37We present the first objective quantitative assessment of the threats to all 359 species of seabirds, 38 identify the main challenges facing them, and outline priority actions for their conservation. We applied 39 the standardised Threats Classification Scheme developed for the IUCN Red List to objectively assess 40 threats to each species and analysed the data according to global IUCN threat status, taxonomic group, 41and primary foraging habitat (coastal or pelagic). The top three threats to seabirds in terms of number 42 of species affected and average impact are: invasive alien species, affecting 165 species across all the 43 most threatened groups; bycatch in fisheries, affecting fewer species (100) but with the greatest 44 average impact; and climate change/severe weather, affecting 96 species. In addition to impacting 86% 45 of globally threatened species, these three top threats also affect 81% of the species currently classified 46as Near Threatened or as Least Concern but declining. Reversing these three threats would benefit two-47 thirds of all species and c. 380 million individual seabirds (c. 45% of the total global seabird population). 48Most seabirds (c. 70%), especially globally threatened species, face multiple threats. For albatrosses, 49 petrels and penguins in particular (the three most threatened groups of seabirds), it is essential to 50 tackle both terrestrial and marine threats to reverse declines. As the negative effects of climate change 51 are harder to mitigate, it is vital to compensate by addressing other major threats that often affect the 52 same species, such as invasive alien species and bycatch, for which proven solutions exist. 53 54

Palabras Clave: captura accesoria, competencia por recursos, contaminación marina, degradación de hábitat, sobrepesca

Marine protected areas (MPAs) form the cornerstone of marine conservation. Identifying which factors contribute to their success or failure is crucial considering the international conservation targets for 2020 and the limited funds generally available for marine conservation. We identified common factors of success and/or failure of MPA effectiveness using peer-reviewed publications and first-hand expert knowledge for 27 case studies around the world. We found that stakeholder engagement was considered to be the most important factor affecting MPA success, and equally, its absence, was the most important factor influencing failure. Conversely, while some factors were identified as critical for success, their absence was not considered a driver of failure, and vice versa. This mismatch provided the impetus for considering these factors more critically. Bearing in mind that most MPAs have multiple objectives, including non-biological, this highlights the need for the development and adoption of standardized effectiveness metrics, besides biological considerations, to measure factors contributing to the success or failure of MPAs to reach their objectives. Considering our conclusions, we suggest the development of specific protocols for the assessment of stakeholder engagement, the role of leadership, the capacity of enforcement and compliance with MPAs objectives. Moreover, factors defining the success and failure of MPAs should be assessed not Giakoumi et al. MPA Success and Failure only by technical experts and the relevant authorities, but also by other stakeholder groups whose compliance is critical for the successful functioning of an MPA. These factors should be considered along with appropriate ecological, social, and economic data and then incorporated into adaptive management to improve MPA effectiveness.