Community Structure Changes of
Subtidal Macrobenthos of Hard
Substrate from Palomino Isle,
Callao - Perú, from 1997 to 2001

J. Argüelles, J. Zavala, A. Taipe,
R. Tafur

Unidad de Investigaciones de Invertebrados Marinos,
Instituto del Mar del Perú, P.O. Box 22, Callao, Perú,
E-mail: jarguelles@imarpe.gob.pe

Introduction

Positive and negative effects of the El Niño event on commercial invertebrates have been described in littoral ecosystems of hard and soft substrates after El Niño 1982-83 event (Arntz and Fahrbach, 1991; Diaz and Ortlieb, 1993; Arntz et al., 1988), however, community structure of hard subtidal macrobenthos and its relationship with commercial populations changes have been scarcely studied.

The objective of this study is to determine subtidal community structure changes and their impact on invertebrate commercial populations like "chanque" Concholepas concholepas and "caracol" Stramonita chocolata.

Materials & Methods

Samples of subtidal macrobenthos were collected and analyzed between April 1997 and October 2001 by diving at Palomino isle (Fig. 1) using an fisher boat.

Fig. 1 Palomino isle, located to south west from San Lorenzo isle, Callao-Perú.

Community analysis was made using cluster and MDS subroutines (PRIMER Program for Windows) on a matrix of abundance by species. Daily sea surface temperature data was available for this period. "Caracol" Stramonita chocolata growth rates were estimated from capture - recapture experiments.

Results & Discussion

Cold and warm periods were observed during 1997. Minimum SST values occurred in April and October, and maximum in February and June. Cooling periods were observed from February to April and from June to October.

During 1998, the maximum SST was reached in February (22.3°C) after a warming period (September 1997 - February 1998). From March to August, a second cooling period was observed, reaching 13,2°C in August. (Fig. 2)

Fig. 2 Sea surface temperature at Cabinzas isle (12o S) during 1997-1998.

The community showed changes characterized by an alternation of dominant species. Four periods were observed: the first one from April to November 1997, characterized by dominance of Balanus sp and Semimytilus algosus; the second one from December 97 to March 1998 characterized by a high abundance of Stramonita chocolata, Discinisca lamellosa and Mitrella buccinoides; the third one from June 1998 to February 2000, in which high recruitment of Pagurus sp and high mortality of Semimytilus algosus characterized the community; and the last period from May 2000 to October 2001, which showed similar structure to that at the beginning of 1997. (Figs. 3; Table 1)

Concholepas concholepas and Stramonita chocolata, commercial invertebrates, were impacted in different ways. Concholepas populations were diminished greatly, while Stramonita chocolata showed greater growth rates during 1997.

Negative and positive effects on "chanque" and "caracol" respectively have been observed (Arntz et al., 1988, 1991; Diaz and Orlieb, 1993). An increment of the natural and fishing mortality in "chanque" was observed during 1997. Natural mortality was related to low availability of food (Semimytilus algosus), and fishing mortality increased because of the high aggregation of this specie by spawning in late spring.

The negative impacts on Semimytilus algosus, Balanus sp, Concholepas concholepas and small gastropods, and positive impact on Stramonita chocolata growth, were the principal conclusions of this work.