Antarctic krill recruitment in the south-west Atlantic sector of the Southern Ocean

Abstract

Antarctic krill are a key component of the Southern Ocean ecosystem and support a variety of predators as well as an expanding commercial fishery. Yet, despite the ecological and economic importance of krill, crucial aspects of their recruitment are not understood. We need greater understanding of these processes in order to predict and model their population dynamics in the light of growing anthropogenic pressures. This thesis identifies three knowledge gaps in krill reproduction and, through mapping, modelling and laboratory experimentation, provides new insights into these research areas. The area of study is the south-west Atlantic sector as it contains the highest densities of krill, key krill spawning grounds and has supported the entire krill fishery since the mid 2000’s. By generating distribution maps of six life stages of Antarctic krill, I identified key hotspots of egg production and nursery areas for larval krill along the Southern Scotia Arc. These maps showed that, although adult krill are widely distributed, the location of eggs, nauplii and metanauplii are mainly restricted to shelf and shelf-slope regions, partitioned spatially from the oceanic distributions of calyptopes and furcilia. By conducting a series of laboratory experiments, I identified the point at which temperature induces hatch failure and nauplii malformations in krill embryos. Hatching success decreased markedly above 3.0 °C, and the percentage of malformed nauplii reached 50 % at 5.0 °C. Furthermore, hatching success was variable and low (mean 27 %) between females. To further understand the whereabouts of spawning at the Antarctic Peninsula, and to test the hypothesis that krill migrate off-shelf to spawn, I conducted a seasonal analysis of adult krill size classes in relation to environmental variables. Contrary to the current paradigm, I found the adult krill population does not migrate on mass to off-shelf waters (>1000 m depth) to spawn their eggs. Instead all length categories of adult krill appear in reliably high concentrations ~ 75 km before the shelf break throughout the spawning season, where temperatures are lower and food availability is higher, potentially increasing growth and spawning potential. This information provides a more holistic view of krill spawning, reproduction and recruitment within the south-west Atlantic sector and provides policy makers with better information on which to base future krill fishery management decisions.

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Identifiers

ORCID for Frances Anne Perry: orcid.org/0000-0003-1560-1506

ORCID for Catherine Lucas: orcid.org/0000-0002-5929-7481

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