Environmental Drivers of Seabird At-Sea Distribution in the Eastern South Pacific Ocean: Assemblage Composition Across a Longitudinal Productivity Gradient

Abstract

Seabird distributions are determined by physical and biological factors operating at variable scales and levels of ecological organization. Accordingly, changes in the composition of the marine avifauna often correspond to large-scale (macro-mega) shifts in water mass properties. Yet, few studies have addressed biogeographical patterns across multiple current systems, spanning from highly productive to oligotrophic waters. In this study, we characterize the at-sea assemblages of nesting seabirds across the Eastern South Pacific Ocean (ESPO), a vast region spanning from the Humboldt Current to the South Pacific Gyre. Employing multivariate techniques, we first identify four distinct species assemblages and then relate their distributions to the underlying environmental conditions. Our results show that Julian day, depth, sea surface temperature (SST), sea surface salinity (SSS), and chlorophyll-α concentration are the most important factors explaining the distribution patterns of these assemblages. Moreover, environmental conditions also explain overall seabird abundance and species richness, two community-level characteristics indicative of ocean productivity. Seabird abundance was best explained by four variables, associated with onshore-offshore gradients (distance to the coast, ocean depth), and the influence of coastal upwelling (mean mixed layer depth, SSS). Richness was best explained by seasonality (Julian day) and by the presence of water mass boundaries (SST coefficient of variation). Our findings underscore the importance of environmental factors structuring the distribution and biogeography of seabirds across gradients of ocean productivity and water mass properties. Understanding the environmental drivers of seabird abundance and richness in the ESPO will inform the prioritization and design of effective marine conservation measures in this poorly studied region.

The role of island physiography and oceanographic factors in shaping species richness and turnover of nesting seabird assemblages on islands across the south‐eastern Pacific

“…Studies have pointed out that oceanographic processes that sustain increased secondary productivity are not the main drivers of seabird species richness at sea, although they have a significant impact on seabird abundance (Jenkins & Van Houtan, 2016;Serratosa et al, 2020).…”

Progress, opportunities and challenges for marine conservation in the Pacific Islands

“…(a) Juan Fernández lobster; (b) Rapa Nui spearfishing; (c) traditional basket trap in Ofu, American Samoa; and (d) cast netting in Moloka'i, Hawai'i. (Photos: (a) A. Muñoz, (b) E. Sala, (c) & (d) A. Friedlander)ecosystems(Easton et al, 2017;Easton et al, 2019;Luna, Varela, Brokordt, & Luna-Jorquera, 2018;Morales et al, 2019;Serratosa et al, 2020; Thiel et al, 2018).The Juan Fernández and Desventuradas islands are distinct ecoregions within the temperate South American Realm. 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 (Friedlander et al, 2016).…”

Potential climate-driven changes to seabird demography: implications for assessments of marine renewable energy development

“…However, the results did include strong negative effects of terrestrial temperature on breeding success in this species (Table 3), which may be linked to heat stress in chicks as hypothesized in previous studies (Smith & Gaston 2012, Michielsen et al 2019. SLM also played a role in breeding success declines in 5 species (Table 3), a variable that has previously been linked to seabird distribution and abundance in other regions, most likely via bottomup influences on prey (Serratosa et al 2020). We detected a negative link between breeding success and SLM in 4 species (black-legged kittiwake, great black-backed gull, northern gannet and razorbill) and a positive link in just one species (Atlantic puffin) (Table 3).…”