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Abstract

Marine top predators play a fundamental role in maintaining the structure and functioning
of healthy marine ecosystems. In the last decades the development of bio-logging (i.e.
deployment of autonomous recording tags on free-living animals) has radically changed
the study of top predators and their interactions with their environment. Combinations
of sensors measuring position (Argos and GPS), environmental properties (water
temperature, light) and proxies for foraging behavior (accelerometers) have enabled relating
migrations of large fish, marine mammals, sea turtles and seabirds to basin scale
patterns of ocean currents, temperature, and productivity. However, what influences
marine predators’ movement at smaller spatial and temporal scales, such as the ones
they experience during their foraging trips, is still largely unknown. This project analyses
the interaction between marine top predators (elephant seals and macaroni penguins)
and sub-mesoscale (few days-months, 10-100 km) ocean dynamics. This is achieved by
combining in-situ observations, bio-logging data, remote-sensing, ecological modelling
and a Lagrangian approach (i.e. based on the tracking of water parcels). The study
is conducted in the sub-Antarctic region around the Kerguelen Plateau (Indian Sector
of the Southern Ocean). This sector of the Southern Ocean provides a useful natural
laboratory for this work in that (i) several marine predators species have large colonies
on the island, (ii) the area is located in a highly dynamical ocean regime dominated by
the Antarctic Circumpolar Current, (iii) the trophic web in the area is relatively simple
and (iv) production is dominated by iron limitation, making it possible to disentangle
physical and ecological effects.
First, I examine whether the mechanical effect of mesoscale currents on the trajectories
of large fast-swimming marine predators is significant. I find that, in spite of what
is often assumed, foraging marine predators are transported by the horizontal ocean
dynamics for a non-negligible part of their foraging trip, exhibiting a ‘quasi-planktonic’
behaviour. This phenomenon is more likely to occur on sub-meso and mesoscale fronts
that are favourable for animal foraging.
Secondly, I focus on how mesoscale turbulence affects the distribution of ocean productivity
by combining a Lagrangian approach with previous biogeochemical and ecological
knowledge of the region. A novel result is that waters that have been recently (∼ 20
days) in contact with the Kerguelen plateau (which is assumed to be the major source
of iron of the region) are more likely to manifest a system dominated by large diatoms.
I parametrise and spatialise a simple model describing phytoplankton community structure
in the area to predict which dynamical niches are more favourable for high concentrations
of diatoms. This result is important because qualitative assessment of the
regional food web shows that the growth of fish larvae and crustaceans (that occupy a large fraction of top predators’ diet) benefit from phytoplankton communities dominated
by large diatoms. The findings of this project support and complement previous
studies about the role of mesoscale dynamics on marine life and open challenging questions
about an “end-to-end” approach to bio-logging observations and ecosystem-based
conservation management.

Item Type:	Thesis - PhD
Authors/Creators:	Della Penna, A
Keywords:	Mesoscale ocean dynamics, Southern Ocean, Kerguelen, Physics-ecology interactions, Open ocean, Ecology of the southern ocean
Copyright Information:	Copyright 2016 the author
Additional Information:	Part II, chapter 1 appears to be the equivalent of a post-print version of an article finally published with a Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/) as: Della Penna, A., De Monte, S., Kestenare, E., Guinet, C., d’Ovidio, F., 2015, Quasi-planktonic behavior of foraging top marine predators, Scientific reports, 5:18063, 1-10 Part II, chapter 2 appears to be the equivalent of a post-print version of an article finally published with a Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/) as: Bon, C., Della Penna, A., d’Ovidio, F., Arnould, J.Y.P., Poupart, T., Bost, C.-A., 2015, Influence of oceanographic structures on foraging strategies: Macaroni penguins at Crozet Islands, Movement ecology, 3;32, 1-11 Appendix A appears to be the equivalent of a post-print version of an article finally published with a Creative Commons Attribution 3.0 Unported (CC BY 3.0) License (https://creativecommons.org/licenses/by/3.0/) as: d’Ovidio, F., Della Penna, A., Trull, T. W., Nencioli, F., Pujol, M.-I., Rio, M.-H., Park,Y.-H., Cotte, C., Zhou, M., Blain, S., 2015, The biogeochemical structuring role of horizontal stirring: Lagrangian perspectives on iron delivery downstream of the Kerguelen Plateau, Biogeosciences, 12, 5567-5581 Appendix B appears to be the equivalent of a post-print version of an article finally published with a Creative Commons Attribution 3.0 Unported (CC BY 3.0) License (https://creativecommons.org/licenses/by/3.0/) as: Grenier, M., Della Penna, A., Trull, T.W., 2015, Autonomous profiling float observations of the high-biomass plume downstream of the Kerguelen Plateau in the Southern Ocean, Biogeosciences, 12, 2707-2735 Appendix C has been submitted to Deep sea research II as: Lagrangian analysis of multi-satellite data in support of open ocean Marine Protected Area design by A. Della Penna, P. Koubbi, C. Cotte’, C. Bon, C-A. Bost and F. d’Ovidio.
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