Euphausiids in the diet of a North Pacific seabird: annual and seasonal variation and the role of ocean climate

Abstract

Across the California Current System (CCS), euphausiid crustaceans are important prey for many vertebrate predators, including the seabird Cassin's auklet Ptychoramphus aleuticus. However, the effects of ocean climate on euphausiid biology, and their consequences for predators, remain poorly understood. Over a 13 yr period (1996 to 2008), Euphausia pacifica, Thysanoessa spinifera and T. inspinata cumulatively averaged about 35% of the annual biomass in the nestling diets of auklets at Triangle Island, but there was marked inter-annual variation. Whereas ocean climate had little influence on the amounts of E. pacifica or T. inspinata delivered, diets included more T. spinifera if spring sea-surface temperatures in the previous year had been lower. Cold conditions might facilitate the production of a strong annual cohort, thus increasing adult biomass in the following year. Within seasons, the amount of E. pacifica in diets declined with date, and the decline was consistent across both warm-and cold-water years. In contrast, diets were especially rich in both Thysanoessa spp. late in the provisioning period in warm-water years, when the harvest of Neocalanus cristatus declined dramatically due to a temporal mismatch between the auklet predator and this copepod prey. Both the annual nestling survival rate and the mean fledging masses of Cassin's auklets were tightly correlated to the amount of N. cristatus in their diets, and for fledging mass there was a further small, additive effect of increased amounts of T. inspinata. Results of the present study add new insight into effects of ocean climate on euphausiid biology in the northern CCS, and their potential consequences for population processes of an important euphausiid predator. KEY WORDS: Auklet · Diet · Euphausiids · Ocean climate · Prey-switching Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 390: [277][278][279][280][281][282][283][284][285][286][287][288][289] 2009 Tanasichuk 2002, Brinton & Townsend 2003, Croll et al. 2005, Suntsov & Brodeur 2008. Research has shown that the population biology of both of these euphausiids is influenced by ocean climate (Tanasichuk 1998a,b, Marinovic et al. 2002, Brinton & Townsend 2003, Dorman et al. 2005), but in a complex manner that remains poorly understood (Abraham & Sydeman 2004). In this marine system, studies on the breeding ecology of Cassin's auklet Ptychoramphus aleuticus, a regionally abundant zooplanktivorous seabird, have provided considerable insight (Ainley et al. 1996, Sydeman et al. 2001, Adams et al. 2004.At breeding colonies in the southern and central CCS, Euphausia pacifica and Thysanoessa spinifera are the primary prey fed to Cassin's auklet Ptychoramphus aleuticus nestlings. Over the course of the birds' spring and summer breeding season, the amount of adult E. pacifica in nestling diets tends to decrease, while the amount of juvenile and adult T. spinifera tends to increase (Adams et al. 2004, Abraham & Sydeman 2006. This dietary switch...

Intra-seasonal variation in zooplankton availability, chick diet and breeding performance of a high Arctic planktivorous seabird

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“…Studies on changes in diet of zooplanktivorous seabirds may be especially informative, because they feed on organisms that respond relatively quickly and predictably to environmental variations (Bertram et al 2001;Sydeman et al 2001;Hipfner 2009).…”

Regional and inter-annual trends in marine growth of juvenile salmon in coastal pelagic ecosystems of British Columbia, Canada

“…Regional-and annual-scale variation in the abundance, species composition, and trophic status of zooplankton has been found off the BC Coast (Mackas et al 2001 Island (Perry et al 1996) and BC (Brodeur et al 2007). In addition, food consumption of birds that have a prey field similar to juvenile salmon and nest on Triangle Island (northwest coast of Vancouver Island) and Frederick Island (northwest Haida Gwaii), varies inter-annually and regionally (Hedd et al 2002, Hipfner 2009). Together, these data suggest that salmon may experience regional and inter-annual differences in their prey field composition and abundance, and that this variation may drive differences in juvenile salmon growth.…”

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Trade-offs in prey quality and quantity revealed through the behavioral compensation of breeding seabirds

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