Ecological response of marine predators to environmental heterogeneity and spatio-temporal variability in resource availability

Abstract

[eng] Seabirds have evolved within an open and dynamic environment, the ocean. As meso-top predators, seabirds are greatly influenced by the oceanographic conditions driving marine productivity, and therefore, distribution of their prey. Consequently, seabirds’ behaviour and, ultimately, life-history traits are greatly influenced, by the ever-changing oceanographic conditions. However, oceanographic conditions are currently changing at ever-increasing rates due to global warming and human harvest impacting marine ecosystems. Thus, seabirds have become particularly vulnerable to these changes. Accordingly, in this thesis, we investigated the ecological responses of seabirds, in terms of foraging and breeding performance, to the spatio-temporal variability of environmental conditions imposed by oceans and exacerbated by climate and human stressors. In particular, we (i) identified the climate and human stressors impacting the world’s ocean, (ii) investigated the actual scale at which seabirds interact with their environment, (iii) assessed how seabirds respond to oceanographic variability by changing their foraging and reproductive strategies and (iv) proposed an integrative tool for the design of marine reserves protecting seabirds and their environment. The objectives of this thesis were accomplished through advanced procedures in the fields of satellite remote sensing and animal tracking. Our results confirmed the unprecedented changes experienced by oceans in the last decades. However, we were able to provide deepest insights on the uneven distribution of climate and human driven environmental changes. When investigating the link between such environmental variability and seabirds’ behaviour, we found that dynamic processes as ocean currents were key factors determining the scale at which seabirds interact with their environment. Environmental features driving the spatiotemporal distribution of prey (e.g. sea surface temperature, chlorophyll-a, sea fronts and persistent areas of productivity) along with industrial fisheries played a fundamental role in determining the foraging distribution of seabirds. However, seabirds’ foraging strategies were largely constrained by limitations imposed by their central-place foraging behaviour and by dynamic factors such as prevalent winds, which influenced individual decision- making in heading directions when foraging. Intra and interspecific competition for resources also modulated foraging distributions, avoiding conspecifics or segregating foraging areas among sympatric species in appropriate stages. In general, we have provided a complete picture of environmental processes affecting seabirds. We argue that this information would be extremely useful for designing suitable management and conservation strategies. Thus, we finally proposed an adaptive framework for delimitation of more meaningful marine reserves that maximises conservation targets for seabirds, while accounting for human activities, environmental and biological factors largely driven seabird performance and, remarkably, the dynamism inherent to marine systems.