Overview of Recent Advances in Oceanographic, Ecological and Fisheries Research on Oceanic Islands in the Southeastern Pacific Ocean

Lat. Am. J. Aquat. Res., 42(4): 666-Advances672, 2014 in oceanographic, ecological and fisheries research on Oceanic Islands 666 1 “Oceanography and Marine Resources of Oceanic Islands of Southeastern Pacific ” M. Fernández & S. Hormazábal (Guest Editors) DOI: 10.3856/vol42-issue4-fulltext-1 Preface Overview of recent advances in oceanographic, ecological and fisheries research on oceanic islands in the southeastern Pacific Ocean Miriam Fernández1 & Samuel Hormazábal2 1Estación Costera de Investigaciones Marinas and Center for Marine Conservation, Departamento de Ecología Pontificia Universidad Católica de Chile, P.O. Box 114-D, Santiago, Chile 2Escuela de Ciencias del Mar, Pontificia Universidad Católica de Valparaíso P.O. Box 1020, Valparaíso, Chile The Chilean oceanic islands have been received Rodrigo & Lara (2014) and Rodrigo et al. (2014) little attention, both scientifically and in terms of conducted a qualitative and quantitative morphological conservation. In fact, the first marine protected areas analysis of the seamount chains and oceanic islands. around these islands were created in the last two years, They used recent bathymetric compilations that include 10 years behind those established in continental Chile. combined satellite derived and shipboard data (“Global This occurred in spite of the high concentration of Topography”), multibeam bathymetric data (from endemic species (Fernández et al., 2014; Pérez-Matus NGDC-NOAA), and a magnetic data set, to establish et al., 2014; Rodríguez-Ruiz et al., 2014) and growing clues about the origin of both seamount chains and their fishing pressure around Chile’s oceanic islands relationships with regional tectonics. Rodrigo et al. (Castilla et al., 2014; Zylich et al., 2014). Nonetheless, (2014) identified 514 seamounts along 2900 km of the a few sporadic studies, associated with both national Easter Submarine Alignment. In general, the largest (e.g., CIMAR, Yáñez et al., 2008) and international seamounts (>1000 m in height) are aligned and have a initiatives (e.g., Friedlander et al., 2013), have larger volume, with an elongation of their bases along contributed to our knowledge of the ecosystems the seamount chain. On the other hand, smaller associated with seamounts and oceanic islands in Chile. seamounts tend to be distributed more randomly with This special volume presents a review and analysis of circular bases. The best possible mechanism to explain the current information available on marine ecosystems the origin of the seamount chains that emerged from the associated with the oceanic islands in the Juan morphological analysis is the existence of a localized Fernández Archipelago and Easter Island Province hotspot west of Salas y Gomez Island. The Easter (Easter and Salas y Gómez islands). Fracture Zone, which produced crustal weakening, may Oceanic islands are characterized by their isolation, also have contributed in the Easter Island region small size and volcanic origins. At distances of 3700 (Rodrigo et al., 2014). These hotspots could explain the and 3400 km respectively, Easter and Salas y Gómez substantial portion of the Easter Submarine Alignment islands are more isolated than other oceanic islands of sea floor occupied by seamounts (27%; Rapopport et Chile. Meanwhile, the Juan Fernández Archipelago al., 1997) in comparison with the Eastern Pacific (6%; (made up of the Robinson Crusoe, Alejandro Selkirk Rapopport et al., 1997). and Santa Clara islands) are 600 km from continental Rodrigo & Lara (2014) characterized the Chile. Chile’s oceanic islands are substantially smaller bathymetry along the 800 km alignment of the Juan than other Pacific islands (Hawaii: 28,310 km2, Fernández Ridge, which ranges from the Friday and Galápagos: 45,000 km2). Easter Island is 164 km2; Domingo seamounts in the west to the O’Higgins Robinson Crusoe Island is 47.94 km2; Alejandro seamount in the east. The results show a continuous Selkirk Island is 49.5 km2; Salas y Gómez Island is 2.5 west-east corridor with a base at ~3900 m depth formed km2; and Santa Clara Island is 2.21 km2 (Newman & by four groups of seamounts/islands with a total of 22 Foster, 1983; Rodrigo & Lara, 2014). These islands are summits. From east to west the four seamount/islands the visible peaks of a chain of seamounts and volcanoes clusters are a) Gamma and Beta seamounts, b) Alfa known as the Easter-Salas y Gómez Seamount Chain Seamounts and Robinson Crusoe Island, c) Duke, (e.g., Kingsley & Schilling, 1998; Simons et al., 2002) Cinque Ports and Dresden seamounts along with and Juan Fernández Ridge (Rodrigo et al., 2014). Alejandro Selkirk Island, and d) Friday and Domingo 2667 Latin American Journal of Aquatic Research seamounts. The superposition of the magnetic pattern ocean. The south Pacific subtropical gyre, where Easter of the western and eastern Juan Fernández Ridge and Salas y Gómez islands are located, has the lowest segments, which showed no correlation with concentrations of pigments and dissolved organic bathymetry, suggests that the faults/fractures of the matter in the world, making them the clearest ocean Nazca Plate played a role in the ridge’s formation. waters on the planet. Von Dassow & Collado-Fabri Although geological evidence supports the hypothesis (2014) reviewed key aspects of the plankton ecosystem of a fixed mantle plume for the origin of Juan and biogeochemical functions relevant to the Fernández Ridge. Rodrigo & Lara (2014) suggest that understanding of marine environments around Easter tectonic processes play a role, fueling the global and Salas y Gómez islands. The scarce information controversy about these competing processes. available (only 10 biological oceanographic expedi- Islands and seamounts have an important influence tions have entered this zone in 105 years, 1905-2010), on oceanographic patterns. The interaction between the suggests that plankton production is limited by a lack physical forcings (e.g., wind and currents) and the of dissolved inorganic fixed nitrogen, not phosphorous seamount/island topography fosters the formation of (Von Dassow & Collado-Fabri, 2014). The availability meso and submesoescale eddies, which promotes the of phosphates allows for nitrogen fixation, unless injection of macro and micronutrients into the euphotic another necessary element, such as iron, is limiting. zone stimulating biological productivity (Sangrà et al., Short-term experiments have suggested iron is not 2007; Hasegawa et al., 2009; Andrade et al., 2014a, limiting, yet iron still likely limits nitrogen fixation, and 2014b, 2014c). In the chain of seamounts and islands thus production, at longer time scales, as the presence associated with the Easter Submarine Alignment and of nitrogen-fixers is exceptionally low compared with the Juan Fernández Ridge, significant increases in Chl- that of other ocean gyres. Although diatoms known to a have been observed, the variability of which is contain nitrogen-fixing cyanobacteria (Rhizosolenia strongly influenced by the presence of meso and and Hemiaulus) appear to be well represented in the submesoscale eddies (Andrade et al., 2014a, 2014c). waters near Easter and Salas y Gómez islands, a diverse Surface and subsurface mesoscale eddies formed along group of heterotrophic, nitrogen-fixing bacteria or the continental coast travel west at speeds on the order photoheterotrophic cyanobacteria may dominate of 2 km d-1 (Hormazábal et al., 2013; Andrade et al., nitrogen fixation in the south Pacific subtropical gyre 2014a). Depending on the disapation methods, some of (Von Dassow & Collado-Fabbri, 2014). The prevalence these eddies may reach Easter Island after ~5 years of these nitrogen-fixing organisms could explain the while others may reach Robinson Crusoe Island after region’s lack of response to iron injection, given their ~8 months (Andrade et al., 2014a, 2014b). The surface functional differences from autotrophic fixers. Despite and subsurface anticyclonic eddies that interact with the the low rate of nitrogen fixation, plankton communities Juan Fernández Archipelago are formed primarily are maintained in the euphotic zone (Von Dassow & within the coastal transition zone between 33° and 39°S Collado-Fabbri, 2014). (Andrade et al., 2014a). The transport associated with The south Pacific sub tropical gyre represents a these eddies could have deep implications for the center of high biodiversity for picoplankton, as well as connectivity of biological communities between heterotrophic organisms such as tinntinids, siphono- islands and between island and mainland areas. phores, and possibly amphipods, although data for key On a smaller scale, Andrade et al., (2014b, 2014c) zooplankton, such as copepods, are lacking. Bacterio- show that the observed formation of submesoscale plankton and small detritus particulates account for up eddies around Eastern Island and the Juan Fernández to 83% of the organic carbon and small unicellular Archipelago could be associated with a strong incident organisms, picoplankton (<3 µm), dominate the flow produced in the contact area between mesoscale plankton in this region (Von Dassow & Collado-Fabbri, eddies and islands. The submesoscale structures have 2014). In the waters near Easter and Salas y Gómez similar sizes to the islands and the Chl-a concentrations islands picophytoplankton represents only 3% of the are several times higher than in adjacent oceanic waters organisms present on average, while the green (Andrade et al., 2014b, 2014c). The formation of these cyanobacteria Prochlorococcus

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