Persistence of hotspots and variability of seabird species richness and abundance in the southern California Current

Jarrod A Santora,William J Sydeman

doi:10.1890/es14-00434.1

Jarrod A Santora, William J Sydeman

Open Access

https://doi.org/10.1890/es14-00434.1

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Abstract

Aggregations of seabirds at sea may provide information on centers of enhanced trophic interactions and concentrating mechanisms, however, to date most studies lack quantification of persistence, a key hotspot characteristic. Persistence statistics may reduce uncertainty about seabird habitat use, improve understanding of the spatio‐temporal scales of pelagic food web dynamics, and inform conservation planning. Using 26 years (1987–2012, 47 surveys) of shipboard surveys from a 300K km2 study area within the southern California Current Ecosystem, we conduct a spatial assessment of the inter‐annual and seasonal dynamics of the persistence of seabird hotspots and identify recurring sites of elevated seabird species richness and abundance. Previous studies document declines in abundance, but were based on broad spatial standardizations to assess where declines may have occurred. Here, we refine the hypothesis that seabird populations have declined off southern California by focusing on persistently used habitats in nearshore or offshore domains. We demonstrate that spatio‐temporal variability of seabird distribution and abundance is characterized by anomalous events embedded within trends. In addition to identifying the locations of persistence of seabird aggregations, we found significant declines in species richness and the density of sooty shearwater (Puffinus griseus) and Leach's storm petrel (Oceanodroma leucorhoa); in contrast, black‐footed albatross (Phoebastria nigripes) abundance appear to be increasing. This assessment provides a spatially‐explicit framework for future evaluations of biophysical drivers of seabird hotspots and their associations and impacts on forage fish and zooplankton populations.

Highlights

Seabird population and community dynamics respond to local to large spatio-temporal scales in marine ecosystems, such that their distribution and abundance at sea can serve as indicators of marine ecosystem variability (Veit et al 1997, Hyrenbach and Veit 2003, Ainley et al 2009, Piatt et al 2007, Sydeman et al 2009, 2015)
The California Cooperative Oceanic Fisheries Investigations (CalCOFI) program has quantified the influence of climate states on marine ecosystem functions (McGowan et al 2003, Di Lorenzo et al 2008), as well as long-term trends in physical oceanographic features (Bograd and Lynn, 2003, Bograd et al 2008) and populations of zooplankton (Roemmich and McGowan 1995, McGowan et al.1998), larval fishes (Hsieh et al 2009, Koslow et al 2011), and seabirds (Veit et al 1997, Sydeman et al 2015)
Study area The CalCOFI sampling of the Southern California Bight includes 6 parallel survey lines that extend from the coast out to 470– 700 km offshore (Fig. 1)

Summary

Introduction

Seabird population and community dynamics respond to local to large spatio-temporal scales in marine ecosystems (e.g., fronts to ocean basins and days to decades), such that their distribution and abundance at sea can serve as indicators of marine ecosystem variability (Veit et al 1997, Hyrenbach and Veit 2003, Ainley et al 2009, Piatt et al 2007, Sydeman et al 2009, 2015). The CalCOFI program has quantified the influence of climate states on marine ecosystem functions (McGowan et al 2003, Di Lorenzo et al 2008), as well as long-term trends in physical oceanographic features (Bograd and Lynn, 2003, Bograd et al 2008) and populations of zooplankton (Roemmich and McGowan 1995, McGowan et al.1998), larval fishes (Hsieh et al 2009, Koslow et al 2011), and seabirds (Veit et al 1997, Sydeman et al 2015). An assessment of the spatio-temporal variability of seabird population and community dynamics will facilitate future spatial integration of the important CalCOFI data set (Fig. 1)

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