Abstract
Despite their importance as a larval source for the aquaculture industry in several countries, natural stocks of pectinids have been heavily impacted by a variety of natural and anthropogenic stressors. Here we studied the key transition from larvae to early recruitment using the largest natural population of the scallop Argopecten purpuratus (Lamarck, 1819) in Chile. We assessed whether thermal anomalies associated to El Nino-La Nina (EN-LN) cycle had a signal in the temperature regime at La Rinconada Marine Reserve and the consequences of this variability for the settlement of competent larvae of A. purpuratus to artificial and natural substrates in this area. For this, we gathered historical data (February 1950-December 2017) regarding satellite-derived thermal anomalies in the El Nino 1+2 region and in situ measurements of sea surface and bottom temperature in the study area. Moreover, we sampled the larval abundance of A. purpuratus in the water column and the settled spat on artificial collectors and on red algae Rhodymenia spp. –their natural settlement surface– between April 1996 and January 2000. Thermal anomalies associated to El Nino-La Nina cycle were strongly related to interannual changes in winter and summer temperature in Antofagasta Bay, with a clearer signal in winter than summer temperature. The increased reproductive activity during September to April seemingly foster the observed pulses in the larval abundance of A. purpuratus, as expected in a semi-enclosed system. In contrast to previous studies, the larval abundance did not show clear responses to the local El Nino-La Nina -related shifts in temperature regimes. Larval settlement of A. purpuratus in artificial collectors increased through the study period while that on Rhodymenia spp. showed a contrasting, decreasing trend. At the same time, the abundance of Rhodymenia spp dropped continuously. All these temporal trends and our statistical analysis implied that, whether EN-LN-driven thermal shifts had an effect on the larval settlement of A. purpuratus, it is masked by the strong and continuous reduction in the availability of Rhodymenia spp. as a settlement surface. This reduction may have consequences for the stability of natural stocks of A. purpuratus in Chile.
Highlights
Pectinids stand among the most important fishery resources in several countries, but dramatic reductions of natural stocks have led to tight regulations aiming to preserve source populations that ensure sustainable fisheries and larval supply for the aquaculture industry (Dickie, 1995; Paulet et al, 1997)
Our study aims to (i) evaluate the potential relationship between the El Niño-La Niña cycle and the thermal variability in La Rinconada Marine Reserve and (ii) assess the consequences of this variability for the settlement of competent larvae of A. purpuratus to natural (Rhodymenia spp.) and Larval Ecology of Argopecten purpuratus enough for temperatures to be elevated by several degrees through surface heating (Castilla et al, 2002; Ashton et al, 2008; Avendaño and Cantillánez, 2008)
Lower summer sea surface temperatures (SSTs) have been registered under neutral conditions and lower winter SST were observed during weak La Niña episodes
Summary
Pectinids stand among the most important fishery resources in several countries, but dramatic reductions of natural stocks have led to tight regulations aiming to preserve source populations that ensure sustainable fisheries and larval supply for the aquaculture industry (Dickie, 1995; Paulet et al, 1997). Scallops populations are affected by El NiñoSouthern Oscillation (ENSO), a quasi-periodic variation in winds and sea surface temperatures (SSTs) over the tropical eastern Pacific Ocean that modify climate patterns in the tropics and subtropics This interannual environmental variability overlaps with human exploitation in the Humboldt Current System, either bringing local collapses or population blooms in coastal species, depending on their biogeographic affinities (Riascos et al, 2009; Carstensen et al, 2010). A warm El Niño episode in 1982–1983 caused population blooms in several populations in Peru and Chile, turning small-scale fisheries into ephemeral multimilliondollar business (Wolff et al, 2007) Landings in this region rapidly returned to low levels (1,410 MT in 1985 and 492 MT in 1986), which promoted the permanent closure of this fishery and regulatory efforts to protect natural stocks (Avendaño and Cantillánez, 1996; Stotz, 2000)
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