Abstract

The Juan Fernández and Desventuradas islands are among the few oceanic islands belonging to Chile. They possess a unique mix of tropical, subtropical, and temperate marine species, and although close to continental South America, elements of the biota have greater affinities with the central and south Pacific owing to the Humboldt Current, which creates a strong biogeographic barrier between these islands and the continent. The Juan Fernández Archipelago has ~700 people, with the major industry being the fishery for the endemic lobster, Jasus frontalis. The Desventuradas Islands are uninhabited except for a small Chilean military garrison on San Félix Island. We compared the marine biodiversity of these islands across multiple taxonomic groups. At San Ambrosio Island (SA), in Desventuradas, the laminarian kelp (Eisenia cokeri), which is limited to Desventuradas in Chile, accounted for >50% of the benthic cover at wave exposed areas, while more sheltered sites were dominated by sea urchin barrens. The benthos at Robinson Crusoe Island (RC), in the Juan Fernández Archipelago, comprised a diverse mix of macroalgae and invertebrates, a number of which are endemic to the region. The biomass of commercially targeted fishes was >2 times higher in remote sites around RC compared to sheltered locations closest to port, and overall biomass was 35% higher around SA compared to RC, likely reflecting fishing effects around RC. The number of endemic fish species was extremely high at both islands, with 87.5% of the species surveyed at RC and 72% at SA consisting of regional endemics. Remarkably, endemics accounted for 99% of the numerical abundance of fishes surveyed at RC and 96% at SA, which is the highest assemblage-level endemism known for any individual marine ecosystem on earth. Our results highlight the uniqueness and global significance of these biodiversity hotspots exposed to very different fishing pressures.

Highlights

  • In 1574, the Spanish explorer Juan Fernández was seeking a faster route between Callao, Perú and Valparaíso, Chile

  • The kelp Eisenia cokeri, which was common on the wave exposed side of San Ambrosio Island (SA) but was not present at Robinson Crusoe Island (RC), and is only known from Desventuradas Islands in Chile, contributed an additional 23.0% of the dissimilarity between islands

  • Planktivore biomass was 2.3 times higher at SA compared to RC (F1,74 = 22.6, p < 0.001) and accounted for nearly 40% of the dissimilarity between islands (SIMPER Analysis)

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Summary

Introduction

In 1574, the Spanish explorer Juan Fernández was seeking a faster route between Callao, Perú and Valparaíso, Chile. By detouring west from the coast he managed to avoid the north-flowing Humboldt Current, and in the process discovered the uninhabited Juan Fernández and Desventuradas islands off the coast of what is Chile [1]. These remote islands are among the few oceanic archipelagos along the west coast of South America, yet our scientific understanding of them is extremely limited [2,3,4,5,6,7]. Located 750 km north of the Juan Fernández Archipelago are the Desventuradas Islands, which are ~ 900 km west of Antofagasta, Chile, and consist of the islands of San Ambrosio and San Félix, along with several small islets [2]

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