Improving Argopecten purpuratus culture in northern Chile: Results from the study of larval and post-larval stages in relation to environmental forcing

Abstract

Scallop management studies including a spat collection program have been carried out within the marine reserve of La Rinconada Bay to protect genetic diversity of scallops, to restock natural populations and to provide wild spat to culture activities in Chile. Plankton sampling and spat collection were used to characterize larval and post-larval stages of the Argopecten purpuratus population within this reserve, between December 1995 and March 2000. Main goals were to determine optimal scallop spat collection area, temporal variations of spat settlement and the effect of collector distance off the bottom, and spat growth within the collectors. Larval sampling showed the almost continuous presence, although in variable abundances, of scallop larvae, except for late August–September. Greatest larval abundances were consistently observed from November–December to April–May of the following year. This pattern was altered during the La Niña event of 1998–2000 with unusual peaks of larvae in late July 1999 and November–December 1999. A significant positive relationship was found between the abundance of the large-sized larvae and Chl a concentration ca. 2 weeks before, between February 1999 and February 2000. Larval growth rates ranged from 3.5 to 7.3 μm day−1. Shallow waters were not appropriate for spat collection; the best spat collection area was located in the northwestern part of the Reserve, in water depths ranging from 15 to 20–25 m. Spat settlement was significantly higher at 1 m and 2 m off the bottom, compared with 3 m off the seabed. There was no clear pattern of differential spat growth with collector distance from the bottom in a given site, but spatial variations were observed in the Bay at 1 m off the bottom depending on depth-related bottom-water temperature. Spat settlement occurred almost continuously between November 1997 and March 2000, but in variable proportions: spat abundance ranged from 12 to 6540 ind.coll.−1. Mean spat growth rate was 175 μm day−1 during the ENSO period, vs. 143 μm day−1 during La Niña. Culture improvements are discussed from these new insights on the reproductive cycle and spat collection of A. purpuratus. The former would facilitate future management practices and would help to restore stocks in the Rinconada Bay.