SPECIAL ISSUE ARTICLE Mountains‐to‐the‐sea conservation: An island perspective Kevin J. Collier 1 | Conrad A. Pilditch 1 | Carolyn J. Lundquist 2,3 1 School of Science, The University of Waikato, Hamilton, New Zealand 2 National Institute of Water and Atmospheric Research, Hamilton, New Zealand 3 Institute of Marine Science, The University of Auckland, Auckland, New Zealand Correspondence Kevin J. Collier, The University of Waikato, Private Bag 3105, Hamilton, New Zealand. Email: kcollier@waikato.ac.nz Abstract 1. Island nations such as New Zealand provide valuable insights into conservation challenges posed by strongly connected and recently developed or exploited fresh- water and marine ecosystems. 2. The narrow land mass, high rainfall, and steep terrain of New Zealand, like many other island nations, mean that land‐based stressors are rapidly transferred to freshwater habitats and propagated downstream to coastal environments via short, fast‐flowing river systems. 3. Freshwater and marine environments are linked through faunal life histories; for example, diadromous fishes, many of which are considered threatened or at risk of extinction, and require cross‐ecosystem conservation to ensure survival of critical life stages and persistence of source populations. 4. Recent invasions of marine and freshwater environments by non‐indigenous spe- cies reveal rapid impacts on a naïve biota and highlight conservation conundrums caused by management aimed at enhancing native biodiversity by improving habitat connectivity. 5. Understanding and managing interconnected freshwater and marine ecosystems is a key concept for local indigenous communities, and highlights socio‐cultural con- nectivity and sustainable local harvesting of traditional resources as key elements of contemporary marine and freshwater conservation planning in New Zealand. KEYWORDS biodiversity, climate change, coastal, ecosystem approach, New Zealand, stream 1 | INTRODUCTION Almost one‐quarter of all sovereign countries are islands (worldatlas. com; worldometers.info–accessed 8/1/19), with many more large islands part of continental nations. Taking the definition for ‘true islands’ by Whittaker and Fernandez‐Palacios (2007), 29 (~62%) of the 47 island states are located in the Indo‐Pacific and Caribbean regions, with New Guinea as the largest. Most islands are or were part of continental shelves, with the remainder being remote oceanic islands with no historical connection to continental landmasses and with distinct biogeographical histories (Whittaker & Fernandez‐ Palacios, 2007; en.wikipedia.org/wiki/List_of_island_countries– accessed 8/1/19). Although islands cover only ~3% of the Earth's land area, in a conservation sense the importance of many is disproportion- ately larger owing to high levels of species endemism and other attri- butes. Notably, mode of origin has a significant influence on island geology and topography, which, in combination with climate and lati- tude, influence the hydrology, physicochemistry, and disturbance regimes that shape biotic communities in associated freshwater and marine environments. Oceanic islands often have steep volcanic land- scapes whereas continental shelf islands have more variable geology and topography (Whittaker & Fernandez‐Palacios, 2007). Received: 14 June 2019 Accepted: 3 July 2019 DOI: 10.1002/aqc.3197 Aquatic Conserv: Mar Freshw Ecosyst. 2019;1–8. © 2019 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/aqc 1