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vol.30 número1  suppl.SympEffects of El Niño 1997-1998 on Commercial Marine Invertebrates of the Peruvian CoastCommunity Structure Changes of Subtidal Macrobenthos of Hard Substrate from Palomino Isle, Callao - Perú, from 1997 to 2001 índice de autoresíndice de materiabúsqueda de artículos
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Investigaciones marinas

versión On-line ISSN 0717-7178

Investig. mar. v.30 n.1 supl.Symp Valparaíso ago. 2002

http://dx.doi.org/10.4067/S0717-71782002030100039 

Effects of La Niña 98-2000 on the
Population Structure of Emerita
analoga,
Lambayeque, Perú

Víctor Alvitres, Jorge Fupuy,
Jorge Chanamé, Adela Chambergo,
Miguel Cortez

Universidad Católica Santo Toribio de Mogrovejo, Perú
Universidad Nacional Pedro Ruiz Gallo, Perú
E-mail: cienciav@hotmail.com, jafupuy@hotmail.com,
jchaname@hotmail.com

Objectives

During the latter years of the XX century, the global climate was affected by the cold episode "La Niña" 1998-2000. This event began in June 1998, and its climatic features persisted until December 2000, with significant consequences for global temperature. The effects of "La Niña" were equally apparent in the coastal area of Lambayeque, Peru, perturbing the inter-tidal community, including Emerita analoga, an important anomuran crustacean which inhabits sandy beaches and occupies a central position in the alimentary chain of the coastal ecosystem.

The life cycle of the intertidal populations is affected by temperature as well as by other variables influenced by climatic changes, which accordingly affect the population dynamics such as growth. According to the literature, "El Niño" has negative effects on E. analoga. The purpose of this research was to study the recovery capacity of E. analoga, based on its population structure during "La Niña" 98-2000.

Results & Discussion

Evolution of "La Niña"

The most spectacular warm event in the century: "El Niño" 1997-98, was present from April of 1997 until June of 1998, and strongly affected the intertidal communities. After this, the global climate was altered by conditions of the cold episode "La Niña" of moderate-to-strong magnitude in the tropical oriental Pacific, which persisted throughout 1999 and 2000. In August-September 1999 a slight and abrupt increment of temperature was observed. According to the reports of the U.S. -French TOPEX / Poseidon expedition and NOAA,"La Niña" therefore occurred in two phases in Lambayeque, Peru: June 98 to July 99 and winter 99 to December 2000.

Structure of the E. analoga population during "La Niña" 1998 - 2000

E. analoga presents accented sexual dimorphism, whereby the males (Max = 23 mm Lc) are only half the average size of the females (Max = 35 mm Lc), but "El Niño" 1997-98 depleted these populations. Thus, sizes were exceptionally small during the first phase of La Niña 98-2000 (Table 1). In the second phase, larger individuals were observed. The tendency toward increased sizes seems to be related to temperature, similar to the increment of the temperature-size during the summers, as well as to the beginning of the second phase of "La Niña" 98-2000. However, this possible association is present with a phase displacement of 1 to 3 months (Table 2, Fig. 1).

Table 1. Variation of the average size (Lc mm) of female and male
E.analoga., during the phases of "La Niña" 98-2000.

STATISTICS

1st Phase
Jun 98- Jul 99

2nd Phase
Aug 99-Dec 2000

Cephalothorax
length

Female

Male

Female

Male

Average

6.9

4.2

14.8

7.7

Standard deviation

3.812

1.138

3.450

1.364

Minim

3.1

3.1

8.0

4.5

Maxim

14.4

6.4

20.1

9.5

n

1761

140

1480

667

Lc average normal: females = 26 mm; males = 13 mm

Table 2. Relationship of size-temperature (OC/Lc mm) according to
sex of E.analoga, during the phases of "La Niña" 1998-2000.

SEX

CORRELATION COEFICIENT

Jan-Apr/
Mar-Jun

99 Jul-Oct/
Sep-Dec 99

Dec-Mar/
Mar-Jun 2000

FEMALE

0.82*

0.87**

0.99***

MALE

0.90*

0.92*

0.83***

Phase displacement of the relationship Size-Temperature: * 2 months, ** 1 month, *** 3 months


Fig. 1 variation of the sizes of female and male E.analoga, in relation to the temperature, during "La Niña" 98-2000.

The size-temperature relationship showed low variability, although large fluctuations with apparent decrease in size were found mainly during winter 1999 and winter-spring 2000, toward the ends of the first and second phases of "La Niña" 98-2000, respectively, indicating a possible influence of recruits which colonized the beach.

In females, during the second phase of "La Niña" 98-2000, only the first two age groups were evident (Table 3). It has been reported that this species lives for up to 3.5 years, whereas the population present during the period of this study still comprised of young individuals.

Table 3. Statistics of age groups of E.analoga females,
during the second phase of La Niña 98-2000.

STATISTICAL

GROUP 1

GROUP 2

Population %

25.81

64.26

Average Lc

8.75

17.95

Standard deviation

2.09

2.50

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