Abstract

The vast and complex coast of the Magellan Region of extreme southern Chile possesses a diversity of habitats including fjords, deep channels, and extensive kelp forests, with a unique mix of temperate and sub-Antarctic species. The Cape Horn and Diego Ramírez archipelagos are the most southerly locations in the Americas, with the southernmost kelp forests, and some of the least explored places on earth. The giant kelp Macrocystis pyrifera plays a key role in structuring the ecological communities of the entire region, with the large brown seaweed Lessonia spp. forming dense understories. Kelp densities were highest around Cape Horn, followed by Diego Ramírez, and lowest within the fjord region of Francisco Coloane Marine Park (mean canopy densities of 2.51 kg m-2, 2.29 kg m-2, and 2.14 kg m-2, respectively). There were clear differences in marine communities among these sub-regions, with the lowest diversity in the fjords. We observed 18 species of nearshore fishes, with average species richness nearly 50% higher at Diego Ramírez compared with Cape Horn and Francisco Coloane. The number of individual fishes was nearly 10 times higher at Diego Ramírez and 4 times higher at Cape Horn compared with the fjords. Dropcam surveys of mesophotic depths (53–105 m) identified 30 taxa from 25 families, 15 classes, and 7 phyla. While much of these deeper habitats consisted of soft sediment and cobble, in rocky habitats, echinoderms, mollusks, bryozoans, and sponges were common. The southern hagfish (Myxine australis) was the most frequently encountered of the deep-sea fishes (50% of deployments), and while the Fueguian sprat (Sprattus fuegensis) was the most abundant fish species, its distribution was patchy. The Cape Horn and Diego Ramírez archipelagos represent some of the last intact sub-Antarctic ecosystems remaining and a recently declared large protected area will help ensure the health of this unique region.

Highlights

  • Kelp forests are the foundation of many of the shallow rocky coasts of the world’s cold-water marine habitats, providing food and three-dimensional structure for a wide range of species [1,2,3,4]

  • We conducted a total of 35 transects at 18 locations within the Magellan Region (Francisco Coloane MP = 4, Cape Horn = 23, Diego Ramırez = 8)

  • Based on Landsat 8 Operational Land Imager (OLI) data, kelp canopy biomass was most dense at the Cape Horn Archipelago with a mean canopy biomass density of 2.51 kg m-2 (± 1.27 sd), followed by Diego Ramırez with 2.29 kg m-2 (± 0.78 sd), and Francisco Coloane with 2.14 kg m-2 (± 1.07 sd)

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Summary

Introduction

Kelp forests are the foundation of many of the shallow rocky coasts of the world’s cold-water marine habitats, providing food and three-dimensional structure for a wide range of species [1,2,3,4]. They produce the largest biogenic structures in the ocean, are important in marine carbon cycles, and constitute one of the most diverse and productive ecosystems on the planet [5,6,7,8]. The region still contains largely unfragmented ecosystems, low anthropogenic impacts, and very low population density [23]

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