f. typica
Cymatocylis
antarctica f. typica
Steenstrupiella
pozzii
Nov. 1996 (present study),
`shallow' stations
32.5
26.1
2.8
7.5
5.7
22
Nov. 1996 (present study),
`deep' stations
20.8
6.8
3.8
43.9
5.7
13.7
Nov. 1994 (Thompson et al., 1999),
oceanic waters*
23.2
1.5
±
6.8
21.4
0.3
Nov. 1993 (Alder, unpubl.)*,***
31.5
0
±
1
12.8
2.1
Nov. 1992 (Fernandes, 1998)*, **
13.7
3.4
±
0.4
74.6
1.1
* samples between 41 and 55° S only;
** surface samples only;
*** (5±15 m) samples only.
Thompson, Alder & Boltovskoy
Southwestern Atlantic tintinnids
351
Discussion
Tintinnid taxocoenoses and chlorophyll a levels indicate that, at the time of the cruise,
`deep' stations were located in the pelagic, purely subantarctic waters of the Malvinas
Current, whereas `shallow' stations were strongly influenced by interaction of the former with the outer shelf waters of the Patagonian Current. Along the shelf-break, the
Patagonian Current comes in contact with the cooler and more saline waters of the Malvinas Current. This leads to the development of a strong and narrow (ca. 35±45 km)
thermohaline front whose inner boundary is located over the 90±100 m isobath (Martos
& Piccolo, 1988; Carreto, 1989; Lutz & Carreto, 1991; Carreto et al., 1995). This front
is strongest during spring-summer and is characterized by enhanced phytoplanktonic
biomass (up to 5 mg Chl a ´ l±1, as opposed to background levels of 0.15±1 mg Chl a ´ l±1;
PodestaÂ, 1997), enhanced production (350±450 g C ´ m±2 ´ a±1; Negri, 1993) and concomitantly higher concentrations of zooplankton (Ciechomski & SaÂnchez, 1983).
A comparison of the data retrieved in November 1996 (this work) with those obtained
in November 1993, 1994 and 1995 along similar transects (TABIA I, II and III cruises)
carried out farther east, in purely oceanic waters (Boltovskoy et al., 1996, 2000;
Thompson et al., 1999; Brandini et al., 2000; see Fig. 1), support these differences in
biological richness. In pelagic waters, mean November (1993±1995) chlorophyll a concentrations in the upper 100 m (between 40 and 57° S) were 0.59 to 0.76 mg Chl a ´ l±1,
with maximum values around 2.2±2.6 mg ´ l±1 (Brandini et al., 2000); along the shelfbreak (this work), on the other hand, the mean value was 1.1 mg Chl a ´ l±1, with peaks
as high as 3.7 mg ´ l±1 (Fig. 2B) (these comparisons are obviously restricted to stations
located within the same latitudinal range, i. e. ca. 41±55° S).
At stations 15 and 16, located around 54±55° W (Fig. 1), isolated specimens of the
tintinnids Dictyocysta californiensis and Ormosella acantharus were recorded, along
with a few shells of colonial polycystine radiolarians (Collosphaeridae). The tintinnids
have been reported as uncommon for the Southwestern Atlantic Ocean (Drake Passage
and Southern Malvinas Current; Balech, 1971; Balech & Souto, 1980; Souto, 1981),
but abundant inhabitants of the Pacific Ocean (Balech, 1962; Kofoid & Campbell,
1929). The Collosphaeridae, in turn, are typical panoceanic warm-water organisms
(Boltovskoy, 1999a). The presence of these plankters supports the existence of a weak,
temperate stream originating at mid-latitudes in the South Pacific which is drawn into
the Drake Passage by the West Wind Drift: the Cape Horn Current (Boltovskoy, 1970;
Balech, 1971; Severov, 1990).
The structure of the taxocoenosis surveyed confirms the pattern shown by previous
quantitative studies (Fernandes, 1998; Thompson et al., 1999): a few numerically dominant species, followed by a much larger list of scarce and very scarce forms. However,
relative abundances of the numerically dominant taxa seem to vary widely, both between studies and geographically: Table 2 presents data on the 6 dominant tintinnids
compared with previous collections. Acanthostomella norvegica f. typica accounts
for large proportions (over 20 %) of the tintinnid assemblage in almost all the collections. Amphorides quadrilineata and Steenstrupiella pozzii are numerically dominant
closer to the coast, where tintinnids in general are abundant, yet their share of the assemblage drops significantly in oceanic waters, as the overall tintinnid contribution declines. Codonellopsis pusilla f. typica and Cymatocylis antarctica f. typica are present
352
Thompson, Alder & Boltovskoy
in relatively low numbers in the present study, with a preference for open ocean waters;
they are practically absent in shelf waters. Codonellopsis balechi in the present study
was almost entirely restricted to one station (number 15; Fig. 4F), whereas in nearby
oceanic waters it was not recorded at all.
Most studies dealing with the tintinnids of this area noted that Acanthostomella
norvegica f. typica, Amphorides quadrilineata, Codonellopsis pusilla f. typica, Cymatocylis antarctica f. typica and Steenstrupiella pozzii are consistently among the seven
most abundant tintinnids here (Balech, 1971; Souto, 1972; Balech & Souto, 1980;
Fernandes, 1998). Given the fact that the corresponding surveys carried out in different
years and seasons, which in this temporally and spatially very dynamic frontal area implies wide environmental differences (e.g., Carreto et al., 1995), this resilience in tintinnid population compositions is remarkable. Our rather scarce knowledge of local
tintinnid assemblage structures, combined with the paucity of information on the environmental factors that influence tintinnid distribution in general, does not allow a reliable interpretation of the conditions responsible for such recurrence. We contend that
tintinnid specific abundance ranges are probably governed by abiotic factors rather than
by food availability. The reasoning for this is that ± on the mesoscale ± temperature and
salinity gradients are probably among the most stable, whereas the distribution of primary production is particularly variable, both geographically and temporally (seasonally as well as interannually; Carreto et al., 1995; Brandini et al., 2000).
As noted above, in the area studied the subantarctic Malvinas Current occupies a relatively narrow south-north band; north of ca. 48° S, eastwards of this current, a hydrologically complex area occurs, with tongues and patches of subantarctic, subtropical
and Central Atlantic waters (the Brazil-Malvinas Confluence Zone in Fig. 1). In agreement with this environmental setting, several warmer water tintinnids, found at the
same latitudes farther offshore by Fernandes (1998) and Thompson et al. (1999) (e.g.,
Xystonella spp., Climacocylis scalaroides marshallae, Eutintinnus medius, Steenstrupiella steenstrupii, Ascampbelliella spp.), were not recorded in our materials. At ca.
40±48° S, open-ocean waters host at least 53 tintinnid species (Thompson et al., 1999),
whereas along the slope only 26 taxa were recorded (this work). Also tintinnid species
diversity was noticeably lower in the core of the Malvinas Current (mean value: 0.968;
this work) compared with the Brazil-Malvinas Confluence Zone (2.014; Thompson et
al., 1999).
Conclusions
Two areas differing in chlorophyll a concentrations and in the relative proportions of
several net microzooplankters could be identified along the shelf-break area of the
southern Southwestern Atlantic. The distribution of tintinnid species, on the other hand,
did not allow discrimination between these two zones. Tintinnid taxocoenoses were
characterized by a few abundant species and a large number of rare ones. When compared with a previous study performed farther offshore in oceanic waters (Thompson et
al., 1999), the data of the present survey indicate that the shelf-break hosts higher chlorophyll a concentrations; also, tintinnid specific compositions and overall diversity differ noticeably with distance from the coast.
Southwestern Atlantic tintinnids
353
Acknowledgements
We are grateful to the Brazilian scientific staff and crew members on board the Brazilian research and support
vessel `Ary Rongel' for their logistic and technical assistance, and in particular to Dr. F. Brandini, chief PI of
the TABIA project. This research was partly financed by grants from the Consejo Nacional de Investigaciones
CientõÂficas y TeÂcnicas (CONICET PIP 4159/97), the Instituto AntaÂrtico Argentino and the University of Buenos Aires, Argentina (UBA EX-040 and TX-084).
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Appendix
Species list and general relative abundance data
Numbers after species name indicate: mean and [maximum] proportion of all tintinnids
in the collection, and station numbers where the taxon was recorded. Species and genera of dubious validity are denoted with an asterisk (*) and a question mark (?), respectively.
Acanthostomella norvegica (Daday 1887) forma typica: 24.96 [96.18]; 1±16.
Acanthostomella norvegica (Daday 1887) forma coxliella: 0.02 [2.74]; 10, 11, 14.
Amphorides quadrilineata (ClapareÁde & Lachmann 1858): 15.27 [76]; 1±16.
Codonellopsis balechi Hada 1970: 9.41 [99.32]; 10, 14±16.
Codonellopsis pusilla (Cleve 1900) forma typica: 24.25 [95.97]; 3±16.
Codonellopsis pusilla (Cleve 1900) forma coxliella: 0.003 [1]; 9.
Codonellopsis sp a: 0.37 [25.50]; 9,10.
Codonellopsis sp b: 0.09 [5]; 9±11.
Cymatocylis antarctica (Cleve 1901) forma typica: 5.32 [30.68]; 1, 2, 4±11, 14±16.
Cymatocylis antarctica (Cleve 1901) forma coxliella: 0.03 [0.80]; 9, 10.
*Dictyocysta californiensis Kofoid & Campbell 1929: 0.02 [1.01]; 16.
Dictyocysta elegans var. lepida (Ehrenberg 1854): 1.40 [16.35]; 1±4, 6±9, 12±16.
Dictyocysta elegans var. speciosa JoÈrgensen 1924: 0.15 [2.70]; 1, 3, 7, 9±12, 14, 16.
Dictyocysta mitra Haeckel 1873: 0.001 [0.06]; 1.
Dictyocysta sp.: 0.002 [0.25] 14.
*Eutintinnus rugosus Kofoid & Campbell 1939: 0.1 [6]; 2.
Helicostomella subulata (Ehrenberg 1833): 1.57 [70]; 1±4, 6, 14.
Ormosella acantharus (Kofoid & Campbell 1929): 0.003 [1]; 16.
Southwestern Atlantic tintinnids
Parundella caudata (Ostenfeld 1899): 0.18 [5.40]; 7, 13, 16.
Protorhabdonella? curta (Cleve 1901): 0.02 [0.46]; 4.
*Steenstrupiella pozzii Balech 1942: 16.63 [93.35]; 1±16.
Steenstrupiella spp.: 0.001 [0.07]; 12.
Tintinnopsis spp.: 0.02 [1]; 4, 9, 10.
Undella claparedei (Entz Sr. 1885): 0.01 [0.96]; 2.
Undella globosa (Brandt 1906±1907): 0.02 [0.32]; 13, 14.
Undella subcaudata subcaudata (JoÈrgensen 1924): 0.008 [1]; 11, 13, 16.
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