Simulating larval Antarctic krill growth and condition factor during fall and winter in response to environmental variability

Abstract

The first winter in the life cycle of Antarctic krill Euphausia superba is a critical period in which larval survival and recruitment to the adult population are highly sensitive to environmental conditions, yet little is known about larval physiological dynamics during this period. An individual-based model was developed to investigate patterns of larval krill growth and condition factor in response to environmental variability during fall and winter, west of the Antarctic Peninsula. Field and experimental observations from Southern Ocean Global Ocean Ecosystems Dynamics cruises in 2001 and 2002 and the Palmer Long-Term Ecological Research program were used to parameterize the model. Growth was modeled by partitioning total body carbon between length and condition factor. Total body carbon was simulated with empirical temperature-dependent rates of ingestion of phytoplankton and respiration, and ingestion of algae grown on a surface to simulate sea ice algae. Light-driven diel vertical migration modulated ingestion of phytoplankton and sea ice algae as a function of latitude, season and sea ice cover. Simulations highlighted 3 environmental processes that controlled food availability, and consequently, physiological condition of krill: the fall phytoplankton decline, sea ice advance and development of sea ice microbial communities, and the late winter increase in sea ice microbial community biomass. Fall phytoplankton dynamics were identified as a major driver of the physiological condition of larval krill throughout this critical period. The model presents a mechanism that links larval krill survival and recruitment to fall and winter variability in phytoplankton and sea ice dynamics along the western Antarctic Peninsula.KEY WORDS: Euphausia superba · Larval Antarctic krill · Condition factor · Growth · Individualbased model · Fall and winter · Critical period Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 452: 27-43, 2012 28 phytoplankton abundance (Meyer & Oettl 2005). Young-of-the-year krill must feed more or less continuously to meet respiratory demands. The first winter, when survival is dependent on larval access to food (Ross & Quetin 1991), is thus a critical period in the life cycle of Antarctic krill.During this period primary production in the water column is limited by decreasing light availability. The formation of seasonal sea ice further decreases light penetration. This results in very low concentrations in the water column of phytoplankton upon which larval krill graze. However, the developing sea ice scavenges phytoplankton and other particles from the water column, so that algae, microzooplankton and nutrients are concentrated in the newly formed sea ice (Garrison et al. 1983(Garrison et al. , 1989). The concentration of algae and other organisms that comprise the sea ice microbial communities (SIMCOs) represents an important seasonal food source for larval krill (Daly & Macaulay 1991, Schmidt et al. 2006. While larval krill feed...

The winter pack-ice zone provides a sheltered but food-poor habitat for larval Antarctic krill

“…Our findings support the view that seasons other than winter are the key to understanding krill recruitment. Combining our findings with previous model results 11,12,38 , we propose the following conceptual model. An early spawning in spring and favourable feeding conditions during summer enables larvae to develop to an advanced stage.…”

“…Previous modelling studies focusing on the interaction between sea ice and the variability in krill biomass have demonstrated that autumn 11 and late winter-spring 38 seem to be the bottlenecks for recruitment success in krill. Recently, a bioenergetic model demonstrated that the observed five to six year oscillation cycle between high and low krill biomass in the western Antarctic Peninsula depends on the food competition between larvae and adults in autumn 12 .…”

“…Along the Antarctic Peninsula, adult krill have a five to six year population cycle with oscillations in biomass exceeding an order of magnitude 9 . According to bioenergetics models, part of the variability is due to interannual variation in reproductive output 11 as well as autumn blooms that may govern the possible overwinter survival rate of larvae 11,12 . In the Bransfield Strait, three krill winter surveys have shown that krill abundance is an order of magnitude higher than in summer, regardless of concurrent sea-ice conditions 10 .…”

Trends, cycles, interannual variability for three pelagic species west of the Antarctic Peninsula 1993-2008

“…Ecosystem structure and function are more likely to be impacted by changes in seasonality than absolute sea ice cover (Massom & Stammerjohn 2010), e.g. earlier water column stratification with alterations in the timing of iceedge or water column phytoplankton blooms (Arrigo et al 2008, Venables et al 2013 and/or an earlier loss or change in location of habitat for species dependent on ice as a platform or a food resource (Chapman et al 2011, Lowe et al 2012.…”

Advances in Physical, Biological, and Coupled Ocean Models During the US GLOBEC Program

“…Starvation was most important in first-feeding larvae. Similar bioenergetics-based modeling has been done for other pelagic species, ranging from juvenile salmon to copepods (Miller et al, 1998;Batchelder et al, 2002b;Neuheimer et al, 2009;Ji et al, 2009;Stegert et al, 2012), euphausiids (Dorman et al, 2011;Lowe et al, 2012;Lindsey, 2014), and larval cod and/or haddock (references above; Leising and Franks, 1999). Many other particular cases from the GLOBEC program could be described.…”