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University of Southampton Research Repository University of Southampton Research Repository Copyright © and Moral Rights for this thesis and, where applicable, any accompanying data are retained by the author and/or other copyright owners. A copy can be downloaded for personal non-commercial research or study, with out prior permission or charge. This thesis and the accompanying data cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder/s. The content of the thesis and accompanying research data (where applicable) must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holder/s. When referring to this thesis and any accompanying data, full bibliographic details must be given, e.g. Thesis: Author (Year of Submission) "Full thesis title", University of Southampton, name of the University Faculty or School or Department, PhD Thesis, pagination. Data: Author (Year) Title. URI [dataset] UNIVERSITY OF SOUTHAMPTON Faculty of Environmental and Life Science Ocean and Earth Science Antarctic krill recruitment in the south-west Atlantic sector of the Southern Ocean by Frances Anne Perry BSc (Bangor University) ORCID ID https://orcid.org/0000-0003-1560-1506 Thesis for the degree of Doctor of Philosophy November 2020 UNIVERSITY OF SOUTHAMPTON Abstract Faculty of Environmental and Life Science Ocean and Earth Science Thesis for the degree of Doctor of Philosophy ANTARCTIC KRILL RECRUITMENT IN THE SOUTH-WEST ATLANTIC SECTOR OF THE SOUTHERN OCEAN by Frances Anne Perry 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. Table of Contents Table of Contents Table of Contents ............................................................................................................. i Table of Tables ................................................................................................................ v Table of Figures ............................................................................................................. vii Research Thesis: Declaration of Authorship.................................................................... ix Acknowledgements ........................................................................................................ xi Definitions and Abbreviations ....................................................................................... xv Chapter 1 Introduction ................................................................................................. 1 Introduction.......................................................................................................... 1 Antarctic krill and the Southern Ocean ecosystem ................................................. 1 Krill fisheries management, climate change and recruitment ................................. 4 Krill distribution and the importance of the south-west Atlantic sector .................. 6 Female maturation, spawning and embryonic success ........................................... 8 Behavioural and environmental controls on krill distribution ............................... 10 Aims and layout of my thesis ............................................................................... 12 Chapter 2 Habitat partitioning in Antarctic krill: spawning hotspots and nursery areas 15 2.1 Abstract .............................................................................................................. 15 2.2 Introduction........................................................................................................ 16 2.3 Methods ............................................................................................................. 18 2.3.1 Overview of the krill databases used for this study ...................................... 18 2.3.2 KRILLBASE-abundance database .................................................................. 19 2.3.3 KRILLBASE-length-frequency database ......................................................... 21 2.3.4 Larval database ........................................................................................... 21 2.3.5 Producing grid maps of krill life stage densities ............................................ 22 2.3.6 Selection of environmental data .................................................................. 22 2.3.7 Environmental habitat analysis .................................................................... 23 2.4 Results ................................................................................................................ 23 2.4.1 Overview of sampling coverage and life stage distribution ........................... 23 2.4.2 Distributions and habitat analysis ................................................................ 24 i Table of Contents 2.4.3 Adults..........................................................................................................30 2.4.4 Eggs and nauplii...........................................................................................30 2.4.5 Calyptopes and furcilia ................................................................................30 2.4.6 Juveniles .....................................................................................................30 2.5 Discussion ...........................................................................................................31 2.5.1 How well do composite maps represent krill life stage distributions? ...........31 2.5.2 Are there spawning hotspots and larval nursery areas? ................................32 2.5.3 Partitioning of habitat by different life stages ..............................................35 2.5.4 Wider implications ......................................................................................36 Chapter 3 Temperature-induced hatch failure and nauplii malformation in Antarctic krill .............................................................................................................39 3.1 Abstract ..............................................................................................................39 3.2 Introduction ........................................................................................................40 3.3 Methods .............................................................................................................41 3.3.1 Overview .....................................................................................................41 3.3.2 Embryos from our field experiments ............................................................42 3.3.2.1 Sampling method and collection of embryos .....................................42 3.3.2.2 Experimental method ........................................................................43 3.3.2.3 Laboratory analysis ...........................................................................45 3.3.3 Embryos from the laboratory experiments ...................................................45 3.3.3.1 Sampling method and collection of embryos .....................................45 3.3.3.2 Experimental method ........................................................................45
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