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vol.30 número1  suppl.SympImpacts of El Niño/La Niña on the Population Dynamics of the Tropical Bivalve Donax dentifer from Bahía Málaga, Colombian PacificStructure and Population Changes of the Marine Benthos during La Niña 1999-2001 in the Coastal Zone near Tumbes, Perú 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 

Using Biological Indicators and
Biodiversity Indices in the Monitoring
of El Niño and La Niña in the Intertidal
of Sandy Beaches (1997 to 2001),
Tumbes - Peru

N. Robles P., Ch. K. Robles R.,
Eva V. Ruiz M.

CONCYTEC - UNT, FCS - Dpto. B. and BQ., DRP -
DPAPP. P.O. BOX 157 Tumbes-Perú,

The littoral of the Tumbes region is characterized as being bathed by the Oriental Tropical Pacific Ocean, with sandy beaches of thin or thick grains, occasionally being a mixture of both structures. In certain zones it is interrupted by beaches of short extension, with a sublittoral of sedimentary rocks that shelter enormous biodiversity with a predominance of gastropods and bivalves. The total range of the littoral of Tumbes is from Punta Capones to Caleta Cancas, 150 km in extent.

The sampling area covers an approximate extent of 1 km. During low tide, a soft slope leaves an extensive intertidal zone with an average of between 50 and 100 meters of sandy beach of great biodiversity. Sampling for the monitoring of the "EN and LN" events was carried out often fortnightly across vertical and horizontal transects, with a separation of 10 meters between every sampling line, in the area of the beach "Hueso de Ballena". The presence of these events is investigated using bioindicators during "EN and LN". The effects of these natural phenoma on biodiversity were also determined.

In this period from 1997 to 2001, both phenoma were analyzed, with conditions during periods 1997-1998 and 1999-2001 appearing totally opposite. During " EN", severe, classic biological indicators appeared in the intertidal zone of H. Ballena beach, specially the group of "swimming Jaivas" with more representative species: Callinectes toxotes and C. arcuatus, besides a considerable increase in the populations of "palabritas or señoritas" Donax asper and Donax obesulus, while the population of "muy muy" Emeritus analogous, remained stable.

Another species that prevailed during this event but with very low indices of abundance was "Caracolito rayado" Olivella columellaris, which is the most widely distributed and abundant specie in this north zone of the Peruvian littoral. According to the pictures and figures, the event "EN" was presented with positive thermal anomalies between + 6 and + 10 ºC, being thought of as an event of major intensity compared to other events during the last 50 years.

In the second period 1999 - 2001, "LN" conditions were present. With negative thermal anomalies of between - 0.5 and - 2 ºC, temperatures were below normal conditions of the historical average of > 60 years. The low productivity of this north zone of the Peruvian littoral was one of the characteristics of this abnormally cold period. The values of Chlorophyll "a" and phaeopigments ranged between 0.20 and 7.79 ug/l. During this period there was no massive presence of any bioindicator of "EN" but the "LN" event occurred with three new species for this northern zone of the Peruvian littoral, the " conical small Snail "Mazatlania fulgurata" muy muy blanco " Lepidopa chilensis and the "Hydromedusae" that are considered as the biological clock of "LN". The most representative genera were: Hybocodon sp. and Dipurena sp.

J. Fupuy, in Lambayeque's department mentions that L. Chilensis was commonly present in 1999-2001 during the "LN" event. On the other hand V. Alvitres mentions that during the "LN" event the population of Emerita analoga was increased and also the growth rate of this species increased in the Chiclayo beach zone.

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