Variability of community structure of Copepoda related

to El Niño 1982-83 and 1987-88 along

the west coast of Baja California Peninsula, Mexico

SERGIO HERNANDEZ, TRUJILLO

Plankton Department (CIClMAR-IPN. COFFIA & BDD

Recipient). PO Box 592, 23000 La Paz. Baja Califomia Sur,

Mexico (e-mail: strujil@vmrediPn.iPn.mx)

ABSTRACT

Copepod community structure and abundance of themost abundant species were studied during 15 cruisesmade between 1982 and 1989 along the west coast of theBaja Califomia Peninsula, Mexico. The number ofspecies and species diversity (Shannon's index) for eachsampling station of the oceanographic cruises wereobtained. Though the zone was dominated during theyear by the tropical copepod component, similaritiesbetween El Niño 1982-83 and 1987-88 were observed.Tropical-equatorial populations were added to theregular tropical composition (50% ) of the community ofcopepods resulting in a wide distribution of thosepopulations in 1982-83 and in 1987-88. The scenarioin 1984-89 (without 1987-88) was significantly differ-ent from both El Niños because of the sea surfacetemperature, the species diversity, and the tropicalcopepod component, although 1982 was similar to 1985in diversity index and number of species. Environmen-tal conditions prevailing along the west coast of BajaCalifomia during El Niño indicate that in 1982-83 theeffect on the copepod community was greater thanduring the 1987-88 event.

Key words: Baja Califomia, copepod community,diversity, El Niño

INTRODUCTION

El Niño refers to a periodic climatic fluctuation of trie

sea surface temperatures (SST) centred in the equa-

torial Pacific. The most obvious sign is warming water

off the coast of Ecuador and Peru, which generally

occurs within a few months of Christmas. The nameEl Niño (Christ Child) was originally simply the localname for the seasonal increase in the temperature ofcoastal waters that occurs around Christmas (Brownet al., 1993). Wolter and Timlin (1993) have devel-oped the multivariate ENSO index (MEI) using thesix main observed variables over the tropical Pacific asan analytical tool to detect the variability oninterannual time scales of the El Niño-SouthernOscillation (ENSO) for the 1950-1993 period,updated to 1998 (K. Wolter, pers. comm.).

The long-term database of MEI (Fig. 1) shows thatthe 1982-83 and 1987-88 periods were strong El Niños,which agrees with the sea surface temperature anoma-lies (Brown et al., 1993; Hernández-Vázquez, 1995).

The change of the marine environment during anEl N iño and its impact on the biological communitieshas motivated many studies of the distribution andabundance of the populations as a measurement oftheir response to extreme physical variations in theocean (Arntz et al., 1985; Wooster and Fluharty, 1985;Torres-Moye and Alvarez-Borrego, 1987; Martínez-López, 1993; Gómez-Gutiérrez et al., 1995; Palomares-García and Gómez-Gutiérrez, 1996; Gárate-Lizárragaand Siqueiros-Beltrones, 1998).

Along the Baja California Peninsula, the commu-nity structure of copepods has been studied during ElNiño and non-El Niño years by Longhurst (1967),McGowan and Miller (1980), Hernández- Trujillo(1991a, 1991b); Hernández- Trujillo (1995), Palo-mares-García and Gómez-Gutiérrez (1996), and Her-nández- Trujillo and Esquivel-Herrera (1997). Theirresults show a north-south and inshore-offshoregradient of the diversity and changes of dominanceand species rank over months and years, and themixture of northern and southern communitiespromoted by the current system has been identified asa source of species diversity in this region.

Because the study area belongs to the NorthPacific subarctic-subtropical transition zone, thewarming of the zone is coincident with the northernflow of North Central Pacific water. The borders ofthese warm waters oscillate latitudinally as a func-tion of climate variability (Pearcy, 1991; Hernández-

Received 24 September 1998

Revised version accepted 1 June 1999

284 @ 1999 Blackwell Science Ltd.

Copepoda and El Niño 1982-83 and 1987-88 285

Figure I. Multivariate ENSO lndex for the 1950-1998 period.

4

3Q)L.::J

tmo.

~ 1-oQ)N.-

-oL.m

-o -1c:m

+-'00

~

2 +

o

-2

-3

Trujillo, 1991a, c; Lavaniegos et al., 1998). Differentwater types meet and mix in the southem BajaCalifomia area; that well-known feature has beenidentified as promoting copepod species richness(Longhurst, 1967; Palomares-García and Gómez-Gutiérrez, 1996). However, the copepod fauna sim-ilarity between El Niño and non-El Niño periods isunknown.

This study, based on zooplankton samples obtainedduring different years ( 1982-1989) and climaticconditions at the Baja Califomia area, examines (a)how did the copepod fauna in El Niño 1982-83 differfrom El Niño 1987-88, and (b) whether the two ElNiño events were more similar to each other incopepod fauna than they were to intervening non-ElNiño years.

research vessels BIO El Puma, B.H. Mariano Mat-amoros, and B.H. Altair. The sampling protocol wasfrom Smith and Richardson (1977) using an obliquetow of bongo nets having digital tlow meters and meshof 333 and 505 J1.m. The contents of the 505 J1.m netwas analysed following the procedure of sorting,identification, and counting of adult copepodsreported by Hemández- Trujillo (1991a). The seasurface temperature (SST) data were collected at eachsampling station using an Inter-Ocean CTD.

To determine the structure and variation of thecommunity of copepods, the Shannon index (H') ofdiversity (Pielou, 1967; Omori and Ikeda, 1992) wascalculated for each station; to determine how evenlythe total number of individuals was distributed amongthe species present, the evenness (E) of the Shannonindex was calculated (Pielou, 1969); E is constrainedbetween 0 and 1.0 with 1.0 signifying that all speciesare equally abundant. A rank-abundance plot wasmade to present species abundance data (Magurran,1988) and to provide a more direct comparison be-tween communities of copepods with different num-bers of species during the period of the study. One-way

MA TERIAL AND METHODS

This study was based on 630 zooplankton collectionsobtained on 15 oceanographic cruises made by CICI-MAR along the westem coast of the Baja CalifomiaPeninsula between 1982 and 1989 (Fig. 2) on the

@ 1999 Blackwell Science Ltd., Fish. Oceanogr., 8:4, 284-295.

286 s. Hemandez- Trujillo

Figure 2. Sampling grid of CICIMAR cruises 1982-1989.

+ 8207

:J 8212

,6 8302

O 8305

<) 8309I

( ~~ "

x24- ,22 I 1i8 1i6 1i4 1i2 1io

LONGITUDE

lffi 1 IX>

analysis of variance was used to test the differences inthe means of number of copepod species, diversityindex, and SST among years. The null hypothesistested was no differences of variables by year; thealtemative hypothesis was that there are differences.

T o determine the interannual relations of thediversity index, a principal component analysis (PCA)was applied to a matrix of Shannon indices at eachsampling station. This method was chosen for itsability, as a diagnostic tool, to reduce the multidi-mensional complexity of the observed field to a rela-tively easily visualized low-dimensional representation(Preisendorfer, 1988).

Data of the species composition of the copepodsrecorded in the study area were classified biogeo-graphically according to the criteria in Hemández-Trujillo (1991a, 1991b) The present paper emphasizesthe tropical component of the taxocoenosis.

The data set of the sea surface temperature, cope-pod diversity index, and number of copepod specieswas used to obtain the deviation (D) of each obser-vation (cruise) from the mean (all cruises) as follows:

D = Oí -X, (1

where Oi is the variable value in the ith cruise, and Xis the mean value in the 1982-89 period.

RESULTS

A total of 144 species was identified. Figure 3 shows

the differences between copepod communities on

cruises between 1982 and 1989. The upper curvesrepresent the least diverse assemblages, dominated byfew species; conversely the lower curves were the mostdiverse. An important feature was that for the fivecruises with greatest diversity, about 15 copepodspecies made up 80% of cumulative abundance. Forthe six cruises with least diversity , about 4 copepodspecies made up 90%. In the remaining three cruises ofintermediate diversity, about 10 species made up 90%.Figure 4 shows more clearly the interannual differen-ces between the two El Niños and the 1984, 1985 and1986 intervening years. T able 1 shows the mostabundant species at each warm episode, and in

intervening years.Figure 5 shows the number of species found at a

station, species diversity (H'), and species evenness(E) vs. the sea surface temperature. There was a directand significant (P < 0.05) relation between thoseproperties and SST, for most years (Table 2).

The interannual number of copepod species, thetropical species composition, diversity index, andaverage SST are shown in Table 3. Compared withother years, 1983 had the greatest number of species,percentage of tropical species in the community, andaverage SST. In addition, a one-way analysis ofvariance showed significant differences between years(P < 0.05, Table 4) in the number of copepod species,diversity index and SST.

The H' index shows a wide range in both El Niñoand non-El Niño years, and the PCA showed thatthere were differences between years (Fig. 6). The firsttwo components explain 42% of the variance,ret1ecting the changes in the diversity of the copepod

@ 1999 Blackwell Science Ltd., Fish. Oceanogr., 8:4,284-295.

Copepodn and El Niño 1982-83 and 1987-88 287

Figure 3. Rank abundance of copepod species by cruise.

100

80~O)(.)cIU

'OC~

.cIUO)>

:¡:;~~E~

u

60

40

20

o

Figure 4. Rank abundance of copepod species in El Niño 1982-83 and 1987-88.

100 ==

:;¡¿:Q-Q)(.)c:!O

-0c::]

.c!OQ)>

~!O:]E:]

U

80

60

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201 4 7 1013161922252831 34374043

Rank

The samples of 1984 and 1985 were positivelycorrelated, and 1986 was isolated. In addition, in thoseyears Calanus pacificus was the dominant species in thecommunity, averaging 88.2% (1989), 84.5% (1988),70% (1985),64.5% (1987),52% (1984),53% (1986),

community during both El Niño events. The samplesof 1982, 19.87 and 1989 are positively correlatedamong themselves and contribute most to component1, while 1983, 1988 and 1989 contribute most tocomponent 2 (Table 5).

@ 1999 Blackwell Science Ltd., Fish. Oceano)!T., 8:4, 284-295

288 s. Hernandez- Trujillo

Table 1. Most abundant copepodspecies along the west coast of BajaCalifomia peninsula in both El N iño1982-83 (upper panel) 1987-88 (lowerpanel), and intervening years 1984,1985, and 1986 (middle panel).

1982-1983

Calanus pacificus

Pleuromamma

abdominalis

Euchaeta marina

Euchaeta flava

Eucalanus attenuatus

Undinula vulgaris

Subeucalanus subcrassw

Paracalanus parvus

Eucalanus crassus

Euchaeta wolfendini

1984

Calanus pacificus

Pleuromamma

abdominalis

Euchaeta marina

Paracalanus parvus

Pleuromamma gracilis

Acartia di1nae

T emora discaudata

S ubeucalanus

subcrassus

Corycaeus speciosus

Oithona fallax

1987-1988

Calanus pacificus

Subeucalanus

subcrassus

Paracalanus parvus

Euchaeta marina

Eucalanus crassus

T emora discaudata

Centropages furcatus

Corycaeus speciosus

Pleuromamma quadrunguláta

Rhincalánus nasutus

Scolecithricella spAcartia danae

Candacia truncata

Scolecithrix danae

T emora discaudata

Candacia catula

Undinula darwini

1986

Calanus pacificus

Euchaeta marina

¡laninalis

Labidocera acutifrons

Euchaeta longicomis

Paraca~nus parvus

Labidocera trispinosa

Pleuromamma abdominalis

Labidocera acuta

Eucalanus bungii califomicus

Scolecithrix danae

Gaetanus pungens

Centropages furcatus

ninalis Labidocera acuta

Eucalanus bungii califomicus

Labidocera acutifrons

40.5% (1982), and 29% (1983) of relative abundance(Hemández- Trujillo and Esquivel-Herrera 1997).

There were positive deviations from the 1982-89mean copepod diversity index in 1983, 1984, 1987 and1988; conversely 1982, 1985 and 1989 had negativevalues (Fig. 7a). For the number of copepod species, thedeviation was negative in 1982 and 1985; there werepositive deviations in 1983, 1987, 1988 and 1989. In1984 and 1986 the deviation was zero (Fig. 7b).

DlSCUSSION

Using SST anomalies off Baja Califomia, Gómez-

Gutiérrez et al. (1995), Hemández-Vázquez (1995,

and Hemández- Trujillo and Esquivel-Herrera (1997)

have provided evidence of ENSO off Baja Califor-

nia. The comparison of the variability of the MEI

and the SST anomalies off Baja Califomia showssimilar trends for the 1980-90 period (Fig. 8). Atime difference of about 3 months occurs betweenthe equatorial El N iño signal and its occurrence inthe southem Baja Califomia (22-27°N) shown bypositive SST anomalies (21-27°N). Although ElNiño 1987-1988, according to MEI at the equatorialarea, lasted from May 1986 to May 1988, its int1uencein the studied area was evident, by the SST positiveanomalies, from July to December 1987 (Gómez-Gutiérrez et al., 1995). During El Niño 1982-83 in thestudied area, the seawater stayed warm longer incomparison with the 1987-88 event.

The rank-species analysis showed different assem-blages with different numbers of species of the copepodcommunity during the two El Niños, and interveningyears along the Baja Califomia Peninsula, which

@ 1999 Blackwell Science Ltd., Fish. Oceanogr.; 8:4, 284-295

Candacia varicans

Euca1anus bungii

califomicusEuchaeta longicomis

Labidocera trispinosa

Oithona plumifera

Oithona robusta

Corycaeus jlaccus

1985

Calanus pacificus

Euchaeta marina

Rhincalanus nasutus

Candacia pachydnct)

Pleuormamma abdor

Paraca1anus parvus

Scolecithrix dnnae

Candacia bipinnata

Centropages bradyiCalanus minor

Acartia dnnae

Euchaeta longicomis

Pleuromamma abdor

Labidocera trisPinosa

Calanus minor

Corvcaeus sbeciosus

Copepoda and El Niño 1982-83 and 1987-88 289

Figure 5. Number of species, diversity, and species evenness of Copepoda in relation to SST along the coast of Baja CalifomiaPeninsula in the 1982-1989 period.

1982 1983

(/)wuw(1.(/)u.o~waJ~:)z

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23 24 25 2' 27 2' 29 30,

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SST

@ 1999 Blackwell Science Ltd.. Fish )ceanol!T ..8:4. 284-295

.

I..

..""

s. Hernandez- Trujillo290

Figure 5. (Contd.)

12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

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19891988

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@ 1999 Blackwell Science Ltd., Fish. Oceanogr., 8:4, 284-295.

Copepoda and El Niño 1982-83 and 1987-88 291

Table 2. Correlation coefficients between variables by year.

Bold p < 0.05.

Table 3. Number of copepod species, Shannon index,percentage of tropical copepod species, and average of SSTalong the Pacific coast of Baja Califomia peninsula

(1982-89).SST

1

0.69

0.66

Diversity index

% ttopical

species0.89 SSTYear Species (n) H' range

1982

1983

1984

1985

1986

1987

1988

1989

29118875693786858

O-~

0.02-3

o-~

O-¡

o-~

0.02-3

0-3

0-3

7080485053656449

22.3

23.2

18.2

20.8

20.3

19.2

22.5

19.9

0.43

0.04

10.53

0.36

0.41 0.80

\

0.24

0.36

1982

SST

Diversity index

Species number

1983

SST

Diversity index

Species number

1984SST

Diversity index

Species number

1985

SS1

Diversity index

Species number 0.63Table 4. One-way analysis of variance of the effect of the

year on the variability of properties measured.1986

SST

Diversity index

Species number

0.700.46

1

0.70

Source of variation SS d.f. MS F H,

Number of speciesBetween yearsWithin yearsTotal

4389.019117.123506.1

7 627.0 20.43 Rejected

623 30.7

6300.710.49 0.66

DiversityBetween years

Within years

Total

SST

Between years

Within years

Total

119.1 7

670.9 623

790.0 630

7.0 15.8 Rejected

0.560.45 0.64

1736.8 7 248.16060.2 618 9.87796.9 625

25.3 Rejected

1987

SST

Diversiry index

Species number

1988

SST

Diversity index

Species number

1989

SST

Diversity index

Species number

0.640.28 0.36

belongs to a transition zone with a relatively constantnumber of tropical species (Palomares-García andGómez-Gutiérrez, 1996). Those assemblages can beconsidered as responsible for the main dynamics of thetaxocoenosis along the west coast of the BajaCalifornia Peninsula. A similar observation in theMagdalena Almejas lagoon system in 1983-84 wasmade for copepods (21 species were 97% of totalrelative abundance -Palomares-García and Gómez-Gutiérrez, 1996) and for phytoplankton (22 specieswere 70-80%, Gárate-Lizárraga and Siqueiros-Beltr-ones, 1998). In 1987-88,20-25 phytoplankton speciestotalled 80-95% of relative abundance in the Mag-

dalena Almejas lagoon system (I. Gárate-Lizárraga,

pers. comm.).The abundance of most copepod species in Fig. 4

can be assumed to indicate the proportion of theresource each uses (May, 1975; Platt et al., 1984),therefore it can be inferred that in 1982-83 theresources were more equally distributed among thespecies than in 1987-88, and in the intervening years1984-86, allowing the occurrence of more species,especially tropical ones. This coincides with the dom-inance of the nannophytoplankton cells ( <20 .um,which are a food item for filter-feeding copepods)during El Niño 1982-83 (Martínez-López, 1993). This

@ 1999 Blackwell Science Ltd., Fish. OceanogT., 8:4, 284-295.

~.04

1.70

~.94

~.75

~.53

1.84

,.49

,.10

292 s. Hernandez-Trujillo

Figure 6. Plot of the second vector vs. the first vector derived from PCA of the annual values of H'. The two component!explain 23% and 19% of the variance.

PRINCIPAL COMPONENTS ANAL YSIS

COPEPOD DIVERSITY

,o

0,8

0,6

0,4N

1-ZwZono~oU

0,2

0,0

.0,2

.0,4

-0,6

-08,

-1,010, -0,8 .06I -04I -0,2 0,0

COMPONENT 1

0,2 0,4 0,6 0,8 1,0

Table 5. Principal Componenr Analysis coefficients.

Year Component 2 Component 2

0.598

0.043

.0.524

0.253

.0.230

.0.0270

0.226

0.020

Component

1982

1983

1984

1985

1986

1987

1988

1989

-0.102-0.1190.3250.032-0.4160.4840.1390.242

-o.

0.

-0.

-0.

0.

0.

0.

0.

19variance 23 15

phytoplankton fraction can develop rapidly and growunder oligotrophic conditions (Des-Abbayes et al.,1989), as were present during this El Niño (Taft,

1985).The statistical analysis showed a significant relation

between SST and number of species, diversity, andevenness (Table 2). This shows a strong link year-to-year. The SST effect on the structure of the

community promotes increases and decreases incomplexity according to the anomaly from theseasonal mean. In addition, the latitudinal thermalanomaly reported for the 1980 decade in the BajaCalifornia area showed that 1982-84 and 1987-88were the most intense warming periods (Hernández-Vázquez, 1995; Hernández- Trujillo and Esquivel-Herrera, 1997), which is consistent with the inf1uenceof the SST on copepod community structure.

Clearly, 1982 and 1983 were more tropical in fau-nal composition than were the remaining years. In1982-83, there were more species with similar abun-dance, but for 1984-88 a few species were dominant.This situation has been observed for phytoplanktonafter the 1982-83 El Niño in the Magdalena Almejaslagoon system (Gárate-Lizárraga and Siqueiros-Beltrones, 1998), and during the 1992 El Niño in theequatorial Pacific (Liu et al., 1996). The variation inspecies diversity of copepods in the central andsouthern Baja California area according to SSTshowed dependence on the number of species present;high values were shown by samples from warm waters(>20°C), and were also shown by samples from tem-perate waters ( <20°C). For all years, sometimes the

@ 1999 Blackwell Science Ltd., Fish. Oceanogr., 8:4,284-295.

063

455

028

346

212

181

276

361

Copepoda and El Niño 1982-83 and 1987-88 293

Figure 7. Time series of (a) anomaly of copepod diversity index, and (b) anomaly of number of copepod species.

(a) DEVIATION OF DIVERSITY INDEX (b) DEVIATION OF THE NUMBER OF SPECIES

0.8

0.6

0.4

-0 0.2

!::

~ °

i:ñ -0.2

-0.4

~.6

-0.8

-1

7

5

(I)Q)

.u 1Q)o.

~ -1O

Z-3

-5

I I I I1986 1987 1988 1989

-7

Figure 8. Multivariate ENSO index and mean coastal SST anomaly. Data of SST reported by Gómez-Gutiérrez et al. (1995) for21-27°N.

uo

1981 1983 1985 1987 1989

-MEI -SST ANOMAL y

copepods separates along the axis of component 1. TheJune 1989 samples clustered with samples from ElNiño years, indicating that the copepod assemblagedistinctness in terms of the abundance of imponantspecies becomes similar for El Niño and non-El Niño

high diversity was due to an increase in the number ofspecies, but was otherwise due to the abundance of

species (Fig. 5).According to PCA, components 1 and 2 together

account for 42% of the variance. The diversity of

@ 1999 Blackwell Science Ltd.. Fish. Oceanogr., 8:4, 284-295.

294 s. Hernandez-Trujillo

December-January 1950 to July-August 1998. Thanksto Dr Michael Mullin for his editorial help. Thanks toDr Ellis Glazier for editing this English-language text.

at the studied area. In Fig. 6 the lower left and rightquadrants consist of samples from non-El Niño years(1984, 1985 and 1986), which have in common anequivalent proportion of tropical species (about 50%),zero or negative deviation from the mean number ofspecies, and mostly negative deviations of the Shan-non diversity index.

According to Hemández- Trujillo and Esquivel-Herrera (1997), high copepod diversity is related tothe invasion of Central Pacific and Tropical EastemPacific currents, and low diversity is caused by theCalifomia Current ( CC) flowing southward. McGo-wan and Walker (1993) attribute high zooplanktondiversity to the changes associated with frontal sub-arctic and subtropical zones, the borders of which aremodified by flow dynamics (Roden, 1991).

The environmental conditions prevailing during ElNiño 1982-83 promoted more transport of copepodspecies from tropical to more northem latitudes thandid El Niño 1987-88. This 'tropicalizing' of the area bythe copepods has been also reported for euphausiids(Gómez-Gutiérrez et al., 1995) and phytoplankton(Gárate-Lizárraga and Siqueiros-Beltrones, 1998)during El Niño.

We found that there are more similarities incopepod fauna among El N iños, because our resultsindicate a regular proportion of tropical fauna in theBaja Califomia region, about 50% for non-El Niñoyears and increase up to 80% in El Niño years. Thepositive and negative deviations of the number ofspecies reflect the influence of the warming andcooling events on the copepod community structure,reinforcing the observation of the 50% minimal pro-portionality of the tropical components. This meansthat the copepod fauna in both El Niño 1982-83 and1987-88 had more similarities than differences amongthemselves, and had important differences comparedwith the intervening years.

ACKNOWLEDGEMENTS

We thank the technical and scientific staff of thePlankton Department of CICIMAR for their partici-pation in the collection of samples. Thanks to UNAMand the Navy Ministry of Mexico for use of researchvessels El Puma, Mariano Matamoros and Altair. Thisresearch was supported by funds provided by Divisiónde Estudios de Posgrado del IPN (842567, 86804,874264,903361,931318) and the Consejo Nacionalde Ciencia y Tecnología {904620). I am in debt toKlaus Wolter of NOAA-CIRES Climate DiagnosticsCenter of the University of Colorado at Boulder whokindly provided me with the bimonthly MEI values for

REFERENCES

Amtz, W., landa, A. and Terrazona, j. (1985) El Niño. Suimpacto en la fauna marina. Bol. I!lSt. Mar PeTÚ-Callao,222 pp.

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