Ecosystems DOI: 10.1007/s10021-016-0078-8 Ó 2016 Springer Science+Business Media New York Ecosystem Oceanography of Seabird Hotspots: Environmental Determinants and Relationship with Antarctic Krill Within an Important Fishing Ground Jarrod A. Santora,1* Richard R. Veit,2,3 Christian S. Reiss,4 Isaac D. Schroeder,5 and Marc Mangel1,6 1Department of Applied Mathematics and Statistics, Center for Stock Assessment Research, University of California Santa Cruz, 110 Shaffer Road, Santa Cruz, California 95060, USA; 2Biology Department, CSI/CUNY, 2800 Victory Boulevard, Staten Island 10314, New York, USA; 3CUNY Graduate Center, 565 Fifth Ave., New York, New York 10016, USA; 4Antarctic Ecosystem Research Division, NOAA Southwest Fisheries Science Center, La Jolla, California, USA; 5Physical and Biological Sciences, University of California Santa Cruz, 110 Shaffer Road, Santa Cruz, California 95060, USA; 6Department of Biology, University of Bergen, Bergen 9020, Norway ABSTRACT The discipline of ecosystem oceanography provides a eddy kinetic energy. The spatial organization, chan- framework for assessing the role of mesoscale physical ges in intensity, and distribution shifts of seabird processes on the formation and occurrence of bio- hotspots indicate different environmental drivers logical hotspots. We used shipboard surveys over nine within coastal and oceanic domains and reflect the years to investigate environmental determinants of seasonal variability of the ecosystem. Our results seabird hotspots near the Antarctic Peninsula, a re- indicate at least eight mesoscale hotspot zones that gion experiencing rapid climate change and an represent ecologically important areas where signifi- expanding krill fishery. We hypothesize that seabird cant krill and predator biomass may be concentrated. hotspots are structured by mesoscale ocean condi- Our ecosystem assessment of seabird hotspots iden- tions that reflect differences in prey distribution tified critical foraging habitat and provided reference within oceanic and coastal waters. We used general- points to benefit research on estimating their trophic ized additive models to quantify functional relation- impacts on Antarctic ecosystems and potential effects ships of seabird hotspots with krill biomass, and a suite from the krill fishery. Our approach is generally of remotely sensed environmental variables, such as applicable to other pelagic ecosystems that are struc- tured by hydrographic fronts and eddies, and con- taining schooling forage species shared by multiple wide-ranging predators. Furthermore, identification Received 18 May 2016; accepted 8 September 2016; of biological hotspots is useful for the designation of Electronic supplementary material: The online version of this article marine protected areas most critical to potentially (doi:10.1007/s10021-016-0078-8) contains supplementary material, endangered wildlife and fisheries resources. which is available to authorized users. Author Contributions Jarrod A. Santora conceived of and designed the study, performed the research, analyzed data, and wrote the paper; Key words: albatross; conservation; ecosystem Richard R. Veit, Christian S. Reiss, and Marc Mangel helped write the assessment; eddy kinetic energy; krill fishery; for- paper; Isaac D. Schroeder contributed new methods and models, and aging ecology; marine protected area; mesoscale; helped write the paper. *Corresponding author; e-mail: [email protected] petrel; spatial ecology; storm petrel. J. A. Santora and others INTRODUCTION heterogeneity of marine ecosystems and patchiness of their prey, seabirds frequently form dense The discipline of ecosystem oceanography focuses aggregations associated with hydrographic fronts on relating populations of marine species and their and eddies because these features tend to concen- interactions to environmental fluctuations to pre- trate prey (Hunt 1991; Bost and others 2009; Scales dict ecosystem responses to climate change and and others 2014). The spatial distribution of seabird exploitation (Cury and others 2008). Pelagic hotspots (areas of consistently high local abun- ecosystems are vast, highly dynamic systems, and dance) may provide information on the spatial experimental design is often difficult or impossible, structure and function of marine ecosystems, as but this challenge is overcome through integration well as location of critical foraging grounds, prey of large, multi-interdisciplinary abiotic and biotic availability, and rates of local prey consumption datasets, combined with numerical modeling to (Piatt and others 2006; Lascelles and others 2012; assess ecosystem dynamics. In particular, ecosys- Santora and Veit 2013). Seabirds are especially tem oceanography studies often examine the role susceptible to fisheries interactions (for example, of mesoscale ocean dynamics on biological pro- by-catch and entanglement; Weimerskirch and cesses, such as eddies (that is, circular movement of others 2000; Robertson and others 2014) and pol- water), occurring on spatial scales ranging from 10 lution (for example, oil spills), making identifica- to 1000 km and temporally, from 10 to 30 days tion of their hotspots a priority for their (Cury and others 2008), and their effect on the conservation in the Southern Ocean (Consta- concentration of nutrients, primary production, ble and others 2000; Hooker and others 2011; and species distributions and interactions (Bakun Harris and others 2015). Furthermore, commercial 1996). The occurrence and spatial intensity of harvest of krill is concentrated near the Antarctic biological hotspots, areas of increased species Peninsula and increased over time (Nicol and oth- abundance, diversity, and/or trophic transfer (Sy- ers 2012), warranting concern about depletion of deman and others 2006), are thought to be linked krill within seabird hotspots. to mesoscale ocean conditions, but functional Petrels, storm petrels, and albatrosses (Procel- relationships among biophysical conditions gener- lariid seabirds) are long-lived (for example, 20–70 ating hotspots are not well known (Suryan and years+) and highly mobile predators, capable of others 2012; Hazen and others 2013; Santora and covering vast oceanic regions during foraging trips others 2014). Through an integration of satellite and post-breeding migrations (Schreiber and Bur- remote sensing of ocean conditions, acoustic sur- ger 2001). They have diverse foraging strategies veys for Antarctic krill (Euphausia superba; hereafter with broad diets and are surface feeders, consum- krill) biomass, and seabird foraging distributions, ing a variety of euphausiids, meso- and ben- we investigate the mesoscale environmental dri- thopelagic fishes, squids, and various vers of seabird hotspots within the Northern microzooplankton (for example, copepods; Croxall Antarctic Peninsula (NAP) large marine ecosystem. and Prince 1980; Ainley and others 1992; Croxall This ecosystem is experiencing rapid climate and others 1997; Cherel and others 2002). Due to change (Meredith and King 2005; Murphy and their collective biomass and demand for krill, pro- others 2013), increasing human presence (for cellariid seabirds may play a major role in the example, tourism; Tin and others 2008), and an trophodynamics of Antarctic marine ecosystems, expanding commercial krill fishery (Nicol and yet their consumption of krill is poorly quantified others 2012). Moreover, there is growing concern compared to penguins, seals, and whales (Croxall that climate change and overexploitation of krill on and others 1984, 1997; Trivelpiece and others regional scales may impact the resilience of this 2011; Watters and others 2013). We used stan- marine ecosystem (Trivelpiece and others 2011; dardized shipboard surveys to investigate the Murphy and others 2013; Watters and others ecosystem oceanography of hotspots for six seabird 2013), and integrated ecosystem assessments of species. We chose two medium-sized fulmarine biological hotspots will benefit ecosystem-based petrels [cape petrel (Daption capense), southern ful- fishery management. mar (Fulmarus glacialoides)], two storm petrels Living at the interface between sea and air, sea- [Wilson’s storm petrel (Oceanites oceanicus), black- birds are excellent indicators of ocean climate bellied storm petrel (Fregetta tropica)], and two variability, availability of epipelagic mid-trophic albatrosses [black-browed albatross (Thalassarche level food resources, and marine ecosystem melanophrys) and grey-headed albatross (Thalas- dynamics and climate variability (Cairns 1988; Reid sarche chrysostoma)]. The fulmarine petrels and and others 2005; Cury and others 2011). Due to the Ecosystem Oceanography of Seabird Hotspots storm petrels breed in the NAP region, while both assess the distribution and abundance of krill and top albatrosses breed outside of the NAP on nearby is- predators. The survey area was partitioned by the lands north of the polar frontal zone (for example, South Shetland Islands, with oceanic waters to the Diego Ramirez Archipelago; Robertson and others north and coastal waters to the south towards the 2007). All these species are primarily krill eaters, Antarctic Peninsula. Circulation in the study area but they do take a variety of fish and zooplankton reflects inputs from the Antarctic Circumpolar Cur- (Croxall and Prince 1980; Ainley and others 1992). rent (ACC), outflow from the Weddell Sea Gyre, and These species represent a range of body sizes and inflow from coastal upstream regions along the flying and feeding strategies (Croxall