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,vj , `/ , - ":,

MicroplAnkton species assemblages at the Scripps pier

from March to Novemher 1983 during the 1982-1984 El Niflo event.

Freda M. B. Reid l , Carina B. Lauge 2 and Martha M. White3

(N&Sa-C?R-11 5553 ) MIC R OPLANKTON SPECIES N65-21926

LSSEMBLAGES A T 76E SCEIPPS PIER FKM MARCH

TC NOVEMEE5 1963 LURING THE 1962-1984 EL

NINO L'VEN7 (Scri , pFs Institution of Unclas

oceanography, La Jolla) 29 p HC A03/MF A81 G3/51 14551

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1 Institute of Marine Resources, A-018, Scripps Institution of Oceanography, UCSD, La Jolla, CA 92093

2 Mueeo Argentino de Cienciae Naturales "B. Rivadavia" Angel Gallardo

470, 1405 Buenos Aires, Argentina. Present address: MLRG A-027,

Scripps Institution of Oceanography, UCSD, La Jolla, CA 92093

3 Scripps Institution of Oceanography, UCSD, La Jolla, CA 92093.

Present address: Marine Ecological Consultants, Encinitas, CA 92024
Introduction

Recent microplankton studies in the Southern California Bight have

included consideration of vertical distribution (Beers _t, e^., 1980),

chlorophyll maximum and surface studies (Cullen e1., 1982), spatial

patterns (Reid et Al., 1978; Eppley at Al., 1984x, 1984b), chlorophyll

maximum mechanics (Cullen and Eppley, 1981), and estimations of carbon

biomaso (e.g., Reid et al., 1970). Prior to this, the main body of

work on microplankton, especially phytoplankLon, was by Allen and

associates in the 19208 to 1940s, when daily quantitative sampling of

near-surface water was carried out at the end of the Scripps Institution of Oceanography pier. This resulted in a large amount of data on

dinoflagellates and diatoms, published in many papers by Allen and

others. Allen (1928, 1936, 1940, 1941) summarized from 5 to 20 yearn

of data, producing useful "baseline" information for the organisms

included in his survey. Sverdrup and Allen (1939) and Sargent and

Walker (1948) related the distribution of diatoms to water masses and

currents off Southern California. Modern computer analyses are

currently being applied to this data by D. Goodman and S. Tont. The

20-year fluctuations in the abundance of diatoms on the California

coast have been considered in Toot (1976) and Toot and Platt (1979).

Balech (1960) compared the species composition at the Scripps pier

during a "warm" period (1957-1958) with that of a "cold" period

(1938-1939), using Allen's samples for the latter.

The occurrence of the E1 Nino event beginning in late 1982 (McGowan,

1984) in the northeast Pacific was the impetus for the initiation of a

semiweekly pier sampling program by the Marine Life Research Group
(MLRC) of Scripps Institution of Oceanography (510). This paper is

based on data collected from March to November 1983, but the pier program is continuing to the present. The ,following questions were

posed: What was the general taxonomic structure of the mieroplankton

at the pier during 1983? Did the samples cluster into assemblages of

species; if so, what were the patterns? Does the pier phytoplankton

reasonably represent that seen offshore? Was the pattern affected by

the increase in water temperature caused by the'kl Niffo condition?

Met ode

From the beginning of 1983, water samples and net concentrated samples 

have been collected every 3-4 days at the 510 pier, usually at midmorning. For the net samples, approximately 20 litres (occasionally

40 litres) were siphoned from the centre of the water mass in the 

flume located at the seaward end of the SIO pier. The flume water is

pumped from a depth which depends on the state of the tide but is

roughly 4.5 m. Water depth at the end of the pier was estimated to

average 6 m. The sample was collected in a carboy prior to filtration

through a small conical screen of 24p-mesh which was immersed in a

perforated bucket of water to reduce pressure on the contained organisms. A jar was inverted on the screen and the sample rinsed into the

jar with 200 ml of filtered sea water. The sample was preserved with

12.5 ml of sodium borate-buffered formalin. An unconcentrated sample

for plankton and chlorophyll determination was collected in a 1.3 1 

Nansen bottle at a depth of from 1 to 1.5 m. Surface temperature and 

wind speed were measured, and wave height and water transparency were

estimated. Chlorophyll was determined fluorometrically as described
- 5 -

by Venrick and Hayward (1984).

Per this report the net-sample microplankton data are considered.

Subesmples were examined in a Sedgewick-Rafter chamber for species

identification and enumeration of cells. Bacteriastrum spp., Chaeto—

c roa app., Skeletonema costatum and Planktoniella muriformis were e

counted as chains or colonies. Counting was done at 150x magnification in strips delineated by an ocular grid until at least 200 cells

had been seen. The entire slide was scanned for rare species. The

data considered here extend from March 1983 to November 1983 (samples

59-779), since during that time the microplankton net-samples were

enumerated by a single person (M.W.).

Whittaker's (1952) percent similarity index was used to compare samples and subsequently a dendrogram was constructed to show clusters of

samples (groups 1 through 7) with similar species assemblages, using

the method of weighted pair groups of Sokal and Sneath (1963) (Figure

1).

During the period under consideration there were monthly cruises by

the California Cooperar:ve Fisheries Investigations (Ca1COFI) in the

Southern California Bight (Ca1COFI line 90, cruises 8304-WE, 8305-EB,

8306-EB, 8308-EB, 8309-EB, 8310-EB, 8311-EB, 8312-NH) during which

surface samples were collected for microplankton analysis. They were

filtered and treated as above. Chlorophyll determinations were made

on separate samples. Microplankton data are compared with those from

the pier.
Results

Figure 1 shows the dendrogram of the PSI between samples. Seven

groups (1,2,3,4,5,6,7) and six subgroups (4A,4B, 5A,5B,7A,7B) were

subjectively determined. Within each group the samples were basically

arranged chronologically. Five samples did not fall into these groups

(numbers 59, 229, 359, 649 and 779). Major groupings can be associated with particular species assemblages (Figure 2), and compared with

the records of temperature (Figures 3 and 4) and chlorophyl's (Figure

5).

A total of 148 taxa (see Figures 2 and 6) was identified, some of them

consisting of species associations (e.&., 1j. seriata "group". Bacteriastrum app.); some of unidentified species (e.g., Protogeridinium

op. Q); and some of larger taxonomic groups (e.g , ., Unidentified naked

dinoflagellates).

Figure 2 shows the total number of microplankton cells per liter

recorded for each of the samples and the temporal variations in the

abundance of the 24 most important taxa. The criterion for inclusion

of a taxon into the category "important" was that its numerical abundance represented > 10% of the total microplankton in at least two of

the 76 samples studied. These taxa accounted for an average of 65% of

the total cell numbers, and, as shown in Figure 6, the majority of the

remaining 124 taxa accounted for lees than 6%. If we compare the

occurrences of these species with the groups of Figure 1, we can

assume that every group of samples was characterized throughout the

year by a distinctive microplanktonic assemblage (see Figure 2). 
- 7 -

Group 1 (Mar 15-Mar 22; samples 69-890 Choetoceroa app. "small",

Skeletonema coetatum and NiE ac is scriats "group" were the most prominent diatom tax& during this period.

Group 2 (Mar 25-Apr 4; samples 99-129) was mainly characterized by

several diatom taxa ( Asteromohalus heotactia, Aaterionella gls is alis,

Chaetoceroe app. "small", Cylindrotheca c r jam, N. seriata

"group", Thalassionema nitzschioides).

In general terms, for both groups, microplankton abundances were

moderately high (between 7000 and 30000 cells/1).

Group 3 (Apr 7 -May 2; samples 139-209) comprised the samples with

highest records of microplankton calla/l (up to 10 5 ) and highest

chlorophyll values (see Figure 5). Several diatom species were frequently recorded (especially A. glacialis, Chaetoceroe app. "large",

Chaetoceroe app. "small", Eemiaulus sinensia; see also Figure 6 for

other taxa), while others, Eucamoia zodiacus, Rhizosolenia atolterfothii, were present only during this period.

Although the boundaries between these first 3 groups did not seem to

coincide with major changes in species composition, or were at least

not as sharp as the ones observed later on during the year (see

below), there were some changes in the relative abundance of individual species, which determined the clustering into different groups.

For example, S. coetatum was rare outside group 1, T, nitzschioides

exhibited its highest abundance in group 2, and E,oz diacv.s and R.

stolterfothii belonged nearly exclusively to group 3.

Group 4 (May 6-Jun 21; samples 219-349) was unusual in that the
arrangement of samples was not in chronological order. Thus, for

example, subgroup A, which mainly enclosed mid-period samples, also

included earliest sample 219, and subgroup B comprised early- and

late-period samples. This pattern can be reined to fluctuations of

the dinoflagellate Prorocentrum micAna . This species was repert4d

from March through November; it was the moot prominent species in subgroup B representing > 70% of the entire microplankton. On the other

hand, subgroup A can be distinguished by the frequent occurrence of

Unidentified cell CO which, although present throughout the year,

exhibited here its highest abundance.

Microplankton abundance was highest during the P. micans dominance

(subgroup B) and lowest in subgroup A, with the exception of sample

229.

The sudden increase and later decrease of P.im cane marked the 3-4 and

4-5 boundaries, respectively.

Group 5 (Jun 28-pug 12; samples 369-499) can be clearly separated into

at least two subgroups; A (samples 369-409), and B (samples 419-499).

While the dinoflagellates Ceratium furca and C. cf. divaricatum were

the dominant forme during the first period (A), the second period (B)

was characterized by relatively high abundance of Laboea app. (ciliates), Protooeridinium divergens (dinoflagellate), A. g}acialis, C.

closterium and Triceratium sp. (diatoms). In addition, Unidentified

cell CO was frequently recorded throughout this period.

Microplankton abundance varied widely (from 2 000-30 000 cells /0

within subgroup A, while consistently low values (< 1000) were
- 9 -

recorded within subgroup B. with one exception; sample 459.

Group 6 (Aug 16-Sep 1; samples 509-549) woo characterized by A. glacial s, which had maximal abundance (> 10 4 call@/1) in August 19 (sample

519). With the exception of this sample, total microplankton abundance woo generally low (<4000 calla/1).

Large changes in A. alacialis abundance marked the 5-6 and 6-7 boundories.

Group 7 (Sep 6-Nov 17; samples 559-769): Several warm water species

(especially Nemiaulue membronaceus, Ii. sinensis, Ceratium extensum)

exhibited highest abundances; others, such as Lentocylindrus meditera eus, Dictvocha fibula, Umbilicosohaera siboaae were very rare outride this group. Relatively large changes in diatom (4. membraneceus), silicoflagellate (D. fibula) and dinoflagellate (C, furca)

abundance marked the A (samples 559-709) -B (samples 719-769) boundary.

Total microplankton abundance was low (<3000 cells/1).

As indicated above, the boundaries between groups of samples did not

always coincide with major changes in taxonomic associations but

rather with changes in the relative abundance of individual species.

Our observations on the "important taxa" allow us to define tentatively a general pattern; Diatom cell numbers and species were consistently high from March through early May, moderately high in midJune, end July, mid-August and end November, and low during the

remaining part of the year. Dinoflagellates, on the other hand, exhibited highest abundances from May through early July, and in November.

Silicoflagellates showed highest values in November, and
 10 

coccolithophorids, with few exceptions, were recorded only in

October-November.

As shown in Figures 1-3 and 5, some of the samples were clustered

separately or fall out of the chronoloical sequence. The reason for

this relates to the specific content of these samples (see Figure 6),

which is different from the general pattern described above (Figure

2). The environmental parameters (water temperature, wind speed) were

not notably different during the anomalous sampling periods (samples

59, 229, 359, 649, 779). Therefore, we cannot assume that they were

implicated in the dissimilarities.

Temperature (Figures 3 and 4)

For the year 1983 there seems to be some relation between changes in

temperature and the major shifts in the numbers of microplankton cello

per liter (Figure 2), and the sample groups designated in Figure 1 and

characterized in Figure 2.

Temperature changes > 0.5 0 C were noted at the boundaries between

groups 2-3, 3-4, 4-5, 54 and 6-7. No accompanying temperature change

was seen at the boundary between groups 1 and 2; however, changes in

the species assemblage were noted (see above). In addition, large

030 C) temperature changes within group 4 marked the A-B boundary,

which was clearly associated with different species dominances (F.

micans and Unidentified cell CO, see above). In contrast, the tem -

perature drop (from 22.5 to 18.20 C) within group 6 was not accompanied by changes in the species assemblage. The temperature differ -

ences at the boundaries of subgroups A and B within groups 5 and 7'
were not as large as the ones described above.

In general terms, the microplankton pulse (mid-March through June)

came during a period of moderate temperatures (14-190 C), while

highest temperatures (18-23 0 C) , recorded from July through midNovember, were associated with lowest numbers of microplankton

calls/1.

An interesting feature of the temperature records is that they

remained well above the 63-year mean during several weeks of the year

1983, especially in March, and from September through mid-November.

Chlorophyll (Figure 5)

Highest chlorophyll values (> 3 mg/m 3 ) were measured in early March,

April and June; and moderate values (> 1.5 mg/m 3 ) in late March, late

April through May and early July. During the remaining part of the

year chlorophyll A values were low (<1 mg/m3 ). The values represent

total phytoplankton chlorophyll; 'Thus a relationship to the limited

taxa discussed here is tenuous. However, changes in chlorophyll A

mg/m3 can be seen at each group boundary (with the exception ' of boundaries 5-6 and 6-7), with the largest change between 2 and 3. In

addition, moderate changes took place within groups 4 and 5, marking

the subgroups A-B boundaries. No chlorophyll change marked the A-B

boundary of group 7. The clear drop within group 3 was accompanied by

a drop in the microplankton calla/1 recorded (Figure 2); no major

changes in the species assemblage we studied could be detected.

Taxonomic notes
Ceratium cf. divaricatum is probably synonymous with Q. trines as used

by Allen and other woreurs, and with q. AM as used by, for example,

Reid sk&1., 1970. This organism varies in call size and shape

depending on the stage of its life cycle.

Laboea app. is a general tam used for sheathed olig p tr'ichous ciliates

of varying sizes.

U {A. We have been unable to determine the nature of

Unidentified cell CO. It is unclear whether it is a phytoplankter or

a zooplanktar. It consista of a ccutral sphere surrounded by smaller

spheres, and measures 20-70 pm. It stains with Rose Bengal, and could

possibly be related to Collozoum op. or a formalin —damaged naked

dinoflagellate.
i

ii 

Discussion j" Conclusion

The complex hydrographic and topographic conditions of the Southern

California Bight confound attempts to understand the structure of the

microplankton populations in both time and space. Spatial patchiness

was studied by Food Chain Research Group (Eppley ILL &J., 1984x; "RIS"

program - unpublished) on the shelf, in October 1981, in February,

March 1983 and in February 1984. Continuously pumped samples were

taken from down to dusk along a 73 km line at the SO-m isobath. This

produced a quasi-synoptic picture of microplankton structure and

reduced the effects of short-period temporal variability. Variation

at a fixed point has been studied by anchoring a ship for four days in

Augut 1978 (Eppley IL al., 1984b) and sampling water at intervals as

it passed. Our work at the Scripps pier was carried out over a much

loaij-s, t;uriud. Use of the pier also facilitated collection of

lsrger-volume water samples, though only one depth was sampled.

The current patterns in the Southern Oalifornia Bight are variable.

Sverdrup and Allen (1939), using data for February through December

1938, described the California Countercurrent flowing northwestward a

few kilometers offshore, except in intensive upwelling periods Which

occurred from March through May at the latitude of the Scripps pier.

They associated the southeast-flowing, cold, upwelled Water with a

shallow mixed layer and found that it contained high diatom abundance.

The long-term means (Wyllie, 1966) confirm this general picture of the

water movements in the Bight. The situation closer inshore, at the

pier, is lase well understood. Winant and Bratkovich (1981) placed

current meters about 10 km north of the Scripps pier within 3.6 km of
Abotract

A semiweekly sampling program at the Scripps Institution of Oceanography pier was begun in 1983 during an "El NiHo" event. Micrcplankton

data for March to November 1983 show a temporal sequence of species

assemblages of the 24 "important" taxa, with a residence time of 1 to

4 weeks. From March to early September the assemblages consisted of

typical neritic taxa. From mid-September to mid-November the presence

of oceanic warm-water species was associated with positive temperature

anomalies characteristic of the "El Ni ge l ' condition. During the 

period studied numerical abundances were low.
. .

the shoreline at the 15-, 30- and 60-m isobaths, during 1978 and 1979.

They found the main longshore currents to be usually southward with

occasional northward components in the fall. The development of

eddies further confuse the picture. Sargent and Walker (1948) studied

diatom populations in eddies in the spring months of 1941. They

related patchy distributions to cyclonic eddies of freshly upvalled

water. Abundance diminished more sharply to the west because of

lateral mixing with offshore lower-nutrient water.

The temporal sequence of species assemblages shown by our data is

chronological with a few exceptions. The assemblages are not repeated

during the nine months of this study, and their sequence is dependent

upon qualitative and/or quantitative changes (Figures 1 and 2). The

fact that these assemblages did not repeat over this period is in general agreement with the statement of Goodman et al. (1984) that each

water parcel would be expected to transport a characteristic species

assemblage. They suggested that diatom-dominated phytoplankton assemblages persist from 1 to 3 weeks. Our data for microplankton lead us

to a similar conclusion (1 to 4 weeks). This is seen in Figure 1, in

which the period represented by two adjacent samples is about a week.

The spring diatom increase described for this and other areas

Allen, 1928, 1936; Reid et al., 1970) occurred in 1983, even though

positive temperature anomalies were recorded. The dinoflagellate peak

was in May-June. However, microplankton abundance at ',:%e pier was

frequently lower than the ones reported in previous years ( for example, Allen, 1922x, 1922b, 1927a, 1927b; Borman, 1927). Allen (1940)

stated that "warm years" (e.g., 1926 and 1931) were unfavorable for

------ -

- _- .
- 15 -

diatome and especially for dinoflagellates. It is difficult to compare numerical data due fo differences in sampling techniques and the

inclusion of disparate taxa. However, our data suggest an overall

reduction in numbers of all taxa (Figure 2).

The species which Allen noted as major contributors are present among

our 24 "important" taxa (g.g., a erio ,Pella alecialis (-Japonica),

Eucamnia zodiacun, Nitzachia seriata, Skeletonema coetatum, T al ssionema nitzschioides, CerAtium furca, C. cf. divaricatum (-trioos7),

Prorocentrum micans, Protoneridinium (=Peridinium) diveraens). Except

for A. alacialie and E. zod acue, the occurrence of the other taxa is

similar to that found in Allen's data (Allen, 1928, 1936, 1941). The

uncertain identification of C. triooe (see Allen, 1941) makes it difficult to compare occurrences, but it is present in the summer months

in both seta of data. Similarly, the combination of Chaetoceros

species precludes useful comparisons.

Concurrent with some of the pier work, similar samples were collected

along CalCOFI line 90 (stations 90.37, 90.53, 90.55, 90.65) during the

"Ca1COFI" cruises of April, May, June, August, September, October,

November and December 1983. The species content of these samples, and

especially the dominant forme, differed from those seen at the pier.

However, some taxa were important in both sets of data at almost the

same time. For example, Chaetoceroe app. "large", Ch. app. "small",

Nitzachia seriata "group", Skeletonema coetatum and Thalaeeionema

nitzsahioides were important at the pier in March and April (Figure

r 2), and in April and May in offshore locations. Umbilicoeohaera siboae and Ceratium extensum were frequently and consistently recorded
offshore from September through November, dnd Di—ctvgcho fibula during

November and December. These three species ware important at the pier

in October and November.

. _ One month before the start of the pier sampling, in early Febru -

ary, the "KIS" transact along the coast 5 km offshore shoved a micro

plankton population dominated by dinoflagellates and tintinnide from

—a

Dana Point to San Diego. Many oceanic forma were included in the

assemblages and there was little resemblance to the early groups in

the pier analysis. Unfortunately, there was no temporal overlap in 

these data, but since the first pier samples (early March) had low 

abundances (< 3000 cells/1) it is possible that there was a major 

change at the end of February, when the pier temperatures were already

well above the mean (Figure 4).

A preliminary scan of material from a second transact ("KIS" studies) 

in mid—March shows a more normal coastal spring diatom population,

with Chaetoceros app. increasing. A more thorough zooplankton 

analysis of the same transact (Brooks and Mullin, pers. comm.) indi -

cates a change from the oceanic conditions seen in February ,. Previous

investigations were equivocal, suggesting close resemblances between

inshore and offshore phytoplankton catches at some times (Allen, 1928)

and recognizable differences at others (Allen, 1941).

Balech (1960) related tae presence of oceanic warm —water microplankton

in inshore waters from August 1957 to May 1958 to the "E1 Ni3o" condi -

tion, exemplified by high temperatures at the Scripps pier (Figure 4)

The temperature profile for 1983 showed similar positive anomalies.

Our records of some species (Bemiaulus membranaceus, Umbilicosohaera
- 17 -

sibogae, CCe atium ex ensum), usually associated with oceanic we=-

water conditions, occurred mainly during October and November 1983

1

y(see Figure 2). Matrai (1984) studied Ceratium species collected in

January 1983 on a line from the Central Gyre across the California

i

Current to the coast and concluded that oceanic, warm-water species

did not move east to the California coast as much as they did during

the 1957-1958 "El Nifio" event (Baleeh, 1960).

The "E1 HifIo" condition shown from temperature anomalies began to fade

in the Equatorial Pacific in early 1984 (Oceanographic Monthly Summare, 1983, 1984). However, the unusually high temperatures have persisted in the California Current (Simpson and Lynn, manuscript) and at

the Scripps pier through December 1984 (Figure 4) Chlorophyll measurements at the pier also remained generally lower than 1 mg/m3 until

1985 (MLBG, unpubl, data).

In spite of the temperature increase during the "E1 Ni -no" year 1983,

the species composition was not unusual, except poaeibly from midSeptember through mid-November, when some oceanic warm-water species

occurred. Whether these species were advected in from the west or

south, or whether seed stocks were activated by the higher temperatures is still in doubt. To date we have no microplaukton data for

1984, so we are unable to ascertain whether the persisting high temperature and low chlorophyll a measurements at the pier are related to

unusual species assemblages at that time.
Acknowledgements

We wish to acknowledge the contribution of Walter Bryan, Teresa Areas,

Cecelia Kemper and George Snyder of the Marine Life Research Group

(MLRG) who were responsible for the endless semi —weekly sampling and

chlorophyll analysis, and also of coordinator, George Hemingway.

Elisabeth Stewart, programmer of the Food Chain Research Group (FCRG),

was generous with time and expertise. We thank Richard Eppley,

John Beers, and Tom Hayward for critical reading of the manuscript.

Guy Tapper handled the preparation of the figures with care and patience. F. M. H. Reid was supported in part by DOE grant DE—AT03-82—ER

60031 (FCRG) and by NASA grant NAGW-458. C. B. Lange was supported by

UNESCO study grant SC/RP 206037.4 and by the MLRG. M. M. White was

supported by NASA grant NAGW-458.
- 19 -

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ugh

September, 1967. Bull. Scripps Inst. Oceanogr. IL, Univ.

Calif. Press, pp. 51-66.

Raid, P. M. H., E. Stewart, R. W. Eppley and D. Goodman, 1978. Spatial

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with eddies off Southern California in 1941. J. Mar. Res. j: 490-

505.

Sokal, R. R., and P. H. A. Sneath, 1963. Principles of numerical taxonomy. W. H. Freeman 6 Co., San Francisco, 359 pp.

Sverdrup, H. U., and W. E. Allen, 1939. Distribution of diatoms in

relation to the character of water masses and currents off southern

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Atlas A, 288 pp.
— 23 —

Cap tions La Figures

Figure 1: Dendogram grouping of phytoplankton net samples according to

the percent similarity index (PSI). Subjective groups and

subgroups are indicated by numbers (1,2,3,4,5,6,7) and

letters (A,B), following a chronological sequence. Arrowed

sample numbers indicate samples that fall out of sequence.

Figure 2: Occurrence and abundance (as a percent of the total micro—

plankton) of the 24 "important" taxa, and fluctuations of

total microplankton abundance (cells/1, note scale change).

Numbers ( 1 -7) and letters (A,B) refer to the groups and subgroups in Figure 1.

Figure 3: Temperature records at Scripps pier (solid line: temperatures

of 1983; broken line: 63—year mean (1920-1982) temperatures).

Numbers 1 to 7 refer to groups in Figure 1. Asterisks indicate samples that fell out of sequence.

Figure 4: Temperature profiles at the Scripps pier for two "B1 NiBo"

events. Dotted line represents 63—year mean (1920-1982) temperature. Shaded areas indicate periods of positive temperature anomalies. Shaded block indicates the period dealt with

in this paper.

Figure 5: Total chlorophyll a measurements at Scripps pier, 1983.

Numbers 1 to 7 refer to groups in Figure 1. Asterisks indi -

cate samples that fell out of sequence.

Figure 6: Occurrence and abundance (as a percent of the total micro—

plankton) of the 124 taxa not included in Figure 2.

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